It does help mileage/cd marginally but usually isn't a cost effective modification if doing for mileage alone. The flow under the vehicle becomes more critical as the vehicle is lowered so a belly pan becomes more desireable. Added benifits are generally improved handly, and depending on opinion looks. On the down side, reduced ground clearance can be an issue, especially living where there is snow. Where I live we have a speed bump that has been known to remove the ground FX off lowered cars.
Supposed to help if 2.7" I think was the magic number but I would recommend a front skirt that is soft or pops up and backwards when hit or one that you can lower and raise - then the underbody will not matter as much.
Funny but 80 rabbits would break the left front coil at 60,000 miles about a 5 inch length from the top end. I actually remember mine breaking as I was pulling out from an exit ramp onto Main road.
Another freebie? How do you keep pulling that off?
OK so you will be doing a DIY right? I'm gonna put a set on my ebay watch list. How hard was it to do? Do you need any special tools? How long does it take? I really like the adjustability feature.
I just know a lot of people and I am very patient when I want things.
Anyway, yes diy. It's not very hard at all. Special tools are a spring compressor but I got one on loan from autzone (43 dollar deposit) or you can get them on ebay for 20 or so shipped. Took my like 1:30 for the first cuz my dad was "helping" and slowed me down a lot, but the second only took like 35-45 minutes, back two have a simple construction so they'll be every quicker.
what is it with honda springs... over 8 years, 3 broke on my accord (all, front, at different times). it's not like i took the car off-roading either.
in aero geek-speak, lowering a vehicle increases its "fineness ratio" - its ratio of length to height. and this is desirable. i hadn't heard of an "optimal" ride height before (2.7).
as for how much it will help, i agree a lot depends on your underbody design & suspension.
lowering my firefly will definitely help because as it sits now, it's very high for its length - i have a ridiculous amount, maybe 5-6 inches, of ground clearance. all 4 control arms angle down quite sharply from the belly plane into the underbody airflow. so shortening the springs will tuck them up higher, and reduce their drag considerably.
on my car, i suspect they went for exaggerated ride height to offer slightly better visibility and improve the "feeling" of safety in such a tiny car. as we know from studies of people who buy SUVs, one of the biggest contributors to their (gnerally false, overall) perception of safety is improved visibility from having higher sight lines.
Somewhere I read - can't seem to find it yet - but the best ground effect clearance for the front skirt is about 2.7 inches - seems that moves enough air around the car instead of under it and reduces air drag. I have about 6 inches and am thinking about adding an adjustable skirt in front that I can raise and lower - should show mpg changes right away.