Reducing Fork Travel - Any threads out and about?- Mtbr.com
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  1. #1
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    Reducing Fork Travel - Any threads out and about?

    I had been looking around quite a bit and trying to find threads on this and just hadn't seen any. I have a few bombers that I would like to reduce from 80mm to get something that fits with original geometry on some older frames.

    I have people elude to doing it in a few threads but never seen any write ups on what they actually did.

    I think it would be awesome on a SID or something else newer on some of the rider bikes I have.

    Hope everyone's Wed is treating them well.

  2. #2
    Phobia of petting zoos.
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    It's Thursday here. 12:45pm. But thanks for the well-wishes.

    A mate of mine wanted to do the same thing on a Xizang with 100mm Bombers that were a bit "chopper-ish". He mentioned it to a local bike shop and they said "yeah, we can do that, no problem".

    So he dropped the fork in and a few days later they were destroked to 80mm. Slipped them back into the bike and... no difference.

    Turns out the destroking from 100mm to 80mm is simply a case of limiting the travel and nothing to reduce the axle to crown.

    That's not to say all forks are the same, and hopefully someone will offer something along the lines of "don't make sweeping generalisations Grumps, you can reduce the a2c on [insert specific model of fork here]".

    Grumps

  3. #3
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    don't make sweeping generalisations Grumps, you can reduce the a2c on Fox forks. You can use spacers in 10mm or 20mm increments and the a2c is reduced accordingly. I haven't reduced one down to 60mm, but I have gone from 140mm down to 120mm and 100mm to 80mm without any issues. The spacer is really easy to install.

  4. #4
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    Don't know if this will help, and it is 15 years removed so who knows where you would find one, but Marzocchi did offer a travel reduction kit that would take your fork down by almost 20mm. It also says that it reduces the overall length of the fork... changes a2c?

    Now if you could find a kit or at least get the specs of the parts in it, you may be in business. The kit is mentioned on Page 13...

    http://www.google.com/url?sa=t&rct=j...aOMq5N4nQq23ag

    John
    1995 Trek 970 - 80mm Atom Race
    1992 Serotta T-Max - 70mm Z3 Light
    1993 GT All Terra - 46mm Mag 21
    (STOLEN)

  5. #5
    rismtb
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    There is a great simple way of reducing vintage mtb fork travel...........go ridged!!!!!!!

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    I am a huge fan of rigid bikes and own many. However this is in relation to older frames that were designed to run suspension, just perhaps a lower amount of travel on those forks.

    Goal is trying to make sure and preserve the intended geometries of the frames but perhaps be able to run a better performing fork.

    The vast majority of the ones that I am thinking of is Bombers since they spanned so many years and can be correct across so many different years.

    Thank you 70sSanO for the Marzocchi manual, even just the chart in there showing the travel of the various forks is super helpful.

  7. #7
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    Quote Originally Posted by datmony View Post
    The vast majority of the ones that I am thinking of is Bombers since they spanned so many years and can be correct across so many different years.
    I bought a 2001 80mm Bomber brand new (in 2001) and had it reduced to 70mm of travel to work with my older frame ('97 Bontrager). Reducing the travel required purchasing new springs that were shorter. The conversion was done by the shop that sold me the fork, so I don't know the exact process, but for the coil version required replacing parts. The air version of the fork is likely reduceable without replacing the springs (as there are no springs to replace).
    Each bicycle owned exponentially increases the probability that none is working correctly.

  8. #8
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    Find RichieB on this forum. He's did a 80mm --> 70mm rebuild and travel reduction on my FOX Float 80 for my Phoenix. Came out great. He can do anything.

    -eric-

    http://www.rumpfy.com
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  9. #9
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    You can get an engineering shop to chop down the legs and as with my indy sl's get them to cut groove's into the base of the stanction,there is a removable clip as found on judy forks.
    some early judy's can be modified to say 50mm travel without this process,some can't and you'd need to chop the stanction down,should be real cheap to do,judy crown's on sid forks should make them shorter too

  10. #10
    DFA
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    Putting a Judy crown on a SID won't reduce your travel. Might do wonders for your tire/crown interface, though.

