Very confused on gear ratio?

[Konkordmusk]

Ahh, yes. I see what you mean. I meant to refer to the complete sum of all ratios from the flywheel to the axle. I suppose "final" ratio means "last"? I was under the impression that "final" ratio meant the sum of the ratios, in one specific gear. Is there a term for that?

Not that I can think of, or know of. The sum of the ratios would change for every gear the transmission shifts to, so it would never be a constant number anyways.

 

[D Farms]

No, a low gear ratio would be 5.29 or 4.88, and would cause the engine to make more rotations per mile. A high gear ratio would be 4.10 and similar, and would cause the engine to have fewer rotations per mile.
Going to a lower (numerically higher) gear will increase your RPMs at a given speed but improve your off the line performance. A higher (numerically lower) gear will get you off the line slower but keep your RPMs lower at a given speed.

when I say high i mean the value of the ratio you know like 2 is higher than 1. a high reduction.

 

[TheManOutside]

Gear ratio has to do with the number of engine rotations per rotation of the axle. A higher gear number means that the engine turns more times for each time the axle turns. Since bigger tires cover more distance per rotation, increasing the gear ratio number means that the engine can turn at the same speed for the vehicle speed.

Ok. This makes much more sense. The lower gears (higher number) are so that the (bigger) wheels can keep up with how fast the engine turns. Correct?

I have always referred to numerically higher gears as shorter gears, and numerically lower gears as taller gears, to prevent confusion. But that might just be me!

I like thinking of it this way. It honestly makes much more sense to me. It feels much more "straight forward." Good way to think of it! Especially if you came up with it yourself, :thumb:

 

[csp]

Ok. This makes much more sense. The lower gears (higher number) are so that the (bigger) wheels can keep up with how fast the engine turns. Correct?

Not quite correct. Lower gears allow the engine to be in a "normal" RPM range where power is made when you make the jump to larger tires (wheels are the part that tires are mounted on). It's a matter of leverage.

Think of it like this. Try to remove a very large bolt tightened to 250 ft-lbs. with a very small ratchet. It isn't going to happen no matter how much force you apply to the ratchet. Switch to a 2' long breaker bar, applying the same force you did with the ratchet and suddenly you can get the bolt to turn. Lower gears are the equivalent of that long breaker bar for your engine trying to turn bigger tires.

I think you have the general idea correct, but your interpretation of what drives what is a bit mixed up.

 

[TheManOutside]

Not quite correct. Lower gears allow the engine to be in a "normal" RPM range where power is made when you make the jump to larger tires (wheels are the part that tires are mounted on). It's a matter of leverage.

Think of it like this. Try to remove a very large bolt tightened to 250 ft-lbs. with a very small ratchet. It isn't going to happen no matter how much force you apply to the ratchet. Switch to a 2' long breaker bar, applying the same force you did with the ratchet and suddenly you can get the bolt to turn. Lower gears are the equivalent of that long breaker bar for your engine trying to turn bigger tires.

I think you have the general idea correct, but your interpretation of what drives what is a bit mixed up.

yeah, I think I understand the concept I'm just having a hard time putting it into words. The breaker bar ""imagery" (?) definitely helped though! :thanks:

I'm not gonna attempt to summarize gears anymore because I don't make any sense

 

[D Farms]

basically when you get bigger tires the engine spins slower to go the same speed, however because the engine makes less power at a lower rpm the truck struggles to stay at speed and then downshifts. the best way i can describe it is like if you started in 2nd gear. the idea behind regearing is that the ammount of spins of the engine stays the same over a mile, so since the bigger tires spin more slowly at the same speed you need to increase your gear reduction(go from 3.90 to 4.88). if you went down to smaller tires you would decrease your gear reduction(go from 3.90 to 3.42). when the truck was designed the engine and transmission were setup to work a certain way, getting bigger tires throws the whole system off, so in order to get it back a higher ratio for the final drive is nessesary.

jist to give you a better idea, the engine output travels through the transmission which then reduces the speed of the output by a certain ammount
Manual transmission: First Gear: 3.830:1, Second Gear: 2.062:1, Third Gear: 1.436:1, Fourth Gear: 1.00:1, Fifth Gear: 0.838:1. Auto transmission 1st 2.804:1, 2nd 1.531:1, 3rd 1.000:1, 4th(overdrive) 0.705:1. then for a 2wd truck the driveshaft goes down to the back axle and gets reduced again by the gears in the differential.

btw final drive is the ratio of the gears in the differential/ differentials.

another thing to consider is that the auto transmission has an overdrive ratio of something like 0.73 and the manual has a ratio of about 0.83.

and now after looking at all of this, i have ths tallest possible combined ratio possible for a 4wd 3rd gen haha... wtf. i didnt realize the manual had thay much better gearing.

