Questions of gearing

[Shaun]

So I have been looking at gearing and what effect it has on speed vs rpm. I am about to convert the back end to a 17 x 5.5" wheel and am wondering about gears. I have seen what can be done to keep it pretty much as it came with 17-41. I like the acceleration and I like the twisties, and occasionally I get out on the highway and give it a run. So what I am looking at is the best all around average, ( I know it all varies).Now depending on tire size this changes gear requirements to keep the same as stock. But the question is what is the actual performance difference between going up a tooth in front or down 1 or 2 teeth in the rear. And what are the favorites out there compared to tires being run and the likes or dislikes. Thanks for looking and the input.

Cheers.
Shaun

[andyb]

http://www.fjowners.com/index.php?board=23.0


Hey look, a whole subforum dedicated to just that question.  Gosh!

Also there's no way to answer until you say what size tire you're intending on using. 

[the fan]

This site:
http://www.gearingcommander.com/

is great for answering your questions. You can easily plug in your tire sizes, gearing options and RPM to find the speeds for any set up you are considering.

An easy way to compare acceleration from set up to set up is to divide the new speed at a given RPM from stock set up at the same RPM and compare

example;
89 fj1200 stock rear tire and gearing should be capable of 105.3mph at 9000 RPM in 3rd gear.
the same bike with a 170/60-17 rear and 17/41 gearing would run 101.1mph at 9000RPM in 3rd.
If everything else remains equal this relates to a 4% decrease in speed but an equal increase in acceleration.

In other words you will reach 9,000 RPM 4% quicker with the second setting than the first.

The downside is that on the FJ you will pull  appx 3640RPM cruising at 60MPH stock. with the 170 rear and 14/41 gearing you willl now pull 3793, a 4.2% difference, which mae affect fuel milage or put the bike at an RPM that sets up and unwanted vibe in the chassis.

Play away, Its free.

[Shaun]

Thanks, I had read the gearing sub forum and the xls sheets, but was still unsure as to what the eventual outcome would be. Seeing it and hearing from others experience are two different things. does adding a tooth to the rear give you better acceleration or does adding a tooth to the front? and now The fan has explained the chart to me it clears up the fog for me.

thanks for that.
Shaun

[fj1289]

The way FJs are geared stock, it is about 2.4:1 final drive ratio - ie, 1 tooth on the counter shaft sprocket is about the same change as 2.4 teeth in the rear.  Given the choice of going down 2 or 3 teeth in the rear - vs - up 1 in the front, I'd go with 1 up in the front.  The tighter the bend you make at the countershaft sprocket, the quicker you'll wear the chain.  Plus, when you raise the rear ride height (that strain of moditis almost always accompanies the 17 rear rim moditis bug!) you will gain more clearance at the swingarm pivot. 

Welcome to the darkside, welcome to modifier's anonymous!  Don't forget to Kookaloo!

Chris