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Fork rake question(8 posts)

Fork rake questionBowWow
Nov 26, 2002 1:37 PM
My current ride has a 73.5 degree head angle and a steel fork with a 45mm rake. What would happen to the handling if I replaced the steel fork with a carbon fork with 43mm rake? The ride is very stable right now. Would it become noticeably quicker steering? Maybe... too quick..? Any thoughts/experience?
OLN Bicycle Test Guide Sayseschelon
Nov 26, 2002 2:11 PM
I cannot remember exactly who said it...but suffice to say, that one night this year when they were doing road bike comparisons, one of the testers said that the rake on road bike forks adding or changing handling characteristics is a myth...and does not do anything.
re: Fork Rake & TrailChen2
Nov 26, 2002 2:45 PM
In reality, reducing rake will increase trail which in turn will "slow" the steering, but in your case it will be a very slight change. In fact if I were you I might drop back to a 40mm rake. You don't need to worry about going from a 45 to a 43, it will work fine. Here is a URL for rake and trail, there are many others.
www.phred.org/~josh/bike/trail.html

Going from a steel fork to a carbon fibre, especially if it is all CF, will take a lot of weight off of your bike.

~Al
re: Fork Rake & TrailChen2
Nov 26, 2002 2:46 PM
Here is another:
www.kreuzotter.de/english/elenk.htm
~Al
Follow-up - shorter rake=shorter wheelbase & greater toe overlap?BowWow
Nov 26, 2002 3:31 PM
Will there be any significant increase in toe overlap with a 43mm or even a 40mm rake? Going from 45mm to 40mm rake loses 5mm of rake, but does it also change wheelbase/overlap by 5mm?

I'm still trying to wrap my head around less rake = slower steering...

Thanks for the excellent input! I love this forum!

Steve
more to consider....C-40
Nov 26, 2002 4:14 PM
You didn't mention your frame size. People who make suggestions about fork rake without knowing the frame size are making uneducated guesses. Changing the rake by 2mm won't make much difference, but all reductions in fork rake will slow the steering a bit. Better to be a bit slow than too fast, though.

Yes, reducing the rake will reduce the front-center dimension, which would increase overlap (by 95% of the rake)if you are currently experiencing this problem. If you already experience overlap, what's the difference if it's increased by a small amount? Overlap is overlap.
Thanks! Doing more research..BowWow
Nov 27, 2002 9:29 AM
..has helped me grasp the HA/Rake/Trail/Front-Center relationship. Both the above sites were very informative, with the phred site giving the best explanation of trail, and the kreuzotter site giving the math. It is clear that if the head angle was 90 degrees decreasing rake would decrease trail, which would speed up the steering. But with less-than-90, decreasing rake actually increases trail, thereby slowing the steering. The the shopping cart example coupled with the diagram cleared it up for me.

I also appreciate the calcualtion you give in your post, that front-center is decreased (or increased) by 95% of the rake. I assume that that figure varies by head angle, where steeper angles give greater changes.

Thanks to all for great input!

Steve
Let's do the math: 45-43 = 2mm more overlap (nm)Kerry
Nov 26, 2002 4:32 PM