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Old 03-31-2014, 06:56 PM   #1
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Default Suspension setup questions

I am looking to tweak my current suspension setup to minimize oversteer on turn in. I feel like I am not able to get back to throttle as soon as I should because the car is tail happy. Once past the apex I am able to really lay the power down but during turn in and heading to the apex on slow speed turns I feel the back end wants to come out to much.

I have been running NT01's and R100 Hoosiers.

3.0 camber front, 5 degrees castor
2.75 camber rear

The car feels very neutral on high speed stuff (wing?) and behaves great at WOT from apex on to track out.

Can I can dial out the turn in issue without taking away from the other positive aspects of the current handling?

AST doubles 850/500
SM 1.8 front bar (27mm?)
1,950lbs dry, fuel cell passengers floor (why spring rates are different?)
OS Gixen Diff (could problem be in the diff tune?)

I am going to start by replacing the 15mm rear sway with a 14mm one. I am also thinking more rear camber (based on tire wear).

I welcome input from you guys who have a lot of experience playing with setup.

Last edited by k24madness; 03-31-2014 at 08:11 PM.
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Old 03-31-2014, 07:50 PM   #2
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What toe?
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Old 03-31-2014, 07:57 PM   #3
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Originally Posted by k24madness View Post
I am looking to tweak my current suspension setup to minimize oversteer on turn in. I feel like I am not able to get back to throttle as soon as I should because the car is tail happy. Once past the apex I am able to really lay the power down but during turn in and heading to the apex on slow speed turns I feel the back end wants to come out to much.

I have been running NT01's and R100 Hoosiers.

3.0 camber front, 5 degrees castor
2.5 camber rear

The car feels very neutral on high speed stuff (wing?) and behaves great at WOT from apex on to track out.

Can I can dial out the turn in issue without taking away from the other positive aspects of the current handling?

AST doubles 850/500
SM 1.8 front bar (27mm?)
1,950lbs dry, fuel cell passengers floor (why spring rates are different?)
OS Gixen Diff (could problem be in the diff tune?)

I am going to start by replacing the 15mm rear sway with a 14mm one. I am also thinking more rear camber (based on tire wear).

I welcome input from you guys who have a lot of experience playing with setup.
I would think less rear camber than that in a high power car. Im finnally happy with just over 2 for trying to put down high amounts of power exiting a turn in the rear and about 3.8 in the front. your car is so light its probably front heavy as well. less rear bar more front. also maybe softer rear springs relative to the front. I like 900/500 on my car but its a bit heavy.
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Old 03-31-2014, 08:02 PM   #4
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What toe?
+1/8" rear
-1/16" front
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Old 03-31-2014, 08:07 PM   #5
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I would think less rear camber than that in a high power car. Im finnally happy with just over 2 for trying to put down high amounts of power exiting a turn in the rear and about 3.8 in the front. your car is so light its probably front heavy as well. less rear bar more front. also maybe softer rear springs relative to the front. I like 900/500 on my car but its a bit heavy.
I think the "high power" class is a bit misleading for my car. While it makes 297whp (dynopac) the torque is only 200. I think the torque thrust is what requires less camber to lay power down. With the low torque rotrex it's still kinda a momentum car. Also the tire wear says I need more camber not less.

I plan to buy a RB front bar from 949 to try as well. The step from 14mm to 15mm rear was the smaller change I wanted to try first. I wonder if I need to back off castor to limit the jacking effect. On the other hand the high castor is what likely allows me to run so little static camber.
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Old 03-31-2014, 08:10 PM   #6
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Positive is in right? Thats a lot of toe in, so thats not the problem. I'm thinking its what bundy is after. You're running the same spring rates that I run with the RB race bar and no rear bar, while being ~150 pounds lighter. I'm surprised you're having trouble putting the power down with the R100s on the A6s even in 2nd gear with a bit more torque than you I have to try to get wheel spin, it normally hooks. I'd figure if you're at track speeds with track aero you have to be putting down close to what I am downforce wise with the speed difference.
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Old 03-31-2014, 08:15 PM   #7
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It's the tight slow speed turns where aero is not in play that it seems to be the problem. Turns 4, 7 and 11 at Sonoma is what gives me the most problems.

As I approach the apex I can roll down the power. I want to get back to throttle before then. If the back was more planted I would feel more confident to do so.
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Old 03-31-2014, 09:02 PM   #8
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I finally got the car to plant the rear well on power on track when I dialed the camber back under 2.5 closer to 2. As a bonus it also helped immensely when trying to launch the car in Pro Solo’s. My front bar is effectively about mid-way between the stiffest two of the Racing beat options. Rear bar is closer to a 12mm or 13mm and I remove it entirely for autocross. I like less rear bar than 949 recommends personal taste I guess. When I set up my car for Time trial under NASA rules the boost gets turned down so I’m making right at 325 RWHP measured on a Dynojet so I’m not that much more power and I’m like 250 lbs heavier than you.
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Old 03-31-2014, 09:14 PM   #9
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Thanks guys. I'll play with rear bar first and then the front. I will start with the 14mm and the stock rear first then move onto the RB front and evaluate the results.
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Old 03-31-2014, 10:24 PM   #10
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I'm going to say (after what your describe low vs high speed grip) that adding more low speed rear down force will fix your problem. Your setup seems pretty spot on. Post a picture of your front and rear aero with a description. I'm willing to bet a wing change/diffuser would solve your problem, or get rid of some of the front aero. Remember that with Miata's the front aero is easy, the rear is the challange.
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Old 03-31-2014, 10:45 PM   #11
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Quote:
Originally Posted by bbundy View Post
I would think less rear camber than that in a high power car. Im finnally happy with just over 2 for trying to put down high amounts of power exiting a turn in the rear and about 3.8 in the front. your car is so light its probably front heavy as well. less rear bar more front. also maybe softer rear springs relative to the front. I like 900/500 on my car but its a bit heavy.
+1

