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  1. #1
    Birdman aka JMJ
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    26" fork running 24" wheel with brake post extenders

    Updated thread - extenders made and installed - go down a few posts.

    Here's the deal. My daughter has a 24" wheel GF Precaliber with a HEAVY Suntour "suspension" fork on it. I have a perfectly serviceable Marzocchi Atom 80 suspension fork gathering dust. My plan was to mount brake post extenders (19mm offset, about $20) inverted on the Marzocchi and run the 24" wheel on it. I'd probably run only 1 spring in the Atom 80 on the non-damper side. Weight reduction should be significant.

    The only real issue I see is the differing axle-to-crown dimensions on the forks causing the Marzocchi to raise the front end of the Precaliber and slackening the steering somewhat.

    By using an existing spare fork, wheel, and V-brakes, expenditure is minimal - just the post extenders.

    Just want feedback from anyone who has tried this already.

    Thanks - JMJ
    Last edited by Birdman; 08-29-2017 at 06:19 AM. Reason: renamed thread

  2. #2
    Riding rigid
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    I too am running a Marz atom bomb fork on my daugther's Scott Contssa, but I'm running disc brakes. I'm trying to source some lighter weight springs for it.

  3. #3
    Birdman aka JMJ
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    www.mtbforksbymark.com might have lighter springs. I'd inquired with him (Mark) in regards to getting Xfly top caps to turn my Atom fork into an air/oil Xfly fork. Apparently the seals are the same, so any of the Marzocchi forks can be run with air instead of coil springs. Just need a way to pressurize.

    JMJ

  4. #4
    Riding rigid
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    Thanks for the tip. I also have a Z5 flylight air fork. Should check the top caps.

  5. #5
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    I did the 24" wheel in a 26" fork on a 24" bike for my son but it was a Manitou and it had disc brakes. Worked great.
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  6. #6
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    NYrr496, Have any photos of that bike? I would love to see!

  7. #7
    turtles make me hot
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    I have pics. I can't get them to load.
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  8. #8
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    Anyone try 26" fork running 24" wheel with brake post extenders-p8020381.jpg
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  9. #9
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    Anyone try 26" fork running 24" wheel with brake post extenders-p8020383.jpg
    Last edited by NYrr496; 08-09-2017 at 05:27 PM.
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  10. #10
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    Quote Originally Posted by NYrr496 View Post
    I did the 24" wheel in a 26" fork on a 24" bike for my son but it was a Manitou and it had disc brakes. Worked great.
    What year fork did you use? What do you think about the axle to crown distance and travel? Any special setup/tweaks? Got the same Precaliber and the same crappy stock fork as the OP. Thanks

  11. #11
    turtles make me hot
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    Quote Originally Posted by jblockers View Post
    What year fork did you use? What do you think about the axle to crown distance and travel? Any special setup/tweaks? Got the same Precaliber and the same crappy stock fork as the OP. Thanks
    The pics are down a few posts. I don't remember what year the fork was. I did nothing special, just a straight up installation.
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  12. #12
    Riding rigid
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    Here is my daughter's bike. 23.5 lbs
    The Marzocchi atom bomb was 1740 grams
    Relaced the wheels to 16 spokes And swapped to an AC rear hub and WTB DH front hub
    Spent some money buying new Flow cranks otherwise most everything else was in my parts bin or Craigslist/fleabay
    Stock wirebead tires, so could probably lose a pound if I spring for some Rocket Rons
    Anyone try 26" fork running 24" wheel with brake post extenders-img_0347.jpg

  13. #13
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    Those are some cool builds. Right up my alley. How do they handle compared to stock with the increase in headset height?

  14. #14
    turtles make me hot
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    I couldn't tell you firsthand, but my son tore it up on that bike. Never washed out on him or anything.
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  15. #15
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    awesome. I am on the hunt now! ha ha. Any way I could use v brakes with the smaller wheel?

