I know there are a ton of threads on setitng up the camber on the 8. I did not want to hijack one of them, off topic questions rarely get answered in the middle fo a thread anyway. So here it is:

Why would you want less negative camber in the rear than in the front? The latest edition of Grassroots Motorsports was testing the new MX-5, and Solstice against a '99 Miata. The did high performance alignments, and were trying to get about 1 degree less camber in the rear. Why?

Everything I read on here, what everyone I know does, and what I have done is setup the car iwth more negative in the rear. I know the miata is little, light, but is is still a RWD car. I know other autocrossers, that drive miatas, that dial in more negative in the rear. This has just been bugging me since I read it, and wanted to get some answers. Thanks in advance.

 

The only thing I can come up with is, if you were autocrossing and wanted to rotate rear of the car. I think I would do it with rear toe-in myself.

 

That would have been my assumption, but I never know. I am still learning as much as I can about setting up a car.

 

For the 8, it seems easier to get more neg camber in the rear than in the front. I think most autoxers just want to max out the camber on both ends, but end up with less in front because that's all they can get.. I could only get -0.8 in front, but -1.9 in back.

 

I think that generally toe is set for transient handling and camber for steady state handling. I think you feel the effects of toe when you tip the car into the turn and you feel the effects of the difference in camber (front - rear) once the car has taken a set.

Also, the front and rear suspension will gain different amounts of camber for every increment of compression or expansion. I think the rear end of the miata gains more negative camber than the front. On a stock suspension which is pretty soft, once the driver tips the car into the turn and gets on the throttle, weight will transfer to the rear of the car compressing the rear more than the front. I would guess that folks who drive C stock miatas who set up their cars with more negative camber up front statically, have pretty even camber front to rear when on the throttle in the steady state part of a turn out on course.

Bruce

 

I agree with Bruce. Most manufacturers set up their cars to have understeer at the limits for safety, hence faster negative camber gain on the rear than on the front. Also, less static rear negative camber on the rear adds traction when accelerating or braking.

 

I guess I will just write into GRM and ask, because it does not make sense, for an atuocross related vehicle test, to set the car up to push. Maybe this week I can get a line into them, and see what they say.

 

I don't think that's quite it.

I think most stock-class autocrossers start by maxing out the front camber and toe and then move to the rear to get the car to handle like they want it to.

There were a bunch of different setups at nationals last year (just going by looks). Some people were running a lot of negative camber in the back. Some weren't running much at all. Too much negative camber in the back can hurt corner exit by allowing wheelspin. It can also hurt braking a bit.

Really only the pyrometer knows for sure.

 

since it is my thread, i will digress...

you mention a pyrometer. I just bought one, and plan to start learning what to look for. Any general ideas. I know that I need to check inside temp, and outside temp after each run. But does this info tell me? Other than one part of the tire is hotter than another. I know that the optimum tire temp varies between tires, but where can i look for that info for my tires.

 

A good starting point is to measure inside, middle, and outside with the probe stuck perpendicular to the tread face and set your camber and tire pressure according to what you see.

If the temperature of the inside of the tire is higher than the temperature at the outside, you have too much negative camber. And vice versa. If the center reading is higher than the outside readings you have too much tire pressure.

You can get in the ballpark like this but you'll still need to tweak the setup of your car to make it do exactly what you want.

 

thanks for the advice. we hae a track day in two weeks, will be fun to see what i find.

 

most people don't have much of a clue beyond playing "monkey see - monkey do", it's been discussed here before

 

about tire temps, or camber setup. or is this trying to make me feel stupid for asking questions, or for trying to learn, rather than "monkey see - monkey do"?

 

I think this thread covers it:
https://www.rx8club.com/rx-8-racing-25/rear-camber-77059/

 

yeah, i am familiar with that thread, i have posted in it. The major discussion there were getting as much -camber as you could, which in turn leads to what happens with different settings. so I see the relevance. sometimes it just takes too long to read through a lot of other info to get the one piece you are looking for.

