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  1. #1
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    650b shock bottom-out shim for seat tube clearance

    Hey! Hoping this helps someone convert a 26" full suspender bike to 650b like it did for me!


    Shock bottom travel reduction instructions

    Purpose: To prevent tire contact with the seat tube at bottom-out travel.

    Background: This simple bottom travel limit shim or washer method has been working flawlessly on my bike for over 2 years. I converted my 26” wheel, 5.5 inch travel full suspension bike to 650b (27.5”) wheels with larger volume 2.3 size tires. But on the first ride of this experimental conversion to a larger wheel than the bike was designed for I discovered that the tire rubbed lightly on the backside of the seat tube when landing moderate jumps. In earlier years with 26” oversize tires on the same bike I was startled by a loud buzz from the tire rubbing the front derailleur cable that is stretched down the backside of the seat tube.

    How do to it: The shims are easily made with thin flat plastic material, such as plastic water bottle material. Thin aluminum, such as cut from a soda-can could also be used. I used a 1/32” acrylic sheet bought from a plastic material supply store called Tap Plastics, http://www.tapplastics.com/shop/product.php?pid=258& . This acrylic sheet can be easily cut and shaped with ordinary paper cutting scissors.

    Simply cut a round piece out of the acrylic sheet with scissors and then cut diagonally inwards towards the center to cut out a hole that would clear the shock shaft. (See photo below.) The diagonal cut in the side of the shim or flat washer allows the shim to be added to the shock shaft without disassembling the shock other than deflating and unscrewing the air sleeve to gain access to the bottom end of the shock shaft. The plastic shim is stiff enough that it remains secure and does not come loose off the shaft while riding.

    Air Shocks: To add one or more shims inside a Fox Float type shocks, such as the RP23 or Float-R, the bottom travel bumper location is easily accessed, by deflating the air pressure and unscrewing the air sleeve by hand and sliding the sleeve away revealing the shaft and small bottom bumper o-ring. This sleeve removal procedure is normally done during the periodic air sleeve oil maintenance recommended every 10 to 40 hours use by Fox. (See Fox service instruction link and graphic below.) The hand loosening of the air sleeve should be done while the shock is mounted on the bike for greatest ease; or if off the bike, a mechanical lever such as a long screwdriver through the shock mount bushing hole or a vise clamping the mount will provide sufficient leverage. This all can be done without removing the shock from the bike in most cases, even to do the periodic oil service.

    The Fox Float bottom travel reduction shim size requires a center hole for the shaft about 3/8 inch or 10mm, the outer diameter overall is 1.5 inch or 38mm. A rough cut is fine; a tightly precise fit is not required.

    Install the bottom limit shim(s) under the wide flat metal washer found inside the Float shocks, on the near mount side of that large washer. After installing the bottom limiting shim(s) wipe some light lube on the seal at the threaded area and screw the sleeve on hand tight again.

    Before airing up an air shock, compress the shock to full bottom travel with the shim(s) in place to see if the tire clears the seat tube. Add as many shims as needed (I needed 2 shims) until the tire clears safely.

    Other brand air shocks may have similar access to the shock shaft.

    Coil Shocks: Coil shocks are also very easy to limit travel. The coil shock must be removed from the bike and the spring removed. With spring removed install the travel limit shim(s) between the rubber bottom bumper and spring perch. After testing the bottom travel tire clearance with shock mounted on the bike without the spring installed but with shim(s) and perch installed, reinstall the spring, perch, and shock onto the bike.

    Forks: Fork bottom travel can be shortened with similar method while lower legs are removed for oil service, using thin plastic shims to limit bottom travel.

    Fox air shock service instruction links:

    http://www.foxracingshox.com/fox_tec...aintenance.htm

    http://www.foxracingshox.com/fox_tec...rvice_Interval

    Related note: If having harsh bottom out problems with Float shocks, regardless of shimming to limited travel, a very nice method to increase rate by limiting volume without limiting bottom travel range was developed by DGC, a pro bike mechanic in South Lake Tahoe. And this method may work the same for other air shock. Here's a link to his technique:
    Shim survey please..........
    Attached Thumbnails Attached Thumbnails 650b shock bottom-out shim for seat tube clearance-650b_shim_floatdrawing.jpg  

    650b shock bottom-out shim for seat tube clearance-650b_shim.jpg  

    Last edited by derby; 06-09-2010 at 06:38 PM. Reason: better title?

