High speed handling response.
Administrator
Joined: Oct 2000
Posts: 20,274
Likes: 4
From: Toronto, Canada
Dude 0.75 degrees is like /\
That is not what you want. You might want to try some rear toe in to control bump steer on your 00. My current alignment (thanks rlaifatt!) is fabtacular:
0 front toe
-1.3 FL camber (max)
-1.8 FR camber
6.8 caster
0.125" total rear toe in
-3.0 RR/RL camber
I don't think you have an alignment problem. Auto-x'ers tend to obsess over alignment because it's one of the few things you can actually change. I think at 130MPH you need to reconsider your suspension. You should try a set of KW's IMHO.
That is not what you want. You might want to try some rear toe in to control bump steer on your 00. My current alignment (thanks rlaifatt!) is fabtacular:
0 front toe
-1.3 FL camber (max)
-1.8 FR camber
6.8 caster
0.125" total rear toe in
-3.0 RR/RL camber
I don't think you have an alignment problem. Auto-x'ers tend to obsess over alignment because it's one of the few things you can actually change. I think at 130MPH you need to reconsider your suspension. You should try a set of KW's IMHO.
Thread Starter
Registered User
Joined: Feb 2004
Posts: 7,087
Likes: 2
From: Dry Branch
Originally Posted by Race Miata,Mar 7 2006, 10:07 PM
I would say your issue is most likely because of suspension/alignment/tires more than aerodynamics. While it can help stabilize high-speed cornering on the track, I wouldn't want a wing to cover up a different problem. I've done close to 130 at the bumpy turn 1 at PR in my S (and same corner on the old faster layout of SIR in my miata) both topdown and I've never felt lift to be a problem. While my miata with full suspension felt extremely stable there, my S with bone-stock suspension has had twitchy backend because of suspension/alignment/tires but not aerodynamics. If I were you, I would 1st narrow down to whether it's the front that's too responsive or the rear that's unstable.
For super responsive front end, some people may not get use to the quick steering response of the S. But seeing you coming from the miata world, I doubt you would be uncomfortable with the S quick steering response.
For a twitchy back end, it should be more noticeable during hard braking even on the straights, varying throttle even very little while mid-corner, and over bumpy pavement mid-corner.
Super responsive front end makes you want to ease up on steering input while twitchy back end makes you constantly correct your heading with steering input.
My MY00 twitchy back end was pretty bad. It was like each rear tire was fighting for its own direction of travel, depending on which of them gets marginally more instant traction. Even with rear swaybar removed and the car understeered a lot naturally, varying the throttle just a tiny bit (I'm not talking about lifting) or hitting some mildly bumpy pavement would bring the tail out mid-corner. It was so bad that even cruising straight on the highway, varying the throttle just a tiny bit would veer the car from side to side. Now that with a new set of tires, the problem seems to be totally gone. I'm waiting to try out on the track to be 100% sure the problem is totally gone. My point is that worn-out rear tires especially unevenly can do some very evil things.
So, are you sure it's the front not the rear of your car that's doing its thing?
For super responsive front end, some people may not get use to the quick steering response of the S. But seeing you coming from the miata world, I doubt you would be uncomfortable with the S quick steering response.
For a twitchy back end, it should be more noticeable during hard braking even on the straights, varying throttle even very little while mid-corner, and over bumpy pavement mid-corner.
Super responsive front end makes you want to ease up on steering input while twitchy back end makes you constantly correct your heading with steering input.
My MY00 twitchy back end was pretty bad. It was like each rear tire was fighting for its own direction of travel, depending on which of them gets marginally more instant traction. Even with rear swaybar removed and the car understeered a lot naturally, varying the throttle just a tiny bit (I'm not talking about lifting) or hitting some mildly bumpy pavement would bring the tail out mid-corner. It was so bad that even cruising straight on the highway, varying the throttle just a tiny bit would veer the car from side to side. Now that with a new set of tires, the problem seems to be totally gone. I'm waiting to try out on the track to be 100% sure the problem is totally gone. My point is that worn-out rear tires especially unevenly can do some very evil things.
So, are you sure it's the front not the rear of your car that's doing its thing?
If anyone thinks I might be covering up an aero problem, PLEASE SPEAK UP!
Everyone - thanks for all the thoughtful responses.
Thread Starter
Registered User
Joined: Feb 2004
Posts: 7,087
Likes: 2
From: Dry Branch
Originally Posted by smracer31,Mar 7 2006, 11:26 PM
from the alignment specs, i would go with 0 toe in the rear, remember the toe in the rear of the s2000 changes as the suspenion compresses. i would however do as i suggested above, add i would say 0.75 toe in in the front on each side and see if that doesnt help your problem. thats is where i would start.
Thanks!