 

That's my approach. Got a problem with it?

 

you're guesses aren't my problem ...

 

I'll share my insight (FWIW) on two points.

First, I think the GRM article had the camber set up the way it did to get the car to rotate better for an autocross course. This would not be the optimum set-up for a track day at Road Atlanta (for instance).

Also, you mentioned using a pyrometer. The information you get from a pyrometer can be confusing if you don't know when to use it. For instance, the temps you get after an autocross run won't tell you much; this is because the car is not being driven in a "steady state." However, if you run the car clockwise on a skidpad to measure the left side tire temps, then run the car counter-clockwise on the skid pad to measure the right side tire temps, you can start to make some worthwhile observations.

 

I'm wondering, is measuring tire temps after an autox run really that bad of an indicator? Sure a skid pad test will give you the best idea of the steady state, but in an autox run you're not in steady state, do you really want to tune for that? Using a probe pyrometer (infrared obviously wouldn't be great) right after a run should give you a reasonable average temp reading for the entire run as the tires don't cool *that* quickly right? Asuming a clean run with no spins or other sillyness.

Maybe I'm missing something...

 

Do you want to tune for that last hard right turn into the finish instead? Or tune for it a minute or two after you come out of it and cooled off on the return to grid?

Depending on how far your grid spot is from the finish, they may or may not cool substantially, but the maneuvers leading into the finish (and any heavy braking after the finish) will definitely mess with the readings. Skid pad is the best place to do it, but we don't always have that option. So you do what you can. If you consider everything that may be influencing the temps and you do it at a number of events, it can be a piece of the puzzle (particularly by showing you if something is really screwed up), but it's not an absolute.

 

The problem with taking temps after an autox run is that you have to think of all the things that went on in that run, and what effect it has on the tire temps. In the end, you realize that you don't know what to make of your readings! For example, if you get a real high reading on the outside of just one of your tires, this is gonna tell you that maybe you came into the turn too hot; it won't tell you how the tire might react to a smooth run through that same turn. If you can adjust the car for steady state handling, the car should become faster in the "sweepers." After that, you can begin to work on fine tuning the transitional handling needed to master the slaloms and "bus stops."

 

except tht you have to take the readings *immediately* after that one turn, otherwise the readings are useless generalized gibberish on anything except a skidpad, and how many autoxes do you ever run with a constant radius line through the turns?

I threw away my pyrometer long ago (or rather I sold it to some other sucker ) and instead have learned to "read" the tire scrub patterns for autox use. IMO a pyrometer for autox does more to lead people astray than give them any useful information.

 

couldn't resist huh? well, this sucker likes gadgets, likes gathering information, pointless, useless or otherwise. And I am doing so more on a track, not autocross. And I gathered decent information, sucker or not.

 

Just a general observation on life, not directed at anyone specifically since it applies to each of us from time to time (some of us more often than others)...

One of the true marks of suckerhood is that the sucker fails to recognize that s/he is a sucker. It's a large part of what makes one a sucker. You can recognize the truly elite sucker sby the extra work they do to take the evidence of their suckerness and use it to further convince themselves that they are not suckers.

 

Back to the original question, GRM's Miata test alignment, and other Miata autocrossers' alignments - be very careful as to WHICH Miata you're talking about!

NA series = 1990 - 1997 Miata
NB series = 1999 - 2005 Miata. This was a minor evolution of the NA series, so many suspension settings are very close.
NC series = 2006+ MX-5. Entirely different suspension, especially at the rear.

The GRM article was about the new NC series - which is based on the RX-8 chassis and suspension, and has NOTHING in common with the NA or NB Miatas. The front suspensions are similar, but the NC rear suspension is like the RX-8's multilink, and nothing like the NA/NB's double a-arm.

Yes, with NA/NB Miatas, the preference seems to be for at least 0.5 more camber in the rear than the front. That won't necessarily apply to the NC or RX-8 - ignore it!