245/45/20

[CcDubya]

Can anyone explain or point me to a thread that explains tire sizes?

I'm considering buying an SRT wheel/tire set. All of the tires are 245/45/20's. I see some people who have 255's or 275's on the rear SRT wheels. I guess my brain has always thought that any given wheel can only accept one size of tire.

Can you put wider tires on the same wheel in back compared to front? What are the pros/cons to same size vs. larger?

[formerice]

If you go on the Tire Rack's web site, check the specs for a given tire, it will show you the diameter of the tire, tread and section width. You can run a wider lower profile on back as long as the diameter stays the same and the rim width is acceptable. The specs will give you a range of wheel widths for a given tire size. They have been helpful for me finding sizes to fit that are different than stock. Even if you don't buy from them, they are very helpful.

[boggart]

Can anyone explain or point me to a thread that explains tire sizes?

I'm considering buying an SRT wheel/tire set. All of the tires are 245/45/20's. I see some people who have 255's or 275's on the rear SRT wheels. I guess my brain has always thought that any given wheel can only accept one size of tire.

Can you put wider tires on the same wheel in back compared to front? What are the pros/cons to same size vs. larger?

That's a lot of info to explain. Don't know what you know and what you don't so I'll give you the most basic and see if that gives you what you're looking for.

On a tire size of 245/45/20 the indiviual numbers all mean something. 245 is the treadwidth. 45 is the sidewall height as a % of the width. So the sidewall is 45% of 245. The last number, as I'm sure you are aware is the wheel diameter. Since the middle number is a %, a 245/45/20 is roughly the same height as a 255/40/20. Some sites, like miata.net have online tire calculators that will let you see exactly the height difference.

Yes, you can put different size tires on the same rim safely. You have to be careful of going too wide, or too narrow. Typically the mfg. puts a tire right in the middle of the range that will fit, the ideal if you will.

There's no good reason to run different size tires on the back than the front. You definitely want them to be the same height of it will mess with the computer. Generally speaking the only reason people run wider back tires is for a cool look. Now, if you're talking drag racing, sometimes you need the wider tire for traction. Generally not the case on street cars. The biggest price you pay for the look is the inability to rotate tires.

[Invader]

to compare tire sizes (overall height)

we'll use 225*60*18 and 255*45*20 as examples

225 (width of tire in millimeters) * 0.6 (60 in the size (height of tire above the rim) = 135

135*2 (because you have sidewall above and below the rim) = 270

270/25.4 (convert mm to inches) = 10.63

10.63 (total height of your sidewalls) + 18 (rim width) = 28.63


255*45*20

255*0.45 = 114.75
114.75*2 = 229.5
229.5/25.4 = 9.03
9.03+20 = 29.03

28.6 original tire height to 29.03 new tire height.

This change in Tire Height changes the number of Revolutions Per Mile.
The change in RPM is what screws with your speedo vs. actual vehicle speed.

http://www.1010tires.com/TireSizeCalculator.asp is a nice link to an automatic calculator where you can play with different sizes. The rule of thumb is no more than 3% difference between old and new sizes.

You also need to look at each tire, and it's approved rim width on which it can mount to make sure it'll fit on the rim/offset you have.

If you go with too large a tire on a stock high offset rim, it can start rubbing on body parts or suspension parts.

You MUST run the same size (outside diameter of the tire) on each axle (or risk destroying your punkin), and if you have 4WD/AWD, across both axles (or risk destroying your transfer case (unless you never put your vehicle in 4WD)).

I've never run staggered fitments, but they look good for sure.

Hope this points you in the right direction.

[smoovmag]

i was wondering the same thing my shop tells me i need 275/40 r20 tires for awd