Tyre Widths for a Lightweight 911

[Captain Ahab Jr]

I am after some advice on what people think would be the optimum tyre width for a high powered lightweight (sub 1800lbs) trackday car.

Tyres would need to be street legal also and I limiting myself to what tyres are available for 15" rims and have room to fit anything from up to 9's on the front to 11's on the rear.

I would consider 16" rims if the tyre choice for this size is much better but prefer the 15" rims as they are more in keeping with the car and lighter too.

I am a little worried what seem to be the preferred choice of tyres for the 9's and 11' s the Michelin TB15's might not get up to temperature and think I maybe better going with a more track focused rubber such as Toyo R888's or Yokohama A048R's on narrower 8's and 9's.

Please add any comments or questions as I am about to spend a lot of money on widening wheels and want to make the right decision.

[Flieger]

I think you will have more, better tire choices with 16 inch wheels. I have 16x7 and 16x8 Fuchs with Advan A048s: 205/55-16 front and 225/50-16 rear. They feel fine in the canyons.

They are no Hoosiers, though.

[petevb]

From a purely performance point of view I think you'd likely be best off going to 17s. That'd give you a wide selection of rubber in the widths you can use with different compounds to choose from.

Assuming you want 15s, my impression is that the TB15s have a softer compound than R888s, and thus I suspect you'll get them up to temp as easily. If you can't you can always play with alignment, etc. The major argument for the narrower rubber would be feel: the wider useful slip angle on a narrower tire can make them feel more "playful" (witness the skinny little tires on an Elise). On the track against the clock, however, the wider rubber probably wins out.

[Flieger]

Adding support for the above statements, tire width does not necessarily increase the size of the contact patch. The main variables are tire pressure and load. The wider tire changes the shape of the contact patch.

Although, I am sure you already knew that. I forgot it was you, Cap'n- been a while. Still interested in a tube frame mid-engine 911 with dual A-arm suspension?

[Bill Verburg]

It would help to know what chassis these are going in

Grassroots has an interesting comparison in the months issue, basically comparing a 255 to 245 tire in a Miata MX5, the Miata being underpowered benefited from the shorter sidewall of the 245 more than the 255

It's all going to come down to you choice of tires, are you doing historic races? Other wise i can't understand why the TB15s are of any interest.

Street legal as in you will actually drive them on the street?

weight and actually dimensions are all over the place, when comparing tires and wheels you need to narrow it down to a few more concrete examples

[Captain Ahab Jr]

Thanks for the suggestions guys, in answer to a few of the questions asked and points raised,

Flieger - good choice of tyres, these seem to be the tyre of choice for any road legal series in the UK. I can't seem to find much more tyre choice with 16's as the max. width for both 15's and 16's seems to top out at a 225 section. Maybe I need to look into available compounds.

Petevb - I am big admirer of your car and an inspiration for my own project. The sensible choice would be 17's and if I were to have a set of track only wheels/tyres this would be the dia. I would go but with slicks. My prefered chocie is 15's as I want the car to be a bit of a sleeper to the average eye.

Bill - tyre choice is for a tubular space frame chassis with an air cooled mid mounted engine, front and rear independent suspension under an early narrow bodied LWB shell with plenty of panels replaced with carbon fibre. I'm trying to do the ultimate sleeper. Still very much at the design and parts collection stage but I'm aiming for 400bhp, 500Nm and 800kgs or there abouts.