Thread Starter
Registered User
Joined: Feb 2004
Posts: 7,087
Likes: 2
From: Dry Branch
Originally Posted by cthree,Mar 7 2006, 11:44 PM
Dude 0.75 degrees is like /\
That is not what you want. You might want to try some rear toe in to control bump steer on your 00. My current alignment (thanks rlaifatt!) is fabtacular:
0 front toe
-1.3 FL camber (max)
-1.8 FR camber
6.8 caster
0.125" total rear toe in
-3.0 RR/RL camber
I don't think you have an alignment problem. Auto-x'ers tend to obsess over alignment because it's one of the few things you can actually change. I think at 130MPH you need to reconsider your suspension. You should try a set of KW's IMHO.
That is not what you want. You might want to try some rear toe in to control bump steer on your 00. My current alignment (thanks rlaifatt!) is fabtacular:
0 front toe
-1.3 FL camber (max)
-1.8 FR camber
6.8 caster
0.125" total rear toe in
-3.0 RR/RL camber
I don't think you have an alignment problem. Auto-x'ers tend to obsess over alignment because it's one of the few things you can actually change. I think at 130MPH you need to reconsider your suspension. You should try a set of KW's IMHO.
I've run a few autocrosses where we have a big dip at one point, and at the time I had to run -2.5 degrees camber in the back to be able to take the dip with minimal upset. Now all the places I run regularly are very smooth, so bump steer isn't an issue (but roll steer is still very noticable). That's not what's going on at speed though, because I'm going straight on a smooth surface.
I wish I could figure out a way to measure the toe out at speed, then I could dial in just enough toe in to compensate. However, I am more convinced that this is a toe issue, because even though static toe is zero there has to be a fair amount of toe out at speed. I think I also need to consider firmer bushings, because that will keep the alignment more constant with increasing speed. I might also try backing off the front camber a little.
Further suspension upgrades are in the works, but I didn't want to start making changes while I have issues on smooth surfaces that might be related to aerodynamics.
However, you and everyone else seems to think that it is NOT aero, so I'm going for additional suspension tuning. Next change is gonna be more toe-in. I'll let you guys know what I think of the result (but give me a few days, because I have to find time to put the car on the rack and time to get out and test the effects).
Joined: Feb 2001
Posts: 4,063
Likes: 365
From: Redondo Beach
Agree that tires can cause evil handling; so can alignment. You definitely need more rear toe if you're running stock suspension -- 1/8" min, some people even use 1/4" (!).
But aero is a big issue too. It's well known that the S makes almost 100lbs of rear lift at 100mph. At 130 or 140mph, it's gotta be closer to 200lbs. There's only so much an alignment (or even full suspension) can do to fight that; eventually you'll need a wing.
But aero is a big issue too. It's well known that the S makes almost 100lbs of rear lift at 100mph. At 130 or 140mph, it's gotta be closer to 200lbs. There's only so much an alignment (or even full suspension) can do to fight that; eventually you'll need a wing.
Joined: Jun 2004
Posts: 473
Likes: 3
From: Charlottesville
Look, I've only been to the track once, so I'm no expert. And I don't mind being proven wrong, but I'd be willing to bet that you need a wing to solve this problem.
You stated that you're happy with the handling on autocross and street, in other words at low and medium speeds. You're only unhappy at high speeds.
What is the one thing that is radically different about high speeds. Yes, the higher forces are going to cause a little more compliance in the bushings. But, for the most part everything is going to be nearly constant or linear with speed. Except for aero effect that are going to go up with the square of speed. Aero will have 4 times the effect at 130 than at 65.
200 lbs of lift in the back. Go sit on your trunk and tell me what that does to your ride height. A rough guess is to assume that 200 lbs of lift will have the same effect in the other direction. That is going to add quite a bit of positive camber to your rear wheels.
My argument is all theoretical, so I don't mind hearing differently from you or someone else with more experience, but that's my $.02.
Oh, one more thing... I think the UK spec for caster is 6.75* (6* 45').
You stated that you're happy with the handling on autocross and street, in other words at low and medium speeds. You're only unhappy at high speeds.
What is the one thing that is radically different about high speeds. Yes, the higher forces are going to cause a little more compliance in the bushings. But, for the most part everything is going to be nearly constant or linear with speed. Except for aero effect that are going to go up with the square of speed. Aero will have 4 times the effect at 130 than at 65.
200 lbs of lift in the back. Go sit on your trunk and tell me what that does to your ride height. A rough guess is to assume that 200 lbs of lift will have the same effect in the other direction. That is going to add quite a bit of positive camber to your rear wheels.
My argument is all theoretical, so I don't mind hearing differently from you or someone else with more experience, but that's my $.02.
Oh, one more thing... I think the UK spec for caster is 6.75* (6* 45').
