# I don't understand the tire thing!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 82Jimmy, Jun 25, 2000.

1. ### 82Jimmy1/2 ton status

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I don\'t understand the tire thing!

What the hell... I can't understand all the numbers what does ?x?x? mean? I know it measures something but don't understand what it measures. I mean some are easy to see the size but some are 3 digits and I don't get it. Probaly the dumbest think anyone has ever ask.

Bigger is Better
Cameron Burnett
82 Jimmy

2. ### UdyRegistered Member

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Re: I don\'t understand the tire thing!

31 (tire dia) X 10.5 (tire width) X 15 (rim diameter) (in inches). 225 75LT15 is a metric designation. 225 is the width (in millimeters). 75 is the "aspect ratio" (sidewall height percentage of the width, or 75% of 225). 15 is still the rim diameter in inches (don't know why, everything else is in mm). To convert from mm to in. divide mm by 25.4. Also note, You'll have to multiply the "aspect ratio" by 2 (after converting from percentage to true dimension) and add in the rim diameter to get the tire diameter.

3. ### bigjbear1 ton statusStaff MemberModerator

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Re: I don\'t understand the tire thing!

If its a flotation tire say 35x12.50xR15, then 35 is the hight in inches, 12.50 is the cross section (not the tread with) in inches, "R" is radial, 15 is the rim diameter in inches. If it look like this LT265/70R16, then "LT" means lite truck, 265 is the cross section in mm, 70 is the aspect ratio, or how tall the tire is in relation to its with, "R"=radial, 16=rim in inches. Here is an old one that is not used much anymore L78-15LT, "L" is the tire hight, about 30" (each letter is a different hight), "78" has to do with the cross section, 15=rim, LT= l.t., The last sizing system that I know of is only used for bias ply tires. It looks like this 18/39.50-15, 18 is the cross section (rember, not tread with) in inches, 39.50 is height in inches, 15 is the rim size in inches. About the only company I know of that uses the last system is Interco, and they only use it on some sizes. If you have a tire size that you want to know about, write back, Jim.

BigJBear '80 GMC

4. ### bigjbear1 ton statusStaff MemberModerator

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Re: I don\'t understand the tire thing!

Good catch Udy, I forgot the rest of the Metric formula. Jim.

BigJBear '80 GMC

5. ### 82Jimmy1/2 ton status

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Re: I don\'t understand the tire thing!

I still don't understand the last part. The rim size. All it says is 16.5 so what would fit that? Like a 16.5x what? Thanks

Bigger is Better
Cameron Burnett
82 Jimmy

6. ### MudFrog1/2 ton status

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Re: I don\'t understand the tire thing!

Why don't you tell us what kind of tire you are looking at and also give us the dimensions of the tire so we can explain based on your tire.

7. ### Scoobydoo1/2 ton status

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Re: I don\'t understand the tire thing!

The 16.5 is the rim size, also common are a 15 or a 16. This is the rim's diameter and has nothing to do with the width. Take the example given above with the LT265/70R16 the LT = Light Truck, and the R = Radial
Take the 265 divided by 25.4 = 10.43" this is your tire width in inches.
Now you take your second number in this case it is 70 so that is 70% of the width multiply the width 10.43 times 70% = 7.3" this is the tire size in inches from the rim to the outer edge of the tire. Since you have a top and bottom you must multiply this times 2. So 7.3" x 2 = 14.6
Now you have to add the size of the rim which in this case is 16". So 16 + 14.6 = 30.6". so this particular tire is a light truck radial that is 10.43" wide and is 30.6" tall and fits a 16" wheel.
It is a little confusing at first but one you know how to do it you will find that USUALLY the metric measurements are much more accurate than the inches for example you grab 5 different brands of 35X12.5 tires and set them next to each other you will find about a 2" difference between them, however if you set the same 5 brands of 315/75 (the metric equivalent) tires beside each other there will only be about 1/2" difference.

8. ### bigjbear1 ton statusStaff MemberModerator

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Re: I don\'t understand the tire thing!

16.5 is the rims diameter. You can use the tire's cross section to decide what rim with you want. A wider rim will make the tire wider and shorter. A narrow rim will make the tire taller and narrower. The tire store can give you the range of rims a tire will fit on. If you have a tire in mind let me know the size, then I can give you more info. Jim.

BigJBear '80 GMC

9. ### 82Jimmy1/2 ton status

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Re: I don\'t understand the tire thing!

Alright I still don't get it...Light truck, will it be okay for a k5? Also what the hell does LT295/75R16C BF GOODRICH ALL-TERR T/A KO mean? I don't know what size they are...

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<font color=red>Cameron</font color=red> <font color=green>Burnett</font color=green>

10. ### 6.2Blazer1/2 ton status

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Re: I don\'t understand the tire thing!

They should be about 11.6" wide and 33.4" tall, and fit on a 16" rim. "LT" or Light Truck states that it if for a pickup or SUV and has a higher load capacity than a "P" (passenger car) rating. Don't let the "light truck" fool you, this designation is not talking about Suzuki's. Light trucks are classified as anything under around a 10,000 lb GVW (or something like that), which means a 1 ton dually is considered an "light truck".

11. ### Blazer791/2 ton status

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Re: I don\'t understand the tire thing!

Just look at the important numbers:

295mm wide (sidewall to sidewall)
75% (of 295mm) sidewall height
16" wheels

The total height of the tire is 16"+(295x0.75÷25.4)+(295x0.75÷25.4)
Wheel+two sidewalls which are 75% of the 295 width, converted to inches.

So if you're into math, you can simplify that to:
16"+(295x0.75÷25.4x2)=33.42" aprox

It's a BF Goddrich tire, the All Terrain model, KO is the new version of the All Terrain.

I really don't care much if it's a tire for Light truck or not. It's more important to choose the right thread and the right brand. Some common sense helps on this. I see many people recommending the BFG ATs for their Blazers, I assume it's the right tire for my Blazer.

If you still don't get it, just ask. I'll try to explain it better.

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