Gearboxes, Ratio's and Final Drives...

[CTWG60 0]

Hopefully this will get made a sticky. It has come to my attention over the last few years that there seems to be a lot of confusion about this particular topic. It happens to be a favorite of mine but I am no expert. I believe I can help with explaining what the deal is with the correct choice of ratios. Of course a lot comes down to driving style and how you want the car to drive. Some people want to hit a certain speed in a certain gear others want to get the most from the engine and some just want the shortest ratio's possible regardless of traction available.

 

Well here goes.

 

Firstly an explanation of a gearbox's job.

 

A gearbox's job is to multiply engine power or energy (torque) so that the engine doesn't stall or bog down and that we get some useful work out of it. We all strive for the best power and torque from our cars but often the gearbox will let you down by not providing enough torque multiplication or too much resulting in wheel spin. Wheel spin however cool is useless in getting from A-B quickly. So the biggest issue we encounter is traction vs acceleration, acceleration is impossible without traction most road tyres in FWD applications (not toyo R888) from research and experience can hold onto about 750lbft x2 as you probably have two front tyres I hope. So we can't really use more than 1500lbft after gear multiplication in dry conditions. So if we are producing 250lbft at the wheels on a dyno and want to achieve maximum acceleration in 2nd gear in the dry without wheel spin we need to multiply 250x6=1500 if our differential has a ratio of 3:1 meaning 1 turn of the wheels = three turns of the diff (or output shaft really) we need to multiply 3x2 to get 6 so we need a 2:1 2nd gear to give us what we are after. So we have established a gear ratio based on a requirement vs available traction. Obviously we can let air out the tyres, run various types of differentials, better compound tyres and front end geometry but the theory remains the same.So if you lose traction in 3rd during full throttle acceleration your gearbox has multiplied the available torque a touch more than the tyres can make use of.

 

OK I wanted to get that off my chest now more on gear ratios.

 

The Differential is the final multiplication of all gears so a first gear of 3 multiplied by a FD of 3 will give you a torque multiplication of 9. But, I hear you ask, how do we know the diff is 3 and first is 3. Well it all comes down to counting teeth. Your gearbox will have an input shaft which does exactly what is says on the tin, it's a shaft running into the gearbox that the engine is connected to via the clutch and inputs it's torque through this shaft. On this shaft are lots cogs or gears which have a certain number of teeth on them, these gears are all fixed to the shaft. Let's say first gear on the input shaft has 10 teeth and the output shaft first gear has 30 teeth, if we divide 30/10 we get 3 so we now know that first gear will multiply the wheel torque by 3. As we slide the gearstick into 1st we are locking the first gear cog on the output shaft to the output shaft itself which then turns the differential gear via the output shaft FD cog or gear, which is actually machined into the output shaft and once again we can do the same calculation on the FD cogs.

 

To be clear the overall effect of torque multiplication may have some people scratching there heads as it all seems a bit weird to be able to make more energy from just cogs. What is actually happening is the effort required by the engine to do a task of work is reduced by the gearbox which has the effect of making it appear to have more energy. It's the long bar and weedy man scenario. :D Basically levers in circles. Ok I'm confusing myself now. :) Just think about it as torque multiplication or task division.

 

OK I'll leave it there for now any comments welcome, if this helps anyone understand let me know. If I'm crap at explaining then also let me know.

 

Next I'll try to explain how to figure out what are the best ratio's for acceleration efficiency.

 

Chris

[Kevin Bacon 5]

Good man, interesting engineering stuff :salute: :D

[Kevin Bacon 5]

Get your Quaife Speedcalc.exe to work and throw up some in-gear speeds and rpm drops from playing around with different final drives and wheel sizes :D

[CTWG60 0]

Kev problem is the 1st and 2nd gear are on the input shaft side are part of the shaft itself and it doesn't matter what diff you throw that won't affect rev drop between gears, and all the input shaft you use although they have different gear ratios VW tend to make the spacing of first and 2nd the same and so the drop in revs between 1st and 2nd is always around 2500rpm. Sucks I know only way round this I can see is a an SQS input shaft and 1st and 2nd gear. Unless there is an input shaft out there I don't know about! You see modern cars are heavy with big wheels so you always end up with a stupid short 1st gear to get it moving and then a short, but not shorten enough 2nd gear so you still end up with a rev drop. Not really looked at 02M boxes yet but I think they are the same. I'll have a poke about later and see if I can find one that maybe of interest. :D

