Page 1 of 4 1234 LastLast
Results 1 to 100 of 365
  1. #1
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596

    Tuning a Tower Pro

    Hi all,

    I've got a Tower Pro 120 mm, with QR15 and tapered steerer. I've been riding it for some months without thinking too much on adjustments. I had it mounted on a new bike, and I had to get used to many different things..

    I weigh around 155 lbs, so I started inflating it at 60 psi. I felt it much soft, so I added 10 extra psi after few weeks. I mainly rode it with this setting, but now and then I noticed some dive when braking, so I rose air pressure to 180 psi. It felt good on the trail, but I wanted to follow a more rigorous process to try and find the best tuning.

    I've read a lot lately. The topic on clydesdales by TrailMaker has been very inspirational, and I'm re-reading the topic on abs+ tuning by mullen119. As @mullen119 underlines, the most important aspect in the fork's tuning is choosing the right spring.

    I don't want to be under- or oversprung, and yesterday I did several test runs, inflating the Tower Pro's air spring at different air pressures. I started at 60 psi, and then I repeated the same trail at 70, 80, and 90 psi.

    EDIT--Absolute+ LSC set to MAX-4. Rebound damping half way through--

    The main part of the test was a steep descent with several big rough obstacles--rock gardens, drops, roots...

    At 60 psi the ride was harsh at times on big hits (! likely because I have only 50 mm of travel left, because of huge brake dive?), and brake dive noticeable. Small bump compliance was excellent though.

    At 90 psi it felt bumpy and again harsh on big hits. I didn't exploit full travel, but only 80 mm.

    The best feeling was accomplished with 70 and 80 psi. Small bump compliance was better with 70. With 80 I felt more control. I used 110 and 100 mm of travel respectively. On the trail my choice was 70.

    I shot some videos of the descent, to have something more objective than just riding impressions, and see how the fork responded with different pressures. Surprisingly, when I watch the videos I feel the better response is with 80 psi. With 70 it seems the fork is constantly too compressed when I brake (it's steep and I brake way too much!)

    Here's the test video for the fork with 70 psi of air:



    What do you think? I'm interested in your opinion, cause I don't have much experience in what I should actually expect, and the exact interpretation of terms like over and under sprung is not crystal clear to me. It's like the first times you taste wine--what is supposed to be good wine and what bad?

    I believe you shouldn't waste an awful amount of travel just for brake dive. But is the dive in the above vid too much indeed?

    I'll link the video for the 80 psi test in a following post.
    Last edited by solitone; 04-29-2013 at 11:54 PM.

  2. #2
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Here's the test ride with 80 psi of pressure:


    On youtube you can find also the other two tests with 60 and 90 psi:
    My videos on YouTube

    With 60 I believe the fork is way too soft, as it's always compressed.

    On the other hand, with 90 it seems too hard, as I don't hit full travel. And this trail is one of the toughest I usually ride, so I think I should use almost all travel available.

  3. #3
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    8,296
    I weigh 190lb and spent some time on a Tower Pro. The fork came w/ a Firm coil and when the air spring pressure was set for proper sag the fork literally used all its travel jumping off a curb I was running max air spring pressure). After talking to a Manitou tech I was advised to try an x-firm spring even though sag was correct w/ the firm. I will mention according to the tech the coil spring is only used for sag & initial fork movement. This MAR's coil spring is in place to remove initial stichion an air spring fork would suffer from. So I installed an X-firm - lost sag and had the same super linear travel gobbler. I came to the conclusion after trying to add oil above the air piston and running multiple pressures / ABS adjustments this was not a fork for my riding style. I do have a Tower Expert w/ ACT that feels great. I will add in your situation I consider brake dive a phenomenon that can be lessened by adding LSC from the ABS damper adjustment. If your fork is riding too far into its travel that is an air spring issue.

  4. #4
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    I forgot to mention I ran those tests with abs+ set to MAX-4 (4 clicks from fully closed). So LSC is already pretty damped.

    You're correct in suggesting that increasing LSC damping would be effective for riding that specific trail. It is steep and pretty smooth but in some very rough sections with drops, rocks, and big roots.

    Nevertheless, for the time being I want to focus on the right spring rate without being influenced by compression damping effects, so I kept LSC half way through.

    BTW, I also set rebound damping half way.

    Do you think the fork uses too much travel with 80 psi as well?

  5. #5
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    8,296
    Quote Originally Posted by solitone View Post
    I forgot to mention I ran those tests with abs+ set to MAX-4 (4 clicks from fully closed). So LSC is already pretty damped.

    You're correct in suggesting that increasing LSC damping would be effective for riding that specific trail. It is steep and pretty smooth but in some very rough sections with drops, rocks, and big roots.

    Nevertheless, for the time being I want to focus on the right spring rate without being influenced by compression damping effects, so I kept LSC half way through.

    BTW, I also set rebound damping half way.

    Do you think the fork uses too much travel with 80 psi as well?
    As I mentioned MAR's uses the coil spring to set the sag point and eliminate the initial breakaway stichion. The main air spring is supposed to handle the majority of the support. I'd purchase an x-firm coil & see if the performance changes in a positive direction. I couldn't live w/ the Pro's air spring characteristics but am quite glad the ACT was available for the Tower Expert.

  6. #6
    mtbr member
    Reputation: Vespasianus's Avatar
    Join Date
    Apr 2008
    Posts
    4,697
    Quote Originally Posted by solitone View Post
    I forgot to mention I ran those tests with abs+ set to MAX-4 (4 clicks from fully closed). So LSC is already pretty damped.

    You're correct in suggesting that increasing LSC damping would be effective for riding that specific trail. It is steep and pretty smooth but in some very rough sections with drops, rocks, and big roots.

    Nevertheless, for the time being I want to focus on the right spring rate without being influenced by compression damping effects, so I kept LSC half way through.

    BTW, I also set rebound damping half way.

    Do you think the fork uses too much travel with 80 psi as well?
    Are you keeping rebound the same at all three pressure settings?
    On MTBR, the reputation is infamous.

  7. #7
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Yes, I wanted to change just one setting a time, in order to not have too factors in.

  8. #8
    mtbr member
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,999
    After looking at the videos, I have a few different opinions.

    Your rebound is set too slow. Even at 80psi, the fork seems a little slow in returning. Your spring rate has a direct effect on your rebound setting, so you should change it with the pressure changes. The rebound seems very slow at 60psi and a little slow at 70psi. I would suggest trying it 3/4 open

    It looks in the video to have pretty good small bump compliance, even at 80psi. I am wondering if your expectations for small bump sensitivity are too high for a short travel fork.


    Judging from the video, I would try this setup: 85-90psi in the air chamber for more support through the mid stroke(preventing dive) 5 clicks open on the compression to help with small bump sensitivity, rebound 3/4 open to help feel more active(this will also help small bump sensitivity) Take another video and post it

  9. #9
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Thanks @mullen119, your suggestions are always much helpful!

    I'll try them tomorrow, I hope it won't rain again

    I agree small bump compliance is very good also at 80 psi. I just noted that at 60 it was unbelievable--the fork completely absorbed small roots and they effectively disappeared. Only at 90 psi it felt a bit bumpy.

