I have an '02 and a 99 Miata. There is less than 400 lbs difference in weight but a world of difference in handling. The Miata turns in better and feels much lighter. It doesn't drift as well, but it does everything else just a little bit better. I am sure that part of the feel difference is the tread width on the tires, but I don't believe that accounts for most of it.

I run 2 degrees negative camber up front and 1.7 in the rear with some toe out in front and only enough toe in on the rear to make sure that under bushing compression I don't get toe out. I have seen where some people are running as much as 6 degrees caster whereas mine will only get 5-5.5.

The alignment on the Miata is similarly aggressive, but with a lot less Caster.

The alignment guy and I did a search and can't find any other cars running nearly this much caster so we began to speculate that maybe the large caster number is part of the difference in feel.

Before I experiment with less caster I thought I would ask if there is a valid reason for this much caster?

Has anyone played with a smaller number and if so what were the results and what seems to be working?

This alignment gives me the least push of any I have tried so far, but it still feels awfully heavy and not as responsive as I would like. I am still running the S02s. If I didn't have the Miata to constantly compare I would probably be happy with the handling.

David b.

 

I've guessed that a lot of caster is dialed in to aid steering feel with the electric steering rack which is pretty numb (at least when compared to cars with exceptionally nice road feel). Backing off on caster will definitely lighten the feel but with some cost to centering and tracking feel. I don't see where experimentation to find your preference will have a large impact on anything else.. go for it.

 

I never thought about the need to compensate for a numb electric power steering. I am wondering if that is it or if there is something "special" about our suspension set up. IIRC lots of caster adds neg camber when you turn the wheel so I thought that might be the purpose. That is the part that worries me. Could less caster lead to more push because of less dynamic camber? Do I have my thinking all backwards here?

Since most other cars call for SO MUCH less Caster I wonder if there really would be much loss of the centering and tracking feel.

Another benefit of less Caster would be the ability to dial in more camber. I don't think I really want to go more than 2 degrees negative on the front, but if I can ever afford R rubber I might.

 

European cars usually have much more caster than domestic cars. I guess this is due to their driving environment. More caster with less negative camber will provide better straight line braking, since the wheels will be more upright. It will also require more steering effort.

I am suspicious that your mechanic cannot get 6 degree's of caster. My mechanic told me that too, but after a significant amount of arguing, he realized that he was turning the bolt the wrong way. Basically, 4.5 degrees is the LEAST amount of caster that he could dial in. The MAX amount of caster is nearly 9 degrees!

 

I just checked the Helm's manual. The OEM alignment spec for caster is 6 degrees. If you really can't get it aligned to that, take it to the dealer, since you must have something bent!

 

[QUOTE]Originally posted by gernby
[B]I am suspicious that your mechanic cannot get 6 degree's of caster.

 

I can see how that would be a factor. However, 4.6 degrees was my MINIMUM caster when I had -1 degree of camber.

 

Brilliant observation and the most likely possibility I've heard.

 

cdelena is correct. Large amounts of negative camber reduce the car's available caster range. David, with S02's I run pretty much the same setting as you and also can get only 5.5* caster. Try increasing front toe out and reducing rear toe in. The car will be a little more lively at a cost of a bit more front inside edge wear. Also, watch your tire pressures carefully. I have found that pressures will increase anywhere from 4 to 12psi from their cold, morning values depending on how aggessively I am driving. Such a large change will have a huge impact on handling. I give them time to warm up and then try to keep them at about 36psi hot front and rear for best handling and wear.

 

Check www.whiteline.com.au for explanation on caster

Caster will increase steering effort, however, it will decrease deflection when your car hits a bump. ie. its a good thing! - previously, caster couldnt be too great b/c of steering effort, but on a light car, or power steering car, this shouldnt be a problem.