Why such tall first gears?

[Ozzie Osmond]

It's very simple, in many cars acceleration is tailing off by the time you get to the red-line and you'll accelerate more quickly in the next gear. There's a difference between marking your rev counter with red-line to protect the engine and marking it with a change point for maximum acceleration.

As always, just because you're making a lot of noise doesn't guarantee you're going fast.

[alangla]

ZesPak said:

BritishRacinGrin said:

Kuga- maybe more likely to be heavily loaded or used for towing, ergo short 1st?

My Patrol had a very short first and second, to get it rolling easily with big loads. Same goes for most vans.

As mentioned above, for some cars it's just enough, some will do it for fuel economy and others will avoid having to go to third for the magic 0-100km/h number.

The other thing is, I guess, that if you're starting away onto a large roundabout in something with a long first gear, you can usually get it established on the roundabout itself before changing up - I found when I was driving the in-laws Ducato based motorhome earlier in the year that if you used first to get the wheels turning, you were usually going for second while you were halfway across the traffic flow & still turning onto the roundabout.

Most trucks (i.e. 7.5-17.5 ton range) with manual boxes had first set so low it was only really usable for very steep hills & off-road stuff, even when loaded. Generally you'd pull away in 2nd & never go near first.

[Scuffers]

Ozzie Osmond said:

So let's hear who, in what car, and where, is taking their car to the red-line in first gear...

never, but not because of what you're getting at.

usually the rev-drop between 1st and 2nd is massive, for example

Gear / MPH
1 / 37
2 / 67
3 / 94
4 / 121
5 / 149
6 / 176

(this is for an Audi S5 with a 7K limit)

so, if you change from 1st to 2nd at the limiter, the engine has to drop some 3,100 Rpm, this is a massive drop for a heavy input shaft/clutch/gearset to be slowed down by 2nd gear syncro, thus it's never going to be a fast change and it's also likely to crash 2nd gear.

the issue is 1st is not a very tall gear in comparison, if you make it a 45Mph gear, the rev-drop would be down to ~2,200Rpm, much more manageable, but would make parking speed clutch drag a problem.

Ideally, you need 7/8 speeds to cover this with 1st as a maneuvering/traffic gear only (much like some auto's do now).

[Speedy11]

Ozzie Osmond said:

It's very simple, in many cars acceleration is tailing off by the time you get to the red-line and you'll accelerate more quickly in the next gear. There's a difference between marking your rev counter with red-line to protect the engine and marking it with a change point for maximum acceleration.

As always, just because you're making a lot of noise doesn't guarantee you're going fast.

For most cars this simply isn't true.

Look at this pic as an example



Torque at the wheels at the redline in 1st is much greater than 2nd @ ~ 6000 rpm

[Martin_Hx]

Dracoro said:

When I had my S2000s, all the time

I must admit it is fun to do in the Civic, although i don't make a habit of it! Rolling at about 10mph then find that red line

Short gearing + Light flywheel, this thread really isn't for me!

[mph1977]

as has been said by other posters

2nd long enough to hit 100kph - meaning a short large van / truck style 1 st would be a huge gearing jump

4 is still seen as 'direct drive' making 6th super overdrive

[IanCress]

Ozzie Osmond said:

It's very simple, in many cars acceleration is tailing off by the time you get to the red-line and you'll accelerate more quickly in the next gear. There's a difference between marking your rev counter with red-line to protect the engine and marking it with a change point for maximum acceleration.

As always, just because you're making a lot of noise doesn't guarantee you're going fast.

This might be the case when changing from 4th to 5th or 5th to 6th, but there's no way that changing from 1st to 2nd early will ever give you MORE power, as the drop in revs is so great. If you're going to red line any gear, then do it in first, as you'll see the biggest benefit.

[cologne2792]

My '84 2.8i five speed Capri manages 43 in 1st, 77 in 2nd and 108 in 3rd. It's over geared due to lack of investment by Ford and the re-using of the four cylinder five speed 'box rather than them spending some money and modifying the existing four speed.

[BritishRacinGrin]

Speedy11 said:

For most cars this simply isn't true.

Look at this pic as an example

Torque at the wheels at the redline in 1st is much greater than 2nd @ ~ 6000 rpm

I'm not sure that saying 'for most cars' and then using an RX-8 for your example is really proving your point, the RX-8 is somewhat of a special case being that it revs to north of 9000RPM and delivers no torque below about 6000. The majority of petrol engines probably have peak torque below 4000RPM.

[Matt UK]

kambites said:

BritishRacinGrin said:

The ratios are probably fine-tuned to maximise fuel economy on the prescribed EU efficiency cycle test thing.

That and often to make sure the car can hit 60 (or maybe 62) in second to avoid the need for a second gear change.

Agreed. In order to hit 100kph in 2nd, 1st needs to be long enough not to leaving a yawning gap.

