So every car has an optimum speed to achieve the best MPG, I am curious if anyone knows what the optimum speed is for our celicas?

Both 5SFE and 7AFE. I know there is an acutal formula to figure it all out, but i dont have it anymore:(

thanks

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I think most cars average best MPG around 50-55. Depends on if you're manual or auto though.

-TC

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About 55 for most cars. In my opinion the difference in MPG between doing 55 and 65 is worth the savings in time. I cruise about 80 mph the whole way to class (about 40 miles each way) and average out to 28 mpg with city driving as well.

This is something I've always wondered about...

Shouldnt we be achieving the best mpg when the engine is at the lowest possible rpms while in the highest gear without bogging the engine?

For example cruising at 40 - 45 mph in 5th gear I'm guessing is around 1.5k rpm and should in theory be burning less fuel per mile than it would at 55 mph at 2k rpm?

I have one buddy that insist that no that's not true but at least with my current understanding of how EFI works it makes sense to me and that the 55mph speed limit is actually pretty arbitrary and a generic 'efficiency point'.

Anyone want to correct / verify this?

thats how i thought it worked. ive always seen it as an rpm thing as opposed to mph.

If you're REALLY wanting to improve your gas mileage, then start looking around at hypermiling sites. there's different driving techniques that can help you increase your gas mileage. After reading a little bit about it and experimenting around with different things, I improved my gas mileage in my work car (hyundai tiberon) from 30 to 36mpg. Generally I think that slower is better mpg wise, but it seems that the biggest gains can be from slowing down your acceleration.

The APA stated that past 100 km/h, every time you increase 10 km/h = 10% more gas

So lets say at 100 km/h = 10 L/km
110 km/h = 11 L/km
120 km/h = 12.1 L/km
130 km/h = 13.31 L/km

sorry i dont know about mpg and miles, we use kms

Also, below 70 km/h you consume less gas with the windows open but pass this point (70 km/h +) its more economic to close the windows and open the A/C

This post has been edited by reko: May 8, 2009 - 9:01 AM

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x2. driving at the lowest rpms at the highest gear while depressing the gas pedal as little as possible to keep it driving at a steady speed without bogging the engine is how you'll achieve your best mpg. higher rpms will increase gas consumption (while rpms are directly proportional to speed while on the same gear, gas consumption is not directly proportional to speed) and driving faster will just increase air resistance (unless you're getting tail wind faster than your driving speed). just my opinion, not sure if this is exactly true.

This post has been edited by azian_advanced: May 8, 2009 - 10:47 AM

I am not looking on improving my MPG as i am very happy with it.

There is a formula to calculate when an engine is its most effecient. by using how many joules of energy it is creating VS the amount of fuel required to acheive that much energy or something like that.

I know that everyone says 50-55 MPH is great, but i want to know what is the best for our cars, not just in general.

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i see what you mean ok, you're looking to find out the most torque one can get while using the least amount of fuel possible. so this no longer has to do with anything with speed then?

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well, the title of the thread says "optimum speed for best MPG" so we assume your talking about gas milage.

that really dont have much to do with engine efficency as much as gearing, and throttle manipulation.

slow and steady gets you the best mpg, but also a very boring life.

or not driving at all

never mind

25 mph for the gt, yeah I know it's slow but you get some serious miles to the gallon there. I forgot where I read that, don't quote me on it.

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Yes,
But there are other factors at play. For instance, if you're doing 1.5k rpms in 5th, you can be doing a lot of detrimental harm to your engine. Causing it to turn over slower than it's supposed to, and keeping it well outside of your power band can harm your crank, rods, and cause some nasty build up on your pistons. A good rule of thumb is to keep RPMS above 2k, and under 3 while cruising. I prefer to shift around 3.5-4 since then I'll be using my power band and allowing my engine to breathe.

If you really want great mileage, accelerate (once) as fast as possible every other time you fill up. This will cause less carbon build ups. These build ups will eventually weigh down your pistons, and cause them to fire incorrectly (think about valving). Obviously, do this safely, and it should only be done once in a while rather than all the time.

After doing this, just cruise. You'll get the gas savings you want, and will also keep your engine healthier. Obviously this is a little bit counter intuitive, but lick up old Jaguars and Ferrari's, it's a method that's required to keep their engines purring.

As far as an equation, I have no idea. Honestly, I don't think that it'll do you much good either, since you would have to keep it at that exact MPH/KPH in order to get the savings. Those equations also don't take into account acceleration, which is one of the biggest forms of gas consumption. If you have a heavy foot when accelerating and a soft one when cruising, you'll likely cancel out any savings you'd make.

Not to mention that it's probably some absurdly low number that wouldn't be safe to drive at on a freeway. Even though most cars benefit around 50-55, you'd be pulled over if you attempted that on a freeway for blocking the flow of traffic.

-TC

^^^ You clearly have never driven in oregon everyone drive 50:( its lame, so i moved to washington;)

I know it wouldn't account for acceleration but i am just thinking about cruising on the freeway for hours at a time, not so much the driving to the freeway part:) lol

I've found consistently that I get my best MPG between 60 and 65. Yes, in OREGON. The 'couve sux anyway.

optimum speed for best MPG, I dont think there is such a thing in terms of practical numbers, there are far more outside affects to your MPG then speed. wind direction, hills, rain, snow, sand dirt, road bumps etc. big gains can be seen from following semi's (or similar huge boxes) (NOT TO CLOSE!) due to the pocket of air there pulling behind them, going against the wind significatly increases the amout of power your engin has to put out to keep at speed, with the wind allows for much less power thus much less ges. similar but more drastic is going up hill or downhill, one trick to saving gas, going up hill is let the car slow down gradualy, dont keep it at speed, going down hill, let the car speed up (coasting) then when you get to flat it can coast further dropping back to speed limit.

I would say optimum speed for best MPG is dependent entirely on the driving conditions, but can probably be averaged.

6, i say 6 miles an hour.... that'll get it