Gear Ratios? - Nissan Frontier Forum
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#1 (permalink) Old 11-09-2007, 12:15 AM
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Gear Ratios?

can someone explain gear ratios for me? i have been looking around the Forum and i cant find anyone that has talked about it.

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#2 (permalink) Old 11-09-2007, 12:24 AM
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the higher the ratio the better accelration the lower the better fuel economy

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#3 (permalink) Old 11-09-2007, 02:43 AM
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Quote:
Originally Posted by qborotali
the higher the ratio the better accelration the lower the better fuel economy
Numerically anyway. Though technically a 3.69 is lower than a 3.13

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#4 (permalink) Old 11-09-2007, 03:00 AM
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Quote:
Originally Posted by Inyourface1650
Numerically anyway. Though technically a 3.69 is lower than a 3.13
Correct. Lots of fun trying to drive around town with 5.36 gears and a small block.

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#5 (permalink) Old 11-09-2007, 09:32 AM
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Quote:
Originally Posted by andrewcote
can someone explain gear ratios for me? i have been looking around the Forum and i cant find anyone that has talked about it.
The gear ratio is the "number of teeth in the ring"/"number of teeth in the pinion". External to the differential, it's the number of driveshaft rotations to the number of wheel rotations; so you can get a rough estimate of your gear ratio by lifting the rear end of the truck, rotating a tire one full revolution and counting the number of times the driveshaft turns. That's why when you change tire diameter, you effectively change the gear ratio (e.g., when you put larger tires on, you need to turn the driveshaft more to get a single rotation of the tire which makes if feel like you have less power).

At least I think I've got all that right. Basically, it's what those guys said.


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#6 (permalink) Old 11-09-2007, 09:47 AM
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I would suggest searching Wikipedia. It's better for stuff like this than Club Frontier....sorry guys...


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#7 (permalink) Old 11-09-2007, 10:37 AM
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my friend just put 4.10 gears in his 07 gt mustang i tihnk from a stock 3.4 somthing i dunno sometihn liek that

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#8 (permalink) Old 11-09-2007, 12:00 PM
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ok thanks alot. so i would want a higher gear ratio for offroading? what would be a good Ratio? its not for my Frontier, im learing up because im about to buy a Sami and i want to learn about this stuff

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#9 (permalink) Old 11-09-2007, 12:17 PM
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Quote:
Originally Posted by andrewcote
ok thanks alot. so i would want a higher gear ratio for offroading? what would be a good Ratio? its not for my Frontier, im learing up because im about to buy a Sami and i want to learn about this stuff
hehe, ok. So numerically higher, the lower the gear ratio. jerry kinda explained it backwards from how I think of it. If you have 4.11 gears, you will turn the driveshaft 4.11 times before you turn the tire. So if you are in 5th gear (2nd Gen 6 speed) which is 1:1 you get 4.11 turns of the engine for one turn of the Tires.

Now obviously the more turns of the engine to the turn of the Wheels means more torque (this is how your transmission works). Offroad (like the sammy) it also effects your crawl speed. My truck, which is a manual, has the lowest rear gear of frontiers 3.69, so I can crawl around very slowly with the clutch fully engaged.

In a sammy, especially with the stock 55HP, its very important to gear em right, otherwise you will not be able to go anywhere for lack of power.

Tires affect gearing in the following ways: lets imagine we are in our scenario above. You in 5th gear, which is 1:1, and you have 4.11's. So 4.11 turns of the engine for every turn of the tire. So when you mess with tire size, you are effectively messing with your final drive ratio. Now, with 31inch tires you travel 31*pi or 91 inches. With a 33 inch tire you travel 103inches for every turn. So see how bigger tires mess with your speedometer? Your spedo thinks your going a foot less every tire rotation then you actually are. You have also effectively made your gearing taller, since every turn of the tire takes you farther. (so your truck will have less power) If you make your rear gears Shorter (or numerically higher, but actually lower) to say, like a 4.33.....You once again be going about the RPM at about the speed you were, effectively correcting for the bigger tires. This is why you see people talking about gearing for 35" tires and such. You lose so much power (beacuse you go so much farther for each rotation of the wheel) its necessary to re-gear the drivetrain to get it back.

SirLurksAlot

Last edited by Inyourface1650; 11-09-2007 at 12:21 PM.
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#10 (permalink) Old 11-09-2007, 12:25 PM
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nice edit, between reading from the start and hitting quote you fixed what I was gonna....

4.10 gears would be nice for wheeling but would kill mileage on road since the engine would constantly be taching higher (well, highway anyway, the other speeds you correct by being in a different gear). I suspect thats one reason why I get the same mileage in this truck with 33's as I got in my '97 D21 with 31's. that pig had 4.56's and tached 3k on the highway.

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