Does a 1% difference in profile% matter?

[FX-MAN]

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]

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]

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]

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

[Falango]

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

[FX-MAN]

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]

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]

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

[ForceFed]

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]

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]

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 wouldn’t drive fast in them.

[Da 6]

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

[1st Gen]

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]

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]

would 195 and 205 make a big difference?

[Falango]

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

[FX-MAN]

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

[crossbow]

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]

what about the ZR rated Vs the H rated arguement?

[crossbow]

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

[ChopstickHero]

yeah, slightly thinner tire is ok. if the stock is 215, then try looking for a 205. of course, it won't make too much of a difference. as long as the tread is aggressive and deep, you will get more grip in the snow.

does the mazdaspeed6 have a controllable differential to change the power balance of the front and rear? IIRC not by the user. the car selects it's modes on it's own.

[FX-MAN]

No one seems to make 17s other than Mazda, and they are about the price of decent alloys, so I got some Hyperblack Motegei 17x7s and Dunlop Wintersport M3 215/50R 17s (which from researching look like the highest performance and grip in the snow for 17" wheels). The difference in the tread width and height over stock is nutz, and the rubber is much softer.

My break clearance on the 17s in the front is INSANE... I was sure it was scraping, but the guys at the shop ran it through their clearance tests and said it looks great, I have driven it for about 100K today and no scraping. So we are looking good.

The funny thing, is that these wheels are much lighter than the stock 18s, so the car feels faster. The ride is not as smooth, but I don't care, these things are going to do GREAT in the snow.

[SNike05]

B(it says it has "All season tires", but I guess that means nothing with 18" low profile).

yeah all these cars that are coming out now with large rims and 4 season low profile tires are really more for looks then 4 season. They just put 4 season on the tire to make people happy. The Protege5 oem tires are the perfect example they had to be the shittiest tire that has ever existed. Even with the slightest water on the road the tire would hydroplane and don't even think about taking them on the snow for me it was a nightmare my first winter.

[Da 6]

yeah all these cars that are coming out now with large rims and 4 season low profile tires are really more for looks then 4 season. They just put 4 season on the tire to make people happy. The Protege5 oem tires are the perfect example they had to be the shittiest tire that has ever existed. Even with the slightest water on the road the tire would hydroplane and don't even think about taking them on the snow for me it was a nightmare my first winter.Reminds me of my neon...at 5 mph cruise I hrdroplaned and slid into a curb. No accel in the turn.

[Mikey444]

I have 205/65R15's on steelies for the winter, works well for me.

[Da 6]

I have 225 replacing the 245. As stated as long as you have a decent non race compound and serious tread you should be better off than stock. If you really wanna get crazy go blizaks or perelli scorpions.