Well now that the Miata will be up on the jackstands for a few more days taking care of a brake leak, I thought I'd go ahead and ask about some tire/suspension stuff.
I'm running the FM Vmaxx coilovers, FM sways, poly bushings, NB mounts.
205/50/15 R888s, what psi should I be looking for hot when I do my first HPDE at the end of the month?
Alignment F/R is:
0 toe
-1.5 camber
5.0 caster
1/16th toe-in
-2.0 camber
Current ride heights as measure yesterday with just over half-tank and no driver. Hub to fender, so not as exact as say ground to pinch weld, maybe I'll do that once it's back on the ground.
FL 12.5"
FR 12.3"
RL 13.1"
RR 13.1"
The car feels great now, but that's only been some spirited backroad driving and hard braking on deserted roads to bed in the Carbotech's. WHich I know isn't close to track driving.
Should I raise the front passenger side a touch, while lowering the rear a hair? I've been reading a .5" rake is good, and I don't want to go to low and end up on the bumpstops.
I would start at 26 front cold and 27 rear cold. Should come up to around 30/32 hot. Watch for tire roll over. If there is alittle roll over, bump the pressures up.
This is just me.
More negative camber in the rear than the front? That's unusual but I don't know about Miata suspension tuning...
Yes, some Miata setups work well that way. Depends on what else you're doing in terms of springs and sway bars.
Overall, looks decent. I know the RA1 likes to be between 38 and 42 hot, but I'm not as sure about the R888. Dig around the Spec Miata forums, they had to run that tire for a while.
I ran them in autocross at 28/28, sometimes even a touch lower. Not sure on track though.
Strangely enough I run Toyo R1Rs at the same pressures. My suspension setup is the same as yours barring the rear sway bar.
Side note, since the car has already been aligned........what would the settings do, if the heights were changed.
In other words, if I raise the FR to match the drivers side, is that going to remove some camber and caster? Or the other way around?
Caster doesn't change with height on double wishbone suspension.
As for camber, depends on where on the camber curve it is, but generally they're designed to gain negative camber when lower than the factory ride height and gain positive camber when higher. So if you're lowered and you go closer to stock ride height by raising it, you'll lose some negative camber.
Your toe will also change slightly on that wheel which could really make the steering feel funny.
What track are you running at?
Very rough guide - Miatas will change about 1 degree of camber for every inch of ride height change. Not a lot of toe change.
^I won't worry about it for now, but that's good to know.
DukeOfUndersteer wrote:
What track are you running at?
www.hallettracing.net
I used to use R888s in 185/60/14 on a Miata in the UK and I usually ran them at stock tire pressures or a little higher. They have fairly stiff sidewalls so tire roll over wasn't a big problem.
However keep in mind that the UK tends to be a little on the cool side.
Running R888s in my vintage race-Spridget.
I run about 38 psi hot on all four corners.
For cooler months (like our upcoming Watkins Glen event in Oct), I'll run 36 hot.
Keith Tanner wrote:
Dig around the Spec Miata forums, they had to run that tire for a while.
How much do you think the dramatically different spring rates come into play vs tire pressures?
The Toyo setup sheet says to shoot for 32-37 hot, while a lot of SM guys were claiming the tires were their in 44-47 hot range!
aeronca65t wrote:
Running R888s in my vintage race-Spridget.
I run about 38 psi hot on all four corners.
For cooler months (like our upcoming Watkins Glen event in Oct), I'll run 36 hot.
Curious, why would you run lower hot temperatures when the weather is cooler.?
Great info from AIM Tire on R888 suspension setup and tire info here:
http://www.aimtire.com/typ_category.asp?Unique=41164.3493287037&ObjectID=6828
Tire pressure copy/paste:
The R-888 with the stiffer sidewall and softer undertread construction requires a bit less initial camber settings and WE BELIEVE increased (over the Ra-1) starting and 'HOT' tire pressures to provide a longer lasting and more consistent experience.
Or you can run very well with your original camber settings and by simply increasing your STARTING pressure.
A performance gain may be experienced by using low starting pressures in the 24-28lb range. However, if when using this low 'starting pressure' you experience a tire that is good for only 3-4 laps and it then falls off it is highly recommended to begin and end with a much higher pressure.
Most Spec Miata's and E-30 series cars have found success by starting with 38-40lbs of air pressure and ending with 43-47lbs of air pressure!
This will be hard for you to believe, but the higher hot or ending tire pressure WILL provide you with BETTER tire wear.
Yes, yes I know this doesn't make any sense whatsoever. But, just TRY IT! And you'll see what I mean.
z31maniac wrote:
Keith Tanner wrote:
Dig around the Spec Miata forums, they had to run that tire for a while.
How much do you think the dramatically different spring rates come into play vs tire pressures?
The Toyo setup sheet says to shoot for 32-37 hot, while a lot of SM guys were claiming the tires were their in 44-47 hot range!
I don't think it would make a massive difference, although I will admit to treating tires as a constant when I'm testing. The weight of the car is similar.
I seem to recall the fast setup for RA1s was different than the Toyo recommended numbers as well.
Dramatically different tire pressures didn't make a huge difference when I went from the bodyrolltastic stock suspension on my 'rolla to rock-hard coilovers. When I was on the same tires I ended up running the same pressures on the front (worth noting: I put in some more negative camber on the front when installing the coilovers) and a little less on the rear since it wasn't rolling onto the sides so much and a good bit of the shoulder tread wasn't being used. I then stiffened the rear (more preload on progressive springs) to compensate the handling balance.
