[DuncanMoto]

The speed thing is a scam. I think milage and speed depend on how they set up the gear ratios more than aero dynamics.

I used to drive to Tennesee and back 2-3 times per year in a 1972 Porsche 914. I got 26 mpg. averaging 65 and 34mpg averaging 81.

The car was a European model with a very tall 5th gear that I could not use under 75mph.

[nt650hawk]

I could drive the Tundra all day at 45 without stop signs and get 28mpg. Still in the same gear @ 65mph I will get 19.5. Same gear 70mph I will get 18 mpg.

When I'm towing the trailer. All the weight is on the trailer not the truck and I just got 9mpg at 65mph. Don't tell me it is not the wind. IT IS ALL ABOUT WIND, resistance and aerodynamics.

Don't get me started about head winds. I know you feel it.

[g®eg]

you nippers aren't old enough to remember the last gas crisis and the "national speed limit" drive 55.

big difference in fuel economy at 55 vs 65 vs 75.

funny thing.. had to teach at Bunker Hill last weekend, so I was heading in on the SE expressway, too early Sunday morning. Set the cruise at 65, and I was getting passed like I was out for a walk

I guess people aren't concerned with saving gas... just bitching about the price of it

[stoinkythepig]

Aerodynamic drag increases with the square of speed so small increases in speed generate large increases in drag. The difference in aerodynamic drag bewteen 55 MPH and 65 MPH is a rather shockingly large 39.66% Increasing speed from 55 to 65, however, does not mean your fuel consumption increases by 39.66%. The reason for that is the parasitic drag of all the moving parts in the drivetrain and the rolling resistance of the tires is using up much more energy than the aerodynamic drag.

The increase in drag from 55 to 75 MPH is 86%, nearly double

Your vehicle likely gets the best mileage at the lowest speed it can do in top gear, without lugging, and without slipping the torque converter. For most vehicles that's 45 to 55 MPH.

The engine's torque peak is where it has the best volumetric efficiency. This is NOT where the engine will get the best gas mileage since the only way to use peak VE, is to be at WOT.

[TheIglu]

Originally Posted by g®eg

I guess people aren't concerned with saving gas... just bitching about the price of it

Bingo. You win the prize!

[Rossy83]

Houston did this a few years back $1.5mil to change all the signs in and around Houston... they changed it back less than 3 months later because nobody gave a shit. They can change the speed limit, but I think the gas saved from people who follow the new speed limit is going to be offset by the people going WOT to pass that slow #*&@&*#!

TX raised the speed limit on I-10 West of San Antonio to 80, there are no cops out there just desert. There is only a speedlimit because they are required to have one for Fed. funding.

[benVFR]

The thing is if the speed limit gets dropped again new cars will be adapted in short order.

1) Gear ratios will be optimized for 55mph, mpg will go way up
2) Fuel mapping may change, mpg may go up a little
3) If people slow down average hp/weight in the cars will likely drop (people switching to four-bangers instead of V8 SUVs, etc..) and there will be an even bigger gain in mpg.
4) If average speeds really do drop safety structures may get toned down to the point vehicle weights start to come down, another huge mpg difference. This could further occur as if the average vehicle weight drops then the safety structure needs drop even further.

My car has total suck ass gearing for highway traveling, but it's pretty aerodynamic and it doesn't really drop much as I speed up. It's rated 31mpg on the highway and I've easily gotten that averaging 75-80mph.. Slowing down might only affect it 2-3mpg. But then again if I had an SUV... If they changed 6th gear to something sane it'd probably pick up 5mpg.

MPG effects on bikes are totally nuts. 55mpg smooth riding on back roads I get nearly 50mpg on my VFR, 75mph highway driving I'm dropping into the high 30mpg range.

If Hilary and McCain think it's a good idea to drop the gas tax for the summer we do not want to see what the federal budget & deficits will look like if either of them ends up in office. (But then again last time I checked Obama doesn't exactly mention saving money often either)

55 feels really slow to me in the car but I think if the car(s) were optimized to loaf along at 55mph I'd be a lot more patient.

[RandyO]

I propose a speed tax, all vehicles must have a gps tracking device, those that choose to speed get a bill from the gov't once a month, if you choose not to pay, they push the big red button that disables your vehicles

I get better milage on the highway with my V-strom 1000 than I did with my SV650, my SV would drop from 50 to 35 my V-strom most of my riding and drivng is on rural new england roads, no painted lines, half the time no pavment, when there is, its often broken, strewn with litter (gravel, dirt, sand, leaves, anything) 45-55 is actually ziping along for the conditions

my strom never gets worse than 39, but best is 43 (44 once) and my 39 on the strom is floggin it, highway, I get the same 41-43 that I get on back roads

it's been so long since I've been on the highway in a cage long enuf to use a tank of gas, the 325e that I have now gets 30-32 but I've never had it on the highway or flogged . the 320i that I had before that got 35 on the highway but a spirited drive up Rt 100 and over 17 was usually under 20mpg

[wylee]

Originally Posted by g®eg

I guess people aren't concerned with saving gas... just bitching about the price of it

Here's someone who understands the general public.

[bertbert2oo6]

it's not really the aerodynamics as much as it is the rpm's of the engine

not only that, i feel like it's kinda inefficient when people spend increased amounts of time commuting to work, rather than actually working..

[Rossy83]

Originally Posted by RandyO

I propose a speed tax, all vehicles must have a gps tracking device, those that choose to speed get a bill from the gov't once a month, if you choose not to pay, they push the big red button that disables your vehicles

Ok now think about the cost to implement such a plan. You can pay for it. And I'll just put a metal box over it so it doesn't get reception.

