Big Wheels - How Big Is Too Big?!

Sektion8

Member
Lifetime Gold Member
Apr 24, 2011
49
Melbourne, Australia
[Sorry for the novel, but I figure more detail is better than less.]

Don't shoot me, but when I saw Smoothie III's, they were everything I was looking for. I've looked at 100's of wheels over the last decade, and I just keep coming back to them. But I need to get it all right 1st shot. Big? Massive? Lasting size-appeal? I figure big-screens start to look small after a few years. But super-thin rubber 'can' look strange on old muscle cars. But there's no rules to all this. It's all a grey area. It seems some get-away with 20" rims. Show cars only? I'm thinking 18's. It seems "It should be fine".

When it comes to sizes/backspacing, the more I read, the more unsure I get. I'm paranoid that I'll go to fit them, and there'll be problems. If I get the tires fitted locally, then it won't be TOO bad, right?

The current wheels are fat, but old & terrible, but they give me an idea of what rubs etc. Do I base things on 'stock', on current, or many other moving goal-posts?! I'm looking to change suspension, big brakes etc. so I fear that I'll make bad fitting decisions, that'll screw me.

The whole project is like 'piggy in the middle'. I've taken a ton of measurements, and photos of where it rubs etc. but I worry (know?!) it'll all change with the new wheels.

Current tires bulge big time, and actual tread contact is much smaller than should be. But I think the bulge seems to help avoid rubbing, since it follows the arches better. Is it all due to tired suspension?! Front only fouls on full lock. Back only rubs when I floor-it, or have people in the back. It all seems like stabbing in the dark.

Stock:
215/70/14

Current:
Front:
15x8
265/50/15
Backspace: 123mm (bit bigger than 4.75"?)
Bulge: 38mm ext, 39mm int
Road contact: 235mm

Front_Wheel.jpg

Front_01.jpg

Front_02.jpg

Front_03.jpg


Back:
15x10
295/50/15
Backspace: 127mm (5")
Bulge: 34.5mm ext, 37mm int
Road contact: 260mm
127mm backspace (5")

Back_Wheel.jpg

Back_01.jpg

Back_02.jpg

Back_03.jpg

Back_04.jpg

Back_05.jpg
 
Last edited:

Da_Raabi

Veteran Member
Jan 19, 2011
1,346
Daytona Beach, FL
I'm no pro but it sounds like you have some sagging suspension issues. If it were me... I would focus on fixing up the suspension first and go from there. If you are planning on changing things anyway, do the wheels last. Brakes should not change much, unless you do some sort of hub/brake replacement, BUT changing steering components/springs/bushings will COMPLETELY change the look and feel of the car, and may solve a lot of your rubbing issues entirely. So my vote is forget the wheels for now, focus on fixing up the suspension and go from there!

Oh and I had the same tires in the back with sagging springs and have NO rubbing issues, so your leaf springs might be shot... Just a thought.
 

Sektion8

Member
Lifetime Gold Member
Apr 24, 2011
49
Melbourne, Australia
Thanks for the info.

It's perfectly possible. Is it something I could measure, or would members know, just by looking at it? It handles quite poorly, rocks around like an old boat. If I had the cash, I'd go whole-hog & go DSE quadralink or something amazing like that. I'll get something more realistic, unfortunately. My total car budget's already gone from $10k to $20k.

Brakes will be Kore3 all-around. Since I can know all the dimensions, would it be hard to compare the wheels to brakes, all in theory? I read that wheels can be custom made for brakes, but that sounds messy to me.

I had another look today, took plenty of photos. Front wheels only foul on hard lock.
Angle_3.jpg

Back_2.jpg

Angle.jpg

Back.jpg

Front.jpg

Side.jpg

Back Wheels:
Wheels_Back.jpg

Front Wheels:
Wheels_Front.jpg
 

stroked383

Veteran Member
Lifetime Gold Member
Jul 18, 2011
764
Saugerties, NY
Nice ride mate, those tires tuck nicely, I like them inside the wheel wells. Like said earlier you probably have worn suspension and bushings. Sounds like some solid body mounts and shock/spring combo is in order.
 

m pozzi

Moderator
Staff member
Apr 9, 2002
2,544
Central California, USA
If you want to stay within a reasonable budget, go with a good aftermarket performance suspension company and replace the old stuff with lowering stuff (springs), good quality shocks, sway bars, and the solid body mount bushings. If you have extra coin, tubular upper arms and cross-shafts that can accept Del-a-Lum bushings and then install these same bushings on the OEM lower arms should be the next part of the build. Make sure these upper arms will give you the desired caster gain as a standalone part. Some companies make you buy both tubular arms to get this. Global West upper arms can be used with the OEM lowers and they sell the Del-a-Lums too.