    You're perfectly right about rebound. 3/4 open is what I usually use. I set it to 1/2 just for those tests, cos I thought it was a more neutral position to begin with.

    5-clicks open means MAX-5 (MAX is lockout, MAX-1 is 1 click from lockout, ..., MAX-8 is LSC completely open), doesn't it?
    Last edited by solitone; 04-30-2013 at 10:28 PM.

  10. #10
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    Do you have the firm or medium spring?
    If 60 psi makes small bumps feel better, then that means you are using a lot of the air spring for small hits. You might want to go with one step softer spring and raise the air pressure a little bit to reduce the brake dive.

    I wouldn't worry about using too much travel unless you are bottoming out. In that case, add a touch more air, and some more oil on top of the air piston.

  11. #11
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Yes I have a firm. But sag seems right. And bumps, even small ones, are absorbed after sag (>20% of travel), hence both coil and air springs contribute. This means small bump compliance is influenced by air pressure as well, doesn't it?

    I fear if I reduce coil spring rate I'd worsen mid stroke support, even with higher air pressures. Am I wrong?

  12. #12
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,307

    Tuning a Tower Pro

    Quote Originally Posted by solitone View Post
    Here's the test ride with 80 psi of pressure:


    On youtube you can find also the other two tests with 60 and 90 psi:
    My videos on YouTube

    With 60 I believe the fork is way too soft, as it's always compressed.

    On the other hand, with 90 it seems too hard, as I don't hit full travel. And this trail is one of the toughest I usually ride, so I think I should use almost all travel available.
    Here is a good guide on tuning the Tower
    http://www.jonesparkchronicles.com/ManitouTowerPro.html
    mtbtires.com
    The trouble with common sense is it is no longer common

  13. #13
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    Quote Originally Posted by solitone View Post
    I fear if I reduce coil spring rate I'd worsen mid stroke support, even with higher air pressures. Am I wrong?
    In theory, you are wrong. If you look at Shiggy's link, the spring curve starts out kind of linear and then flattens out as the air piston starts moving and the spring and air are acting at the same time. This flattening out is the lack of mid stroke support you are complaining about. If you go with a softer spring and higher air pressure, then the start of the curve is less steep, but since you use more air, the middle of the curve is more steep so you get more mid stroke support.

    Try this: Pump up your shock to the usual pressure, and leave the shock pump hooked up. Sit on the bike so that the fork sags. If the air pressure increases, that means that the air piston is already moving just from the sag. If this is the case, then that also means that you can keep the same sag if you go with a softer spring and use more air pressure. Then the air piston will take over during a later part of the stroke.

  14. #14
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    Assuming that you set the same final pressure to prevent bottom out on big hits...

    Then the difference between running a softer spring vs firmer spring is that:

    The spring (force) curve for the firm spring rises steeply at first, then flattens out, then rises again to the final value.

    The spring curve for the soft spring is more linear is that it rises more steadily towards the final value.

    From here, I leave the interpretation of mid-stroke support to you and the other more experienced suspension tuners.

    For the firm spring, it takes more force to reach mid stroke, but add a tiny bit more force and the fork compresses a lot.

    For the soft spring, it takes less force to reach mid stroke, but you can add a lot more force and the fork will only compress a little bit more.

    Which one counts as mid stroke support?

  15. #15
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Today i tried the same trail with mullen119's suggested settings.

    LSC set to MAX-5, and rebound to 3/4 open.

    Here's the result with 80 psi:


  16. #16
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    And here with 85 psi:



    I tested it also with 90 psi, but unfortunately my camera stopped working, so no video for that.

    Anyway, I liked 90 psi the less. But I don't trust impressions so much--you know, taste needs to be trained!

    What do you think of the two videos? I felt both 80 and 85 good. Perhaps I preferred 85. It was as if the fork had infinite travel. It never felt harsh, even on rough hits. And I had no complaints as for small bump compliance.

    BTW, is rebound still a bit slow?

    With both settings, although I had LSC 1 click more open than in my previous tests, there was no bobbing when riding uphill (on saddle), even on paved roads.

    With 80 psi I measured 15 mm of sag and 113 mm of used travel. With 85, 11 mm of sag and 111 mm of travel. With 90, 11 mm of sag and 100 of travel.

    Sag measurements don't appear to be very consistent, I don't rely on them too much. They are on the low side, though. I'll try and measure sag again, and see if results are similar.

  17. #17
    mtbr member
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,999
    Both videos lookedbetter. 85psi looked the best. Much less diving and stayed up in its travel much better. Still looked to have pretty good small bump compliance too. Rebound looked good at 85psi and just a tad slow at 80psi. Your sag numbers or pretty low, Make sure you are checking with the compression fully open, But if it feels good, dont worry too much about it.

  18. #18
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Thanks for your taking the time and watch the videos!

    Yes, I checked sag with LSC fully open. Anyhow, different measurements give different results, to me it's difficult to have a precise measure of static sag. I'll try again though.

    And I wonder how significant it is, considering I don't ride with abs+ fully open..

    BTW, I measured sag in a "neutral" position, standing up with moderate weight on the front wheel. Do you measure it on saddle instead? In that case i'd have even smaller figures.

    --EDIT--
    I compared the 2 videos shot at 80 psi, the 1st with rebound damping set to MAX-1/2, the second to MAX-3/4. Rebound is tremendously better in the 2nd vid. It seems the fork stays higher on its travel, although pressure's the same and compression damping is even 1 click more open.
    Last edited by solitone; 05-02-2013 at 02:52 PM.

  19. #19
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    In theory, you are wrong. If you look at Shiggy's link, the spring curve starts out kind of linear and then flattens out as the air piston starts moving and the spring and air are acting at the same time. This flattening out is the lack of mid stroke support you are complaining about. If you go with a softer spring and higher air pressure, then the start of the curve is less steep, but since you use more air, the middle of the curve is more steep so you get more mid stroke support.
    Yes, I think a Medium spring is an option I should explore. I'd be curious to see spring curves to compare spring rate for different coil springs and air pressure, though. I asked for them to Manitou's CS, and the guy who supported me was very kind, but unfortunately he had no spring curves to send me. I'll try again..

    I just fear that it'd be difficult to get a proper mid-stroke rate with a softer coil spring. The two springs (coil and air) are in series, so both springs influence rate in the mid range. In the following picture, I drawed in green the spring curve for a Firm spring. For the same air pressure, the spring curve with a Medium spring would be the red curve. The softer spring lessens the rate in the mid range.

    Tuning a Tower Pro-spring-curves-examples.jpg

    It's true that increasing air pressure would increase rate, but I wonder at which point the higher air spring rate would compensate the lower coil spring rate. It may well be that I end up with a softer MARS spring in the mid range, and then the spring spikes (dashed red line in the picture above), as TrailMaker describes in the guide Shiggy linked.

    Difficult to say without real spring curves or experimentation!

  20. #20
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    I don't know where you got those curves from, but they're probably wrong. The reason is that both the firm and medium spring will be fully compressed at full stroke, so the final force for those two curves has to be the same. And if the firm spring is so firm that it is not fully compressed, then the green curve is still wrong because the slope at 120mm should be less than at 0mm.

