And when I installed all my new front suspension components before Nationals.....when we started on the rack it had north of 4.3 degrees front camber.

 

Chassis/CA's stock and original: -4.05°, -4.00° max at 4" pinch. No doubt I would get more at 3.75" pinch, but not going there. Reduced my camber to 3.3° Ft, 2.7° Rr.

 

-2/3 usually on the rear. I've found 275s on 11s tend to lower the desired pressures some though.

I was told the current year model a6s have wear characteristics or a7s... Long useful lifespan. Who knows.

We can get about 3.8-3.9 front camber but we aren't that low.

 

Good stuff here. *subscribed*

What kind of caster do you guys run? Do Miatas tend to benefit from lots of caster for autocross the way many other cars do?

Neal

 

I still havent gotten to the point where caster number matters besides being even side to side. Camber is so much more important than caster and at 2.8* static I dont have enough for the hoosiers. I dont even know what my caster number is, I'm too lazy to finish the calculation I just do enough of the calculation to know that I'm even side to side at basically maxed camber and the most caster I can get. Once I can get 3.5*+ of front camber I'll start worrying about caster.

 

I've been getting into the world of BSP with my MSM. Currently my only real competition is a supposed 375hp 2012 VW Golf R. He has been roughly 0.5-0.7 seconds faster than me at the last couple events. My friend also runs his grey MSM with us and is nipping at my heels. We are all still running street tires.

 

Well, that's sorta true. Except that more caster gets you more camber where it matters...when the wheels are turned. One way to think of caster is as "dynamic camber". So a certain amount actually gives you a more ideal scenario. Less static camber when the wheels are straight (better acceleration/braking), but more camber when the wheels are turned.

In reality, it's all a compromise and dependent on your geometry, of course. And there are other side-effects. Aside from increased steering weight, the the other thing caster does is to increase the weight-jacking effect. In effect, your corner weights will diverge more as the wheels turn with more caster. (probably why the effort is higher, I suppose)

Depending on your setup, the weight-jacking can be a good thing. But that depends on other factors, too. For example, it un-weights the inside rear tire more, so if you run a Torsen diff this might be a problem.

On a Miata, there is a lot of cross-talk with caster and camber. In other words, they're part of the same adjustment. The same eccentrics on the lower arms adjust both. So if you want max caster, it will reduce the max static camber you can achieve.

That's really the main reason I was asking. I'm curious what balance people have found to be beneficial between the two. We haven't done much experimenting yet...

Neal

 

Some of it will depend on your bushing material. I know in SP you all can't run Spherical bushings(unless that was in a fast track I missed), so most of the top cars run Delrin all over the place. The stiffness of Delrin will limit the amount of caster you can get up front and the amount of toe you can get in the rear.

 

That's a new one on me. How does bushing material affect geometry??

 

Delrin doesnt allow much axial misalignment. So you cant turn the adjuster much in the caster (front) or toe (rear) direction.

 

Ah, so you're sayint it affect geometry, per se, but yeah, it certainly will bind off-axis.

But on a Miata, the upper and lower arms don't follow the same arcs. So if you use zero-compliance, single-axis bushings in all locations, it will bind regardless of your alignment settings.

I'm a huge fan of Delrin, and poly makes an awful bearing material. But I'm pretty particular about suspension bind. We made a hybrid set of bushings that uses poly on one end of one arm on each corner. The poly will require more maintenance, but has enough compliance to eliminate bind. We spent a LOT of time finding the right combo and fitting it properly.

But we can run any alignment settings we want...

Oh, and if you bought bushings that don't allow you to get full adjustment, it just means you have the wrong bushings. You cant make a one-axis bushing into a multi-axis heim joint, but you can certainly have the hole be offset or at the right angle you need.

 

They don't have to move in the same arc, they just have to have the inner pivots for each arm be co-linear. The ball joints on the upright will take care of the rest. Delrin works fine for the front upper bushings.

--Ian

 

Good catch. You're right. Though to be totally pedantic, I think we're looking for "coplanar", no? All four points on the same plane...

But maximizing positive caster using stock arms requires that the rear eccentric be fully out. Depending on what you're doing with the front eccentric, this could move it a good bit away from being coplanar.

Also worth noting that deciding when something is "binding" is a judgement call, I suppose. With stock arms and a non-stock alignment, it will probably never be perfectly spot-on.

Neal

 

If the four inner pickup points aren't coplanar then the fore-aft distance between the outer pivot points will change as the suspension moves up and down. Since the front suspension has balljoints on the outer pivots, this can happen without binding. Not so much in the rear.

--Ian