Rake/Trail/Handling ??

[bhungerford]

Ok, so i did a search, and didn't find too much, this might be interesting for some:

If i have a bike with a 72 degree HT angle and current fork that is 400mm axle to crown, and 44mm rake and switch that to one that is 376mm axle to crown, and 45mm rake, what would one expect in terms of handling changes?

the extra 1mm of rake would make the trail less and handle quicker, but being shorter, wouldn't that then effectivelly steepen the HT angle and thus make it about a wash in terms of trail and handling?

Just been thinking about this lately and trying to see if i'm thinking in the right direction...any comments welcome :)

[Samster]

[.]

[Samster]

here's a thread (http://forums.thepaceline.net/showthread.php?t=29455) from a ways back re: my issues with fork rake.

[dauwhe]

What about the difference in length? That's very nearly an inch. Curious what impact the axle-to-crown distance has. Wouldn't that cause problems with the brakes if that changed?

Dave, ignorant of all things related to forks

[mosca]

That 24mm length difference will pretty much change everything, i.e. HTA, STA, BB drop. I'd be careful there. It's probably best to lay it out on BikeCad or some other program to see what the changes would be graphically. Gestalt and all that...

[Smiley]

The axel to crown length is known as the SPAN of the fork and Yes everything changes if that dimension is that big of a difference.

[RudAwkning]

Ok, so i did a search, and didn't find too much, this might be interesting for some:

If i have a bike with a 72 degree HT angle and current fork that is 400mm axle to crown, and 44mm rake and switch that to one that is 376mm axle to crown, and 45mm rake, what would one expect in terms of handling changes?

the extra 1mm of rake would make the trail less and handle quicker, but being shorter, wouldn't that then effectivelly steepen the HT angle and thus make it about a wash in terms of trail and handling?

Just been thinking about this lately and trying to see if i'm thinking in the right direction...any comments welcome :)

That axle to crown difference would mean that one of these forks was built for "long reach" brakes, no?

[dauwhe]

I think it's even too much for that. Difference between long-reach at bottom of slot (57mm) and short reach at top of slot (39mm??) is less than 20mm.

Could these two forks be designed for different wheel sizes?

Dave

[Orin]

I think it's even too much for that. Difference between long-reach at bottom of slot (57mm) and short reach at top of slot (39mm??) is less than 20mm.

Could these two forks be designed for different wheel sizes?

Dave

Sounds like the first is a cyclo-cross fork and the second a regular road fork.

Orin.

[bhungerford]

hey, thanks for the replies...mis-read the span distance, one is 400mm, 44 rake, the other is 390mm, 45 rake. both for 700c wheels. in case you're all wondering i'm thinking of getting a Surly Long Haul trucker fork for my cross check to do some touring with it. not sure if it will work or not, might just buy the fork anyways, as it's only like 70 bucks and would be a good learning experiment as to how the changes in dimensions feels on the road.

i would tend to agree that the length will affect the ST angle and BB drop somewhat.

[RPS]

as it's only like 70 bucks and would be a good learning experiment as to how the changes in dimensions feels on the road.

i would tend to agree that the length will affect the ST angle and BB drop somewhat.Changes in road feel you experience will also be due to other differences in the forks -- like stiffness -- so you shouldn't attribute all change to the dimensions.

As to ST, HT, and BB drop changes, you can estimate that with a little geometry by assuming the frame will rotate about the rear axle.

[mosca]

In my semi-informed opinion, you should be ok with 10mm shorter fork on that bike. BB will drop slightly, HT and ST angles get slightly steeper, but starting with the cross-check geo, I can't imagine you'll have any problems as it's already got fairly relaxed angles and high-ish BB. I say go for it!

[bhungerford]

ok, thanks for the comments, i'll order the thing and give it a try here in the next few weeks, always cool to get some opinions from others around the country(world) :beer:

[Tom Matchak]

In the case described here (10mm shorter axle-to-crown, 1mm more offset), the HT and ST angles will be about 0.5 degree steeper than with the original fork. The BB will be about 4mm lower. The new trail will be about 4mm shorter than before.

[mosca]

Oh, yeah - Chris King is making a +5mm crown race, so if you're using a King headset you could split the difference there.