Tuning a Tower Pro
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.
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.
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.
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.
Originally Posted by solitone
Are you keeping rebound the same at all three pressure settings?
Originally Posted by solitone
On MTBR, the reputation is infamous.
Yes, I wanted to change just one setting a time, in order to not have too factors in.
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
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.
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.
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?
Tuning a Tower Pro
Here is a good guide on tuning the Tower
Originally Posted by solitone
The trouble with common sense is it is no longer common
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.
Originally Posted by solitone
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.
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?
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:
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.
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.
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.
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.
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..
Originally Posted by beanbag
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.
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!
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.
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.
Originally Posted by beanbag
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.
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.
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.
Originally Posted by ktm520
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.
Originally Posted by beanbag
How do you know that? Do you know what force is needed to fully compress a firm spring?
On my medium spring for a 100mm minute pro, it takes maybe about 100 lbs to fully compress that spring.
I'll do the test you suggested, as well as measuring sag again--hopefully getting more precise measurements.
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