How is your rear tire wear? What's your tire pressure?
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Old 03-31-2014, 11:20 PM   #12
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I'm going to say (after what your describe low vs high speed grip) that adding more low speed rear down force will fix your problem. Your setup seems pretty spot on. Post a picture of your front and rear aero with a description. I'm willing to bet a wing change/diffuser would solve your problem, or get rid of some of the front aero. Remember that with Miata's the front aero is easy, the rear is the challange.
Front aero's the hard part, you can only get so much from a splitter and canards, you can keep making the rear wing bigger and better if you need more rear downforce, and add in a well designed diffuser its game over. The problem once you start to get into a larger range of speed with aero on a production car is balancing that low speed. A good wing is going to have about the same efficiency over the whole normal speed range, where that splitter starts out fairly efficient and gets slightly better with speed until the top of it kind of stalls. My aero setup is pretty damn good at auto-x speed, but is too rear biased that slow and it just gets worse as I get faster. When you have to transition between on aero and off aero you have to choose. Do you want to setup the car to work when its off aero and sacrifice some of the performance when on aero or do you want to just drive around it when your not on aero and make it faster when on aero.
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Old 04-01-2014, 02:34 AM   #13
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If you're lucky... a 14mm or even the stock 12mm rear bar might get you what you're looking for. (If you need the stock rear bar, let me know. I've got a few extra and are close by in Rohnert Park...)

If you end up being between the two, then try dialing out some camber from the rear as Bundy suggested... too much HP and not quite enough contact patch when you get on the throttle early.

Sidenote: When will you be at Sears Point next? June with NASA? Or???
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Old 04-01-2014, 02:54 AM   #14
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Quote:
Originally Posted by jacob300zx View Post
I'm going to say (after what your describe low vs high speed grip) that adding more low speed rear down force will fix your problem. Your setup seems pretty spot on. Post a picture of your front and rear aero with a description. I'm willing to bet a wing change/diffuser would solve your problem, or get rid of some of the front aero. Remember that with Miata's the front aero is easy, the rear is the challange.
I don't think it's an aero problem. Low speed is more likely mechanical. High speed is where aero comes into play and that's where the car is working best.
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Old 04-01-2014, 02:58 AM   #15
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+1

How is your rear tire wear? What's your tire pressure?
Front tires wear slightly on the inside. When you stand the tire up (off the car) they lean inwards. The rears are the opposite. They lean towards the outside.

I am thinking less rear sway bar will allow the tire to have more camber due to the camber curve. I am going to start there.
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Old 04-01-2014, 03:01 AM   #16
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Originally Posted by SchmoozerJoe View Post
If you're lucky... a 14mm or even the stock 12mm rear bar might get you what you're looking for. (If you need the stock rear bar, let me know. I've got a few extra and are close by in Rohnert Park...)

If you end up being between the two, then try dialing out some camber from the rear as Bundy suggested... too much HP and not quite enough contact patch when you get on the throttle early.

Sidenote: When will you be at Sears Point next? June with NASA? Or???
Thanks Joe. I think I have the stock one in the shop. I am planning a test day on April 7th at Sonoma. I got a great driver who can help me shakedown the car and give me some data to overlay. If all goes well I may have some great lap times to report.

Last edited by k24madness; 04-01-2014 at 04:25 AM.
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Old 04-01-2014, 01:44 PM   #17
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Good info here... Setting up suspension and handling

"Corner entry oversteer;
Rear shocks are too soft in rebound.
Rear ride height is too high (too much rake) compared to front."

"Steady state oversteer during all turns or low-speed turns cornering;
If rear tire temps are optimum, with fronts too low, stiffen front antiroll bar; if rear temps are too hot, soften rear antiroll bar (most likely).
If rear tire pressures are optimum, decrease front tire pressure. Increase if chunking occurs.
Improper rear camber. "
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Old 04-01-2014, 02:28 PM   #18
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Originally Posted by k24madness View Post
Thanks Joe. I think I have the stock one in the shop. I am planning a test day on April 7th at Sonoma. I got a great driver who can help me shakedown the car and give me some data to overlay. If all goes well I may have some great lap times to report.
Something to think about. Lowered Miataís have huge amounts of camber gain in bump especially in the rear. The rear upper A-arm gets pretty far off level and really sucks the top of the tire in as it gets bump travel. It's also weird that I can set up my Spec Miata 1.6l NA with lots of rear camber and its faster steady state and doesnít make enough power to overcome cambered out tires accelerating off corners with foot flat to the floor so overall itís a faster setup for that car. If I put that much negative camber in my beast however it gets sketchy trying to roll on power mid corner it just wonít change forward velocity without getting loose. Optimal alignment for the beast Miata starts to more closely resemble what you would find on an Australian V8 Super car.
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Old 04-02-2014, 03:03 PM   #19
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Swap the SM front for a 1.125 RB front bar. Experiment with on or two clicks less rear compression damping.
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Old 04-02-2014, 04:47 PM   #20
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Thanks guys. I'll report back after some further testing and sway bar swaps.
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