Considering upgrade wheels
 

1991 C4 base convertible owner here. Really looking hard at a wheel upgrade. the saw blades will stay in the fold but some new shoes will breathe life into the looks of this car. There’s a guy that did some updates to a 95’ red convertible that I’m pretty impressed with. (see here: https://www.corvetteonline.com/tech-...es-and-brakes/)

I think lowering the car an inch made a difference. That’s worth the effort. Luv the wheels but not the price. There’s similar for a lot less. Upgrading the break components for a wheel with more reveal seems essential.

I guess what I’m clueless about is all the wheel size stuff and what my limitations are. The 91 base convertible has 17 x 9.5 +56mm rims all the way around. The guy that wrote that article upgraded to 18’s with different tire widths and offsets.

So, if I intent to lower my 91 with that lowering kit what should I do for maximum visual and handling improvements? What CAN I do for size and width without additional modifications? Do I have to stay with +56 offset rims regardless of size?

Looking for some smart input on this cuz I literally have ZERO experience with this stuff.

This should help you understand and compare sizes.

https://tiresize.com/comparison/

Thanks!

I've replaced my stock springs lowering my car 1 inch and replaced my rims with 18" on my '95. Now I'm running 275/40ZR18 front and rear. I have a spreadsheet that does the conversions so you can see what tire size you need to keep the same or desired height and width. Here are the equations:
Sidewall height = [Width (275)]/100*[Aspect Ratio (40)]/25.4 (conversion factor) = 4.33"
Width: [Width (275)]/25.4 = 10.83"
Total diameter: [Sidewall height (4.33")] *2+ [rim diameter (18)] = 26.66"

You don't have to keep the same offset. If you upgrade your front brakes to the C5/C6 style you do need to be cognisant to ensure your calipers will clear.

Here is mine with the lowered stance.

https://cimg4.ibsrv.net/gimg/www.cor...05c5119049.jpg

Thank you!
When I bought the rims, used, they came with rubber already on them. They are Goodyear Eagle F1s. I don't have any complaints about them.

here is a nice C4 specific wheel guide
https://cimg7.ibsrv.net/gimg/www.cor...21ccbcd743.jpg
. I went with wheels from here,https://www.oewheelsllc.com/

very happy with them. I did 17 x 9.5 front and 18 x 10.5 rear. 275's all the way around. future plans will be 315 rear and 1-1.5 lowering kit

You can go with whatever size you want, but be aware that changing the offset/backspacing effects how the rim sits flush with the body, so don't stray too far from 56mm (on the 9.5" width) and you're just fine if you care about how that looks. Just try to visualize the difference in offset vs how it will sit relative to the body. A few mm doesn't mean much, but 15-20 does. I have 18x9.5 front and 18x10.5 rear, C5 style rims from OE Wheels that I got years ago. The wider rear rim has a slightly smaller offset to sit flush with the body.

Very helpful! Thanks. OE’s prices are very good. Have you been pleased with them?

Also, what size tires did you put on those rims?

I'm running 275s on front and 295/35/18 rear, Continental ExtremeContacts

Perfect. Thx!

here is a good example of above consideration of wheels flush with menders. my all black wheels were 17x8.5 and 18x9.5 C5 wheels the new wheels 17x9.5 and 18x10.5

https://cimg8.ibsrv.net/gimg/www.cor...4cfaaf3634.jpg
https://cimg0.ibsrv.net/gimg/www.cor...0f74c12b63.jpg

The practical limitation front and rear on an 88-96 C4 is 11" wheels with 50mm offset, and 315 tires. That's the most you can fit under the fenders without poking out, realistically. However, 315 tires in any diameter are not plentiful. 18x10 or 18x10.5 at around 50-54mm offset are a good option, and there are lots of tires you can choose from in 285/35r18 or 295/35r18, and they are in the correct range of outside diameter for a C4. If you go with a 9.5" wheel, you can probably fit offsets anywhere from 40-56mm - anything more will look too "tucked in" and be a little goofy looking. On a 17x9.5, stick with the stock tire size of 275/40r17, and for an 18x9.5 go with 275/35r18. Easy peasy. IMO, it's best to go with a square fitment (same sizes front and rear). That looks better, grips better, and allows full tire rotations.

Comprehensive response and is so helpful. Thanks!!

You're welcome. I forgot to add that there are some 19" options, but IMO the C4 is too small a car to look right with 19" or bigger wheels. It's way, way smaller than a C5/6/7, and so the tall wheels start to look goofy.

i probably won’t go bigger than 18” and am strongly considering sticking 17 x 9.5 all around. I’ve got a steel blue 91 convertible and I’m thinking machine faced TSW Nurbuhgring or similar. That’s mock-up w 18’s. Looks fine w 17’s too. Lowering an inch would look good. Otherwise I’m thinking 5 spoke c5/C6 style. Not sure I like chrome in this car. Any thoughts? All around ride and handling is more important to me than just handling.
https://cimg0.ibsrv.net/gimg/www.cor...0f7ad9599.jpeg

I think your plan is a good one. Any five-spoke design looks good on any C4, but those TSWs are great looking too. All else being equal (same tire model, etc.), the 17s should ride a bit better than 18s due to having more sidewall to absorb bumps. There are real differences in ride quality between different tire models within the same size, though.

I was hoping Matthew would chine in this discussion. I learned a lot from him and currently run 275/40/17 fronts and 315/35/17 rears. I like the look but still may go 315 squared as stated above.

Definitely getting the input I was seeking. Thanks all. I just put new rubber on the saw blades so I’m leaning toward 17’s and moving the tires to a new wheel at the stock size.

Looking at the TSW specs for that wheel it looks like my options are:

17” @ 17 x 9 w a 50mm offset (will my stock 275/40/17’s fit)?
18” @ 18 x 9 w a 50mm offset (tire recommendations)?
18” @ 18 x 10.5 w a 65mm offset (what tire size)?

If I go 18”, which of those options is best for my 91 and what tire size would be recommended?

9" is the minimum recommended wheel width for a 275/40 tire (9-11"). That will work - not ideal for best track times, but it will be fine on the street. This offset will work nicely.

Same as above, and the tire size could be 275/35r18 on the wide end, or a 245/40r18 on the narrower end. The latter is probably a better overall fitment for this width tire.

You'd need 1/2" spacers to run these wheels, which is fine to use. You may need longer wheel studs to use them, though. For tires, either 285/35r18 or 295/35r18. I'd go with the 285s.

This is kind of an opinion-based, pro/con decision. To my mind, if you jump to 18s and pay for new tires, go with the wider 10.5" tires and spacers. They'll look better and give better performance. Your car will stand out from most C4s that have narrower rolling stock. People will compliment your car without exactly knowing why it looks badass compared to other C4s. I don't think you gain anything by going to the 18x9. If you're going to stick with 9" width wheels, then you might as well stick with the 17" wheels and use the tires you already own. That's money you can spend on other things.