Offroad Tires and MPGs

[jsc7002]

what size tires?

1500 extra lbs?

he is running 265/75, and he has 1500# worth of tools in the KJ and his front and rear bumpers and winch and rock rails and skids and all of the other off road parts adds up real quick!

 

[theholybull]

I have to believe that those getting 10 mpg may not have taken into consideration that when increasing tire height the distance the tire covers on each revolution increases this throws off the odometer and speedo actually. If this is not corrected for your calculations will give lower mpg than your actually getting.

 

[tjkj2002]

I have to believe that those getting 10 mpg may not have taken into consideration that when increasing tire height the distance the tire covers on each revolution increases this throws off the odometer and speedo actually. If this is not corrected for your calculations will give lower mpg than your actually getting.

My speedo has been calibrated,compared to my GPS my speedo/odo is within 1-2mph of what the GPS is reading.Can't get much better then that since my speedo/odo was 3-4mph off right from the factory.It is normal for any speedo to be up to 5% off(+/-) from the factory.

 

[theholybull]

I believe your also carrying around 1500 Lbs with you. 10 mpg I can understand. 10 mpg from a 1 or 2 inch jump in tire diameter seems like it may be worth mentoning. Just trying to help.

 

[jsc7002]

I believe your also carrying around 1500 Lbs with you. 10 mpg I can understand. 10 mpg from a 1 or 2 inch jump in tire diameter seems like it may be worth mentoning. Just trying to help.

try it you will have MPGs around there, and his tires are 3" larger then OEM, my tires are 2" larger and weigh A LOT more then my OEM wheels and tires, there is just a bunch of little things that factor into the bad MPG

 

[CHUD]

, there is just a bunch of little things that factor into the bad MPG

bigger, fatter tires = greater rolling resistance = lower mpg.

 

[theholybull]

Let me show what im talking about.

stock 225x75x16 = 29.2" tall X 3.14 = 91.96" circumference

BFG 32x11.50x15= 31" tall X 3.14 = 100.48" circumference

That means every revolution of the larger diameter tire the vehicle travels farther.

Stock cir. in feet 7.66
BFG cir in feet 8.37

1 mile= 5280 ft

Stock 5280/7.66= 689.29 revolutions of the tire to cover 1 mile
BFG 5280/8.37= 630.82 revolutions of the tire to cover 1 mile

So with the larger tire you cover more distance per revolution, the truck still thinks that you are covering 1 mile in 689 revolutions when you are actually covering 1.1 miles (689.29X8.37=1.1). If this is not taken into account when figuring the mileage then your calculations will not be accurate.

Aw shown above there is a 10% error in the speedo I did the calculations for above. So if the MPG calculated to be 14.2mpg the actual mpg would be 15.6.

NOW due the everyone knows friggin everything about everything on the internet I will say this. YES adding more mass to the wheel and tire increase the amount of energy required to move them, and stop them for that matter, and will cost you some mileage.

I AM NOT SAYING THIS IS THE CASE FOR EVERYONE. It just may help someone out there who may not have considered it.

 

[tjkj2002]

Let me show what im talking about.

stock 225x75x16 = 29.2" tall X 3.14 = 91.96" circumference

BFG 32x11.50x15= 31" tall X 3.14 = 100.48" circumference

That means every revolution of the larger diameter tire the vehicle travels farther.

Stock cir. in feet 7.66
BFG cir in feet 8.37

1 mile= 5280 ft

Stock 5280/7.66= 689.29 revolutions of the tire to cover 1 mile
BFG 5280/8.37= 630.82 revolutions of the tire to cover 1 mile

So with the larger tire you cover more distance per revolution, the truck still thinks that you are covering 1 mile in 689 revolutions when you are actually covering 1.1 miles (689.29X8.37=1.1). If this is not taken into account when figuring the mileage then your calculations will not be accurate.

Aw shown above there is a 10% error in the speedo I did the calculations for above. So if the MPG calculated to be 14.2mpg the actual mpg would be 15.6.

NOW due the everyone knows friggin everything about everything on the internet I will say this. YES adding more mass to the wheel and tire increase the amount of energy required to move them, and stop them for that matter, and will cost you some mileage.

I AM NOT SAYING THIS IS THE CASE FOR EVERYONE. It just may help someone out there who may not have considered it.

Come drive in Colorado Springs for a week and your mpg's will nose dive also,always going up hill for some dumb reason.Oh and did I mention my speedo already is calibrated for my 31.9" tall tires and 4.10 gears?

 

[jnaut]

I done mine in baby steps so haven't noticed that much change went from stock 235-70s, then 245-70s, next 255-70s, and now 265-70s still get 19/20 easy at 75 plus on the road though!

When is it recommended you get a new, beefier axle? What I mean is, what's the largest tire you can put on the libby with stock axles?

 

[tjkj2002]

When is it recommended you get a new, beefier axle? What I mean is, what's the largest tire you can put on the libby with stock axles?

32" is what I would say would be the max for the front diff and from the fact you can not gear any lower then 4.10's and the amount of lift needed to be able to run 33"+ tires will kill your front CV's.The 8.25 is virtually as strong as a D44,the 8.25 uses C-clips which is the weak point,and can handle 35" tires with a light foot.