Driving lower speeds in a high gear

[Jim Prower]

I can drive around in 6th at about 35, and the SE-R's just fine. It'll pull in that gear from 30 as well. I only have to go down to 4th at 25 or less.

Granted, redline is at 6,000.

 

[homeforsummer]

It can cruise at 30 in 6th, if the road is downhill or level, and you don't need to accelerate...

And it should be more economical doing so. If I don't need to accelerate I tend to stick it in as high a gear as possible, just enough to maintain, but not gain momentum. If I need to accelerate I'll change down, but I'll never keep it in a lower gear than necessary just to cruise.

Unless say I'm getting ready to overtake on an A road, where I may drop from 6th to 4th or 3rd while the approaching traffic passes, where I'm then ready to accelerate immediately as soon as the road is clear.

The other exception is my Beetle, which in my limited time driving it I tend to keep it in whatever gear is comfortable for the speed. Old VW flat-4s apparently don't like to lug (they're torquey but not designed for chugging at low revs) so I'll tend to keep it in whatever gear gives me a decent amount of revs, rather than whichever one saves the most fuel. I don't really care what MPG the Beetle gets since it's not a car I'll be using for high mileages.

 

[daan]

And it should be more economical doing so.

Economical being relative... 💡

 

[ozyran]

I was doing some research this morning and came across a post on a forum that said something about accelerating your car from a low speed in a higher gear puts too much pressure on your engine. For example, when rolling up to a red light and it turns green when I'm doing ~5 mph I'll leave it in 2nd gear and accelerate away, using the low rpm torque of the motor. This could be anywhere from 1,300-1,600 rpm. Depending on the speed I'm traveling, I'll pretty much do this in any gear.

Bad for the motor? I know it's better for mileage which is why I've been doing it. Filled up last night and got 37.6 mpg on the last tank. 👍

The only real concern I've seen when it comes to lugging the engine is that you're turning low RPM and placing a high load on the engine. High load = high stress, low RPM = low oil flow.

The combination of high stress and low oil flow isn't generally good for an engine, as I understand it.

I can drive around in 6th at about 35, and the SE-R's just fine. It'll pull in that gear from 30 as well. I only have to go down to 4th at 25 or less.

Granted, redline is at 6,000.

Running a Powerstroke I take it?

 

[Keef]

Economical being relative... 💡

The road I usually take to get anywhere of importance is slightly downhill both ways, as my house is near the middle of it. When my engine is cold I never have to touch the gas pedal from the moment I turn the key until the lights at either end of that street. I just use my 2500 rpm cold idle all the way through the gears. That ends up in 5th at 35 mph, 10 over the limit.

 

[Famine]

And it should be more economical doing so. If I don't need to accelerate I tend to stick it in as high a gear as possible, just enough to maintain, but not gain momentum. If I need to accelerate I'll change down, but I'll never keep it in a lower gear than necessary just to cruise.

The Baron hates this.

Around town in 5th - relatively steady 30-35mph - you'll see mid-twenty mpg. Keep it in 4th and you'll see mid thirties. If you're bobbing from 20-30mph, you may as well stay in 3rd and get 30s. Urban book is 24. If you stay in 5th you'll meet it. In 4th we destroy it.

Try the rule of tens (cruising in gear = 10mph * gear) for a couple of tanks and see what happens

 

[savage388]

There may be extra wear and tear accelerating from low rpm in a high gear but I really have yet to see any. I drive a 1.6 liter with 90,000 miles and I'll pull it full throttle from low revs(no tach so I don't know how low) to around 4500 rpm daily just to keep up with traffic on the hills and the car runs like a top. Also the syncro in 2nd is toast so that makes for some really hard 3rd gear pulls. So I don't really see the problem with sticking it in a high gear and putting around at 2 grand or less all day.

 

[homeforsummer]

Try the rule of tens (cruising in gear = 10mph * gear) for a couple of tanks and see what happens

I can try it but suspect it won't work in my car. Gears are too closely-stacked, so in several of the gears at the "correct" speeds it'd be doing around 3k rpm, which is no good for economy at all (in the Fiat as a rule if you can hear the engine, UR DOIN IT RONG, as far as economy is concerned).

