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Old 05-20-07, 05:50 PM   #1
karlkras
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Fork rake... does 2mm make a significant diff?

Hi,
I'm facing the reality that I may need to replace my current threadless steel chromed fork with a carbon model since the current (bought used with the frame) has been cut too short for me. I'm guessing this had originally been a threaded conversion gone bad. Too bad too, this is a pretty cool older Pinarello frame...
Anyway, this is a 1" steerer, and is measured at a 45mm rake. Wheel on, there's still a fair amount of space between tire and fork. Given this, would purchasing a replacement spec'd at 43mm work for me? or is this a big difference? Also, are there other factors I should be concerned with in determining the proper replacement fork? I'm aware that the steer length is important, I'm only considering 300mm in length so I avoid the problem that I have now.
thanks,
Karl
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Old 05-20-07, 06:13 PM   #2
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The reduction in rake will increase the trail slightly slowing the steering. Key word here is "slightly" - I doubt you will notice the difference. A bigger factor is trying to match the fork length. Carbon forks are typically longer than lugged steel forks so when you install the new fork it will raise the front end of the bike some which will further slow steering. It's all a mater of degree and again you may not notice. If you do decide to go forward with the fork swap I suggest that you try to find one that's on the shorter side of average to ward off any issues.

http://www.sheldonbrown.com/rinard/forklengths.htm

Good luck.
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Old 05-20-07, 07:56 PM   #3
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After selling my wife's bike I found myself with an extra Ouzo Pro fork exactly like the one I had installed on my Trek except it was a 40mm rake instead of the 43 on the Trek. I decided to try the 40 because I thought I would like more trail. Actually I was surprised that I could feel a significant difference, fut after a couple of rides I was fully adjusted and wasn't sure which fork I liked better so I left the 40 on the bike and sold the 43. So I would say that you will feel a difference, not only a difference in trail but also a difference in material. I think I would probably prefer a 43 to a 45 or the longer fork arms because of the increase in trail.

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Old 05-20-07, 08:48 PM   #4
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I switched from a 45mm to a 43mm rake when my carbon fork was marginalized by a crash. Aside from a little more toe overlap, it seems a little more twitchy, but it still handles fine. I did have to readjust the saddle fore/aft due to the slight change in geometry.
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Old 05-20-07, 09:02 PM   #5
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more trail should make a bike less twitchy right? or am i wrong?
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Old 05-20-07, 09:22 PM   #6
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Quote:
Originally Posted by Surferbruce
more trail should make a bike less twitchy right? or am i wrong?
You are right!
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Old 05-21-07, 08:01 AM   #7
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Quote:
Originally Posted by Surferbruce
more trail should make a bike less twitchy right? or am i wrong?
You are correct, at least for normal riding speeds.
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Old 05-21-07, 09:10 AM   #8
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Quote:
Originally Posted by Surferbruce
more trail should make a bike less twitchy right? or am i wrong?
That's what I've heard, but I swear the shorter wheelbase seems to make my bike more twitchy. Either way, 2mm didn't make a big difference. It "felt" different, but rides just fine.

btw I never did understand the concept of trail. Is it because the axle is behind the handlebar? Aside from that, the fork extends the axle forward from the headtube, so I never understood how that could be "trail"?

EDIT: nevermind, I get it now. I looked it up on wikipedia and realized that the headtube line is angled but the line for the axle is vertical, so they intersect and the axle point is then trailing.
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Last edited by urbanknight; 05-21-07 at 09:17 AM.
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Old 05-21-07, 09:26 AM   #9
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Quote:
Originally Posted by urbanknight
That's what I've heard, but I swear the shorter wheelbase seems to make my bike more twitchy. Either way, 2mm didn't make a big difference. It "felt" different, but rides just fine.
I read somewhere that increasing the trail can make a bike feel more twitchy at slow speeds, but more stable at high speeds. I think that may fit the experience I had with my Trek. My Colnago has a lot more trail than my Trek due to the more laid back head tube angle and it is way more stable feeling even with a 43mm rake offset as compared to the 40mm on the Trek. My perception is that the HTA is more critical than the rake offset.

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