IntegraR0064

Camber change from caster alone = caster*sin(steering angle)

Steering angle is angle of the wheels.

So if we assume a typical steering angle of 10 degrees (I haven't looked to see what a typical steering angle would be - anyone else done this to see what steering angle is when the steering wheel is turned maybe 90 degrees or so?), then just as Matt said, you can expect a hair under 0.2 degrees difference in camber from 1 degree of caster.

So the ballpark you should be shooting for in my mind is trading 0.2 degrees of camber for 1 degree of caster. If you get more camber for that much caster then go with the camber, if you get less camber then go with the caster. Keep in mind the inside wheel will lose camber at the same rate from caster. In other words, for example, lets say you find you can add 1 degree of caster at a loss of 0.2 degrees of camber, so you're right on that line. In a turn at 10 degrees steering the outside wheel will have the same amount of camber either way. However the inside wheel would have 0.4 degrees more camber if you had done the camber option (because you added the 0.2 deg camber, plus you're not losing an additional 0.2 from camber loss from additional caster). Of course the inside wheel is far less important than the outside wheel. Also keep in mind obviously at 5 degrees steering you only get half(ish) the camber from caster, or at 15 degrees you get more camber. Plus of course you have to remember the unpredicability - with camber it's easier to balance front and rear traction, whereas if it's all in caster then at high turn angles you'll oversteer and at low turn angles you'll understeer. It's all a balancing act. But hope this helps you have a general idea.

My guess is that you're going to end up mostly maxing out camber, but then maybe giving up the last 0.1 or 0.2 degrees of camber for caster, but I haven't tried to max everything out on this car so I don't have experience.

//steve\\

The deal I was hoping to get on some other parts fell through so I'm most likely going to be keeping my J's camber joints and therefore will be able to get max caster and the exact amount of camber I want. Looks like I won't have to give anything up. At least I learned a little something

sto405

For you guys running .2 total toe with -2 camber or more, are you useing a toe arm kit? Or the factory arms?

Random1

In this class (SCCA Solo STR - Autocross) you cannot run anything but the stock OEM part.

IntegraR0064

So I haven't played with rake much. Anyone that has, I'm wondering what your opinion is on how much it affects things?

My rear shocks are not as short as I'd like them to be, it looks like I was reaaally close to bottoming them out at the last event last year. And now I lowered the front bar setting two notches since then, so the car will actually roll even more (some quick calculations tell me around another .05" in the rear of spring travel).

Ride height is about 13" in front, and just a little more in rear, maybe 13.1". Spring rates are currently 800 F/700 R, Gendron hollow front bar now on 4/6, no rear bar. Last event last year I had this exact setup with the Gendron at 6/6 and it was understeer city, and like I said I was a hair's breadth away from bottoming out the rear shocks.

I don't want to bottom out the shocks. So to fix this, I'm trying to decide between:
1) Raising the rear spring perch another 0.2" or so and making no other changes. I want to raise it more than I probably need since raising it will make it roll more again plus I'd like to have a little more wiggle room.
2) Buying a miata bar for the rear and putting the front gendron at maybe 5/6 and tuning from there. That should get rear roll about to what it was before with the front bar at full stiff and no rear bar. Then only raising the rear height slightly, maybe another .1", just for wiggle room. This would just be a temporary solution since I'd really like to design an adjustable sway bar for the rear if I really want a rear sway bar, but I'm guessing the rates would be miata-bar-ish and I don't have time to do that right now.

So my question is, how do you think those two options will compare? I've got a pretty good idea of what the effect of the sway bar changes will be but is a difference of 0.1" of rear ride height really going to change anything balance-wise?

Pretty sure I'm going with option 2, but even then I'm adding some rake compared to now so I'm curious about the rake effects specifically.

Of course our test and tune is this weekend on sunday, and I've got tons to do (mostly non-car related) in the mext couple weeks so I really want to add as little as possible work.

Edited for clarity

nlink720

Jon,

I'm not sure what will be best for you, but I like my mx5 rear bar. I do suggest getting two 21mm or slightly bigger split collars to put on the other side of the pressed sway bar retainers that come on the mx5 bar. Mine moved laterally about 1/4" and it was causing the bushing lubr to slide out and the bushing to become dry. I ordered two aluminum ones from mcCarr to limit lateral travel on mx5 bar. I can get u the part number at a later time, but I think I went with13/64 to approximate 21mm.

See you Sunday.

berny2435

Our setups are sort of similar if you get the miata rear bar. I’m not slammed either. With my front bar at 5 of 6 on one side and 4 of 6 on the other, my car understeered at mid to corner exit the other day. With my rates 700/650 I don’t think the miata rear bar is enough bar to be fast in the sweepers on my setup. More camber might have helped but I think overall the front just sees too much load and causes it to loose grip first. I’m going custom and or Gendron bar rear. There’s a good chance I am hitting the front bump stops though and that might have led to the bad pushing and more rear bar will help keep the roll down. I can’t really go much higher on spring rates due to my shock valving, maybe 750 front and 700 rear but I think the best quick fix is a heavier rear bar. I’m going to raise the front 0.1” to even out the rake front to rear when I put the new rear bar on as well.
I as well be doing a test and tune soon. Hopefully I’ll have my new rear bar on before then.

IntegraR0064

thanks guys, that's helpful. Noel, I thought you could just hammer those retainers over and then that would hold it, did you try that? If you did, then if you can send me that part number that'd be awesome.

nlink720

Jon,

You can hammer them over, but mine still had a minimal amount of slop I will update you with part number tomorrow. Passing through NC on way back to MD.

legend4life

Would the GC extended billet mounts help with this? I wonder if they would fit in the front.