 

All other gears of course are interchangeable and the GXV 02S is the king of short shifting no matter what FD you use! :D

[CTWG60 0]

So ok I said I'd explain about choosing the correct cogs so as you don't lose wheel torque between gears. Assuming that of the 111 views this thread has had some people actually read it, I will continue. :sleeping:

 

You'll quite often hear people saying when they change gear they drop right onto peak torque in the next gear and how cool it is. To be fair this is no bad thing but what actually matters is how much multiplied wheel torque you went from in one gear and to in the next gear. If you had 1500lbft in gear one at 6200rpm and changed into 2nd dropping 2200rpm to 4000rpm where the wheel torque available was 1300lbft regardless of the fact that peak torque is at 4000rpm you just lost 200lbft of torque at the wheels. You need a taller 1st or a shorter 2nd so that when you change gear you lose little wheel torque and thus get the most acceleration from your engine. The same is true in the following gears and this is when you hear people talking about short ratio gearboxes were the difference between one gear and the next is small and so no wheels torque is lost.

 

I'll go through the calcs for this but if anyone wants a very useful spreadsheet that will do this for you pm me your email address. To make use of it though you will need to know your wheel dimensions, gearbox code/ratios and have a rolling road print out for your car.

[mort1414 0]

very interesting read thnx

[CTWG60 0]

Your welcome thanks for the feedback.

[Gareth_16V 0]

Was doing a similar thing the other day, and I wonder if anyone has the frontal area and drag coefficient of a 'Rado so that the aero load can be put into the spreadsheet too....

[CTWG60 0]

coe of drag is something like 0.36 I think. Frontal Area I don't know although there was a thread on dubforce covering that subject.

[s1m0n 0]

Cd: 0.32

Frontal area: 1.81 m2

Cda: 0.58

 

problem is the 1st and 2nd gear are on the input shaft side are part of the shaft itself

 

Not if you have a Gemini :norty:

[Topaz2008 0]

I have a 1.9 G60 running a 68mm pulley producing about 200BHP. I have purchased a Wavetrac diff and plan to get this fitted to a spare gearbox and at the same time have the box overhauled. I have been reading on the forum various posts on gearbox ratios & final drive ratios but can not seam to draw a conclusion on what is the right way forward. The only observation I have with the car is that it would be better to be able to hit 60MPH in 2nd gear rather than having to change to 3rd.

 

Any advice on the best ratios and final drive would be very helpful

[Philmo 0]

CTWG60

It's not possible to avoid a drop in torque at wheels when changing up, unless .... wait for it .... you have a torque curve that slopes down from left to right!

I noticed at the last Stealth RR day some NA engines do this from about 3.5k rpm.

What does a typical oiler torque curve look like?

[CTWG60 0]

CTWG60

It's not possible to avoid a drop in torque at wheels when changing up, unless .... wait for it .... you have a torque curve that slopes down from left to right!

I noticed at the last Stealth RR day some NA engines do this from about 3.5k rpm.

What does a typical oiler torque curve look like?

 

Of course, but I think you know what I mean. Having a smooth wheel torque transition between gears is the ideal scenario, so that when you change gear at the optimum rpm your next gears wheel torque is as close as possible to the previous gears wheel torque figure at the next gears lower rpm.

[CTWG60 0]

I have a 1.9 G60 running a 68mm pulley producing about 200BHP. I have purchased a Wavetrac diff and plan to get this fitted to a spare gearbox and at the same time have the box overhauled. I have been reading on the forum various posts on gearbox ratios & final drive ratios but can not seam to draw a conclusion on what is the right way forward. The only observation I have with the car is that it would be better to be able to hit 60MPH in 2nd gear rather than having to change to 3rd.

 

Any advice on the best ratios and final drive would be very helpful

 

If your rebuilding I'd get a VR CHN,CCM code box and swap everything into a 4 pot 02A casing.

[Topaz2008 0]

I have a 1.9 G60 running a 68mm pulley producing about 200BHP. I have purchased a Wavetrac diff and plan to get this fitted to a spare gearbox and at the same time have the box overhauled. I have been reading on the forum various posts on gearbox ratios & final drive ratios but can not seam to draw a conclusion on what is the right way forward. The only observation I have with the car is that it would be better to be able to hit 60MPH in 2nd gear rather than having to change to 3rd.

