Custom Igleheart fork length

[M952]

I have recently built up a 20.5" 1994 Litespeed Obed using a 425mm Salsa Cromoto fork, and found the (roughly) 69.5 degree headtube angle is more slack than the factory-designed 71.5 degrees.

This model was offered with the Rock Shox Mag 21 with 2.3" of travel or the Quad 10 with 1.7" of travel. I've seen various equivalent axle to crown lengths online for these forks, but figured I'd ask here for input.

I'm looking into having a custom Igleheart fork built, as it seems most rigid forks are now designed for 80+ mm of travel, which ruin the appearance and handling of an older bike.

What length axle to crown do you recommend for a rigid fork for my Obed?!

 

[M952]

Re:

And before you ask, yes I ride this off road. It doubles as my road/commuter during the week, though...thus the Gatorskins

 

[Lhatch4]

I think it looks good with the fork length that it has. If you want a more early 90's look then figure out how much shorter you need to go in order to make the top tube parallel to the ground.

 

[shamobius]

Re:

410mm axle to crown...

 

[troje]

Re:

Or 395... top tube should be horizontal with this Litespeed. Should be relatively easy to measure the atc reduction needed.

 

[danson67]

Better to work it out using the bike itself:

Pack things (books, plywood, cardboard etc) under the rear wheel until the head angle is the 71.5 you're aiming at.
Measure the height of the stuff under the rear wheel and subtract that length from the current fork length to give you the fork length you need.

All the best,

 

[M952]

Re:

Great suggestions!

I'll be sure to follow up when the new fork is installed.

 

[xerxes]

Re:

Pack things (books, plywood, cardboard etc) under the rear wheel until the head angle is the 71.5 you're aiming at.
Measure the height of the stuff under the rear wheel and subtract that length from the current fork length to give you the fork length you need.

Surely that'll be slightly off, because the forks are at an angle. :?

 

[danson67]

True, you're right, the vertical distance (packing thickness) will be slightly shorter than the angled distance of the measured fork length because of the fork offset.
The method is basically just raising the floor beneath the rear wheel and calculating how far vertically below that floor the front wheel is.

However, for example, for 40mm of packing, we're talking an underestimate equal to the difference in length of the adjacent side and hypotenuse of a 40mm triangle with a 7 degree opposite angle (typical fork angle offset), ie: 0.3mm...

Not exact, but a lot better than trying to work it out from any quoted fork travel, length, sag, etc. and probably well within the tolerances of any measuring here (and the dimensions of the frame and forks in question)

All the best,

 

[Lhatch4]

I vote that we ban any member who tries to teach us trigonometry ;-)

We don't need no education. We don't need no thought control. All in all your just another brick in the wall.