Rear tyres size increase?

[TheSebringOne]

Gsuds, are you now putting on GY F1s 255x40x17s 94Y on the 94+ rims? What was the exact size of the Toyo Proxys as I'm a little confused as to the 94Y as oppose to 91Y on the standard 245x40x17? The 94Y may not fit?

[markc]

Hi Guys,

The 91Y, 94Y part is the Load Index rating of the tyre and has nothing to do with either fitment as such, or year, of manufacture or anything else.

I'm currently running Bridgestone Potenza S03-Pole Position's in the 225x45x16 (89Y) and 255x40x17 (94Y) combo ie 1 size (width) up both front and rear on my car.
They've been fine and I've not noticed any significant differance in handling feel or balance to the previous Potenza RE711's (215 Fr & 245 Rr) that were fitted.

For some reason I find tyre tech fascinating, probably because it's confusing so please excuse the "know enough to be dangerous" information that follows and use or dismiss as you see fit...

Load Index (LI) is a standard tyre industry measurement and is quoted, and marked on the sidewall, for all new passenger car tyres. However, it (LI) does not indicate the sidewall stiffness even though it is probably related in some way to it for a particular tyre design (brand & model) at least. Seems logical to me?

Sidewall stiffness is not, as far as I can tell, measured in any industry standard way by the tyre manufacturers so can't be compared between tyres from the same manufacturer let alone differant ones!

Sidewall stiffness is a function of the design and construction of the particular model of tyre.

A Load Index of 91Y translates to a 615Kg max load for the tyre, 94Y translates to 670Kgs. I don't know what the "Y" sufix represents but it definately isn't the speed rating in this case.

Assuming for the moment that the NSX weighs 1400Kg, the oft quoted 42 Front/58 Rear (percent) weight distribution gives the rear tyres a static load of 406Kg each and the fronts 294kg each.

Even assuming the car is fully loaded with 2 large passengers and a boot full of luggage you'd be hard pressed to get anywhere near the typical 89-94Y Load Index found on "NSX spec" tyres.

So what does it all that mean? I've no idea except that the following observations are probably all true...

1) The original fitment designs for the 15/16 and 16/17 wheels from Bridgestone (RE010) Yokohama (AH022) and Dunlop (SP8050), and indeed the Bridgstone RE040 spec'd for the 2002 cars are all no longer readily available and some no longer produced at all.
2) Tyre technology has moved on in leaps and bounds since the NSX came out and these tyres were designed.
3) Many modern tyre designs (of the correct size and speed rating) are likely to work well on the NSX.
4) Some will be quantifiably better than others ie max lateral grip (in G's), wet/dry braking performance, noise etc.
5) Some will be subjectively better than others ie feel and feedback.
6) Some people will prefer one design over another.

Phew, I enjoyed that

Cheers

Mark

[Silver Surfer]

Pic for James to ponder on tyre spec.

SS

[gsuds]

Gsuds, are you now putting on GY F1s 255x40x17s 94Y on the 94+ rims? What was the exact size of the Toyo Proxys as I'm a little confused as to the 94Y as oppose to 91Y on the standard 245x40x17? The 94Y may not fit?

I now have GY F1 245/40/17 on rear. Was Toyo Proxes T1R 255/40/17.
G

[markc]

Hi gsuds, all the details please what Load Index are your F1's?

Mark

[michaelw]

I have just ordered some CE-28's from Dali - superb service BTW but I am now having problems getting tyres.

I have managed to get the fronts (215/40/17) in the GS/D3 but can't get the rears (255/35/18 or 265/35/18). I have just been told that the GS-D3 have been replaced by the Asymmetric in certain sizes has anyone tried these?

I have spoken to Goodyear and they say that ideally you shouldn't mix the 2 but it will be OK. They don't do the new tyre in the size I need for the front or the old tyre in the rear size so I have no choice but to mix - oh great!

On a different tack are the Bridgestone SO-2's as good as the old SO-3's?

Apparently the new tyre has a harder compund and stiffer sidewall on the outside and a softer compound on the inside.


Michael.

P.S. Sorry if this is a bit of a threadhijack but may be worth considering what is available and checking stock before deciding which tyre to go for.

[gsuds]

Hi gsuds, all the details please what Load Index are your F1's?

Mark

Haven't a clue

[Senninha]

James,

Plenty for you to digest. One small point I have been told by many that isn't clear from your original post is balance F to R. If you go up at the rear, go up at the front as well. If you dont then you run the risk of inducing higher levels of understeer the first time you go for a spirited drive. If you've driven a stock Elise then you'll know the feeling.

HTH, Paul

[AR]

215 f 255 r is about as usable as it gets for a street NSX on 17/17. 225 is nice but with no PAS is a pain parking drivers not built like Popeye.

[gsuds]

Agree Ary - had 225f with the 255r, one reason I've downsized again is slightly better steering precision with 215, and less weight with non-PAS.