SJW

Hi, all. Seeking some advice regarding wheel and tire fitment for my '94 ragtop. I'm looking at replica chromed C5 Y2K thinspokes on the OE Wheels website. Seems they have two sizes to choose from.

18 x 9.5 that is said to fit at all four corners on my car: https://www.oewheelsllc.com/CV05-180...C5-style-wheel

17 x 8.5 that is said to fit only the front: https://www.oewheelsllc.com/Corvette-C5-Wheel-chrome

Questions:

1. I've been very impressed with the Michelin Pilot Sports that I've had on my C4s, but I'd prefer to not limit myself too much with respect to tire selection. Does this suggest that I'll be better off with the 18 x 9.5 wheels at all four corners?

2. What size tire is ideally suited to an 18 x 9.5 wheel? I'd like to keep the O.D. as close to OEM as possible, to preserve speedometer accuracy.

3. What size tire is ideally suited to a 17 x 8.5 wheel?

4. Of those that are available to fit these wheels, what do y'all like for tires these days?

Many thanks in advance for any and all advice.

Live well,

SJW

SJW

ttt

BuckeyeROC

I've been looking for new wheels and tires for our 86 Vette with the goofy 32mm offset.

Use this site to compare tire sizes to retain or get close to the factory rev/mile: https://tiresize.com/calculator/

I can't help you on your other questions. Since our's is going to be a daily driver, our tire selection focus is different. But what I am seeing is that you need to select your tire for you situation then see what sizes they are available in. The 18x9.5's all around might be a better solution for you. We have been looking at 16x9.5 and 17x9.5 rims and the tire selection isn't quite as good as I expected. Wheel and tire sizes have obviously grown over the years.

hcbph

Here's what IMO is a better website for tire/wheel comparisons. https://www.wheel-size.com/calc/?whe...cl=50mm&sr=0mm
I went with 18"x9.5" +40 rims on my 86 with 255x40zr18 tires. Fits like the oem's did but a whole lot better selection today.
I found a place with a range of rims for the early C4's with the correct offset so you don't need spacers. I don't know if it's ethical to post the site or not but if you send me a pm I'll pass along the web info. No connection to them other than I bought my rims there in the past.

WVZR-1

@SJW No first hand experience but if the 1st link is correct I'd pass on those, those are stated as being 65mm offset . If correct I'd pass.. Regarding tire sizes 285/35-18 gets as close as you can likely get for a x 4 for your car. I like that choice and there seems to be many choices regarding tires. A 285/35-18 seems to be spec'd for a 10" wheel but would do 9.5 - 11. I'd maybe shop 'tires' first that you believe will suit you and then maybe shop wheels. I'd shop for something in 10"

I don't shop Tire/Rack but they seem to display 26 tire choices.

For an idea of profile maybe check this ZR-1 that used to live in MD that had 285/35-18 on the front. You should have no trouble finding other snapshots of C4's with 285/35-18.

An ideal wheel might be 10" @ 50 mm

https://www.corvetteforum.com/forums...ot-sports.html

Many ZR-1 run a 285/35 on the front - here's another with 18 X 10 Shelby

http://www.zr1.net/forum/showthread....light=285%2F35

KurtK

9.5's will work all the way around . I am considering going that route since their are not a lot choices for the 285s, and having tires that can be rotated.

rusty76

I just picked up my 93 today and I now know I'm going back to the stock rims which the PO had in his garage, that leaves what size tire to use. The PO had a set of 255/45R17 tires mounted. They're dated 2009, they gotta go. I was wondering if that is the size I should stay with . . . why not he used 'em.

I checked the stock size listed on VetteFacts.com which showed 275/40ZR-17. After spending time on that site linked in this thread, TireSize.com I think I'm going with 245/45R17 tires. The only difference between the 245 and the 275 is 1.2" in width, every other measure (shown in the tire calculator) is the same between them. The 255/45R17 that the PO had mounted were larger in diameter and circumference which I think would impact the speedo. Given the amount of rubber these cars have I don't think I'll notice any difference in performance in daily driving. There are way more choices and more tires at lower prices in the 245 size. Have I missed anything obvious?

