Rigid forks: Effect of increase/decrease in Axle-Crown length
 

Hi all,

Can anyone help me to understand the effect of getting a longer / shorter fork?

I'm replacing the rigid, 1 1/8th rigid threaded fork on my '97 Trek (26 inch wheel) with a 1 1/8th rigid threadless fork. I'm running lovely old canti brakes, but want a disc-ready fork to be ready for the future when disc brakes rule the world.

There are several options out there, but they all have either a shorter or longer axle-crown length than the old fork: Most are longer, made to replace suspension forks.

The old fork: 405mm A-C

Possible replacements:
- Identiti Tuning Fork: 395mm A-C
- Surly 1x1 - Shorter version: 413mm A-C OR Longer version: 453mm A-C
- Surly Instigator: 447mm A-C
- Surly Troll: 453mm A-C
- Surly Big Dummy: 425mm A-C
- Gusset Jury: 405mm A-C

I had my eye most on the shorter Surly 1x1, but they're out of stock everywhere and I suspect they're possibly phasing them out as the trend goes to longer forks. The Identiti fork is the cheapest option.

I don't want to make the bike noticeably lower at the front end as 90s MTBs are already quite aggressive in their saddle-handlebar heights (bars inches below , but the way it's been described to me, a 10mm shorter fork will partly bring the front end closer to you as the bike pivots around the rear axle, so won't have the same effect as say, using 10mm less in spacers below the stem.

Having said that, I put the front wheel on a 50mm thick book to measure the increase in handlebar height of a 50mm longer fork, and it raised it 4.5cm as marked on a wall, so it seems the height of the front end is still affected quite a bit...

I don't mind making the front of the bike a bit higher, for comfort, though have seen lots of people saying that increasing the fork length puts extra stress on the head tube welding, which I'd be worried about on an older bike...

Any input appreciated,

Sb88

Deleted :P see mechanics section you also posted in.. redundantly..