Ok, this question must sound dumb,, but please hear me out. My neighbor says gears are not larger or smaller, but that the teeth count is just altered to get a different RPM. I can almost imagine this, but would like to see pictures. I always thought you just got a bigger diameter ring gear to get a higher number like 3.90, etc...

 

Don't know if I can paste this table in here ... but you'll see that it is the count of the teeth (the two numbers are the count of the teeth on the ring and then the pinion) - not the size of the ring that makes the difference (this is not a Corvette parts list ... don't use these numbers ... example only)

(OEM) GM 7.25" FRONT RING & PINIONS
PART # TEETH RATIO
26039760 40-13 3.08
26039764 41-12 3.42
26035261 41-11 3.73
14071743 41-10 4.10

 

Maybe this will answer your questions.

http://www.carbibles.com/transmission_bible.html

 

to increase mechanical advantage, then one gear must grow bigger than the other (or one pulley has to get larger than the other).

And like mentioned earlier, the tooth spacing must be the same on both meshing gears. For one gear to have more teeth than the other (and the tooth-to-tooth spacing remain the same so they will mesh with each other)... one gear has to be larger than the other.

ignore your neighbor (and never buy a used car from him).

.

 

very true, if you want the ratio's to change. meaning if you want a 2 to 1 ratio. you must have a gear with twice as many teeth of the same size. so say, one has 10 teeth and one 20 teeth of equal size. equal size gear diameter's will transfer rpm's at the same speed, 1 to 1. unequal gear teeth will not mesh together very well .

LOOK AT A BICYCLE. same situation with gears and teeth as with a bike chain. the way gears in a tranny work is similar to how the rear gears of a ten speed bike work.

 

any two gears have a pair of "pitchline diameters", the smaller gear has a pichline diameter and the larger one has one also. The gear ratio is based on the ratio of these diameters, and the number of teeth are a variable in the design process. The numbers of teeth are calculated based on the amount of load being transferred, noise considerations and speeds.

If you want to change the gear ratio, you can make the pinion gear smaller and/or the driven gear larger, adjust the tooth counts so that you get the right numbers on each gear and go from there. But if the overall gear ratio is changing, one of the gear sizes has to change, either up or down...

 

Thanks, gang. It sounds like the verdict here is that the outer Ring gear will be bigger in diameter, as I would expect.

Seems to me the only way to get different ratio using only teeth would be to cause some teeth to skip contacting another tooth, which would be wasted energy. Or to reshape a tooth at an angle so that movement is not matched on each side, but dissipated on one side.

I'll keep clicking any links provided on this thread.

 

I think part of the confusion here is you are picturing the gears in the differential ... while others are talking about the gears in the transmission ...

Either way ... your "friend" is wrong ....

Take the differential (which is what I think you are picturing) and let's go from there ...

The outer "ring" gear doesn't change in size (you'd have to alter the differential housing to fit a laarger ring gear) but the inner pinion gear does change in size.

It has to .. as others have pointed out (and I tried to in my earlier post but didn't make clear) the "advantage" of gears is that they are DIFFERENT sizes ....

Take the differential ... if the pinion gear is x diameter, and the ring gear is twice as large, then you get a 2:1 ratio .... every time the pinion turns 360 degrees .. the ring gear turns 180. Doesn't matter if the ring gear has 20 teeth and the pinion has 10 ... or that the ring gear has 100 teeth and the pinion has 50 .... it is the difference in DIAMETER of the two gears that makes the difference.

If I want a 1:1 ratio, I have to increase the size (diameter) of the pinion so that every time the ring gear turns 360 degrees, so does the pinion.

Hard to picture ... but I think you get the idea ... I hope (and the fault is mine for a bad explanation .. not yours)

 

Transmission gears are generally parallel shaft gears and do change in outside diameter as the ratio changes in most cases, however in slight ratio changes it can be done with tooth spacing.
Differential gears however are another animal all together because they are hypoid gears.
As the ratio gets higher numerically the ring gear gets thicker, not larger in dia. and the pinion gets smaller in dia. with fewer teeth up to a point.
Then the diff. case must move closer to the pinion thus the reason for different series cases ie. 2 series, 3 series, 4 series etc.

 

I Changed Gears From A 3.42 To A 2.73 Had To Change The Housing Also..... Size Due To Size According To Chev

 

... by design, the gears in the same tranny that have more teeth will have to be larger in size (ie, diameter), and the ones that have less teeth will be smaller. This is the way in which gear ratios in trannys are designed - by the ratio of the number of teeth between the two gears that are messed together based on which gear you are in (1st, 2nd, 3rd, etc, etc).