 

Any advice on the best ratios and final drive would be very helpful

 

If your rebuilding I'd get a VR CHN,CCM code box and swap everything into a 4 pot 02A casing.

 

So the CHN,CCM is the gearbox code for a VR6? and its internals will fit into my G60 02A box? Sorry to sound a bit dumb but I am new to this and want to understand the options I have before I approach somebody to do the work. When I look on ETKA for my car there are approx 10 different gearbox part numbers listed. Does that mean that the G60 was manufactured with up to 10 different gerarboxes?

 

Gear Box.pdf[/attachment:3e6ih2zh]

[CTWG60 0]

 

So the CHN,CCM is the gearbox code for a VR6? and its internals will fit into my G60 02A box? Sorry to sound a bit dumb but I am new to this and want to understand the options I have before I approach somebody to do the work. When I look on ETKA for my car there are approx 10 different gearbox part numbers listed. Does that mean that the G60 was manufactured with up to 10 different gerarboxes?

 

Gear Box.pdf[/attachment:y3jaft2w]

 

yep chn,ccm are vr6 boxes with internals that can be used in a g60 box. Try Vince at stealthracing for more info and to have the work done or gearboxman. No the corrado had maybe 10 different gearboxes, some of those codes are 16v, g60 and vr.

[neil20vtc 0]

im currently building a 20v mk2 using the engine and box from my corrado do you know if vr internals and a tdi 5th will fit into my 9a 16v 02a housing? ill also be getting a quaife diff fitted at the same time

 

 

cheers neil.

[CTWG60 0]

im currently building a 20v mk2 using the engine and box from my corrado do you know if vr internals and a tdi 5th will fit into my 9a 16v 02a housing? ill also be getting a quaife diff fitted at the same time

 

 

cheers neil.

 

Yes all 02A internals are interchangable, the tallest 5th available would come from an ASD code diesel box, my next box will include an ASD 5th, AGK 3rd and 4th, and asd 1&2. I was going to use a diesel final drive but know considering a vr one.

[g60 supercharger 0]

hi very intresting thread :salute:

i need a little help i've being thinking of get a cnt deisel gearbox for my g60 its cause i want to have a longer 1st and 2nd gear and i want to be able to hit 60 in 2nd

will it be a gd idea?

is there some sort of thing u can work out what u will get out of each gear??

thanks for help

andy

[Topaz2008 0]

I think this what you are after :Dgearspeeds.v2.xls[/attachment:2mpzvsxr]

[g60 supercharger 0]

but what where can i get info about the final drive and all that..?

cheers and

[Abdul 0]

Awesome right up mate, not that i really understand much of it!

 

Now a quick question which is kind of but not so relevant to the topic lol, what is the actual difference between a mk3 and rado vr6 gearbox?

[Topaz2008 0]

but what where can i get info about the final drive and all that..?

cheers and

 

The attachment shows the details of all the boxes fitted to the Corrado during its life :D

 

02A Gearbox Ratios 2.xls[/attachment:1veif1fk]

[Kevin Bacon 5]

Thought I'd add this in here as it's quite handy to know if considering a gearbox upgrade.

 

O2A - Corrado/Golf 3/MK2 G60/Rallye

O2S - 6 speed version of O2A - MK5 Golf - All non GTI models basically, i.e. low torque.

O2M - MK4 R32, Leon Cupra R, some late TDIs, Audi TT etc

O2Q - MK5 R32, MK5 GTI, A3 3.2 etc - No speedo worm drive

O2E - MK5 DSG - wet clutch - No speedo worm drive

O2? - MK6/MK7 DSG - Dry cluch - No speedo worm drive

 

4 cylinder O2M/O2Q will bolt up to 1.8Ts, 2.0 TFSIs etc, but not 6 cyl 12 or 24V.

 

4 or 6 cylinder 02M/O2Q can be converted to 6 cyl FWD with casing - p/n O2M 301 107 S. O2Q will also need the O2M's worm drive sensor. O2M and O2Q will need a standard output flange for the offside.

 

O2S can be dismantled and fitted into 6 cyl O2A clutch housing for a nice 6 speeder :D

[lukavr6 0]

hi there!

 

can anyone please explain to what is the difference between the AGK and CCM gearboxes? i have a 2.9 litre ABV in my rrado, which has been redone allover, and i am trying to get the best possible gearbox on.

 

which one of the two you recomend?

 

thanks,

cheers, luka