Best tire size for 03 M45?

[darcwun]

I have to replace the oem tires for my 03 M45. I was thinking of stepping up to the 245s on the stock wheels. I was wondering if i should go with 245/40 or 245/45. 245/40 would reduce the diameter by .6 inches while 245/45 would increase it by .35 inches.

not sure which will provide better ride quality and noise, and if there will be any rubbing concerns with either.

[Boon]

I went with 245/45's and there are no issues with rub or noise.

You can go 245/40's if you want, but you will just have a bit of a rougher ride and a bit more wheel gap.

I would recommend 245/45's, I got some BFG G-Force SS's and love them. Great tire for a great price.

[M45Caliber]

I am also running 245/45 - 18's -- Yokohama Avid W4S -- these tires are uni-directional, but they are quiet, grip like velcro, and are amazing on wet streets (which, admitedly I see little of in AZ) They also have a fairly high treadwear number, so they should last over 30K miles (I hope)

Check tirerack.com for comparisons and pricing guidelines. Keep in mind that you will always pay more locally because the TRack price does NOT include mounting or balancing (obviously). But, I take their price, add about $20, and that's in the Ballpark when I hit Discount Tire locally.

[szh]

I use 245/45-18. Widest you can do with the 7.5" inch widths of the stock OEM wheels.

See the stickies for a list of tires ...

Z

[mcrews]

I use 245/45-18. Widest you can do with the 7.5" inch widths of the stock OEM wheels.

See the stickies for a list of tires ...

Z

I run 255/45/18 kuhmo asx on my 02 Q45 stock rim 7.5 " wide.I got almost 40k on the first set and am on my second set.

[xerexabante]

Did you move to Cali?

[szh]

I run 255/45/18 kuhmo asx on my 02 Q45 stock rim 7.5 " wide. I got almost 40k on the first set and am on my second set.

Okay, but a few things to be aware of:

1. The minimum rim width for a 255/45 tire is typically 8.0 inches, with a recommended range of 8.0" to 9.5" (typical measurements are done at 8.5") for most tires in that size. While 7.5 is not far below the minimum width (particularly since the aspect ratio is still a reasonable 45), it is probably a bit more unsafe to do this stretch. Just be aware of this issue and that it is not recommended - tire manufacturers specify rim ranges for a good reason.

2. When mismatching the recommended rim range and the tire dimensions ("a stretched tire", albeit somewhat nominal in this case), you may find that the end result is not necessarily better performance.

3. For example, in this particular case, because the rim is narrower than the minimum of the range, the tire edges will "lift" up a bit at normal inflation pressure - the section width changes and the tire profile is altered from manufacturer measured nominal.

4. And, because of the lifting, the effective track width is reduced from the spec'ed values (255/45-18 tires are usually measured on 8.5" wide rims) from the tire manufacturer. In fact, it may even be reduced to the point where the 245/45 tire actually puts down a bit wider tread on the ground (at the same tire pressure) than a 255/45 tire. So, the point of using a wider tire becomes a bit nullified! So, the handling of a 245/45-18 on a 7.5" rim may thus be bit better than a 255/45-18 on a 7.5" rim.

5. BTW, it is not a good idea to reduce tire pressure in an effort to compensate for this minor edge lifting effect, since that could reduce the load index too much for our heavy cars. Too low a pressure is unsafe in a different way.

The point of all this geekiness is that it is usually much better to match the recommended rim width range and the tire widths, particularly if you get even lower aspect ratio tires! Of course, for most people who rarely drive at 9/10ths, the effect is probably minor.

FWIW, I am not a fan of massively stretched tires (not what you mention here, of course ... this is not that bad!) although people like to do this for some reason. Their choice. This is a fundamentally unsafe practice - when at speed or over bumps. You could lose the bead seating explosively and that would be fatal at high speeds.

Z