Rear sprocket...

[Cobblesmacker]

This isn't one of my modifications, perhaps not even a modification at all. Anyway, I was cruising along a private road that looks a lot like the A38/M5 between Ashburton and Worcester at about 100mph. I do the journey often and it gets a little boring.

Short story long, in fifth gear I realised the engine was doing almost exactly 6000rpm @ 100mph, which means at 12000rpm (end of redline), I'd theoretically be travelling at ~200mph. I'd be shocked if the bike made it there but it begs the question, is my sprocket upgraded, my speedo, my rev counter...? I'm not sure how many teeth it is 'supposed' to have so I wondered whether you guys could tell me the oem sprocket toothing.

[FJ1100mjk]

1985 FJ1100: 17/42

[Cobblesmacker]

Sorry, you reminded me I should add 1995 FJ1200... but thanks for the swift reply! I can't really check my toothing until it's light tomorrow. What a poorly planned post of mine. 

R.

[Cass]

All the models came with a 17 tooth front sprocket but the rears were different.
The FJ1100 was classed as a sports bike so had lowest gearing (meaning more revs per given speed) and came with a 41t. This allowed it to top
out in top gear (5th) with a top speed of 144 mph. Please remember these are true speeds and you would need to add approx 5% to make it a
speedo reading.
The FJ1200 1TX and 3CV (86-90) came with a slight smaller sprocket of 40t. This was due to the slightly torquey nature of the bigger 91cc engine.
This meant the top speed was increased to 148mph.
Finally came the 3XW (91-95) FJ1200.
By this time Yamaha had made it into a full tourer so geared it with a 39t rear sprocket. The top speed was, in theory, 151 mph, but due to the
less revvy nature of the 1188cc engine and the extra weight, it always had difficulty pulling to the 9500rpm red line.

[Cobblesmacker]

Brilliant, thanks Cass. Strangely, I'm replying late because I have been doing a little work in Paignton recently. Due to head down again on Tuesday.

Considering 100mph @6,000rpm, a quick head sum gets me to a theoretical speedo reading of 158mph at 9,500rpm. Which sounds spot on with what you said.

[FJmonkey]

Have fun with this. www.gearingcommander.com....