Would you be comfortable losing 2" of Tire diameter?

[dealmaker]

So I've been considering going to a 21" rear rim for the GT (going 20" on front).

My wheel tyre guy says that HRE have told him that the new Pirrlei Pzero nero "supercar specific" tyre - the 375/20/21 is a perfect fit on the GT!

Whilst a 375 on the back sounds great I am a little worried about the overall diameter and rolling radius.

According to my calcs the gearing will drop by around 7% - which I know might actually be a good thing (not like I need that 250mph theoretically geared top speed every day!)...but I am more worried about the ride height and size of the wheel in the wheel-well/arch.

The stock tire is 28.9" tall - the "new" Pirelli is 26.9" tall - so I lose 2" off the overall diameter and 1" of ride height! The car has KW coil overs fitted so I guess I can adjsut it to suit - but I don't want it looking like there is a foot and a half of fresh ari bwteeen the tire and the arch - and what about that lowered ride height (car is already 1.5" lower than stock at the back)

So whats the thinking on this - is it within acceptable limits?

Thanks!

 

[Empty Pockets]

So I've been considering going to a 21" rear rim for the GT (going 20" on front).

My wheel tyre guy says that HRE have told him that the new Pirrlei Pzero nero "supercar specific" tyre - the 375/20/21 is a perfect fit on the GT!

Whilst a 375 on the back sounds great I am a little worried about the overall diameter and rolling radius.

According to my calcs the gearing will drop by around 7% - which I know might actually be a good thing (not like I need that 250mph theoretically geared top speed every day!)...but I am more worried about the ride height and size of the wheel in the wheel-well/arch.

The stock tire is 28.9" tall - the "new" Pirelli is 26.9" tall - so I lose 2" off the overall diameter and 1" of ride height! The car has KW coil overs fitted so I guess I can adjsut it to suit - but I don't want it looking like there is a foot and a half of fresh ari bwteeen the tire and the arch - and what about that lowered ride height (car is already 1.5" lower than stock at the back)

So whats the thinking on this - is it within acceptable limits?

Thanks!

'Might be helpful to simply take some cardboard & cut out a couple circles with the diameter of both the proposed front & back wheel/tire combo, prop each up against the existing wheels/tires, step back a few feet from the car and take a look at what the new setup would look like. (You could position them representing your proposed KW height adjustments, too.)


Edit: Ignoring the ride height adjustments via the KW's, I'd be reluctant to drive a car lowered that much on public roads. One would think you'd be 'remodeling' your belly pans every 10 feet (or 14 meters [whatever it is] in your case!).

 

[Pete S.]

And I suppose on a smaller radius the heat will increase as the same given spot on the tire will be in contact with the road more often; though this could be compensated for with different tire compounds. I think one of the GT Guy's would know best.

Pete S.

 

[B.M.F.]

So I've been considering going to a 21" rear rim for the GT (going 20" on front).

My wheel tyre guy says that HRE have told him that the new Pirrlei Pzero nero "supercar specific" tyre - the 375/20/21 is a perfect fit on the GT!

Whilst a 375 on the back sounds great I am a little worried about the overall diameter and rolling radius.

According to my calcs the gearing will drop by around 7% - which I know might actually be a good thing (not like I need that 250mph theoretically geared top speed every day!)...but I am more worried about the ride height and size of the wheel in the wheel-well/arch.

The stock tire is 28.9" tall - the "new" Pirelli is 26.9" tall - so I lose 2" off the overall diameter and 1" of ride height! The car has KW coil overs fitted so I guess I can adjsut it to suit - but I don't want it looking like there is a foot and a half of fresh ari bwteeen the tire and the arch - and what about that lowered ride height (car is already 1.5" lower than stock at the back)

So whats the thinking on this - is it within acceptable limits?

Thanks!

The Perilli 375 is a scam. Its a sales gimic also and tread width is only loke 12''s. The 355-25-21 is the tire you want, close to the same size as stock and 14'' of tread width. I have pics of a set as a friend is putn them on his car along with some 21*13 360 forged Straight 5 wheels with the centers wrapped in carbon.

 

[Gordo]

Hi guy's. I'm looking to change the wheels on my GT also. B.M.F - would it be possible for you to forward the pics of your buddies car with the 355/25/ R21 tires. :cheers

 

[dealmaker]

The Perilli 375 is a scam. Its a sales gimic also and tread width is only loke 12''s. The 355-25-21 is the tire you want, close to the same size as stock and 14'' of tread width. I have pics of a set as a friend is putn them on his car along with some 21*13 360 forged Straight 5 wheels with the centers wrapped in carbon.

Guys,

Who makes the 355/25/21 - i cant seem to find anything on the internet?

Are we agreed that 255/30/20 is nealry the optimal size for front?

Thanks!!!!!

 

[Fast Freddy]

......

 

[ChipBeck]

No way!

I'm not comfortable losing 2" of anything!

Chip

 

[B.M.F.]

Guys,

Who makes the 355/25/21 - i cant seem to find anything on the internet?

Are we agreed that 255/30/20 is nealry the optimal size for front?

Thanks!!!!!

Perilli does, they come stock on the Ferrari 599Gtb. 800 a tire when he bought them and there were only two sets in country, other guys wanted 3000 for the pair. There should be more now.

 

[timcantwell]

Personally, I would'nt do it. My Bentley has 22" wheels with very slim sidewalls (Pirelli P-Zero Rosso's). They look awesome, but with three piece wheels, they tend to lose air fairly quickly. With the small volume of air, there is VERY small margin for error, a one-pound loss results in 1/8th inch "sag" due to air loss! I have to check pressures every time I leave the garage and hope that I don't hit a pot hole along the way. There is very little between the rim and the road. Plus, it is very difficult to get these low profile tires and big wheels in proper balance due to "out-of-round" tolerances. I am constantly fighting with some "wobble" at some speed even after lots of dynamic balancing and indexing using a Hunter Road Force system. I ran 20's and 19' front to back respectively on one of my GT's and have the same set-up on one of my Vipers (CCW wheels). I found those to look and perform great while not sacrificing ride quality. There was about less than a half inch loss in total diameter with that set-up.

 

[fjpikul]

Wow, Cantwell must have laid down on the ground to take that picture.