Lowered Suspension = Noticably lower drag?!

[serialk11r]

I didn't really get to document these but among the mods done this winter, I used clear PVC sheet to cover up about 1/3 of the total grill area (I shoved the license plate into the center of the grill but at the front of the bumper, so this is perhaps effectively a half grill block), didn't get to test if it had any improvements for fuel economy.

However, the past 2 days I installed some new OEM replacement struts (KYB GR2) with lowering springs (1.4" front, 1.2" rear), and just got it aligned (there was like ~0.4 degrees toe when they hooked up the Hunter machine but I am betting almost all of that is from the lowering).

The day before I went driving and measured the manifold vacuum on a flat stretch of highway with no cars in front of me for maybe 200 feet, and did the same today.

Conditions:
RPM: 3045+/-5 from the logs, speed: ~58mph OBD, 61mph speedo, 55mph extrapolated from radar.
Coolant temperature: 85C, no oil temperature gauge but I had been driving for over an hour in both cases.
Outside temperature: something like 22+/-1 C both days
Manifold vacuum:
Before suspension change: 20.8 in Hg
After suspension change: 21.2 in Hg
(both constant for 5 samplings, 1 second sampling interval on Torque)

I didn't record the "mpg" because the mpg calculated in Torque seems to always be off by a lot and I didn't bother to calibrate it as I don't want to log an entire tank of gas, I only look at it when I want to feel good about the "44 mpg" I'm getting (that's probably not actually 44).

Using atmospheric pressure of 30 in Hg, that's a 1.3% decrease in fuel usage! With the spring rate changes and my weight reduction (lightweight muffler, removed spare tire), the overall change in height is ~-37mm front -31mm rear, and the car is now raked about 0.14 degrees more. 37mm at the front with my 185 tires is a 37mm*185mm*2=0.014m^2 or ~0.3% reduction in frontal area. Maybe the little rubber wind deflectors are now doing their job better since they're much closer to the ground.

[aardvarcus]

Funny you should mention it, I just got finished last week installing new shocks/struts, 1” lowering springs, and new sway bars on my Celica. I was also doing rust removal and repainting the underbody suspension sub frames at the same time. Took it in for an alignment, told it was way off.

The car felt like it had lower drag, mainly based on how it coasts down hills now, but I have been driving my truck while I did all this work so I don’t have a good A-B feel on it. (Definitely lower drag than the truck!)

I just ran the first normal tank of fuel through it this week, got about the same fuel economy I had been getting, but those tanks were from November when it was significantly warmer. I think once it warms back up the car will show a slight improvement.

[NeilBlanchard]

Correcting the alignment would make coast better. But lowering it may well *increase* drag, because of greater inference with the ground. With less space, the air gets more turbulent. There is an ideal distance above the ground, and typically it seems to be ~6" or so.

[serialk11r]

Possibly (the higher drag thing). I don't really have anywhere to coastdown test (not going to do it on a public road), so this is unfortunately the best I can do. I can't run through full tanks to get meaningful results because I do so little driving and my engine is cold half the time.

I think the Spyder rode a little over 6" off the ground stock, I've now reduced that to roughly 5". Stock, the wheel well gap was simply massive, now it looks like a stock BMW. I believe raking the car forward should help the aero over the top of the car since the rear end is not high enough to meet the template, and the underbody aero is garbage. The rear tires are 205s which is a bit wider than most econoboxes, so the reduction in air going to the tires might have a decent positive effect.

I think it coasts a little better now but it's hard to say. Now that I have new shocks the ride quality is a little better despite the stiffer springs, so I might try to pump the tires up a little more to see if I can get more coasting distance. Currently they're at 36/40psi front/rear (on the door it says 28/32 or something) since the ride was kind of harsh for my taste.

Handling wise I think there's a bit of improvement. Less body roll because of the stiffer springs, and less brake dive. I have very little negative camber and Macpherson struts so the camber loss might have been a problem. I took a very sharp turn today at 30mph that used to make the car slide a tiny bit, zero drama this time.

[oil pan 4]

What ever you do don't ruin the ride to get the car lower to pickup a tiny increase in MPGs.
My friend replaced the strut/spring assemblies on his 1999 sunfire he drives to work.
With the new springs the car rode almost 2'' higher, to his surprise MPGs remained with in the cars standard tank to tank deviation.
So he lost no measureable MPG and the ride to and from work was a lot better.
After a few months the springs settled and now it only rides an inch higher.

[Neen]

All other variables ignored....lowering your suspension would at least lower your frontal area which would lower your cdA

[aerohead]

After study of the official SAE practice for coastdown testing,I have little confidence that any of us could meet the stringent criteria to pull it off,such that you could measure subtle changes as would result from lowering the car.
This sort of thing would be relegated to a wind tunnel where every conceivable variable could be tracked and recorded for later data reduction.
In the article about the recent land speed record for the VW Jetta hybrid,they noted that the dual mirror delete,wiper delete,narrower tires,and lowering, were not enough to affect a Cd change,but did lower frontal area so as to definitely effect CdA,as already mentioned.

[serialk11r]

Originally Posted by oil pan 4

What ever you do don't ruin the ride to get the car lower to pickup a tiny increase in MPGs.

Of course. As I mentioned, the increased comfort from the newer shocks balanced out the reduced comfort from the lower springs.

[30mpg]

I installed Koni shocks and noticed that it also stops better and from time to time I drive the waggy like a track car

[Big Dave]

I lowered my F-350 4" in the front and 6" in the rear and noted a 1.0 MPG improvement.

Truck was in alignment before and after.

Truck drives fine.