Economy after larger tire - Fuel Economy, Hypermiling, EcoModding News and Forum

bandit86 · 02-08-2023, 09:50 AM

2007 grand Cherokee diesel, engine is notoriously high revenge for diesel and many said that much lower gear would be nice to have. So I got new tires and I went up from 29.5" to a 32" diameter tire. Before with the old worn 29.5" tires my average fuel economy was 10.5 l per 100 km Now with the brand new all terrains it is 11.2 But the odometer used to be showing 5% too fast now it shows 6 km to low so I don't know how to calculate that extra percentage into the calculations. I basically go almost 10% more than I did before so the slight increase still shows like it should be A benefit Big because I cover more distance. After the first 80 miles average is down to 10.9, but i also changed axle and transfercase fluid. Gps verified distance traveled, 170 but only logged 159 on odometer

freebeard · 02-08-2023, 02:22 PM

Thanks

Quote:

Thanks: 3
Thanked 19 Times in 15 Posts

Rookie numbers.

oil pan 4 · 02-08-2023, 03:14 PM

I went with the next size larger tires on my wife's car and they are usually $20 to $25 cheaper per tire then what's it's supposed to have.

freebeard · 02-08-2023, 03:43 PM

On my VW panel van I ran staggered [bias-ply] tires: 6.00x14 front and 8.20x15 rear.

It was mostly for downforce from the slanted roof.

Topped out at 85MPH, I used to race Vovlos through the Coast Range.

bandit86 · 02-08-2023, 06:08 PM

Quote:

Originally Posted by freebeard

Thanks

Rookie numbers.

None of the other forums I visit have that option I always forget about it

cRiPpLe_rOoStEr · 02-09-2023, 03:55 AM

Quote:

Originally Posted by oil pan 4

I went with the next size larger tires on my wife's car and they are usually $20 to $25 cheaper per tire then what's it's supposed to have.

Nowadays some sizes in my country simply can't be found so easily from the most traditional tire brands, and 14" tires are sometimes cheaper than the 13" ones which used to be mainstream until around 10 to 15 years ago.

laser3kw · 02-17-2023, 07:37 PM

I have an offset number built into my MPG spread sheet to account for the larger size tires. It calculates true mileage based off the odometer reading as entered. Makes calculations more accurate.
Your 32" calculate to be 8.5% larger than the 29.5" but you GPS vs odo shows 7%.
Also sometimes larger tires can be significantly heavier by pounds (kilograms). That can impact fuel mileage.

cRiPpLe_rOoStEr · 02-21-2023, 04:05 AM

Last time a friend asked me to calculate wheel well clearance of a set of tires he was willing to fit to his truck, I also had to point out to him how it could affect acceleration and how much he should de-rate the GVWR in order to keep the climbing ability. Changing tire sizes is not so plug-and-play at all...