Thoughts on Tyre size, please

[Brett James-McCall]

All,
I am in a position that I am going to order my wheels in the next 2 weeks. Sadly due to exchange costs and having a small child, I will have to with knock-ons later and just go with Image bolt-ons for the time being. Ah well, upgrading later and tinkering is all part of the fun!

The most important thing is for me to actually get the car on the road!

So here's the question. What tire sizes would peo;le recommend for a GTD? I have a coupld of oprtions open for the rear, but it will depend on whether I go for a pure road tyre, or a track tyre that you can use on the road. BTW I have to run 17" due to the brakes I have on the front.

So if I go road, I have the option (with the tyres I am looking at) of either a 275/40 or a 285/40; meaning I would look for either a 225/50 or a 235/50 on the front. This would be running Kumho's KU31

On the track based tyre I have the option on the rear of 274/40, 315/35 or a 335/35; this means I would also have a further option of a 245/45 on the front. This would be running Kumho's V70a compound in Hard

My car will be mainly road but will go on a few track days.

Thanks for the thoughts and advice upfront!

Brett

 

[Howard Jones]

Here's what is on my GTD.

PSE BRM's Knock offs 8X17 front and 10X17 rear

Sumotomo 245X40X17 front 315X35X17 rear

I also run the car very low on ride height. 3.75 inchs at the front and 4.25 at the rear. I've never seen a GTD this low but it does improve grip. The springs are a stiff 350F and 450R. The offset will make a difference but I don't remember what mine are. They are however the standard GTD numbers that were on the old fake 15" Hasselbrads (sp?) that came with the car.

Important points, 245X45X17 will not fit on front whereas 245X40's will. The 45's are just too tall. 315's on the rear are at the min wheel width but seam to work fine without any clearance issues. Both on the front and rear the bodywork is standard, not flared but the fiberglas lip on the inside of the front wheel arch is trimmed down the 3/8" max. The leading edge of the sill covers have also been trimmed down to a 1/2 inch at the bottom vertical lip in the wheel well but they otherwise are standard and look better in my opinion. I have NO tire rub at all, ever, on or off track.

 

[Brett James-McCall]

Looks like I am going to go with:

Front 235/40 17
Rear 285/40 17

Thanks to all for the replies both Howard above and a few PMs I sent when no one else replied.

I went for this for a few reasons:
1/ One member here, whom I hold in the highest regard informed me that I should look to have a 24" on the front and 26" at the rear to make the car 'sit' right. This combination gives me 24.4" and 26"; the closest I could get.
2/ I could have gone 335/35 on the rear, but a few people in work worried about over tyring the rear. In the end a 911 only has a 285 rear, so that was a pointing factor
3/ Cost. Having decided that I was going bolt-on due to costs, this option also saves me a further £400 against running the really wide rears. So this money can go towards getting an exhaust instead.

Time to roughly position the body in the next couple of weekends to take some measurments!!

Thanks to all
Brett

 

[Tim Kay]

FYI, current Porsche GT3 RS run 305mm (415 bhp)

 

[Brett James-McCall]

FYI, current Porsche GT3 RS run 305mm (415 bhp)

You're assuming I am running 415bhp Maybe in a few years when I can afford a better gearbox and play with the engine...