Spreading 91mm forks to fit 100mm hubs

Ive got an old hi-ten steel frame im building up (my first), the fork ends are the old low end 91mm spacing and the spare wheel I have is the standard 100mm.

Are there any real implications from spreading the forks to fit the hub, obviously it may slightly weaken the integrity of the forks, but enough for me to worry about on a cheap winter beater? Im not likely to crack the crown or anything am I?

And whats the best way to go about it, just pull the legs apart while getting the wheel in or should I be a little more delicate? Using a method slightly similar to Sheldon’s or something else…

Cheers.

You’re looking at 4.5mm/side, the equivalent of converting a 6spd rear triangle to 10spd. Bigger than most cold sets, but probably fine, especially for 1020 carbon steel.

However… You’ll probably find that there are some spacers between the cone and locknut, so you can remove them and drop the spacing a few mm, then you can probably elastically flex the fork over the hub with no cold set required.

If you can fit it in elastically, it’ll be better for your bike handling, as your first try at this may end up spreading one side more than the other, offsetting the front and rear wheels in the vertical plane, so it won’t track perfectly straight. I’ve done it before with no dramas.

Blakey is on the money - I ran a 100mm hub in 90 something forks for some time without problems - just “elastic” it in and ride.

Blakey is really on the money.

I personally think it is a very very good idea to remove the washer and spacers so the forks are just elastically spread assuming that the forks are the classic brazed crown and legs.

Especially on the cheaper end you can never be sure of the quality of the brazing. The joint is not really designed to handle the direction of force and the type of force required to cold set them. A failure at this joint could be really bad. Really really bad.

It can be done but you need to take precautions to not over stress the crown set.

Thanks for the advice guys, I’m not sure if my wheel has any spacers I can remove, I don’t think it does but I don’t really know much about this so here are some pics of my hub so maybe you guys can clear it up for me.


Cartridge bearing hubs right? Doesn’t look like there’s anything to remove.

If you can’t flex the fork over the hub without really forcing it, either change wheels or forks.

Keep in mind that bending the legs out will also splay the dropouts, which will then have to bend back to parallel when you tighten the nuts. The less the better.

Do what Blakey said, or find a 100mm fork somewhere real-cheap-like.