[Bird of Prey]

My car has direct drive with a 6.20-1 . I can do a slight burn out , it drives like it should . But I would like to have more torque . If I put a reduction gear to the motor at 2.0-1 and then a rear gear of 4.00-1 , would it be more torque to the rear wheel ? Does it mater the amount of reduction if it goes to one ratio or if you divide it by two gears at the same ratio ?

 

[ishiwgao]

the simple answer to your first question is, yes, by putting the 2:1 gear and then 4:1 gear, you essentially get a total reduction of 8:1 at the wheels, which will give you more torque to the rear wheels (up to a given rpm, more on that later).

for your 2nd question, which will also be an elaboration on the first question's answer, please understand that gears do not "give" or "take" torque, nor do they "give" or "take" power. I suggest you read up more on what gears and a gearbox does. It will be a simple read on wikipedia or something. It is not a complex subject.

gears basically shift your working rpm range of your motor by multiply your torque but at the same time dividing your rpm. a jet engine running at 100,000rpm with 10Nm or torque can still drive your wheels travelling at 500rpm (around 50km/h give or take) if it has a 200:1 gearbox reduction. This will then give you a torque of 2000 Nm. obviously the gearbox with a ratio of 200:1 isnt very practical, but it is theoretically possible. but the gearbox isn't giving or taking torque, it is just shifting the torque curve by the factor of the gearbox ratio. likewise, the power of the jet engine remains the same with or without the gearbox.

I'm sure others here will have a better explanation than mine, but for a start this can help you.

EDIT: oh yes, and to your 2nd question, it doesn't matter (in terms of power and torque) whether you use 1 or 2 gearboxes to reduce the ratio, for eg. a 8:1 gearbox vs a 2:1 then a 4:1. it does matter when you think of why you would want to increase the complexity of your overall car design by using 2 gearboxes instead of 1, or maybe the costs involved in making 2 gearboxes instead of 1 etc.

 

[Karter2]

Better to use a single 8:1 reduction gear (if thats the ratio you chose), than to use a 2 step reduction of 2:1 and 4:1 ( or 4:1 + 2:1 .. No difference)... Because each reduction gear will have friction losses (5-10%) depending on the gear design. You do not want to double the losses if you can avoid it.
(But am i guessing the 4:1 is the rear differential and the 2:1 would be a extra reduction box ?).
Remember , you will also halve your max speed also.

 

[brian_]

If you replace 6.20:1 reduction with 8:1 reduction, you'll have more torque at the same motor speed... but at a lower road speed for same motor speed.

Two stages of gearing will lose a little more power to friction than one stage of gearing, but that's not a problem with proper gearing. If you use hypoid gears (the typical "rear end" of a rear-wheel-drive vehicle) each stage of that loses several percent, but spur gears (as all the gears are within a transmission, and the final drive gears of a transverse transaxle) only lose a couple percent per pair. Most production EVs use two stages of gearing, because the roughly 7:1 or greater reduction that they need is not reasonable to arrange in one stage (one pair of gears).

My understanding of the proposal is that the current 6.20:1 and proposed 4:1 gearing are hypoid gears of a rear end, and the additional 2:1 would be an additional gearbox. If the gearbox is a simple single pair of gears it would only lose a couple of percent, but if it is something like auxiliary underdrive it will likely be a planetary set and will have a bit more friction.

Gearboxes don't change the amount of power passing through them (other than that mechanical loss to friction), but they trade between torque and speed. More torque = less speed, and less torque = more speed. It's the same as an electrical transformer or converter, trading off between voltage and current.

 

[dcb]

fwiw, you might be able to "just" throw more amps at the motor for the occasional burnout too. But I wouldn't expect much greater acceleration if you are already near the traction limit.

 

[Bird of Prey]

OOPPSS , I ment 2.0-1 reduction gear and 3.08-1 rear end . Hope I am asking it right ? Do 2 or more gear reductions at the same ratio make more torque then just one gear at the same ratio ?

