Gear selection for economy

[themoog75]

I recently did a speed awareness course, and one of the guys running it was conducting a conversation about gear selection. I suggested that 4th gear was perfectly suitable for a 30 mph limit whereas he said 2nd at 20, 3rd at 30, 4th at 40 and 5th at 50. I pushed him as to why 3rd at 30 was better than 4th and his answer was "it's a more flexible gear, and your car will be doing around 1700 rpm in that gear at that speed."

This has led me to conduct some experiments regarding rpm, gear and speed, using my Peugeot 206 1.4, and here are my results:

20mph - 2nd = 2250rpm, 3rd = 1500rpm, 4th = 1100rpm, 5th = 800rpm.

30mph - 2nd = 3150rpm, 3rd = 2200rpm, 4th = 1750rpm, 5th = 1300rpm.

40mph - 2nd = 4500rpm, 3rd = 3000rpm, 4th = 2300rpm, 5th = 1700rpm.

50mph - 3rd = 3800rpm, 4th = 2950rpm, 5th = 2250rpm.

60mph - 3rd = 4600rpm, 4th = 3500rpm, 5th = 2750rpm.

70mph - 3rd = 5500rpm, 4th = 4250rpm, 5th = 3250rpm.

As far as I can tell I am better off using 3rd at 20mph, 4th at 30mph and fifth everywhere else...not only do they fall within the flexible rev range the course tutor was talking about (lets face it, a 1.4 with 75bhp isn't going to pull strongly anyway) but it's also more economical to be 1 gear higher than was recommended to me. This will also be more mechanically sympathetic to the components in the engine (not over revving but also not labouring) and should help keep repair bills down and help maintain longevity of the car as I am in a position where it has to last me for a couple of years yet. It's mostly used for the daily commute and I am currently averaging 45mpg and cover almost 200 miles per week...for now, economy is king and sympathetic driving is all I am prepared to do in it.

Or have I got it wrong? Would my car in fact be happier at 2200rpm at 30mph? Should I be a bit more spirited with my driving style? Any thoughts or comments would be very welcome.

[themoog75]

Max_Torque said:

"flexible" is irrelevant

That's pretty much what I thought at the time. Tbh I am perfectly capable of controlling the car in fifth gear at 30mph. In fifth at 20mph though I find the car is pulling itself along and when I dip the clutch to change down the revs jump before settling. This along with there being no chance of accelerating at all unless I change down suggests it isn't the safest way to drive. When I mentioned 'labouring' the engine, I was referring to being in too high a gear at too low a speed and totally negating any economy benefits.

I brim the tank every time I fill up and calculate the mpg from there. I also et the tyres to the manufacturers recommended psi at the same time as filling up. Over the last four weeks I spent the first 2 doing as the tutor suggested (2nd at 20, 3rd at 30 etc) and got 43.9 and 44.1 mpg. Over the last two weeks I have used my method of 3rd at 20, 4th at 30 and have got 44.8 and 45.6 mpg. For the next 2 weeks I will try the highest gear at the lowest speed method and see how that goes.

[themoog75]

Pica-Pica said:

As for economy? Just get the car into the highest gear it is comfortable with. Judging by my 335d Auto that seems to be any gear that matches 1250 rpm. So for modern cars a quarter to a third of peak revs.

Your 335d is a massively different best to my 206 1.4 though, although I completely get the meaning and I am sure I can experiment and find what the car is comfortable with. Wouldn't mind your torque output though...I think I am supposed to have about 75 bhp and 88 lb-ft torque...Interesting to note that the 206 2.0 hdi only makes 90 bhp yet develops 154 ft-lb torque.

Official fuel consumption figures for my car says 42 mpg, which I am exceeding at present, but I am sure I can squeeze a few more mpg out of it yet.

Edited by themoog75 on Saturday 16th June 13:00

[themoog75]

Highest gear at lowest speed has seen my little 206 return figures of 49.08 mpg this week. I am suitably impressed by that...almost diesel economy from a 16 year old 1400cc petrol.

[themoog75]

Wooda80 said:

themoog75 said:

As far as I can tell I am better off using 3rd at 20mph, 4th at 30mph and fifth everywhere else.

I may regret asking this, but considering the effort put into the extensive tabulation in the first post and currently being stuck in that dull, empty void between Saturday afternoon and Saturday night, I'll go for it:

So when you are driving in a 30 limit, and presumably therefore your speed ebbs and flows with the traffic between 20 and 30 mph, given your remark in the above quote, are you generally in 3rd gear, 4th gear, or continually swapping between the two?

Err...neither. As I said in my last post, highest possible gear at lowest possible speed gives me the best economy, and as much as possible I leave a big enough gap to maintain a constant speed, thus minimising the need to brake or change gear often. Clearly this isn't always possible and common sense wins over in most situations. Driving through my town at half five every morning, I am lucky to see another car so 5th is totally fine, and driving back I miss the rush hour traffic so again, 5th is fine.