[xRIEx]

Dog Star said:

My old R1 would do something mental like 108mph in first.

I think mine may have done 99 in first, on the speedo at any rate.

[Mr2Mike]

BritishRacinGrin said:

I'm not sure that saying 'for most cars' and then using an RX-8 for your example is really proving your point, the RX-8 is somewhat of a special case being that it revs to north of 9000RPM and delivers no torque below about 6000. The majority of petrol engines probably have peak torque below 4000RPM.

And once again we enter the misunderstood and tedious world of engine torque vs power. The gearbox is a torque multiplier, and it provides the highest multiplication in 1st. Torque at the wheels in 1st gear at maximum engine power RPM will be greater than in 2nd gear at maximum engine torque RPM for almost any car. If this wasn't the case then it would never be worth dropping a gear or two to gain better acceleration (though this might be a difficult concept for many drivers).

On a petrol engine maximum power will usually be fairly close to the red line. Diesels are a bit different as torque tends to drop off a cliff face at high RPM so it's rarely worth approaching the red line.

Edited by Mr2Mike on Monday 11th August 11:32

[xRIEx]

BritishRacinGrin said:

Speedy11 said:

For most cars this simply isn't true.

Look at this pic as an example

Torque at the wheels at the redline in 1st is much greater than 2nd @ ~ 6000 rpm

I'm not sure that saying 'for most cars' and then using an RX-8 for your example is really proving your point, the RX-8 is somewhat of a special case being that it revs to north of 9000RPM and delivers no torque below about 6000. The majority of petrol engines probably have peak torque below 4000RPM.

I've not driven an RX-8 (or any wankel), but looking at the torque graph it's claiming about 170Nm at 2000rpm, about 125 lb.ft?

I don't know if that actually means much without factoring in subsequent gear ratios though.

Doesn't a wankel have a 3:1 reduction between rotor(s) and output shaft also? (Again, doubt it makes any difference to the overall maths of the system.)

[RichardD]

chris watton said:

..TVR Tamora, redlining to over 7k rpm in first and occasionally second.

It must be well over 7k rpm !

Do you know what final drive that would be with please?

[chris watton]

RichardD said:

chris watton said:

..TVR Tamora, redlining to over 7k rpm in first and occasionally second.

It must be well over 7k rpm !

Do you know what final drive that would be with please?

This is from the Gearboxman website:

Close ratio kit gearing:
1st: 2.527:1
2nd: 1.675:1
3rd: 1.259:1
4th: 1:1
5th: 0.87:1

http://www.gearboxman.co.uk/infot5.html

Forth and fifth are the same ratios as the standard box.

ETA - Depends on the diff ratio too - standard is 3.43, but many have a 3.73 final drive ratio.

[shoestring7]

35mph isn't that tall. I dislike the (thankfully) old fashioned practice of short 1st and 2nd gears - unless its a commercial vehicle. A lot of this dates back to the days when gearboxes were poor, so manufacturers built small capacity long stroke engines that would pull away in 2nd, avoiding another change. I can remember amusing(!) passengers by changing to 1st at 40mph in my 205Gti.

SS7

[thatdude]

Tall? 35 mph?

A yamaha R1 does about 100 mph in first gear

Anyway, in all seriousness...at idle, with the clutch engaged, what is the speed the car is travelling at?

[AW111]

Ozzie Osmond said:

So let's hear who, in what car, and where, is taking their car to the red-line in first gear...

Me.
(Modified) mk1 MR2, pulling onto the highway, 8,250 rpm (fuel cut is at 8,300). And occasionally off the lights : redline is almost exactly 60kph, which is the urban speed limit.

Peak power at 7,800 rpm, and still more force/torque at the wheels at redline in first than at 5,500 in second.

Redline in the top 4 gears is over the speed limit, so I have to make do with 1st and 2nd gear

[kambites]

Ozzie Osmond said:

It's very simple, in many cars acceleration is tailing off by the time you get to the red-line and you'll accelerate more quickly in the next gear. There's a difference between marking your rev counter with red-line to protect the engine and marking it with a change point for maximum acceleration.

As always, just because you're making a lot of noise doesn't guarantee you're going fast.

Actually bouncing the car off the limit is obviously not a good idea, but I haven't driven many cars where you don't want to get to within a few hundred RPM of it which is usually well into the "red zone".

Certainly in all three cars I currently own, the fastest way to drive is to push them well into the red.

Edited by kambites on Monday 11th August 11:58

[RichardD]

chris watton said:

This is from the Gearboxman website:
...

Thanks, has been a while since I saw the CR ratios and they are taller than I remembered!

Looks like close to 7300rpm required for the 60/90 speeds with the shorter final drive and :-

not even 7000rpm with a 3.45 final drive ! (based on 245/50*16 rubber)