MatthewMiller

That 18x9.5 has 9mm too much offset compared to a stock 9.5" C4 wheel. It will look funny because the wheels will sit too far inward. Taht's easily solved with at 1/3-1/2" spacer, though. I'd go for 1/2" to set the wheels out just a bit more than stock C4 wheels. And yes, with spacers they'll fit at all four corners. Basically, with 9.5" wheels you want something in the range of 45-50mm offset. Spacers subtract offset from a wheel.

That 17x8.5 has 2mm too much offset, but that's probably not enough to worry about. Not sure why they'd say they would only fit the fronts. They'll fit all four corners. But I think you'll regret not going to 9.5s.

Questions:

Both wheel sizes have a lot of tire choices.

I'd go with 275/35/18. That retains the stock tire diameter and the width is a good fit on that wheel width.

Proper size is 245/45/17. Same reasons as above.

Depends on the use. For just driving around the street and some winter use, a good value tire is the Riken Raptor. For more performance (i.e. grip), the Continental ExtremeContact Sport is a killer choice at a decent price, with best-of-class rain grip and near-best dry grip. There's nothing bad about the Michelin Pilot Sports, of course, but I think the Conti gets close (maybe better in the wet) for less money.


The best tire size will be 275/40/17 if you have 9.5" wheels, and 245/45/17 if you have 8.5" wheels. In 93, your car either came with the "staggered" width of 8.5 front and 9.5 rear, or it came with 9.5 at all four corners if it had the Z07 performance suspension option. So you need to verify your wheel widths first, and choose tires accordingly. The good news is that there are lots of choices in either tire size, and plenty that have size options in both sizes if you have the staggered wheel widths.

SJW

Thanks much for all of the great advice. Regarding spacers, what's the safe limit with respect to stud length? I don't anticipate this being a problem, but it seems sensible to ask.

Live well,

SJW

MatthewMiller

The rule I always see is At the minimum, thread engagement length must be equal to or greater than the diameter of the fastener. In other words, if the stud is 1/2-inch in diameter, the nut must engage onto the stud by at least 1/2-inch. If you cannot meet that with a spacer, then it's not too hard to install longer studs.

rusty76

I've been reading . . . uh,oh!! . . . about tires, specifically what came on my car. It's interesting how different sources provide differing information. I stumbled across a GM specifications manual for the 1993 Corvette and it showed the front tires as 255/40ZR17 on 8.5" rims and the rear as 285/40ZR17 on 9.5" rims. This morning I decided to take a look at the stock wheels and tires that came with my car (not on it) and that's exactly what I found.

Last night I was entertaining myself by looking up as many of my car's RPO codes as I could find and XAA was one. That one is "XAA - Front Tire (P255/45ZR17)", yet more conflicting information. I did find the code "QB6 - 17x8.5 Front and 17x9.5 Rear Aluminum Styled Wheels" so at least that checks out.

MatthewMiller

That's all consistent. The base cars came with 8.5 front wheels with 255/40 tires, and the 9.5" rear wheels with 285/40 tires. I believe 93 was the first year for this staggered fitment. The goal was to again soften the ride and make it less prone to tramlining. But the performance suspension option (I think it was Z07 in that year) came with 9.5" wheels and 275/40 tires all around.

On the staggered wheel-width setups, it's probably better for most people to move to 245/45 front tires and 275/40 rear tires. There are a lot more tire options in those sizes, and those sizes are more appropriate widths for those wheel sizes.

rusty76

I was driving it yesterday and was thinking about the tendency toward bump steer with the current 11.5" wide front tires. I looked up tramlining and yea, I've noticed that effect but the bump steer is more pronounced. I'm going to have a good look at the front suspension sometime soon to be sure everything is in good working order because, unless it's the overly wide front tires doing it, I wouldn't expect a C4 to experience bump steer.