[deslock]

Fuel consumption is determined by engine efficiency at the RPM and throttle required to generate enough power to overcome air drag and other forces (internal friction, rolling friction, accelerating your fat ass, gravity if you're on a hill, etc).

Here's the bad news: the power required to overcome air drag is a *cubic* function of velocity (since power is force X velocity).

I dunno of any fuel consumption graphs for bikes, but for reference here's one for a TDI (from this fairly interesting thread):


As far decreasing speed limits goes, don't worry about it. Any efforts to do so have been crushed. Likewise, government controls (via GPS tracking, etc) would never work (due to technical and logistical difficulties as well as the masses never accepting it... we're way too libertarian in this country to live with something like that).

Keeping your speed low, engine tuned properly, tires inflated, RPMs low, and staying off the throttle will all contribute to increasing MPG (if you're really that worried about it).

[stoinkythepig]

Originally Posted by bertbert2oo6

it's not really the aerodynamics as much as it is the rpm's of the engine

not only that, i feel like it's kinda inefficient when people spend increased amounts of time commuting to work, rather than actually working..

So, it's just gearing? If I replace the rear sprocket on my 9R with a 25 tooth, I should be able to go 300 MPH, and I'll get 100 MPG at highway speeds. And if I put in an extra hour or two at work, I can get 120 MPG. Excellent.

[TheIglu]

Originally Posted by stoinkythepig

So, it's just gearing? If I replace the rear sprocket on my 9R with a 25 tooth, I should be able to go 300 MPH, and I'll get 100 MPG at highway speeds. And if I put in an extra hour or two at work, I can get 120 MPG. Excellent.

Remember, science is made up by wizards and witches!

It's "the man" trying to hold us down!

(yet another example of people just spouting mind diarreah)

[benVFR]

Just go out and try to ride your bicycle fast if you doubt aerodynamics.

Or heck take all the fairings off your motorcycle and sit up straight and see what it feels like at 100mph.

If you look at some of the websites/forums for people who are obsessed with gas mileage you'll see some freaked out econocars which have had massive aero work and they get close to achieving 100mpg, etc.. but they look like something out of a sci fi movie.. it really is all in the aerodynamics.

http://forum.ecomodder.com/showthrea...90.html?p=2110

I think that's been posted before here.

[RandyO]

Originally Posted by Rossy83

Ok now think about the cost to implement such a plan. You can pay for it. And I'll just put a metal box over it so it doesn't get reception.

you might want to get up to date with GPS/GLONASS/Galleo technology

who's going to pay for it... you, me, everybody

Originally Posted by deslock

Likewise, government controls (via GPS tracking, etc) would never work (due to technical and logistical difficulties as well as the masses never accepting it... we're way too libertarian in this country to live with something like that).

you might be a libertarian, but the masses are sheep, after all, we have the Patriots Act

[Honclfibr]

Originally Posted by RandyO

you might be a libertarian, but the masses are sheep, after all, we have the Patriots Act

GO PATRIOTS!

Wait, what?

[deslock]

Originally Posted by RandyO

you might be a libertarian, but the masses are sheep, after all, we have the Patriots Act

True dat, but to be fair to the sheep, the Patriot Act wouldn't have passed without post-911 posturing and panic.

The 55 MPH federal speed limit implemented in the 1970s came about because of the nexus of both the fuel crisis and shifting attitudes about speed and safety. Today, automobile advocacy/lobbying groups are better prepared to prevent that from happening again.

[snowborder]

Originally Posted by wylee

How about not littering whether anyone is behind you or not?

In most western states it is a $10,000 fine and jail time for fear of wildfires... for throwing lit cigs.

[enzo_f1]

As soon as China starts making gas it will be cheap. It will probably screw up your tank and carbs, valves, and pistons though, everything they make is cheap.

[Pittenger5]

82 mpg!
Of course, I spent as much time as I could cruise controlling at 65 or so on the way to the track, and then would get someone doing 50 in the fast lane, slow down, eventually they'd move and to try to get back to speed the mpgs would drop instantly. So like someone said eariler, until people can learn to use the proper lanes a slower speed limit wont help a whole lot. People go (basically) as fast or slow as they want anyway.

[ceo012384]

Originally Posted by tsanto

I dont know much about aerodynamics but on a modern car the difference in 65mph and 75mph cant be that much in gas milage.

The second statement certainly verifies the first in your post.

The aerodynamic drag force on a moving object goes up with the SQUARE of the velocity.

For example, if the drag force on an object were 100 pounds at 50 miles per hour, it's about 260 pounds at 80 miles per hour. I.e. the force is 2.6 times the first even though the speed is only 1.6 times the first.

[d3ad1ysp0rk]

Any reduction in consumption from the US will be too small to reduce prices since the gas will just go to China instead..

Kinda ridiculous that because SOME cars get better gas mileage at 55 it should be the speed LIMIT. If my car gets better mileage at a higher speed, it's insane to limit that, unless it's a safety issue. I feel that enforcing the "Slower traffic keep right" laws and allowing people to make their own choices in regards to what speed they travel (within reason) is best.

[RandyO]

to all those who are spouting that their cage gets better milage at 65-70 whatever mph

your full of shit, you haven't driven at 55 long enuf to know what milage you get at 55, aerodynamics makes that much of a difference no matter how streamline your cage is

[Kham]

i'll go with Randy because he's been around as long as dinasaur.

my question is how do you determine if 55 works for every cars and especially modern cars? where exactly does aerodynamic comes into play for 18wheelers and for prius for example? i say start with 18wheelers. too many of them on the roads. then there's traffic congestions each days for each cities. that's gotta count for something. how do you solve that without going broke.