Tire Designations ?

Hello,

Read up on it, but still a bit confused over the tire designation numbers.

As an example, let's assume a 225/65 R17.

Everything stays the same in the designation, except for the /65 in my examples below.

So,

a. If it was a /60 or a /70, (rather than the /65) these would also fit just fine on a 17 inch rim. True ?

b. If so, then what actually also changes; is it the O.D. then of the tire, slightly ?

c. Is it usually O.K. to vary tires on a car by having /60 or /70 rather than perhaps what came with it, the /65 ?

What implications ?

Thanks, B.

Reply to
Bob
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225 = Distance between the sidewalls in MM when the tire is properly inflated ( ) Some folks say it's the tread width but it isn't.

Aspect Ratio - 65 is a percentage of the sidewall measurement. In this case it would be 139.5 MM This is the distance from the bead to the tread face.

R = Radial tire construction.

17 = inch size designation of the rim the tire fits. (all rims are actually built using metric measurements in this case 432 MM).

Changing the aspect ratio changes everything except the rim size.

225/65 R17 = diameter 28.5", Sidewall 5.76", Circumference 89.5", Revolutions/mile 707.5 Speedo reads 3% higher (approx. 2mph)

225/60 R17 = diameter 27.6", Sidewall 5.31", Circumference 86.8" Revolutions/mile 730.3

225/70 R17 = diameter 29.4", Sidewall 6.2", Circumference 92.3", Revolutions/mile 686.4 Speedo reads 3% lower (approx. 2mph)
Reply to
Steve W.

Hi,

Really good explanation.

Thank you very much.

BTW: Usually safe to go up or down by /5 ? /65 oem to /60, e.g. for new different tires

Bob

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Reply to
Bob

As long as you keep the speed difference in mind and the load and speed ratings are ok then yes.

Reply to
Steve W.

They should also say how long the material will last before failing. I recently found out that the material wears out before the tread. For low mile drivers the tread will be fine but the actual tire material is worn and the tires need replacing.

I now buy tires with low tread life ratings for this reason.

Reply to
Electric Comet

A while back, you could see 225/65HR17 . The speed designation. Your not suppose to interchange front back with different speed tires. Lower aspect tires probably don't matter as much as 70 series.

Obviously clearance must be achieved with selected sizes. People try increasing basic tire size if going to lower aspect. Like 235/60 or whatever.

Greg

Reply to
gregz

Speed ratings are still there, sometimes in the sizing sometimes after it. Keep in mind that those ratings are for sustained speed, not occasional excess.

Forgot to mention in the first answer. Sidewall height also has a BIG effect on ride quality and handling. The taller the sidewall the better the ride as there is more area to flex over bumps and road irregularities. However the shorter the sidewall is you get better handling due to the lack of that same flex.

Both have bearing depending on the vehicle you want the tires for.

Tires for your off roading 4X4 will want taller sidewalls for better flex and traction off road. Plus the taller tire gives more ground clearance. The taller sidewall also helps protect the drive train from sudden shocks as they absorb more abuse.

By the same token, the tires you put on your Ferrari will want shorter sidewalls to maximize the lower COG and give you predictable handling.

Reply to
Steve W.

g wrote: "A while back, you could see 225/65HR17 . The speed designation. Your not suppose to interchange front back with different speed tires."

If, hypothetically, you have T(118mph/190kmh) on one axle and H(130/210) rated tires on the other, what is the danger of that if you never exceed

70mph/112kmh in your lifetime of driving?
Reply to
thekmanrocks

No real danger.

Reply to
Steve W.

A higher speed on front will produce oversteer. Generally higher speed rating has stiffer sidewall. Tire pressure will also affect flex.

Greg

Reply to
gregz

There is no danger. The whole "speed rating" thing is a bunch of boy racer nonsense that means nothing to people driving on the highways in anything like a remotely sane manner. Today's tires have a huge safety factor as far as how fast you can safely drive on them. Also keep in mind that the speed ratings were based on tires loaded to at least 85% of their rated load. That's far higher loading then the perhaps 60 to 70% of max load users would typically see.

Reply to
Ashton Crusher

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