255/50-16's on D-90s Yes or No
07-29-2005, 10:51 AM
#31
Race Director
Ok, my $0.42:
Tifo, Dan, and Matt are right. They know this stuff. IIRC, Matt works with tires to earn his living, so I HOPE he knows what he's talking about!! But let me echo their thoughts, as well as state my own drivel here:
First off, don't confuse tire height with tire width. It is the difference in tire width that relates to tire stagger, not the difference in tire height. (IE: contact patch front to rear)
Side note: What's the deal with understeer? If Porsche engineered our cars with understeer, isn't that a good thing? Good questions, and I'm glad you asked!
First, some definitions: Understeer: when the front of the car looses traction sooner than the rear. (aka: push, plow, tight). Oversteer: when the rear of the car looses traction sooner than the front (aka: fishtail, loose, 'back end wants to come around.)
The reason most cars have understeer engineered into them is for safety. If a car is understeering, most often the best way to gain control back to the driver is for the driver to slow down. And guess what: the common driver, in panic situations does exactly that - he either lifts off the throttle, and/or taps the brakes, and 'miraculously' the car is back in control.
Now the same is not true with oversteer - if the car is in an oversteering situation, there is less grip at the rear wheels. Lifting or braking at that point will only decrease the amount of grip the rear wheels have to work with, due to weight transfer, often causing the slide to turn into an all-out spin. Often, a driver needs to plant his foot on the throttle to keep the back end from loosing anymore grip.
So why would anyone want oversteer instead of understeer? Again, good question, grasshopper! Typically, the most effective way to combat understeer is to slow down. When racing, who wants to slow down? With a car that is setup with a slightly oversteering attitude, the driver has more tools to select from in going around the corner. He can plant his foot on the throttle, as long as he doesn't go beyond the grip limits of his tires. He can do throttle steering and get the car to 'run the tangent' around the corner. Ideally, a race car driver would want his car setup neutral (little of either understeer and oversteer) with a slight tendancy to oversteer.
(End side note)
Ok, back to the issues at hand...
In my experience, the best results that I have gotten out of tire selection is going with 8Jx16s at all four corners, shod with 245-45/16's. That eliminated the staggered tire setup, and helps to dial out much of the understeer that's engineered into our cars.
Unfortunately, some autocross classifications are pretty strict about putting bigger wheels on cars, espeically in the stock classes. If that is your case, or you simply don't have $$ or storage space for extra wheels & tires (Note: I have a total of 14 spare wheels/tires in my garage, not counting my street wheels/tires! ) then the next best alternative is to run with 7Jx16 front, shod with 225-50/16's, and 8Jx16 rear with 245-45/16 tires. You can help dial out the understeer in that case with tire pressure adjustment, and/or sway bar adjustments (if your class allows sway bar upgrades).
Hope this is clear as mud now....
-Zoltan.
Tifo, Dan, and Matt are right. They know this stuff. IIRC, Matt works with tires to earn his living, so I HOPE he knows what he's talking about!! But let me echo their thoughts, as well as state my own drivel here:
First off, don't confuse tire height with tire width. It is the difference in tire width that relates to tire stagger, not the difference in tire height. (IE: contact patch front to rear)
Side note: What's the deal with understeer? If Porsche engineered our cars with understeer, isn't that a good thing? Good questions, and I'm glad you asked!
First, some definitions: Understeer: when the front of the car looses traction sooner than the rear. (aka: push, plow, tight). Oversteer: when the rear of the car looses traction sooner than the front (aka: fishtail, loose, 'back end wants to come around.)
The reason most cars have understeer engineered into them is for safety. If a car is understeering, most often the best way to gain control back to the driver is for the driver to slow down. And guess what: the common driver, in panic situations does exactly that - he either lifts off the throttle, and/or taps the brakes, and 'miraculously' the car is back in control.
Now the same is not true with oversteer - if the car is in an oversteering situation, there is less grip at the rear wheels. Lifting or braking at that point will only decrease the amount of grip the rear wheels have to work with, due to weight transfer, often causing the slide to turn into an all-out spin. Often, a driver needs to plant his foot on the throttle to keep the back end from loosing anymore grip.