  2. #2
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    You can also purchase nylon washer from your local hardware store. They come in assorted thicknesses / internal hole diameters. The washers are just flexible enough to twist past the shock shaft w/ a single slit. Once in place they look almost factory.

  3. #3
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    Quote Originally Posted by keen
    You can also purchase nylon washer from your local hardware store. They come in assorted thicknesses / internal hole diameters. The washers are just flexible enough to twist past the shock shaft w/ a single slit. Once in place they look almost factory.
    Yes, my home made method is ugly. But I used it to show how easy it can be done. And in either case the shims are not visible when a shock or fork is reassembled.

  4. #4
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    Thanks for the info. I just did this on a DT Swiss XM180 to shorten the stroke on a Mojo SL and will add shims for a 650b conversion. Here are some pics of nylon washers cut, a Fox 10mm fork shim(clips on), how it looks on the shock and rear wheel clearance.
    Attached Thumbnails Attached Thumbnails 650b shock bottom-out shim for seat tube clearance-img_2619.jpg  

    650b shock bottom-out shim for seat tube clearance-img_2620.jpg  

    650b shock bottom-out shim for seat tube clearance-img_2622.jpg  

    650b shock bottom-out shim for seat tube clearance-img_2625.jpg  


  5. #5
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    Quote Originally Posted by lml427
    Thanks for the info. I just did this on a DT Swiss XM180 to shorten the stroke on a Mojo SL and will add shims for a 650b conversion. Here are some pics of nylon washers cut, a Fox 10mm fork shim(clips on), how it looks on the shock and rear wheel clearance.
    Much cleaner looking. Thanks for posting pics.

    Many suspension bikes would need much less shim thickness for 650b tires to clear the seat tube at bottom travel. Generally, for most suspension bikes there is about 2.5 times rear wheel travel to shock shaft travel. Forks of course are 1:1 travel with the wheel.

    The shims also reduce air volume and the deep travel air spring ramp-up progression is increased proportionately to the reduced travel if the shim is as wide as the inner diameter of the chamber.

    If having harsh bottom out problems with Float shocks, regardless of shimming to limited travel, a very nice method to increase rate by limiting volume without limiting bottom travel range was developed by DGC, a pro bike mechanic in South Lake Tahoe. And this method may work the same for other air shock. Here's a link to his technique:
    Shim survey please..........

  6. #6
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    Thanks for the additional info. I keep learning alot from this forum and greatly appreciate it. Here is what I am trying now. I have both a DT Swiss XM 180 (55mm stroke) and a Fox RP23
    (50mm stroke) Pushed for my Mojo SL. Both strokes need to be shortened for 650B and the DT for both 650B and 26". The DT is very linear with very little ramp up (may cause harsh bottom out), very plush. My RP23 seems to ramp up very hard with a kind of dead feeling rebound, but can handle very harsh riding. I am 6'4 225 lbs. and I know it is hard on an air shock. Here are pictures of rubber spacers that can either go behind the DT factory bottom out to take up air volume or in as a spacer, which will take up volume and soften bottom out.
    Attached Thumbnails Attached Thumbnails 650b shock bottom-out shim for seat tube clearance-img_2626.jpg  


  7. #7
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    I remember a few years ago I tested a Santa Cruz Superlight with a 650B rear and the only reason it would not work is the wheel hit the seat tube at full compression. This method would make that frame work with 650B and its a perfect candidate for conversion with its low BB and 2:1 shock compression ratio. It gets one thinking! I still have the pics. It fits the rear with a Neo Moto 2.3 tire and the derailleur clears.
    Attached Thumbnails Attached Thumbnails 650b shock bottom-out shim for seat tube clearance-superlight1.jpg  

    650b shock bottom-out shim for seat tube clearance-superlight-compressed1.jpg  


  8. #8
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    Quote Originally Posted by Waterat Pat
    I remember a few years ago I tested a Santa Cruz Superlight with a 650B rear and the only reason it would not work is the wheel hit the seat tube at full compression.
    A Superlight would be a great conversion to 650b. Low BB, efficient climber, and the moderately steep frame geometry would be more relaxed in handling and feel for enduro trail riding with 650b.

  9. #9
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    Great info......just doing this now on RFX conversion...

