Why are top gears in so many cars so short??
Discussion
kambites said:
300bhp/ton said:
kambites said:
Personally, I'd like to see the actual overdrive unit make a comeback. I rather like the idea of having, say, a 5-speed close ratio manual box with an option to extend the final drive ratio by 50% for motorway cruising. Obviously some off-roaders have high and low range, which is much the same thing, why not cars?
I did a thread on this, must be a year ago I should think.Personally I loved the 4+2 OD boxes in the MGB. Not only did it offer the perfect blend of gearing options, it was also huge fun to use. And when "cruising" you could minimise the number of shifts you needed to make. I've only ever driven a few 6 speed manual cars, but in most of them you get the sense that you are constantly changing gear, which I found less than appealing.
Rawwr said:
Quite impressed with new Fiesta with it's little 1.0 tri-cylinder. Spins at 2,500rpm @ 70mph in 5th, which is really rather good for what it is.
On face value it is I guess. Although if that 1.0 litre is boosting 1 bar from the turbo, then it's dynamic or 'effective' displacement is 2.0 litres. Also a turbo designed to boost from low rpms will give a big mid range torque hike, thus allowing taller gearing.
james_gt3rs said:
The MR2 mk3 does 3000rpm at about 75mph, meaning you can get 40mpg on the motorway, pretty impressive for a sports car I think!
No doubt acceleration is quite poor in that gear though; Subjective, I know, you'll probably be happy enough with it, but someone else might find it too slow.There seem to be a few people among the earlier replies to this thread, who believe that because their engine pulls well in top now, that they can get away with a taller gear for motorway driving easily, and not suffer loss of performance. However, you may be surprised. My 350Z pulled like a train in 5th, but 6th was a surprisingly lacklustre gear, feeling very lazy and sluggish, and that was pulling 2,500 rpm so it wasn't like it was stupidly low RPMs either.
My Puma only has 125 bhp, so to make the most of it, it has to have short gearing (4,000 rpm @ 80 mph), which it does, and it makes the car feel so much quicker and nicer to drive than it probably really is. Possibly hard to believe, but my Puma is better in top in terms of acceleration than the 350Z was! But then, the Puma will be red lining at 6,500 rpm at 125 mph, whereas the 350Z would be just getting into its stride.
Personally, I've had cars that have had tall top gears, and they are an utter pain in the arse unless you've got some kind of auto. I'd rather have a few less MPG for much better drivability. Each to their own, though.
Mr2Mike said:
98elise said:
Don't assume that lower revs for the same road speed automatically means more mpg.
A car takes x power to sustain a set speed, regardless of the engine rpm. The difference mpg between two different rpms is down to the efficiency (ie losses in the engine) at a given rpm. You need to know at what rpm the engine is most efficient.
Lower engine speeds and higher throttle openings will most always be more efficient under cruise conditions.A car takes x power to sustain a set speed, regardless of the engine rpm. The difference mpg between two different rpms is down to the efficiency (ie losses in the engine) at a given rpm. You need to know at what rpm the engine is most efficient.
TameRacingDriver said:
No doubt acceleration is quite poor in that gear though; Subjective, I know, you'll probably be happy enough with it, but someone else might find it too slow.
There seem to be a few people among the earlier replies to this thread, who believe that because their engine pulls well in top now, that they can get away with a taller gear for motorway driving easily, and not suffer loss of performance. However, you may be surprised. My 350Z pulled like a train in 5th, but 6th was a surprisingly lacklustre gear, feeling very lazy and sluggish, and that was pulling 2,500 rpm so it wasn't like it was stupidly low RPMs either.
It has dick all to do with the RPM, and everything to do with the torque multiplication. Dropping 500rpm might only result in 2% less flywheel torque, but the change in ratio can mean a 15% drop in wheel torque.There seem to be a few people among the earlier replies to this thread, who believe that because their engine pulls well in top now, that they can get away with a taller gear for motorway driving easily, and not suffer loss of performance. However, you may be surprised. My 350Z pulled like a train in 5th, but 6th was a surprisingly lacklustre gear, feeling very lazy and sluggish, and that was pulling 2,500 rpm so it wasn't like it was stupidly low RPMs either.
I'm sure you know that, for the record...
james_gt3rs said:
TameRacingDriver said:
kambites said:
That's why god invented the gear stick.
And you want to be constantly changing gears on a motorway, do you? Righto....TameRacingDriver said:
james_gt3rs said:
TameRacingDriver said:
kambites said:
That's why god invented the gear stick.
And you want to be constantly changing gears on a motorway, do you? Righto....TameRacingDriver said:
kambites said:
That's why god invented the gear stick.
And you want to be constantly changing gears on a motorway, do you? Righto....If I really want to accelerate hard on the motorway in my car I use third gear, but I've done that maybe five times in the six years I've had it. I think I can cope with the stress of having to make an extra gear change every 14 months.
Edited by kambites on Wednesday 19th June 11:13
TameRacingDriver said:
Personally, I've had cars that have had tall top gears, and they are an utter pain in the arse unless you've got some kind of auto. I'd rather have a few less MPG for much better drivability. Each to their own, though.
So just don't use top gear, leave it in 5th or 4th or something.The worst offender I've ever known was an 05 Transit flatbed that we had as a site vehicle at work.
This thing was so low geared that in 5th gear at 70mph, it was getting on for 4000rpm! It had the old 2.5 non common rail turbodiesel engine which was a rough, noisy, clattery old thing even at low engine speeds. The noise, vibration and fuel consumption at 70mph were all so bad that most of us resorted to sitting behind any convenient lorry doing 56.
We've just replaced it with a shiny new 'un, which has the newer 2.2 TDCi engine producing a similar power output (about 90bhp). But it's got a nice 6 speed gearbox, and in top gear it's doing well under 3000rpm at 70mph. Nice quiet engine too, and manages close to 30mpg compared to the old heap's 17!
This thing was so low geared that in 5th gear at 70mph, it was getting on for 4000rpm! It had the old 2.5 non common rail turbodiesel engine which was a rough, noisy, clattery old thing even at low engine speeds. The noise, vibration and fuel consumption at 70mph were all so bad that most of us resorted to sitting behind any convenient lorry doing 56.
We've just replaced it with a shiny new 'un, which has the newer 2.2 TDCi engine producing a similar power output (about 90bhp). But it's got a nice 6 speed gearbox, and in top gear it's doing well under 3000rpm at 70mph. Nice quiet engine too, and manages close to 30mpg compared to the old heap's 17!
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