Balancing Front and Rear Tire Sizes

[Mkelcy]

I'm thinking about wheels and tires for my '68 project car, and I need a little advice concerning front and rear tire sizes.

The car will emphasize handling. It will have a 21st Century front clip (C5 components, R&P steering, coilovers, sway bar), mini-tubs and the Lateral Dynamics rear suspension, as well as a healthy 383 (460-480 hp) and a Viper 6 speed in front of a 4.11 rear.

I think (but have not confirmed yet) the 21st Century front clip will let me go to up to a 275 front tire, and the minitubbed rear will allow up to a 315 or so. However, I'm just not that excited about paying $300+ per tire when I replace the rear tires and I want the car to be balanced rather than being over-tired on the back end. Finally, I really like the Nitto 555's as a street tire.

So I've been thinking about a 285-35-18, 285-40-18 or a 295-45-18 for the rear and a 275-40-17 for the front.

Any thoughts out there about running a 45 profile tire on the rear?

Any thoughts about the 275-285 or 275-295 stagger?

My only concern is perfromance, not impressing someone who wants to see how big the rear tires are.

Thanks.

[Mkelcy]

Let me simplify my question: will a 45 profile tire likely provide more vertical compliance and better traction, or will it allow more movement over the contact patch and reduced traction?

[Payton King]

I have a 21st century clip and a very slight mini tub on the back(just took it to the frame rails) My car is a 69 so I have a touch more room in front and back.

I am running a 245/45/18 on front and 285/40/19 on the rear. This is a rim and tire package off of a C6 corvette. As long as you run at least and 18 up front a 275 will fit no problem. I actually bolted the rears (285/19) up front and they cleared as well. The front rim is 8.5 and the rear is 10. If you increase the front rim width make sure you put the additional width to the inside...if stock vette offest is 6.175 on an 8.5 incher and you go to 9.5 then the back spacing needs to be 7.175. Just an example as I cannot remember the stock back spacing.

I am not sure you can find a 45 profile tire in a 285 or 295 without it being a sport truck tire.

Steve (Penny) is running a 275/18 on the 21st Centruty Clip.

[Mkelcy]

Originally Posted by Payton King

I have a 21st century clip and a very slight mini tub on the back(just took it to the frame rails) My car is a 69 so I have a touch more room in front and back.

I am running a 245/45/18 on front and 285/40/19 on the rear. This is a rim and tire package off of a C6 corvette. As long as you run at least an 18 up front a 275 will fit no problem. I actually bolted the rears (285/19) up front and they cleared as well. The front rim is 8.5 and the rear is 10. If you increase the front rim width make sure you put the additional width to the inside...if stock vette offest is 6.175 on an 8.5 incher and you go to 9.5 then the back spacing needs to be 7.175. Just an example as I cannot remember the stock back spacing.

I am not sure you can find a 45 profile tire in a 285 or 295 without it being a sport truck tire.

Steve (Penny) is running a 275/18 on the 21st Centruty Clip.

Thanks for the reply. Although the C6's have gone to an 18" front, 19" rear, do you think you give up anything with wheels that large? That's a lot of mass to slow down.

The reason I asked about the 45 profile tire is that the Nitto 555 comes in a 295-45-18 size that might work pretty well with a 255 or 275-40-17 in front.

[Payton King]

opinion based on discussions over the years. The 15 inch steel rallys I had with a 235/60/15 weigh more than my 18 or 19 inch rim and tire. The diameter of the overall package is not any different on the 18 set as opposed to the 15 inch set....both were about 25.5 to 26 inches tall. The 19s on the rear are about 27.5. I think you are referring to rotational inertia where you account for diameter and mass of the rotating object. In our application you will not be able to feel the braking difference between the 17 and the 18's. Now go to a big set of heavy chrome 22 and that is another story.

I have also had discussions with people who race for a living and they stated that race cars seem to handle better with a stager in width from front to back. 4 of the same size just is not the same. No hard and fast rules on what the ratio should be, but I would guess that GM did their homework on the C6 and the C6Z06. 245-285 and the z is 275-325.

Another subject that I have no real world expierence in is how wide a tire do you actually need. Tires need a certain amount of heat in them to make them work...just read about the AM corvette and that will give you and example. They posted great numbers but they even said if they could have gotten the tires up to temp it would have been better. Most of that is probably the compound they were using and the short runs they were making. On a race track they are probably perfect. I know if you are running a 245 on front and 335 in the rear, you will have a difficult time getting enough heat in the rears without overheating the fronts.

Their are way more qualified people on this forum to discuss this than me...hopefully they will jump in.

If you are going to go with a 9.5 rim in the front you will probably need an 18 inch rim for the added clearance on the tie rods or you will need to put steering stops in the rack.

[Silver69Camaro]

Speaking in generalities, you'll want the front tire to be about 80-90% of the rear tire's width. I tend to stay more on the 85-90% on our cars. So a 295 rear tire should have a 255 to a 265 front tire. 265 would be preferred.

[Mkelcy]

Payton & Matt: Thanks, that's exactly the discussion I was looking for.