    Reducing travel on Marzocchis is the same as their moto forks. A spacer on the carts above the top out springs and shorter/softer springs.

  11. #11
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    Late response here - I somehow missed this thread when you started it. I've actually been thinking we should start a general, more inclusive, "frankenfork" thread - to document ideas, successes, and available options. Not just travel reduction, but ways to swap steerer sizes, accommodate cantilever bosses, etc. It's only going to get harder to keep some of our good, older bikes suspended, right?

    I've spent the last year doing a little bit of all of the above, with reasonable success. I'll share one below that answers some of your specific questions, with pictures, but should probably start with a few general comments:


    1) On the off-chance you're considering this for one of those Bontrager projects that you've been working on, you might consider NOT reducing the travel. If you read enough threads here, you'll notice that many (probably more than half) of riders actually prefer an 80mm fork to the 64mm they were designed to take. This alone could become a long discussion, but here's my take on it, summarized as simply as I can:

    Stock bontragers seem to have been designed to fit best when climbing - almost like they were purpose-built for it. In other words, when the front end is significantly higher than the back. The steep seat tube angle and resultant rider position borders on preposterously aggressive for flat riding, and is downright scary for downhills... but works fantasic when climbing - even without getting out of the saddle. The low-for-the-era front-triangle gave good clearance, even when the front was elevated. Their unique, reduced-offset/increased-trail fork crowns were designed to stabilize steering, even when unweighted and riding up hill at slow speed. And all of this is even more pronounced in the larger sizes, because the head-tube/ stack-height dimensions didn't scale up with the rest of the frame. Tall riders do NOT experience a bontrager the same way that an average or shorter rider does. Some misguided theory about how tall people have longer arms and legs - but not longer torsos?)

    But, since you likely don't spend all your time climbing, you can get a more versatile ride by increasing the a-c dimension of your fork, and raising the front end a bit. Head and seat tube angles will STILL be steeper than modern bikes, but familiar. The trail figure will increase, but, if you're using a non-bontrager-specific crown, it's probably pretty close to the original design intent. Since they had more-than-adequate standover clearance, it's not likely an issue. The only down-side is a higher bottom bracket. And any change is pretty minimized on the larger frames, due to the long wheelbases.



    2) All other things being equal, ALL FORKS, REGARDLESS OF TRAVEL DIMENSION, ARE THE SAME LENGTH WHEN FULLY COMPRESSED. This might be insultingly obvious, but I mention it because I found all sorts of misinformation out there, when I started to experiment on my own, and some of it could really confuse the process. In other words, the travel (and a-c length) is increased or decreased at the up-stroke, by determining how far the fork can telescope - NOT by limiting how far it can compress. You'll see people say that limiting travel will damage the fork by "causing it to bottom out sooner." It doesn't - they all bottom out at the same point.... the bottom. And you'll see people say that reducing the travel will put undue stress on the headtube. It won't. It's a lever. If anything, It's a shorter lever except when it's bottomed out, at which point it's exactly the same lever. [edit: re-reading Uncle Grumpy's post, it sounds like that shop did it the other way, so I guess it's physically possible to limit the down-stroke on a bomber... but obviously wrong.]

    3) As Laffeau noted, it's probably a lot easier to properly reduce the travel of an air fork than a coil spring fork. I don't know how Bombers work, so my experience is based on various Rock Shox and manitou models.

    As you'll notice from the inflation instructions of any adjustable-travel air fork, the shorter the travel setting, the higher the initial pressure required. This would suggest that forks are intended to achieve a certain spring/resistance when measured at the fully compressed position. ( Longer travel starts with less pressure, but compacts more volume into the same small space as a shorter-travel fork, at the bottom, such that the pressure is ultimately the same.)

    Sometimes you hear of people reducing the ride height by simply increasing the negative pressure and decreasing the positive pressure. But that doesn't seem to make sense to me, and probably DOES lead to jarring bottom-outs. The proper way to do this is to install travel limiters, and to increase the pressure accordingly. The upshot of this is that you'll have a stiffer fork at the beginning, but won't bottom out any sooner or more frequently or more violently. So, if you're looking for "plush," you may not find this a perfect situation. But if you're looking for steering control and predictability, it's great.

