I am thinking of having my rims widened. I was wondering what size tires are you guys who have 15" x 10" wide tires? Also, what back spacing do you have. One a side note, I drove my car 160 miles yesterday, the furthest I have driven it in one sitting since I owned it. I notice my spedometer is 10 mph off. Any ideas? The speedo said 85 MPH @ 3500 RPM. Could the PO have put gears in it? If so, any idea on what size?

 

One method to get in the ballpark: safely raise and secure the back of the car. Allow the rear axle to hang free. Ensure that the transmission is in neutral and emergency brake off. Rotate a rear tire one revolution while counting the number of turns the driveshaft and/or the rear pinion makes.

Marking the driveshaft or pinion with a piece of chalk will help reference.

If the driveshaft/pinion makes 3 and half turns, most likely a 3.55 rear ratio. If it makes a tad over 4 full turns, most likely a 4.11 gear and so on.

Let us know what you discover.

 

No one running 10" wide tires?

 

I run 10" wide tires on the CJ. 8" wide rims, now this is on a 33" tall tire. For a 28" tire, I would expect a 9" max width rim. You are talking about the section width of the tread aren't you? Al

 

Al, I know some guys have the 15" x 10" rally wheels for their cars. I am needing to know the back spacing and what tire size they are running. I am thinking about widening my '78 Ralley rims.

 

265/50/R15 all around - stick out just a little. 265 tires are 10.4 inches wide.

 

Do a search, this topic has been addressed several times. 10" wide rims are tough to fit - most end up sticking out past the fender when not done right (if you add flares, then no problem). I used to have 10" wide Convo Pros with 5" backspace (see picture). Needed to shorten the mono spring (1/2" or 3/4") on each side. Also, need the offset trailing arms. I ran 275-60/15s which still stuck out a little past the fender. I didn't like the 275s on the 10" rim - they really look better on 8" rims. You can't go to 5 1/2" backspace with tires that fit 15" rims (275-60, 295-50, etc.) because they have greater section width (the "bulge") and will rub on the frame/wheel well. You can run increased backspace with larger rims (17s and up).

If you just want to upgrade the width of your tire, I would put a 275-60 on the stock 8" rim.

 

There's a massively popular thread here on C3 General Discussion on 18 inch wheels. First of all, I'd advise you to move on from 15 inch wheels. There's just not that many tire options in 15 inches. I have 17 inch wheels on my 68 and am looking for 18 inch wheels for the 70. For the 68 I have Billet Vintiques 17 inch Rallye wheels that look like, from about 20 feet away, the stock 15 inch Rallye wheels your Corvette came with. Right now I'm targeting the Torque Thrust II American Racing wheels with 18 inch diameter. They look like the 15 inch Torque Thrust wheels of years ago.

I think now, and in future years, your selection of 15 inch tires will be very limited.

It's really frustrating trying to learn what the biggest rear tire you can fit. I have offset trailing arms, it appears I can run an 18 inch wheel, 9.5 inch rims, and 5 inch backspacing. I think there are people who have said they can run this tire without offset trailing arms.
Then there's the issue of the ebrake cable bracket if you don't have offset trailing arms. Arrggggh!

 

Run by Discount Tire, they can measure and tell you what will fit.

 

Gator, I have done a search and didn't feel the need to go through 10 pages of tire topics. Can I narrow the search to just the c3 section? That may help. 68/70 thanks for the advice. I am wanting to run 295/50/15 tires. What I cannot get past is, the earlier rallies are offered in a 15 x 10 inch rim, and I know some on here are running them, but I don't understand why they can run those 15 inch rims and I can't run 15 x 10 on mine. I guess I am not understanding. But, I will look at the 18" rims. I just wanted a resto mod, but completely stock looking. Sort of a sleeper, if you can use that term for Vettes.

 

For my 68, I bought Wheel Vintiques 17 inch Rallye wheels. From 20 feet away, they look exactly like the stock Rallye wheels,with the chrome trim rings and the stock hubcap "hats." They are aluminum wheels, polished aluminum simulates the chrome trim rings. These wheels are now made by Billet Vintiques. My problem is the hubcap "hats." They look exactly like stock hubcaps but they're not. The stock hats fit by compression, but they won't fit into the Billet Vintiques wheels...maybe a patent problem..if you buy the Billet Vintiques hubcaps, they are steel with a cheap chrome flash plating so they rust out very quickly. Stock GM was stainless steel.

