18 replies to this topic

[Bruce McNutt]

Hi,

I’m new to Spec Miata racing . However I have been Road Racing for 19 years. I’m trying to set up the suspension on my 2000 Miata and I really need some advice from SM Gurus. My car is a brand new build including the suspension. Recently I took it out for my maiden race with this car. Turns out, it happened on a double race weekend. Therefore I had 5 races including 4- 15 lap Sprint races & a 1-hour Enduro as well as a practice/qual session on BOTH days. Same for Sat & Sun. I did 10 races in total. The first 3 races, I could not get the car to power out of any corners without serious oversteer. I kept backing off the rear swaybar until the only way to make the car behave was to disconnect it on one side. But throughout the rest of the races I did not feel the car could bite into the corners, tire wise.

I originally set up the car on a professional state of the art alignment machine as per Jim Daniels on-line recommendations. However according to my alignment guy, he could not adjust the car to the max camber settings that Jim recommends. So, here are my specs as raced. If you can give me any suggestions to improve this car – I’D BE GREATLY APPRECIATED!

Our track is tight 1.5 miles, 11 turns & bumpy. Clockwise.

2000 Miata (never in any accident) – super low mileage Torsen LSD, 27mm from bar.
205/50ZR15 Toyo R888 (stickers – see photos after 10 races below). The tires were run 5 races and then rotated (front to rear) for the other 5 races. Tire pressures were approx. 38psi hot.

FL (ride height = 5” to spot weld on rocker)
4.8 deg caster
0 toe
-1.9 deg camber

FR (ride height = 5” to spot weld on rocker)
4.8 deg caster
0 toe
-1.9 deg camber

RL (ride height = 4-3/4” to spot weld on rocker)
0 toe
-2.5 deg camber

RR (ride height = 4-3/4” to spot weld on rocker)
0 toe
-2.5 deg camber



Its obvious I need more neg camber. But 2.5 is all I can get according to my alignment guy. So if anyone can provide me with some suspension setup advice – I’D BE GREATLY APPRECIATED.

Thanks,

Bruce McNutt

[trimless]

I'm no expert but here's my free advice.

Lower the car to 4.5" both front and back and see what you get on camber. You should see at least 2.3 to 2.5 degrees up front at these heights. Running the allowed aftermarket "fatcat" bump stops will offer more adjustment on the ride height without running into the bump stops so if you don't have these on the car I highly recommend them.

I also suspect your over steer issue was caused by having the ride height lower in the rear. Get the ride heights even then corner weight the car.

[dmathias]

I'm no guru, but here goes: Did you start with full-tread (unshaved) tires? In the dry?

My broken-record advise: forget measuring at pinch welds. What matters is the distance from the top of the shock to the bottom of the bumpstop, measured with the car's weight on the springs.

You did not supply corner weights - you did corner weigh the car, didn't you? Hard to say what's happening otherwise.

-Denny

[Glenn]

Hi,

I’m new to Spec Miata racing . However I have been Road Racing for 19 years. I’m trying to set up the suspension on my 2000 Miata and I really need some advice from SM Gurus. My car is a brand new build including the suspension. Recently I took it out for my maiden race with this car. Turns out, it happened on a double race weekend. Therefore I had 5 races including 4- 15 lap Sprint races & a 1-hour Enduro as well as a practice/qual session on BOTH days. Same for Sat & Sun. I did 10 races in total. The first 3 races, I could not get the car to power out of any corners without serious oversteer. I kept backing off the rear swaybar until the only way to make the car behave was to disconnect it on one side. But throughout the rest of the races I did not feel the car could bite into the corners, tire wise.

I originally set up the car on a professional state of the art alignment machine as per Jim Daniels on-line recommendations. However according to my alignment guy, he could not adjust the car to the max camber settings that Jim recommends. So, here are my specs as raced. If you can give me any suggestions to improve this car – I’D BE GREATLY APPRECIATED!

