Wheel and tire sizes? Is wider worth the weight?

[rairdan93]

This year I'm looking at 2 options for wheels and tires for my 05 mustang.  I'm curious to what your guys thoughts are on tire widths and whether tire/wheel overall weight should be a huge concern.  I want to run RE71Rs again. In Street Touring I can run up to 11" wide wheels and 315 tires.

Option 1: Forgestar CF5 19x11 wheels with 305/30R19 tires.  Total weight per corner is 58lbs.
Option 2: Forgestar CF5 18x10 wheels with 285/30R18 tires.  Total weight per corner is 48lbs.

The 285 tire is 1.4" shorter than the 305 and 0.8" narrower in tread width.  I have camber plates and a decent suspension set up.  Vorshlag helped me decide on which suspension components to go with.  They have a crazy amount of knowledge on making these cars go around corners. From my research I have found rotational inertia in the form of wheels and tires is not a huge concern in autocross. Is it? And that wider is better when it comes to heavier cars but some initial turn in response might be compromised. The shorter tire would make me lose a few mphs in second gear but would help my torque down low.  I'm not terribly concerned about that because I rarely touch the 2nd gear rev limiter.  What do you guys think? Is the .8" of tire width worth the 10lbs?

[K.P]

I would bet the general consenus is going to be that wider is better.

Also, if you are buying your Foregestars new, I would suggest ordering sooner rather than later. I was initially told my wheels would be ready in 4-6 weeks, which has now been pushed back to 10-12 weeks with my order being rushed.

[Apex Carver]

It's too bad you cant do a 18x11 setup with 305's as that's what I would say would be ideal. Have you looked into the rivals? You could throw 315's on a 18x11.

[94boosted]

I'd say the lateral grip you'll gain with the wider wheel & tire will offset the unsprung weight penalty for autocross.

If you're really worried about weight you could also step up to a fully forged monoblock wheel not a rotary-forged wheel as they should be lighter than the forgestar.

[Dr Dave]

One thing missing in the discussion is centre or height of gravity/mass. While 0.8" wider tires will improve cornering, 0.7" higher center of mass will decrease cornering speed, in this case the end result will likely be improved cornering, but you'll be losing some of what you're gaining. I like Apex Carver's suggestion of 18x11, 305's, but tire manufactures don't always make exactly what we need.

[Reijo]

I'd say the lateral grip you'll gain with the wider wheel & tire will offset the unsprung weight penalty for autocross.

If you're really worried about weight you could also step up to a fully forged monoblock wheel not a rotary-forged wheel as they should be lighter than the forgestar.

Agree with Tom.  For autox, wider is better is the mantra (within limitations of the rules).  A typical autox course is 1 km. long and 22 turns.  For example, Race City was 2.2 miles (3.5 km) with 11 turns.  A narrower tire would offer less aero-drag and friction resulting in higher speeds on the straights.  So, a road course is different.  If you do both track and autox, you might want to have separate sets of tires.

R

[rairdan93]

Thanks guys! I ended up getting 19x11 Forgestars but the F14 wheels instead of the CF5. They had blanks for the F14s so I will hopefully get them by April if I'm lucky.