The way I understand it, it's the ratio in the gearbox which transmits power to the dif!
i have heard thathigher the number, the faster acceleration, but the lower top speed. Vice Versa with a lower number !
NZTools,
Sep 29, 9:42pm
It is the diff that determines the final drive ratio, ie 4.11:1 higher acceleration than 2.77:1, but the latter will give a much higher top speed and better cruising revs at 100kph.
lazz323,
Sep 29, 9:47pm
so my theory of higher first number is greater acceleration compared to lower first, but being lower will have better power gains up top correct!
skin1235,
Sep 29, 10:01pm
the term final drive used to refer to the dif, then overdrive g/boxes came about and it was also used to gauge the 'final' from the g/box prior to overdrive boxes the top gear was always 1 to1, with o'drive it became 1 to .85 or whatever the manufacturer built the 6 sp boxes of today still use a single o/d but space the lower gears better and drop the diff ratio to achieve acceleration racing boxes often have 1 to 1 as their 3rd gear, and 3 o/d gears above it
your last comment should read "but better speed in top", it most certainly will NOT have better power, lower ratios sap the power
mrfxit,
Sep 30, 3:56am
Yep all good until you got to thelast bit. High ratio's + low torque = suck the power = simply not enough power/torqueto push/pull the higher speeds that higher ratio's can supply Lower ratios consume the power = engine rev's out too easily = not enough revs available for higher speeds
nzfatie,
Sep 30, 11:52pm
Nope.Skin is right.a 4.5:1 diff is High Ratio, while a 3.0:1 is Low Ratio because the mathematical difference (ratio) between 1 and 4.5 is greater than between 1 and 3.0. People often confuse this because a High Ratio diff provides Lower Gearing (more power/torque) while a Low Ratio diff provides Higher Gearing (less power/torque).
mrfxit,
Oct 1, 12:02am
HUH .
rob_man,
Oct 1, 12:43am
Yeah, another one of those. Here's how it is, the higher the number, the lower the ratio. That is, the lower geared it is. That is that commonly used method to describe diff ratios. Edit; it gets better when you describe the overdrive at the gearbox. The lower nubers give a higher ratio.
gunhand,
Oct 1, 12:50am
Well ill put my 10c worth in here.it works like this,Pie = M C squared. And everything that goes up must come down (like petrol and a hookers knickers) therefore you have gravity.And a Worm hole dosnt have worms in it, unless its in ya lawn.See, ask me "I" know what Im talking about.
klrider,
Oct 1, 2:08pm
Its the last kilometre before you get home.
timmo1,
Oct 1, 2:53pm
No silly, its when you've spent xxxx amount of money on the engine, but nothing uprating the gearbox- The final drive is that brief moment when the engine is singing just before the gearbox goes bang
mrfxit,
Oct 1, 2:59pm
LOL ummm yep, thats how I have known it for uuummm 40+ years
The 1.1 Drive ratio was top gear & was taken from the gearboxoutput shaft on a non overdrive gearbox (commonly a 3 or 4 speed manual) THEN the early overdrive's & 5 speed gear box's come in to it. it's not really until in recent years that manufactures have been altering the ratio spread across 5 or 6 speed gear box's Remembering that it was fairly common to be able to bolt on an overdrive unit to a few english gearbox's.(Roote Group & Jaguar in particular)
mrfxit,
Oct 1, 3:01pm
Or the diff. Last diff I broke didn't even whimper or bang, just wasn't there when I touched the go peddle.after cruising down a hill.
un_known,
Oct 1, 6:33pm
and hence why its less confusing to use the terms long and short rather than high and low.
purple666,
Oct 1, 7:15pm
Ok now I don't understand modern cars at all but I always thought top gear wasn't really a gear as such but just locking the input and output shafts together to give a final drive ratio of 1:1. Or at least that is how it was on every gearbox I had ever worked on and as mentioned above, overdrive was a unit that fitted behind the gearbox.
rob_man,
Oct 1, 7:27pm
Essentially the same for a five speed, fifth gear is in between the gearbox and the tailshaft housing and is an overdrive.
mrfxit,
Oct 1, 7:29pm
Nope. Long /short ratio's normally refers to how many mph/kph you can get from any specific gear at specific rev's. Certain combinations of gearing will give "longer leg's/ shorter legs per gear it's very similar but the reference isn't the same & that reference is more to do with the final drive ratio's (diff).
mrfxit,
Oct 1, 7:30pm
Until recently, but theres been so many changes that it's hard to tell WHAT the burgers are up to
skin1235,
Oct 1, 8:08pm
an over drive is any ration that comes below 1 to 1 early o/d's were clip on usually after the gearbox ( triumph actually slotted them cable activated just between the driveshaft and the pinion shaft ( diff) modern gearboxes including auto's generally have at least one overdrive gear, some have more than one, they all drive off the layshaft though, no longer behind the g/box as said before, purpose built race boxes often have up to 3, and a low ratio ( high speed) diff, 2.8:1 is a common diff ratio
if you can get 150kw at the wheel, putting another gear in there at a higher ratio (.85 :1 or 1:.1.2) will not get you more kw, in fact it will reduce it
an aside here, mk2 zeds, brit auto 2 speed, had a 2.4 ratio diff, amazing to clip that up behind a 4sp mk3 manual box, (they were 1:1 in top but had a lower 1st to push the heavier body from a standing start) speedo was way out of whack, tickets came in fast and often wasn't more power - but more speed from the existing power, and in top gear that was a lot less than normal for a zed too, slightest rise was drop a gear
mrfxit,
Oct 1, 9:05pm
"Drop a gear" LOL yea knew that feeling about 10 years ago. Had an auto commodore wagon that blew the box, so I slotted in a Toyota 5 speed & totally forgot about the diff ratio of 2.9/1 compared to the manual commy of 3.90/1.ish One whole revolution made a heck of a difference. Couldn't use 4th around town & 5th was basically open road down hill
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