I've been thinking about going to 245/45 tires on the front, just as you said, to improve the range of available tires but also because I'm thinking it might lessen harshness. As an old guy, I'm not so much interested in absolute performance but I also don't want to emasculate the bull so I was thinking the 245/45 might be a good compromise since it keeps all the dimensions of the 275/40 with the exception of being 1.2" narrower.

Right now my car has the Z06 wheels and those 13 1/2" rear tires make the car feel like a roller skate with steel wheels. It's not so bad on a smooth road but there aren't many smooth roads in New Jersey.

MatthewMiller

Kind of depends on what you mean by "bump steer." Typical bump steer means a change of total toe angle with suspension movement, but not typically a change of overall steering for the car. That is, bump steer doesn't usually cause the car to veer one way or the other when the suspension compresses and rebounds. Zero bump steer is desirable, but not very attainable in any car. We do our best to minimize it. But if you're getting a change of direction with suspension deflection, something else is going on. It could be either front or rear suspension, and don't forget that the halfshafts are also part of the rear suspension (they comprise the upper lateral arms) and so their u-joints need to be in good shape.

Generally, it's best to fit the tires that will work best on the wheels you are using, rather than just pick tire size without regard to wheel size. So if you have 8.5" front wheels, then 245s will work well. 255s will give a softer ride and less tramlining on the same wheel, but will sacrifice some steering response and race the CG and Roll Center of the car (because they are also taller) and therefore likely slightly reduce cornering grip. Out back, if you have really wide wheels (guessing 11" or 12") then you need to keep wide tires on them. You can go narrower with narrower wheels, of course.

BUT...don't overlook tire pressures. Lots of people put much wider tires on their cars but run the same pressures as they did with their prior narrower wheels and tires. That's not how this works! The whole point of going with wider wheels and tires is to put more rubber contact patch on the ground, but if you don't reduce pressures then you lose at least some of that advantage. So if, for example, you ran 35psi with 9.5" wheels and 275 tires out back, then you can probably run 30 psi with 315s, or maybe even less. That also has the benefit of getting you some of your ride quality back, so that it doesn't feel like a roller skate.

Joshie225

Rusty76,

A 245/45R17 tire is meant to fit a 7.5-9" wide wheel. This means a good fit on your 8.5" wide front wheels, but not your 9.5" rear wheels. The lip of the rear wheel will stick out beyond the tire sidewall and be highly subject to curb rash. Yes, there are tons of 245/45R17 tires out there as they fit a lot of Mustangs. A good tire in that size isn't that much less expensive ($20 or less in many cases) than a 275/40R17 that will fit the rear properly. 285/40R17 are less common and more expensive. My car was built with 9.5" wheels front and rear so I have 275s all around.

rusty76

Thanks to both of you for your input. Whichever way I go it will be an improvement over the tires currently on it 275/35-18 front and 325/30-19 rear. I'm going back to the stock rims later in the summer. I'll decide what sizes when the time comes. Till then I'll think on it some more. Part of the fun of owning this car.

I checked the pressure in the tires when I brought it home and the PO has all 4 at about 34.

SJW

A very tardy "Thank you!" to the respondents. Things have been insanely busy, but I finally got around to ordering a wheel and tire package from OE Wheels this week. Special thanks to Matthew Miller, as I took his advice on wheel and tire sizes. I went with the Michelin Pilot Sport 4 S, on the 17x8.5 front, 18x9.5 rear wheels.

Looking forward to their arrival, and to putting the floor jack to good use, hopefully as soon as next week. I'm tired of looking at the peeling chrome in the barrels of the wheels that are on the car now, and the tires are tired (pun intended).

Live well,

SJW

rusty76

SJW, hopefully you'll post pictures of the new wheels and tires in this thread when you get them mounted. I'd like to see how your car looks with them mounted. I'll probably buy new tires in time for next summer and will probably go with 245/45 front and 275/40 on the rear as Matthew suggested.

I also have to find a used front rim as one of mine is so badly damaged it's not worth fixing

SJW

Will do. But, note that I went with 275/35ZR18 on the rear, as recommended by Matthew in post #8.

Live well,

SJW

rusty76

I see that, looking forward to seeing how they look.