ST1300 gearing tech info

tomhanman

Joined
Jul 14, 2013
Messages
5
Location
France
Hello all, following on from my intro, I'd like to appeal for anyone who has some real clear info on the gearing of the ST1300 to present it here. I am looking to put the engine and box in a car, and I am having trouble calculating the real ratios - trying to take into account primary reductions, gear ratios, final drive, wheel size etc. I'd like to get hold of all this info as well as have you all tell me what revs you do in 5th at say 60mph. So that I can calculate and corroborate. I look forward to hearing, many thanks,
Tom.
 
Transmission:​
5-speed, hydraulic wet clutch. 2.57 1.72 1.29 1.04 .862
Final Drive:​
Enclosed shaft with integrated dampers, 2.833:1
RPM at 60 MPH:​
3,200

Says the interwebs.
 
Hi st1300r, thanks, yes I have found that site. But it doesn't add up! At least when I do the calculations on 5th gear ratios and tyre diameter and final drive it doesn't come out at 3200 60mph. So there is a primary reduction and I don't know what it is. I could calculate it given several speed/gear/rpm correspondant points, but for the moment I am still in need of more info. Anyone have the service manual or more techie stuff?

Thanks.
 
The attached spreadsheet should contain the information you need.

--Mark
 

Attachments

  • topspeed.xls
    10 KB · Views: 72
Very interesting info, thank you both very much...

just one thing, they don't seem to agree!!

Mark's spreadsheet gives a speed at 3200 engine rpm of 60.239mph.

Andrew's specs give a calculated speed at 3200 engine rpm of 59.1mph.

Obviously very very similar, but in completely different ways...

For both I've used the tyre circumference used in the spreadsheet 1.997m, which is not the mathematically calculated circumference of the tyre which is 1.948m. I understand that the real rolling circumference is different from the mathematically calculated version, but it is clearly different at different speeds, pressures and loads, so I find it a bit foolish to try and second guess it. I am probably wrong so I have used it.

The specs have a primary reduction of 1.785, and a secondary 'reduction' of 0.925 (which would be the opposite of a reduction) whilst the spreadsheet has the same primary and no mention of this 0.925 secondary. However, the specs give a final drive reduction of 2.833 whilst the spreadsheet uses 2.571 these are different by almost the same amount as the 'secondary reduction' (which if multiplied by 2.833 gives 2.620).

It is all very confusing! Obviously they are pretty damn close as an outcome. But what is important for my situation is knowing where all these reductions (and multiplications) occur as I will have to replace the final drive with a differential final drive. So for the moment I remain confused about what ratios are where.

Any others to give a casting vote?

Continued thanks,
Tom.
 
tomhanman said:
The specs have a primary reduction of 1.785, and a secondary 'reduction' of 0.925 (which would be the opposite of a reduction) whilst the spreadsheet has the same primary and no mention of this 0.925 secondary. However, the specs give a final drive reduction of 2.833 whilst the spreadsheet uses 2.571 these are different by almost the same amount as the 'secondary reduction' (which if multiplied by 2.833 gives 2.620).
Click to expand...

The spreadsheet is incorrect. It appears that I poked the first gear ratio (2.571) into the final reduction field. That number is close enough to 2.621, which is the product of the secondary (0.925) and actual final (2.833) ratios, that the answers were at least in the neighborhood. Change cell C5 in the spreadsheet to "=2.833*0.925" and you'll get the right answer.

Interestingly, the 2003 and 2004 owner's manuals don't list the secondary reduction, so I must have got the figures from the service manual. :shrug1:

I took a few minutes to improve the spreadsheet, correcting the mistake, adding room for extra reductions and a sixth gear in the transmission and adding a section that calculates RPM in top gear for a bunch of road speeds. A copy is attached, and I've given it a permanent home in the General section of STWiki.

Sorry about the error; I can't believe it took nine years to catch it. (You may want to check my math in the RPM-in-top-gear section.)

--Mark
 

Attachments

  • topspeed.xls
    14 KB · Views: 14
Mark, that is marvellous!

I haven't done too much checking - lightning doesn't strike twice etc. etc. A couple of years ago I bought a heat-pump from a German company called Dimplex. Big company, high end stuff etc etc - German! And I couldn't get to grips with the specs quoted, so I called them up on their tech helpline and explained. My explanation was met with silence, then some shuffling papers, then some german in the background, then the most uncomfortable of apologies - they had made an error. It felt a little as though they were going to engage the firing squad as soon as I hung up the phone!

This now is a fantastic tool, so thank you. I can chop and change things to try and find a compromise. I presume that primary and secondary reductions and internal to the gearbox. So if I remove the prop and final drive it is simply the final drive ratio that changes. Its very difficult to create a mix of revs and power balance. I'd be gearing it to a max speed of between 110 and 120mph. So in theory I should get a ratio for 8000rpm at 120mph. With 205,50,15 wheels/tyres that means a diff ratio of 3.215 which is very convenient as the Landrover Freelander diff is 3.21 and available in LSD form.

However, that does mean cruising at 81mph (here in France thats the motorway limit) in fifth at 5400rpm, which might be a bit tiring. But the car ain't ever going to go faster than that, so I can't gear it taller or I'm wasting the power band in 5th and I don't want to have to change down on inclines all the time.

Earplugs. or am I wrong?

Thanks again Mark, really really helpful.
 
IMHO, I'd gear it quite a bit higher, unless your geared top speed is chiseled in stone, then your stuck. I wouldn't want to cruise at 5400rpm when you can gear it now to get better mileage...
 
Hi Mike...

I agree, yeah sure, I'd love to cruise at 1800rpm at 80mph...

But this is a big heavy car, well small light car but very very very big and heavy bike, so the wind resistance, rolling resistance, gearing losses, weight etc are all going to be much higher, whilst the wheel size will be smaller (a gear in itself)

BHP is pretty much a totally useless piece of information except that it will govern your top speed, it is the limiting factor there.

Torque is what counts for acceleration (and it is this that is multiplied by a reduction gear).

So if I want to be able to do 120mph (which I don't really, 100 would do me fine, but then I would be cruising at 6500!!) then I think I need to ensure that the (fairly low) 113bhp of the ST1300 engine is doing all of its good work when I need it. It arrives at 8000rpm, although it is pretty steady from 7000 to 8000 so with 195,45,16 wheels/tyres and the available 1:3.21 diff the theory says that at 8000rpm I can do 40mph in 1st, 60mph in 2nd, 80mph in 3rd, 100mph in 4th and 120mph in 5th. This allows me to cruise at 80mph in 5th at 5362rpm. At 5362rpm the engine produces about 80bhp.

If I found a diff that was say 1:2.5 (honestly don't know where but I'm sure one can find such a thing) it would give this at 8000rpm:
55mph in 1st, 75mph in 2nd, 105mph in 3rd, 125mph in 4th, 155mph in 5th and allow cruising at 80mph at 4175rpm. All this in theory, but wether it would have enough torque to get me to any of those higher speeds in the taller gears I am not sure.

At 4175rpm the engine is producing about 55bhp, and I very much doubt that that would be sufficient to keep the car rolling even on the flat at 80mph let alone if one should encounter a hill. Plus I would have some serious doubts about the ability to get the thing moving in 1st uphill in a gear that could take me all the way to 55mph (1st in my standard Citroen C4 110bhp turbo diesel with lots of torque takes me to about 20mph).

So whilst the desire to get better mileage is entirely shared by me, the fear of under gearing it and not being able to pull away swiftly or having to change down whenever there was a headwind are greater.

But really if anyone can allay these fears then I'll go searching for a shorter diff...?

Tom.
 
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