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. |
What toe?
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Originally Posted by k24madness
(Post 1116805)
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. |
Originally Posted by Leafy
(Post 1116827)
What toe?
-1/16" front |
Originally Posted by bbundy
(Post 1116834)
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 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. |
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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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. |
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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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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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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Originally Posted by bbundy
(Post 1116834)
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.
How is your rear tire wear? What's your tire pressure? |
Originally Posted by jacob300zx
(Post 1116884)
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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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??? |
Originally Posted by jacob300zx
(Post 1116884)
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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Originally Posted by cordycord
(Post 1116890)
+1
How is your rear tire wear? What's your tire pressure? 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. |
Originally Posted by SchmoozerJoe
(Post 1116936)
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??? |
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. " |
Originally Posted by k24madness
(Post 1116941)
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.
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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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Thanks guys. I'll report back after some further testing and sway bar swaps.
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Originally Posted by k24madness
(Post 1117680)
Thanks guys. I'll report back after some further testing and sway bar swaps.
54107 for DOT tires. I use the 54106 1.25" bar for anything 225 Hoosier or bigger. I think Bundy uses a custom 1.25" too. |
Originally Posted by k24madness
(Post 1117680)
Thanks guys. I'll report back after some further testing and sway bar swaps.
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Originally Posted by bbundy
(Post 1117706)
The 1.25" racing beat front bar is hugely stiff compared to the 1.125” the difference between the two is drastic if you swap between those two you will likely have to do other changes to get some balance back.
Crusher on 225 R6's with full aero at NASA nationals (Miller) was seeing sustained 1.6g on the flat turns with long peaks of 1.75g in a few of the slightly cambered turns. That was 900/500 with the 54106 bar IIRC. |
Originally Posted by emilio700
(Post 1117742)
Yup. 250 in/lbs raw rate difference and they don't overlap. I found >1100lbs/in sway bar rate started to become necessary at around 1.55G sustained at typical race ride heights and 2100-2400lbs, give or take. So that's 225 Hoosiers or more. We use the 54106 for that. For 205 Hoosiers or harder compound 225's (less grip), the 1.125 x .188" wall and the 14mm seems to work over a variety of spring rates and vehicle weights.
Crusher on 225 R6's with full aero at NASA nationals (Miller) was seeing sustained 1.6g on the flat turns with long peaks of 1.75g in a few of the slightly cambered turns. That was 900/500 with the 54106 bar IIRC. |
Originally Posted by bbundy
(Post 1117767)
I think I’m marginally stiff enough. Thought it might be better to go to stiffer springs versus stiffening the bar though. Currently 900/500as well. I might try stiffening one notch front and rear on the bars or maybe just the front. It would be bout like the big racing beat 14mm combo then. With 245 Hoosiers on 10's it has ridiculous grip. Turn 2 at Pacific 180 degree flat sweeper taken in 5th gear. Not too long ago I would have thought that would be insane and I don’t remember when exactly I lost my sanity.
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Originally Posted by emilio700
(Post 1117742)
Yup. 250 in/lbs raw rate difference and they don't overlap. I found >1100lbs/in sway bar rate started to become necessary at around 1.55G sustained at typical race ride heights and 2100-2400lbs, give or take. So that's 225 Hoosiers or more. We use the 54106 for that. For 205 Hoosiers or harder compound 225's (less grip), the 1.125 x .188" wall and the 14mm seems to work over a variety of spring rates and vehicle weights.
Crusher on 225 R6's with full aero at NASA nationals (Miller) was seeing sustained 1.6g on the flat turns with long peaks of 1.75g in a few of the slightly cambered turns. That was 900/500 with the 54106 bar IIRC. |
Dean Thomas just did a 1:43.7 in my car the first session out on old R100's. We lost RR tire. Swapping out for new ones now. Thinking a 1:42 or less is possible today. He really likes the setup.
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Originally Posted by k24madness
(Post 1119086)
Dean Thomas just did a 1:43.7 in my car the first session out on old R100's. We lost RR tire. Swapping out for new ones now. Thinking a 1:42 or less is possible today. He really likes the setup.
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Originally Posted by emilio700
(Post 1119093)
Tweaks I suggested worked OK then?
After we installed new 245/R100 tires Dean did a 1:41.6 I managed my personal best time of 1:47.2 I bled pressures to 24 hot (from 26) and the car feels even better. Gonna send Dean out again after lunch and go for the 1:40.xx |
The afternoon sessions were no faster. Mostly
1:42's. The track got really hot and tires were starting to get greasy. Overall I am thrilled with the way the car felt and the results. Thanks everybody for the help dialing out that turn in oversteer. Props to Emilio for sharing his expertise. I believe a 1:41.6 is a new Miata lap record for Sonoma. |
Oh man... now I see this.
(I was looking for something to do today, could have come watched you at SP.) Sounds like the car is all set. And a new record? Congrats! |
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