Just out of curiousity, why does the Z06 run a 17inch front wheel and an 18inch rear? There must be a performance advantage, but hell if I can figure out what it is. Any ideas?

 

I wonder the same thing.... maybe it is so they can run a higher profile tire up front which I think may help in vibration and also prevent rolling over onto the rim on hard turns.

Has anyone done this stagger - got pics?

 

The diameters are different, too, so it might be a styling issue mainly. The rear wheel wells are bigger. I've driven a C5 with 17" wheels all around (with 315s in back -- fun fun!) on the track before and it worked great, but the rear wheels are noticably small with that setup.

-Max

 

I've asked that question a bunch of times. I even tried searching the Corvette forum but no real answer. I was told maybe for gearing but then why 17's up front, they could be 18's all around.

Here is my guess: 18's in the rear to counter the torque and less tire spin from bigger and heavier wheels. 17's up from for more sidewall and a softer ride from pot holes, dips, bad roads, etc.

 

17s look small on the back of the C5 because the wheel well is bigger. The FD has roughly the same sized wheel wells, so it probably would not look as natural as it does on the C5. I think they chose tires that have roughly the same sidewall height, so the rears are probably about an inch bigger in diameter. The rear end of the C5 is relatively big, so the bigger wheels and tires look right.

I don't think there is any significantly deeper engineering reason. You will get better traction with a larger diameter tire because it has to deform less to get the same contact patch. Perhaps that is why those chose larger rear wheels and designed the heft of the rear end and the size of the wheel wells around that choice, but I think it is more likely that the decision was made more on the styling end of the development process and not for a specific engineering reason. That's just my guess -- I could be quite wrong, but I doubt it. They may have done it for a number of reasons, including styling and engineering, too. But I don't think there is any "magical" reason for the choice.

-Max

 

Styling... Thats about the only reason for it-
They look 'odd' with 17's all around-

 

Max was right. All hail the Maxster

Reply from Z06Vette forum:
The answer is in "All Corvettes Are Red", its a great read....

Yes, the larger wheels are in fact for looks. To tell the truth, the
designer of the C5 wanted a 2" difference, IE 19" rears, but was shot
down.....

JC

 

I really can't see on my pc moniter that well, but on the 1st pic, I see a Mazda emblem. And on 2nd pic, I see a Corvette emblem.

Please tell me if I'm wrong.

 

I only do this on the FC's and it's precisely for the reason Max has stated.

Now, SleepR1's interest in doing this is in relation to limited tire selection within a specific brand. As well as the fact that the additional sidewall height will help for the reasons stated above.

i.e. 245/40/17 and 285/30/18 are much easier combination to find withing the same tire while retaining almost identical outer diameters front and rear. Why the reason for the 285/30/18, well you can ask Max as he's the Master advocator of this tire. lol.

Very simple answer actually, retains stock gearing while providing the most contact patch available.

 

I find this interesting. I never noticed the difference in the wheel wells on the C5, but personally from a guy with stock wheels felt that the low hoodline of the FD felt that a 18" looks on the border of being too large, while in the back the 18 looks fine (esp. with some sort of rear wing/spoiler)

Those who have seen 18"s know better than I as I've never seen one with 'em.. Please advise especially if you see my perspective..

Rishie - changed my mind on the wheels - want GTN's gun metal.. don't want the polished 57pro's.

 

Why is it that we should only do it on an Fc? What can happen to an Fd that would make it a bad idea!?!?

 

Contrary to popular belief this is NOT done just for styling and coolness. It's actually done to maintain a specific wheel and tire height (for gearing), AS WELL AS working with aerodynamic drag (the width of the wheels DOES affect this). A (not so) quick example is as follows...

Chevy Corvette Z06
MT 6spd
405 bhp
Cd .31
Redline 6500
Rear End 3.42

Stock Wheels
17" x 8.5" front

18" x 9.5" rear

Optional Wheels
17" x 9.5" front

18" x 10.5" rear

Stock Tires
P245/45ZR-17

P275/40ZR-18

Optional Tires
P265/40ZR-17

P295/35ZR-18

Here's how the gears and speeds will work out with the 2 setups...

