LrngCrv

Did a search on this but couldn't find what I was looking for.

So my question for discussion on this is, assuming same sized ring and pinion gears, would the 4.11s be fundamentally stronger than the 4.10 ratio just based on the fact that there are less teeth (making them larger) on the two gears or is there more surface area contacted on the teeth with the 4.10s making them stronger?

What is the advantage of the 4.10 ratio over the 4.11 or vice versa?

Old SStroker

A 4.10 usually has a 41 tooth ring gear and a 10 tooth pinion gear. (41/10=4.10)

A 4.11 usually has a 37 tooth ring gear and a 9 tooth pinion. (37/9=4.111...)

IMO there is very little difference in strength if the steel, machining and heat treating is identical. In a hypoid gearset like we use in rear ends, there is more than one pinion tooth in contact with the ring teeth all the time. The difference in contact area between a 9 or 10 tooth pinion is minimal.

Buy the best quality gearset you can afford and have it installed properly. That is more important than the small diffeence in tooth count.

alamantia

iTrader: (10)

i always wondered that my self. My theroy is this... hypoid gear teeth slide across each other, at any given time there are at least two teeth in contact with each other with 9 teeth on a pinion yes the pinion teeth ere a little larger than with 10 teeth but because you divide that 9 by 360 degrees for 40 degrees of the rotation that tooth is sliding on the ring gear whereas with 10 teeth on the pinion its only sliding for 36 degrees, durring the durration while its sliding across the tooth in front of it is almost done sliding across and the tooth behind it starts sliding across. I believe that a 9 tooth pinion gear will take more of the load on the middle of the tooth than a 10 tooth gear but at the same time the tooth is bigger, I believe its a wash. I always wondered why a 1 inch diameter 33 spline axle is stronger than a 1 inch diameter 31 spline axle. If both axles are the same diameter why would many small teeth be stronger than a few big teeth. Getting back to the Ring & pinion gears though.. In a 7.5 10 bolt neither matters anyway, they both are weak.

BlackScreaminMachine

iTrader: (17)

I very much agree and feel the same about that subject, well said.

magnum-gto

The minor diameter of the 33 spline axle is larger than the minor diameter of
the 31 spline axle.

LrngCrv

I would have used an example with a more extreme difference in the number of teeth and still have a similiar ratio but the 4.11 and 4.10 are common, it isn't because I am looking at which gears to install. It's just something that I was wondering from an engineer's viewpoint, what makes them decide on how many teeth to use for a particular gear ratio.

Hmm, good points, hard to understand the degree differences when they are so close but the spline comparision is something that seems most people just accept without understanding why.

Is that the only reason it would be stronger? That would make for a small difference than what is usual with them wouldn't it?

Old SStroker

Physical limitations mostly. There is a fixed distance from the pinion centerline and the ring gear mounting flange on the differential carrier/spool. To have a minimum amount of beef below the teeth in the ring gear, you limit the pinion diameter. Also for a given ring diameter, you are limited to how many teeth you can have and still have adequate strength.

I suggest 44 teeth might be near the upper limit and 36 or 37 close to the lower limit for 7.5-9.5 inch ring gears. Pinions can go to about 7 teeth minimum. That gives you a max reduction of 44/7 or 6.29 which is a very short track gear. If you stay below 5.00:1 and 44 teeth you get 9 tooth minimum pinions.

As far as manufacturing or "generating" the hypoid teeth, the smaller the number of teeth on the pinion, the more spiral/helix you get. A 7 tooth pinion might require a smaller cutter and cost more to produce than a 9-13 tooth pinion.

One possibility is more total contact surface with a greater number of splines even though the individual "teeth" are smaller. The nominal contact should be along the pitch diameter, but the male and female splines effectively have nearly line contact rather than full tooth engagement. I suppose you could rate the stength not only by the larger minor diameter but also by the ratio of the number of splines.