    A coil fork, on the other hand, typically has a more linear spring rate. But to reduce travel without changing the actual spring length, you'd have to pre-compress the metal, and leave it there always.. never having a chance to rest. Not being a metallurgist, I think this would lead to spring set or fatigue and shortened life. If you want the plushness of a coil spring, I think you need to source shorter springs, and they'd probably need to be correspondingly stiffer, too.

    4. Unless you're striving for a 100% era-appropriate build, get as modern as you can find, but don't worry about getting the 'best' or lightest fork you can find. Presuming that you need canti studs, this may save you a lot of heartache, since they're harder to find in top-end models . Even a mid-range modern fork is way better than a top-of-the-line fork from the mid-90's. Especially the damping. Modern damping is a damned revelation, really. (No pun intended.) And remote lockouts are cool. Kind of like a power window in your car - you don't need it, but you sure get used to having it quickly.

    5. All this said, I think it's a totally worthwhile project, to maintain a bike that's designed to work with shorter travel. You almost forget how much more consistent (and fun) the handling can be - closer to a rigid experience (without the edge) than to a modern suspended bike that has to work across a wider range of a-c heights.
    Last edited by iamkeith; 04-14-2015 at 04:36 PM.
    We still hang bike thieves in Wyoming [Pedal House]

  12. #12
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    Great response Keith. This question was in relation to a few other projects that are sitting in the wings versus the bontragers. For the Bontys (which I think I finally found the medium I have been searching for, should be here in the next week or so) I am either going to run a switchblade or Mag21 on the large and then once the medium is here, that will be running either a 80mm bomber or the 1" SID I have. I bought that SID years ago for a P series ritchey I hoped to stumble on and that I have still yet to ever find.

    I do think a Frankenfork thread is a really good idea.

  13. #13
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    OK, here's my most recent reduced-travel frankenfork project. In this case, I needed V-brake studs as well as a shorter a-c dimension. As a welcome change from the usual mind-numbing VRC-based project though, I was able to use a 1 1/8" steerer instead of a 1", which allowed me to use some much newer options as a starting point.

    My philosophy is that, no matter how classic or valuable your frame happens to be, the fork is still just a mass-produced, Taiwanese piece of junk, which neither detracts from or adds to the bike. (RS-1, Mag 21/22 and some White Brothers models being the possible exceptions?) So I wanted something as new as possible, to take advantage of latest technology and so that I would have a better chance of finding parts / re-build kits down the road. I don't want to have to do this again because, if you haven't noticed, even 1 1/8" steerers are getting hard to find.

    For Rock Shox forks, the 1 1/8" steerer puts all of the 32mm stanction forks into play. If you need a 1" steerer, you're going to have an easier time working with the 28mm ones, where a 90's Judy crown can be swapped to SID forks from all the way up to 2008(?). But, at that point, 64mm was a standard travel setting, achievable with standard parts.

    The most unique thing about this project of mine is that I was reducing travel beyond what it is "supposed" to accommodate. I'm happy to report that it works fantastic. If you don't have the V-brake criteria that I did, this whole process is probably still valid for similar forks, even up to current (2015). Here's what I ended up working with:

    - 2012 Recon Gold Fork RL (I think 2011 to current are still the same).
    This is supposed to be adjustable from 80 to 120mm lengths. As I mentioned, this is just a mid-range fork, and comparatively inexpensive, available in the $300 ballpark.... but it's still a lot better than a 90's Judy. Solo air is theoretically more robust and is simpler to tune than dual air. Remote lockout & motion control damper on this one.

    Through this process, I learned that Rock Shox seems to do this thing when they upgrade their upper-end forks, where the old components and tooling are migrated down to the new lower-end forks. So much of this Recon actually corresponds to the previous version of the Reba. It helps to know this when looking for parts!

    FYI, there is also a Recon SILVER, which is an entirely different fork. (It uses steel stanctions which are a different gage / interior diameter than that of the aluminum (gold), so the internals are completely different, too.

    Here's what the stock fork looks like, for reference:

    Reducing Fork Travel - Any threads out and about?-recon-gold-2011-13.jpg

    - V-Brake lowers, from a 2009-2010 Reba.
    This is one of the parts that has "migrated." So I think it also fits (or may be listed as) a 2010 Tora part, or a 2010-2011 Recon part. For 2012 and beyond, I don't think they bothered still making it or specifying what it would fit, because they assume everybody has disc brakes.

