Dually truck tire replacement

[paulbeauchemin]

Have an F350 dually with tire size
LT 245/75R17 121/118R

Obviously I need same diameter. Wonder how important aspect ratio is to match current tires (original are Yokohama tires)

[parker_rowe]

paulbeauchemin wrote:


I see - if replacing just one of the tires in a dually that this would be critical

But if you replace all 4 is aspect ratio critical?

As long as it isn't 4wd, no. Front and rear tires need to be the same diameter in 4wd, or the transfer case won't be happy.

[Grit_dog]

paulbeauchemin wrote:

parker.rowe wrote:
Aspect ratio? As in the "75" in that tire size?

That is pretty important. It IS the tire height.

245=tread width in mm
75=sidewall height as a % of tread width. ex: 245 x 0.75=183.75mm
17=rim diameter in inches

So...

total sidewall height in mm = 183.75*2=367.5
total sidewall height in inches = 367.5/25.4=14.47 inches
total diameter = 14.47+17 = 31.47 inches

Of course, there are discrepancies from tire to tire and manufacturer to manufacturer. But that is what the numbers are suppose to mean.

I see - if replacing just one of the tires in a dually that this would be critical

But if you replace all 4 is aspect ratio critical?

No, it's not. Neither is diameter within reason. Small change in dia will be indiscernable. Even a couple inches in dia will not make much difference.
I'd run 255-80-17s. A little extra meat on the rims would be nice compared to 245s.

[paulbeauchemin]

parker.rowe wrote:
Aspect ratio? As in the "75" in that tire size?

That is pretty important. It IS the tire height.

245=tread width in mm
75=sidewall height as a % of tread width. ex: 245 x 0.75=183.75mm
17=rim diameter in inches

So...

total sidewall height in mm = 183.75*2=367.5
total sidewall height in inches = 367.5/25.4=14.47 inches
total diameter = 14.47+17 = 31.47 inches

Of course, there are discrepancies from tire to tire and manufacturer to manufacturer. But that is what the numbers are suppose to mean.

I see - if replacing just one of the tires in a dually that this would be critical

But if you replace all 4 is aspect ratio critical?

[parker_rowe]

Aspect ratio? As in the "75" in that tire size?

That is pretty important. It IS the tire height.

245=tread width in mm
75=sidewall height as a % of tread width. ex: 245 x 0.75=183.75mm
17=rim diameter in inches

So...

total sidewall height in mm = 183.75*2=367.5
total sidewall height in inches = 367.5/25.4=14.47 inches
total diameter = 14.47+17 = 31.47 inches

Of course, there are discrepancies from tire to tire and manufacturer to manufacturer. But that is what the numbers are suppose to mean.

[BenK]

Suggest using "rev's per mile" over just dia...have found there is difference between exact same dia's, but different OEMs and even within the same OEM, but different models

[donn0128]

You have to be careful to maintain the distance between tires. Too clode and they could rub under load causing a failure. So yes aspect ratio is important on a dually