Stock Tires
---------------------------------
25.346" Front
26.129" Rear
Gearing=175.950mph


Optional Tires
----------------------------------
25.681" Front
26.661" Rear
Gearing=179.533mph

With the first setup you will have a her top speed, but slower acceleration, the second one will be vice versa. The larger wheel on the second setup makes the top end gearing actually shorter (numerically higher) so that you can get a higher top speed out of the car. Both have a nearly identical size to the naked eye (so you don't notice that one is smaller than the other...the package not the front being smaller than rear). One (the second one) will have a higher Cd because it's a wider tire causing more drag, but will have better handling (stiffer sidewall). The second setup will also work with the top speed due to the fact that since the gearing is shorter (numerically higher) the rpms will not drop lower (which is usually where less rwhp is...). This is because they want the engine to be at a certain rpm when you shift to that final gear (most likely 5th...6th appears to be more for fuel economy) to maximize both the gearing and the aerodynamic hp needed to get a higher top speed. This car will need approx. 259rwhp in order to reach the top speed of 175.533

I'm running out of time right now so I have to go, but either way I hope this helps someone see what all this wheel and tire sizing is REALLY all about .

 

Why would top speed (in each gear) be a factor when deciding on OEM wheels? GM could easily change the gearing to accomplish this. Your second argument sounds more viable; taller wheels can provide better grip with narrower tires than smaller wheels. Even so I still tend to think it was for style.

 

I really believe it is just a function of styling and what would fit in the respective wheel wells. Obviously the car and its ride heights were designed to accomodate a 1" tall rear tire. If they had used an 18" front tire, they have need tires with a very low profile to have ended up with the same overall diameter as the current 17's have.

This isn't THAT uncommon, Acura NSX's come this way, as did the Lotus Esprit, and some italian exotics Its likely not so much a matter of using a larger tire in the rear, but using a smaller in the front to acheive a lower hood line... especially in mid-engined cars.

As far as the FD goes, the reality is that most aftermarket lowering spring (and even most folks who set up their coilovers) end up lowering the rear significantly more than the front to achieve a consistent front to rear "gap". The cars stock "rake" looks a little jacked up in the rear... very noticeable with 17-18" wheels. SO, theoretically you could run a 17" front and 18" rear wheel/tire and the additional diameter would likely only return the car to its stock "rake" figure a 245/40/17 front (24.7" diameter) and a 265/35/18 rear (25.3" diameter) for a difference in diameter of .6" and a difference in radius (and therefore ride height) of about .3"... which is about the difference F/R lowering on a set of Racing beat springs, or the high to middle perch on a koni shock. The actual sidewall heights of thos tires aren't that much different (3.65" to 3.81") so it won't look goofy with one "regualr" and one "rubber band" sidewall. You'd fill out your rear wheel well, and not tear up the fender lips in front.

Your call on the actual looks of a 17/18 combo on the FD, but i've seen pictures of it so folks have already done it.

 

I Agree

 

Think of it this way CCarlisi, which one is more expensive to modify or produce...tires or gearing? Think about the tooling neccessary to get the gears you want for the car, and then think about the tires that you DON'T have to tool and can simply get somewhere else. Not to mention that not very many people besides myself have any idea what the tires do to the gearing of a car anyway so why would you go for the smaller set, that's not cool right??? At least the how most people usually look at the wheel and tire size situation. Of course this also has to do with the ride quality, but to me that takes a backseat to everything else. Check out the suspension forum for the setup that I'm about to get for my FC. You'll see that it took a great deal of thought into figuring out the package that I wanted (having to go here and there to find stuff is a bit of a hassle, but to me better than having to settle for something else that won't work the way you want it to.)

 

I have noticed the rear gap increases on the FD with larger tires and most guys have coil overs to compenstate. It is not as dramatic as the Corvette though.

I was going to do Meister S2R's 17F & 18R because they only make 9" in 17's and I wanted 10" wide. My problem with 18's in the rear is the damn price of the rubber! ...too much $

Those Corvette wheel/tire setups are not options, they are for the Z06 model.

There were alot of cars at the LA Auto Show with larger rear tires then fronts and one concept car with 21" rears.

 

That's a great bit of work, but you overlooked one thing: the M12 and MN6 transmissions have different ratios anyway.
The truth is, I'd bet it's so you can find the right tire sizes and profiles.

Dunno- let's ask the masters.

http://forums.corvetteforum.com/zerothread?id=490657

And why the hell is this thread like 10 feet wide?

 

Ahhhh...but I DID NOT overlook the ratios I simply used the ratios for the ZO6 manual tranny instead of bothering to use them both. This is because I was showing what would happen if you used the different sized wheels and tires with a specific gearbox (they share the axel ratio, but not the other gears except 4th). The gearing in the MM6 and M12 are different, but they also have different power MM6 cars have less power (350@5200 and 375@4400). But I should've pointed out that there are different gear ratios depending on what corvette you have.

Oh yea, I have NO IDEA why the thread is 10 feet wide but it's damn annoying.