Tire Width Ratio front to rear

[EPorsche]

I was watching the Motor Trend Science of Speed video on the 997 GT2 while cornering and it stated that for rear weighted cars the idea tire width ratio from front to rear should match the weight distribution of the from front to rear. Has anyone on the forum achieved this setup? If yes, did you notice an advantage in handling, especially when cornering to prove them right or wrong?

[Bill Verburg]

Originally Posted by EPorsche

I was watching the Motor Trend Science of Speed video on the 997 GT2 while cornering and it stated that for rear weighted cars the idea tire width ratio from front to rear should match the weight distribution of the from front to rear. Has anyone on the forum achieved this setup? If yes, did you notice an advantage in handling, especially when cornering to prove them right or wrong?

front to rear ratios are a tuning tool, like sway bars, springs, alignment etc.

want more over-steer? use narrower rear wheels and or tires early 911s used a square setup 185/50 on 6x15 all around, '73 RS w/ a little more power/torque was the first street legal non-square set up using 185/70 on 6 and 215/60 on 7 all x15 for a little less understeer. '76 Carrera had options that ranged from that used on the '73RS to 7&8 x15 w/ 205/50 & 225/50. Not as much stagger as '73 but the lower profile tires run at lower slip angles and thus run cooler w/ more grip. The f/r weight ratios of all 911s are grouped pretty closely together so generally the more power/torque the more stagger and the lower the profile of the tire, usually lower in back than in front

want less under steer? use wider front wheels and or tires.

[EPorsche]

So Bill, in my case I have a narrow body '77 with an SC motor making about 190hp that I'm looking to add rear flares. I have three choices SC, ST and turbo. The ST's are expense as all get out. Which would work better if I planned on keeping the 205/55/16 in the front? How wide of a rim/tire combo would work w/o spacer?

[Bill Verburg]

Originally Posted by EPorsche

So Bill, in my case I have a narrow body '77 with an SC motor making about 190hp that I'm looking to add rear flares. I have three choices SC, ST and turbo. The ST's are expense as all get out. Which would work better if I planned on keeping the 205/55/16 in the front? How wide of a rim/tire combo would work w/o spacer?

I'd just use SC flares in back, 7ET23.3 front 8ET10.6 in back 205/55 & 225/50 tires, Fuchs come in those sizes in either 15 or 16. If you have a little more to spend 9ET15 Fuchs in back w/ 245/45 tires but now you are locked into 16s too

[EPorsche]

Bill,
The reason for me asking those questions about how wide to go is that I track the car (not as much as I would like) and would like to work up to about 5-7 DE a year. The last several times on the track (CMP) I notice the back end would over steer a lot the better I became. I've added adjustable Koni's on all four corners but haven't had the opportunity to try them out yet. Just thought more rubber back there would help.

[Bill Verburg]

Originally Posted by EPorsche

Bill,
The reason for me asking those questions about how wide to go is that I track the car (not as much as I would like) and would like to work up to about 5-7 DE a year. The last several times on the track (CMP) I notice the back end would over steer a lot the better I became. I've added adjustable Koni's on all four corners but haven't had the opportunity to try them out yet. Just thought more rubber back there would help.

It all depends on how serious you are and how much $ you want to spend

for track use 930 flares all around w/ 9 & 11 wheels is the way to go, but you need an updated suspension and brakes to go w/ it, none of this is inexpensive.

You can fit up to 8 & 9.5 wheels on an SC w/ the right ETs(look here for some suggestions)

You also need to decide 15, 15, 17 or 18

what you decide on depends on tire availability in the sizes you want to use, for occasional track days there are lots of great choices of tires, On a modestly powered car I'd try to keep the rear OD to 25" or less, and the rear overall width to 11"(less is easier to fit) and in front match the rear in OD and width 1-2" less.

Nice main stream combos are 205/225 x15, 225/245 x16, 225/255 x17

also be aware of the profiles for track use lower is better and you want somewhat of a f/r match usually one step lower in back ie 205/50 or 205/55 w/ 225/50 or 225/45 w/ 255/40 x17

[EPorsche]

I have 16's

[Bill Verburg]

Originally Posted by EPorsche

I have 16's

when I had 16's I had 7 & 8 then later 8 & 9 then 7 & 9, all Fuchs
w/ 7 & 8 I used 205/55 and 225/50
w/ 8 & 9 I used 225/45 and 245/45, the fronts aren't a real good fit because of the wheel ET and width
w/ 7 & 9 I used 205/55 and 245/45, this was a great all around combo, 225/45 would work well on the 7s w/ 245/45 rears too

Look at all the selections that are available from the various tire manufacturers, there are several sticky ways to go for hi perf street and occasional track days