    Keep in mind that the air piston has an area of about 1.1 sq inch, so if you are running 80psi, then the piston is not even moving until you put 88 lbs on it. On my medium spring for a 100mm minute pro, it takes maybe about 100 lbs to fully compress that spring. If I were running the medium spring at your pressures, then my spring would have been pretty much compressed in the midstroke range and mostly relying on the air.

    Like I said earlier, leave the pump attached to your air chamber and see how much the fork compresses until the air piston starts moving. I think you should be running a softer spring to get more sag anyways.

  21. #21
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Quote Originally Posted by beanbag View Post
    The reason is that both the firm and medium spring will be fully compressed at full stroke, so the final force for those two curves has to be the same.
    Have you tested the spring rate or is this speculation? I assume Manitou doesn't publish the spring rates. I've got a Tower Pro on the way so I'm reading up on the Mars setup.

  22. #22
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    ^^

    No no, it was just speculation. As I said, I'd like to have real spring curves, but unfortunately I don't have any for Firm and Medium coil springs.

    As far as I know, the only available spring curves currently available are the following, which refer to the XX-Firm (AKA Clydesdale) coil, though. These curves where provided to TrailMaker by Manitou's chief engineer Ed Kwaterski, and he published them in the interesting doc referenced by shiggy.

    Tuning a Tower Pro-manitoutowerproclydecoilgraph.jpg

  23. #23
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Ya, I read TrailMaker's article. Although the absolute numbers in that chart don't apply to softer springs, it gives a very clear picture of what part of the curve the different variables affect. As far as spring rate goes, it's not that hard to measure. I like having curves to look at, but I doubt I will go down that road with this fork unless I have issues.

    If you haven't already done so, I strongly urge you to experiment with the low speed rebound setting. It seems to be the most widely overlooked aspect of suspension setup and can make or break the action.

    I'm curious to hear if anyone has played with revalving the high speed rebound.

  24. #24
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by ktm520 View Post
    Ya, I read TrailMaker's article. Although the absolute numbers in that chart don't apply to softer springs, it gives a very clear picture of what part of the curve the different variables affect.
    Yes, but the thing those graphs don't tell you is where (i.e. at which point in travel) the curve for softer coil + higher pressure becomes greater than that for stronger coil + lower pressure.

  25. #25
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    I don't know where you got those curves from, but they're probably wrong. The reason is that both the firm and medium spring will be fully compressed at full stroke, so the final force for those two curves has to be the same.
    You're perfectly right. Those curves where just sketches I drawed, and I was wrong. As you said, final force has to be the same with both coils.

    On my medium spring for a 100mm minute pro, it takes maybe about 100 lbs to fully compress that spring.
    How do you know that? Do you know what force is needed to fully compress a firm spring?

    I'll do the test you suggested, as well as measuring sag again--hopefully getting more precise measurements.

    Cheers

  26. #26
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    I measured my spring by holding a flat plate over the top and then putting most of my weight into it.

    That chart you have shows the spring curves for your firm coil. I dunno about your coil, but mine for a 100mm fork can compress by less than 2" before it bottoms out (e.g. the blue plastic push rod hits the metal compression rod).
    Next time you have your spring out, you can see how much yours compresses and get the force value from the chart.

    There is something weird about the manitou chart in that the 90 psi black curve starts to diverge from the spring at below 50 lbs. That is odd.

  27. #27
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    Quote Originally Posted by solitone View Post
    Yes, but the thing those graphs don't tell you is where (i.e. at which point in travel) the curve for softer coil + higher pressure becomes greater than that for stronger coil + lower pressure.
    All you need is to measure the height / volume of your air chamber, and then you can calculate these curves out yourself.

  28. #28
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    There is something weird about the manitou chart in that the 90 psi black curve starts to diverge from the spring at below 50 lbs. That is odd.
    Yes, because the air piston should begin move at about 100 lbs

  29. #29
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    Try this: Pump up your shock to the usual pressure, and leave the shock pump hooked up. Sit on the bike so that the fork sags. If the air pressure increases, that means that the air piston is already moving just from the sag. If this is the case, then that also means that you can keep the same sag if you go with a softer spring and use more air pressure. Then the air piston will take over during a later part of the stroke.
    I've measured how much the fork needs to compress so that the air piston starts moving. As usual, it's difficult to have accurate measurements, next time I'd better ask a friend to help me.

    Here are the results. I also noted sag figures where available, but I need to measure sag again to have more accuracy:

    • 70 psi: air piston moves at 8 mm (sag 28 mm)
    • 80 psi: air piston moves at 11 mm (sag 12 mm)
    • 85 psi: air piston moves at 15 mm (sag 11 mm)
    • 90 psi: air piston moves at 17 mm (sag 11 mm)
    • 100 psi: sag 12 mm


    As you see, only with 70
    and (perhaps) 80 psi the piston moves from the sag. With 85+ psi the piston moves later in travel, therefore sag depends only on the coil spring rate. This explains why sag doesn't change increasing air pressure from 85 to 90 psi.
    Last edited by solitone; 05-04-2013 at 08:26 AM.

  30. #30
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    I did the same test on my fork and the piston also moves before I think it is supposed to. I think there must be a trapped air space somewhere, or some kind of rubber bumper or o-ring under the piston that allows it to move around. I never had the air piston out so I wouldn't know.

    In any case, I made some plots for MY fork. I guessed on the spring rates. Also, the final force came out to be a little too low so I am missing various air pockets trapped in other parts of the fork.



    In any case, I used to have a medium spring but now I run a soft spring. It ends up giving a smoother and more linear curve.

  31. #31
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    I did the same test on my fork and the piston also moves before I think it is supposed to.
    Do you refer to my piston, or to what is shown on Manitou's plots?

    I don't know whether or not my piston moves before it is supposed to.

    --EDIT--

    BTW, why the force of the MARS spring at full travel (100 mm) is lower then the force of the air spring alone, in your plots?

    We said the coil spring is fully compressed at that travel, so the force of the MARS spring should only depend on the air spring.
    Last edited by solitone; 05-03-2013 at 01:06 PM.

  32. #32
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    u add the dotted plots horizontally to get the total travel

  33. #33
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    I'm afraid I don't get it. In your graph, the red and blue continuous lines (MARS spring) peak to 170 lbs at 4 inch displacement (100 mm). In contrast, the green dotted line (air spring) is much higher at 4 inches, although it's not shown.

  34. #34
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    you don't actually end up compressing the air chamber 4 inches. it compresses 2 inches and the spring compresses 2 inches and thus the fork compresses 4 inches. You are supposed to read this graph like it is sideways, i.e. you pick a force value first and then read off the displacements.

  35. #35
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    OK.

    I measured the air piston movement again, and I confirm that 80 psi are enough to reach the point where the piston moves at a displacement equal to sag. More than 80 psi, and the piston moves at a displacement greater than sag.

    So, for pressures >= 80 psi, sag is given only by the coil spring, and it is 11-12 mm--too little, because the firm coil is too hard for my weight.

