Rear end ratios

coshoo · Feb 7, 2016

I'm familiar with the usual decimal ratios on automotive rear ends- 4.11, 3.10, and such. But I saw a reference on an old car board to a 4-1/10 ratio- how does one convert that to the more familiar decimal equivalent?

Mike Groom · Feb 7, 2016

Do you think someone didn't understand that it's 4.11 to 1,3.25 to 1, etc?

Zachary Hoyt · Feb 7, 2016

1/10 is the fractional equivalent of the decimal 4.1 which is very close to the 4.11 you mentioned. Maybe they were less precise in those days and figured that was close enough.
Zach

Goose · Feb 7, 2016

If we're nitpicking, shouldn't it properly be 4:11?

Paul Janke · Feb 7, 2016

There are both 4.10 and 4.11 ratios. I once saw a chart listing the number of teeth on both ring and pinion gears for all of the different gear ratios. There is also 4.55 and 4.56. I have seen four wheel drives where the front end was just slightly faster than the rear end, probably to allow for less binding while cornering.

Goose · Feb 7, 2016

I guess I meant 4.11:1

Mike(NEOhio) · Feb 7, 2016

There are 4.09s, too.

Paul Janke · Feb 7, 2016

Thank you. If I knew, I had forgotten.

fixerupper · Feb 7, 2016

My old Power Wagon has 4:10 in the front and 4:11 in the rear. Doesn't the front axle always run a twitch faster than the rear axle?

the tractor vet · Feb 7, 2016

also the size of the ring gear determines the ratio . as in a 9 inch to a 10 inch a 9 1/4 or 9 3/4 and so on . say ya have a 8 3/4 Mopar and it is a 3.23 and a Ford 9 inch and that one will be a 3.25 One maybe a 4.10 and the next size up or down will be a 4.11 -4.13 . Same goes for big trucks one make rear ya may get a 4.33 but step up to the next heavier rear and now it is a 4.44

Jeff B. · Feb 8, 2016

The ratio refers to the number of times the driveline (input) turns to make one turn of the wheels (output). A 4:10 ration will turn the driveshaft 4.1 times for every turn of the wheels. 3:50 would be three & a half turns to one. Think of it as degrees of a circle. A 4:10 ratio is virtually the same as a 4.11 One turns 4.1 turns of a circle, the other turns 4.11 turns. Same with 3:50 vs 3:54 and 3:90 vs 3:92. They are indistinguishable in actual use. The reason for small differences are due to design features or limitations of manufacture.

Jeff B. · Feb 8, 2016

I should add that those numbers are expressed as 4.11:1, meaning 4.11 turns to one turn. That was probably what the guy with the old car was trying to say.

Determined · Feb 8, 2016

(quoted from post at 15:14:16 02/07/16) I'm familiar with the usual decimal ratios on automotive rear ends- 4.11, 3.10, and such. But I saw a reference on an old car board to a 4-1/10 ratio- how does one convert that to the more familiar decimal equivalent?

Technically 4 - 1/10 would equal 4 to .1 or a 40:1 ratio.
Most likely it should have said 4 + 1/10:1
4 + .1 = 4.1 or 4.10:1 gear ratio.
Different manufacturers produced different combinations to come up with the final ratio.
A common example would be in a GM corporate 14 bolt rear end, both of the following are available.
A ring gear with 41 teeth divided by a pinion gear with 10 teeth that results in a 4.10:1 ratio.
A ring gear with 37 teeth divided by a pinion gear with 9 teeth that results in a 4.11:1 ratio.
Lots of variations in carrier size, application, factory versus aftermarket gear sets etc.

Rear end ratios

coshoo

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Mike Groom

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Zachary Hoyt

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Goose

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Paul Janke

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Goose

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Mike(NEOhio)

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Paul Janke

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fixerupper

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the tractor vet

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Jeff B.

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Jeff B.

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Determined

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