Sixth gear

E

edd_jedi

Active member
Having done quite a bit of motorway driving over the last few days, I've had a rare chance to use sixth gear. I haven't had a car with 6 gears before, I haven't even had a manual for a few years, so I'm somewhat disappointed with how useless it is :headbang:

Surely the whole point of a sixth gear on a fast car is either as an 'overdrive' gear for economical high speed cruising, or to enable the car to reach a high top speed. So why they have geared it to be only a couple of hundred revs below 5th gear is beyond me!

In sixth gear the 3.0 cruises at 70mph on about 3k revs, which isn't bad, but I'm sure the car would be far more economical if it was only at about 2k revs at that speed. And although I haven't had a chance to take it on the autobahn yet, I also don't see how the car has any hope of reaching its supposed top speed of (limited) 155mph if it's going to redline long before that?

It seems like a real waste of time to give the car six gears when it fulfills neither of the above. Has anybody looked in to adjusting the ratio for sixth gear in their Z4? I'm a bit disappointed with it as my last 2 BMWs (both autos) would cruise at about 2k revs up til 80mph, which is no doubt why they were so economical at high speeds.
 
edd_jedi said:
Having done quite a bit of motorway driving over the last few days, I've had a rare chance to use sixth gear. I haven't had a car with 6 gears before, I haven't even had a manual for a few years, so I'm somewhat disappointed with how useless it is :headbang:

Surely the whole point of a sixth gear on a fast car is either as an 'overdrive' gear for economical high speed cruising, or to enable the car to reach a high top speed. So why they have geared it to be only a couple of hundred revs below 5th gear is beyond me!

In sixth gear the 3.0 cruises at 70mph on about 3k revs, which isn't bad, but I'm sure the car would be far more economical if it was only at about 2k revs at that speed. And although I haven't had a chance to take it on the autobahn yet, I also don't see how the car has any hope of reaching its supposed top speed of (limited) 155mph if it's going to redline long before that?

It seems like a real waste of time to give the car six gears when it fulfills neither of the above. Has anybody looked in to adjusting the ratio for sixth gear in their Z4? I'm a bit disappointed with it as my last 2 BMWs (both autos) would cruise at about 2k revs up til 80mph, which is no doubt why they were so economical at high speeds.
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Totally agree with you, mine doesn't have 6 gears but often wish it did when on the motorway cruising...to drop the revs down, saving fuel as you said, but now I know it will not make much difference, i would expect/want the rev's to drop to about 2k when at 75mph in 6th gear
 
andrewr said:
I may be wrong, but I'm sure my 3.0 sits at around 2200 revs at 70mph.

Andrew.
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I think more like 2500-2700... I cant remember.

I agree entirely though Ed, 6th gear always seemed very lackluster with such a small drop in rpm.
useless for top end also unless you're absolutely bonkers and push the car to its limits...I never did.

p.s done the rear door seals on the e39 today, didnt take too long either and I haven't seen the engine management light for awhile :rofl:
 
Mine's an auto and 3,000 RPM in 6th is 90mph, pretty much exactly. I believe the gear ratios are slightly different between auto and manual, but not that different. You sure you were reading the instruments right ?
 
you wouldn't attempt max speed in 6th anyway. as you said its an overdrive cruise gear.

155 is easy in a 3.0 if your not getting there i would get your car looked at, im trying to be nasty but i was hitting it with ease on the autobahn and i find that if your arsing about its easy to hit silly speeds here.
 
I find at 80 in 6th it is still under 3000 revs. This will deliver 38/39 mpg if I drop to 5th revs go upto 3500 and mpg drops to 35. I have never been tempted to 155 mph so unsure what rev limiter would stop at.
 
Worth saying I still have loads of pull in 6th gear if I prevent the box from changing down. The torque in 5th and 6th is one of the things I love about my car on motorways.

If you leave it in 6th then it should easily hit the limiter at 155 without running out of revs, though it may take a while to get there. In 5th it may be possible to go past 155, but not sure - certainly Ms can, but of course they rev higher anyway.
 
I was coming back from Oxford some time ago and it was about 1am. Got off M40 and hit the M25 and the road was empty so I was in 6 just cruising... or so I thought as when i looked down I was doing 135 and the engine and pedal still had more to give... cant remember what the revs were but no way were they near the red line.

If you go on youtube you'll see nutters in Germany taking it to 155 with ease so yes the car can do it.
 
using a gear calculator and the ratios for my 3.0i 70 is about 2450 rpm and 3k = ~85. 155 is up at 5500.. its all calculated so you'll need to add some real world rpm in there but it shows its possible

123billy its easy done, i wasn't paying attention on a straight bit of motorway and was doing 70+/- 70% :D
 
Couldn't agree more mate, too long for spirited driving, too short for it's real purpose, motorway cruising. I was complaining to my mate just yesterday about how stupid the 6th ratio is.
 
Hi Edd, I asked a similar question a few weeks back, I have a 3.0si and my car reads 3k at 70mph. I thought it seemed high. Someone here replied that perhaps clutch is slipping but I have no other symptoms of this and economy etc is good.

Need an Si owner that's been on the autobahn to find out what the rev's were at 155! Perhaps it works as an overdrive once you hit 140 or so :D
 
One thing I will say is when i did a speed close to that years ago in my Saab 9-3 Aero, I was holding on for my dear life and both hands were on the wheel double tight... In the Zed I genuinely thought I was cruising and had one hand on the wheel.

Around town when on roads with speed humps, i just leave it in 3rd as the gears seem a bit lazy in the lower rev band but full of torque (depending on gear in relation to speed) then once at 3500rpm and above in whatever gear the car goes into nutter mode as that is when the full horses are kicking in.

I did 1500 miles around France earlier in the year taking in Le Mans on route and I was in heaven :D Trust me... If any of you get to do a 300 - 400 mile run on a good road, on a good day with the roof down, the smile on your face will say it all when you get out the other side :driving:
 
I'll double check next time I'm out on the motorway but I know for a fact the difference between 5th and 6th in terms of RPM was no more than a few hundred, I tried it out a few times. Seems a few other people agree so hopefully it's not a problem with the car.
 
are you on different wheels? that will make a difference if the rolling diameter is different.

rpm to speed conversion is roughly (rpm*tire circumf*60)/(final drive*gear ratio*1600)

a 255/35/18 wheel works out at 2750 rpm for 70mph but changing the diameter by ~5% will yield ~3mph difference this would be achieved simply by swapping to a 255/35/19 tire

having said that going up in wheel circumference will reduce the rpm needed to achieve a speed. 70mph will be achieved at 2600rpm on 265/35/19s

NOTE, this is a theoretical calc based on given figures so not taking into account any kind of losses due to the transmission etc.
 
I remember thinking this exact thing on the drive back after having just bought the car. The car came with a quad exhaust conversion and gets significantly louder after about 2,500 rpm and I was struggling to keep it under those revs whilst cruising on the motorway.
 
Hadies said:
I remember thinking this exact thing on the drive back after having just bought the car. The car came with a quad exhaust conversion and gets significantly louder after about 2,500 rpm and I was struggling to keep it under those revs whilst cruising on the motorway.
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It won't sit under those revs at 70 on the motorway for sure, but 3,000 at 70 is definitely too high. I can't see the auto gearing being so different to the manual, nor can I see that wheel size would make such a pronounced difference either. Strange one this :?
 
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