Research your wheel and tires around what brakes you'll end up running. If the brakes are 13" or under (rotor diameter), you should be able to stay with a 17" wheel. Anything larger for rotor size and it's 18's and above. As you haven't 'tubbed the rear and will most likely be staying with an OEM front sub, a 17x8" wheel for the front will be good (255 tire) with 17x9.5" for the rear (275 tire). There are wheel manufacturers out there that have this size wheel in the proper backspacing and many on this forum use them now.

If you come into some extra money for the build, then start thinking about replacing the front sub, widening the rear, and going aftermarket rear suspension and axle assembly (Ford 9").

Then start thinking about the drivetrain ...

Lots of possibilities but you can achieve your goal in stages. You have a really nice RS and when done, will be a good handling car.

Mary Pozzi
 

Twisted_Metal

Administrator
Staff member
Lifetime Gold Member
Feb 26, 2004
30,850
Bloomington, MN
<edit> Good answer, Mary!!!!

You've got those wheels wells stuffed as full as they can with normal suspension travel and stock front arms.

The fronts are going to rub at full lock. 265s are wide for these cars....245 or 255 is pretty much the max on any size wheel

Right now.... You have a little too much backspace (which puts the tires into the frame) but less backspace would put them into the fender lip and rear of the fender well. You're at the maximum width of the front combo no matter what you do with springs or front alignment geometry.

The rears are rubbing on the inside and outside when loaded down.
(Is the parking brake cable cutting a groove into the tire yet? :eek: )

A stiffer rear suspension will minimize the rub but it looks like the quarter lip was already trimmed and there is no more room to work with back there without beating some metal with a BFH.

Some of the rear rub is because of sidewall flex in turns. Shorter sidewalls on new bigger tires will help prevent that but.... you have to keep in mind where the lip of the rim runs with bigger wheels.

You've got good measurements to work from.
You're already using all the space you have so keep your new wheel/tire combination no larger than what you have.

Good Luck!!!

There's a pretty good thread about combinations here. http://www.nastyz28.com/forum/showthread.php?t=47101
 
Last edited:

m pozzi

Moderator
Staff member
Apr 9, 2002
2,544
Central California, USA
Pretty much the max width for a 17" front is 275 and YOU WILL get rub on the bar, frame, or both in full turns. You'll also get rub on the underside of the fender wells close to where they bolt to the fender lip areas under compression. Backspacing must be perfect and that will help but not totally eliminate any interference. This is on a lowered car ...

I tried to run a 295 on the rear and the sidewall flex got rub on the outside of the leaf spring. It wasn't huge, but there nonetheless. On a 9.5" wide 17" wheel, the tread pad was also bowed and lessened the contact patch with the ground. Moral to the story is don't go too wide.

Most people don't take into account the sidewall flex that occurs during lateral forces and under braking. You'll have to look closer at this if you want to run a smaller diameter tire as the sidewall aspect ratio is larger and the ability to flex greater.

The fender lips on my Camaro were rolled and that helped a bit. There are other, uhhh ... non-approved body methods that are used to give additional clearance room too.

Just my .02 here ...

Mary P.
 
Last edited:

Twisted_Metal

Administrator
Staff member
Lifetime Gold Member
Feb 26, 2004
30,850
Bloomington, MN
Good info on 17s , Mary!
Yes... 275s "fit" but I meant 245-255 is max without rubbing, up front.
(At full lock, stock height, with the correct wheel backspace.)

I think my son runs 255s on 17s and they just touch the frame on rare occasion.

245/60-15s are a great fit but since he's looking at different wheels... It doesn't really matter.
 

sbca96

Veteran Member
Oct 25, 2004
2,897
Santa Barbara, Ca
Running 275/40R17 all around on the '78 Camaro. Hotchkis springs, Bilsteins, a
set of poly sub-frame bushings and PTFB uppers. WS6 bar up front. So far we
haven't noticed any rubbing. Granted we haven't pushed as hard as Mary.

Tom
 




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