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Fork rake question(5 posts)

Fork rake questionJuanmoretime
Sep 17, 2002 5:42 PM
What will ging from a 43 rake to a 45 do to my steering?

Thank you for the help!
re: Fork rake questionjhart11
Sep 17, 2002 6:18 PM
Your wheelbase will increase by 2mm. This will make your bike slightly less resposive while cornering. You may notice that your bike is a wee bit more slugish. You can balance an agressive headtube angle (greater than 73.5 degrees) with a relaxed fork rake.

On the other hand, moving in the opposite direction--to a rake of 40mm will make your bike MUCH more resposive-possibly too much, depending on your frame's headtube angle (combining a 73.5 degree headtube angle with a 38 or 40 degree rake would make for a sketchy handling bike).
re: Fork rake questionjjohnson05
Sep 17, 2002 7:19 PM
Just the opposite!
dead wrong...C-40
Sep 18, 2002 8:40 AM
Steering response is determined primarily by the amount of trail, not the wheelbase. The greater the trail, the slower the steering and tendency to maintain a straight line.

Increasing rake reduces that amount of trail and speeds up the steering response.

Trail = (R/tanH) - (rake/sinH) where R is the radius of the tire and H is the head tube angle (HTA).

The first half of the equation is the trail without any rake. As you can see, all rakes reduce the the total amount of trail.
At long last I finally think I understand trail.Leisure
Sep 18, 2002 3:40 AM
It took a long time toiling about how rake affects handling, but finally I think I get it.

The two millimeters shouldn't do too much to you low-speed steering changes by affecting wheelbase length; most of the influence will be on higher speed handling. A 45 rake will have less "trail", which means the part of the tire that contacts the road will not be as far behind the steering axis. What this does at high speeds is apply less force against the wheel to auto-center your front wheel.

A simpler system that makes for a better illustration is just looking at the front wheels of a shopping cart. The wheel contacts the ground behind the axis the assembly pivots around - this is the trail. You steer the cart in any direction, and the floor moving against the trail will cause the wheel assembly to steer until the wheel is spinning with the floor.

When people say that a bike with more trail is more stable, what they mean is that the front wheel stays centered while needing less active correctional force from the rider. You can, for example, take your hands off the bars more easily and expect the bike to keep going straight.

I actually prefer arrangements that ended up having less trail. Now that I get the theory, I think what I'm preferring is handling that isn't influenced as much by different speeds and also lets me turn the bars where I want (as opposed to letting the bike handle itself). Less trail offers this for me. Well, that's about as well as I understand it.