  36. #36
    mtbr member
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,999
    A lot of great info in this thread on how to tune the Mars spring system. Either beanbag or Solitone should make a guide with the tips and tricks to make sure you have the correct coil spring for your weight and what not. The spring system is complex enough that a lot of people have problems setting it up, and a guide on here would help a lot of people.

  37. #37
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Sure! As soon as I complete my tests I'll wrap up all information in a how to guide.

    I've just ordered a Medium Ride Kit and soon I'll be able to try the new setup.

  38. #38
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596

    some more videos

    This evening i shot some more videos.

    Here is the test with 90 psi, that last time I didn't manage to record:


  39. #39
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596

    new vid 85 psi

    And, as a comparison, here a new recording with 85 psi, that last time was really poor quality:



    All other settings are the same: firm coil, LSC damping MAX-5, HSC stock trail shim stack, rebound damping MAX-3/4.

    Please comment!

  40. #40
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596

    85 psi on a different path

    And a longer descent on another path, which should allow to check the fork's behaviour on different conditions (fork inflated with 85 psi of air).



    Here there are no steep sections, but the surface is generally rougher, with many boulders.

    As in previous vids, there's a pretty amount of mud because of the heavy showers we have been experiencing in the last weeks here. So the camera lens isn't always clean.. Sorry for that!

  41. #41
    mtbr member
    Reputation:
    Join Date
    Nov 2012
    Posts
    239
    If you really want to tune your Tower, you can get the tuning kit which will allow you to do some pretty specific types of adjustments. It ain't cheap, but if you are a tinkerer and want to dial it in, that will pretty much handle anything you desire.

    I still have to replace my spring to the firm, but I confess - I a little nervous on attacking that yet. I want to arch the videos a few more times.

  42. #42
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    All you need is to measure the height / volume of your air chamber, and then you can calculate these curves out yourself.
    Is it really that easy? Is it a simple cylinder?

    Do I need to just measure my air chamber's height to get its total volume, and subtract the volume of oil (should be 5 cc in my case) to know the volume of air?

    But then what gas compression model should I use, to get pressure increase from volume decrease (i.e. travel)? Boyle's law? It wouldn't be appropriate, though, 'cause on high speed compressions air temperature can't be assumed as constant.
    Last edited by solitone; 05-09-2013 at 03:42 AM.

  43. #43
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by iCollector View Post
    If you really want to tune your Tower, you can get the tuning kit which will allow you to do some pretty specific types of adjustments. It ain't cheap, but if you are a tinkerer and want to dial it in, that will pretty much handle anything you desire.
    Yes, you're right, I'm aware of that possibility, and it's an exciting option I already explored with my old(er) Minute Expert.

    For the time being, though, my focus is finding the correct spring rate for my weight/riding style. Afterwards, I'll try and tune also the shim stack.

  44. #44
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Quote Originally Posted by solitone View Post
    Is it really that easy? Is it a simple cylinder?

    Do I need to just measure my air chamber's height to get its total volume, and subtract the volume of oil (should be 15 cc in my case) to know the volume of air?

    But then what gas compression model should I use, to get pressure increase from volume decrease (i.e. travel)? Boyle's law? It wouldn't be appropriate, though, 'cause on high speed compressions air temperature can't be assumed as constant.
    Yes, Yes, and ideal gas law. P1*V1=P2*V2

    You don't have to buy the 200$ tuning kit to revalve the ABS. Download the tuning guide from mullen119's thread and go buy shims from your favorite shim supplier. Depending on what you want to do, it should only require buying a few shims @ 2$ a piece.

  45. #45
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    Oh right, you are supposed to use adiabatic gas compression. That would account for a few extra pounds at full compression. Also don't forget psi gauge vs absolute pressure.

  46. #46
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Yes, in fact I already have most of needed shims--Manitou CS posted them to me for free !! when I was tuning my Minute Expert.

    I'll start with Boyle's.

  47. #47
    mtbr member
    Reputation: ric426's Avatar
    Join Date
    Jul 2007
    Posts
    422
    I've been following this thread with great interest and it's got me wondering, is there a noticeable difference in performance and settings once a Tower Pro is "broken in"? The reason I ask is that I've only got about 8 hours on mine and the settings and air pressure I'm using to get the desired results are *way* different than the OP's. Should I get the recommend 20 hours in before I make any significant changes like ride kit, etc.?
    I'm 183lbs. ready to ride, using a 100mm QR15 Tower Pro with a 2011 Spec Camber 29. I'm working on setting it up for maximum plushness on the small to medium hits (knowing that I'm trading that for a fair amount of mushiness when pedaling standing) because of my old, arthritic wrists. So far I'm getting the best results at 70 psi, rebound at 1/2, compression damping at 1 click from full open (!), though I'm not getting as much sag as I'd expected. At my weight, I wouldn't think I'd need a medium spring though.
    Overall, my settings sound pretty light compared to what's being discussed in this thread, so I'm wondering about the break in period. My main riding area is pretty tame with the biggest drops around 1', but I've yet to notice any bottoming out.
    We don't stop playing because we grow old; we grow old because we stop playing.

  48. #48
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    I didn't notice any brake-in on mine, even though Manitou say it takes several hours to break it in.

    As for your light settings, I also would be using lighter settings if my rides didn't include very steep descents, with rough sections.

    Consider that Donn, a guy at 29eronline, weighs like me, but is using a Soft spring with 70 psi, as he commented to the following video of his, so a much lighter setting as well:



    My current setting though is what I prefer for heavy trail/all-mountain riding. I'll see what changes are needed when I install the new Medium spring.

    It's strange you don't get the desired sag. With 70 psi and the stock firm spring, I have a 25% sag (measured in attack position, though--probably it's a 15-20% on saddle, but I'm lighter than you).

  49. #49
    mtbr member
    Reputation:
    Join Date
    Nov 2010
    Posts
    3,042
    Quote Originally Posted by ric426 View Post
    Overall, my settings sound pretty light compared to what's being discussed in this thread, so I'm wondering about the break in period. My main riding area is pretty tame with the biggest drops around 1', but I've yet to notice any bottoming out.
    I have a Minute Pro which is pretty much the same fork in a 26" wheel version. There is a break in period where the fork gets smoother and stiction goes down or disappears, and that's about it. The settings I used didn't change. Like solitone, I have a lot of super steep and rough sections on my local trails, plus I like to ride aggressively so I run much heavier settings than usual. I'm 150 lbs and run 105psi, 5 clicks from full closed on compression, and 1/8 of a turn from full open on rebound.

  50. #50
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    FYI I redid my plot with adiabatic gas compression and got about 40 more lbs at full compression. It seems closer to real-world values. So I suggest you do it that way.

  51. #51
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    I hope I'll manage, as soon as I measure the air chamber's height.

    Regarding its volume, do I need to take into account also the air pushrod?

    Name:  Clipboard03.jpg
Views: 721
Size:  3.4 KB

    I'm not sure, but does this rod lie inside the air chamber? Sorry for the dumb question..

