Lowering=Improved aerodynamics?

[Polk]

MSN autos gives ride heights. I found that over the years ride height has increased. If I remember right, my 2009 has about 2" more ground clearance than my 1995 did.

I am in the process of gathering parts to lower my 2009 by 2" for a variety of reasons, one of which is squeezing a little more mileage out of it. I can report back on the change in mileage, though it could be a little while before I have any info.

I got my drop done yesterday. I will spare you all the gory details (unless you want them...), but my drop came out pretty minor at 1 5/8" in back and 1 1/4" front. I will continue logging my gas mileage and report back. I typically log 500~600 miles per week, so it should not take too long to have some meaningful numbers. We will soon see if even a little drop helps MPG!

 

[BlueChariot]

Thanks man. It would be nice to compare the differences between different drops, but any data is helpful. lol

 

[Polk]

So far I have had two tanks of gas with measurable mileage (no towing, hauling, or other non-routine driving), and the mileage increase is almost hard to believe! Right before lowering, my mileage for the last ~2000 miles was 25.5. And last year I recorded my mileage for ~9000 miles and it was 25.7. So fairly consistent.

After lowering, and recording for two fill-ups over 733 miles my mileage has been 29.0! There is a second variable, however. Before lowering I measured the toe-angle and camber. The toe was about 1/8" toe out. Odd. It drove fine, tracked well, and showed no uneven tire wear at 40,044 miles on the original tires when I lowered it. After lowering I set the toe very close to zero; maybe 1/32 or less of toe-in. It still tracks fine. Maybe I am used to twitchy sports cars, so I don't notice? But either way, excessive toe in or out can make a difference in mileage since it takes a lot of energy to scrub the tires in that position. How much is hard to say. I could believe that toe could be half of the mileage increase, since it was pretty wacky before and I now have it at a very efficient setting. So 1.5-2mpg increase from the lowering?

One last thing. I would say that 80-90% of my typical miles are highway, often 70-75mph. Obviously slower speeds are going to give less return since aerodynamics play a smaller role as speeds decrease.

 

[Jason]

Not RBV related, but my Jeep lost 1.5 mpg avg. over 15 plus tanks with a 3 inch lift.

 

[Froggmann]

Thanks for the feedback Polk, I've been interested in the real world numbers. It makes my decision to lower my truck more urgent.

Are you going to check mileage again and report back?

 

[Polk]

Hey Froggmann, I do have one more fill-up since my last post.

So far my mileage has varied quite a bit with the first three tanks. 28.6mpg, 29.5, and the latest was 27.2. The last did involve carrying a bit of a load for ~60 miles and I had a few trips where the speedo was wound up a little extra (a call-in to a hospital 31 miles away Friday evening does not lend itself to gentle driving...). That still works out to 28.4, an improvement of 2.9mpg. I can't complain too much about that.

 

[Jason]

My mileage is the same daily drive. I only drive the Jeep to work as I drive the M3 everywhere else.

 

[BlueChariot]

The Jeep losing mpg's makes sense, you're adding soem weight, and lifting which basicly is the opposite aerodynamic affect of lowering.

I am a bit shocked at the difference with just a 2 inch drop. Thanks for the data. Now I'm wondering even more what the 3/4 drop would do.

 

[Polk]

I am a bit shocked at the difference with just a 2 inch drop. Thanks for the data. Now I'm wondering even more what the 3/4 drop would do.

Keep in mind about the alignment I mentioned. Going from 1/8" toe out to zero toe is going to make a difference in mileage. Since I don't have any way to know without adjusting the toe angle for a few tanks of gas (and I am not going to do that!), I am simply going to give about half of the improvement to the lowering and half to the alignment.

 

[BlueChariot]

Yes, but it still makes me wonder if a lower drop has an exponential growth in difference or if it's more fixed.

 

[Froggmann]

I recently lowered mine about an 1.25" FR and 2.5" rear, last weekend I got to test the mileage. Previously on the same trip, the truck was averaging about 16.8mpg--last weekend it got 18.1mpg, both figures on E-85. I expect the figure to improve further after the truck is properly aligned.