[cwkamin]

Hi! I'm new to this forum and just purchased a low-mileage '96 Buick Roadmaster wagon. I want to get some Torq Thrust II wheels (or something similar) but don't know whether to go with a 16", a 17" or an 18" (figure on them being 8" wide). I want the wheels/tires to fill the wheel well for a modern version of the classic look. The wagon will be a cruiser and I have no intention right now to modify the suspension. Which diameter wheel is BEST supported by the aftermarket? What is a reasonable width to look aggressive but not rub the fender lips? What offset should I look for?

Thanks!

Carl

 

[Fix Until Broke]

Welcome!

Do you want to go with a larger diameter tire as well as rim?

Any of those diameters are well supported in both rims and tires. If you want to go bigger, skip 19" and go straight to 20"

Larger rim with same diameter will typically have a slightly rougher ride and make things tougher on the shocks/springs due to the heaver assembly.

I believe you can go up to ~29" outside diameter of the tire and have minimal (if any) clearance issues assuming that the car doesn't have a lot of settling, bad body mounts, etc.

If you're not looking for handling and such, easiest is to stay with ~stock width and offset, just pick the rim and tire diameter you want.

Picture for comparison - guessing you'll end up somewhere between these two
Stock on the left 15" rim, 225/75/15 tire
Not stock on the right with a 20" rim and 255/55/20 tire (31" diameter)

 

[Fred Kiehl]

The stock diameter for a wagon is about 28 inches. Any substantial deviation from that will cause about 3 mph per 1" of tire diameter (larger diameter will cause the speedometer to be off slow). You can use any combination of wheel/tire that will give you the 28" diameter. For instance, a 17" wheel with a 255-60-17 tire will be about 28" in diameter. Tires are light, wheels are heavy, and a taller sidewall will give you a smoother ride. Make sure you have the stock +6 mm offset, or you may run into rubbing issues. An 8" wide rim on the front, with the +6 mm offset, will be fairly close to tubbing the outer tierod end. At 8.5" wide with +6 mm offset, you have about 1/16" of clearance at the tierod end, and must use tape-a-weights to balance the wheels.

 

[Marky Dissod]

If you want to fill wheel wells without rubbing fender lips or modifying the suspension ...
Anything wider than 255 will not fit in the spare wheel well, and will rub the sidewalls against the inner rear fender lips (the ones you can't see from outside unless you get UNDER the wagon).
To fit a 255/70R15 in the spare wheel well of my wagon I had to deflate it first.
When I needed a spare, reinflating it before installing it was a pain in the ass.

Fix Until Broke is generally correct about 29" tall tires being the tallest tires that can fit without modifications.
235/75R15 is 29" tall, and is the OE tire size for Cadillac Fleetwood limos.
(There's a thread where he explains what he had to do to install 31" tall tires.)

255/70R15 - 5 tire options (several ISSF members use without issue, classic meaty fatass tire)
255/65R16 - 8 tire options
255/60R17 - 4 tire options
255/55R18 - over 50 tire options
255/50R19 - over 50 tire options
255/45R20 - over 50 tire options
255/40R21 - 8 tire options

18" wheels will cause less suspension stress than 19" or 20" wheels.

 

[95wagon]

What about a 255 -50-18 on the 18-8 4-1/2 bs ?
Similar outside face position as impala wheel
Similar tire dia to stock so it doesnt look undertired or a 4x4

Wheels not so big that the classic torque thrust look doesn't get cartoonish.
Not so big the brakes look like door knobs.

Tie rod clearance ? Is that your drop spindles Fred ?

" 3 mph per 1" of tire diameter "
it is a percentage change , NOT a number.

 

[cwkamin]

Thanks for all of the input! I'm not really inclined to go any larger than an 18" wheel. I presume the 255 width works well with an 8" wide wheel? The deciding factor, then, for me would be the wheel size which has the most support/options from the tire industry. Like I said, I don't want any rubbing issues and my main goal is to have a classic looking wheel with a wider tire (with a real sidewall for ride/handling) and to keep the wheel well from looking "empty".

Thanks!

 

[Fred Kiehl]

If you want to fill wheel wells without rubbing fender lips or modifying the suspension ...
Anything wider than 255 will not fit in the spare wheel well, and will rub the sidewalls against the inner rear fender lips (the ones you can't see from outside unless you get UNDER the wagon).
To fit a 255/70R15 in the spare wheel well of my wagon I had to deflate it first.
When I needed a spare, reinflating it before installing it was a pain in the ass.

Fix Until Broke is generally correct about 29" tall tires being the tallest tires that can fit without modifications.
235/75R15 is 29" tall, and is the OE tire size for Cadillac Fleetwood limos.
(There's a thread where he explains what he had to do to install 31" tall tires.)

255/70R15 - 5 tire options (several ISSF members use without issue, classic meaty fatass tire)
255/65R16 - 8 tire options
255/60R17 - 4 tire options
255/55R18 - over 50 tire options
255/50R19 - over 50 tire options
255/45R20 - over 50 tire options
255/40R21 - 8 tire options

18" wheels will cause less suspension stress than 19" or 20" wheels.

I have run Impala wheels with 255-50-17s on the rear, and they do not rub anywhere.

Thanks for all of the input! I'm not really inclined to go any larger than an 18" wheel. I presume the 255 width works well with an 8" wide wheel? The deciding factor, then, for me would be the wheel size which has the most support/options from the tire industry. Like I said, I don't want any rubbing issues and my main goal is to have a classic looking wheel with a wider tire (with a real sidewall for ride/handling) and to keep the wheel well from looking "empty".

