2nd Gen Non-Engine/Transmission tires

[Wyomingcowboy]

Hey guys, I recently got lucky and purchased a set of 4 17" wheels with some pretty good tires. I had 265/70/16's on there and these are 265/70/17's. My one and only spare is a 235/85/16. Anyway, I picked up something on the interstate and blew one of the 17's yesterday (of course it had to be one of the tires with the most tread ) and now I'm contemplating replacing the tire or waiting and buying new ones this fall. I would not like to have to buy a new 17" wheel for a spare, however. Is there a tire size that is the same circumference for a 16 AND a 17? I have stood the two side by side and noticed very little difference but didn't actually measure to see what exactly it is. Anyone else run into this problem? I like the idea of having two sets of tires/wheels; one for knobby mud tires when I go hunting in the fall and have an easy swap back to more economical hwy tires the rest of the time.

 

[kenny61]

Hey guys, I recently got lucky and purchased a set of 4 17" wheels with some pretty good tires. I had 265/70/16's on there and these are 265/70/17's. My one and only spare is a 235/85/16. Anyway, I picked up something on the interstate and blew one of the 17's yesterday (of course it had to be one of the tires with the most tread ) and now I'm contemplating replacing the tire or waiting and buying new ones this fall. I would not like to have to buy a new 17" wheel for a spare, however. Is there a tire size that is the same circumference for a 16 AND a 17? I have stood the two side by side and noticed very little difference but didn't actually measure to see what exactly it is. Anyone else run into this problem? I like the idea of having two sets of tires/wheels; one for knobby mud tires when I go hunting in the fall and have an easy swap back to more economical hwy tires the rest of the time.

It will take a little research on your part but most of the tire manufacturer websites will list the circumfrence and you can match them up

 

[rjrkihap]

Hey Cowboy,

The 265/70r17 is suppose to be the same size as the 265/75r15. Also, the 235/85/r16 is also suppose to be the same size as the 265/70r17. Of course there will always be a slight difference between manufactures. Go to your tire shop and have them pull the 17 and 16 down and compare for yourself.

Good luck

Ron

 

[Batphreak]

This might help solve your circumference issue. Here is the formula that all those little numbers mean:

265 (Tread width in milimeters) / 70 (Aspect ratio of tread width to sidewall height) / r17 (Wheel diameter in inches)

So, to get that to a tire OD (and circumference if you wish) you would do this:
I assume you want inches so convert 265 to inches: 265/25. 4 = 10. 4331"
70 is your aspect ratio so the sidewall is: 10. 4331 * 0. 7 = 7. 30315"
Your OD is: 17 + 2*7. 30315 = 31. 607"
To get a circumference just use pi: 31. 607*3. 14 = 99. 246"

 

[Allnew2Me]

Check out this site for a tire calculator. You can enter your stock size and the one you are considering and it will show you all the dimensions, with or without the wheel. It's fun to play with.



Wheel / tire size calculator / comparer - RIMS-N-TIRES

 

[OldRetiredAFGuy]

Try this one also:



Tire Size Calculator - tire & wheel plus sizing



I like it because it gives you revs/mile, circumference, overall diameter, and the % delta between your original tire and the potential new tire size.

 

[Road Dog]

If you look up the tire specs at some place like Tire Rack - Your performance experts for tires and wheels there's a tire diameter listed. Generally an xxx/70R17 has the same diameter as an xxx/75R16.

And it just happens that:
265/70R17 = 265/75R16 = 235/85R16= 31. 8"

Running a different diameter tire is fine on the front but not the back if it has a limited slip diff.

 

[SSolderitch]

REVS per mile is more useful, I think tire rack shows that so you can compare manufactures. you will see the slight difference for the same size.

 

[Batphreak]

Why rely on Tirerack and such. Revs per mile is very easy to calc. once you know diameter.

Circumference(in inches) = Dia(in inches) * 3. 14

Revs per mile = Circumference(in inches) / (5,280*(12))

I just prefer to know the calc myself.

 

[fest3er]

Why rely on Tirerack and such. Revs per mile is very easy to calc. once you know diameter.



Circumference(in inches) = Dia(in inches) * 3. 14



Revs per mile = Circumference(in inches) / (5,280*(12))



I just prefer to know the calc myself.

The main reason you want the mfr's revs per mile is because the loaded radius of any tire is always smaller than the unladen radius. For example, you can have two tires with identical unloaded diameters of 31", but one has a loaded radius of 15" and the other has a loaded radius of 14". Translating again, the tire with the 14" loaded radius will turn about 385 degrees for every full turn of the 15" radius tire. With an open differential, this won't much matter. But with a clutched diff, that 7% difference is made up by the clutches slipping.



If you find two tires with almost identical loaded radii, you can probably make up the difference with air pressure.



Of course, this all only matters if one is anal-retentive about things like wear, handling and safety margins; the happy-go-lucky driver is happy when the engine starts and luckily goes to her destination. Most drivers fall somewhere in the middle.

 

[Batphreak]

The tire manuacturer isn't the one responsible for loaded radius of the tire. All the tire manufacturer is responsible for is the maximum pressure capability and the maximum load capability at that pressure. The vehicle manufacturer is the one responsible for putting the specs on recommended tire inflation and load rating at that pressure. With heavy duty tires that recommended pressure is generally the max rated by the tire company because the vehicle is designed to work the tires at or near their limit.