  52. #52
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Quote Originally Posted by solitone View Post
    Consider that Donn, a guy at 29eronline, weighs like me, but is using a Soft spring with 70 psi, as he commented to the following video of his, so a much lighter setting as well:
    Keep in mind that body mass is not an absolute when determining spring rate. It is merely a starting point. Frame geometry, cockpit, rider height, etc. all play a role in how the weight is distributed between the front and rear wheel.

    Quote Originally Posted by solitone View Post
    I hope I'll manage, as soon as I measure the air chamber's height.

    Regarding its volume, do I need to take into account also the air pushrod?

    I'm not sure, but does this rod lie inside the air chamber? Sorry for the dumb question..
    No, the pushrod is outside of the air chamber.

  53. #53
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by ktm520 View Post
    No, the pushrod is outside of the air chamber.
    Ok, thanks, it's simple then!

    EDIT: Here's a nice picture from the Clydesdales thread showing this:

    Tuning a Tower Pro-manitou_mars_preload_increase.jpg
    Last edited by solitone; 05-20-2013 at 01:07 AM.

  54. #54
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Standard volume of semi-bath oil in the air chamber is only 5 cc, as written in 2012 Service Manual, isn't it?

    EDIT: yes, it is. I've read it in several other places too.
    Last edited by solitone; 05-20-2013 at 12:35 AM.

  55. #55
    mtbr member
    Reputation: ric426's Avatar
    Join Date
    Jul 2007
    Posts
    422
    I think I just took about 1/2 pound of weight out of my Tower Pro. I opened it up for the first time tonight to try a different coil spring and couldn't believe how much grease was packed in there. I think they must be having a contest at the factory to see who can use up the most grease in the fewest forks and I found the winner. The spring and stanchion were pretty much filled with grease and it has already mixed with the semi-bath oil and turned it into a murky sludge that I need to clean out. What's the best way to clean out the lower part of the stanchion and the inside of the casting before I reassemble it? I don't want to use any solvents that may cause problems with the plastic and rubber parts. I've cleaned some of the small parts with isopropyl alcohol but haven't sprayed any in the big parts yet.
    We don't stop playing because we grow old; we grow old because we stop playing.

  56. #56
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    Just wipe it out with a paper towel, and expect some of the remnant grease to mix with your next batch of oil.

  57. #57
    The White Jeff W
    Reputation: jeffw-13's Avatar
    Join Date
    Apr 2008
    Posts
    5,398
    I really have nothing to add to this thread except that it scratches my OCD where it itches the most. Thanks to all of you
    No moss...

  58. #58
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Got my new Tower Pro 120 mounted on the SB95 and got a short ride over the weekend. I'm 165lb, 6'2". Initial setup (firm spring) was 60psi which netted 20% sag. Not what I was hoping for as Manitou suggested the firm spring. I typically prefer closer to 25%. Set the lsc wide open and left it there. Lsr at 3/4 out.

    Compared to the Reba XX, this fork has amazing action. No spiking on square edge and stayed up in the stroke, except for heavy braking. As I feared, with only 60psi, the dive wasn't terrible, but too much for my taste. I bumped the air up to 70 and although it fixed the dive, plushness took a big hit. I've got a med spring on order. I guess I'm not surprised that I need a softer spring as my body position and cockpit setup favors more rear weight bias. For reference, I was only running 70psi in the Reba. The SB also has a fairly slack front end.

    I didn't really play with the lsc at all, but the stock trail stack definitely had too much platform for me when closed. I pulled one of the platform shims (19 x .2).

    Only complaint is the lsr adjuster. Why did they go with such a small adjustment range and no detents??? I will get over it, but it's nice to be able to reach down and dial a few clicks.

  59. #59
    mtbr member
    Reputation:
    Join Date
    Nov 2010
    Posts
    3,042
    Quote Originally Posted by ktm520 View Post
    Compared to the Reba XX, this fork has amazing action. No spiking on square edge and stayed up in the stroke, except for heavy braking. As I feared, with only 60psi, the dive wasn't terrible, but too much for my taste. I bumped the air up to 70 and although it fixed the dive, plushness took a big hit.
    Try running 60-65psi with the compression knob 4-5 clicks from full open. The fork stays quite plush until you get to 6 clicks, and 4-5 clicks should be enough to help with brake dive issues.

  60. #60
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    In any case, I made some plots for MY fork. I guessed on the spring rates. Also, the final force came out to be a little too low so I am missing various air pockets trapped in other parts of the fork.
    I finally managed to take a measurement of my Tower Pro air chamber. As I wrote here, its height is 107 mm.

    Taking the air cap shape and the oil volume (5 cc) into account, I end up with an effective air height of 105 mm.

    I started by plotting a spring curve for the XX-Firm (Clydesdales) spring, with a pressure of 130 psi. We have real data for this curve (purple line in the following graph), so it's possible to compare my results with real data.

    Tuning a Tower Pro-manitou.gif

    I didn't remove my stock coil spring, so I didn't measure it. I assumed it compresses 60 mm before it bottoms out. Here is the curve I get (continuous line is my curve, dashed line is Manitou's):

    Tuning a Tower Pro-60mm.jpg

    As you see, I get significantly higher forces in the second half of travel. Please consider I did not even use adiabatic compression law here, but isothermal law, because otherwise I would have got even higher results.

    Looking at Manitou's curve, it seems coil spring compresses much more than 60 mm. I tried with 95 mm, and I got a better fit:

    Tuning a Tower Pro-95mm_2.jpg

    In the last portion of travel, though, I still got an excessive rise in force.

    So I thought I made some error when measuring air chamber height. I thought the fork was fully extended, but perhaps the piston was not at its lowest position? Maybe the coil spring was pushing it up and my measurement came short?

    The point is I get a better fit if I suppose the air chamber is taller. With a 119 mm air chamber I get this curve:

    Tuning a Tower Pro-95mm_119mm.jpg

    If I use a height of 140 mm ( possible??), as well as adiabatic law, I get the best fit:

    Tuning a Tower Pro-130psi.jpg

    which also fits quite well the 90 psi curve:

    Tuning a Tower Pro-90psi_2.jpg

    So, my question now is--is it possible that my measurement (105 mm) was sooo wrong? A height of 140 mm does not seem reasonable to me.

    @beanbag how did you measured your chamber height? How tall is it for your Minute Pro?

  61. #61
    mtbr member
    Reputation:
    Join Date
    Nov 2012
    Posts
    239
    ...My brain hurts! Yikes!

  62. #62
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    I don't see why you are guessing at things that you can easily re-measure. (coil spring compression, air chamber height)

    Mine measured out at a little under 4" for a 100mm fork.

    I can also tell that you messed up the math. Looking at your plots, it seems that you assumed a spring rate for the coil at 300 lbs / 60 mm, or 5lbs/ mm. So in your first plot of a 60mm coil, I see 400 lbs at 98 mm. The spring is fully compressed. In your second plot with a 95mm spring, I also look at 400 lbs and see the displacement at 106mm. But the spring is supposed to be compressed by 20mm more, and the air chamber is supposed to be compressed the same. Yet you only show 8mm more compression.