So why would anyone want oversteer instead of understeer? Again, good question, grasshopper! Typically, the most effective way to combat understeer is to slow down. When racing, who wants to slow down? With a car that is setup with a slightly oversteering attitude, the driver has more tools to select from in going around the corner. He can plant his foot on the throttle, as long as he doesn't go beyond the grip limits of his tires. He can do throttle steering and get the car to 'run the tangent' around the corner. Ideally, a race car driver would want his car setup neutral (little of either understeer and oversteer) with a slight tendancy to oversteer.
(End side note)
Ok, back to the issues at hand...
In my experience, the best results that I have gotten out of tire selection is going with 8Jx16s at all four corners, shod with 245-45/16's. That eliminated the staggered tire setup, and helps to dial out much of the understeer that's engineered into our cars.
Unfortunately, some autocross classifications are pretty strict about putting bigger wheels on cars, espeically in the stock classes. If that is your case, or you simply don't have $$ or storage space for extra wheels & tires (Note: I have a total of 14 spare wheels/tires in my garage, not counting my street wheels/tires!
) then the next best alternative is to run with 7Jx16 front, shod with 225-50/16's, and 8Jx16 rear with 245-45/16 tires. You can help dial out the understeer in that case with tire pressure adjustment, and/or sway bar adjustments (if your class allows sway bar upgrades).Hope this is clear as mud now....
-Zoltan.
07-29-2005, 11:18 AM
#32
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My bad- I didn't realize this was for auto-X... yes, the gearing dif would DEFINATELY hurt Auto-X.... the stock gearing is too tall already for most auto-X, when you consider the 30-35mph 1st gear Integras, CRX's, Sciroccos, etc, that normally run those courses... THEN, you throw in the turbo-lag, &, youre REALLY hurting,.. of course... this may not be for a turbo at all, but, now I'm too lazy to scroll back up & read...
255/50 = 127.5,mm of profile... that's a LOT! My '89 Integra had 195/60/14's, which was 117mm of profile & I got to where I thought THAT was too much... the 245/45 is 110.25mm... I think the 255/40 (102mm) is about perfect for street, but, I could handle a little shorter- I think anything much below ~95mm is getting short for street, but, that depends on where you are, etc...
255/50 = 127.5,mm of profile... that's a LOT! My '89 Integra had 195/60/14's, which was 117mm of profile & I got to where I thought THAT was too much... the 245/45 is 110.25mm... I think the 255/40 (102mm) is about perfect for street, but, I could handle a little shorter- I think anything much below ~95mm is getting short for street, but, that depends on where you are, etc...
07-29-2005, 11:57 AM
#34
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To me, putting on way too wide tires because they are cheap, or a good deal, makes no sense! It's like wearing a size 14 Nike when you have a size 10 foot, just because the sneakers cost $2! They still don't fit in the end!
07-30-2005, 12:43 AM
#35
Johne, that picture is what I was trying to describe, I am just not an artist.
Fact remains that this is wrong setup. It will be the wrong setup this year, next year, and forever.
The White 944 looks cool with those wheels but it must be an effing dog...no where near enough torque to need a wheel that wide. Might as well mount some chrome 20s
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Fact remains that this is wrong setup. It will be the wrong setup this year, next year, and forever.
The White 944 looks cool with those wheels but it must be an effing dog...no where near enough torque to need a wheel that wide. Might as well mount some chrome 20s
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07-31-2005, 05:55 PM
#36
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Originally Posted by Matt H
Fact remains that this is wrong setup. It will be the wrong setup this year, next year, and forever.
The White 944 looks cool with those wheels but it must be an effing dog...no where near enough torque to need a wheel that wide. Might as well mount some chrome 20s
The White 944 looks cool with those wheels but it must be an effing dog...no where near enough torque to need a wheel that wide. Might as well mount some chrome 20s
I'd love to see someone like Tifo or Z-Man do back to back track runs with 16's and 17's on their cars. You'd have to run the same brand and model tires just to keep compounds out of the equation, but methinks it would surprise a few folks.
08-01-2005, 10:35 PM
#37
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Tough crowd at $35 a tire. The 255/50's aren't that bad, sure, not what one would buy most of the time, but reset the rear ride height as best you can, re-align, use the S2's torque, go in-slow, out-fast, and have fun!
Of course, fresh Hoosiers (or whatever) in the optimal sizes will be faster. They won't be $140 for a set of four, though.
Of course, fresh Hoosiers (or whatever) in the optimal sizes will be faster. They won't be $140 for a set of four, though.
