Be sure not to go too low in tire sidewall ratio if you live in an area with not-so-perfect roads.

 

You are correct, now try changing the circumference without changing the diameter.

The 265/35/18 - 295/35/18 combo works just fine on a C5. The 295 is slightly shorter than your stock 275/40...but the only error will be the speedometer reading slightly fast, which as stated, can be adjusted with one of the many programming tools out there. It is not an asbolute neccesity, the error will be very slight, and it won't adversly affect any other of the car's systems.

 

Thanks guys.Again you have come to the rescue.I have my brand new chrome thinspokes already in the garage waiting to go on next week.Finally got rid of the wagon wheels.I almost freaked out when i read the first post saying you could not run 18's all around.

 

No. I am currently running 265/18s front and 295/18s rear. Trying to keep the overall tire diameter the same, or very close, helps too. Especially if you have an A4. This is not difficult to do if you check your choices in Tire Racks specs categories. They show all tire specs for all the brands they carry. Very useful. HTH

 

Should I go with a 40 ratio instead of 35 for ride comfort and safety.

 

Difficult to say without knowing what width tire and brand you're looking for. The ratio you will wind up choosing will be determined in large part by how close to factory tire diameter you can stay for the width tire you're choosing. Of course if you're able to reprogram your computer then don't worry too much about speedometer error since that can be adjusted. If you're able to stay very close to the factory original diameter you can eliminate the re-programming step since any error is usually so small it's basically a wash.
Example: Goodyear Eagle GS-D3
245/45-17 = 25.7" diameter (stock size)
275/40-18 = 26.8" diameter (stock size)

BF Goodrich KDW2
265/35-18 = 25.3" diameter
295/35-18 = 26.1" diameter

In the example above, the speedometer error winds up being less that 2%. Pretty small. BTW, this is exactly the tire combo I went from and to.
I guess the main thing to decide first is: what brand, style and size you're interested in. From there, look into what is available from each of the brands you're looking at.
BTW, "safety" is a somewhat general term. In some ways a 35 can be more "safe" than a 40 (less sidewall roll under during high speed cornering enabling higher cornering speeds). At the same time some might say a 35 is "less safe" since the rim of the wheel sits closer to the ground and may be a bit more susceptible to damage from a severe pothole. If I were you I wouldn't get too caught up in the 35vs40 debate. In practical day-to-day terms these two are pretty much the same overall. Either one is going to be somewhat less "comfortable" than say a 60 or 70 series, but "comfort" is also something that is very subjective too and that's a whole 'nother argument there. HTH
Robert

 

Obviously not, because circumfrence is proportional to radius (C= 2 x pi x radius). Most handheld programmers want tire diameter (D=2 x radius.)

 

Now Sully, we all know that little tire ain't gonna handle yer 427ci monster motor.

 

But Jim, they are are Nitto "R" Compound Race tires. Very Sticky.

 

jules, You seem to be talking about rim size and not tire size. Rim size won't matter, as I have heard of others here putting 18" rims all around their Vette.

But when you buy tires, as others have said, just buy tires sizes that give you the same circumfrence as stock tires. That way , it won't screw up your odometer or Active Handling.