Suspect the Baron's extra weight means you'd be using a little more throttle than is healthy to maintain economical progress at that speed in a higher gear, so it probably prefers a lower throttle opening in a lower gear.

Incidentally, I tried using the "sport" mode for a bit in my car* - the engine map changes to offer wider throttle openings below 3k rpm, which makes it massively more responsive at low revs (also great for charging up motorway inclines instead of dropping a gear). I thought it might allow me more precise control for better economy, but it made zero difference most of the time and was slightly worse overall - presumably the car prefers wider, mushier throttle openings in the normal map to smaller applications of bigger quantities of fuel and air in sport.

*I do use sport mode occasionally, just not usually when I'm trying to be economical...

Edit: I've not got a lot to do today so I might see what my trip computer says I'm getting in each gear using the rule of tens.

 

[Famine]

Baron has a current fuel economy gauge (with a needle and everything!) as well as a digital trip computer. Which is remarkable considering it's a 1998-introduced, nearly entry-level model (2.5 litre straight six... "entry-level" ) of a large, heavy, estate variant of a German saloon car - as if someone driving the V8 will care about it or be able to reach the 50 on the gauge

It's good fun to watch it and tinker with throttle positions and gears.

 

[TP1]

I never put it into first gear when breaking, even when coming to a full stop.
My car has the engine the size of a loaf of bread (3 cylinder, 35 BHP) and putting into first gear any other time than leaving feels like being rear ended, plus it will also feel really hard to put it into gear.

Progressively downshifting and breaking till 2nd gear and then just breaking in neutral till stop, or cruising in neutral if I'm significantly far away and have no cars around me that I'd bother going slow, is how I roll: no fuel wasted, no breaks heated up; just perfect.

 

[homeforsummer]

Baron has a current fuel economy gauge (with a needle and everything!) as well as a digital trip computer. Which is remarkable considering it's a 1998-introduced, nearly entry-level model (2.5 litre straight six... "entry-level" ) of a large, heavy, estate variant of a German saloon car - as if someone driving the V8 will care about it or be able to reach the 50 on the gauge

It's good fun to watch it and tinker with throttle positions and gears.

Bee-Ems have had those little swinging gauges for yonks - I think they've only recently stopped including them in the dials. They're quite useful really and fairly easy to work out what MPG (roughly) you're getting at a glance.

The Fiat's is an electronic one and seems accurate enough (my lifetime MPG readout says 43.7mpg, my own on-paper calculations come to 42.2 - 3-4% difference probably explainable by speedometer discrepancy) so I assume the instant read-outs are fairly accurate too.

 

[Crash]

Baron has a current fuel economy gauge (with a needle and everything!) as well as a digital trip computer. Which is remarkable considering it's a 1998-introduced, nearly entry-level model (2.5 litre straight six... "entry-level" ) of a large, heavy, estate variant of a German saloon car - as if someone driving the V8 will care about it or be able to reach the 50 on the gauge

It's good fun to watch it and tinker with throttle positions and gears.

I have the swinging needle mileage gauge on my 325iX also and it's sort of become a game to see if I can get it to read as high as I can while maintaining regular traffic speed on the freeways.

 

[Famine]

Good to know it's not just me then

I can keep it pegged between the 30 and 50 (Imperial mpg, rather than US mpg) marks pretty much all the time now, which isn't bad for 1.7 tonnes of straight six - rated at 28mpg combined

 

[Crash]

I hate you. My car is apparently rated at 18 US mpg combined (that's from the US DoE). Doing about 2/3 highway and 1/3 city driving, I average about 23 US mpg. I can keep my gauge between 20 and 40 US mpg unless the hill is really steep.

My car weighs about 3000 pounds and I get crappier fuel mileage than you do.

 

[Famine]

I drive really fast too

I guess the decade between the engines (the M52 in mine was a 1994 development, the M20 in yours was 1985) makes a hell of a difference. Possibly the 4WD too?

 

[homeforsummer]

Not to mention aerodynamics. E30s are rather brick like, E39s are quite sleek by comparison. And we all know estate cars have marginally better aerodynamics than sedans, too.

 

[Famine]

Yeah, but aerodynamics only come into play at high... oh, right.