got an 03 coupe with 18's...i know they take 245 45 18....will 245 40 18 be ok? rear of course.

see simple...thanks

 

just make sure you keep rear overall diameter larger than front and everything will be OK

 

Why of course? It's actually common for members to run 245/40s front and rear when having 18" wheels. Gives you slightly better high speed control you can feel...Gary

 

Google search a tire diameter calculator. If the difference between the front and rear = or > 3% I would not run the tire. The VDC will be affected. If it isn't at least the stock diameter I wouldn't run it. That's just me though.

 

as long as you keep your rear larger than front, VDC don't give much crap about what size you run.

I ran several different sizes and never had any issues with VDS. As long as your front tires spin faster than rear.

 

What's happens if the front is bigger than the back how does it effect it ?

 

Agreed!

 

The VDC will be affected

 

I don't understand how will it effect the VDC and does it hurt?

 

I had to do that one night to track down a wheel vibration problem. My slip and abs lights came on at highway speeds. Based on wheel speed calculations the car will think the wheel are slipping.

 

What if you run a square setup? That's how I plan on running snow tires in the future. I've seen at least one post on MY350 where there was no problem with that.

 

VDC is set up to have so that your front tires spin faster than rear, If you make your rear tires smaller in diameter than front VDC will think that you are constantly spinning out of control. So as a result it will cut down a power to avoid spin out and apply brakes to stop tires from spinning (in theory)


I'm not sure about square setup. I don't think that it's going to be too much of an issue because both wheels going to spin with same speed, that is not as bad as having rear spin faster than front. Sedans come equipped with square setup from factory, and they are equipped with same VDC system, so I doubt it's going to be an issue.

 

I could see a problem with changing the tire size alot but we are only talking about a 45 to a 40

 

No problems here when I put my 225/55/r17 Blizzaks on all four corners.