Maths is not my strongpoint so I need some guidance on how to work out which gear ratio/final drive combination is likely to be the most long-legged when looking at a particular car on paper. These vary between versions of the same car, particularly, of course, when automatics are brought into the equation.
I think I can work out that anything under a 1:1 ratio is an 'overdrive' but final drive ratio presumably then determines the real-life effect when comparing vehicles. Ideally, I would want a formula which gave the Autocar-type summary quoting miles per 1,000rpm in top gear.
Yours confusedly
David Millar
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plus you need the tyre size and profile so you can work out a rolling circumference.
try
www.mtv411.com/auto/gear-tire-speed-calculator.htm
or
www.motorcycle-dk.com/downloads
have fun!
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That top link looks correct but does not work properly for some reason. Second attempt:---
www.mtv411.com/auto/Gear-Tire-Speed-Calculator.htm
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You could tell in a moment how a car would feel cruising from those mph/1000rpm figures in the back of Autocar/Motor/both?
Anything around 18 a bit busy.....24 plus was good.
David W
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Anything around 18 a bit busy.....24 plus was good.
If you're lucky enough to have a '91 Rover 414 you'd find that fourth gear is ideal for extended high speed motorway cruising!
Keeps it in the meaty range between 5,500 and 7,000 revs.
Now, if I could just find out why it uses so much oil....
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Parp, Parp!
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ToTH
maybe that is why one of these is abandoned just up the road
midnight raid?
Maybe the weasels will give you a hand?
toot toot
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ToTH maybe that is why one of these is abandoned just up the road midnight raid?
>>Maybe the weasels will give you a hand?
Been looking for an abandoned one for ages - I could do with a new wheel trim!
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Parp, Parp!
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FiF
Brilliant. That look's to be just the thing.
To answer why I need to know, it's because the magazines tend to publish information only on review models or manual versions with a top spec engine and don't cover the autos or the smaller engines. If you can't get your hands readily on, say a Renault Kangoo diesel Trekka, it's useful to work out if it's worth chasing one up in a dealer miles away for a test drive. Unless it's a Honda S2000 revving up to 8000rpm, I don't want to be running a long journey at 18.3mph per 1000rpm.
David
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David
Not entirely sure what the question is here, but here goes.
FiF is right that you need the tyre size to add into the equation, but that really is first principles. More useful is the 'tyre revs/mile' figure.
You'll find there are slight differences between different makes of the same nominal size tyre, but these aren't significant. Armed with that information, based on the axle ratio an accurate miles an hour/1000 rev/min can be calculated:
60,000/axle ratio = tyre revs per hour
Tyre revs per hour/ tyre revs per mile = mile an hour per 1000 rev per min (assuming a 1:1 top gear in the gear box)
If it's an overdrive, ie les than 1:1, divide the figure you've just obtained by the ratio.
That said, DW is right - all you need is the makers data on miles/hour per 1000 revs.
Regards
John S
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Absolutely - there is a "too much info" category.
WHY would you want to delve into final-drive ratios etc.?
HOW the manufacturer achieves the cruising performance MUST surely be of secondary import to WHAT that performance is?
What is the difference between driving 2 cars,
1) low final drive with direct fourth and "overdrive" fifth
OR 2) much higher final drive with direct fifth?
Answer:- not a lot.
This then leads us to the real practical development - modern turbo-diesels produce so much torque that a fifth-gear gearing is possible seen only in very powerful cars of say, 10 years ago.
SWMBO's Skoda Fabia Tdi is doing 93mph at 3000 in 5th!
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