Thread Starter
Registered User
Joined: Feb 2004
Posts: 7,087
Likes: 2
From: Dry Branch
I can't thank you guys enough.
Twohoos - As this discussion has unfolded and I've thought about it more, I have convinced myself that toe has to be at least a part of the issue here. At speed, the car is toeing out, and that's making the car turn-in quicker. It may not be the only thing going on, but it has got to be a factor. 1/8-inch impresses me as being a good starting point.
I also want to thank you for posting some lift numbers. I wish we had some real numbers to bounce around, but 200 lbs. is probably within an order of magnitude.
I know there is a substantial amount of lift, regardless of the exact amount, and that's my concern. If what I'm feeling is due to lift unloading the tires and altering the alignment then the last thing I want to do is mask it. Clearly though, I do need some toe for high speed operation, and ALSO some way to cancel out the lifting at the back end. Once the suspension is resorted with the SC I'll probably end up going back to the motor looking for more power, and eventually a wing is going to be a must anyway, so you are absolutely correct.
OK, I'm going to go to 1/8-inch toe-in at the front, and add some kind of wing. I may also try a little toe in at the back. Can anyone tell me which wing or wings will get the job done with the fewest downsides?
Teamking - I'm no expert either, but I'm pretty sure that any car with flexible bushings toes out more as speeds increase, and toe can make a big difference in the initial turn-in response. At the same time, as you say, 200 lbs. or so is a heck of a lot of lift. Rounding the weight with driver to 3000 lbs. and assuming a 50/50 F/R split, the rear tires only carry 1500 pounds of weight (under static conditions). 200 pounds is a reduction of over 10%. Add in the unfavorable geometry changes as the back end rises and we're no doubt looking at a substantial reduction of available traction at the back. Like you, I'm just theorizing, but I can't believe that we have enough lift in the back to worry about.
Your argument makes perfectly good sense, and I appreciate the input. As I said before, I'm going to go with more toe in, and a wing, because it's pretty obvious (now) that I have too little toe in for high speed operation, and that I have to deal with the lift sooner or later.
Good catch on the UK specs.
We obviously forgot to do our conversion the last time we aligned the car. Fortunately, I'm still on the high side of the US spec. Interestingly though, more caster should improve straight line stability, so I obviously need to fix that too.
Now I have to start looking at wings. Anybody have any suggestions?
Twohoos - As this discussion has unfolded and I've thought about it more, I have convinced myself that toe has to be at least a part of the issue here. At speed, the car is toeing out, and that's making the car turn-in quicker. It may not be the only thing going on, but it has got to be a factor. 1/8-inch impresses me as being a good starting point.
I also want to thank you for posting some lift numbers. I wish we had some real numbers to bounce around, but 200 lbs. is probably within an order of magnitude.
I know there is a substantial amount of lift, regardless of the exact amount, and that's my concern. If what I'm feeling is due to lift unloading the tires and altering the alignment then the last thing I want to do is mask it. Clearly though, I do need some toe for high speed operation, and ALSO some way to cancel out the lifting at the back end. Once the suspension is resorted with the SC I'll probably end up going back to the motor looking for more power, and eventually a wing is going to be a must anyway, so you are absolutely correct.OK, I'm going to go to 1/8-inch toe-in at the front, and add some kind of wing. I may also try a little toe in at the back. Can anyone tell me which wing or wings will get the job done with the fewest downsides?
Teamking - I'm no expert either, but I'm pretty sure that any car with flexible bushings toes out more as speeds increase, and toe can make a big difference in the initial turn-in response. At the same time, as you say, 200 lbs. or so is a heck of a lot of lift. Rounding the weight with driver to 3000 lbs. and assuming a 50/50 F/R split, the rear tires only carry 1500 pounds of weight (under static conditions). 200 pounds is a reduction of over 10%. Add in the unfavorable geometry changes as the back end rises and we're no doubt looking at a substantial reduction of available traction at the back. Like you, I'm just theorizing, but I can't believe that we have enough lift in the back to worry about.
Your argument makes perfectly good sense, and I appreciate the input. As I said before, I'm going to go with more toe in, and a wing, because it's pretty obvious (now) that I have too little toe in for high speed operation, and that I have to deal with the lift sooner or later.
Good catch on the UK specs.
We obviously forgot to do our conversion the last time we aligned the car. Fortunately, I'm still on the high side of the US spec. Interestingly though, more caster should improve straight line stability, so I obviously need to fix that too.Now I have to start looking at wings. Anybody have any suggestions?
Joined: Feb 2001
Posts: 4,063
Likes: 365
From: Redondo Beach
Originally Posted by RED MX5,Mar 8 2006, 11:56 AM
OK, I'm going to go to 1/8-inch toe-in at the front, and add some kind of wing. I may also try a little toe in at the back.
