Bump, anyone able to shed light on my ratio question?
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Bump, anyone able to shed light on my ratio question?
The final drive is just before the output to the gearbox.
To sort the different ratios for the IRD i would have to think. Maybe tonight.
I think i have it all on spreadsheet at home.
Cheers!
oh wait, i realised one of the pages I linked to actually says 'manual gearbox' at the top. Wasn't interested in thinking about that, yet.
I saw where it said 'Jatco' and thought it was the auto. I'm still confused.
I'm more used to thinking about motorcycles, thankfully a much simpler system.
Crankshaft -[primary reduction gears]> countershaft -[transmission gears]> output shaft -[chain (final) drive]> rear wheel.
Definitely will appreciate it if you can help put the correct picture in my head!
Scuse me if I'm repeating what others may of already said, trying to clear the muddle from own head as much as anything. Going to be some maths ahead.
I think the words 'Final Drive' are being misused a fair bit in the literature I've been reading. IMHO there is only one 'Final' drive and that is the last and 'final' gearset before the wheels - which is usually the diff gearset. All the other 'final' drives that I keep reading about often aren't really all that 'final' as there's often another gearset after them. You could call if final for the particular gearset you're talking about I suppose - like gearbox final, ird final, diff final etc.
In the Freelander we've got a few gearing reductions from the engine - we've got gearbox final reduction, gear selection reduction (ie 5th gear) as well as IRD reduction for the front wheels. The back adds a bit more complexity with rear diff and other IRD gearing which I won't go into.
Here's a standard L series gearbox - which is PG1 type gearbox S7EMU (ref. Rover PG1 gearbox - SELOC TechWiki)
1st 3.25
2nd 1.895
3rd 1.222
4th 0.848
5th 0.649
Final output ratio 3.647
So in 5th gear, in an L Series, the gearbox has a reduction of 2.366903 (3.647 x 0.649) for each engine RPM (1000rpm = 422.5 gearbox output RPM) then from the gearbox output it enters the IRD
Here's a standard 1.8 gearbox - which is also a PG1 type gearbox S4EM with the same gears and a different final output
1st 3.25
2nd 1.895
3rd 1.222
4th 0.848
5th 0.649
Final output ratio 4.2
So in 5th gear, in a 1.8, the gearbox has a reduction of 2.7258 (4.2 x 0.649) for each engine RPM (1000rpm = 366.8 gearbox output RPM) then from the gearbox output it enters the IRD
The gearing difference being because the petrol 1.8 is designed to rev higher than the diesel.
Enter the IRD. I think there's 3 different ratio IRD's out there with different 'final' ratios - the 'old one' which is 1.458, the >2000 one which is 1.467 and the V6 which is 1.359. They are all married up to different gearboxes - which alters the vehicles overall gearing reduction. Lets assume we've got the 1.467 one on an L series with L series gearbox. So in the L series at 1000rpm (engine) we've got 422.5 gearbox rpm entering the IRD - with its reduction of 1.467 that gives us 288rpm leaving the IRD to the wheels - which means the wheels are turning at 288rpm for each 1000rpm of the engine in 5th gear.
Freelander tyres are about 2.177m in circumference for 195/80r15 when new and fully inflated - so if the wheels are turning at 288rpm then they're travelling 37.6kmh for each 1000rpm of the engine - which means at 100kmh you're doing 2658rpm
Long winded I know - but in answer to 'where that ratio of 1.467 fits in' - its simply the overall reduction ratio of the IRD - taken from the gearbox to the front wheels - 422.5 goes into the IRD and 288 leaves the IRD - that's a ratio of 1.467. On the diagram it would be represented by the horizontal line that goes through the front drive outputs.
Clark
[quote=Mockery;951859]Been thinking a bit more about the IRD thing...
Wondering where that ratio of 1.467 or 1.359 fits in the pic quoted below.
Where they say 'final drive', is that the rear diff ratio, or the last thing out of the gearbox?
Would you need to swap anything else to keep the front & rear wheels in sync?
Is the fitment likely to just be a straight bolt-up?
I fired an email to Ashcroft transmissions, I figure they should be able to say for sure one way or the other whether it could work.
If it does, I figure you could be quite comfortable driving 31" wheels with that ratio, as it's an equivalent step as my current off-road setup is from my road wheels.
Just gotta figure how to make them fit... end up with about 2" lift from wheels, probably require at least 3" on the suspension ...I've got ideas, ways and means will be found...
Reply from Ashcroft:
Quote:
Hi,the ratios are different on the early and later type IRD's, there are 2 early types, one for petrol and one for diesel and 2 later types, one petrol and one diesel,the 2 early ones are the same ratio, the 2 later ones are the same ratio,the difference between the petrol and diesel is the breather and the cooler, if you change these you can swap them but if they are both the late type the ratios will be the same,Dave