Caster angle, or trail?

Joined
Dec 8, 2002
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Cincinnati
I am about to set up my front axle on my next rig. So I was sitting here thinking to much and I had this thought.

When we upsize tires it increases the trail on the contact patch. should I decrease the caster to get the trail back to near stock? What does all this do with the Ackerman angle?
 
Joined
Aug 11, 2003
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82
From my understanding, the bigger tire the more caster? Someone correct me if I'm wrong. I've heard of 5-7 degrees for 40-44" tires. I have 35's with 1 degree, works great. If you want to increase caster you will need to cut and turn the knuckles.
 

John Smith

In the garage
 
 
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Jun 7, 2004
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Big tires like more caster. I am currently running 5deg on 36 bias IROKs and it tracks great. Does not follow ruts in the road at all and has great return to center on the steering wheel. I may drop it down to 3deg if I find I am getting funky tire wear.
 

71-CRUISER

 
 
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May 26, 2004
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Atlanta, GA
TLCA_Paul said:
When we upsize tires it increases the trail on the contact patch. should I decrease the caster to get the trail back to near stock?
Stock caster is about -1*. With larger tires most people cut and turn to end up at around -5* or so.

TLCA_Paul said:
What does all this do with the Ackerman angle?
Absolstly nothing. Ackerman has to do with steering angles. IE the inside tire has to turn sharper than the outside tire due to the outside tire traveling around a larger diameter than the inside.
 
Joined
Dec 8, 2002
Messages
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Cincinnati
I'm not saying anyone is wrong, just chating a bit.

Here is how I got this thought. With stock caster and larger tires the geometry gives you a contact patch trailing the rotational center of the tire. So when you add even more caster it will add more trail. Giving the truck a shopping cart effect. Yea it will go straight down the highway no problem. However if you have any toe in it will also add camber. Also when you steer on the trail it will push the truck more sideways.

That being said I will probably set mine up at around 5* and have adjustment in the arms to play with. Yea I plan on making it street leagle. Maybe even drive it to Moab? That is if I ever get back to working on it.
 
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