  63. #63
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    I don't see why you are guessing at things that you can easily re-measure. (coil spring compression, air chamber height)
    Ok, I re-measured my air chamber height, this time pushing down the air piston, and it's 116 mm high. If I release pressure from the air piston, it goes up (as if there is a spring pushing it up ), and I end up with a mistakenly short measure.

    As for the coil, I didn't have time to remove casing, so I still don't know how far it compresses. Plus, I don't have a Clydesdales spring, and I'd like to compare my results for a Clydesdales spring with Manitou's curves, so that I can check whether my model fits Manitou's data.

    Anyhow, my point is that, even assuming the coil compresses by 95 mm (should be far more than it's supposed to), at the end of travel I get greater forces than real ones. Here is what I get with an air chamber 116 mm high, using isothermal compression (an underestimate):

    Tuning a Tower Pro-116mm_95mm.jpg

    Quote Originally Posted by beanbag View Post
    Mine measured out at a little under 4" for a 100mm fork.
    So 100 mm for a 100 mm travel fork. I wonder whether my measurement is still short. But I'm sure I pressed the air piston all the way down, and I didn't end up with a measurement of 120 mm.

    Quote Originally Posted by beanbag View Post
    I can also tell that you messed up the math. Looking at your plots, it seems that you assumed a spring rate for the coil at 300 lbs / 60 mm, or 5lbs/ mm.
    That's right. I took such rate from Manitou's graph.

    Quote Originally Posted by beanbag View Post
    So in your first plot of a 60mm coil, I see 400 lbs at 98 mm. The spring is fully compressed. In your second plot with a 95mm spring, I also look at 400 lbs and see the displacement at 106mm. But the spring is supposed to be compressed by 20mm more, and the air chamber is supposed to be compressed the same. Yet So in your first plot of a 60mm coil, I seeyou only show 8mm more compression.
    I'm not sure I understand this.

    In the first graph, the curve steepens up after 60 mm, in the second after 95 mm--i.e. after the coil is fulled compressed. The curves are flattened out between 26 mm (where the air piston starts moving) and either 60 or 95 mm. In this range the coil and the air springs work in series. To me this points out that the two coils can compress 60 and 95 mm respectively before bottoming out.

  64. #64
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    Quote Originally Posted by solitone View Post
    In the first graph, the curve steepens up after 60 mm, in the second after 95 mm
    Well that's where ya screwed it up. The curve steepens at 300 lbs, and 475lbs respectively. It steepens based on the y value, not the x value. Recall that I said to add the dotted lines curves horizontally, not vertically.

    BTW, my curve happens to match manitou's just fine


  65. #65
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    wait... I just realized that in the cross section picture you posted there is a little spring under the air piston. So that would explain why the piston starts moving prematurely. Smart move by manitou as that smooths out the transition.

  66. #66
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    Well that's where ya screwed it up. The curve steepens at 300 lbs, and 475lbs respectively. It steepens based on the y value, not the x value. Recall that I said to add the dotted lines curves horizontally, not vertically
    Yes, that's right, I see what you mean. My curves above are wrong. I'll try to draw them again and see what I get.

    Quote Originally Posted by beanbag View Post
    wait... I just realized that in the cross section picture you posted there is a little spring under the air piston. So that would explain why the piston starts moving prematurely. Smart move by manitou as that smooths out the transition.
    Mmmmm.. interesting. That might explain the springy feeling when I pushed the piston down, even though its movement seemed greater than what would be allowed by such a small negative spring.

    Actually, first I let air out of the fork, then removed the air cap trying to keep it at full extension, and measured 116 mm.

    Secondly I compressed and re-extended the fork, and measured a smaller height (by 10-20 mm, don't remember exactly). Then I pushed the piston down with a rod, and measured again 116 mm. If I didn't push the air piston down, it would go up again.

    I'm confused by the original measurement of 116 mm, taken without pushing down on the piston. So I'm not sure that springy effect was in fact caused by that little coil under the air piston.

  67. #67
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Quote Originally Posted by solitone View Post
    I'm confused by the original measurement of 116 mm, taken without pushing down on the piston. So I'm not sure that springy effect was in fact caused by that little coil under the air piston.
    Has anyone confirmed that there is actually a small coil under the piston? It's not shown in the service manual or parts breakdown, and it's also not shown in other cross-sections I've found. In this system, it would only serve as a top-out bumper. The main coil smooths out any breakaway friction in the piston seal.

    My guess is that the coil is preloaded when installed. If there isn't a small coil under the piston, looks like it could be as much as 10mm based on your observations. Also, when does the coil bind? That will make a huge difference on the end of the curve.

    Keep in mind these curves are purely static. The force in both springs will not always be balanced during dynamic inputs.

    I'm waiting for my medium spring to show up. When I install it, I will take all of these measurements on my fork (120mm).

  68. #68
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    XX spring
    free length - 80mm
    compressed - 36mm

    x spring
    free length - 80mm
    compressed - 36mm

  69. #69
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    BTW, my curve happens to match manitou's just fine

    I replotted the curve, following beanbag's indications (thank you beanbag!), and this time it seems consistent with his.

    These are my usual assumptions:
    • Coil spring: XX-Firm, 60 mm compression (an overestimate, based on ktm520's data);
    • Air spring: 130 psi, 116 mm chamber height, 1.0 sq in piston area;
    • Isoentropic gas compression law (k = cp/cv = 1.40)

    And here is the curve I get, together with Manitou's for comparison:

    Tuning a Tower Pro-fig.gif

  70. #70
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Quote Originally Posted by ktm520 View Post
    Has anyone confirmed that there is actually a small coil under the piston? It's not shown in the service manual or parts breakdown, and it's also not shown in other cross-sections I've found. In this system, it would only serve as a top-out bumper. The main coil smooths out any breakaway friction in the piston seal.
    On further thought, a coil under the piston would also smooth out the transition when the air spring initially starts to move (the knee in the curve). Manitou's curves would suggest that there is a coil there.

  71. #71
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by ktm520 View Post
    XX spring
    free length - 80mm
    compressed - 36mm

    x spring
    free length - 80mm
    compressed - 36mm
    Here are the data that Randy at Manitou Tech wrote me:

    • XX-Firm: 80 mm free length. Solid height is about 36.8 mm. Allowed travel is about 39.7 mm after the 4 mm of preload is accounted for (4 mm + 39.7 mm = 43.7 mm total).
    • X-Firm: 86 mm free length. Solid height is about 33.5 mm. Allowed Travel is about 46.5 mm after the 4 mm of preload is accounted for (4 mm + 46.5 mm = 50.5 mm total).


    So we now have two further pieces of information:

    1. Coil spring travel depends on spring rate;
    2. The spring is indeed preloaded (4 mm).


    @ktm520 why spring preload would explain the air piston behaviour I observed?

  72. #72
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    I think Manitou's curves are calculated anyway (notice that there's no spike when hitting the bump stop) and if you want to use that as a spring length, you should turn off adiabatic compression to get your curve to match theirs.



    BTW, don't go nuts trying to match it exactly. The whole point initially was to show that a softer spring will give you a more linear curve.

