Thread: Math Question

Tweet

To determine the final drive ration when running an overdrive trasmission, would you multiply the rear end gear times the overdrive gear or ???? ie, would a car with a 4.11 rear gear and a .75 overdrive gear be the same as running a 3.08 rear gear with a 1:1 trans top gear???? 4.11X.75=3.08????

You got it, Dave! Multiplying ratios gives final ratio, Whether gearing up or down.

Originally Posted by Dave Severson

To determine the final drive ration when running an overdrive trasmission, would you multiply the rear end gear times the overdrive gear or ???? ie, would a car with a 4.11 rear gear and a .75 overdrive gear be the same as running a 3.08 rear gear with a 1:1 trans top gear???? 4.11X.75=3.08????

Short answer . . . yep - if nothing else changes.

Thanks guys!!! Just doing some contemplating on gears for the Camaro to go on the street.....and of course the Ranchero for going to Bonneville someday... Calculations put the Ranchero final drive ratio, figuring in the Salt Flat tires that Goodyear has, at 1.69:1..... Then the big IF the car will pull 5,000 RPM in top gear, 264 mph..... hmmmmm... Anybody into aerodynamics and know off hand what the drag coefficient of a chopped Ranchero with A pillars laid back and and air dam on the front is??????


Actually, only need to go 200 to get my B-Ville 200 mph club patch.... (Only, geez!!!!)

Originally Posted by DennyW

...As you can see, the larger tires reduce your final drive ratio to 3.30—a measurable difference. You can also do this to determine the effect of smaller tires on the final drive ratio...
.

I am too tired to crunch numbers today but I believe, and correct me if I am wrong, that changing tire size does not actually change your drive ratio or gear ratio (if you are using those terms synonymously). If you change tire size, and hence the circumference, it has the "effect" (performance wise) of changing your gear ratio.

It's an easy way to change the performance of your ride (for people like me who have never tore into a rear end ... ) as long as is doesnt negatively impact the appearance of your ride.

Yeah, been on there, lots of neat stuff... I must of skipped school the day they covered aerodynamics.... Anybody want to loan me their wind tunnel?????

Dave,I will make this real simple for you.Do a search on Randy ring and pinion.
They have a calculator on there that will tell in an instant what you want to know. just enter your gear ratio, tire size,and given speed.click solve.
Its a great tool.
Tim

yup, all them wind tunnels were either broke or in use. What I need is a virtual wind tunnel.....or at least a little aero knowledge!!!!

Randy,
I've got the good calculators, unfortunately they don't take things like drag and rolling resistance into the equation..... Heard somewhere to deduct 10% from what the calculator computes as top speed to allow for drag and fraction, have no idea if that is accurate or not..... Anybody got any opinions?????

Anybody into aerodynamics and know off hand what the drag coefficient of a chopped Ranchero with A pillars laid back and and air dam on the front is??????

Dave,

To quote Craig Breedlove (kind of), you could either set a speed record - or an altitude record for Rancheros.

Originally Posted by Henry Rifle

Dave,

To quote Craig Breedlove (kind of), you could either set a speed record - or an altitude record for Rancheros.

yup, that is certainly one of my concerns, too!!!!