[LeanBurn]

Not to hi-jack this thread, but my GMC Sierra (as listed below) needs tires. Currently at 90kph or 55mph on the speedo (but 87kph or 54mph on the GPS), it turns at 1800prm. I have a running average of ~12L/100km or 19 mpgUS unloaded and not towing. I am going to still get Load E, LT tires (So I will retain my load carrying capabilities), but I want to change from the 245/75R16 to 235/85R16. So 10mm skinnier and 10mm taller.

So in making this tire size change I will correct my speedo to actual speed, reduce aero profile of the tires and lower my rpm at speed.

I did this tire sizing with the 1997 5.7L suburban I used to have and obtained some really decent mpg numbers for a nearly 20 year old truck. In contrast it loafed along at 1600 rpm at a GPS verified/speedo correct 90kph(55mph).

This truck has a lot more power and torque as well as a tow/haul mode I didn't have with the suburban (I had to used 3rd gear) (both have same 3.73 rear gearing, so I don't feel it will hurt me in the towing/hauling department a bit.

245/75R16 IMPERIAL METRIC
Section Width: 9.65 in 245.00 mm
Rim Diameter: 16 in 406.4 mm
Rim Width Range: 6.5 - 7.5 in
Overall Diameter: 30.47 in 773.90 mm
Sidewall Height: 7.23 in 183.75 mm
Radius: 15.23 in 386.95 mm
Circumference: 95.72 in 2,431.28 mm
Revs per Mile: 682.67/mi
Actual Speed: 62.14 mph 100.00 kph


235/85R16 IMPERIAL METRIC
Section Width: 9.25 in 235.00 mm
Rim Diameter: 16 in 406.4 mm
Rim Width Range: 6 - 7 in
Overall Diameter: 31.73 in 805.90 mm
Sidewall Height: 7.86 in 199.75 mm
Radius: 15.86 in 402.95 mm
Circumference: 99.68 in 2,531.81 mm
Revs per Mile: 655.57/mi
Actual Speed: 64.71 mph 104.13 kph
Speed Variance: 3.97% too fast.
Diameter Variance: 4.13%

Thoughts?