 

[dcb]

OOPPSS , I ment 2.0-1 reduction gear and 3.08-1 rear end . Hope I am asking it right ? Do 2 or more gear reductions at the same ratio make more torque then just one gear at the same ratio ?

no, a 2x and a 3x result in a 6x reduction. Or a 3x followed by a 3x would result in a 9x reduction.

There may be additional losses with one approach vs another, typically you would see 10x or less done in a single stage though from what I've seen (where practical).

 

[brian_]

My car has direct drive with a 6.20-1 . I can do a slight burn out , it drives like it should . But I would like to have more torque . If I put a reduction gear to the motor at 2.0-1 and then a rear gear of 4.00-1 , would it be more torque to the rear wheel ?

OOPPSS , I ment 2.0-1 reduction gear and 3.08-1 rear end . Hope I am asking it right ?

As already explained, the stages of gearing multiply the effect of each other, so a 4:1 stage and a 2:1 make a 6:1 overall. So now that this is clear, the answer to the original question is "no": there would be no more torque to the rear wheel.

Does it mater the amount of reduction if it goes to one ratio or if you divide it by two gears at the same ratio ?

Do 2 or more gear reductions at the same ratio make more torque then just one gear at the same ratio ?

No, one stage or fifty stages, the same overall ratio of gearing is the same overall ratio of the shaft speed coming in and the shaft speed going out, so it its the same ratio of torque (other than what is lost in the gearing).

The power transmitted by a rotating shaft is the speed multiplied by the torque (in appropriate units, if you actually want to do the math). You can't make power with gears, so if you multiply either speed or torque by some gearing ratio, you divide the other one (speed or torque) by the same ratio.

 

[Bird of Prey]

Ok , cool . I will run with that . Just needed to hear it from some one smarter then me .

 

[brian_]

.. typically you would see 10x or less done in a single stage though from what I've seen (where practical).

While there's no problem doing 10:1 or even more in a single stage, the gear sizes are the practical limitation which make this unlikely in a car.

In a typical final drive or "rear end", the final gear is the big ring around the differential. To get a greater reduction ratio, this gear can be made larger, but that this a bulk and weight problem. In a small car, the case around this gear would be a ground clearance issue if it were much bigger than those commonly used.

The other gear of the ring-and-pinion set is the small pinion gear which drives the ring. To get a greater reduction ratio, this gear can be made smaller, but at some point that becomes a strength and wear problem with too few teeth on the gear.

The current ratio in the car of 6.20:1 is already extreme - very few automotive ring-and-pinion sets have a ratio this large. While even more extreme ratios than 6.20 are available, what manufacturers put in cars is normally no where near that; something in the range 3.5:1 to 4.6:1 would be typical of normal cars. Up to 7.40:1 and as tall as 3.00:1 are available for the Ford 9" (which is presumably what's in the T-Bird, if that's the car we're talking about), so there should be no need to resort to a separate reduction box.

The other size issue which causes manufacturers such as Nissan and Tesla to choose 2-stage gears for the Leaf and Model S is that they have the motor parallel to the axle shafts, and they need enough distance between the motor shaft and the axle that the axle shaft for one side can go past the motor. With a high ratio and a wide shaft spacing, the larger output gear of a single stage with 8:1 or 10:1 reduction would be huge.

 

[dcb]

bump:

fwiw, you might be able to "just" throw more amps at the motor for the occasional burnout too. But I wouldn't expect much greater acceleration if you are already near the traction limit.

if you can get more torque out of your motor, you might not need to mess with the drivetrain.

 

[galderdi]

If you have a working drive train I would be reluctant to alter that for the reasons already mentioned.

However there is another way to make better use of the available torque without changing your drive train. (although technically my suggestion might still be considered part of the drive train).

If you have enough ground clearance you might consider running wheels and tyres with a smaller rolling diameter. Reducing rolling diameter is a quick and simple way to effectively lower your final gearing. Particularly if you are only looking for a small improvement. Plus it is easily reversable if you aren't happy with the result.