Back-end Wiggle at High Speed: how can I eliminate?
May 23, 2005, 02:18 PM
#47
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Originally Posted by 90GSX-03EVO
I agree that there are a lot of Evo owners out there that don't know enough about these cars. The ones who say the stock clutch sucks, that the synchros are weak, blah blah blah....
I've also owned both the GSR and the RS. In a straight line from 140 or so down to 50, the GSR stays straight while the RS tries to walk the back end around. This is by simply getting on the brakes fairly hard, not locking up the tires. Alignment might be a solution, and a very likely one, but at the same time, I've heard multiple people who have driven both the GSR and the RS and they all say the RS is twitchier at higher speeds.
I've also owned both the GSR and the RS. In a straight line from 140 or so down to 50, the GSR stays straight while the RS tries to walk the back end around. This is by simply getting on the brakes fairly hard, not locking up the tires. Alignment might be a solution, and a very likely one, but at the same time, I've heard multiple people who have driven both the GSR and the RS and they all say the RS is twitchier at higher speeds.
May 23, 2005, 07:06 PM
#48
uhm... toe in will make your rear more stable. get a real wing, don't bother with an evo wing.
if you want to get a vg it will only decrease your cd without the wing... with the wing it will increase the wing's efficiency to reduce lift.
getting an underbody plate might reduce lift as it takes away the airpocket that the bumper creates.
otherwise you'd have to get a real diffuser to really see actual downforce... and even then it's hard to get a well made one. apr makes a cf one that looks like it's very functional, but that will cost you dearly.
the varis does not fit the evo8 bumper... nor the evo9... the evo9 bumper may improve rear end downforce... but is not a tru diffuser.
and that vishnu piece is not made correctly... the slats should get larger as you get more towards the rear... it should seperate the air as long as possible... you're just letting vortices form between the slats before the air exits the rear of the car.
if you want to get a vg it will only decrease your cd without the wing... with the wing it will increase the wing's efficiency to reduce lift.
getting an underbody plate might reduce lift as it takes away the airpocket that the bumper creates.
otherwise you'd have to get a real diffuser to really see actual downforce... and even then it's hard to get a well made one. apr makes a cf one that looks like it's very functional, but that will cost you dearly.
the varis does not fit the evo8 bumper... nor the evo9... the evo9 bumper may improve rear end downforce... but is not a tru diffuser.
and that vishnu piece is not made correctly... the slats should get larger as you get more towards the rear... it should seperate the air as long as possible... you're just letting vortices form between the slats before the air exits the rear of the car.
Last edited by trinydex; May 23, 2005 at 07:12 PM.
May 24, 2005, 01:48 AM
#49
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Originally Posted by TexasRS
Isn't it true that what you're describing with the RS can be eliminated with an increase in rear toe????
May 24, 2005, 05:02 AM
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I think someone posted before that .5 rear toe would be enough to make the rear more stable, yet not cause unreasonable tire wear. Does that sound reasonable to everyone else? Thanks.
May 24, 2005, 06:03 AM
#51
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If that's in degrees, maybe. I think of toe in inches, so I don't have a point of reference for how much toe 0.5 degrees is.
If that's 0.5 INCHES, hell no - a half inch of toe in would be enormous.
We also need to differentiate between "per wheel" and "total toe" - the latter being the sum of both formers.
I'd put it on the rack (or string it yourself) and add 1/16" of toe in per side, and see how that feels.
DG
If that's 0.5 INCHES, hell no - a half inch of toe in would be enormous.
We also need to differentiate between "per wheel" and "total toe" - the latter being the sum of both formers.
I'd put it on the rack (or string it yourself) and add 1/16" of toe in per side, and see how that feels.
DG
May 24, 2005, 06:14 AM
#52
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Originally Posted by FarNorthRacing
If that's 0.5 INCHES, hell no - a half inch of toe in would be enormous.
You wouldn't be able to get to 0.5 inches per side in the rear without modifying the control arms. Which is probably a good thing.
May 24, 2005, 06:41 AM
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All modern alignment rigs are all in digital degrees.
If you're doing it with string and a tape measure, or the modern equivalent (laser) then you're obviously in inches.
Try this
Deetz
If you're doing it with string and a tape measure, or the modern equivalent (laser) then you're obviously in inches.
Try this
Deetz
May 25, 2005, 03:50 PM
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Nice document, keeping that for reference.
Sounds like there's 2 arguments here, one for Aerodynamics, one for alignment.
I've had my stock GSR up to 140+, and it felt quite stable. i didn't feel any unreasonable twitchiness (other than the stiff springs).
At those high speeds, I would think aerodynamics would help more than a solid alignment
Sounds like there's 2 arguments here, one for Aerodynamics, one for alignment.
I've had my stock GSR up to 140+, and it felt quite stable. i didn't feel any unreasonable twitchiness (other than the stiff springs).
At those high speeds, I would think aerodynamics would help more than a solid alignment
May 26, 2005, 10:04 PM
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I vote tire pressures in this case. 45 psi is way to high for everyday driving. The rear tires should be lower if you want stability. I run stock pressures and it takes a lot to get the rear end out. Also, the max pressure on a tire is rarely, if ever, the "recommended" pressure for the tires. The recommended pressure is what the manufacturer puts inside the driver's door (assuming you are running stock sized tires).
The EVO is very sensitive to changes in tire pressure. I can usually tell when the pressures on mine are off.
I would recommend starting with Mitsu's recommended pressures and go from there.
Cabo
The EVO is very sensitive to changes in tire pressure. I can usually tell when the pressures on mine are off.
I would recommend starting with Mitsu's recommended pressures and go from there.
Cabo
May 26, 2005, 10:19 PM
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wouldn't lower pressure decrease sidewall ridgity? the tire pressure would affect hop...i would investigate the temp. (shock oil) or even the rear rebound.
May 26, 2005, 11:15 PM
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Originally Posted by Matthew333
wouldn't lower pressure decrease sidewall ridgity? the tire pressure would affect hop...i would investigate the temp. (shock oil) or even the rear rebound.
May 26, 2005, 11:23 PM
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Yes, I run 45psi but not on stock tires. Khumo ECSA ASXs. The max psi is 51.
Based on your advice, I decreased the rear pressure to 42psi. Tomorrow I will drive on the highways and see if I notice a decrease in rear twitch.
It seems like there is a lack of consistant support for the effectiveness of the wing, or am I mis-interpreting some of the posts? Any other RS owners who have experienced high-speed twitch, and have advice?
Again, I will try the lower tire pressure and report back....I really like to keep my front tires at 45psi (because of the quicker turn-in handling). Again, I just decreased my rears to 42psi. I had considered decreasing the rear to 40psi (and keeping the front at 45), but I thought that may be too large of a difference b/w front and back.....Is that correct? Would that be unsafe?
Thanks!
Based on your advice, I decreased the rear pressure to 42psi. Tomorrow I will drive on the highways and see if I notice a decrease in rear twitch.
It seems like there is a lack of consistant support for the effectiveness of the wing, or am I mis-interpreting some of the posts? Any other RS owners who have experienced high-speed twitch, and have advice?
Again, I will try the lower tire pressure and report back....I really like to keep my front tires at 45psi (because of the quicker turn-in handling). Again, I just decreased my rears to 42psi. I had considered decreasing the rear to 40psi (and keeping the front at 45), but I thought that may be too large of a difference b/w front and back.....Is that correct? Would that be unsafe?
Thanks!
May 26, 2005, 11:58 PM
#60
Originally Posted by TheGVR4kid
Get some cannards in the rear!
