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265/70r17 Vs 265/60r17 Tires

pm26

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pm26 Senior Enthusiast

pm26

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If I replace my stock 265/70R17 tires with 265/60R17 tires, what will be the approximate reduction in the tire circumference? The goal is to effectively achieve 4.10 gearing from 3.73 gears that I have. I need to reduce the tire circumference by about 10%. Unfortunately tires in this size are not available in too many low profiles for SUV/truck applications.

 

How do I correct for the speedometer error? By reprogramming the ECU? Would a dealer do this for any size tire (within reason of course).

pm26 Senior Enthusiast

pm26

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Never mind, I think I can figure this out.

 

The original tire aspect ratio is 0.70 so that height/width of the tire is 0.70

For the new tire this number is 0.6

 

Because the width is the same, the reduction in tire sidewall height is 14.3 percent

 

The radius of the rim is 8.5 inches, or 216 mm.

 

The height of the 265/70R17 tire sidewall is x/265 =0.7, or x= 186mm

 

The overall radius of the rim + original tire sidewall is 216 + 186 = 402mm

 

The height of the 265/60R17 tire sidewall is x/265 = 0.6, or x = 159 mm

 

The overall radius of the rim + new tire sidewall is 216 + 159 = 375 mm

 

The old tire circumference is 2*PI*r = 2*3.14*402 =2525 mm

 

The new tire circumference is 2*3.14*375 = 2355 mm

 

The percentage of the old tire circumference in the new tire is 2355/2525 *100 =93.3 %

 

Therefore, the reduction in the tire circumference is 6.7%.

 

The effective new gear ratio is 3.73 *106.7% = 3.98 or approximately 4.00

 

So, by replacing the 265/70R17 tires with 265/60R17 tires, I will achieve the equivalent of 4.00 gear ratio, which is pretty close to 4.10.

 

This is a simple and easily reversible mod when doing some heavy trailering. Kumho offers an SUV tire in this size for about $ 100/piece.

 

The speedometer will read 6.7% too high, so at previously indicated 75 MPH it will read 80 MPH. Nothing too drastic.

pm26 Senior Enthusiast

pm26

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Thanks, I ran the tire sizes through the calculator and came up with speedometer reading 6.6% too high. My tedious calculations show 6.7% after rounding it off. So my numbers are correct. :crackup:

pm26 Senior Enthusiast

pm26

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It may take some time to adjust to the 'elephant riding a tricycle' look. JMHO.

 

LOL, I do not think it would look that bad. HD 2500 and 3500 series actually came with 245/80R16 tires which are smaller in height than my stock tires.

arzinet Enthusiast

arzinet

Posted
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Aside from how odd that might look, I don't think it would be a safe change. You also need to consider the load rating of the new tires, and from what I can tell, those 265/60R17s are going to have significantly less load capacity than the 265/70s.

 

IMO, if you want to change the gearing, then you should just bite the bullet and change the gearing.

pm26 Senior Enthusiast

pm26

Posted
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Aside from how odd that might look, I don't think it would be a safe change. You also need to consider the load rating of the new tires, and from what I can tell, those 265/60R17s are going to have significantly less load capacity than the 265/70s.

 

IMO, if you want to change the gearing, then you should just bite the bullet and change the gearing.

 

The idea was that if I needed to pull a heavy trailer say only once a year, I would consider changing the tires. Yes, the load rating per tire would be reduced from about 2500 lbs to about 2150 lbs, which is still acceptable. I like my 3.73 gears for all around driving.

 

Incidentally, a 265/60R17 tire stands 26.4 inches tall, while a 265/60R17 tire stands about 31 inches high. So, the overall riding height of the truck would drop only by 1.6/2, which is 0.8 inches. Not very noticeable.

arzinet Enthusiast

arzinet

Posted
Posted

So... your plan is to use the tires with reduced load capacity only when you're towing heavy loads? :crackup:

cide1 Enthusiast

cide1

Posted
Posted

Difference between 26.4 and 31 inches is 4.6 inches. 4.6 / 2 = 2.3 inch drop in ride height. It will be quite noticeable. If I already had the wheels, and was in your position, I might do it. If I had to buy wheels and tires, just not worth it. If it makes the difference between towing and not towing, I would get 4.10s installed and have the dealer flash the ECU for the new gears. If you do go for it, I will reiterate what other members have said, and watch the load rating on the tire. A blowout with a trailer is not fun.

 

 

Doug

 

 

 

 

 

Aside from how odd that might look, I don't think it would be a safe change. You also need to consider the load rating of the new tires, and from what I can tell, those 265/60R17s are going to have significantly less load capacity than the 265/70s.

 

IMO, if you want to change the gearing, then you should just bite the bullet and change the gearing.

 

The idea was that if I needed to pull a heavy trailer say only once a year, I would consider changing the tires. Yes, the load rating per tire would be reduced from about 2500 lbs to about 2150 lbs, which is still acceptable. I like my 3.73 gears for all around driving.

 

Incidentally, a 265/60R17 tire stands 26.4 inches tall, while a 265/60R17 tire stands about 31 inches high. So, the overall riding height of the truck would drop only by 1.6/2, which is 0.8 inches. Not very noticeable.

 

pm26 Senior Enthusiast

pm26

Posted
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So... your plan is to use the tires with reduced load capacity only when you're towing heavy loads? :crackup:

 

The slightly reduced load capacity is the penalty one must accept to effectively reduce the gearing, which provides more torque at the rear wheels, which makes towing that load much easier. The Kumho tires I looked at are V rated and they have lower loading capacity. Somebody else may make higher capacity tires in that size, close to the original 2500 lbs. I would have to search.

pm26 Senior Enthusiast

pm26

Posted
  • Author
Posted
Difference between 26.4 and 31 inches is 4.6 inches. 4.6 / 2 = 2.3 inch drop in ride height. It will be quite noticeable. If I already had the wheels, and was in your position, I might do it. If I had to buy wheels and tires, just not worth it. If it makes the difference between towing and not towing, I would get 4.10s installed and have the dealer flash the ECU for the new gears. If you do go for it, I will reiterate what other members have said, and watch the load rating on the tire. A blowout with a trailer is not fun.

 

 

Doug

 

 

 

 

 

Aside from how odd that might look, I don't think it would be a safe change. You also need to consider the load rating of the new tires, and from what I can tell, those 265/60R17s are going to have significantly less load capacity than the 265/70s.

 

IMO, if you want to change the gearing, then you should just bite the bullet and change the gearing.

 

The idea was that if I needed to pull a heavy trailer say only once a year, I would consider changing the tires. Yes, the load rating per tire would be reduced from about 2500 lbs to about 2150 lbs, which is still acceptable. I like my 3.73 gears for all around driving.

 

Incidentally, a 265/60R17 tire stands 26.4 inches tall, while a 265/60R17 tire stands about 31 inches high. So, the overall riding height of the truck would drop only by 1.6/2, which is 0.8 inches. Not very noticeable.

 

 

 

 

26.4 was a typo. My bad. I corrected it to 29.4 inches, which is the right height. So my original calculation of the drop in riding height is still correct.

lowrider Enthusiast

lowrider

Posted
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Just curious as to why you didn't think about something like 265/65/17? My truck came with 245/70/17 General AmericaCraps. I wanted to maintain the same tire height with a wider tire so I replaced with 265/65/17 Goodyears. Your reason for a tire change, while being different from mine, could utilize the same tire. A change to the 265/65/17 will not be as drastic as the 265/60/17 size.

 

Lou

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