How "BIG" Tires affect Traction Control?
12-19-2016, 09:46 AM
#21
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
Perhaps not for maximizing acceleration traction, but it doesn't take as much pressure change to affect the understeer-oversteer handling balance. 3 or 4 psi more up front than out back seems to be a good place for street and occasional autocross, 2 or 3 might be better for big track time.
If you go crazy with tire pressure tuning, particularly with significantly lowered rear tire pressure, you can even make an understeering FWD car oversteer whether you're on the throttle or getting off of it (kind of scary).
Norm
If you go crazy with tire pressure tuning, particularly with significantly lowered rear tire pressure, you can even make an understeering FWD car oversteer whether you're on the throttle or getting off of it (kind of scary).
Norm
Last edited by Norm Peterson; 12-19-2016 at 09:48 AM.
01-09-2017, 07:07 AM
#22
4th Gear Member
Join Date: Mar 2012
Location: Texas
Posts: 1,044
Track build& street
I'd like Norm to chime in here, I really enjoy chicanes and S curves on the coastal hwy's where I reside. If increasing front tire pressure 2-3 lbs to help my cornering ability I am all in. I normally run equal 32 lbs on all four, it increases to 34-35 as the tires warm up. Norm, will I feel a difference in handling if I increase the fronts a couple lbs? Man, I enjoy learning this stuff!
01-09-2017, 10:24 AM
#23
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
I have always found that 3 - 5 psi more in the front tires than in the rear tires improves turn-in response, and as long as I'm not carrying rear seat passengers or a LOT of trunk load for significant distances I'm not afraid to drop the rears a couple of psi below "door sticker".
Sam Strano mentioned doing something similar, back when he was running an early S197 in F-Stock . . . have to look back 7 or 8 years but I think it might still be accessible.
The idea is that higher inflation pressures reduce slip angles, as long as you don't get carried away with it, anyway.
It also stiffens the tire structure against lateral loads and moment loads about a vertical axis (where the contact patches are slightly rotated or twisted away from the plane of the wheel center). This part is a 'cornering stiffness' thing, and probably more important during cornering transients than at steady-state.
Less pressure does the opposite, and allows the rear slip angles to run at slightly increased slip angles at any given amount of cornering g's. Together with reduced front slip angles is the basic definition of reduced understeer.
With reduced rear pressure, your drive tires are slightly more compliant, which adds a little cushion against a little too much throttle resulting in a lot too much tailhappiness. Won't eliminate it, but it does give you a little more margin against it.
It's still possible to feel the difference in street driving, at least in back to back testing over the same curves.
On the street I normally run about 35/31 (cold) against the sticker's 32/32 recommendation, on the track I like to see something like 38/35 (sort of hot, taken after cooldown), which usually means I have to bleed out a little after the first session seeing that a 5 psi increase is entirely likely.
I may drop that rear pressure another psi or so, now that I've got firmer springs installed. Maybe that'll let me increase the rear shock settings and take a little more of a small bounce out without running into harshness. As far as I know, neither set of tires was ever stock for any Mustang, any generation, nor were either of the wheel sets stock for a 'regular' GT.
Norm
Sam Strano mentioned doing something similar, back when he was running an early S197 in F-Stock . . . have to look back 7 or 8 years but I think it might still be accessible.
The idea is that higher inflation pressures reduce slip angles, as long as you don't get carried away with it, anyway.
It also stiffens the tire structure against lateral loads and moment loads about a vertical axis (where the contact patches are slightly rotated or twisted away from the plane of the wheel center). This part is a 'cornering stiffness' thing, and probably more important during cornering transients than at steady-state.
Less pressure does the opposite, and allows the rear slip angles to run at slightly increased slip angles at any given amount of cornering g's. Together with reduced front slip angles is the basic definition of reduced understeer.
With reduced rear pressure, your drive tires are slightly more compliant, which adds a little cushion against a little too much throttle resulting in a lot too much tailhappiness. Won't eliminate it, but it does give you a little more margin against it.
It's still possible to feel the difference in street driving, at least in back to back testing over the same curves.
On the street I normally run about 35/31 (cold) against the sticker's 32/32 recommendation, on the track I like to see something like 38/35 (sort of hot, taken after cooldown), which usually means I have to bleed out a little after the first session seeing that a 5 psi increase is entirely likely.
I may drop that rear pressure another psi or so, now that I've got firmer springs installed. Maybe that'll let me increase the rear shock settings and take a little more of a small bounce out without running into harshness. As far as I know, neither set of tires was ever stock for any Mustang, any generation, nor were either of the wheel sets stock for a 'regular' GT.
Norm
Last edited by Norm Peterson; 01-09-2017 at 10:30 AM.