# Shortening Manitou 26" fork for 20" wheels



## TigWorld (Feb 8, 2010)

I've posted some of this up in the kids bikes section but this might also be of interest to guys needing to shorten a fork for a particular frame build. I modified this fork for my daughter's 20" racing BMX to give her some front suspension on the rocky single track we ride.










I started with a Manitou Sport fork with its easton outers and pressed/bonded on dropouts.

To get the brake bosses in the right position I needed to shorten the outers by 50mm. I also shortened the inners to get the geometry back to close to normal for the 20" bmx frame.

I was concerned about how machining the tubes from within the dropouts would go, but surprisingly once I'd bored the inside of the tube ends that remained in the dropouts to about 0.2mm wall thickness (felt about as thick as a soft drink can) they simply came out of the dropouts.










Pressing the dropouts back on required some care with alignment and I made up a large flanged dummy 100mm front axel to clamp the dropouts together for the start of the reassembly pressing process.

All in all the fork is light, stiff and works surprisingly well on the bike. While these forks were sorta crap on a 26" bike, they seem just the thing for a 25kg kid on a 20" bike. I've got them configured for about 40mm travel.

More info a pictures here.


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## Blaster1200 (Feb 20, 2004)

Instead of looking for old Manitou forks, why not just get an early Answer (before it became Manitou) fork for a 20 inch BMX bike? Although I have not looked lately, there are plenty of them out there. They were briefly popular in BMX racing some time bike until racers found them to be useless in BMX racing. However, they should be ok for trail riding.


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## kampgnar (Apr 13, 2007)

Answer ProForx, good times.


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## pvd (Jan 4, 2006)

I love it! I need to do something like that that will work with disc brakes. Quality front suspension for 20" is impossible to find.

I love what you did with the gearing on that bike too. Really cool.


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## TigWorld (Feb 8, 2010)

Thanks pvd. As an aside, I've used your suspension fluid cSt chart many times until I bought a 20l drum of Silkolene Pro RSF 5wt and revavled all my moto forks for that.

In my searches for suitable forks I did not find any that had disc brake tabs that looked suitable for shortening. Anything with one piece or cast lowers looked impossible to do.

Blaster1200 - I used the Manitou Sport because it was given to me by my LBS. I couldn't find much info on the Answer BMX fork and what I could find said it was crap and that the pros who had to use them put solid internals in. I'm not sure if they even had brake bosses - a lot of BMX racing doesn't involve a front brake. Also 2 weeks of searching the internet revealed not a single one to buy.

Now that I know everything works out, I'd probably try to scavenge a Manitou 3 or 4 type fork as you can get spring/hydraulic damper kits for these and that would probably result in a much better overall suspension package. Elastomers are pretty sucky although if you're only talking about 40mm of travel they sort of do the job.


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## Blaster1200 (Feb 20, 2004)

TigWorld said:


> Blaster1200 - I used the Manitou Sport because it was given to me by my LBS. I couldn't find much info on the Answer BMX fork and what I could find said it was crap and that the pros who had to use them put solid internals in. I'm not sure if they even had brake bosses - a lot of BMX racing doesn't involve a front brake. Also 2 weeks of searching the internet revealed not a single one to buy.


Ah, you are right...they did not have brake bosses.


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## mattty (Feb 26, 2009)

_I need to do something like that that will work with disc brakes. Quality front suspension for 20" is impossible to find.
_

Saw this and had to mention that a friend of mine successfully converted an old inverted Marzocchi shiver SC to an awesome kids downhill fork. He slid the bolt-on crowns downward and used an old set of upper crowns, from a fullsize DH version he had laying around, for the uppers


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## Andy FitzGibbon (Jul 7, 2007)

White Bros. makes a 20" 80mm travel air fork for recumbent bikes.










Has adjustable rebound and compression and rim and disc brake mounts. No lockout or platform. Available in 1 1/8" threadless and 1" threaded and threadless. It might be kind of spendy for a kid's bike, though, at around $700.
Andy


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## TigWorld (Feb 8, 2010)

Nice find.

Yep, $719 is a bit more expensive than a shut and cut on a Manitou free from the LBS. Looks pretty cool. Someone else also makes a carbon suspension fork for 20" recumberants but the problem with racing BMX rims is that they have a larger diameter than normal 20" freestyle/jump BMX rims. If anyone wanted to order one of these forks they would really need to check that the brake bosses are in the right place for their version of 20" rims.


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## Blaster1200 (Feb 20, 2004)

TigWorld said:


> but the problem with racing BMX rims is that they have a larger diameter than normal 20" freestyle/jump BMX rims.


Huh???

The 20" tires on my 20" dirt jump BMX bike are the same size as the tires on my 20" BMX race bike.


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## dr.welby (Jan 6, 2004)

Blaster1200 said:


> Huh???
> 
> The 20" tires on my 20" dirt jump BMX bike are the same size as the tires on my 20" BMX race bike.


He's talking about the 20 x 1 3/8" race tires on minis (451 bead seat), not standard 20s (406 bead set).


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## pvd (Jan 4, 2006)

20" tires come it 406mm and 451mm ISO diameters. Generally, 451 is used on the more narrow tires.


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