Low Gear Ratios = Lower Strength?
Shel Belinkoff
gear ratios equate to weaker gears. This is because, for a given size ring
gear, the lower ratio requires more teeth, and, therefor, the teeth are
thinner. How accurate is this?
I suspect it's inaccurate, and here's why: While thumbing through a
catalog recently, I was looking at the varios ratios that were available
for different axles. What I found was that, in many cases, the lower
ratios actually used fewer teeth on the ring and, simetimes, the pinion
gear. This would lead one to believe that, in certain cases, the lower
ratios were stronger than even the stock or higher ratios. For examples,
let's look at the popular Ford 9-inch:
Ratio Teeth
----------------------
3.50 35-10
4.86 34-7
5.67 34-6
6.20 31-5
Based on these figures, the lower ratio should be stronger than the higher
ratio. What's the truth? Are lower ratios inherently weaker than higher
ratios, but for reasons other than the size or number of teeth on the
gears? Or are they not always weaker?
Shel Belinkoff
beli...@netcom.com
Randy Hinds
: For as long as I can remenmber I've heard that, for a given axle, lower
: gear ratios equate to weaker gears. This is because, for a given size ring
: gear, the lower ratio requires more teeth, and, therefor, the teeth are
: thinner. How accurate is this?
: I suspect it's inaccurate, and here's why: While thumbing through a
: catalog recently, I was looking at the varios ratios that were available
: for different axles. What I found was that, in many cases, the lower
: ratios actually used fewer teeth on the ring and, simetimes, the pinion
: gear. This would lead one to believe that, in certain cases, the lower
: ratios were stronger than even the stock or higher ratios. For examples,
: let's look at the popular Ford 9-inch:
: Ratio Teeth
: ----------------------
: 3.50 35-10
: 4.86 34-7
: 5.67 34-6
: 6.20 31-5
Hmmm. Correct me if I'm wrong, but it seems to me that you
mean *higher* gear ratios (numerically lower) have more
teeth. 3.50 is a higher gear ratio than 6.20.
Also, I had always thought that the teeth were the same size/thickness,
and that in order to get more teeth on the ring gear, they
made the ring gear bigger. A while back, I was interested in
going from a 3.55 to a 4.10 in my Dana 44 IFS and I heard a
few responses that I needed a larger 'differential carrier' because
the ring gear for the 4.10 set is too large.
(I haven't yet figured out what a differential carrier is.)
--
/\ ( -Randy | ran...@kentek.com | It's always
/^ \ /\ "My opinions are | Systems Administrator | best to be
/\. .\ /^ \ /\ my own only. You | Kentek Information Systems| prepared for
/. \ .. / . \/^ \ can't have 'em!!"| Boulder, Colorado | the worst.
christopher graves
: For as long as I can remenmber I've heard that, for a given axle, lower
: gear ratios equate to weaker gears. This is because, for a given size ring
: gear, the lower ratio requires more teeth, and, therefor, the teeth are
: thinner. How accurate is this?
: I suspect it's inaccurate, and here's why: While thumbing through a
: catalog recently, I was looking at the varios ratios that were available
: for different axles. What I found was that, in many cases, the lower
: ratios actually used fewer teeth on the ring and, simetimes, the pinion
: gear. This would lead one to believe that, in certain cases, the lower
: ratios were stronger than even the stock or higher ratios. For examples,
: let's look at the popular Ford 9-inch:
: Ratio Teeth
: ----------------------
: 3.50 35-10
: 4.86 34-7
: 5.67 34-6
: 6.20 31-5
According to Lloyd Novak (in his experience), the taller gears like say
3.30:1 or 3.73:1 are much stronger because the pinion gear is larger
relative to the ring gear. A diff with a 3.73:1, combined with a
granny low transmission and a reasonable sized tire (30-32) is just fine
for trails like the Rubicon-- this also from Lloyd. I got this in a brief
discussion once when I called Novak Enterprises.
Chris.
Christopher R. Graves
gra...@cs.colostate.edu
David Stockton
: Hmmm. Correct me if I'm wrong, but it seems to me that you
: mean *higher* gear ratios (numerically lower) have more
: teeth. 3.50 is a higher gear ratio than 6.20.
Well, it's the ratio of crown wheel teeth to pinion teeth, and some
ratios only have one feasible combination of numbers to get that ratio.
I grew up in a town that was home to a major gear manufacturer, and a
schoolfriend became a designer there.
I would not get too worried about whether higher or lower ratios
confer weakness simply because of numbers of teeth, I understand that
the possible differences are pretty small compared to the effects of
quality of manufacture and design:
Choice of steel
quality of hobbing
hardening process
tooth profile design
helix angle
pinion axis offset and hypoid tooth shape.
lubrication
possibility of corrosion due to water ingress
Vehicles needing extremely low axle ratios have used a number of
methods to avoid the need for either impossibly large diameter crown
wheels or else tiny, weak pinions. One solution is to have a small
diff, crownwheel, pinion, with epiyclic gear reduction added in the
shafts to the wheels. These could be close to the diff, or located out
in the hubs. Another is to use normal (spur) gearboxes out in the hubs -
this is often used to get the axle raised above the wheel centre to get
the bonus of huge ground clearance.
