Need help with gearing please?

[Pat Conlon]

.... but the conversion to a 17" rear wheel and 160/70 tire does spin a bit faster at the same speed....

Bill, did you mean a 170/60 tire?

[Bill_Rockoff]

You know what?  I forget.  I've had 160/70, 170/60, and 160/60 back there.  I'll have to look when I get home.

It seemed to corner the best with the 160/60 back there, but it's geared pretty short that way.

[Tuneforkfreak]

I've been riding with 18/40 gearing for the last few weeks and it's been all good. Yesterday I received my 38 T rear sprocket. I installed it last night and took it out to see what it would do. I think for cruising 18/38 is going to be just fine for me.

[holes41]

I've been riding with 18/40 gearing for the last few weeks and it's been all good. Yesterday I received my 38 T rear sprocket. I installed it last night and took it out to see what it would do. I think for cruising 18/38 is going to be just fine for me.

I have 18, 38 in my toolbox just waiting until I can afford a new chain. Can you tell me if it made the bike feel like it is down on power or just gave it longer legs? I don't want to be disapointed with a feeling of power loss but cruising at 4500 rpm is driving me nuts.

[aviationfred]

I have been running the 18t/38t combo for a little over a year. I have not had any low gear power issues. It definitely will give you longer legs.

Tire sizes also make a small difference in your speed vs rpm's

I have 120/70/17 and 180/55/17 tires. My 5th gear rpm's are as follows.

3000 rpm = 54 mph

4000 rpm = 72 mph

5000 rpm = 90 mph

Fred

[Tuneforkfreak]

I'd say that  initial take off is a bit drawn out  but that's to be expected and I got used to it after my first ride. It by no means  dogged the bike ( It still has plenty of power)The longer legs are exactly what I was shooting for. Now I'll find my self  in fourth gear until I check up the tach to the speedo and realize I have one more to go. It's like , Oh ya that's what we where shooting for right there! I did notice the slow down help from down shifting was decreased so that comes into play for my riding style but not a deal breaker. The gearing changes I've done ( 17/ 40) (18- 40)  and (18-38) have all been on stock  chain length which I think is 110 link? so really if you think about it, gear changes are pretty simple if you'd like to set up for round town stuff or freeway. Also I'm on a stock 16 wheel.

[andyb]

At ~22,000 miles and completely stock, mine made peak torque at 7,000 rpm and peak power at 8,500 rpm.  I'll have to find my dyno chart and recreate my hp-vs-rpm spreadsheet from three computers ago to get other data points, but it's pretty strong at 5,000 rpm.

Gearing a bit taller wouldn't hurt anything.  I found the stock gearing on my '89 to be fine, but the conversion to a 17" rear wheel and 160/70 tire does spin a bit faster at the same speed so my effective gearing is shorter these days.  Maybe an 18T next time around would be the ticket. 

Of course, the motor can comfortably handle extended moderate use of revs.  The lower you gear, the more oomph you have right now!

My personal take is on a stock machine, 17/41 would be about ideal (17/40 with the 170/60R17 works out to about that).  But then, I didn't buy a 1188cc machine for low cruise rpm and mileage, I bought it to go like hell when I tell it to!  If you really are uncomfortable with cruising at 4krpm or above, consider a quieter exhaust--if it's aftermarket, odds are you can repack it for a great effect-- and/or earplugs, which I consider absolutely mandatory on any ride of more than a mile or so.

In fairness, my FJ is on 16/42 right now but that's for other reasons, and is far too short to go any real distance on.  Unexpected wheelies in first are a laugh a minute, though. So.... the motor can handle whatever gearing you want to throw at it.  I use the reaction of the chassis as the limiting factor to base my judgement on.  Also on 17/40 with the shorter tire, the wife can be made absolutely silent, other than a high-pitched squealing noise by using the lower gears in anger...something about keeping both wheels on terra firma!



Gears are cheap.  Buy whatever and fuck around with it.  The motor will comfortably handle really silly long gears, but it's a hoot with short ones too.