  73. #73
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Quote Originally Posted by solitone View Post
    Here are the data that Randy at Manitou Tech wrote me:

    • XX-Firm: 80 mm free length. Solid height is about 36.8 mm. Allowed travel is about 39.7 mm after the 4 mm of preload is accounted for (4 mm + 39.7 mm = 43.7 mm total).
    • X-Firm: 86 mm free length. Solid height is about 33.5 mm. Allowed Travel is about 46.5 mm after the 4 mm of preload is accounted for (4 mm + 46.5 mm = 50.5 mm total).


    So we now have two further pieces of information:

    1. Coil spring travel depends on spring rate;
    2. The spring is indeed preloaded (4 mm).


    @ktm520 why spring preload would explain the air piston behaviour I observed?
    I don't know what to say about the physical dimensions of the springs. I measured the two spring I have, pretty hard to screw up. There will manufacturing variances, but 5mm would be a lot. Any preload on the spring will un seat the piston if there is not air in the chamber. Look at the cross-section view again.

    beanbag, why is there a knee in your air spring curve (green dash line)? Should be a smooth curve.

  74. #74
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by ktm520 View Post
    I don't know what to say about the physical dimensions of the springs. I measured the two spring I have, pretty hard to screw up. There will manufacturing variances, but 5mm would be a lot.
    It seems the Medium is about 5 mm shorter than the X-Firm:
    Manitou Tower Pro Fork for Clydesdales - Techical

    @ktm520 is your compressed length the solid height of the coil, or the allowed compression (i.e. when the blue plastic push rod hits the metal compression rod)?

  75. #75
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    Quote Originally Posted by ktm520 View Post
    beanbag, why is there a knee in your air spring curve (green dash line)? Should be a smooth curve.
    ...
    Quote Originally Posted by ktm520 View Post
    On further thought, a coil under the piston would also smooth out the transition when the air spring initially starts to move (the knee in the curve). Manitou's curves would suggest that there is a coil there.

  76. #76
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by beanbag View Post
    if you want to use that as a spring length, you should turn off adiabatic compression to get your curve to match theirs.
    BTW, shouldn't we use a polytropic process (k around 1.2 ?), rather than an isothermal (k=1) or adiabatic process (k=1.4)? Is a fork's compression so quick that the process is really adiabatic? Polytropic is something in between.

    BTW, don't go nuts trying to match it exactly. The whole point initially was to show that a softer spring will give you a more linear curve.
    Yes, but this is an interesting game, and I'm learning and understanding a lot

  77. #77
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Quote Originally Posted by solitone View Post
    @ktm520 is your compressed length the solid height of the coil, or the allowed compression (i.e. when the blue plastic push rod hits the metal compression rod)?
    solid height, therefore 44mm of displacement for both coils. Like beanbag said, this kind of stuff is splitting hairs. Play around with the numbers in your spreadsheet and you will see that it makes very little difference.

    beanbag, ha, got me there. What were your assumptions for the negative coil, just curious?

  78. #78
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by ktm520 View Post
    beanbag, ha, got me there. What were your assumptions for the negative coil, just curious?
    And how the preload (4 mm) of the main coil spring should be accounted for?

  79. #79
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    No assumptions, its just math. F=kx+b, b=k(preload), This shifts the entire curve up.

  80. #80
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    ^^ ok, I edited my question

  81. #81
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by ktm520 View Post
    No assumptions, its just math. F=kx+b, b=k(preload), This shifts the entire curve up.
    The odd thing is this upward displacement is not shown in Manitou's curves--they all start at 0 lbs:

    Name:  todo.gif
Views: 426
Size:  9.3 KB

    A 4 mm preload would result in 20 lbs for an XX-Firm coil (rate 4,95 lbs/mm), and should be noticeable in the graph.

  82. #82
    mtbr member
    Reputation:
    Join Date
    Nov 2010
    Posts
    3,042
    Nope. The coil spring and air spring are in series, which means the spring system starts moving as soon as a)the preload force is exceeded or b)the friction in the air spring seals is overcome, whichever comes first. Let's say for example the preload on the coil spring is 20 lbs, and there's 3 lbs from the friction in the air spring seals. The system starts moving as soon as you put mure than 3 lbs of force on it. Manitou's charts might be a bit optimistic in starting at 0, but it's probably close enough that it doesn't matter.

  83. #83
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    The short answer is 1.4. The longer answer is you can do a bunch of calculations to show that it is probably 1.4.

    For the under-piston coil spring, here is how I guessed the values: I looked at the manitou curve for 130 psi, and looked for the force at which the total curve starts to deviate from the linear main spring curve. This is when the air piston lifts off and starts moving. It looks around 90 lbs, so that means that at full compression, the under-piston spring preload is around 40 lbs. (90 lbs external force + 40 lbs under-piston spring preload = 130 lbs = 130 psi. Next, you go to 130 (+ a little) lbs, which is approx the point at which the piston should be moving by itself and the under-piston spring should be unloaded. The deviation from the linear main spring curve is maybe about 1/3 inch, so that is approx the length of the under-piston spring.

    As for the 4mm preload, who gives a F? Manitou probably assumed that by the time you are using an xxfirm spring, u r such a fat ass that the rest of the frame is probably bending by 4mm or more, so that cancels it out.

  84. #84
    mtbr member
    Reputation:
    Join Date
    Nov 2004
    Posts
    2,506
    Quote Originally Posted by beanbag View Post
    As for the 4mm preload, who gives a F? Manitou probably assumed that by the time you are using an xxfirm spring, u r such a fat ass that the rest of the frame is probably bending by 4mm or more, so that cancels it out.
    This is the best post in this thread.
    That would make a great t-shirt

  85. #85
    I'm just messing with you
    Reputation: wv_bob's Avatar
    Join Date
    Sep 2005
    Posts
    5,424
    Quote Originally Posted by the mayor View Post
    This is the best post in this thread.
    That would make a great t-shirt
    Only available in size XXL
    Chasing bears through the woods drunk with a dull hatchet is strongly not advised

  86. #86
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Being on the light end of the sprectrum (160lb), I'm looking at the difference between a med and firm spring. I was most interested to see how sensitive the setup is to small pressure changes and reducing the air volume. For example, the difference between a med and firm at 25% sag is only 2psi and very little difference in progression. I don't know what the spring rate is for the med but I assumed 73lb/in based on the trend across the firm, x, and xx springs. We'll see how it performs in reality.

  87. #87
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by aerius View Post
    Nope. The coil spring and air spring are in series, which means the spring system starts moving as soon as a)the preload force is exceeded or b)the friction in the air spring seals is overcome, whichever comes first. Let's say for example the preload on the coil spring is 20 lbs, and there's 3 lbs from the friction in the air spring seals. The system starts moving as soon as you put mure than 3 lbs of force on it. Manitou's charts might be a bit optimistic in starting at 0, but it's probably close enough that it doesn't matter.
    This is true when you completely deflate the air chamber. But when you have 130 psi of air in, you need at least 130 lbs to move the air piston (area of piston 1 sq in). So the system moves as far as the coil is compressed--i.e. when force exceeds the preload of 20 lbs.

  88. #88
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by ktm520 View Post
    the difference between a med and firm at 25% sag is only 2psi and very little difference in progression.


