Transmission Gear Ratio Convention

Question

I own a 2003 Mitsubishi Evolution, and I was looking at the transmission's gear ratio here: http://www.jackstransmissions.com/pages/evo-8-9-transmission-gear-ratios

I can't tell if I'm misinterpreting the mathematics of the gear ratios, but I noticed that the ratio differences get smaller the higher up the gear. Does that equate to smaller differences between gear teeth as the gearing is higher?

Is that the convention for gearing selections? I would think that the ratio differences would increase (not saying that the gear ratios themselves increase, but the differences in ratios between consecutive gears increase).

Answer 1

I think your understanding of gear ratios is incorrect. As the gear ratio goes up numerically, you get a larger torque multiplication advantage. A 2:1 ratio gives you twice as much torque leverage than you have at 1:1. A 3:1 ratio gives you three times as much advantage.

Looking at the first gear ratio of the stock EVO8, it shows the number: 2.928. This means the input of the transmission (engine side) turns 2.928 times for one turn of the output going to the differential. The differential provides another reduction in turning, which provides your final drive number, which I believe is the top number of 4.53:1 (4.53 engine revolutions per one turn of the output shaft going to the wheels). As it says in the data below this, at 3000 rpm, the speed of the vehicle should be around 17mph. As you go to subsequent gears (2nd, 3rd, 4th, 5th), the ratio goes down and engine speed goes down. So, when you are in 5th gear at 3000 rpm, your vehicle speed is now 70mph. This equates to a lot better speed for the same amount of engine work.

I don't know if this helps you understand it any better ... if not, please leave comments and I will explain further.