6th Gear Query

[P1H]

This sounds like a stupid question and most likely is a stupid question....

Nevertheless, [aside from not being able to accelerate quickly and react] are there any disadvantages to driving a car in 6th gear at slow speeds i.e. 25-30mph when in traffic.

Basically, does it put any undue stress on the enginge?

Cheers,

[edit: I'm referring to my Honda CIvic Type R EP3]

Edited by P1H on Tuesday 17th April 11:11

[DanDC5]

Aside from not accelerating very quickly it won't do anything bad. I stick the Integra in 6th pretty much all of the time once I'm upto whatever the speed limit is.

[MX7]

Yes, it can do. Also, engines aren't usually at their most efficient at very low revs.

[Cupramax]

It depends how high the gearing is and the engine itself. My A5 will pull from 1000rpm in 6th quite happily on the flat but its a 3.2 V6, I'm guessing a small engine would labour badly. You wont do the engine any good whatsoever doing this.

[McSam]

No, but if you want to use sixth at such a low speed, don't go giving loads of boot because you will labour the engine. For crawling along under no or very little power, no problem.

In most cars, there's usually only a slightly bigger difference between fifth and sixth than there is between fourth and fifth. So it's simply an extra gear, nothing special about it!

[P1H]

MX7 said:

Yes, it can do. Also, engines aren't usually at their most efficient at very low revs.

I see, can you explain why that might be?

[McSam]

Generally an engine is capable of its highest part-load efficiency at low revs, but not so low that you approach the stall speed of the engine. Depending on what car you're talking about, optimum will usually be 1500-1800rpm.

[MX7]

P1H said:

I see, can you explain why that might be?

I don't know what car you're thinking of, but, for example, with DMFs the transmission feels so smooth, that people change up at very low revs, not realising that their flywheel is working overtime to compensate.

[Ledaig]

Try to think of it this way….

Imagine you are riding a push bike, first off you want to start in 1st gear – it’s all nice and easy as the ratio take the force you are putting in and turning into motion with no bother whilst you comfortably sit on the saddle.

Now try and do the same standing start whilst in 6th gear, suddenly the power you are putting in can no longer be turned into forward motion with ease, in fact you end up standing on the pedals to get things moving, thereby putting more power in for less out and subjecting the driveline to unnecessarily high forces.

[P1H]

McSam said:

No, but if you want to use sixth at such a low speed, don't go giving loads of boot because you will labour the engine. For crawling along under no or very little power, no problem.

In most cars, there's usually only a slightly bigger difference between fifth and sixth than there is between fourth and fifth. So it's simply an extra gear, nothing special about it!

That makes a lot of sense.

The only reason I referred to the 6th gear is because it happens to be the top gear on my car, perhaps should have been 'topgear query' but then I imagine the thread would have be boycotted!

[David87]

In most cars, 3rd or sometimes 4th will be the gear you should usually be in between 25-30mph. I doubt my Focus would happily cruise in 6th at that kind of speed.

[P1H]

McSam said:

Generally an engine is capable of its highest part-load efficiency at low revs, but not so low that you approach the stall speed of the engine. Depending on what car you're talking about, optimum will usually be 1500-1800rpm.

Aha, I'm referring to a Honda Civic Type R EP3, because of its gearing, 6th gear at 30-40 is around 1500 revs so that should be fine.

[vixen1700]

Learning the gearing on the EP3 Type R too. Although I've done about 600 miles in it since 31st March.

I find it's fine at 45 in 6th and pulls very strongly with no stress at at all, any thing lower than that, I'd change down.

[7mike]

Presumably, if you're in traffic your speed will fluctuate due to constantly changing conditions? I'd suggest, no sooner are you into sixth than you will be needing something lower. I personally find selecting a gear ratio that allows flexibility without the need for constand gear changing far more fuel efficient (I'm presuming that's your motivation for using sixth in these conditions).

[cragswinter]

interesting topic & i was thinking about this just the other day. in a steady 30 mph crawl i'll stick the Z4M in 6th, it's chugging over at about 1100rpm.

the reason i was thinking about was this:

when doing this speed i can usually look pretty far ahead & spot when i may need to speed up, and in this case i usually drop to third or fourth before accelerating as the traffic allows.


however......

i'm well aware of the various sensors & fly by wire throttle that the s54 3.2 ///M engine my car has, so, if i were to floor the throttle in 6th at 1100rpm, would the "computer say no" & the ecu feed the engine the required amount of air & petrol to stop the engine from unnecessary labouring but merely safely gradually increase speed within the limits of the design?

[BorkFactor]

Is doing this not what sometimes causes premature wear of the DMF in modern diesel engines, and some petrol engines?

[Krikkit]

Have a look here for brake-specific fuel consumption info - i.e. what happens out there in the real world. Interesting reading.

[P1H]

Ledaig said:

Try to think of it this way….

Imagine you are riding a push bike, first off you want to start in 1st gear – it’s all nice and easy as the ratio take the force you are putting in and turning into motion with no bother whilst you comfortably sit on the saddle.

Now try and do the same standing start whilst in 6th gear, suddenly the power you are putting in can no longer be turned into forward motion with ease, in fact you end up standing on the pedals to get things moving, thereby putting more power in for less out and subjecting the driveline to unnecessarily high forces.

A very good analogy, but I wondered if this was the case in a car when you have already got up to speed, i.e. 30mph, as I imagine the effort required to keep the car moving at 30mph is next to none [on a flat road without an immense headwind]

[MX7]

Ledaig said:

Try to think of it this way….

Imagine you are riding a push bike, first off you want to start in 1st gear – it’s all nice and easy as the ratio take the force you are putting in and turning into motion with no bother whilst you comfortably sit on the saddle.

Now try and do the same standing start whilst in 6th gear, suddenly the power you are putting in can no longer be turned into forward motion with ease, in fact you end up standing on the pedals to get things moving, thereby putting more power in for less out and subjecting the driveline to unnecessarily high forces.

Nicely worded.

[Ozzie Osmond]

Driving in too high a gear is daft and is actually the worst thing you can do to your engine. Modern engines can take high revs no problem but labouring the engine is very bad, causing accelerated wear to major internal components.

Imagine you're riding a bicycle. When you're pedalling fast in a low gear the bike is easy to move forwards. But if you put the bike in a high gear you find yourself having to stand on the pedals and apply immense force to get/keep the bike moving. It's exactly the same inside an engine.

At the end of the day using a bit more petrol in a lower gear is massively cheaper then ruining your engine.