    Have you got some charts to illustrate it? I'm also interested in this, as my weight is similar (155 lbs).

  89. #89
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    Quote Originally Posted by the mayor View Post
    This is the best post in this thread.
    That would make a great t-shirt
    Quote Originally Posted by wv_bob View Post
    Only available in size XXL

  90. #90
    squish, squish in da fish
    Reputation: fishwrinkle's Avatar
    Join Date
    Jul 2012
    Posts
    1,655
    hiya solitone. so i started asking questions in the shimming thread, but it turns out i'm not to that point yet so i thought i'd continue posting in the tuning thread. so solitone, i got the x-firm in there 2 nights ago and took it out on a 15 mile journey that kinda pissed me off, not fork related but trail sanitizing. thats another thread. so i'm set as of now with x firm spring, 100 psi, 3/4 open rebound and abs+ set at 5 clicks from full open or 4 from LO. i am using full travel having bottomed it once or twice and brake dive is still quite evident. even at an attack stance with chest on the bars. after i installed it, just messing around in basement, i noticed a lot of sticktion and it felt very linear. this however disappeared on the trail. i still have more messing to do, but i am happy for the moment. thanks for the helpful words

  91. #91
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Got some measurements from my fork (120) yesterday. There is a coil spring under the piston, but it is somehow retained so I couldn't easily remove it. I did measure its travel at 9mm. I had the piston out but forgot to measure its diameter. It is closer to 28mm, eyeballing with a scale. Chamber length to top of crown is 116mm with the coil fully extended. The chamber cap is mostly hollow so it doesn't reduce the volume significantly enough to factor.

    fishwrinkle, I'm not sure what you consider "quite evident" dive, but you do realize that you can't eliminate dive. That is without running an overly stiff spring and damper. I would play with reducing volume (adding oil/grease to air chamber) next. This will give you more bottoming support and will also slightly help with dive. +5cc will make a big difference.

    I'll post some curves comparing a med and firm coil when I get chance. I want to update my spreadsheet with these measurements first.

  92. #92
    squish, squish in da fish
    Reputation: fishwrinkle's Avatar
    Join Date
    Jul 2012
    Posts
    1,655
    thanks ktm, i do realize that you can't eliminate dive, but it is hardly better than a firm spring. my next move was going to add oil to the topside. grease? so you're saying any petrol based product to take up volume? i think i'll stay with oil, redline 5w.

  93. #93
    mtbr member
    Reputation: ktm520's Avatar
    Join Date
    Apr 2004
    Posts
    1,567
    Yes, grease. Oil will eventually migrate past the oring on the piston. You could pack grease in the underside of the cap and it would probably stay put. 90w gear oil (fox float fluid) will work better than 5w redline, which is really thin. Mobil one gear lube is easily to find. Any non-porous object that won't knock around inside will work. It would be nice if Manitou made some plastic spacers that snapped into the top cap.

    Oil is quick and easily reversible, so I'd use that for testing. Once you settle on a setup, you might want to find something more permanent or live with refilling the chamber with oil frequently.

    Ya, I'm not surprised you didn't see a huge difference between the two springs. Verifies that the spring curves I've been calculating are semi-accurate.

  94. #94
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    8,296
    Quote Originally Posted by fishwrinkle View Post
    thanks ktm, i do realize that you can't eliminate dive, but it is hardly better than a firm spring. my next move was going to add oil to the topside. grease? so you're saying any petrol based product to take up volume? i think i'll stay with oil, redline 5w.
    I added 15wt fork oil above the air piston in 5cc increments in an attempt to add progression to a very very linear feeling air spring (was running 110psi & an x-firm coil) I made it past 25cc of oil and started limiting travel. I went so far as to place a coil spring between the air piston & the top cap - this was the biggest tuning improvement I had made to the fork. At that point I decided to just buy a second Tower Expert and stop trying to re-engineer the Pro.

  95. #95
    squish, squish in da fish
    Reputation: fishwrinkle's Avatar
    Join Date
    Jul 2012
    Posts
    1,655
    ah yeah, now that you say that, i do remember reading the oil will make its way south. then again i thought it was the bath oil mixing with the grease. memory sucks when i don't get enough sleep, thanks for the tip.

  96. #96
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    1,196
    Quote Originally Posted by keen View Post
    I added 15wt fork oil above the air piston in 5cc increments in an attempt to add progression to a very very linear feeling air spring (was running 110psi & an x-firm coil) I made it past 25cc of oil and started limiting travel. I went so far as to place a coil spring between the air piston & the top cap - this was the biggest tuning improvement I had made to the fork. At that point I decided to just buy a second Tower Expert and stop trying to re-engineer the Pro.
    When I undid the Nixon IT and went with a coil neg, I ran into the same tuning issue. I used Thudbuster elastomers on top of the piston to take up space and give the last 1 inch or so some more cushion. That worked well also.
    lean forward

  97. #97
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,873
    Quote Originally Posted by fishwrinkle View Post
    thanks ktm, i do realize that you can't eliminate dive, but it is hardly better than a firm spring.
    That's because at 100 psi, the air piston starts moving way before the spring is fully compressed.

    add more air

  98. #98
    I'm just messing with you
    Reputation: wv_bob's Avatar
    Join Date
    Sep 2005
    Posts
    5,424
    If oil will make it past the piston, air would too, wouldn't it? (I put +5cc in mine yesterday)
    Chasing bears through the woods drunk with a dull hatchet is strongly not advised

  99. #99
    mtbr member
    Reputation: solitone's Avatar
    Join Date
    Apr 2011
    Posts
    596
    When I measured my air chamber, I also noticed there was no oil above the piston. It likely flowed down, then.

    Just bought some syringes so I can add the standard 5 cc.

  100. #100
    I'm just messing with you
    Reputation: wv_bob's Avatar
    Join Date
    Sep 2005
    Posts
    5,424
    Did you notice a corresponding loss of pressure?

    When I source an XX-firm spring and take the shock back apart for installation I guess I should drain all the oil over the piston too so I know how much is there and can check it periodically. When I deflated it before the first disassembly, the fork was laying on the workbench and a good amount of oil shot out with the air.
    Chasing bears through the woods drunk with a dull hatchet is strongly not advised

Page 1 of 4 1234 LastLast

Similar Threads

  1. Tower Pro: Flexy?
    By gfs69 in forum 29er Components
    Replies: 11
    Last Post: 01-17-2013, 02:10 PM
  2. Tower Pro or Slide RL2?
    By tiSS'er in forum 29er Components
    Replies: 10
    Last Post: 11-30-2012, 10:02 PM
  3. Manitou tower Pro?
    By KEITH21 in forum Shocks and Suspension
    Replies: 0
    Last Post: 01-12-2012, 08:03 PM
  4. Tower Pro set-up
    By petey49 in forum Shocks and Suspension
    Replies: 2
    Last Post: 10-13-2011, 05:45 PM
  5. Kalepa from Tower
    By rat7761 in forum Hawaii
    Replies: 0
    Last Post: 03-18-2011, 11:57 PM

Members who have read this thread: 9

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •