On 8" rims what would be the optimal width tire/sidewall angle for auto-x? Let me draw a rudimentary diagram of the choices of the contact patch with the ground when different width tires are fit to what we'll call an 8" rim:

1: /__\ 2: |__| 3: \__/

What are the advantages/disadvantages of each?

It seems like most people go with a relatively straight sidewall (am I wrong?)..Is there a reason for this? If sidewall siffness is what you want, will not increasing tire pressure help if you have a wider tire than rim, if you want to make sure not to roll the tires?

 

17" or 18 in wheel?

 

17"

And this isn't for a 350z, it's for my friends EVO8. So I am notnecessarily concerned with a staggered diamter for VDC or anyhting of that nature.

I'm just trying to figure out what the advantages are of straight or angled sidewalls, and why people choose particular setups. His tires are Hoosier racing tires. Can't remember if they're the a3s04 or 5's.

 

most of the people I know who do track events with EVO8s use 235/40-17 R-compound tires on an 8" wide wheel... I've never heard of anyone intentionally putting a too-wide tire or too-narrow tire on a wheel just to make a certain sidewall configuration; not sure there's any real benefit there, and more likely there's more harm than good

If your tire is not wide enough for the rim-width, you will cup the center section of the tire. If the tire is too wide for the rim-width, you will make the center section of the tire bow out. Neither is very good. The idea is to have as much tread on the ground as possible. As for sidewall stiffness, you just need to find a tire that has the turn-in feel that you want.... some or softer and some are firmer, just depends on the tire.

Increasing tire pressure only goes so far before it's not a solution... on the track, tires will heat up and the air inside will expand... if you start with high pressure, you may exceed the recommended max pressure for the tire.

 

What size Hoosier is he running and what width wheel is he using?

 

I'd go with a 245/45/17 or a 275/40/17 kumho 710 on the evo for auto-x both will fit. The 275 will be faster IMO. 275 kumho 710 will be the fastest auto-x tire you can get on an 8" wheel.

 

Hey guys, i'm gonna try to find out his configuration. I'll let you know asap.

 

For the same sized tire, running a wider rim will improve the sidewall strength allowing lower pressures (more grip) and improved steering response.

Last year I ran 245/40 Kumho MX on the Perofrmance 18x8 rims. Fit was good but I needed a good 43-44 psi to prevent roll over.

This year I'm running a set of Rays 18x8.5" all round on a new set of Kumho MX 245/40 as well. I can run a good 3-4 psi less thanks to the wider rim at the same camber as last year.

Having said that, running an ultra wide tire (as they do in Solo2) will provide more ultimate grip at likely a lot less sidewall strength and steering precision. For the street, it's best to use a rim width within the manufactuers recommended range.

 

he's running 245/ 40 or 45/ 17 on stock yokohama EVO 8 rims (whatever their width may be).

He was thinking that a tire with a sidewall like this /___\ would perform better than |__| or \__/.


But I guess the above dimensions fit perfect from what he says