Really Neat Differential Demonstration! - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 11 (permalink) Old 04-08-2011, 09:29 AM Thread Starter
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Really Neat Differential Demonstration!

Hey, I know it's been a while, but I StubledUpon this and thought it might be interesting for you guys. It does a great job of breaking it down. I would have to ask you guys exactly what the more specific numbers are referring to when you discuss differentials. Pretty neat little flick none the less. Hope everyone's doing well, and if this is in the wrong spot, feel free to move it.


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post #2 of 11 (permalink) Old 04-08-2011, 10:03 AM
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Amazing how educational and relevant is is still today.


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post #3 of 11 (permalink) Old 04-08-2011, 10:16 AM Thread Starter
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Definitely is... I'll be honest, it enlightened me. I'm assuming some of the figures like 3.73 and stuff refer to the gears.
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post #4 of 11 (permalink) Old 04-08-2011, 10:28 AM
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Quote:
Originally Posted by SelfTranscendentD View Post
Definitely is... I'll be honest, it enlightened me. I'm assuming some of the figures like 3.73 and stuff refer to the gears.
Yep, good assumption. 3.73:1 ratio equals 3.73 revolutions of the pinion gear (drives the axle) for every 1 rotation of the ring gear....higher the number of the pinion gear the larger amount of torque, lower the overall top speed of the vehicle will be.
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post #5 of 11 (permalink) Old 04-08-2011, 11:58 AM
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BUT, that depends on the gear ratios in the transmission, if you have gear ratios that turn the drive shaft faster, you can make up for that loss in top vehicle speed, but ratios spinning the driveshaft faster will reduce the torque.

Thats how OverDrive came around, to spin driveshafts even faster to improve engine economy or top speed of the vehicle, without having to sacrifice the torque "multiplication" of the lower gears and the axle.

Which brings you to Final Drive Ratio.

The axle ratio doesn't mean much without the ratios from the transmission. And the final drive ratio is the top gear multipled by the axle ratio.

Note: people like to talk about how the V6 has taller axle ratios, but the V6 has a different transmission, with different gear ratios for each gear, and if you were to do the math, you would find every gear, the final ratios are very close between the V6 and V8.

Don't Forget: Tire Diameter has a huge effect as well, the speed the vehicle moves per tire rotation changes with the tire diameter, so changing the tire diameter has an effect of the drive ratios, just as if you changed the axle ratio. That is why people that fit huge wheels/tires to a vehicle have to change the axle ratios or the vehicle drives like a dog.

It a linear relationship, so if you fit tires that are 10% larger in diameter, you'll see a 3.2% reduction in torque, 20% larger you'll see a 6.4% reduction, but improvements in top speed and mileage. (You may need to check my math on that, I may be wrong on the actual figures, and it actually might be worse).

And we haven't even gotten into rotational inertia.

Nor did the films get into LSD's. But basically, its NOT hard to imagine, in those films if you fit clutches inbetween the two axle, it would resist the two wheels moving at different speeds, but allow it to do so if the force was great enough to overcome the clutches, and it would also help limit the difference in speed between the two. The film didn't get into that first and simpliest "open" differentials, would sometimes let wheels spin at different speeds when you would NOT want them to do so. By limiting the slip between the two sides, you strike a compromise where you allow them to spin at different speeds when needed, but resist them spinning at different speeds when they should spin at the same speed.


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post #6 of 11 (permalink) Old 04-08-2011, 12:10 PM
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Quote:
Originally Posted by Mongo View Post
BUT, that depends on the gear ratios in the transmission, if you have gear ratios that turn the drive shaft faster, you can make up for that loss in top vehicle speed, but ratios spinning the driveshaft faster will reduce the torque.

Thats how OverDrive came around, to spin driveshafts even faster to improve engine economy or top speed of the vehicle, without having to sacrifice the torque "multiplication" of the lower gears and the axle.

Which brings you to Final Drive Ratio.

The axle ratio doesn't mean much without the ratios from the transmission. And the final drive ratio is the top gear multipled by the axle ratio.

Note: people like to talk about how the V6 has taller axle ratios, but the V6 has a different transmission, with different gear ratios for each gear, and if you were to do the math, you would find every gear, the final ratios are very close between the V6 and V8.

Don't Forget: Tire Diameter has a huge effect as well, the speed the vehicle moves per tire rotation changes with the tire diameter, so changing the tire diameter has an effect of the drive ratios, just as if you changed the axle ratio. That is why people that fit huge wheels/tires to a vehicle have to change the axle ratios or the vehicle drives like a dog.

It a linear relationship, so if you fit tires that are 10% larger in diameter, you'll see a 3.2% reduction in torque, 20% larger you'll see a 6.4% reduction, but improvements in top speed and mileage. (You may need to check my math on that, I may be wrong on the actual figures, and it actually might be worse).

And we haven't even gotten into rotational inertia.

Nor did the films get into LSD's. But basically, its NOT hard to imagine, in those films if you fit clutches inbetween the two axle, it would resist the two wheels moving at different speeds, but allow it to do so if the force was great enough to overcome the clutches, and it would also help limit the difference in speed between the two. The film didn't get into that first and simpliest "open" differentials, would sometimes let wheels spin at different speeds when you would NOT want them to do so. By limiting the slip between the two sides, you strike a compromise where you allow them to spin at different speeds when needed, but resist them spinning at different speeds when they should spin at the same speed.
? who was talking about trans. ratios or final drive ratios? I just plainly explained what 3.73:1 meant for him...lets not try to confuse people here Mongo. Some people aren't as mechanically oriented as either of us, sometimes the easiest answer, just the answer to the question asked works the best for them to understand. right? If they then ask about trans. ratios, overdrive ratios, what tire size (height) does to overall ratios then explain that separately.

Last edited by CommandSystemsGo!; 04-08-2011 at 12:12 PM.
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post #7 of 11 (permalink) Old 04-08-2011, 02:20 PM
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Quote:
Originally Posted by Mongo View Post
... The film didn't get into that first and simpliest "open" differentials, would sometimes let wheels spin at different speeds when you would NOT want them to do so...
ie. at the 0:50 mark when an open differential would have been no more beneficial than the one wheel drive.

Great video, though. Even knowing the principals it's fun to see a rudimentary demonstration every once and awhile.

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post #8 of 11 (permalink) Old 04-08-2011, 03:00 PM
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Quote:
Originally Posted by CommandSystemsGo! View Post
? who was talking about trans. ratios or final drive ratios? I just plainly explained what 3.73:1 meant for him...lets not try to confuse people here Mongo. Some people aren't as mechanically oriented as either of us, sometimes the easiest answer, just the answer to the question asked works the best for them to understand. right? If they then ask about trans. ratios, overdrive ratios, what tire size (height) does to overall ratios then explain that separately.
Don't take offense, I was NOT trying to contradict you in any way, only adding the additional information.

BUT, I take your point, I'm turning on a firehose when people have just put their lips up to the little stream at the fountain.


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post #9 of 11 (permalink) Old 04-08-2011, 03:11 PM
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Originally Posted by Mongo View Post
Don't take offense, I was NOT trying to contradict you in any way, only adding the additional information.

BUT, I take your point, I'm turning on a firehose when people have just put their lips up to the little stream at the fountain.
No offense taken...your a vast "spigot" of knowledge...rock on!
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nice demo, interesting comments. Informational.


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