mild throttle-on push; tuning suspension tips
 

I've been working on dialing in the suspension for my local track. At this point, I've got it reasonably sorted with-in the limitations of my equipment and tire/rim selection. I have found the limit of too low and have raised the spring perches 1/2 turn from the point it would hit the bumpstops hard in left/right transitions. It pushes mildly when throttleing up, but you can easily point it with a little additional throttle. (the rear tires are heating up and running a full 2# higher than the front). It's very drivable in all corners except turn 12... the most important as it is the corner leading onto the front straight. It pushes enough to delay full throttle until very late in the corner exit. Next race is at the end of April... not a lot of time to test and tune; so looking for some tips on how to make my current suspension package work a little better. Here's what I've got so far: 2004 MSM. Typical spec miata suspension. The car is quite a bit heavier than a SM, weighing in at 2535 with driver and one gal fuel. Track is mainly clockwise. tire temps after minimal cool down; approx 60sec. I started with 50% cross; ride height changes were made evenly at all 4 corners, I doubt it is still perfect.

LF: 4 1/4 @ pinch weld RF: 4 1/4 @ pinch weld
-2 3/4 camber -2 1/2 camber
zero toe zero toe
hot press 38# hot press 38#
in ----> out in -----> out
160 152 160 140 114 110

LR: 4 1/2 @ pinch weld RR: 4 3/8 @ pinch weld
- 2 1/4 camber - 2 camber
zero toe zero toe
hot press 38# hot press 38#
in---- > out in-----> out
172 157 161 123 126 121
rear bar set at middle setting

-tires available: Nitto 225 45 15 and Kumho 225 40 17
-no spacers, but still 3/8 room due to narrow tires/offset

Shocks are not adjustable, so I can't just add to rear compression, etc.

tires/wheels aren't optimal. The Nitto's are OK for practice, but not sticky enough to race with; so Q and race is on the narrower Kumho's and OEM 7" wide rims.

I was just going to add a notch to the rear bar, but others here had advised a small rear bar. So I thought I'd ask for the forum's input.

Upgrade for the SM suspension to something that isnt crap, or at least put stiffer springs in the back.

I'm working on the upgrades as I go thru this next season. For right now, I'm working with what I've got. So come on leafy: let's put some lipstick on the pig.

I have a good selection of springs and could change out the rears to a higher rate.

I have ordered a set of more appropriate rims, however the season has started well in advance of the wheel shipping date... so I'm working with the rims/tires that were available to me at the time of the March SCCA race season opener.

I've got a little room to adjust camber, ride height could go up a little, or could add some spacers to the front.


I guess my real questions are:
Q: increasing front neg camber would seem to help turn in and mid corner, but I'm not sure if it'd help corner exit... as this seems like a weight transfer problem?
Q: add 50# more rear spring vs. rear bar? limited t+t days before April race/mindful of trackside changes.
Q: would adding more front track width with spacers give a noticable effect?
Q: would the torsen cause the car to understeer under power? kinda like a locker would?

My initial comment was going to be that 38psi is significantly higher than I run my NT-01s (8psi more) but if you have an 8* delta across your LF at Portland with the center lower, I'm not sure what you could do better on that corner. Maybe just tighten up the rear to get better balance or or rotate with the loud pedal! :giggle:

All the other corners I can; but on T-12 I can't seem to rotate it with throttle on... I just push until I scrape the the wall.

My first though on Leafy's response was that: "If the SM suspension is so crappy, they why are they beating me up on this segment of the track"
After a little thought, I'm realizing that even the basic turbo miata is quite a bit faster than even a "fast" spec miata... by several seconds a lap. The SM suspension seems a bit "wobbely" at speed and is really stretched in both corner entry and exit when compared to a regular Spec Miata.

I think Leafy's right, I am going to need to play with the spring rates to get the platform more stable and up the rear rates a little to get the rear to rotate. (?800/500?) I'll get around to getting all the right parts together as the next few years progress. For right now I'll work on getting the car to throttle up 20' sooner @ the T-12 exit... and just have a blast doing it!

Try raising the rear 1/4"?

I could do that. It'd be a lot easier to change-up trackside than major changes. For this month, I'm hoping just to get around T-12 a little better... I need to be able to get to full throttle aprox 20' sooner without pushing into the wall. (yes I did scrape drivers mirror and left rear tire)... All-in-all the suspension handles reasonably well. It is a bit undersprung. By the time I get the neg camber right, it is too low and onto the bumpstops. I've got too narrow tires now, so it's a little easier on the suspension. I'm going to try: more neg camber front and back... more spacers to the front... increase the rear ride height 2 turns (1/4 inch) and then have the availability of ratcheting up one/half knotch at the rear bar for the next race... all reversable trackside.