Does a 1% difference in profile% matter?

FX-MAN · Nov 12, 2005

I did some math based on stock tires, and got tire sizes that may work for the stock rims, I am just curious what % difference in the profile aspect ratio is acceptable? How many % points can you push the profile before the car will show the wrong mph, and have issues?

Stock = 215/45R 18

Based on the math, it looks like 225 is out for 17 and 18 (I get like 225/48.64)
225/54.28 18 (225/55R close enough?)
235/41.7R 18 (so 235/40R)
235/46.57 17 (so 235/45 is close but is that not close enough?)

Falango · Nov 12, 2005

http://www.miata.net/garage/tirecalc.html

Tells you exactly how far off your speedo is depending on the size of wheel/tire you go with.

FX-MAN · Nov 12, 2005

That is REALLY helpful thanks!

What would a Mazda mechanic tell you would be the most your diameter should change? I have a list of 12 tire sizes that end up with close diameters (the most off they get is 9mm in total diameter including the rim)

I am guessing that you could actually burn through 4.5mm of tread over the life of a tire, so 9mm total difference in diameter can't be that bad. Is there some sort of standard rule though?

traitorhound · Nov 12, 2005

3% is the general rule of thumb when changing tire sizes

Falango · Nov 12, 2005

The best would be to just stick with stock. Why would you want to go with a different profile anyway?

FX-MAN · Nov 12, 2005

Because this car can't handle the snow at all. I traded my RX-8 for this car so that I could still drive when it snowed. I want 16" or 17" steel rims, and snow tires.

I have had my Mazdaspeed6 for 8 days, took it to the mountains to snowboard, and almost got stuck on the top of the mountain. Stock tires just have ZERO grip in snow, even with AWD it's worthless in the snow on the stock tires. I was almost level and just COULDN'T slow down or stop. It was terrifying, and with AWD I actually expected this car to do much better in the snow (it says it has "All season tires", but I guess that means nothing with 18" low profile).

Falango · Nov 12, 2005

Ah ok, following ya now. I would expect it to perform better in winter conditions. Go narrower obviously so the tire will bite better.

FX-MAN · Nov 12, 2005

Narrower? Wouldn't a wider tire have more traction in the snow?

ForceFed · Nov 12, 2005

FX-MAN said:
Narrower? Wouldn't a wider tire have more traction in the snow?

No its the cookie cutter effect..thinner tire will cut through the snow while the wider ones want to ride on top of it.

FX-MAN · Nov 12, 2005

Good to know, I was thinking more rubber hitting the ice would be better (like the same reason you don't want low profile tires, because less rubber hits the road), but I guess it's not the same when you are talking width Vs. length on the road?... I can't find a much narrower tire than 215 to go with 18s or 17s which will work with the current diameter. So far I have a couple options for decent snow tires. I am looking to get a Dunlop SP Winter Sport M3 (they seem to have best snow performance for 16"+ rims)

IF I can get 16" steels past the huge breaks, I will be picking up 205/60R 16s then. Otherwise, I'll have to go with 17" and 215/50R 17s (I'll only lose 4.1mm in diameter, I shouldn't even notice that on the speedometer)

1st Gen · Nov 12, 2005

Wide tires are good for dry pavement. On snow, you want the most psi you can get. That means narrow tires with an aggressive tread, and all the same size. You can get sawdust retreads if you want but, I wouldnt drive fast in them.

Da 6 · Nov 12, 2005

funny since my 6i cuts thru snow like a champ on mis***lins 17's stock. Isn't the tire choice summer tires?

1st Gen · Nov 12, 2005

If the snow is real cold, then any tire should do okay. It depends on the conditions of course. As a general rule, more pounds per square inch is good.

Falango · Nov 12, 2005

Exactly what Forcefed said, a narrower tire wants to cut through the snow, while a wider tire wants to ride on top. The higher psi you get on the narrower tire will allow the tire to "slice" through the snow better. Sorry I had to throw that in there, lol.

dark86 · Nov 13, 2005

would 195 and 205 make a big difference?

Falango · Nov 13, 2005

Not a huge difference, it's only a 10mm, or 1cm difference.

FX-MAN · Nov 13, 2005

The stocks are 215, is that wide for the snow?

crossbow · Nov 14, 2005

The tire compound is more important then the width of the tread.

If you have really thin tires with a crappy cheap tire compound, its going to suck compared to a wide tire with a well designed tread/compound.

Da 6 · Nov 14, 2005

what about the ZR rated Vs the H rated arguement?

crossbow · Nov 14, 2005

If your utilizing Z rated tires in the snow/slush/ice, you've got other problems

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Does a 1% difference in profile% matter?

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