Thanks!

Remember that the offset must be +6 mm, or they will have clearance issues.

 

[Marky Dissod]

255- width tires work fine in any 18" wheel between 7"-9" wide.

Note Fix Until Broke's pic.
The rear of his 31" tall 255/55R20 tire is tight to the body at the back of the tire.
He did NOT just stick 'em in, he paid quite a bit of attention to the suspension to fit them in.

255/55R18 (29.04" tall) will fit inside all four corners just fine - if the ISSF's history repeats itself.
However, note that 255/55R18 may NOT fit in the spare wheelhouse without deflating it.
235/60R18 (29.10" tall) will fit in all 5 positions with no issues. (Most similar to OE for limos.)

 

[95wagon]

Remember that the offset must be +6 mm, or they will have clearance issues.

In regards to clearance ,
the " correct " offset is dependant on wheel width .

 

[95wagon]

Case in point using this calculator you get a visual view what changes will do to where the wheel- tire will sit .

Alloy Wheel & Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit

Alloy Wheel & tyre fitment calculator - it calculates inset, poke, speedo error, tyre stretch and loads more.

www.willtheyfit.com

The Impala SS rim and tire is known to fit and be far enough outboard to visualy look good
Use its numbers for your baseline
255-50-17 17 x8.5 + 6mm offset

You will see that when using a more common 8" with you can alter the offset somewhat .

One thing that some get caught up with is offset verse backspace.
Stupidly ( to me ) back space is actual back flange , not bead to mounting surface.

Comparing the two you have to ROUGHLY add 1/2 an inch.

 

[95wagon]

This represents an Impala 8.5 + 6mm
Vs an 8 +0 ( 4.5 back space )

 

[91ss]

Just to add, to figure your offset from BS, it's relative +1" wheel width. Flange is on both sides.

 

[95wagon]

If you play with the numbers , you will see that
0mm would put an 8" outside clearance the same as an Impala SS
12mm would put an 8" inside clearance the same as an Impala
6 mm of coarse would center it the same as Impala so 1/4" more clearance inside and outside..

An 8 4.5 back space is a 0mm
AN 8 5.0 back space is a 12mm

The one thing you can " fix" too much back space , you cant fix too little.

 

[ayilar]

@cwkamin -- good luck with the wheels, you've got plenty of good advice above.

Do you have photos and some history about your car?

 

[cwkamin]

I'll have some pics shortly, its being shipped right now. It's a 48k mile car and the elderly male owner recently passed away. The guy I bought it from got it at the family's estate sale- he is an MG/Avanti guy and couldn't pass it up when he saw it but elected to move on to another project. It's metallic blue with (of course) the LT1. More to come shortly, the wagon is currently in transit.

My plan is to tint the rear windows, do the wheels/tires and a cat-back exhaust system of some type (preferably Flowmasters) and then ENJOY THE HELL OUT OF IT!

 

[ayilar]

Thanks! Look fwd to the pics.

 

[Fred Kiehl]

If you change the offset, you put the centerline of the tire at a different position vs. the steering components, which puts additional stress on the steering components. It also changes the arc that the wheel/tire takes in the wheel opening, and can cause interference when simultaneously turning and compressing the suspension, especially when using a wide wheel/tire combination. If you lower the car, it is further aggravated. Should you use drop spindles, they push the wheel 1/2" out, so you must have a +18 mm offset to return the wheel to its original position. 0 offset will also move the rear tires closer to the body and can cause interference, especially because the bodies of these cars are notoriously crooked on the frame.

 

[95wagon]

Arguing the fine points of front end geometry with a person that has a car in the weeds on drop spindles seems somewhat pointless.
Yes the scub radius will be different between an 8.5 +6 vs 8.0 +0
That said have you ever actually measured it?


The outside edge of the wheel would still be in the same position relative to the body.
I will concede a 8 +6 would be more of a sure thing but stand by the 8 +0 fitting as it will have the same outside clearance as the Impala wheel with 255 that many of us run.

To take the factory design geometry for comparison,
Second gen F body has the same spindle geometry , correct ?
Now look at the offset- backspace of the factory optional 8 inch rim used with that same spindle . It isnt +6 is it ?

While not " right " on paper, the 15-8 truck rally will barely fit with its -12mm . Not recomending it but the sky didn't fall on its users.

 

[crm114]

Hi! I'm new to this forum and just purchased a low-mileage '96 Buick Roadmaster wagon. I want to get some Torq Thrust II wheels (or something similar) but don't know whether to go with a 16", a 17" or an 18" (figure on them being 8" wide). I want the wheels/tires to fill the wheel well for a modern version of the classic look. The wagon will be a cruiser and I have no intention right now to modify the suspension. Which diameter wheel is BEST supported by the aftermarket? What is a reasonable width to look aggressive but not rub the fender lips? What offset should I look for?

Thanks!

Carl

Hi Carl. I just bought a 94 wagon this fall and picked up some Torq Thrust's in 17x8, because that's the Impala size and because I wanted to keep some sidewall. After looking all through the available tire combos that don't rub, I wish I had bought 18's. There are a lot more tire options out there in 18 than 17.
Cam

 

[Fred Kiehl]

If you want to maximize your tire options, staying with the stock offset will be your best choice.