    I'm limiting travel for my RFX conversion (thanks Keen for all your help). Couldn't readily find a used RP23 X 1.75 so got myself a X 2.0 and have tried one rubber washer thin shim but its not enough. So soon I'll open it up again to add a thicker one or add a elastomer left over from my PRS saddle. Its the hardess one they make for the PRS system, and its 10mm thick. I thought it could work because it'll compress at the end of the stroke. If I find its too thick, I'll just get out my belt sander and take a couple mm's off at a time. Any comments if this is a good idea or not? Or should I stay with a thick, more rigid dense, rubber washer?
    Thanks

    PS. Also wondering about the real world experience of compressing an air shock all the way. Does this really happen a lot? Perhaps riding style dependent like hucking or extreme AM?
    Anyway, I have a few more months to get advise and play since my 'extreme knee injury' still has me banned from mtb. Good news, is the doc gave me clearance for road 2 days ago, and I did my first ride yesterday and all is good!
    Attached Thumbnails Attached Thumbnails 650b shock bottom-out shim for seat tube clearance-mvc-066s.jpg  

    We told you 650b rocks! Riding converted RFX for years!

  10. #10
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    Excellent! Thanks for starting this thread Derby. I've been loving the 650b front on my Mojo, and just started pondering what I'd need to do to convert the rear.....garage tinkering time is limited these days, so thanks for shedding some light.
    JR

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    Quote Originally Posted by Spongebob
    I'm limiting travel for my RFX conversion (thanks Keen for all your help). Couldn't readily find a used RP23 X 1.75 so got myself a X 2.0 and have tried one rubber washer thin shim but its not enough. So soon I'll open it up again to add a thicker one or add a elastomer left over from my PRS saddle. Its the hardess one they make for the PRS system, and its 10mm thick. I thought it could work because it'll compress at the end of the stroke. If I find its too thick, I'll just get out my belt sander and take a couple mm's off at a time. Any comments if this is a good idea or not? Or should I stay with a thick, more rigid dense, rubber washer?
    Thanks

    PS. Also wondering about the real world experience of compressing an air shock all the way. Does this really happen a lot? Perhaps riding style dependent like hucking or extreme AM?
    Anyway, I have a few more months to get advise and play since my 'extreme knee injury' still has me banned from mtb. Good news, is the doc gave me clearance for road 2 days ago, and I did my first ride yesterday and all is good!
    Go to a hardware store and pick up some nylon washers. They come in a variety of ID / OD's and after slit can be flexed enough to make a perfect fit on a shock shaft.

  12. #12
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    Seems like a Fox (slotted) fork spacer would be perfect. I only seem to find them stock in 10 mm size, but it seems it could be cut in half w/ an hot knife or grinder parting tool or chop saw to get to 5 mm?

  13. #13
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    Or stacking

    Quote Originally Posted by buggymancan
    Seems like a Fox (slotted) fork spacer would be perfect. I only seem to find them stock in 10 mm size, but it seems it could be cut in half w/ an hot knife or grinder parting tool or chop saw to get to 5 mm?
    a number of washers to gain 5mm of thickness. i cut my own and they worked well.
    Wreck the malls with cows on Harleys

  14. #14
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    Does this mod adjust the eye to eye at all, or does it simply adjust the stroke?

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    The eye to eye does not change. It simply limits the stroke.

  16. #16
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    I ended up stumbling upon some nylon washers at ACE Hardware that are 3.8" ID, which equates to 9.5mm, and about .5mm in thickness....used some wire clippers to snip an angled slot in them, and with the slightly under sized diameter they stay put nicely. I forget now how many I used.... I believe it was 7 or 8...anyway, very clean, simple, and about $1. Light-tuned RP23 already bottomed way too easily at full travel, so added Fox's med. volume adjuster shim for more progression.....and it's money!

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    Bumping this super helpful thread. Thanks, contributors!

    Mike

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    Cool Thread guys, I have done the front of my HD and love it, going to do back now after this advice. Still have first HD frame so any advice. I have a SLR on it's way (when they have stock, another story for another day) and after my results with the test on 650B i would love to build it from the start as FULL 650B - any advice here, has anyone done a SLR?

