Caster vs Rake

Pharaoh XJ

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I have been working on an A-arm suspension & searched here on caster angle

I found out that you can design you caster angle in the upright ( which i understand clearly )
or in the design of the arms ( that is what I dont get) which I am confusing with RAKE angle !!

any help?
 

rharriman

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Castor anlge has to do more with the contact area of the tire through the travel of the suspension and rake angle has more to do with the effects of anti-dive. Or that is how I understand it.

Castor angle includes both the spindle geometry and the arm design as all three components affect castor, which involve the spindle angle in relation to the ground. All three also effect scrub raduis. Try to find a book by Herb Adams titled Chassis Engineering or Tune to Win by Carrol Smith. Both are less then $20 form Barnes and Noble and both are excellent references if you plan to design your own suspension components. There are also some really good suspension calculator avaliable on the internet.

In the arm design there are also other considerations such as bump steer, and shock position at full bump to insure proper shock valving and eliminate excessive tuning and falling rates. I haven't been doing this as long as many guys here on race dezert and am looking forward to seeing if my explanations are good or not and to see any additional comments as well, Good luck with your project and hope some of this helps, I know the books will if you deside to buy them.
 

FABRICATOR

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Caster angle is how much the steering pivot axis is tilted, forward or rearward from vertical, viewed from the side of the car. Farther back on top is positive, farther forward on top is negative. Castor is not a significant design factor of the upright.

King pin inclination (KPI) is how much the steering pivot axis is tilted outward at the bottom, from vertical, as viewed from the front of the car. KPI is definately a design factor of the upright and will dictate, to some degree, contol arm length ratios.

Rake is really a term used for motorcycles and, for the most part, is the same thing as caster.
 
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Pharaoh XJ

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Wow thx !!

But there is something about rake that is different from caster is that in caster angle doesnt affect wheel travel trajectory while in rake the travel the wheel advance & retard with travel. Correct ???
 

FABRICATOR

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Wow thx !!

But there is something about rake that is different from caster is that in caster angle doesnt affect wheel travel trajectory while in rake the travel the wheel advance & retard with travel. Correct ???
Caster does not affect the path of the wheel. However, anything that causes caster change, like a lot of anti-dive or arms that are mounted at an angle for other reasons, will change the path of the wheel. Unlike a pavement car, there is also quite a bit of natural caster change due to the changing attitude of the chassis.

Wheel trajectory and rake angle always run parallel with a typical telescoping fork on a motorcycle. But there again, chassis attitude will change the effective distance, or "trail", between the two.
 
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