KMK454

I've been looking at some wheels and just wanted to bounce the calculations off of some folks here to see if my thinking is right.

The car is a 91 RS (B4C), regular J65 disc brakes all around - no 1LE brakes. Plan to lower car on springs and adjustable panhard, nothing beyond that. Probably Eibach Sportlines, H&Rs, or Detroit Speed springs.

Tires in all scenarios are 275/40/17.

Wheel 1:
17x9.5 ET6 Square Setup

• Rear Backspace - 5.5" - no issues, slight inset from fender, could correct with 3mm spacer if wanted to
• Front Backspace - 5.5" - possibly hitting tie rod / suspension, might need 3mm to 6mm spacer unless I'm ok with not going full wheel lock

This setup should not extend beyond the fenders, but the front wheel might be close to flush if running a 6mm spacer.

Concerns: Does the above check out? Will this setup require rolling fenders if the car is lowered?

Wheel 2:
Ronal R15
17x9.5 ET3 Square Setup (got the ET by converting their advertised backspace of 5.375" to offset)

• Rear Backspace - 5.5" - no issues, slight inset from fender, could correct with 3mm spacer if wanted to
• Front Backspace - 5.3" - possibly hitting tie rod / suspension, might need 3mm spacer unless I'm ok with not going full wheel lock

This setup should fit almost flush with the fenders on all 4; plenty of pictures of these on Firebirds and Camaros to show this.

Concerns: Does the above check out? Will this setup require rolling fenders if the car is lowered?

The third option is 17x9 ET12, which I know will fit with a .25" spacer up front and should have no issues with fender clearance as this offset will "tuck" a little more.

Thanks!

//<86TA>\\

iTrader: (14)

5.5 will hit in the front so a small spacer will be needed, other than that your math is good and the wheels will work for you

//<86TA>\\

iTrader: (14)

Fender rolling will depend on how low you make it, but with a centered rear axle and good suspension it shouldn't be needed

Zach/90\irocZ

iTrader: (6)

Lower you go you will need to roll you gain about 1/2 inch clearance in rear

Front is kinda weird to roll due to fact wheel well is attach to inner lip of front fender aka part that you need to roll and I personally had to remove for some wheels I ran

Tibo

iTrader: (15)

I say go with an 18 so you don't have to worry about tie rod end clearance or that lip around the top of the strut body. As soon as I put my 17s on I wished I had bought 18s.

KMK454

Thinking about doing just that... found a cool set of wheels I like in 18. Probably go 18x9 with 275 rubber all around. Just trying to determine offset.

paul_huryk

If you go 18" and a 275 tire, shoot for a 9.5" or 10" wide wheel - 9" is too narrow to keep the sidewall under control.

KMK454

Interesting, many of the 275/35/18 tires say that a 9" wheel is their minimum.

What would you recommend for offsets on an 9.5? I'm not looking to go flush to the fender lip, and would rather err on the side of needing a small spacer vs. having too much wheel. Car will be lowered.

Edit - also looks like the hub sticks out about 2", another curveball for wheels with a deep dish/inset face.

Zach/90\irocZ

iTrader: (6)

Min isn't best width for best performance start pinching the tire and side wall stability isn't there as compared to wider rim

Look at some Japanese race cars the used wider wheels to put wider wheels that where slightly stretch which created a stuffed side wall which enhance performance response etc hence where the origin of those extreme stretch tires originated from but they took it too a new level lol nowadays

paul_huryk

Actually we should all take note of the comment below. Also BMW is known to use wider than normal wheels for the tires they mount - especially the 3 series, mounting a 225-45-17 tire on a 8" wheel; GM put 245-50-16 on the 16" x 8" wheels for the 3rd gens.

There is an optimal wheel width for every tire - usually it is 0.5" to 1.0" less than the tire section width. So if you have a 255 tire (10.02" section width), you should run a 9" to 9.5" wheel to be optimal. 275 tire would call for a 10" wide wheel. Of course there are always issues with clearance under most cars - you can't fit a 10" wide 17" wheel in the front of a 3rd gen (and not have it stick out), but a 18" x 10" will fit.

I find it hilarious when some toolbag mounts a 225mm tire on a 11" wide wheel, that is not safe nor does it look good.

KMK454

Good points, thank you Zach and Paul.

The points about stretching make sense and I understand the impact sidewall flex has on steering feel and handling response. I guess I've just seen so many people say 275 is fine on a 17x9, so it surprised me that 18x9 would be a little too narrow with a 35 series sidewall.

The offset issue is fairly easy at this point, but the new concern is the hub length up front. From a picture I found posted with a 2" adapter, it appears that piece protrudes 2 inches from the mounting surface, meaning you'll either need a thick wheel face or a wheel with positive offset requiring a spacer. Or, a tall center cap (like the GTA wheels).

Not my picture, but was posted here by I think InfernalVortex, who said it was a 2" adapter:

Zach/90\irocZ

iTrader: (6)

Lol yes I know and I ask then why and they have no idea the origin of it

I was reading that in some racing organizations tire size was limited and they found out that running wider wheel offer a performance gain while staying within the rules not to mention drift cars notice gains in areas and to include tires where cheaper by fitting smaller tire and burning them up drifting

I just really think it's crazy as well and the amount of effort to do this and stretch a tire like that is simply comedy

Zach/90\irocZ

iTrader: (6)

Yes some guys run narrower tire on 18 because they might fear rubbing issues slot of times they run to be safe and then step up to wider tire up front 275 285 295 might all rub at full lock but the tuck nicely

As far as hub any adapter size iirc above 1.50" should clear hub as fat as center cap for wheels less than that you run to issues of center cap not being able to put one on 2in you should have any issues and if your running big brake kit that can change min required spacer if you want have center cap on