    ROCKSHOX REVELATION does it fit 650B? I hear the LYRIK does, I need fork for SLR. I want to make my SLR my X-country bike and my HD my play bike, I have a 29er but just find it DULL with that weedy 110mm thin stanchion fork although I have THU-AXLE, the whole setup odd but it does go fast downhill and it does roll nicely. Any advice to keep it light and fun?

  19. #19
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    ROCKSHOX REVELATION does it fit 650B? I hear the LYRIK does, I need fork for SLR. I want to make my SLR my X-country bike and my HD my play bike, I have a 29er but just find it DULL with that weedy 110mm thin stanchion fork although I have THU-AXLE, the whole setup odd but it does go fast downhill and it does roll nicely. Any advice to keep it light and fun?[/QUOTE]

    2009 Revelation fits thats the year they used the Pike lowers which also fits. Both are good choices for a stiffer 650B fork. I run a 20mm Pike.

  20. #20
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    Quote Originally Posted by MOJODAVE View Post
    Cool Thread guys, I have done the front of my HD and love it, going to do back now after this advice. Still have first HD frame so any advice. I have a SLR on it's way (when they have stock, another story for another day) and after my results with the test on 650B i would love to build it from the start as FULL 650B - any advice here, has anyone done a SLR?
    ....
    The original HD140 (without the recently increased seat tube tire bottom out clearance) will clear 650bx2.3 easily with no mods. The HD160, both versions, need to limit bottom travel using shock travel shims (very minimal for the new HD160 with added seat tube clearance).

    The SL-R did NOT clear my 650b wheel in the chain-stay, in one of the first batch displayed at the Sea Otter Classic in April 2011 before they were available retail. Clearance was too short, not event a shorter small race tire would have cleared. I'll try fitting my wheel again this year into a production SL-R, maybe the tire clearance is improved to be as much as the SL (which does clear pretty easily with a minimal shock bottom travel limit shim).

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    Thanks for the info, the frame arrived and I took a wheel with tire, put it in - it fits with about 3-4mm to spare. Let the air out the shock and at complete bottom out it touched the frame. I will take a photo later and post it. Did my HD160 front wheel and just love the feel.

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    Ok not very good with this stuff, got a question via Private message typed a long reply only to be told I have to have made 10 posts before I can do that so if I sound like I am posting crap, I need my 10 posts or have I got this wrong.

    To answer the question - yes the wheel spins with 3-4mm clearance with a Stans Crest Rim and Schwalbe 2.25 rubber hoof. I have not put the cluster or anything on yet need to pick up that today. I will keep posting with progress to get my posts up and to keep you informed.

  23. #23
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    Took some photo's of HD (white) and SL-R (Black/Blue) so you can see the clearance.
    Attached Thumbnails Attached Thumbnails 650b shock bottom-out shim for seat tube clearance-14022012047.jpg  

    650b shock bottom-out shim for seat tube clearance-14022012044.jpg  

    650b shock bottom-out shim for seat tube clearance-14022012049.jpg  


  24. #24
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    Quote Originally Posted by MOJODAVE View Post
    Took some photo's of HD (white) and SL-R (Black/Blue) so you can see the clearance.
    That is GREAT news. Ibis responded to the 650b advantage and increased the clearance of the SL-R swingarm for production.

    I had tried fitting my 650b wheel in one of the first run of a few, maybe 5 early press release SL-R's, which was no where near clearing any 650b tire. Ibis again impresses by quickly responding and correcting a "design defect"

    The Mojo SL and earlier Mojo C also clear 650b with the same space as your SL-R appears to. It's enough for all but sticky leaf days, and sticky leaves or layering mud are just as bad with more tire clearance. Prior to my HD I rode my Mojo C with 650b for 4 years with no problems specific to the larger wheel size. The finish inside the stay yoke near the edge knobs gets worn a little over the years from mud grinding and small rock scrapes, but the tires never rub if the wheels are fairly true.

    Very sorry to hear about the mtbr firewall to be able to reply to a PM. It's unfortunate a very few repeat banned creeps and drunks make it hard for the 99+% of riders new to mtbr discussion wanting to sign up and quickly contribute. The new policy seems to have effectively reduced the frequency of toll posts a lot.

  25. #25
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    Thanks for feedback, maybe that was the delay of the SL-R getting to market. If they made it better then all is forgiven. Shimming my HD tonight and going to give the FULL 650B conversion a whirl tomorrow evening.

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