So, I went to Discount Tire and ordered my tires that I will have installed on the stock wheels for winter use. However, the size of the tires I picked were not in stock. Also, they didn't have any available TPMS sensors, so those are also on order. I'll have to go back Saturday to get everything installed.

Now my dilemma.

The stock tire size for my car is 235/50/18, however they do not make the Yokohama AVID TRZ tires in that size. Therefore, I thought I'd go with 225/50/18 instead. With this other tire size my speedo would be off 1.4% too fast, reading 60 MPH when I'm actually going 59.1 MPH. The sidewall would be 0.2 inches shorter, the diameter would be 0.4 inches smaller, and revs per miles would go from 740 to 751.

But since the 225/50/18 wasn't in stock he set me up with 225/55/18's. With these tires the difference from stock is as follows. My speedo would be off 1.8% too slow, reading 60 MPH when I'm actually going 61.1 MPH. The sidewall would be 0.3 inches taller, the diameter would be 0.4 inches larger, and revs per miles would go from 740 to 727.

What tire size should I go with, 225/50/18 or 225/55/18? The salesman mentioned that the smaller tire could put stress on the transmission and it's not a size that my car should use, but the larger tire is fine. Is this true?? I personally wouldn't think it would matter at all as long as the change isn't drastic. With both tires there's going to be a difference from stock, I'm just curious what you all would think about this. I need to call them today to make a change before they place the order.

Thanks all!

 

I actually don't know what's better, unfortunately.

I will comment that the 235/50-18 doesn't seem to have many choices compared to some 245 and 255 widths. This tire size has been around for awhile (the Mercury Marauder used it as well). I hope we see more choices in the future.

 

Yeah. On Discount Tire's website they actually do have the 225/55/18 as an optional tire choice. Therefore, I guess that makes it so that that particular tire would be a better option. I hope they can give me the online tire price too!

 

Why not try and go with a 245/45? I know it's not much of a differance but I wouldn't want to go with a skinnier tire.

 

i agree ^^^^ if anything i would want to go with a wider shorter tire.

 

It really isn't too big of a difference either way based on the image/calculations from this link...
http://www.miata.net/garage/tirecalc.html

 

Aren't these for winter/snow use? Get the 225/55. It'll be fine, since you don't need 'em for any performance reasons. The skinnier tire does better in snow.

 

you are correct. just reread that theyre for winter. since thats the case if the tires you have arent beat to hell id have them put back on the stock rims and pick up a real set on summer tires.

 

I wish I could, but these tires really sucked during last year's winter months. They're fine for summer driving though. Thanks all for your input. I've made my decision and will be going with the 225/55/18's.

 

Sorry I got here late for this discussion. I think you made the correct decision. The narrower 225.55s should work better in the snow.

Your tire salesman is either an idiot or has been listening to too many war stories. A small tire size difference will not "strain" the trannie.
I have heard numerous absurd stories over the years from tire salesmen, who IMO typically know about as much about tires as car salesmen know about cars, i.e. 0.00% of nothing.

One told me my ABS wouldn't work if I went up one size, and actually refused to sell me tires "on principle."
I was plus-one-ing before the term came into vogue, I think I know what I'm doing most of the time.
If not I guess my ABS is toast! Whatever.

Some moron at the local Discount Tire told me, when I was looking at alloy wheels, that my stock steels must weigh 30 or 35 pounds or more.
That is utter fantasy, they come in somewhere around 20-22. Standard GM 16" steelies weigh about 24, I have four of them sitting in my garage, and they're bigger than mine.

I was researching tires for these cars, and discovered what looks like new (to me anyway) Continental ExtremeContact DWS which do very well in Tire Rack winter and HP all-season tests. They appear to be too new for any driver feedback yet.
They come in 235.50.18 and at this point that's what I'd like to put on the Super I'm negotiating.

Also the 235 are only marginally larger (0.3" diameter) than the 225.50.18 stock rear tires on the GXP. These tires also come in 255.45.18 and 245.55.18, both of which are within small margins (0.1" larger or 0.2" smaller) of the OE tires. I would have no problem using such small margin differences.
They also appear to be symmetrical, not unidirection, IMO a big advantage on the GXP.

 

Thanks for the tips. They're on and so far they're pretty nice. A lot less road noise. It snowed this morning and they seemed good. It sucks to have to put the stock wheels back on though. Now I just have an ordinary SS. It's sad.