Gear ratios
 

What exactly is a gear ratio ? What does something like 3:79 or 4:11 or 4:33 mean ? I would really appreciate it if someone could explain it to me in a simple manner. Thanks

a gear ratio is the number of times the drive shaft turns to make the rear wheels turn.

example:

4:11 means the drive shaft turns 4.11 times to turn the rear wheels 1 time

Or is it that the drive shaft turns 4 times to turn the wheels 11 times?

Nope what Ceb said is correct.

4.11 is going to get worse fuel millage than a 3.29 but the 4.11 will have alot more pulling power anyone know why?

Because it is spinning more times to move the rear wheels one time, it is creating more inertial energy and transferring that to the wheels. So the higher the ration, the more energy transferred to the wheels and subsequently the road, which equals more torque or pulling power. Simple physics.

Really though, that's just a wild blind guess!! :idea: But I think I'm on the right track.

Not necessarily. It depends on all the variables. Different engines and HP ratings, transmissions, final drive ratio's, how it's driven, etc. 8) 8)

Re: Gear ratios
 

Thanks guys. What can I say, I've got a NC education.

Many thanks for all your responses....they certainly gave me a much better idea about the issue. Cheers and drive safe everyone.

Thats why heavy haulers usually have rear ends with numbers like 4:11, 4:30, 4:56, even 4.88 mated to 18 speed transmissions with overall reduction ratios around 20:1. Sometimes with extra brownie boxes with granny gears for even more reduction. When you're trying to move loads nearly twice the size of the average truck, you want a lot of low gearing.

Well, because the 4.11 is geared lower. I had a 77 half ton Chevrolet, with a 350, 3speed, 4.11 rear. Shoot, at 65, my motor was turning about 3,000 RMP. Not very good fuel milage, but that pickup would pull what takes a brand new 1 ton to pull. :P

The Military ordered their CUCV (Commercial Utility Cargo Vehicle) pickups (the 80's Chevrolet C20's specifically) with 6.2 diesels, TH400 autos and 4.56 gears. With the non/OD 3 speed auto and the 4.56's , top speeds of 65 mph with the engine screaming for mercy was the norm but those CUCV's could pull pretty good at low speeds and pulling was not something the ol 6.2 diesel was known for in civillian garb, since GM geared those trucks for efficiency in lieu of power.

Yeah, that's really low holing it. :lol:

Another fun thing to play with is LEGO gears and motors. Try to stop the output shaft on the 1.5V LEGO motor with your bare hands. No problem at all. Now plug it into a geartrain, and try to stop the final drive with your fingers. The deeper the reduction, the harder it is to stop that shaft. If you gear it down enough, one of those wussy little motors has enough power to twist a LEGO axle right in half.

You see PackRat, as I said in the other thread, I can't understand not even half of what you write :) It sure sounds good though. Man I wish I knew even an 1/8 of what you knew.

I just tend to absorb a lot of generally useless information. Comes from having a lot of free time to surf the net and do research on various things. :lol:

Packrat, is that TDI part a homage to Volkswagen by any chance ???

Yep, my dad and I both own TDI's (mine is a 98 and his is an '06). My uncle has a 2002 Jetta TDI wagon, my cousin and her husband both have Jetta TDI's, a 1999 and a 2004 and my other cousin and her husband have a 2004 Jetta TDI. I started a mini TDI revolution. :lol:

Mine is going to be traded in on my dads next vehicle purchase and I'm going to buy his '06 from him. I drive it most of the time anyways, he usually commutes to work on his motorcycle when it's warm. The best used TDI purchases are the ones where the owner kept good maintenance records and what better record is there than to be a personal witness. 8)

I bought a diesel car because I missed the sound and smell of diesel and I couldn't afford a big pickup so I split the difference and got a VW diesel.