Tire Expertise Please!

BigRed · 01-09-03, 01:15 AM

Ok currently I have 16" rims with 255/50 R16's on

I WANT to go

Y2K Rim so

17" all the way around however if I stick with 255/50's the exterior diameter is going to be to big for the car by an inch..

So I need help determining a tire size to make up the extra inch of treadwall.

Also Im going 9.5 wide on the front so a 50 with do BUT if I go wider for the rear whats the typical rear width for a little more hot rod appeal and whats the tire size.

Also whats the widest I can put on a 9.5 inch rim (Id like to keep all four rims the same for availability reasons)

Thanks guys

rrubel · 01-09-03, 08:24 AM

When you start going to 'plus' sizes you lower the cross-section to make up for it. I'm pretty sure that my 17" wheels use a 45 front and 40 rear (I have the 8.5" fronts). 17" is +1 for a 16"-stock car.

Go to Tirerack.com or discounttiredirect.com and use their tire calculators to see what's the best fit for you. I looked at tire options in stock and +0 sizes for a 93 Vette since that's what my wheels were off of; you, obviously, would look at ones for a 2k Vette.

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Vettelt193 · 01-09-03, 09:36 AM

Here are a few calculations to help you...

TIRE DIAMETERS:

255/50/16 = 26.04 inches
255/45/17 = 26.04
275/40/17 = 25.66
285/40/17 = 25.98
315/35/17 = 25.68

Can you even buy y2k rims bigger than 9.5 inches wide? with a 9.5, a 285 or 275 works best... you can fit a 315, but it tends to look a bit stupid.... let me know if you need any other help, all the tire sizes listed here will fit best

BigRed · 01-09-03, 10:39 AM

I thought the 255 part was sidewall height and the 50 part was thread width?

I really don't want skinnier tires

Cause I see the 255/45 R17's have the same exterior diameter as 255/50 R16's (That seems odd to me)

So whats the 255/50 R17 tires measure out to?

Remo · 01-09-03, 11:11 AM

Chad,

All the folks that replied to your question have given good solid information. Incidentally, here's how to read those confusing tire size numbers. Example 225/45/17.

255 - indicates the width of the tire (the bigger the number the more tire touches the street).
45 - is the profile of the tire or the distance from the wheel rim to the edge of the tire. (the bigger the number the taller the tire.
17 - of course this the diamiter if the wheel. The wheel is usually available in several widths - such as 8.5, 9.5 etc.

With this explaination, you can see what Vettelt193 was doing with the tire size matrix he provided you.

Hope this helps - Remo

rrubel · 01-09-03, 12:48 PM

To refine that last post a bit, the width (255) of the tire is from bead to bead (down the side, across the tread, up the other side). The height (45) is the percentage of the tire that's used for the sdiewall (ie, in 255/45/17, the tire is 255mm wide and 45% of it is sidewall height - 22.5% per side).

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CKA_Racing · 01-09-03, 07:21 PM

Is the offset on stock y2k wheels going to work on your '85?

rrubel · 01-09-03, 09:29 PM

With a $200 set of adapters, they'll work fine...
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Mr Mojo · 01-09-03, 11:52 PM

Quote:

Originally posted by Remo
Chad,

All the folks that replied to your question have given good solid information. Incidentally, here's how to read those confusing tire size numbers. Example 225/45/17.

255 - indicates the width of the tire (the bigger the number the more tire touches the street).
45 - is the profile of the tire or the distance from the wheel rim to the edge of the tire. (the bigger the number the taller the tire.
17 - of course this the diamiter if the wheel. The wheel is usually available in several widths - such as 8.5, 9.5 etc.

With this explaination, you can see what Vettelt193 was doing with the tire size matrix he provided you.

Hope this helps - Remo

To get a little deeper here, the 255 is actually the section width, or the width from sidewall to sidewall, so the tread could actually be a little narrower than the section width, all depends on the type of tire.

255's = about 10"

Mad-Mic · 01-10-03, 12:01 AM

i've seen them on another C4 in my neiborhood that was for sale. the owner told me they fit with no mods.

not sure if this was true or not

i got 17" 88-90 series rims on my 87 vette and they fit perfect with 285/45/17's all the way around. i don't think the 315's would fit since there is only about a 1/4 inch left before it hits the stock muffler but if you got modded muffs then you'll probably be fine.

BigRed · 01-10-03, 02:06 AM

GOT IT! Now it makes perfect sense to me thank you all very much!

So Im looking for a 45 series tire as to keep the diameter the same and 255 front and up to a 315 for rear but from suggestion 275 or 285 is a good choice.

And yes with the earlier C4's we have a wacky offset so I will require adapters, no big deal. Actually I think they will make the system look cool giving the rim depth from the calipers/rotors.

Ken · 01-10-03, 02:16 AM

Ain't it neat how you get so many responses in such a short period of time? I saw when you first posted this last night Chad and today you have tons of feedback. If it's ok with you guys I'm going to add a little info as to the second number to which y'all refer--the "aspect ratio."

ASPECT RATIO

The "aspect ratio" of a tire is the ratio of its section height to its section width. The smaller the number, the shorter the sidewall and the wider the tire. Low aspect ratio tires started with 60 series some time ago, then progressed to 50 series and now 45, 40 and even 35 series tires. Shorter aspect ratio tires (60 and less) are usually considered to be performance tires because they lower vehicle ride height, have a wider tread and put more rubber on the road to improve handling. But the shorter the sidewall, the harsher the tire rides.

A tire's ability to support a given load depends on its air volume. If you go to a lower aspect ratio tire with a shorter sidewall, the tire must be wider to maintain the same air volume. If you just go to a shorter aspect ratio tire without increasing width, the load carrying capacity goes down. That's why when you go from a standard wheel to a Plus 1 wheel, the rim is usually wider to accommodate a wider tire.

It's important to follow the tire manufacturer's recommendations as to load capacities when going to larger wheel and tire sizes. There's no hard rule that says you have to drop 10 points in aspect ratio when increasing wheel size one inch, but that's the general recommendation.

_ken