Gear Ratio's Explantation

[Mark Gregory]

In my owners manual it says my gear ratio is this . Reo Royale Victoria 13 - 53 4.07 to 1

Reo Royale Coupe 13 - 49 3.77 to 1

Could someone explain this ratio and what is the difference between the 2 different cars . Thanks

Edited December 15, 2014 by Mark Gregory (see edit history)

[Beltfed]

As far as the rear end is concerned...the first number tells you how many times the drive shaft will turn for one revolution of the rear wheel. The higher the first number the lower speed you will be able to drive before running out of rpm of the engine, but it is a trade off as you get more torque. Vehicles such as heavy trucks and jeeps will have high first numbers as they need high torque but are generally low speed vehicles. A general rule is the lower the first number the better gas mileage you will get as the motor is turning less rpm's at a given speed.

[joe_padavano]

More specifically, in the numbers 13-53, 13 is the number of teeth on the pinion gear and 53 is the number of teeth on the ring gear. Divide 53 by 13 and you get 4.07 (actually, you get 4.0769, which should have been rounded up to 4.08). The ratio is thus 4.07:1, meaning that for every 4.07 turns of the driveshaft, the tires turn once. The other car, with the 3.77:1 ratio, sees the tires turn once for every 3.77 turns of the driveshaft.

Gears multiply torque. Think of a lever - the 4.07:1 gears have a longer "lever", so the car accelerates more quickly, but since you have to push that longer lever further to raise the load on the other side, the engine RPMs go up faster, so you are limited in top speed based on engine redline (and aerodynamic drag, but that's a different discussion). Assuming the same engines and same car weights, the 3.77:1 gears would cause the car to accelerate more slowly, but would allow a higher top speed. And as noted, since the engine spins more slowly at a given road speed in the 3.77:1 car, that car will usually get better gas mileage.

[Beltfed]

Mr. Padavano,

Very well done!

[Mark Gregory]

Excellent answer Joe . Where were you when I was in High School ? I could have used your knowledge . Thanks for your's and Beltfed help .

[Rusty_OToole]

The Royale was Reo's top luxury model, comparable to Cadillac or Packard. The Victoria and Coupe are body styles. The Victoria is a short 2 door sedan, the coupe is an enclosed 2 passenger car.

Heavier cars got lower gear ratios so the engine could pull the load more easily. The really heavy models like sedans and limousines, must have gotten even lower ratios.

Lower gears = higher numerically. In other words, 4.07:1 is a lower gear ratio than 3.77:1, meaning lower in speed.

[Larry Schramm]

If you would like really low ratios, look at the trucks. Everything from old ones to new ones that have trailer towing packages.

[JACK M]

On the short tracks we run in the mid 6,s for final ratio, longer tracks require a taller gear.

With a quick change rear end we will install what we think might be right for the track, run a few laps then punch a recall on the tach.

If the engine is turning faster than we want we will stick in a taller gear (the opposite if the engine doesn't turn as fast as we want) With the quick change I can swap ratios in just a few minutes.

Of coarse I have to carry several sets of ratios. These are two gears that can be swapped by removing a rear cover. They work in conjunction with a 4:89 to 1 ring and pinion by adjusting the speed of the drive line before it gets to the pinion gear.

So, I carry a list of ratios that have worked at each track that we visit, this way I can get as close to final set up as I can before we head out.

Back when, we ran 9 inch Ford or 8 3/4 Mopar rear ends and they are much more difficult to swap out. We also sometimes ran in second gear and adjusted accordingly, although that costs horsepower.

Edited December 15, 2014 by JACK M (see edit history)

[Steve Braverman]

so..... how do you spell the brand name of a very popular quick change-ratio rear axle. I do not think that it is "Franklin" but people keep asking me about such axles. I suspect that since Franklin steering boxes were popular with race car builders that they assume that Franklin also made the quick change-ratio axles. They did NOT!

Frankland

[rsb]

Here's a good video that may help to explain why it works.

[39BuickEight]

I always liken it to riding a bike. The bigger the first number is, in this case 4.07 vs. 3.77, the easier it is to pedal, but you can't go as fast. The lower the number is, the harder it is to pedal and get going, but you have a higher top speed.

[JACK M]

Yes, Frankland is a quick change brand. Although 'Winters' is the most common in my circle of friends these days.

I have seen this video concerning the differential before and I find it quite interesting. A lot of effort was done to explain differentials.

However that doesn't really go into ratios.

To expand on ratios on the race tracks. If you multiply the rear end ratio by the transmission gear ratio it will give you a final ratio. So If I am running a 1.45 second gear with say a 3.56 rear end it would yield a 5.16 final ratio (ok for a very long track). My local track seems to like a ratio in the mid 6's so I look for a 4.56 rear end and my 1.45 second gear it will yield me a 6.61 final. We also run a much larger right side tire than on the left and I can slightly adjust engine rpms with tire size.

Incidentally we completely disable (eliminate) the differential with a spool affair on the ring gear or by welding the spyder gears solid to prevent one wheel from turning at a different speed than the other.

Fun stuff...