Widest tyre on standard alloys?

[Nodster]

Hey

I seem to recall that you can "plus 10" on tyre width in the back of my mind. At the moment I have 255/40/19R up front and 275/40/19R on the rear. Standard custom pack 3 forged 19" alloys. Would I be right in thinking the widest I can go is therefore 265/40 front and 285/40 on the rear?

I really like the wheels and don't want to change them.

I'm just trying to eek out as much rubber on the road as possible as I think I'll be struggling with the Supercharger. At the moment I can get the rear to squirm with very little effort pulling away in a straight line (not even gunning it) so I'm just thinking for when the time comes what I can do to improve things. The Potenza Sport tyres at the moment are relatively new so I won't be changing them out for a wee while yet.

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[Gnatsum21]

Hey

I seem to recall that you can "plus 10" on tyre width in the back of my mind. At the moment I have 255/40/19R up front and 275/40/19R on the rear. Standard custom pack 3 forged 19" alloys. Would I be right in thinking the widest I can go is therefore 265/40 front and 285/40 on the rear?

I really like the wheels and don't want to change them.

I'm just trying to eek out as much rubber on the road as possible as I think I'll be struggling with the Supercharger. At the moment I can get the rear to squirm with very little effort pulling away in a straight line (not even gunning it) so I'm just thinking for when the time comes what I can do to improve things. The Potenza Sport tyres at the moment are relatively new so I won't be changing them out for a wee while yet.

Besides tires you should look at suspension/IRS components/stop the hop/etc. to keep the enchilada straight and on the road when flooring it with a supercharger.

 

[Nodster]

Besides tires you should look at suspension/IRS components/stop the hop/etc. to keep the enchilada straight and on the road when flooring it with a supercharger.

Yeah good suggestion. I already have the full steeda IRS kit. (IRS bushes and rear bracing). I also have their billet rear vertical links. Is there anything else I can do for the rear?

Car isn't lowered but I was trying to stay away from that.

 

[NightmareMoon]

If you’re searching for grip, the right tire choice (brand, model) is more important than tire width. Keep that in mind.

that said, there aren’t a ton of 285/40 tires. If the tire you want comes in a 285/40 it would fit fine… but some 285/35s work well and its not very pinched at all on a 9.5” rear.

on the front 9” wheel some of us crazy autocrossers have done up to 285/35 too (with a small 5mm spacer) but without the right tire with a stiff sidewall, I wouldn’t recommend it, becuse its pretty pinched so with the wrong tire, handling will be squirmy and even then with that much pinch you’re not putting the outside edges of the tire on the ground most of the time unless you’re in a corner. 265 of course would be fine on the front for most normal tires.

 

[Nodster]

If you’re searching for grip, the right tire choice (brand, model) is more important than tire width. Keep that in mind.

that said, there aren’t a ton of 285/40 tires. If the tire you want comes in a 285/40 it would fit fine… but some 285/35s work well and its not very pinched at all on a 9.5” rear.

on the front 9” wheel some of us crazy autocrossers have done up to 285/35 too (with a small 5mm spacer) but without the right tire with a stiff sidewall, I wouldn’t recommend it, becuse its pretty pinched so with the wrong tire, handling will be squirmy and even then with that much pinch you’re not putting the outside edges of the tire on the ground most of the time unless you’re in a corner. 265 of course would be fine on the front for most normal tires.

Yeah there is more choice moving to a 35 profile too, but I popped the details into a tyre calc and it said not recommended due to the percentage difference over stock. I guess it means for the speedo. No idea if that is illegal or not.

 

[Skye]

Yeah there is more choice moving to a 35 profile too, but I popped the details into a tyre calc and it said not recommended due to the percentage difference over stock. I guess it means for the speedo. No idea if that is illegal or not.

A general rule of thumb is +/- 3% from the factory diameter. Speedo, ABS, transmission and other electronics could be affected. At the extremes, the car might mis-judge an event and not brake as well as it could, or as expected. Might shift "weird". Saying all that...

The variance is often exceeded without issue. I'm sure there's a limit with each car. I don't know what it is with the GT or other models.

 

[Nodster]

A general rule of thumb is +/- 3% from the factory diameter. Speedo, ABS, transmission and other electronics could be affected. At the extremes, the car might mis-judge an event and not brake as well as it could, or as expected. Might shift "weird". Saying all that...

The variance is often exceeded without issue. I'm sure there's a limit with each car. I don't know what it is with the GT or other models.

Ah OK interesting thanks for that. Yeah I see people on here with 305/35 and I just wonder how they therefore get away with it. If that makes sense. I'd have to do some further research.

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