I really like their looks, but I won't buy them for the 70. A set of four, including the rust prone hub caps, cost $2500. A little pricey, but if they had the quality, I'd go for them again.

 

Thanks again. The only problem is, my car is a 78 and those rallies are a different pattern than the rallies I have. But, I will definitely keep all options in mind.

 

Yes, narrow to the C3 section. You can run 15 X 10s but have to do some mods (offset trailing arms, relocate parking brake line, shorten the mono spring, etc.). If you run them without a 5" BS, they will stick out beyond your fenders. Some don't mind that look, some add flares. Good luck.

 

Looked at my rear tires today just to refresh my memory. 15 inch Torque Thrust wheels from the '70's; 8-1/2 wide wheels.

Running Mickey Thompson size 26x10.00R 15LT. Not sure of the wheel back space but the tires are just little beyond my fenders with standard trailing arms.

 

I have 15X10 Torque Thrust D's on the rear of my 69. The tires are Mickey Thompson N50's. The tires are a little over 12 in. wide. The rims have 3.75 in. backspacing. The trailing arms are stock and the brake cable is in the stock location. The tires stick out about 2 in. I like the look but some may not.

 

Are these 15 inch rims? Has anyone run 8 inch in the rear and 7 in on the fronts? I like the staggered look but unsure if it would look good on a 79. These are the exact rims I want but was thinking of doing 8 inch rears with 7 inch fronts. Thoughts?

 

these are C4 - 17" Dia. 9.5" width rims, 10.5" wide tires, they will fit.
minor grinding on brake bracket, not relocated.

 

FWIW, depending on the tire in question, I've found that rims which stick 1/2" further out than does a stock 8"x15" w/4" BS will fit many a C3 without issue. This simple gain means one may need only increase BS by 1/2" over stock to fairly readily fit a 9" rim. Out back, I've seen where up to 5.5" BS has fit without extensive work, and as much as ~6.25" BS with some moderate frame work above the TA pocket (as per BeeJay, for example). So, there certainly are C3s out there with 10"x18", and even wider rear rims without flares. That said, not every C3 has precisely the same set of clearance issues, so YMMV. And, as has been mentioned, larger diameter rims usually reduce/eliminate clearance issues with the TA and parking brake bracket, tho the need to have the rear leaf spring narrowed is hard to avoid.

Up front, the same goes for the 1/2" additional outer width, while it may start becoming impractical to increase BS by more than an additional inch (tho some have claimed to have done successfully). Among issues one might encounter here may be that of clearing the steering knuckle and/or outer tie-rod end (particularly in the "slow"/manual ratio position), the upper CA at the ball joint area, and inner fender well rub at full steering lock. In either case, not stepping up to larger diameter rims will make it more difficult to increase width without resorting to flares.

But, whichever end we're looking at, my best advice on rim fitment is to measure, measure, and measure again before actually spending any money. Also, don't rely on wheel manufactures to necessarily know everything on which their rims might fit. And, don't let any of them make you convert the maths from offset to BS. IMHO any of them who honestly want to help you get things right should do this for you.

In closing what has inadvertently become somewhat of a lecture, I caution anyone against running too wide of a tire section width for a given rim width, as doing so will tend to compromise sidewall stability during hard cornering. If in doubt, a fair rule of thumb would be to just keep tread width (not to be confused with section width) within an inch of rim width, erring towards the tire being the narrower of the two. And, for those who might tend to press things during the twisty bits, be aware that a having a significantly different amount of section width variation from the rims on each end of a car can result in a noticeable difference in how each end responds and/or builds cornering force. HTH


TSW

 

Thanks skunk grwat reply,

Did anyone catch the rim size in this threads red car?

Some cat on here runs 15 x 10 all four with 295 50 15 all four....

 

heck I have a set of ralleys ,that a friend had cut down the middle and had extra metal re-welded ,so I think they are like 12 inches wide ,he used them for racing