 

[TheManOutside]

basically when you get bigger tires the engine spins slower to go the same speed, however because the engine makes less power at a lower rpm the truck struggles to stay at speed and then downshifts. the best way i can describe it is like if you started in 2nd gear. the idea behind regearing is that the ammount of spins of the engine stays the same over a mile, so since the bigger tires spin more slowly at the same speed you need to increase your gear reduction(go from 3.90 to 4.88). if you went down to smaller tires you would decrease your gear reduction(go from 3.90 to 3.42). when the truck was designed the engine and transmission were setup to work a certain way, getting bigger tires throws the whole system off, so in order to get it back a higher ratio for the final drive is nessesary.

jist to give you a better idea, the engine output travels through the transmission which then reduces the speed of the output by a certain ammount
Manual transmission: First Gear: 3.830:1, Second Gear: 2.062:1, Third Gear: 1.436:1, Fourth Gear: 1.00:1, Fifth Gear: 0.838:1. Auto transmission 1st 2.804:1, 2nd 1.531:1, 3rd 1.000:1, 4th(overdrive) 0.705:1. then for a 2wd truck the driveshaft goes down to the back axle and gets reduced again by the gears in the differential.

btw final drive is the ratio of the gears in the differential/ differentials.

another thing to consider is that the auto transmission has an overdrive ratio of something like 0.73 and the manual has a ratio of about 0.83.

and now after looking at all of this, i have ths tallest possible combined ratio possible for a 4wd 3rd gen haha... wtf. i didnt realize the manual had thay much better gearing.

Yeah, this makes sense. I think I got the hang of this now. I said I wasn't gonna try to explain it again, but who cares I'm gonna do it again lol

You get lower gears (higher number) so that the engine turns with the wheels the correct way/amount of times to give the most "correct" ride possible (like how it was designed out of the factory).

What happens if you have an incorrect gear ratio based on your tires? (35 inch tires with 3.73 ratio for example)?

 

[ShooterMcGavin]

Yeah, this makes sense. I think I got the hang of this now. I said I wasn't gonna try to explain it again, but who cares I'm gonna do it again lol

You get lower gears (higher number) so that the engine turns with the wheels the correct way/amount of times to give the most "correct" ride possible (like how it was designed out of the factory).

What happens if you have an incorrect gear ratio based on your tires? (35 inch tires with 3.73 ratio for example)?

Your engine would be turning very slowly for the vehicle speed. Imagine driving down the highway at 75 mph and your engine is at 1,500 RPMs. That's just an example, I don't know the exact numbers.

The point is, for the speeds regularly driven, the engine would not be within its optimal power band, which is usually above 2,000 RPMs. An auto transmission would constantly be down-shifting, and either transmission type would feel a serious lack of power.

 

[TheManOutside]

Your engine would be turning very slowly for the vehicle speed. Imagine driving down the highway at 75 mph and your engine is at 1,500 RPMs. That's just an example, I don't know the exact numbers.

The point is, for the speeds regularly driven, the engine would not be within its optimal power band, which is usually above 2,000 RPMs. An auto transmission would constantly be down-shifting, and either transmission type would feel a serious lack of power.

Ok. So, I'm guessing with higher gears (lower number) and smaller tires, your revs would be too high, right? I think I'm starting to understand this stuff finally haha

 

[csp]

Nope you're still bass-ackward. Lower number means lower engine rpms for every rotation of the tires.

Not sure at this point why it's so hard to comprehend. 2.73 to 1 gears means fewer engine revs than 4.10 to 1

 

[Scramble]

Wow. 16 years?? Congrats man :bravo: It's still going strong, I'm guessing? How many miles do you have? I find it extremely awesome that you still have it.

As for the diff stuff, I'll see what I can find, but I'll probably end up getting 4.1's, seems like those are the most common.. Also, how bad is it driving with a lower number gear ratio with ~33 inch tires? Are there vibrations, is it sluggish, etc.?

Thanks, the body & frame are solid. I blew the head gasket around 143,000 & had the engine rebuilt. I have 153,000 miles now & 10,000 on the motor. I have zero vibrations now with lots of new parts. I'm pretty sure it was the new ES steering rack bushings that got rid of my steering wheel vibrations but I did LBJ's, UCA's & OTRE's at the same time so it could have been a combination of all.

 

[TheManOutside]

Nope you're still bass-ackward. Lower number means lower engine rpms for every rotation of the tires.

Not sure at this point why it's so hard to comprehend. 2.73 to 1 gears means fewer engine revs than 4.10 to 1

Agh. Sorry, I meant to put with a lower gears (HIGHER number) and small tires your revs would be too high. Sorry, I messed up pretty bad in my last post. My bad...