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Old 03-28-2009, 05:52 PM
Bart II Bart II is offline
 
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Default Widest / largest tires (split from: 295 50 16 tires)

I am new to this site. My 87 GN has rarely been driven over the past 10 years. I am thinking about getting it out of mothballs.

Can anyone tell me what the widest tire is that will fit on my GN without modification to the wheelhouses or notching the frame rails.
Specifically, what wheel size, backspacing etc. I would like to fit a 295 or a little wider if possible on after market wheels.

Thanks
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Old 03-28-2009, 06:59 PM
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Lightbulb Re: 295 50 16 tires

Quote:
Originally Posted by Bart II View Post
Can anyone tell me what the widest tire is that will fit on my GN without modification to the wheelhouses or notching the frame rails.
Specifically, what wheel size, backspacing etc.
*sigh* You and a lot of other people...

There is not a simple answer, oddly enough. And every time one is produced, some one insists that they managed to shoehorn something larger onto their car without changing a thing.

Keep in mind that the basic Regal is a car that was never designed for monster rubber, steamroller wheels, etc. So when you try to shoehorn all that under it, it really doesn't want to fit.

In addition, there are a lot of "It depends..." clauses that get added into the answer for such a question. There are many factors that have to be considered that help define the answer:
- Are you looking for a street setup, drag setup, or both.
- Will the car be lowered at all?
- Do you care about running your wheel arch trim?
- Would you consider rolling the inner lip of your wheel arch for clearance?
- Would you consider notching your frame for clearance?
- Are you considering a larger than stock wheel? (diameter and/or width)
- Is it important for you that your speedometer be correct? (it does matter to your ECM and TCC lockup patterns)
- Planning to do any hard cornering?
- Planning to do any front suspension upgrades or brake upgrades? (i.e. aftermarket A-arms and/or 16 F-body rotors, Baer brakes)
- Are you going for looks, performance, or both?

As few thoughts that might help with your questions:
- Anything much wider than a 275 on the rear on the rear will be difficult to fit.
- Lower profile wheels (short sidewalls) or drag-only setups (no high speed turns, and little rear axle swing) allow for more tire width in the rear.
- A wheel backspace greater than 4" on the rear may cause the tire to rub the frame if no notching is done.
- A wheel backspace of 3.5" or less on the rear will likely cause a tire on an 8.5" or wider wheel to rub the wheel arch trim if it is present or the lip is not rolled.
- Tires wider than 225 on the front will likely rub the frame at full lock. But only at severe lock, and that is only typically done in parking lot maneuvers.
- The stock tire diameter is ~26".
- It is possible to alter speedometer and VSS readings to account for large tire diameter changes via speedometer gear changes in the transmission.

Others, feel free to contribute.
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Old 03-29-2009, 12:52 PM
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Default Re: Widest / largest tires (split from: 295 50 16 tires)

EXCELLENT synopsis Scott! Nice to see all those thing gathered up in one place!

One quick addition ... many of these cars do NOT have the rear end perfectly centered in reference to the frame. This can be due to many causes, including:
- Tweaked frame/twisted frame from a million drag strip passes
- Worn bushings in the control arms
- Bent control arms
- Tweaked/wallowed front lower control arm bushing mounts (especially prevalent on any cars that launch hard and have had control arm relocation devices ... like SouthSide bars ...)
- Sagging springs
- Worn shock mounts/bushings
- Worn/missing/rotted body mount bushings (causing the body to not be square on the frame)

Bottom line, these all can cause the rear to not be perfectly centered in the car. When stuffing the absolute maximum size tire under a Regal, these factors can make one side or the other rub on either the frame or the wheelwell arch DESPITE the exact same combo working on another car.
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Old 03-29-2009, 03:01 PM
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Default Re: Widest / largest tires (split from: 295 50 16 tires)

BOTH of you, GREAT info... Maybe that info should be made into a sticky??? You both have answered a multitude of questions that everyone seem to be asking on putting really wide tires on these cars... Tom G.
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Old 03-29-2009, 03:40 PM
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Thumbs up Re: Widest / largest tires (split from: 295 50 16 tires)

Stickified.
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Old 09-29-2009, 07:51 PM
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Default Re: Widest / largest tires (split from: 295 50 16 tires)

Just saw this post. Better late than never? I stuffed a 295/50 R15 under 2 of my stock 87 TTypes with the stock rims. The brand was a cheapy Futura Brand sold by Pep Boys and made by Cooper tire. They fit just fine and only rubbed if there were people in the back seat or if I cornered hard. Other than that they fit fine and looked good.





I got the idea from a friend named Ray and his Blue 87 T aka the "Blue Monster"



HTH
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Old 09-29-2009, 08:42 PM
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Thumbs down Re: Widest / largest tires (split from: 295 50 16 tires)

That is so horribly not right...

They'll be worn down to the cords in the center before the sides ever get close to having the molding nubs gain sight of the ground.
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Old 10-01-2009, 03:41 PM
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87geeinn 87geeinn is offline
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Default Just my .02

Here's some pics of the 275/50/15 MT ET Streets on a stock rim. This set has approximately 1,500 miles on them and I run them at a consistent 25psi for a little extra grab. The 275 width is slightly larger than what is suggested by MT for appropriate rim width size. However, I'm not seeing a terrible wear pattern on mine. Perhaps the lower air pressure allows the tire to relax and have a "thicker" contact patch. Dunno. Note the wear bars in the third picture: The outermost bar reveals that there is slightly more tread left on the outer portion of the tire, which is to be expected. However, the short lifespan of those particular tires, to me, negates the slightly uneven wear pattern. Perhaps more miles will show a more evident inconsistency. The biggest downside to running a fat tire on too skinny of a rim is how the car tends to roll to one side when making sharp turns at high speeds...especially when running a lower air psi. One has to take this into consideration with regards to how one wants their car to handle.

Note the extremely close clearance between the frame and the tire and how it shined up the rail just a bit. That's on the passenger side. There's been no contact on the driver's side. As was noted prior, each car will be different based on the numerous variables. In my case, I have new variable rate springs, poly body mounts, Bilstein shocks and tubular upper and lower control arms, and a 1" sway bar.
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Old 10-01-2009, 06:37 PM
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Exclamation Re: Just my .02

Quote:
Originally Posted by 87geeinn View Post
The biggest downside to running a fat tire on too skinny of a rim is how the car tends to roll to one side when making sharp turns at high speeds...especially when running a lower air psi. One has to take this into consideration with regards to how one wants their car to handle.
Or if they want it to handle. And ET Radial isn't an autocross tire, anyway.

I still contend that wrapping your rims in tires that are too wide is not a good idea.

Let us know how they work and what they look like in 5000 or 10000 miles.
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