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post #1 of 12 (permalink) Old 11-16-2009, 09:34 PM Thread Starter
 
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Tire size compatibility

so my car uses P215/70/R15 tires, would a P225/75/R15 fit without issues. As I understand it, that means it has 10 more mm of "width", and is 5% larger from rim to tread.

I would imagine this would change my speedo to read faster than I'm really going?
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post #2 of 12 (permalink) Old 11-16-2009, 09:37 PM
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It would work, but you would probably be better off going with 225/65/15. It will affect your speedometer readings to a lesser degree. If you went with 225/75 it would cause your speedometer to read slower than your actual speed since your wheels will be larger in diameter.

Whenever you increase width, you need to decrease the sidewall height ratio to maintain a certain diameter.

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post #3 of 12 (permalink) Old 11-17-2009, 06:39 AM Thread Starter
 
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right, slower not faster....

I'm just asking cause I was trying to find some winter tires, and it seems finding 225/70/15 isn't so easy, but there are some other sizes around.

I was also looking at CTC for Nordic tires, and it was a $2 difference between my size and the 75's.... I thought larger tires couldn't hurt in the snow.

Anyway those are too expensive at $102-$105 each tire......screw that.
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post #4 of 12 (permalink) Old 11-17-2009, 07:30 AM
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i ran a 275/60/r15 on my stock fan blades on the rear of the car without issue for 3 years
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post #5 of 12 (permalink) Old 11-17-2009, 08:10 AM
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Also - a narrower tire will help you more in snow than a wider tire.

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post #6 of 12 (permalink) Old 11-17-2009, 08:32 AM
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225/75R15 is like a small truck tire. Alittle too tall for a car in my opinion. I think the best all around size for the fans would be a 235/60R15. The seem to fit the styling of the car alittle better being wider. I also think that are just over 26 inch tall or right on the money at 26inc. Your stock size I beleive is almost 27 but the speedmeter would be hardly noticeable.

Just remember, the 215=section width in mm, the 70= percentage of sidewall according to section width.

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post #7 of 12 (permalink) Old 11-17-2009, 05:15 PM Thread Starter
 
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First, I should mention I was looking for second hand snows, not buying new ones due to price.

Secondly, I don't quite understand why a wider tire would need to be shorter(Rim to tread) to keep the speedo the same....wider shouldn't affect it.

I also have to ask, why a narrow tire is better in snow, I would think more surface area = better traction...... How does narrow help?

I would actually like to see some of the tire sizes to get an idea of how it would look. If I get snows, I'll only be getting them for the back, it may help handling having them on the front, but money is an issue.

new tires next spring are all around.
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post #8 of 12 (permalink) Old 11-17-2009, 06:44 PM
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A narrower tire cuts through the slop better. Wide tires tend to 'float' over snow and slush more. With a wider tire the vehicle weight it distributed across a larger area and thus less pressure between the tire surface and road surface exists (pounds/sq. in). When the botttom number gets bigger the total argument gets smaller (pressure=force/area). More importantly though, the front tires need to be pushed through heavy snow/slush. Think about having to push a board through snow, what would be easier a 1 inch wide board or a 4 inch wide board? In there lies your answer. For snow tires i would get either 215/70/15s or 205/75/15s.

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post #9 of 12 (permalink) Old 11-17-2009, 07:05 PM
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To maintain the proper speedometer calibration when not changing gears, the tire circumference needs to be the same. If you increase the width of the tire, leaving the sidewall height ratio the same, with the same rim size you will have a larger circumference (rim size + ( 2 x sidewall ratio x tread width). If you increase any one of the factors, you will increase the circumference. You need to compensate by decreasing one of the other factors; either rim size or height ratio.

A narrow tire is better in snow because of this:

Take a 3,800 lb T-bird with 60% front and 40% rear weight distribution. That means 2,280 lbs on the front wheels and 1,520 lbs on the rear, translating to 1,140 lbs on either of the front wheels and 760 lbs on either of the rear wheels. If your wheels 215 mm wide, that's a weight distribution of roughly 53 pounds per cm of width on the front and 35 pounds per cm of width in the rear. If you want good grip on snow, the snow needs to be compacted as tightly possible and the best way to compact snow tight is to put as much compacting force on it as possible over a given surface area. The best way to do this, therefore, is to get a narrower tire.

Think about snow shoes - they are large and flat. They distribute the weight over a large surface area and the person walking on them "floats" on top of the snow. Regular shoes dig in far and deep.

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post #10 of 12 (permalink) Old 11-17-2009, 07:27 PM Thread Starter
 
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Quote:
Originally Posted by theterminator93 View Post
To maintain the proper speedometer calibration when not changing gears, the tire circumference needs to be the same. If you increase the width of the tire, leaving the sidewall height ratio the same, with the same rim size you will have a larger circumference (rim size + ( 2 x sidewall ratio x tread width). If you increase any one of the factors, you will increase the circumference. You need to compensate by decreasing one of the other factors; either rim size or height ratio.

A narrow tire is better in snow because of this:

Take a 3,800 lb T-bird with 60% front and 40% rear weight distribution. That means 2,280 lbs on the front wheels and 1,520 lbs on the rear, translating to 1,140 lbs on either of the front wheels and 760 lbs on either of the rear wheels. If your wheels 215 mm wide, that's a weight distribution of roughly 53 pounds per cm of width on the front and 35 pounds per cm of width in the rear. If you want good grip on snow, the snow needs to be compacted as tightly possible and the best way to compact snow tight is to put as much compacting force on it as possible over a given surface area. The best way to do this, therefore, is to get a narrower tire.

Think about snow shoes - they are large and flat. They distribute the weight over a large surface area and the person walking on them "floats" on top of the snow. Regular shoes dig in far and deep.
Quote:
Originally Posted by coolhandzep View Post
A narrower tire cuts through the slop better. Wide tires tend to 'float' over snow and slush more. With a wider tire the vehicle weight it distributed across a larger area and thus less pressure between the tire surface and road surface exists (pounds/sq. in). When the botttom number gets bigger the total argument gets smaller (pressure=force/area). More importantly though, the front tires need to be pushed through heavy snow/slush. Think about having to push a board through snow, what would be easier a 1 inch wide board or a 4 inch wide board? In there lies your answer. For snow tires i would get either 215/70/15s or 205/75/15s.
that all makes perfect sense now. I really wasn't thinking of the board analogy, but the snow shoe analogy I was, just backwards I guess lol.

I might see if I can find some 205's, but I didn't want to buy a whole set.
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post #11 of 12 (permalink) Old 11-17-2009, 07:36 PM
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Unfortunately, the best way is the expensive way, try to get all four. Being able to go forward or reverse is great, but the ability to turn and stop is even better. The fronts steer and do most of the braking, this is something to think about.

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post #12 of 12 (permalink) Old 11-18-2009, 06:53 AM Thread Starter
 
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oh I have trust me. thats the problem with RWD.... at least a FWD car only needs 2 to cover everything lol.

I gotta see what I can find and afford..... I may not even be able to get a set at all.

I did OK last year without them, but my tires now are starting to show signs of wear and age.
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