Our track is tight 1.5 miles, 11 turns & bumpy. Clockwise.

2000 Miata (never in any accident) – super low mileage Torsen LSD, 27mm from bar.
205/50ZR15 Toyo R888 (stickers – see photos after 10 races below). The tires were run 5 races and then rotated (front to rear) for the other 5 races. Tire pressures were approx. 38psi hot.

FL (ride height = 5” to spot weld on rocker)
4.8 deg caster
0 toe
-1.9 deg camber

FR (ride height = 5” to spot weld on rocker)
4.8 deg caster
0 toe
-1.9 deg camber

RL (ride height = 4-3/4” to spot weld on rocker)
0 toe
-2.5 deg camber

RR (ride height = 4-3/4” to spot weld on rocker)
0 toe
-2.5 deg camber



Its obvious I need more neg camber. But 2.5 is all I can get according to my alignment guy. So if anyone can provide me with some suspension setup advice – I’D BE GREATLY APPRECIATED.

Thanks,

Bruce McNutt

Try running HOT pressures closer to 44. YES that right, these are RACE tires not street tires with race compounds.

[Glenn]

Try running HOT pressures closer to 44. YES that right, these are RACE tires not street tires with race compounds.

Also for SP these are not even close to being worn down enough What tread depth did you start with?

[Mike Collins]

Looking at your tires you need more camber on the left side of the car and less on the right.

Your car is too high. With you or someone your same weight in the car lower the car to between 4.25" and 4.5" to the factory pinch weld. You have reverse rake in your car now. I normally end up with the rear .125" higher than the front.

Like Glenn said try higher hot tire pressures.

[Bruce McNutt]

Thanks a lot guys for the info. The tires were brand-new stickers. I did not corner weight the car as I had no access to scales. I was sitting in the car, the whole time it was on the alignment machine. I will re-adjust the ride height with the rear 1/8" higher than the front. Then perhaps I'll be brave enough to reconnect the rear bar. But I definitely need more camber. 44psi? really?

[Danny Steyn]

R888's can handle and use BIGGER pressure adjustments than the RA-1's - experiment with wide swings in the same sesssion and you will see what we mean.

[Bruce McNutt]

We have another crazy double weekend on Aug 20/21 with an insane amount of track time & 10 full races. I will try all of this throughout the weekend.

What about toe? Our track is tight and twisty without long straights. What do you think about a little bit of toe?

[Glenn]

We have another crazy double weekend on Aug 20/21 with an insane amount of track time & 10 full races. I will try all of this throughout the weekend.

What about toe? Our track is tight and twisty without long straights. What do you think about a little bit of toe?

No more than 1/16 out F and 1/16 in at R You REALLY need to scale the car! GAWD knows what the cross and rear bite is.

[fishguyaz]

My broken-record advise: forget measuring at pinch welds. What matters is the distance from the top of the shock to the bottom of the bumpstop, measured with the car's weight on the springs.
-Denny

denny,
in the spirit of being a broken record, can you elaborate again on the measurements from bump stop to top of the shock.
my pinch welds are so buggered up that i could use a different starting point for a baseline.
i ask because i am sure that i am not the only one with the question, and good info is nice to have redundant.

I thought i recall reading you say go 3/4", but please confirm.
thanks

[Jim Drago]

denny,
in the spirit of being a broken record, can you elaborate again on the measurements from bump stop to top of the shock.
my pinch welds are so buggered up that i could use a different starting point for a baseline.
i ask because i am sure that i am not the only one with the question, and good info is nice to have redundant.