  16. #16
    Birdman aka JMJ
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    To use v-brakes, you will need a way to lower the brake posts. I was planning on using brake post extenders mounted inverted.

    Promax extenders are inexpensive, but might not be long enough. 18-19mm vs. the 25mm offset of a 24" wheel in the 26" fork.

    JMJ

  17. #17
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    Alternative to lowering the brake post is to raise the fork-ends (which also keep the geometry from jacking-up. )
    Suspension fork shortening

  18. #18
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    The flip side is to use new wheels too. Where can I get a set of light weight wheels with disc front and rim rear in 24" THat would work great too!

  19. #19
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    Quote Originally Posted by Steve Adams View Post
    The flip side is to use new wheels too. Where can I get a set of light weight wheels with disc front and rim rear in 24" THat would work great too!
    Economically: I'd either go for it or not ....
    You can (on one end) stick on a RST F1rst air... and still use the v-brakes and the AC will be compatible. Expense is fairly minimum compared to all the little bits you'd spend changing a fork/wheels...

    Or just get new wheels and forks and stick on some SLX/XT brakes and drivetrain...

    GrayJay's fork shortening is great but for me more about the art of the possible....

    Previous experience makes me feel you end up spending more trying to cut corners and its actually cheaper long term to just go of the whole hog... (and use/buy parts than can be transferred to the next bike)

  20. #20
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    YEah....his frame is a cheaper bike, but I would love to just make it cool for him...he has autism and gets very attached to things. ha ha...So as long as I build it and it's "mostly" the same....we are good.

  21. #21
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    Quote Originally Posted by Steve Adams View Post
    YEah....his frame is a cheaper bike, but I would love to just make it cool for him...he has autism and gets very attached to things. ha ha...So as long as I build it and it's "mostly" the same....we are good.
    From posted weights from luggage scales I haven't seen any significant differences in weights on 24" frames regardless until you are at the extreme end and exotic materials...

    Someone on a UK forum stripped down a cheap own-brand "almost supermarket" bike (a retailer that sells car bulbs, wrenches etc. i.e. not a proper bike shop) and it was 200g less than a big name frame. They likely were made of the same tubes in the same far eastern factory or if not very close...

    The F1rst Air's are actually very good (certainly for a fork at that price) and as a cynical grumpy old git it takes a lot for me to say expectations were exceeded....

    To put that in perspective I have just upgraded my own Revelations to Pike's ... and my expectations are just about met .. the kids FS bike has just had a new set of SID's (its designed to take a edit: [s]24"[/s] 26" fork... and even though I got these 1/2 price I still need to pay for tuning for his weight and they are only marginally lighter than the F1rst's .)

    The SID's are miles better than the XC28's that came with the kids Norco... HOWEVER so are the F1rst's...and his XC bike is sticking with the F1rsts...
    (6 weeks delay at the moment plus your shipping time)
    https://www.bike-discount.de/en/buy/...ion-fork-51499

    These are not AS good as the SID's.... but really work and they worked out of the box... very low pressure but simple and effective. He even rode downhill on these before his new FS bike.. worse possible case, he wrecks them but they cost LESS than the CSU unit for a SID/REBA.... and they are very simple to service..
    (I know its possibly a concern to get spares but your talking worst case you can replace them for little more than a professional service) and they work much better than say low end Rockshox that need tuning

    So back on cheap frames.... I bet its as good as most more expensive ones...
    The choice of changing wheels etc. (and then going disc/11 speed) however is a biggy ... the dependencies stack up really quickly once you go past stuff like bars, stem, seat-post.. i.e disk if you get a new front wheel with disc mounts then why not get a rear with a cassette instead of freewheel.... then if you get disc brakes why not get the shifters that fit to the brakes (especially for kids hands) .. etc.

    Based on this I'd say change the bars, saddle, stem etc. and you can drop a few hundred grams AND make the bike look cool .... but as soon as you mess with drivetrain and wheels you are looking at an investment to take to the next bike.

