Crime does not pay - at least not when speeding:) - Fuel Economy, Hypermiling, EcoModding News and Forum

lowglider · 06-20-2012, 11:20 AM

So, I had a 90km each way trip today and about 70km of that was highway with neglible sea level difference.

Felt in a very scientific mood, so I did an A-B test on the highway.
A: Driving up to 170km/h where safely possible on the open road and up to 130km/h in the tunnels while keeping at least a 2 second distance behind the vehicles upfront. Tried to use as little brakes as possible, but still had to brake a lot due to lane changers who forget their turn signal before they go on the speeding lane.
Result: average speed of 123km/h and a fuel consumption of 7.2litres/100km.

B: Driving up to 140km/h on the open road and 110km/h in the tunnels.
Result: average speed of 114km/h and a fuel consumption of 5.2litres/100km.

The car was a Renault Laguna 1.5dCi with A/C on all the time and the stereo blasting Helix through 9 speakers

I didn`t expect a big difference in average speed or the fuel economy, but going only 8% faster for 38% more fuel has been a hit in the face. Not to mention driving slower has yet again proved to be more relaxing because I almost never had to use the brakes.

So, speeding does save time on an empty road, but in average traffic conditions it is only up to a certain point that you are rationally saving time, beyond that it is only a hazard and a big no no for both your wallet and your nerves

JRMichler · 06-20-2012, 01:09 PM

Quote:

Originally Posted by lowglider

So, speeding does save time on an empty road, but in average traffic conditions it is only up to a certain point that you are rationally saving time, beyond that it is only a hazard and a big no no for both your wallet and your nerves

Good point. You slowed down by 30 KPH (18%) , but your average speed dropped only 9 KPH (7%). The additional travel time was only 3.5 minutes.

oil pan 4 · 06-20-2012, 03:27 PM

Well when you double your speed, the horse power required to maintain that speed goes up by a factor of about 8.

Cobb · 06-21-2012, 09:12 PM

Yupp, at least not if you are the lead vehicle. Ive found if you draft it doesnt hurt as bad, but its better to coast than brake for mpg and if you got a hybrid, to charge its pack.

I found it interesting that over all my tank average dips by 5 when I choose to go 55mph vs keeping up with traffic.

UFO · 06-22-2012, 02:04 AM

Quote:

Originally Posted by oil pan 4

Well when you double your speed, the horse power required to maintain that speed goes up by a factor of about 8.

I think it's a factor of 4, but it certainly is a lot.

Diesel_Dave · 06-22-2012, 10:32 AM

Quote:

Originally Posted by UFO

I think it's a factor of 4, but it certainly is a lot.

The drag force is a second order equation, i.e. double the speed and the drag force is 4 times greater. However, doubling the speed also doubles the rate at with the force is applied, hence, 8 times the power.

UFO · 06-22-2012, 01:04 PM

Thanks, I did not know that.

oil pan 4 · 06-22-2012, 11:16 PM

Quote:

Originally Posted by Diesel_Dave

The drag force is a second order equation, i.e. double the speed and the drag force is 4 times greater. However, doubling the speed also doubles the rate at with the force is applied, hence, 8 times the power.

This is driving force behind the reason a car with roughly 100 horse power with the proper gearing like a 5-speed neon can top out at about 100mph, but it takes a nextel cup car with its roughly 800hp engine to go hit a top speed of some where around 200mph.

SentraSE-R · 06-23-2012, 12:13 AM

I concur with the OP. High speed data below are based on 100+ mile drives with cruise control set. 35 mph data are short drive numbers for comparison.