Unsprung weight ?

[Gstick]

Serious question about unsprung weight & MPG.

If I were to spend the cash on Volk 17 x 8" forged wheels, (which are 10 lbs lighter per the OEM OR wheel) would I notice a MPG gain using the OEM size 265/70/17 ?

The tires would be BFG KO2's Load Range C, which weigh 46 lb vs the 39 lb OEM tire.

I know the 5th gen 4R's aren't bought for fuel mileage, I was just wondering if the 10 lbs per corner saved would show a MPG gain.

 

[mo_mo]

Nope

 

[ads2539]

40 lbs is less than 1% of the weight of the vehicle. Assuming reducing unsprung weight is twice as effective as reducing other weight (I read that online), you’re effectively reducing the vehicle weight by 80 pounds (less with the heavier tires).

According to the EPA, a 100-pound weight reduction will improve MPG by 1%-2%. If you were getting 15 mpg with the heavier wheels, you’d get 15.3 mpg with the lighter wheels assuming the full 2% and a 100-pound weight reduction. I don’t think you’d notice that.

 

[lewdog998]

Besides overall reduction in total vehicle weight, the main benefit of reducing unsprung weight is better suspension performance....due to lower mass moving up and down...it can react more quickly. You also get some acceleration and brqking benefits because its wheel /tire weight.

 

[Bmnorm2]

Serious question about unsprung weight & MPG.

If I were to spend the cash on Volk 17 x 8" forged wheels, (which are 10 lbs lighter per the OEM OR wheel) would I notice a MPG gain using the OEM size 265/70/17 ?

The tires would be BFG KO2's Load Range C, which weigh 46 lb vs the 39 lb OEM tire.

I know the 5th gen 4R's aren't bought for fuel mileage, I was just wondering if the 10 lbs per corner saved would show a MPG gain.

40 lbs is less than 1% of the weight of the vehicle. Assuming reducing unsprung weight is twice as effective as reducing other weight (I read that online), you’re effectively reducing the vehicle weight by 80 pounds (less with the heavier tires).

According to the EPA, a 100-pound weight reduction will improve MPG by 1%-2%. If you were getting 15 mpg with the heavier wheels, you’d get 15.3 mpg with the lighter wheels assuming the full 2% and a 100-pound weight reduction. I don’t think you’d notice that.

Besides overall reduction in total vehicle weight, the main benefit of reducing unsprung weight is better suspension performance....due to lower mass moving up and down...it can react more quickly. You also get some acceleration and brqking benefits because its wheel /tire weight.

All good points.

Additionally, you are reducing the wheel mass by 10 lbs, while adding 7 lbs back in the tires and at the worst location (largest radius). The heavier tires have a huge Moment of Inertia (~I=MR^2, where R is the ~16" the radius of the tire). It is unlikely you will see any measurable change.

So, your unsprung mass reduction is only ~12 lbs and you may have actually increased the tire+wheel combined inertia with the heavier tires which would reduce acceleration, braking, turning, and in theory mpg.

Its basically a wash as proposed.

 

[honda250xtitan]

All good points.

Additionally, you are reducing the wheel mass by 10 lbs, while adding 7 lbs back in the tires and at the worst location (largest radius). The heavier tires have a huge Moment of Inertia (~I=MR^2, where R is the ~16" the radius of the tire). It is unlikely you will see any measurable change.

So, your unsprung mass reduction is only ~12 lbs and you may have actually increased the tire+wheel combined inertia with the heavier tires which would reduce acceleration, braking, turning, and in theory mpg.

Its basically a wash as proposed.

sounds like a win. hes offsetting the heavy tires by buying light wheels. its better then using stock wheels. you gotta be a better enabler man!

 

[Bmnorm2]

sounds like a win. hes offsetting the heavy tires by buying light wheels. its better then using stock wheels. you gotta be a better enabler man!

Haha, you are right! Let me try again.

OP, you likely won't see any change in MPG. The lighter wheels enable you to put on the heavier bad ass tires without penalty. You should do it!

Report back with pics!

 

[MasterFoo]

Volks ftw!

 

[Plan B]

40 lbs is less than 1% of the weight of the vehicle. Assuming reducing unsprung weight is twice as effective as reducing other weight (I read that online), you’re effectively reducing the vehicle weight by 80 pounds (less with the heavier tires).

According to the EPA, a 100-pound weight reduction will improve MPG by 1%-2%. If you were getting 15 mpg with the heavier wheels, you’d get 15.3 mpg with the lighter wheels assuming the full 2% and a 100-pound weight reduction. I don’t think you’d notice that.

That has to be one of the most informative posts I’ve read on here. Thanks man

 

[2021nightshade4x4]

I also don’t want unsprung weight to be so light it’s like riding on cardboard wheels held on by toothpicks.


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[Gstick]

I appreciate all of the input. One thing that I know for sure, changing up to a 255/75/17 cost me a little over 1 MPG loss. But I believe that it is because of all of the rolling hills here in southwestern PA and the slight change of ring/pinion ratio causing more downshifting.

This might sound strange but my 2010 SR5 4R got about 2 more MPG than my 2019 TRD OR does, (both 4x4) and I did have the Billies 5100's @ 1.75" leveling the front of the 2010.

 

[4Liberty]

See my signature for my specs...
When I was factory stock my average highway MPG was 19.5 Dunlop tires.
When I put the heavy 59 lb per tire General Grabber ATX tires on I lost 2 mpg.
Then later I got the Dobinsons lift and hardly noticed any loss in hwy mpg after the lift. My lift didn't effect my mpg much at all....the heavy E load tires did.
Might consider going with the Firestone Destination XT tires next time as they are 12 lbs lighter than my Grabbers....or try to find a C load in LT275/70R17 next time but not much to choose from in 275. I can't run LT285/70R17 as I have JBA UCA's....they would rub in my UCA's.

 

[tpetsch]

Negative -40 pounds of unsprung weight is always a positive move for the ride, handling and getting the suspension to work at it's optimal, think rebound control after hitting a bump in the road at speed, the lighter the wheel/break assembly the easier for the suspension to handle the force. On the 4Runner application though you will probably benefit mostly during acceleration because you can never really get the wheels and -those heavy off road tires by design- tire, brake/rotor etc assembly light enough like on a sports car, and the engine will work harder to get that extra 40 pounds accelerating from a dead stop effecting your MPG. Once up to speed it's pretty much all the same then for the fuel savings. So if you do a lot of stop & go you will see more of a benefit with the 4Runner. Probably not worth the initial investment though unless your all ready shopping for new a wheel & tire. I autocross and 40 less pounds of unsprung weight would be huge in terms of performance all around which would result in better times on the course, on the 4Runner probably not so much because the robustness of the parts needed to keep the vehicle reliable for potential off road use
are generally heavy by design, unless you spend a boatload I'm sure.