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+/- 2mm of rake...what, if any, effect will this have?(9 posts)

+/- 2mm of rake...what, if any, effect will this have?SS_MB-7
Jul 8, 2002 3:31 AM
My cyclocross frame was designed around a fork with a 45mm rake. I am looking to upgrade the fork to a carbon model (AME, Wound-Up, etc.). However, neither of these forks have 45mm rakes. The AME has 47mm (+2mm) and the Wound-Up has 43mm (-2mm).

I understand the effects of decrease/increase rake on trail, in that, it increases/decreases it, respectively. However, will +/- 2mm have a noticeable effect? If so, which would be better (AME or Wound-Up)?

Ride Hard,
Mike B.
stabilitybigrider
Jul 8, 2002 6:11 AM
Less rake will give you a quicker steering less stable bike while more rake will give a more stable steering slower responding front. Two millimeters either way may not be huge but should be noticable. I would find a fork with a 45 rake. If I had to choose between those two choices I would pick based on what I was riding. If you are not doing anything "rough" and staying on good stuff then go with the 43, if you are riding rough cyclocross courses opt for more stability.
Steerabilty VS Stability, rakes, trails, et aljose_Tex_mex
Jul 8, 2002 7:13 AM
Mike B.,
The rake goes to the old Steerabilty VS Stability question. When you increase one you decrease the other.

Consider three types of forks, The type that:
1) that curve out ahead - call it positive rake.
2) have no curve - call it zero rake.
3) curve back - pretend you took the positive rake and turned it around 180 degrees - call it negative rake.

When you play with the curvature of the fork you change the trail of the fork. The distance between a straight line through the steering axis into the ground and by dropping a perpendicular from the mid point of the axle to the grtound. Check this out on-line as it's kind of difficult to explain without a diagram. http://www.phred.org/~josh/bike/trail.html

When the fork has a positive rake the effect is a shorter trail - it's least stable but most steerable. Although, not "least stable" to the point of danger - just wrt the three cases above. This is the most steerable fork.

WRT the above - When the fork has no rake the trail is less and the bicycle is more stable but less steerable. It's the optimum blend of steerability and stability.

WRT the above - when the fork has a negative rake it will be the most stable but the least steerable which is why you never see it around.

This is why kids bikes nearly always have a straight fork -in order to help them with both factors.

So, if you increase the rake - you decrease the trail, increase steerability and decrease stability.

If you decrease the rake you increase the trail, increase stability and decrease steerability.

From http://www.juliuss.clara.net/bicycle_handling.html :
"Increased trail (less fork offset/shallower head angle): The bicycle will keep to a straight line better, but will resist turns. There will be less reaction to rider lean and shifts in weight. Objects on the road surface will deflect the bicycle more.

Decreased trail (more fork offset/steeper head angle): The bicycle will be quicker into turns. There will be more reaction to rider lean and shifts in weight. Objects on the road surface will deflect the bicycle less."

Hope this helped...
Fork CurvatureChen2
Jul 8, 2002 8:44 AM
Actually a fork's curvature is not a measure of rake. A straight fork can have as much rake as a curved fork because the straight fork will have a more abrupt change in angle just below the steerer.
~Al
True - It's just easier to visualize (nm)jose_Tex_mex
Jul 8, 2002 11:02 AM
Thanks for the great explanation, Jose!kapalua
Jul 8, 2002 10:31 AM
Thanks for the great explanation, Jose!jose_Tex_mex
Jul 9, 2002 11:15 AM
You're very welcome kapalua. I appreciate the kind words. I thought someone out there would enjoy a bit of techy stuff.
Best of Luck...
I agree with everything you wrote, but....SS_MB-7
Jul 8, 2002 11:20 AM
Thanks for your post. While I agree with everything your wrote, will +/- 2mm really have that much of an effect? Or, is it like the "Princess and the Pea"?

Sorry for the sarcasm, but have you looked at 2mm on a ruler? It's tiny. However, I guess since this 2mm is measured at the axle, it is magnified at the wheel's contact patch. I haven't actually gone through the trig to determine the actual trail difference +/- 2mm of rake will make, but I am just wondering if I'll be able to 'feel' it.

Ride Hard,
Mike B.
Simple answerNessism
Jul 8, 2002 11:51 AM
I doubt you will notice much difference either way. You would likely be able to notice a difference however if going from a 43 to a 47.

One thing to keep in mind is that carbon forks are usually longer in length then steel forks. This causes the head angle to slacken ever so slightly during carbon fork upgrades.

Good luck.

Ed