    One great thing (recommended by POAH previously) are really good quality cables. This makes it much easier on small hands and is also a easy way to do some cool colors...

    I also changed a few things like the cable crimps, a few bolts to alloy ones (water bottle cage bolts etc.) so all in all a few $ that gives the bike a bit of understated bling ... I let my kid choose his cable colour to match pedals etc.

    Disc brakes or not is possibly more influenced by WHERE you ride....
    I got tired of the creak/squeek but our climate means mud most of the year and our local trails are sand mixed with the mud so it really annoyed me hearing every squeak/scrape... (as soon as the wheels were slightly out of true)
    His old V brakes stopped him fine... it was my hearing that suffered...
    Last edited by Steve-XtC; 08-14-2017 at 07:47 AM.

  22. #22
    Wēk Ss
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    Ran Rockshox SID (old version) for both my kids' 24" bike. Worked great. Used discs up front.

  23. #23
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    Yeah totally understand...but for the cost...really...it would be cool just to spank out his frame with all cool stuff. INCLUDING wheels. I really would like to get a set of aluminum hubs with disc front and V rear...anyone know where I can get a set new? and I have been eyeballing those RST's already. HE's getting 2 new trailcrafts next year...but wants to keep his bike he has now as well...ha ha...dad's boy! bike collector already!

  24. #24
    Ride Fast Take Chances :)
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    19mm offset brake extenders are too small. You need 26mm. I was going to go the same route, but am just going to make a custom brake drop.

  25. #25
    Riding rigid
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    My wheels were rebuilt with a AC hub I picked up for cheap and a WTB front hub I had from an old build. Reused the stock rims and spokes. Followed the instructions on Tigworld's site for paired spokes. Built both with 18 spokes. Rear wheel 729 grams and front wheel 713 grams. 1442 grams. The WTB hub was a DH model, so heavier than normal XC hubs. The stock rims were 391 grams.

  26. #26
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    Quote Originally Posted by Steve Adams View Post
    Yeah totally understand...but for the cost...really...it would be cool just to spank out his frame with all cool stuff. INCLUDING wheels. I really would like to get a set of aluminum hubs with disc front and V rear...anyone know where I can get a set new? and I have been eyeballing those RST's already. HE's getting 2 new trailcrafts next year...but wants to keep his bike he has now as well...ha ha...dad's boy! bike collector already!
    I'd go for the disk brake conversion instead of the v-brake change if you are going for the fork.

    e.g.
    https://www.amazon.co.uk/A2Z-Unisex-.../dp/B001O9PHMW

    Then you can get wheels built or buy a pair. (and next year he has a spare set you can put a different tire/cassette on and have the luxury of switching wheels between bikes)

    I built some Novatec D771/772 hubs onto Stand Crest with CX-Ray spokes .. these are incredibly strong and light. (About 1200g a pair from memory without cassette/tires/valves - certainly lighter than my own carbon 27.5 wheels)

    You could also buy Trailcraft Wheels ... only a little bit heavier.. (on their site)
    If your doing a proper job you can get the cranks from them as well and fit it out 1x11.

  27. #27
    Birdman aka JMJ
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    Adapters made

    I fabricated some 25mm extenders. Also had to make sleeves for the Marzocchi brake stud bolt holes to hold the fork together. The extenders have a dowel pin that interfaces to the brake spring holes of the fork to help fix their orientation.

    Not pretty, but I think it'll work.

    I'll try mounting it up this weekend and post the results.

    JMJ
    Attached Thumbnails Attached Thumbnails Anyone try 26" fork running 24" wheel with brake post extenders-img_5512.jpg  


  28. #28
    turtles make me hot
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    Quote Originally Posted by Birdman View Post
    I fabricated some 25mm extenders. Also had to make sleeves for the Marzocchi brake stud bolt holes to hold the fork together. The extenders have a dowel pin that interfaces to the brake spring holes of the fork to help fix their orientation.

