does 225/50/16 = 245/45/16?

[TrunkMonkey]

this may seem like a noobish question, but i'm still learning about tires and suspension. please bare with me.

i currently run 225/50 on 16x8 wheels. i'm considering stepping up to 245/45/16, but considering how wheel width affects a tire's section width, is this really an upgrade?

the rule of thumb is that for ever 1/2" of additional wheel width over a tire's specified measured wheel width, you add roughly .2" to the section width. most 225s have a 7" measured wheel width and most 245s have an 8. the fuzion HRi's that i have are pretty wide for a 225. unmounted, they measure close to 9.75" wide. (some of this may be due to the fact that they may have been stretched since they've been mounted and driven on before, but i noticed they were very wide when they were brand new. i'll measure them again when i mount them on my new wheels.)

calculations would say that the fuzions would have a new section width of 10.15". that's wider than most 245s on 8" wheels. even if they don't stretch, 9.75 is as wide as most 245s. i've noticed that every bit of the 225s tread is making contact with the road. would this be so with 245?

is there any REAL benefit to switching to 245?

sorry if this is long winded.

-demetrius

[Exar-Kun]

first, total contact patch area is a function of weight and inflation pressure.

You'll only be changin the shape of the contact patch and the overall surface area of the tire..

THat being said, I don't really see a benefit in doing the conversion from a 225/50 to a 245/45 due to those reasons, as well as the relative rarity and higher cost of a 245/45/16 versus the 225.

As far as the technical aspect of your question, you're better off looking at the MFR table of section width and tread width to determine how "square" a tire is...the closer the two numbers are, the more square (better) it is.

Take the ADVAN NEOVA and Sport, if you check, most if not all the sizes have identical section and tread widths, which is why (if you ask autocrossers, etc) they "measure wide" and you should really keep the rim width in the acceptable range to keep from causing distortion of the contact patch.

overall...stick with the 225/50 on a 8" rim. You're getting a good contact patch shape, gaining a bit better steering repsonse (due to effective shortening of the sidewall) and wider patch (due to slightly wide rim), in a cost effective tire size.

-Chet

[TrunkMonkey]

thanks a million chet.

-demetrius

[AZhitman]

Meech - You can also look at TireRack... they have full specs on each tire size, that will help as well.

Personally, I'd make that change, but for different reasons (more load rating, better heat dissipation, and more wheel protection).

[TrunkMonkey]

i still haven't made up my mind. if there's nothing to really gain, then i can't talk myself into spending the cash.

of course checking tire rack didn't help any. i can get a dirt cheap set of sumitomos for less than 300 shipped. it wouldn't hurt to have an extra set of tires around just to play with.

-demetrius