donaldso718

Hey guys, I'm a complete newb at understanding tire sizing. I have 18" Aspec wheels and need some help on the best tire size for it. Any recommendations?

Can someone explain the first 3-digit # and the middle 2-digit # to me in laymans terms? I have googled it, but I still don't really understand it. Which # makes the sidewall smaller (low profile) or bigger? And what does the number mean if it's higher or lower? If anyone can explain this in a simpler explanation I'd apprectiate it, thanks guys.

TLin05

Try looking here: http://www.rimsntires.com/rt_specs.jsp

245/40-18 is best 18" size in my opinion. Gives a tad more rim protection and fills the wheel wells out a little better.

Turbonut

iTrader: (1)

That's the size.
Go to the following and you'll get all your answers, plus you can compare all the tires:
http://www.tirerack.com/tires/tiretech/tiretech.jsp

Bearcat94

http://www.1010tires.com/TireSizeCalculator.asp - Tire Size Calculator. Stay within 3% of the original size.

Original OE size is 235/45-17.

First 3 digits - 235 - is the Section width of the tire in mm; the width at the widest point.

2nd digits - 45 - is a ratio for sidewall height. In this case the side wall is 45% of the section width; or 235mm x .45 = ~106mm sidewall height. If it were, for example, 245/40, then sidewall height would be 40% of 245mm.

3rd digits - 17 - is the radius of the wheel; i.e. 17 inch wheel.

donaldso718

Thanks that website is very helpful! Tirerack says I should go with 235/40zr. What pros or cons are there by going with wider 240?

Bearcat94

There is no 240. 10mm increments only.

Wider means more footrprint (good for traction) but more rolling restiance. Wider generally looks better. Too wide and they'll rub.

donaldso718

Oops I meant 245 as was recommended by TLin05. Would 35 still have good rim protection? I live in NYC by the way.

Thanks for the answers! Everyone has been very helpful, much appreciated!

Turbonut

iTrader: (1)

Tire Rack lists the OE size, but if you read on they also recommend the Plus Concept, for not only wheels, but also tires.

I always recommend a 245/45-17 as replacement for the 17", and 245/40-18 for the 18". You'll be glad you purchsed this size!!!!!

So far it's unanimous 245/40-18.

Yonkers914

iTrader: (1)

I had 18in a-specs on my TL and i was running 235/40/18 tires and worked well.

Turbonut

iTrader: (1)

It's not that they don't work well, they are small not only in diameter, but tread width, and when they wear slightly they look like roller skates with the short sidewall and exposed wheelwell, and just think, a 245/40-18 would work even better. Many make a mistake and purchase 235/40-18.

Let's look at it in a different light:

235/45-17 25.32"
235/40-18 25.40"

245/45-17 25.68" ******
245/40-18 25.71" ******

****** Remember this size

Yonkers914

iTrader: (1)

oh ok lol just throwing it out there. ur def. right though the outsides dont look as beefy as the inside of my tires. BUt these tires came with my car but when they wear out i'll prolly change to 245/40-18 .