how much hp do you get when you shed lbs? I hgave read something like 20 lbs =1hp gain? How much mpg do you gain when you shed lbs? I have read 17 lbs shed = 1mpg.

Anyone know anything about this? have a valid equation? just wanting some opinions?

was considering that with a friend along at 185 lbs and some luggage at 30 lbs i must be loosing what....10 mpg or maybe 12 hp? that is the equation i am looking for and i know somebody has figured this out!

 

R U serious?

You don't gain any HP no matter how much weight you shed. You're HP you have are always the same, but they work better when they have less weight to push around.

your formula for 'gain/loose mpg' when you add or shed weight makes no sense. IMO you can't say xyz weight will give you xyz better/worse fuel econ.

Lets say you have a Civic that gets 33 mpg (average city/hwy) with you as the driver. You're formula is telling me if you add 170 lbs you will be getting 10 less MPG or if you add 340 lbs you will be getting 20 mpg less (in other words 13 mpg)?



If there was a formula of how much mpg you loose by adding weight, it would be different for each vehicle. For example a Surburban gets lets say 14 mpg with just the driver. You could probably add another 900 lbs to a Surburban and get 11 mpg (est). So that way you may loose 1 mpg for every 300 lbs. However a small car like a Civic may loose 3-4 mpg if you ad 300 lbs.

Note the above mpg are just given as an example, not taken from any test of anything.

They say not to drive with extra weight saves gas, but it's not something huge like take the tool box out of the trunk and get 3 extra mpg. Maybe you will get an extra 0.2 mpg, but over a lifetime that can ad up to something.

I think you are over estimating the weight penalty to the mpg. IMO the weight of one person (180 lbs) here or there probably don't have much effect. If there was a ballpark I'd say it's closer to 1 mpg for every 150 lbs (est. this is not a proven fact, but one I have observed from hundreds of thousands of miles driving both with and without people in the car).

 

BTW I have a S2000 with hardtop (~44 lbs) and spare tire (~25 lbs) and about 10 gal of gas ( + or - ~70 lbs) and I can't tell any difference with or without the hardtop or with or without the spare tire or with or without a full tank of gas.

Now if I was measuring acceleration it may be a tenth of a second quicker without the hardtop but seat of the pants dyno it doesn't feel any difference.

But I can tell a difference when I have 200 lb passenger robbing my HP.

 

[QUOTE=rai,May 30 2006, 02:08 PM]R U serious?

 

One other thing, while lower weight should net you better MPG, there is also something about gearing and power. For example a 3-series Diesel could weigh as much or more than a M3 while getting more MPG but it's slower b/c of gearing and HP.

I know that example is not 100% b/c the diesel has an advantage to mileage, but you could even take a car like the Accord I4 vs the Accord V6. Even if you weight adjusted them so that the I4 was as heavy as the V6 the I4 would still get better mileage, but it'd be slower.

If you drive 55 mph on the HW you will get a lot better gas mileage than if you drive 85 mph, but you'll spend more time driving.

It's all a trade off, a car like Accord could get better mileage if you put the engine from the Fit in it, but it would be very slow.

That's the trade off with larger/heavier cars; you have to have bigger engines = more HP = worse gas mileage.

The RS4 is about the size of a Civic /Jetta (inside), but it weighs 3600 lbs with 420 ho, has to pay $2100 gas guzziler tax not to mention getting under 20 mpg (average) but it is quick.

 

I believe what he is thinking about is when I have heard people say that losing 14 lbs. on the s2k is the performance equivalent of gaining 1 hp.

They arrived on this figure because that is the s2k's power to weight ratio: 2,800 lbs / 200 whp = 14 lbs/hp.

 

most sportbikes are about 350lbs at 150hp. cant say they get excellent gas millage but they handle so sweet.

reducing weight of rotational stuff is inportant sonehow compared to static stuff.

a 5th gen honda-vx weight was <2000lbs if you toss out the floor mats. it got good gas milage with little technology.

once various car manufacturer's engineering organizations have given birth to the last suv it will be interesting to see the next hatches.

 

i do not know which number to use to equate? i am just asking if anyone does. one person has said loose 14 lbs and "gain" one hp. that sounds interesting. i know your car does not have a brake hp increase!
again i am asking if anyone has a good idea of how much is lost or gained due to weight???

i ask again if anyone knows this stuff? in my experience for example that if you shed 200 lbs your car acts like it has another 10 or so hp, just my guess. also if i load up the trunk and add a passenger my mpg goes down maybe by 2-3.

i also think that if you carry 10 lbs of stuff in the trunk it must take away from your mpg, how much is what i am asking????