18" Wheel/Tire Diameter

[Atenza2003]

Ok guys. I was thinking about this a while now and also have been seeing everyones input on the subject of getting 18" rims on our 6's and how it'll affect the ride. Well, I found out this:

SIZE SIDEWALL DIAMETER
stock 215/45-17...........4.23 in............25.46 in
225/40-18...........3.54 in............25.09 in
215/35-18...........2.96 in............23.93 in
215/40-18...........3.38 in............24.77 in
215/45-18...........3.81 in............25.62 in

Now, when upgrading to a bigger size rim and tire, you should always stay as close to the stock wheel diameter as possible so you won't screw up your car and for these reasons:
1) Speedometer Error- Your speedometer might say your going 50 mph, but in reality you might be actually going anywhere in between the range of 45-55 mph.

2) RPM error while driving- You might be rev'ing at a certain rpm but if the diameter is bigger or smaller than stock, the revolutions of the tire, will affect the rpm's.

3) Smaller Diameter- You will have a bigger wheel gap than stock and a lot more suspension space, when the car suspension gives.

4) Larger Diameter - You will have a smaller wheel gap, WHICH IS NICE :) , BUT YOU MAY HAVE PROBLEMS RUBBING THE FENDERS AND SUSPENSION, because the tire/wheel setup has a larger diameter than stock. You wouldn't be able to lower you car, because the tire/wheel combo are already to big.

Reasons 1-4 is stock with no lowering/drop.

Now with all this said, I was wondering. I don't wanna be like other people who don't care about their cars and get 19's when their stock size were 14's and they set everything wrong on their car. Mine is a daily driver and I want it in good condition while hooking it up.
What do you guys think I should do, and you can also do this. Should I get the 215/35-18 (1.53 in. smaller than stock) with Eibach Springs or 215/40-18 (.69 in. smaller than stock) with Eibach springs. The difference in diameter from stock are both pretty small. The 225/40-18 which has a nice smaller diameter of a .37 in. smaller than stock, BUT we all see the problems we are seeing with everyone who got that tire size. Scraping and rubbing, even sometimes after rolling the fenders.

Sorry if this whole thing confused anyone.












:D :D

[Atenza2003]

.............SIZE ............SIDEWALL ........DIAMETER
stock 215/45-17...........4.23 in............25.46 in
........225/40-18...........3.54 in............25.09 in
........215/35-18...........2.96 in............23.93 in
........215/40-18...........3.38 in............24.77 in
........215/45-18...........3.81 in............25.62 in


Sorry for the weird positioning.

[Atenza2003]

One more thing that I forgot..sorry... Umm
5th reason- Affect on gas mileage. again, because of the revolutions of the tire, being bigger or smaller in diameter than stock.

[GreenNuggs]

I don't think anyone has had problems with rubbing on 225's I would go with the wider for a handling advantage.

And I don't know if your RPM assumption is correct? RPM has to be metered at the flywheel. Step on the gas in neutral and the REVs go up!

[WhoDiddy]

i hve probs here runnin a 225/40/18HR :( i rolled fenders to fix taht prbo. no rubbing now;)

[Atenza2003]

Yes I know you do have problems with 225 WhoDiddy.. Honestly the fender rolling helped and that's it? I heard others say the same thing, but when they have weight in the back seat, they still rub once in a while. I don't want that problem because I always have the back seats full. SAO that's why I was thinking of the 215/40-18 PLUS rolling my fenders, just in case.

[eduartejr]

how do you roll your fenders?

Elmer