Brain teaser for people who like math.

"AntiSpeed" (AntiSpeed)
10/13/2016 at 17:40 • Filed to: None

So I’m hoping to run my car for the first time next weekend and I need to figure out the right gear ratios. I found a post on a forum for the car and track I need, but the final drive ratio is wrong. Here’s what they suggest for a 9:31 final drive:

1st: 21:30

2nd: 22:28

3rd: 24:27

4th: 25:26

The final drive in my car is 13:36 and changing it involves taking apart the differential and buying a very expensive new ring and pinion. Does anybody know how to calculate what I need to put in my gearbox? I barely passed high school algebra.

Pic of my car for your time.

DISCUSSION (7)

71MGBGT Likes Subarus of Unusual Colors > AntiSpeed
10/13/2016 at 17:51

http://www.wallaceracing.com/gear-speed.php

Edit, I don’t think that that’s what you’re looking for. Sorry about that.

Aaron M - MasoFiST > AntiSpeed
10/13/2016 at 17:57

13:52

Aaron M - MasoFiST > Aaron M - MasoFiST
10/13/2016 at 17:58

I may have done that wrong. Hang on.

Aaron M - MasoFiST > Aaron M - MasoFiST
10/13/2016 at 17:59

Definitely did that wrong, that’s 9:36. Sorry.

Aaron M - MasoFiST > AntiSpeed
10/13/2016 at 18:05

OK, take two. Your final drive simplifies to 2.77:1, and the desired final drive (31:9) simplifies to 3.44. That means you’re going to need (3.44/2.77) = 1.24 times more reduction in the gearbox.

So: 21:37, 22:35, 24:35, and 25:33, though those are rough approximations.

You can tell a Finn but you can't tell him much > AntiSpeed
10/14/2016 at 09:22

Shoot me an email charlie.cpk [at] outlook.com. I played around a little bit with a spreadsheet to figure out what kind of gearing you would need, but it won’t exactly match the example gear ratios. What are the current gear sets in your transmission, or gear sets that were previously installed? Based on the example given I figured gearing for each gear having 50 or 51 teeth combined between the two gears. Quick and dirty you are looking at:

1st 18:32
2nd 20:31
3rd 21:30
4th 22:29

If you send me an email I can send you an excel spreadsheet that you can use to calculate the gears that you need and give a little more explanation for how I got the gearing listed above.

AntiSpeed > You can tell a Finn but you can't tell him much
10/14/2016 at 12:10

Sent!