What Size Front Tires
05-16-2011, 04:36 PM
#17
Race Car
Thanks 4 feedback.....Stock 8"/10" rims have stock 8.86"/11.2" tires so going up to 235/295 would be small 0.4"/0.5" increase to 9.25"/11.6". Would this be detrimental to handling? Thought at least going up to 235 on the front would reduce understeer?...........but then I'm new to this stuff.
05-16-2011, 06:54 PM
#19
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IMHO I think understeer on a 993TT is not a problem for a street driven car, even with spirited driving on your favourite twisty mountain pass. It becomes a problem when driving at 8/10th or more, which for most law abiding folk only occurs at the track. Further, as DM993tt has alluded, the solution is found from modification of multiple inputs, of which, tyre tread width is but a very small component.
Generally speaking, going from street rubber to R Compund rubber provides 1 to at the most 2 seconds per minute lap time advantage. Going from R Compound to semi-slicks (Hoosiers) another 1-2 seconds. Full slicks, another 1-2 seconds. The black magic arts of sway bar settings, -ve camber , toe in/out, front end spring rates, corner balancing and front end down force are the means of dialing out understeer and improving turn in. Then or course is the even more important matter of driver technique on corner entry and throttle management at mid corner - balancing initial understeer with later oversteer.
So where does tread width fit in to this equation? When you are talking about minor changes like the difference between 225 and 235 (which at tread width level is usually less than the expected 10mm), it lies at the very bottom of the list. Certainly 245, 255 and even 265 as some here have on street cars, may offer a little more tangible advantage, but without the right settings and balance between front and rear, tyre alone will add marginally to lap times.
So why go wider? Either for looks (to fill those guards) or because the tyre you want only comes in that size now e.g. MPSC's. If you need to solve an understeer problem, look at a broader set of solutions, that may well involve wider tyres as a component. Never oversize the tyre beyond the manufacturer's rim width recommendations, both for safety and performance reasons.
Generally speaking, going from street rubber to R Compund rubber provides 1 to at the most 2 seconds per minute lap time advantage. Going from R Compound to semi-slicks (Hoosiers) another 1-2 seconds. Full slicks, another 1-2 seconds. The black magic arts of sway bar settings, -ve camber , toe in/out, front end spring rates, corner balancing and front end down force are the means of dialing out understeer and improving turn in. Then or course is the even more important matter of driver technique on corner entry and throttle management at mid corner - balancing initial understeer with later oversteer.
So where does tread width fit in to this equation? When you are talking about minor changes like the difference between 225 and 235 (which at tread width level is usually less than the expected 10mm), it lies at the very bottom of the list. Certainly 245, 255 and even 265 as some here have on street cars, may offer a little more tangible advantage, but without the right settings and balance between front and rear, tyre alone will add marginally to lap times.
So why go wider? Either for looks (to fill those guards) or because the tyre you want only comes in that size now e.g. MPSC's. If you need to solve an understeer problem, look at a broader set of solutions, that may well involve wider tyres as a component. Never oversize the tyre beyond the manufacturer's rim width recommendations, both for safety and performance reasons.
05-17-2011, 10:31 AM
#20
Race Car
Super post. Thanks a bunch. Will stick with stock size.........
IMHO I think understeer on a 993TT is not a problem for a street driven car, even with spirited driving on your favourite twisty mountain pass. It becomes a problem when driving at 8/10th or more, which for most law abiding folk only occurs at the track. Further, as DM993tt has alluded, the solution is found from modification of multiple inputs, of which, tyre tread width is but a very small component.
Generally speaking, going from street rubber to R Compund rubber provides 1 to at the most 2 seconds per minute lap time advantage. Going from R Compound to semi-slicks (Hoosiers) another 1-2 seconds. Full slicks, another 1-2 seconds. The black magic arts of sway bar settings, -ve camber , toe in/out, front end spring rates, corner balancing and front end down force are the means of dialing out understeer and improving turn in. Then or course is the even more important matter of driver technique on corner entry and throttle management at mid corner - balancing initial understeer with later oversteer.
So where does tread width fit in to this equation? When you are talking about minor changes like the difference between 225 and 235 (which at tread width level is usually less than the expected 10mm), it lies at the very bottom of the list. Certainly 245, 255 and even 265 as some here have on street cars, may offer a little more tangible advantage, but without the right settings and balance between front and rear, tyre alone will add marginally to lap times.
So why go wider? Either for looks (to fill those guards) or because the tyre you want only comes in that size now e.g. MPSC's. If you need to solve an understeer problem, look at a broader set of solutions, that may well involve wider tyres as a component. Never oversize the tyre beyond the manufacturer's rim width recommendations, both for safety and performance reasons.
Generally speaking, going from street rubber to R Compund rubber provides 1 to at the most 2 seconds per minute lap time advantage. Going from R Compound to semi-slicks (Hoosiers) another 1-2 seconds. Full slicks, another 1-2 seconds. The black magic arts of sway bar settings, -ve camber , toe in/out, front end spring rates, corner balancing and front end down force are the means of dialing out understeer and improving turn in. Then or course is the even more important matter of driver technique on corner entry and throttle management at mid corner - balancing initial understeer with later oversteer.
So where does tread width fit in to this equation? When you are talking about minor changes like the difference between 225 and 235 (which at tread width level is usually less than the expected 10mm), it lies at the very bottom of the list. Certainly 245, 255 and even 265 as some here have on street cars, may offer a little more tangible advantage, but without the right settings and balance between front and rear, tyre alone will add marginally to lap times.
So why go wider? Either for looks (to fill those guards) or because the tyre you want only comes in that size now e.g. MPSC's. If you need to solve an understeer problem, look at a broader set of solutions, that may well involve wider tyres as a component. Never oversize the tyre beyond the manufacturer's rim width recommendations, both for safety and performance reasons.
05-17-2011, 02:42 PM
#21
Race Director
I've also found that tire pressures have a large impact on the front end push.
I run like 34/36, and have found that the car understeers much less than the stock setting.
I run like 34/36, and have found that the car understeers much less than the stock setting.
05-17-2011, 04:16 PM
#22
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MPSC and Pirelli Corsa R's - 26-27 F and 28-30 R!.
05-17-2011, 04:56 PM
#23
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05-17-2011, 05:29 PM
#24
Former Vendor
225/40 18 or 235/40 18 both work, and are the best sizes for an 8.5" wheel. They keep proper OD and don't get too big as to (usually) cause rubbing.
Please call me if interested or if I can help.
Please call me if interested or if I can help.
