ring and pinion gear calculator?????

[buffblazer]

ok i must have a head full of rocks because not to long ago i pulled my 10 bolt apart and counted the teeth and i cant remember the exact number but when i did it i calculated it and it came out to 3.73 which is what the glove box says its supposed to be. well i was on 4lo today messing around and it says for my set up 350/sm465/208 at 65mph im supposed to be running 2,468rpm with 33 inch tall tires but when im driving 65 down the highway i run about 2.750 almost 2,800 i know that tachs aint always perfect but 300rpm difference? that should be almost 4.10's right? and i counted like 4 times am i just stupid or could maybe my front be different?

 

[Greg72]

Torque converter slippage...

 

[YZEATER]

465's have a torque converter???

why worry about it. check your ratio again. jack up one wheel and spin it 2 time and count the revolutions of the pinion. 3 and 3/4 turns in 3.73 and so on.

 

[buffblazer]

Torque converter slippage...

im running a sm465 i was playing around with the calculator and it says that if you go up on tire size you drop in ratio true enough but is it calculating your factory ratio or the new lower ratio because of the tires?

 

[Greg72]

My bad.... No TC effects with a 465 obviously. (must......drink......more......coffee)

The tire diameter is probably inaccurate enough to prevent you from getting a true value. Most tires don't measure at large as their advertised value.

A much more accurate way to get diameter would be to mark the sidewall of the tire and roll forward something like 10 complete revolutions along the ground, then measure the traveled distance. Solve the diameter backwards from the measured circumference value.

Using 10 revolutions should help give a very precise circumference number with minimal error.

 

[joecowap]

Check your actual tire size! Even thoug it's manufactured saying 33" it could easily fluctuated an inch in either directions. Super swampers have to be the worst about this.

 

[oneofthefewbmx]

My bad.... No TC effects with a 465 obviously. (must......drink......more......coffee)

The tire diameter is probably inaccurate enough to prevent you from getting a true value. Most tires don't measure at large as their advertised value.

A much more accurate way to get diameter would be to mark the sidewall of the tire and roll forward something like 10 complete revolutions along the ground, then measure the traveled distance. Solve the diameter backwards from the measured circumference value.

Using 10 revolutions should help give a very precise circumference number with minimal error.

indeed....im sure this is probably the culprit....i would jack up one tire and double check the gear ratio again (as stated before) just to be sure

 

[tRustyK5]

For the rev's to be off by 15% the tire would have to be 15% smaller than advertised...which gets it down to a 28" tire. Highly doubtful IMO.

I'm guessing you have 4.10's.

As for counting teeth, there isn't any need for that BS. The edge of the ring gear is stamped with the ratio. 41/11 is 3.73, 41/10 is 4.10's.

Rene

 

[Wasatch K5]

Buff,

The calculators you mention are theoretical models as opposed to actual numbers. For example when you plug 33" tires into the calculator it assumes that the actual diameter of the tire is 33". In reality tire diameters are rarely the exact size. A BFG A/T size 33x12.50x15 is actually 32.7 " in diameter.

Also, your vehicle is loaded and the tires bulge. That bulge reduces the actual diameter somewhat. How much depends on tire pressure and weight on the tire.

At 65 mph you are going 65/60 x 5,280 = 5,720 feet per minute, or 68,640 inches per minute.

A 33' tire theoretically travels 103.673 inches per revolution (33 x Pi)

68,640/103.673 = 662.08 tire revolutions per minute (at 65 mph)

662.08 x 3.73 (axle ratio) = 2,469 rpm
662.08 x 4.10 (axle ratio) = 2,714 rpm

But again, this is theoretical distance traveled and doesn't account for the change in diameter due to load.

If you do as Greg72 suggests (you'll need a 100' measuring tape) you will have an accurate tire circumference and you'll be able to calculate the "real" tire diameter (which would be equal to twice the "static loaded radius")

At that point you can take your real world numbers and plug them into the calculator, or do the math yourself.

 

[4X4HIGH]

Just lay a straight edge off the top of your tire and measure from it to the ground and that's your true tire diameter (for this purpose anyways) to figure out gear ratio working backwards.

MPH X gear ratio X 336 divided by tire diameter = RPM's

(65 x 3.73 x 336 = 81,463.2) divided by (33") = 2468.58 RPM
(65 X 4.10 X 336 = 89,544.0) divided by (33") = 2713.45 RPM
(65 X 4.10 X 336 = 89,544.0) divided by (32.5") = 2755.2 RPM

I'll bet you have 4.10 gears and your tires are roughly 32 1/2" actual height which would put you at 2755 RPM's

 

[buffblazer]

well that makes a lot of sense i think i will go measure and find out