: Also, I had always thought that the teeth were the same size/thickness,
: and that in order to get more teeth on the ring gear, they
: made the ring gear bigger. A while back, I was interested in
: going from a 3.55 to a 4.10 in my Dana 44 IFS and I heard a
: few responses that I needed a larger 'differential carrier' because
: the ring gear for the 4.10 set is too large.
: (I haven't yet figured out what a differential carrier is.)
Well, they can only make the crown wheel (ring gear) so large
before the axle grounds!, the only other route is a smaller pinion, and
this is the thing that reduces strength.
The diff carrier is the lump that holds the shafts of the gear
quad that performs the differential action, It has a flange onto which
the ring gear is bolted. It has extended sections by which the main diff
bearings support it. the drive shafts exit through the centres of these
extended sections.
Diffs are tricky things to assemble. Your first worry is to make
sure that the ring gear bolts are secure. You most definitely don't want
even one to come loose or break.
The diff's main bearings are normally adjustable, you need to get
the right amount of end-float, but you also need to get the diff located
correctly in the side-to side sense. The pinion bearings are also
sometimes adjustable - how far the pinion sticks in to the ring gear's
territory, as well as for its own endfloat. All this adjustment is to
get the contact patch between the pinion and ring gear teeth to sweep
over the correct zone with the diff both conveying torque in the
forwards and the overrun conditions. Without the benefit of factory
jigs, this is possible given some care, experience, patience, confidence
patience etc. You'll need a dial gauge and some "engineer's blue".
Cheers
David
Stephen McCabe
: For as long as I can remenmber I've heard that, for a given axle, lower
: gear ratios equate to weaker gears. This is because, for a given size ring
: gear, the lower ratio requires more teeth, and, therefor, the teeth are
: thinner. How accurate is this?
: I suspect it's inaccurate, and here's why: While thumbing through a
: catalog recently, I was looking at the varios ratios that were available
: for different axles. What I found was that, in many cases, the lower
: ratios actually used fewer teeth on the ring and, simetimes, the pinion
: gear. This would lead one to believe that, in certain cases, the lower
: ratios were stronger than even the stock or higher ratios. For examples,
: let's look at the popular Ford 9-inch:
: Ratio Teeth
: ----------------------
: 3.50 35-10
: 4.86 34-7
: 5.67 34-6
: 6.20 31-5
The 5.11:1 rear axle ratio I ran in my last rally car was notorious for
breaking a tooth off the pinion. It happened to me three times in 2 years.:-(
The higher (numerically lower) ratios were considered stronger, but were
too tall to be useful.
Here's my theory:
Lower (numerically higher) ratios have fewer pinion teeth. (AOFBE)
Thus, the average load/pinion tooth is higher and the number of stress cycles
(loading/unloading) is higher for a given distance covered. (AOFBE)
Now, if I remember correctly, the actual stress AND the number of stress
cycles determines the fatigue life of a component.
So we have higher stress and more stress cycles = shorter fatigue life.
Any metallurgists/ material scientists out there care to comment ?
Steve
BTW, (AOFBE) means All Other Factors Being Equal.
Andrew Murdoch
>Shel Belinkoff (beli...@netcom.com) wrote:
>: For as long as I can remenmber I've heard that, for a given axle, lower
>: gear ratios equate to weaker gears. This is because, for a given size ring
>: gear, the lower ratio requires more teeth, and, therefor, the teeth are
>: thinner. How accurate is this?
With lower gear ratios the thing to consider is that the loads carried
through the gear teeth is greater. To allow for this the gear teeth
should be, and are made stronger by either making the teeth wider or
changing the material properties and suurface treatments of the teeth.
In so far as modulas (or pitch) is concerned, the greater the modulas,
the greater the strength, so sometimes the modulas is changed. The
number of teeth on a gear is related to the modulas and the diameter of
the gear.
So to answer your question, smaller teeth does mean a weaker gear.
However in most cases when modifications are made the entire gear must be
made larger to allow for larger teeth that are strong enough to carry a
greater load.
Murdo
Agent 86
have a 3.73 put in but people to me save my money because it will not
help your MPG much any info about rear ends Running a 454 in it 3/4ton HD
Please e-mail me
Stephen McCabe (smc...@hpqt0197.sqf.hp.com) wrote:
: Shel Belinkoff (beli...@netcom.com) wrote:
: : For as long as I can remenmber I've heard that, for a given axle, lower
: : gear ratios equate to weaker gears. This is because, for a given size ring
: : gear, the lower ratio requires more teeth, and, therefor, the teeth are
: : thinner. How accurate is this?
: : I suspect it's inaccurate, and here's why: While thumbing through a