    It's pretty easy to visually identify though, and that may be the safest way to know if it will work. Older versions didn't have the "bulge" at the middle of the leg, and newer versions are "hollow" looking (hardware is recessed) at the bottoms of the legs.

    Reducing Fork Travel - Any threads out and about?-v-lowers.jpg

    - Additional All-Travel Spacers kit for 2013 Recon/XC32/XC30 forks.
    Once again, a part that may be listed differently depending on where you find it, but still the same thing. There seem to have been a LOT of different Rock Shox spacer configurations and shapes from over the years but this one seems easy to identify visually. They're simple cylinders, with grooves or actual segments, separating them into 10mm donuts. They look like this:

    Name:  all travel kit.jpg
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Size:  29.2 KB

    STEP #1: REDUCE
    To reduce travel , you simply add donuts to the plunger on the left leg. I don't think you even need to take the whole fork apart to do this, but I was changing legs too. Tech manuals and instructions are readily available at the SRAM website.

    Reducing Fork Travel - Any threads out and about?-recon-w-spacers.jpg

    No donuts = 120mm, 2 donuts = 100mm, 4 donuts = 80mm, etc. But they are grouped as singles, pairs and triples so, with an full kit, you can play with various combinations and achieve 10mm increments like 110mm or 90mm just as easily! If you're really ambitious, you could even shave one down for smaller adjustments, like Rumfy probably did on his fork above. I just used 50mm of spacers (pair and triple) to achieve 70mm travel. But the (un-sagged) a-c height actually ends up at 438mm, which is within a couple of millimeters of the 63/64 mm forks that the bike was designed for.

    STEP #2: SET
    So now you have to figure out what pressure to use, since you are outside of the specified range. For normal-size (non-waif) riders, the confusing chart, that's stuck on the back of the original fork...

    Reducing Fork Travel - Any threads out and about?-solo-air-settings.jpg

    ...basically distills down to this:

    - For 100 mm travel setting and above, set the air pressure at the rider weight minus 80 lbs.

    - For 90mm travel setting, set the air pressure at the rider weight minus 60 lbs.

    - For 80 mm travel setting, set the air pressure at the rider weight minus 40 lbs.

    Extrapolating from there, you can then assume:

    - For 70mm travel setting, set the air pressure at the rider weight minus 20 lbs.

    So a 180 lb rider, at a 70mm setting, would want 160lbs of air pressure. Give yourself +/- 5 psi for fine tuning and rider preference, and you're good to go. I have had no problem using the higher pressure. It doesn't "blow out gaskets," as you may see some people caution. Remember the fundamental principal that, when fully compressed, ALL settings ultimately yield the same maximum pressure.

    STEP #3: LABEL & DECORATE
    Assuming your new lowers don't have any stickers on them, you can find all sorts of custom ones on ebay, to color coordinate with your bike. Or you could leave it classy, blank and stealth. I wanted a few notes for future reference (part of the reason I'm taking the time to make this post, too: posterity. Otherwise I'd eventually forget what I did and what I had), so I used some crude but kinda-neat looking dymo labels... And a touch of home-state pride.

    Reducing Fork Travel - Any threads out and about?-img_0569.jpgReducing Fork Travel - Any threads out and about?-img_0570.jpgReducing Fork Travel - Any threads out and about?-img_0571.jpgReducing Fork Travel - Any threads out and about?-img_0573.jpg

    The finished project:

    Reducing Fork Travel - Any threads out and about?-frontfenix.jpg
    Attached Thumbnails Attached Thumbnails Reducing Fork Travel - Any threads out and about?-recon-w-spacers.jpg  

    We still hang bike thieves in Wyoming [Pedal House]

  14. #14
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    Super cool. That is exactly what I was thinking as I wrote the original thread.

    I am quite jealous of your and Rumpfy's Phoenixes. I have a good share of the bikes I lusted after snatched up and in the collection but one of those continues to elude me.... Just like the p-series ritchey and the Brodie......

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