PP axle ratio negated by larger tire

[RBGT]

With the manual GT, the rear axle ratio is a more aggressive 3.73 vs the standard 3.55.

That is a 5% increase - however, the PP rear tires at 275 40 R19 are 2.6% larger in diameter vs the standard 255 40 R19s.

That means the effective axle ratio is only 2.4% higher and probably barely noticeable.



I haven't ordered the PP myself (but got the brakes + AE) and thinking one can simple use 275 35 R19 in the rear.

That increases the rear axle ratio by 4.1% over the PP rear tire - so effectively the same rear ratio. The smaller diameter tire will also have less rotational inertia.

The K-brace and 2x front springs are a few hundred dollars - the "drift brake" is a gimmick to me. Want the rear wring delete anyway.

Not a fan of the PP wheels as they completely cover us those beautiful Brembos (and look like BMW M clones).

I am missing something here or does that make sense?

Sponsored

 

[RBGT]

The difference is with the PP you get Torsen and standard you the regular LSD.
Not sure how much difference that makes for road use?

There is also the "unique" stability control (software settings I assume).

 

[marcekb]

however, the PP rear tires at 275 40 R19 are 2.6% larger in diameter vs the standard 255 40 R19s.

Same size sidewall, wider tires. Diameter is the same, right?

 

[RBGT]

Same size sidewall, wider tires. Diameter is the same, right?

No, the sidewall is taller on the 275 40

Standard sidewall is 4.0"

PP 275 40 sidewall is 4.3"

 

[JS1951]

Will 275s fit the wheel width?

 

[RBGT]

This is what Im thinking for the rear.

shorter 275s

 

[RBGT]

Will 275s fit the wheel width?

I think new wheels needed.

The standard wheels are 8.5" and if they are shiny then I'd def. like to change them.

The PP wheels are too busy and cover up the brakes.

 

[RBGT]

Compares to stock - the smaller 35 ratio tires are actually a closer size.

PP 275 40 R19 = +2.6% larger

Proposed 275 35 R19 = -1.5% smaller

 

[RBGT]

Will 275s fit the wheel width?

The 275 is 10.8inch wide

Recommended wheel range is 9 - 11" according to tiresize.com

Standard wheels are 8.5"

 

[Zcarmenb28]

The smaller dia tire won’t fill the fender well very well, and will leave huge fender gaps. The tire will look too small on the car. 2nd: by going to a smaller dia tire you’re reducing the contact patch since it’s affected by the diameter (larger dia tire has longer contact patch front to back). It’s why dragsters use tall tires. Not only will the contact patch be smaller and thus less grip, the torque at the rear tire will be slightly multiplied. So slightly more torque and slightly less grip. Compounded it might be a slight problem. Plus you’ll be shifting gears sooner (maybe not a bad thing for spirited driving). I’d stick with the 275/40/19 if it was me.

 

[marcekb]

No, the sidewall is taller on the 275 40

Standard sidewall is 4.0"

PP 275 40 sidewall is 4.3"

Interesting... Thanks!

 

[RBGT]

The smaller dia tire won’t fill the fender well very well, and will leave huge fender gaps. The tire will look too small on the car. 2nd: by going to a smaller dia tire you’re reducing the contact patch since it’s affected by the diameter (larger dia tire has longer contact patch front to back). It’s why dragsters use tall tires. Not only will the contact patch be smaller and thus less grip, the torque at the rear tire will be slightly multiplied. So slightly more torque and slightly less grip. Compounded it might be a slight problem. Plus you’ll be shifting gears sooner (maybe not a bad thing for spirited driving). I’d stick with the 275/40/19 if it was me.

The 275 35 are only 1.5% shorter than the stock 255s.
The width is 8% more than the stock 255s.

The contact area should still be more than stock I believe.

I suspect those drag guys with huge tires get more aggressive rear axles?

Also, most of them make way more torque than stock.

Yes, gap will be 0.2" = 5mm larger with the 275 35 vs stock but thats probably not noticable?

 

[RBGT]

Without the 3.73 rear diff, the 275 40 R19s become a bit too tall.

The 3.55 ratio goes down to 3.46 - I feel a bit on the low side?
Plus the larger rotational inertia of the larger wheels might make it feel more sluggish.

I suppose that's why the picked the 3.73 for the PP.
The actual final drive ratio isn't all that different from the stock one.

 

[Zcarmenb28]

The 275 35 are only 1.5% shorter than the stock 255s.
The width is 8% more than the stock 255s.

The contact area should still be more than stock I believe.

I suspect those drag guys with huge tires get more aggressive rear axles?

Also, most of them make way more torque than stock.

Yes, gap will be 0.2" = 5mm larger with the 275 35 vs stock but thats probably not noticable?

I thought you were comparing 275/35 to the 275/40 on the PP. and 255/40 isn’t nearly enough tire even on a stock GT.

Still; 275/35 are 0.5” smaller Dia than even the small 255/40. It won’t look good IMO. 295/35 would match the 255/40 but then you’d need much wider wheels.

 

[RBGT]

I thought you were comparing 275/35 to the 275/40 on the PP. and 255/40 isn’t nearly enough tire even on a stock GT.

Still; 275/35 are 0.5” smaller Dia than even the small 255/40. It won’t look good IMO. 295/35 would match the 255/40 but then you’d need much wider wheels.

Yes 295 35 would be almost identical.

Wheels will be new regardless.

Would the 295 35 fit without issues/rubbing?

I had those on my previous V8 R8. I also feel the 255s are not enough for the heavier GT with more torque than the R8.
Also, the R8 was AWD.

I'm thinking 275 minimum for the rear or perhaps 285 - 295.

305 is probably overkill to stock power?

Its not just looks, acceleration and grip are more important to me.

Sponsored