I’m not a complete chowderhead when it comes to cars, but one little thing has always befuddled me; the terminology used for rear axle (differential ring-and-pinion) ratios.
Common ring-and-pinion gear ratios run from roughly 2.8 to 1 to around 4.11 to 1.
Is 4.11 to 1 a “high” ratio, or a “low” ratio?
Posting because I’ve been curious about what “high gear” and “low gear” mean vis a vis 10-speed bikes since I was about 10 and wonder if it’s the same answer.
In gearhead circles a 4.11:1 gear set is referred to as a “low.” However, it is obviously numerically higher.
Mathematically, 4:1 is a higher ratio than 3:1, but it produces a lower gear (more mechanical advantage) and thus may be called a lower gear ratio. It’s calculated as # of ring gear (driven gear) teeth divided by # of pinion (drive gear) teeth, since ring gears have more teeth than pinions. This allows expressing the ratio as X:1, with X being greater than 1, but gives the inverse proportion between high ratio and low gear. A 3.6:1 ratio would be 0.278:1 if it were done the other way round, a format most find awkward.
On a bicycle it’s different. The drive gear (front chainring) has more teeth than the driven gear (rear sprocket), so the comfortable X:1 format is the other way round – # of chainring teeth divided by # of sprocket teeth. Often it’s not expressed as the ratio itself but the ratio times the tire circumference, which is called gear inches. Thus 100 gear inches is a high gear, while 40 gear inches is a lower one.
I had 2 cars of the same body, engine, model, 4 speed auto trans, etc.
The first Firebird V-6 had 2.73 rear end ratio and would lope down the freeway at about 1800 rpm at 70 mph. It was slower on the pick up from a start but the gear ratio was much easier on the car and gas mileage at highway speed.
Second V-6 car, same model but a few years newer had a ‘performance’ package with a 3.42 rear end. A lot quicker off the line or up the freeway on ramp, but it was not much of a freeway car. The transmition topped out at too low a speed. Compared to the previous car it was doing about 2200 rpm at 70 mph. Poorer mileage, but more fun on the back roads. It needed an extra tranny gear or overdrive.
Third Trans Am Firebird V-8 has a 3.23 rear, still with the 4 speed auto, that is about right.
Manual transmission cars with more gears, like a 6 speed, tend to have a lower geared rear end for quicker pick up because they have more gear options in the tranny.
Thanks to everyone who responded. 4.11 = “low”; got it! 