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Kids bike - fork clearance question

slyfink

Turbo Monkey
Sep 16, 2008
9,784
5,600
Ottawa, Canada
So my oldest son seems to enjoy mountain biking. He has a Commençal Ramones 24, which is a 24" fully rigid "plus" bike (24"x2.6). After a couple of 12 mi rides, he's mentioned his hands hurt by the end. Given that summer camps are likely to be limited this summer, I figured if we ride together he should have a fork.

It seems that the only option I can actually get my hands on is the Suntour XCR 24" (1-1/8" steerer, disc brakes, QR dropouts). On the site, they say Max tire width is 54mm.

So my question is, will the 63mm tires he has on there now fit? I emailed Suntour to ask. They didn't have the measurement of the space between the legs, but said that each side has to have 6mm clearance to the arch.
I found these pictures from a post on MTBR from 2016:
1590514898301.png

1590514912517.png


to me, it looks like he'll have plenty of clearance to the legs. And as I recall, wide tires on wide rims aren't much taller than "normal" tires. I wish I knew what size those tires in the picture are...

Unfortunately, I can't go and try his wheel in a fork as they won't be available till mid-June (2 weeks!) and my shop doesn't carry that sort of item, they'd be special-ordering it.

I suppose I could always get a skinnier tire if I find the 2.6 doesn't fit, but I find "plus" tires work well for him overall...

Any thoughts?

edited to add: it's probably worth mentioning that I'm willing to invest a little in this bike. My oldest (9) will be riding it at least through to the end of this year, and my youngest (7) will probably inherit it next year for a couple of years.
 
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slyfink

Turbo Monkey
Sep 16, 2008
9,784
5,600
Ottawa, Canada
straight 1 1-/8 steerer, or tapered? manitou makes a 24" kids fork but its tapered only
straight. I just called S4 (a tuner/distributor here in eastern Canada). They recommended a Manitou Markhor, dropped to 80mm travel. A2C would then be around 430mm (it's listed as 450mm at 100mm travel), and Commençal recommend a 400mm fork. With sag, I think I'm in the right ball-park. Now I have to sell my wife on the idea....
 

slimshady

¡Mira, una ardilla!
So my question is, will the 63mm tires he has on there now fit? I emailed Suntour to ask. They didn't have the measurement of the space between the legs, but said that each side has to have 6mm clearance to the arch.
Your issue isn't the leg separation or the distance to the arch, but when the fork gets completely compressed. The tire would hit the crown and your kid will learn how to do a somersault in less than a second.

You coul probaby limit the travel by adding a thicker bottom out bumper in the fork lowers. Just put it inside the lowers, making contact with the casting. This works, versus shortening the travel by spacing out the shaft connecting the lowers to the stanchions, which won't work because the bottoming height/free space between the tire and the crown would be the same, just the A2C when uncompressed would change.
 

slyfink

Turbo Monkey
Sep 16, 2008
9,784
5,600
Ottawa, Canada
More traction is safer!
In the end it was a war of attrition! "fine! just buy what you want, as long as I don't have to hear about your stupid g-d fork anymore". :D

Your issue isn't the leg separation or the distance to the arch, but when the fork gets completely compressed. The tire would hit the crown and your kid will learn how to do a somersault in less than a second.

You coul probaby limit the travel by adding a thicker bottom out bumper in the fork lowers. Just put it inside the lowers, making contact with the casting. This works, versus shortening the travel by spacing out the shaft connecting the lowers to the stanchions, which won't work because the bottoming height/free space between the tire and the crown would be the same, just the A2C when uncompressed would change.
Agreed. this is why I went with the 26" fork. No more crown clearance issue. And then I might be able to use it on another frame... Maybe.
 

slyfink

Turbo Monkey
Sep 16, 2008
9,784
5,600
Ottawa, Canada
plus it'll be slacker, and we all know that's better. best to teach your kid that lesson now.
And if I need new cranks for it, it'll have moar clearance for longer (not kid-sized) ones. It currently has crappy 152.5 cranks that like to work loose (cup and cone shimano BB). Shortest NX cranks are 155. win-win!