Gearing up/down - Your friends the Sprockets

[pdbnorth12]

My efforts to address the upgrades from previous owners continues.

I have not pulled the gears to check the numbers, but given the current RPM vs speed, it's obvious that the bike was geared down. (4000 @ 55 mph in 5th)  The factory sprockets for the 89-93s looks to be 17 front, 40 rear.  As near as I can figure, using "Gear Commander", 4000 RPM should be around 65-66 mph on the OEM 17/40 sprockets.

The results are that 1st gear really doesn't seem to have much of a point, and traveling at 65-70 mph seems much more frantic than I had anticipated. The current sprockets must be something along the lines of 15 front, 42 rear. I'm changing them out, regardless of their numbers. To anyone that might be gearing down for more low end, I mean no disrespect, but the 1200 seems to have more than enough grunt to tool around town in, and I'm not looking to win any stoplight derbies.

To the highway warriors who put on hundreds of miles in a day, what are you running? Did you stay with the original 17/40, or did you gear up to get even longer legs?  I'm looking for a relaxed experience where I'm not always looking to shift into the imaginary 6th gear.

Thanks,
Paul

[Flynt]

To the highway warriors who put on hundreds of miles in a day, what are you running?

Many, including me on the '92, run an 18 front...  a little easier on the chain and gives big bang for the buck (1 more in front =~ 3 less in the rear).  I like 18/41 on Wizard and get ~5K at 80mph and TONS of power on tap even in 5th.

The '84 is stock gearing (17/40 I think) and is ~5,300 at 80mph...  also fine for me as I prefer to be close to Kook zone most of the time on that one.

Frank

[jscgdunn]

I find 18 38 a pretty good mix.

Jeff

[FJ1100mjk]

I ran the stock 17/42 on my FJ1100 for the last four or so years, then switched to 18/40 before I went to the Black Hills for the Central Rally. Did so, because of the hundreds of miles of freeway travel to and from. I liked the taller ratio for 80+ highway speeds. It helped the buzziness that I would normally endure at those speeds with the stock ratio. However, you do lose a little pep/snap with the taller ratio in the first two gears, but its not that noticeable, nor reason to switch back to the lower, stock ratio. My two cents.

[FJmonkey]

I have been running on 18/38 gearing and find it well suited for both long distance and my canyon rides. I am most likely down a gear lower in the twisty parts and still find myself trying to shift into 6th gear on the freeway.

[markmartin]

I like the 18-38.  It's great on the open road and if you want more grunt, just shift down a gear...or two.

[ribbert]

I settled on 18/41 (odd numbers) after trying a few different ones and I ride a bit of everything.  Even this slightly higher gearing takes a bit of the sting out of acceleration. I wouldn't want to lose any more.

I like my default highway cruise speed to be at no less than 4000rpm.

I found this to be the best compromise for me.

Noel

[pdbnorth12]

Thank you all for your input. I've been crunching some numbers:

15/41 = 2.73
17/40 = 2.35
18/41 = 2.28
18/38 = 2.11

It's pretty surprising how low the previous owner(s) had chosen to gear the bike, given the comparatively narrow spread of values between stock and the longest legs suggested by the group so far.

I had not thought of 18/38 as even a possibility, but I can see the draw for long rides, especially now that the state has increased the interstate speed limits to 70 mph. How does that combo handle the occasional stop and go traffic, clutch-wise?  I like the idea of 10% less chain wear.

I'm intrigued.

Paul

[markmartin]

Stop and go is  not an issue.  I only notice having to really slip the clutch when riding 2-up and fully loaded, especially starting out going up a hill, out of a parking lot, etc. 

I do like the taller 1st gear in town.  Parking lots and just turning right or left onto a street from a stop is smoother.  I found I always wanted to shift to second half way through my turn when I had the stock sprockets. 

[Arnie]

The FJ has buckets of torque to get you rolling from a stop, so stop and go in town is not an issue.
The main changes of going to lower (numerical) ratios is how busy the engine SOUNDS at highway crusing speeds, roll-on acceleration in the higher gears, and to a small extent fuel economy.
Also, be aware that most all those who have fitted those 18/38 sprockets have also fitted 17" wheels to their bikes.  The overall diameter of a low-profile 17" tire is SMALLER than the stock tall 16" OEM tire. That smaller OD tire/wheel effectively raises the sprocket ratio.

[ribbert]

Arnie, I thought the OD of the 17" wheel was much the same.

Noel

[Pat Conlon]

With the stock size being 150/80-16 (25.4"dia)
the 170/60-17 (25"dia) will add 1.7% engine revolutions per mile
the 180/55-17 (24.8"dia) will add 2.6% engine revolutions per mile.

Here's a cool conversion chart showing the effect at various speeds: http://tire-size-conversion.com/tire-size-calculator/

[FJmonkey]

According to www.gearingcommander.com the difference between the 16" and 17" wheel/Tire combos show the 17" to be slightly smaller. The stock 16" wheel with stock tire has a wheel circumference of 79.95 inches. A 17" wheel with a 180/55 tire has a circumference of 77.9 inches. That makes the OEM rear 25.45 inches in diameter and the 17" diameter 24.79 inches. So the calculated diameter difference is 0.66 inches, or 0.33 from the axle to the ground. Actual differences will vary as many have reported differences in tires depending on manufacturer....

[Firehawk068]

Arnie, I thought the OD of the 17" wheel was much the same.

Noel

I just went out to the garage and measured the OD of CapnRon's old rear tire, and my old rear tire.

Standing up, measured from the floor with a straight-edge, and a square.

Metzeler  150/80-16 = 24.5" diameter
Michelin   180/55-17 = 23.5" diameter

Granted, these were not mounted on a rim, and were both worn out completely.
But the 17" rear is slightly shorter.

For gearing, mine is currently set up with 18/42 combo.
Next time, I'm probably going with a different rear sprocket (maybe 40, maybe 38)
It has plenty of low end grunt, and down the freeway 5000rpm is around 80-ish mph.
I wish I had a 6th gear. 

[pdbnorth12]

Also, be aware that most all those who have fitted those 18/38 sprockets have also fitted 17" wheels to their bikes.  The overall diameter of a low-profile 17" tire is SMALLER than the stock tall 16" OEM tire. That smaller OD tire/wheel effectively raises the sprocket ratio.

Good information, Arnie. My mileage very well may have varied with the stock rim and tire configuration. 

I'm calling my shot: 18/40.

Paul