Jim Rogers

I'm researching tires for my '85's. 255 50r16 are unavailable at this time, but 245's are available and perfectly fine with me.

However, one of my cars has the Z51 package and, thus, 9.5" wheels. Mounting 245's on 9.5" wheels is way out of the tire/rim fitting ranges, and in the archives I have found posts that say that it's not safe, it will look funny, or that it can't even physically be done at all (although in one case it was actually done-- accidentally). So I probably won't be doing that.

I like the turbines/salad shooters and I do no competitive driving, so I could probably get a cheap set of 8.5" turbines to replace the 9.5's that are on there, but that brings up the question of whether there is any problem with using the 8.5's with the Z51, which is just a reflection of the question of why 9.5's were used in the first place.

Looking through the archives, I found this thread:

http://forums.corvetteforum.com/c4-g...y-z51-c4s.html

but there were only a few comments that addressed the question-- it mostly discussed the combinations of wheels on various years/packages. The only hint is that someone says you get better handling with the wider wheels.

So my questions are:

1. As a practical matter for my car, are there any issues with swapping stock base (8.5") turbines in place of the 9.5" Z51 turbines currently on my Z51-equipped '85? I'm guessing there is not, since I don't care if there is a slight decrease in handling (since I don't do anything competitive), but just wanted to check first.

2. Out of curiosity's sake, *would* there be any change in handling? Why were 9.5's part of the Z51 package, even though they came with the same tire size as the base package? I assume for better handling, but I don't know (due to my own ignorance) how wheel width would affect handling if the tire size is the same.

In this piece, tire rack says that:

So GM went outside the tire fitting range to do 9.5" wheels, so I assume there must have been some compelling reason for it-- but what was it? And if there is a rationale for it, would it not apply to justify 245's on a 9.5" wheel? Or is whatever benefit you get from a 255/9.5" combo lost if you push it too far with a 245/9.5" combo?

Many questions there, any insights appreciated.

Tha shu

Why not just buy tires that fit the 9.5 rims? Seems silly to go through all that trouble just to avoid buying a slightly wider tire.

Jim Rogers

The only tires that fit are the 255 50r16, and they are unavailable and it is unclear if/when they ever will become available again.

pmihaltian

Because the 255/50 VR 16" tires are no longer available. However, 245/50 VR 16" tires ARE available. This is what the OP is asking about....

Tha shu

I realize this, I was just unaware that the only size tire to fit those rims were the 255/50 VR16" tires. I do know that they fit other widths to 9.5" wide rims, that was my reason for asking.

pmihaltian

I have the same issues and concerns with my 86 Vette as I am still running 16" tires. However, I have run out of time with these and need to replace them ASAP.

For what it's worth, I have run 255/50 x16" tires on my 10" BBS wheels, front & back, for over 25 years now with absolutely no problems or ill effects. I have had no high speed related problems at all. The car handles like a slot car. What's more the BBS wheels are 36 lbs lighter than the OEM Corvette wheels.

I too am considering the 245/50 x 16" tires and would love to mount them on my 10" BBS wheels. Soooooo, while I do not know the answer to your question, I am very interested in a proper and knowledgeable response.

rodj

Fitting the tire to a 9.5" rim made the tire" tighter" ; less sidewall flex resulting on a better footprint when cornering.
Z51 was the " Performance Handling" package intended for guys who wanted to race around corners in weekend;
hence the stiffer suspension and bigger swaybars , faster steering , etc.

dk86vette

I may have missed something, but Summit has a number of 255/50R16s available: http://www.summitracing.com/search/D...6/?Ns=Rank|Asc

Most are Drag Radials, but the BFG 97802s should work alright...

Jim Rogers

That's interesting-- 255mm tires on a 10" (254mm) rim is even further out of spec than 245mm tires on a 9.5" (241mm) rim. If that's working (and you say it works well), then maybe it's not crazy to put 245's on my 9.5" rims? Do they look weird? Some say that kind of tightness will look ridiculous.

