Actually you are the one on the wrong page. I am not concerned with what the car thinks about the change at this point. I am well aware of the differences between the FRC and the Z06 as this ain't my first rodeo. There are all kinds of variences between wheel and tire combo's that are being used on C5's and I am throwing out one possible option and given the variences listed, wondered if anyone saw a glaring problem. According to the info I found concerning the rear tires, the "smaller" Hankook tires would make 2 additional revolutions over the distance of one mile. I doubt that the computrer would notice??? The percentage of error in distance over a mile would be .00249%.

 

781 revolutions per mile on the rear OEM Goodyear runflats, and 803 revolutions per mile on the 285/35/18 Hankooks. That's 22 additional revs per mile, which comes out to 2.82% more...

 

so let me make sure i understand you here...
you're only wanting to compare the V12s to a set of Z06 tires and you don't really care how either set relates to the tires your car came with from the factory. is this right? if so, then you have to consider one more variable: stock Z06 tires are already a bit smaller than your stock tires & going even smaller than is going to create an even bigger speedo/odometer error & possibly start causing the ABS/TC to act up... which is all we've been trying to tell you.


here's where i was basing my assessments of your thought process:
that's OEM for a Z06, not a FRC

ps - it's usually good practice to get an alignment with each new set of tires anyway - especially when changing sizes. that way you maximize your handling capability, tire life, ride quality, & fuel economy

which means the tires that all the systems in your car are programmed for are almost an inch taller than the V12s - which will cause a lot more than .002% error

^^this

we're just trying to make sure that you know that regardless of the fact that you won't have your old wheels anymore, you're still looking at tires considerably smaller than what you're currently using. really, i'd imagine you should be able to just have an engine tuner go in & change the tire sizes in the computer & everything would be fine no matter what sizes you ended up running (assuming these cars are like the GM trucks i'm more familiar with)

 

and just as a matter of perspective, you can put a 305/70-18 all terrain on a Z06 wheel if you want. assuming you have the right adapters, you could swap this out with a 35" tire on a truck & it'll be just about the same. it has nothing to do with the 295/35-18 that GM originally put on it if it ain't going on another Z06

 

Good point, but the comparison I am making is the difference between my posible combination and someone who had the same car as mine and swapped on Z06 wheels with the stock size supercar tires. I do see that the 2.82% would make a difference in the speedometer calibration. But to further my point, anyone who just puts on Z06 size wheels and tires will see a 2.496% change too. So we are back to a .324% percent difference in that regard.

 

okay, gotcha. you're saying that you're fine with the already-known calibration error of dropping down to Z06 sizes, and you're just debating on whether or not you can handle going even smaller than that

 

Am I missing something here? I thought that putting Z06 wheels on C5 FRC's, verts or coupes was pretty common practice. By some of the comments made I'm surprised the federal government hasn't stepped in an outlawed the swap!

I'm not looking for conformation of my idea, just info on thoughts about the two sizes listed for a FRC car. It's going to be one or the other and I'll deal with the other issues as they arise.

 

sorry. let me back up a little:
i was originally under the impression that you were trying to look at the size difference between the V12s & Z06 tires without considering how much smaller they both are in comparison to your stock tires on the car now (which is how your first few posts sounded). i was just affirming that i see you've already considered that.

there ain't nothing wrong with running Z06 sizes - heck, i just bought a set today for my FRC in almost-Z06 sizes (using an 18" front) because i couldn't find non-R compound 305/35s i liked. that said, i'm having my tuner adjust the tire heights to reflect that change, though

 

Wow... Just wow.

This is getting complicated. Those sizes will work, they're not ideal but they will work. If you want positive confirmation call Tire-rack's tech support service and ask them. Those guys are ridiculously knowledgeable on the subject of tires.

I've never heard of smaller tire sizes (as a whole) creating AH/TC issues; it's the delta of the two sets (front and rear) that needs to be given thought. The diameter of your rear wheels must be a MINIMUM of .5" taller than your fronts. I believe the stock height difference is somewhere around 1".

The upside: Slightly better gearing.

The downside: Your speedometer will be out of calibration by a small margin, your odometer will register slightly more miles than actually traveled and your wheel wells will look like $hit. Also, the better gearing will almost definitely lead to a shorter tread life for your tires unless you drive like you have Ms. Daisy in the seat next to you. If the tires you're getting are free then they're probably worth it. If they are only slightly cheaper than the proper size than you might want to take the effect of the gearing on tread life into consideration.

But, if you just need a set of tires for now until you can get the right ones they will work...

GL

 

A little further explaination as to why I brought this up. After considering the use of the Hankook tire sizes, I find a craigslist as for 2 of the rear Hankook sizes. The ad has a picture of the tires mounted and as far as I could tell they looked ok. The ad said they were new but he had decided not to use them on his car (don't know what kind of car he has). For $300.00 for both rears in new condition and within driving distance peaked my interest. But in the back of my mind I wondered if there was a problem with the size. Before I was able to make contact with the seller the ad was closed. Actually the ad was closed before I had posession of the Z06 wheels. I'm still a little on the fence about which way to go on this but I'll have to make a decision this week.