Tire sizes

[Clodfobble]

We need to replace the back tires on the minivan ASAP. The two front tires are newer, and do not need replacing. Our mechanic is a good guy and he told me to save a lot of money by ordering the tires online and having them shipped to his location, rather than buy them from him. So I've been looking at the sizes.

The sticker on the driver side door lists three acceptable tire sizes, one of which is 215/60-16. The actual tires currently on the vehicle, however, do not match this. They are 205/60-16.

The right thing to do would be to get two more of the wrong size so they match the front tires, right? Because having diferent-sized front and rear tires would be worse than having all four slightly off from the manufacturer's specs, right?

[sweetwater]

If the current front tires are one of the three acceptable sizes for the van, then I'd get 2 more of the same size & type (don't mix radials and non-radials, all that). I'd probably stick with the same brand, too, but that's because I'm a bit Monk-ish and it would bother me tremendously to have different brands scattered around the vehicle after the first rotation. Would the tire guy be able to help you?

[classicman]

yeh - don't have different sized tires :

[footfootfoot]

It is almost always best to have four matching tires. The 205s are slightly smaller diameter. should be ok, and cheaper than 4 new ones.

[jinx]

Yeah, go with the same size as the fronts. If you were going to have a problem with a non-recommended size it would be with the fronts.

[Trilby]

Originally Posted by footfootfoot

It is almost always best to have four matching tires.

I know.

When you have mis-matched tires it's easier for the police to recon your car.

[Urbane Guerrilla]

That first three-digit number is the width of the tread in millimeters. It's quite okay if the difference between tread widths is only 10mm. Doesn't amount to anything at the rims.

[lumberjim]

tire size:

205 = mm acroos the surface patch
60 = 60% of the 205# and represents side wall height
16 = inside tire diameter or wheel diameter.

so, 215-205 = 10mm, 10mmx 60% = 6mm diameter diff...no big deal


also, differing tire height only really matters on an AWD vehicle

[footfootfoot]

Right. Not the Dia. I always get that wrong.

[Clodfobble]

Thanks everyone. I ordered the smaller size to match what is currently on the car... and five minutes later a sales rep called me to make sure I really, really wanted to order tires that were so completely not to the manufacturer's specifications. (Aside from the 205-215 disparity between the tires and the wheels, it turns out we actually have non-standard wheels on the vehicle in the first place.) I assured him I did. With any luck they'll be here before the weekend.

[Beestie]

Originally Posted by lumberjim

Definitive, complete, reliable information.

Good stuff.

[tw]

Originally Posted by Clodfobble

I ordered the smaller size to match what is currently on the car... and five minutes later a sales rep called me to make sure I really, really wanted to order tires that were so completely not to the manufacturer's specifications.

Manufacturers (the engineers) would define what size tire the vehicle needed. Then the manufacturer would sell the car with a tire size smaller. Undersized tires would wear much faster. Then you bought properly sized tires. I thought these cost control games had terminated decades ago.

[xoxoxoBruce]

Passenger Tire Sidewall Information
Example: P215/65R15 89H
“P” means this is a Passenger car tire as opposed to a light truck tire. P-metric is the U.S. version of a metric tire-sizing system.

“215” is the section width of the tire in millimeters from sidewall to sidewall when fitted on the recommended rim.

“65” is the aspect ratio of the tire, the ratio of height to width. This particular tire's height is 65% of its width.

“R” indicates that this tire is built with Radial construction. Other types of construction are indicated by the letter “B” for Belted Bias construction, and the letter "D" for Diagonal Bias construction.

“15” is the diameter of the wheel in inches.

“89” is the load index. Different numbers correspond to different maximum loads. This particular tire has an industry-standard maximum load of 1,279 lbs.

“H” is the speed rating of the tire. This particular tire has an industry-standard maximum service speed of 130 mph. Some tires use an older European system that features the speed rating in the size description of the tire.

The letters “DOT” certify compliance with all applicable safety standards established by the U.S. Department of Transportation (DOT). Each tire also features a tire identification number consisting of up to 11 numbers and letters.

The sidewall also indicates the type of cord and number of plies used in the sidewall and under the tread.

Light Truck Tire Sidewall Information
Most of the markings on a light truck tire sidewall have the same meaning as those on passenger tire sidewalls. The following additional markings apply only to light truck tires.

“LT235/85R16” is the size designation for a metric light truck tire.

“LT” stands for Light Truck.

“LOAD RANGE D” identifies the load and inflation limits of the tire.

“MAX LOAD SINGLE 2623 LBS AT 65 PSI COLD” indicates the maximum load rating of the tire and corresponding minimum cold inflation pressure when used in a dual configuration.

TIRE GRADE
Tire Grades: Uniform Tire Quality Grading System or UTQG
The Department of Transportation requires tire manufacturers to grade passenger car tires based on three performance factors: treadwear, traction and temperature resistance.

Treadwear
The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200 would wear twice as long as one graded 100. Your actual tire mileage depends upon the conditions of use and may vary due to driving habits, service practices, differences in road characteristics and climate.

More Than 100 - Better
100 - Baseline
Less Than 100 - Poorer
Note: Treadwear grades are valid only for comparisons within a manufacturer's product line. They are not valid for comparisons between manufacturers.


Traction
Traction grades represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The traction grade is based upon "straight ahead" braking tests. It does not indicate cornering ability.

A - Best
B - Intermediate
C - Acceptable
Temperature
The temperature grade represents the tire's resistance to the generation of heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperatures can cause the materials of the tire to degenerate and reduce the life of the tire. Excessive temperatures can lead to tire failure. Federal law requires that all tires meet the minimal requirement of Grade C.

A - Best.
B - Intermediate
C - Acceptable
LOAD INDEX & SPEED RATING
While there is no industry-wide definition of Load Index, truck tires are frequently marked with a ply rating and equivalent Load Range. These markings are used to identify the load and inflation limits of that particular tire when used in a specific type of service.

Many tires are available in speed-rated versions to match the speed capabilities of the world’s fastest cars. Generally, it is recommended that a speed-rated tire be replaced with a tire having an equivalent or greater speed rating.

However, if you never drive at speeds near the limits of your speed rated tires, you may choose to replace them with tires having a lesser top speed rating.

In situations where tires having different top speed ratings are mixed on a vehicle, the maximum speed certification is limited to the top speed certification of the tire with the lowest speed rating.

Speed ratings do not indicate how well a tire handles or corners. They certify the tire’s ability to withstand high speed.