Head Tube Angle and Fork Rake ??

[snah]

I know this kinda question has been covered in multiple threads, but thought I'd add another.

Last night picked up a Lynskey R255 on the cheap, at least I think so. The specs show a M/L with a 72.5 head tube and 73.5 seat tube, calls for a 43 rake fork. My question, I have a unused Reynolds sitting in my garage, with a 45 rake. My main ride is a Peg, using the same fork and 73 for both head and seat tubes.

If I use the 45 on the Lynskey, what difference would I expect:

1. Compared to the ride of the Peg?
2. Compared to using a 43 on the Lynskey?

Thanks!!

[tuscanyswe]

I know this kinda question has been covered in multiple threads, but thought I'd add another.

Last night picked up a Lynskey R255 on the cheap, at least I think so. The specs show a M/L with a 72.5 head tube and 73.5 seat tube, calls for a 43 rake fork. My question, I have a unused Reynolds sitting in my garage, with a 45 rake. My main ride is a Peg, using the same fork and 73 for both head and seat tubes.

If I use the 45 on the Lynskey, what difference would I expect:

1. Compared to the ride of the Peg?
2. Compared to using a 43 on the Lynskey?

Thanks!!

1: Even if this was possible to tell you in theory its impossible to answer since the frames could have been designed with different axle to crown measurements for the fork and we dont have that info.. So with out that info the headtube angle is irrelevant (well its no longer exact at least) as it could be different with either fork than the 72.5 it was suppose to have with the correct axle to crown length fork.

2. Assuming both forks same brand and model in 43 and 45 rake. Slightly faster steering since increasing the rake would reduce the trail. In theory.. Would you be able to tell a difference at all? Probably not.

[carpediemracing]

Someone I know swapped forks on his bike after something happened to the original one. Rake was off by 2 or 3 mm. He noticed a difference, but it was subtle and, to paraphrase him, it really didn't matter.

If it's a new-to-you bike I doubt you'd notice anything untoward.

If after a while you put a 43mm fork on that frame, I bet you'd notice a subtle difference. Less rake should give you more trail so the bike will be a bit more stable in a straight line. Also the front wheel will flop a tiny bit less.

[ColonelJLloyd]

No one would be able to tell he difference between 2mm rake all else being equal (and they're both "road" forks so we can assume an A-C that is close enough to be considered equal). You're fine using what you have.

[bobswire]

For those wanting to find their trail. Nice calc. > http://yojimg.net/bike/web_tools/trailcalc.php

[drewellison]

No one would be able to tell he difference between 2mm rake all else being equal (and they're both "road" forks so we can assume an A-C that is close enough to be considered equal). You're fine using what you have.

I recently did a fork swap on one of by bikes. In researching different carbon road forks, the ac length varied by up to 12mm IIRC. That can make a huge difference in geometry and handling.

[cinema]

a-c is a bigger difference. add in 2mm rake difference you could probably tell a difference if the forks are a different length.

On another note, does anyone know how manufacturers measure axle to crown? is the correct way the theoretical line parallel to the steer tube?

[snah]

I think I can add a bit to my question, Lynskey recommends 367 ac and 43 rake fork. From what I find, my Reynolds Ouzo Pro is 372 ac and 45 rake. I needed schooling in this stuff, what are thoughts comparing the two?

[Peter B]

You likely couldn't tell the difference if riding back-to-back, certainly not beyond an initial reaction. Since you have no frame of reference, you'll think it handles just fine.

And it will.

[ColonelJLloyd]

On another note, does anyone know how manufacturers measure axle to crown? is the correct way the theoretical line parallel to the steer tube?

I'm not a framebuilder, but the term is "axle to crown" and there's really only one way to measure that, right? Center of axle to the place where the crown race sits in a straight line.

I think I can add a bit to my question, Lynskey recommends 367 ac and 43 rake fork. From what I find, my Reynolds Ouzo Pro is 372 ac and 45 rake. I needed schooling in this stuff, what are thoughts comparing the two?

Doesn't the a-c need to increase as fork offset does in order to keep the frame geo (HTA and STA) the same? Again, I'm not a framebuilder and am not sufficiently caffeinated at this time.

[cinema]

I'm not a framebuilder, but the term is "axle to crown" and there's really only one way to measure that, right? Center of axle to the place where the crown race sits in a straight line.

but the a-c measurement would change based on the rake if it were measured that way

[ColonelJLloyd]

but the a-c measurement would change based on the rake if it were measured that way

I don't follow. It's a static measurement. Each fork after it is made is going to have a fork offset and a-c measurement and that's that. If you took two otherwise identical forks where one had an offset of 45mm and the other had offset of 60mm, the one with 60mm would have a longer a-c measurement. Both could be installed on a the same frame with the same resulting HTA and STA.

http://i130.photobucket.com/albums/p260/BillyGoat71/tt.jpg

[Desert Fox]

I know this kinda question has been covered in multiple threads, but thought I'd add another.

Last night picked up a Lynskey R255 on the cheap, at least I think so. The specs show a M/L with a 72.5 head tube and 73.5 seat tube, calls for a 43 rake fork. My question, I have a unused Reynolds sitting in my garage, with a 45 rake. My main ride is a Peg, using the same fork and 73 for both head and seat tubes.

If I use the 45 on the Lynskey, what difference would I expect:

1. Compared to the ride of the Peg?
2. Compared to using a 43 on the Lynskey?

Thanks!!


FWIW, last year I swapped out a Serotta S3 (47mm rake, 372mm a-c) for a Pegoretti Falz (45mm rake, 368 a-c) on my Holland (72 head angle) and really couldn't perceive any difference in steering (other than the Falz being stiffer). The slight increase in the effective head angle due to the lower a-c of the Falz pretty much negated any increase in trail.

[false_Aest]

Just did a mock-up to see what a 5mm difference in A-C does to other stuff.
Then looked at what it'd take to change the HTA by 1 degree.


Original
A-C: 367mm
HTA: 73*
Rake: 45mm
Trail: 56mm
STA: 73*
STANDOVER: 765mm
BB HEIGHT: 261mm

+5mm
A-C: 372mm
HTA: 72.7*
RAKE: 45
TRAIL:57mm
STA: 72.2*
STANDOVER: 768
BB HEIGHT: 263mm

A-C: 385
HTA: 72.0
RAKE: 45mm
TRAIL: 62mm
STA: 72
STANDOVER: 774
BB HEIGHT: 268