I thought i recall reading you say go 3/4", but please confirm.
thanks

Josh
Yes you want 3/4 or more, closer to an inch. I and many others use the ride height as it is easier to check. We also know what our shock clearance is at that ride height. But whatever your reference point is, we are measuring the the distance Denny mentions above and that is the real number that matters.
Jim

[Motor City Hamilton]

Josh
Yes you want 3/4 or more, closer to an inch. I and many others use the ride height as it is easier to check. We also know what our shock clearance is at that ride height. But whatever your reference point is, we are measuring the the distance Denny mentions above and that is the real number that matters.
Jim

+1 Agree with Denny and Jim. Pinch welds are not the same all the way around. No factory measurement spec for that area. I do know one spec miata racer who had his lazer leveled and cut at a frame alignment shop. I measured shock travel. I run the fat cats bump stop set up. I measured 3/4" of travel to the bump stop front and I like around 7/8" rear. I measured using a small tie wrap on the shock shaft.

1.) with you in car...
2.) bounce car to set ride height...
3.) roll back and forth to remove any suspension bushing binding...
4.) have skinny crew buy crawl under car (might be best up on setup stands or wood risers for the budget guy) and push tie wrap down to sit on top of shock body...
5.) slowly jack up one side of the car...
6.) measure distance between bottom of tie wrap to bottom of bump stop...
7.) repeat on other side...
8.) repeat, repeat, repeat until you get desired measurements.
9.) For last step, measure ride height somewhere else to be used as your future measuring point. I chose to measure from an inner mounting point since it is "less" likely to get bent than pinch welds. In the front, I use the flat cross member bar under the trans, the back big bolt. For the rear, I use the flat part of the inner frame bracing bar, under the front bolt. On my car, my front measuring point at 10.5 CM = about 3/4" of travel and the rear measuring point at 13.5 CM = about 7/8" of travel. I am finding that as I have become a more smooth driver, I have been able to start sneaking my ride heights lower and lower.

[dmathias]

You can also make simple go/no go gauges out of bent coat hangers, so when the car is on the ground with the driver's weight in the seat, you can reach in through the wheel and measure shock to bumpstop clearance.

Coat hanger gauge looks something like this: [_,------------------

See if you can mooch off of someone at track with scales. Start at 50% cross and wedge (most likely) or de-wedge depending on track. Accepted wisdom is < 0.5% wedge.

[FTodaro]

without know your cross wt its hard to tell you what you can do to get better results. More camber would help but as said above you will get more camber with a lower RH so I like to get my car down to 4 5/8 all around then when I adjust the camber you can loosen the lower ball joint and pry on it you may get some movement. I always put a pry bar on the lower A Arm when I am making the front bolt camber adjustment, you cannot rely on just the adjuster. you can cheat out ( not the illegal cheat) the caster bolt (rear adjuster ) a little to get more camber but the more caster you put in the car the harder the steering wheel will be to turn.

You can also stager the front caster, if you like to play with your set up. I have done this for certain corners. more positive caster in the LF will make the car turn right better.

[Bruce McNutt]

Thanks guys! This is all great info!
I have yet to cross weigh this car. I will soon though, before the Aug double. My latest question; how can you achieve a 50/50 cross weight with 200lb me in the left side while keeping a left/right ride height the same measurement?

[dstevens]

Measure/setup with you or a more or less equal weight distribution in the car.

[davew]

Thanks guys! This is all great info!
I have yet to cross weigh this car. I will soon though, before the Aug double. My latest question; how can you achieve a 50/50 cross weight with 200lb me in the left side while keeping a left/right ride height the same measurement?

That is the $64,000 trick.

We setup a car last week. The driver spent countless hours trying to get it right. Before giving up. When we started, the car had 679 pounds of cross weight. YES< 600 POUNDS!!! It actually sat pretty level, the right side was a even but a little high. When we finished, the car had 1 pound of cross, sat level, and had 3* camber all around. Apparantly it worked, he won two races this weekend.

Dave

[Bruce McNutt]

Thanks a lot guys! I did get this car handling much better. Shaved 3 seconds off my previous time and way easier to drive. Now you guys opened up a can of worms. Now I need one of those damn Race Engineering engines to get in the front! LOL.

Couple of pics from Sunday Sep 24.