Does ride height effect fuel consumption.
Does ride height effect fuel consumption.
(OP)
Was curious fo the effects of ride height on an auto in relation to fuel consumption. I am trying to resolve an argument and would like some solid info to back it up. I am thinking that, on an average car, a lower ride height would result in a better mpg rating. Resoning: more air going over the car as opposed to going under it.
Opinions?
Opinions?





RE: Does ride height effect fuel consumption.
RE: Does ride height effect fuel consumption.
Rod
RE: Does ride height effect fuel consumption.
Opinions?"
So, do you want opinions or solid info? Evelrod has given you some solid info. I'd agree that that is the trend, for a normal car. However, there is a trade-off. As you reduce the ride height there is less air that is being forced into the venturi. But, the venturi has a narrower throat, so you accelerate that smaller amount of air by a greater amount, so it has a higher speed, which causes higher drag losses, as it passes amongst the underfloor components.
P530 in Milliken shows a wind tunnel experiment that shows Cd INCREASING as the ride height decreases.
As in most real engineering problems, it is a compromise.
Cheers
Greg Locock
RE: Does ride height effect fuel consumption.
Can't say as I am in agreement with that approach. It goes counter to my experience with road race cars.
Rod
Old age is where you still have something on the ball but are just too tired to bounce it.
RE: Does ride height effect fuel consumption.
FWIW in the weird and wonderful world of solar car racing we found that you could trade ride height off against angle of attack - my guess is that we were probably tuning for ZERO lift, and hence induced drag. The change in skin friction drag is relatively unimportant in that application.
Cheers
Greg Locock
RE: Does ride height effect fuel consumption.
Hope this helps.
Best regards,
Matthew Ian Loew
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Does ride height effect fuel consumption.
This are hard values BUT for that particular body shape. How ever it does represent general trends very well. One point to remember - when Cl(f) was improving Pitch moment was changing also and Cl(r) was degrading. If one asks me what is more important overall Lift (hopefully negative) or aero balance - I'll vote for balance.
RE: Does ride height effect fuel consumption.
Was your testing done in a windtunnel, or on a road?
Because if your windtunnel doesn't have a moving roadway, you're going to get some misleading results.
RE: Does ride height effect fuel consumption.
This wasn't my study It's just a SAE paper that seemed to answer intitial thread question.
On the rolling road in the WT: It's a matter of cars right height. We don't whant boundary layer to get thick enough (in model area) so it will effectively reduce the body to ground clearance. Moving belt under the car (there are some other ways to deal with BL build up) does help to reduce this problem. It's not that easy thought as there many other problems arasing - like suction of the belt to the model for example in case of high downforce produced by underbody of model.
How ever it is assumed that with normal street car (ride height over 100mm) BL build up is not an issue.
If you study a race car (ride heights 60mm and lower) moving road is eccential.
If you're in between than it's up to you :)
One thing to remember - by it's nature wind tunnel is not giving you absolutely correct numbers - being within 10% of on track measured data is considered good.
Sorry for my English
Thanks
RE: Does ride height effect fuel consumption.
But to answer your question... Which is better for MPG, I would say lower. Yes it creates more DF, but weigh is not too much of an issue, because you are slipping through air more efficiently. With all cars except high end sports cars and racing cars with complete underbody diffusers, lifting your car up will cause so much turbulence that it will drag your car back like a dog on a leash.
Now for my favorite part.... everything above is to be taken for entertainment purposes and I could be wrong so please do not regard anything I write as a fact. Just trying to help.