    Not pretty, but I think it'll work.

    I'll try mounting it up this weekend and post the results.

    JMJ
    Nice job.
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  29. #29
    Birdman aka JMJ
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    Installed

    I installed the fork. Ran into some issues. I had to file away some of the mounts, as the brake pads were hitting them. Broke out the big file and went to work.

    Next, the brake arms were hitting the mounting bolts. I used some washers to extend the brake posts out a bit, thus moving the arms clear of the bolts. Ground a chamfer on the bolt heads just to be safe. Fit-up was fine, while still engaging the tensioning springs in the provided holes on the extenders.

    Next, I go to mount up the wheel... front wheel is 3/8" axle, not 9mm! Won't fit in the fork dropouts (measure twice, cut once, right?) Argh. Luckily I was going to convert the front wheel to 9mm QR anyway, so I did that too. I already had the 9mm hollow axle kit with a QR skewer, and it was surprisingly easy to do.

    Finally, everything mounted up fine.

    I pulled the spring from the left leg, and jacked up the preload on the right side (damper side). Action was silky smooth, even with a single spring. Sag was about right, and travel went from 50mm to 80mm.

    Say what you want about those old (2001 era) Marzocchi Bomber forks (I have 4 X-flys and 1 Atom now), they are rigid enough and can handle left/right spring mismatches just fine.

    Brake action is fine - no sponginess. Feel is on par with the rear brake. If this was for an adult, I'd be more concerned, but my daughter has spagetti arms, so no danger of overloading the front brake.

    Only dropped about a pound off the bike (just under 25lb), but the fork actually does something now. Jacked up the front end only a tad (a bit over 1"), but it still handles fine (a bit slower). Bonus is no more 15mm wrench needed to mount on the bike rack!

    Anyone try 26" fork running 24" wheel with brake post extenders-thumbnail_img_5513.jpg

    Anyone try 26" fork running 24" wheel with brake post extenders-thumbnail_img_5514.jpg

    Anyone try 26" fork running 24" wheel with brake post extenders-thumbnail_img_5518.jpg

    So, lessons learned:
    1 - extending downwards (24" wheel in 26" fork) means clearance issues galore since you're overlapping the extenders & brakes. Non-issue with discs
    2 - check your axle size fits the new fork. Non-issue is using a disc hub with MTB fork
    3 - Marzocchi uses fine-thread bolts for the brake posts, so these were special ordered, and only available in socket head (not button head), plus you need a 7.9mm diameter spacer to retain the fork legs to the fork arch. Finding the actual Marzocchi bolts for these old forks is nearly impossible.

    It can be done, but if you have the resources and/or parts, save yourself the heartache and go with a disc brake or just use a 26" wheel.

    JMJ
    Last edited by Birdman; 08-26-2017 at 08:06 PM.

  30. #30
    Ride Fast Take Chances :)
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    Nice work and thanks for sharing. Clearance is is issue and I mocked up by brakes to check where they would hit. Right on the brake bosses of course. Will still work but is tight.

    Right now all of brake force is pushing on the pins and friction from the bolts. I was worried about this and am making an arch that connects over the wheel to a center hole on the SID fork. This will brace it better if my boys ever want to get rowdy with the brakes.

    I think you have just enough support and should be fine as long as a bigger kid doesn't ride the bike. Not like my 7 year old even uses the front brake anyway.

  31. #31
    Birdman aka JMJ
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    You are right. The design is marginal if a stronger rider grabs a real handful of front brake. I'd considered an arch design but thought I'd try this approach first.

    I can always add an aftermarket brake booster if the posts start spreading.

    JMJ

    FYI - I made a 2nd set of extenders if anyone needs them.
    Last edited by Birdman; 08-28-2017 at 06:28 AM.

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