Makes sense-- do you have any idea if that principle (of making the tires "tighter" on the rims) would extend to the 245/9.5" combo?

The g-Force Sport is indeed the right tire, but if you try to put them in the cart it says they are currently not in stock and will have to be special ordered. It says they expect to ship on 9/20, but I think that's a mistake. BFG is not making that tire right now (at least as far as I know) and they will not be able to special order it.

Had me excited for a minute, though!

Tom400CFI

As a practical matter, there will be no issues. As a "handling" matter, there will also be no issues until you reach the absolute limit of traction on dry pavement...then you would notice (if you had very accurate measurin gequipment) an extremely slight reduction in maximum traction. Unless you're in a competition environment, you won't notice any change in "handling". Car will drive the same. Actually, in some cases the narrower tires will improve "handling" such as during straight line travel; the car won't pull/dart as much.



See above. No SOTP difference. I was sure that they didn't come w/the same tire size; the 8.5" rim came with a 245/50 R16...1cm narrower -I thought. Rodj's post says otherwise though, so now I'm not sure, as he knows his stuff! Anyway, the Z51 came with the 255 width tire to achieve maximum possible lateral grip (at the time) for that chassis and price point.





What ever benefit you have w/the 255, you lose with the 245. However, the benefit will not be something that any normal person would notice. In fact, new 245 tires will likely provide more traction than your old 255's simply b/c the rubber compound is...new. Of course over time that will degrade but my point is that there will be not discernable difference between a 245 and a 255 on the street. If a 245 will fit safely on the 9.5 rim, and not look stupid...run them. Otherwise, have you looked for a 265/45-R16? IF that exists, that would probably be the best solution.

Jim Rogers

OK-- good to know, thanks for that.

That was my suspicion, that the only differences would be at the limits of handling-- something that I would only experience in an emergency.

Edit: Forgot to mention that this source says that only 255's were used on every c4 or handling package:

http://www.corvetteactioncenter.com/...usp_chart.html

Yeah-- I don't need any convincing on the 245's, so those are my remaining questions-- is it safe? -- will it look stupid?

Only one non-competition tire-- and it's an extreme performance tire. Too expensive and wasted on me with my non-extreme driving ability.

Thanks.

dk86vette

Knew I missed something.

Kumho makes a few, but I think they're the only ones that do... just means they're expensive. =(

PLRX

255/50ZR16

oldalaskaman

amen

Zralou

How about 275's, I believe they will fit 9.5" rims.

Sara Lou

Jim Rogers

Unfortunately there are no 275's for a 16" rim (except for some 70 aspect ratio truck tires).

pmihaltian has given me some hope that the 245's will work on the 9.5" rims, but if not, there is pretty much no tire other than the 255/50/16 for that wheel (at least none that make sense for me).

So I either decide to go for that, or I'll be in the market for some used 8.5" turbines since it appears there will be no problems using those on my Z51.

Thanks for the idea, though.

rodj

The '84 was supposed to come std with a 15 x 7" w/215/65-15
and the 16" rims as a option.
In the end ,all 51,000+ cars ended up with the 16" rims and 255/50 -16 tires.
IIRC it was specially developed by Goodyear for the C4 and the biggest tire available in the USA at the time

http://www.joby.se/corvette/div/corvette_wheels/
http://www.motorera.com/corvette/1980/vet84.htm

Tom400CFI

Yep...as usual, you're right on.

I'm GLAD that the base wheel was never used.

pmihaltian

Here are a couple of photos of my 255/50 x 16" tires on OEM 9.5" rims and again on BBS 10" rims. I can't really tell any appreciable difference.

I do not know if the 245/50 tires would look the same or not.

Jim Rogers

@rodj-- Did you have any opinion about the wisdom of mounting 245's on a 9.5" rim? Way out of spec, but pmihaltian seems to have no problems with 255's on 10" (which is even worse). Just wondered what your opinion might be, but no problem if you were taking a pass on the question.