Hello.I just picked up a 2001 F4i with 6300 miles on it and had it out for the first ride yesterday. Now, I've never had such a high-revving bike before so I don't know if my experience was normal for a stock F4i but I was doing 65 mph and the revs were about 4500 or so. The RPM # might not be exactly right, but my point is that it was higher than I'd expect. Even my 916 runs at far fewer revs at that speed. I asked the previous owner if he had geared it down but he didn't think so and I haven't counted sprocket teeth yet to compare with stock but thought I'd see if my bike is at least in the ballpark of RPM @ speed.
Thanks for the help

 

Front should be a 16, rear is a 46 - as long as you can count, you can work out if your bike is correct ;-)

https://sprocketcenter.com/c-1390019...2001-2006.html

 

Thanks, Rockpool. I'll whip out the abacus and get started!

 

Or you could use math. Rear tire should be a 120/55R17 indicating 120mm wide, 55% high, 17" (416,5mm) diameter that gives 482.5mm diameter total. Let's ignore the flat spot.

gear ratio of the rear and front sprockets is 46/16 = 2.875

You said 64mph? In "regular" measurements that's 28.61 meters per second.

One revolution of the wheel takes you 2piR along the road - 151.5cm or 1.515 meters. That means you're moving at 18.8 wheel-revolutions per second.

so, to work out the front sprocket revolution speed at 28.61m/s multipled by the sprocket ratio gives you a front sprocket RPS of 54.

6th gear crank-to-sprocket ratio is 1.131 according to the book, so crank should be spinning at 61rps, or 3664rpm.

My bet is your front sprocket is oversized, and your rear is undersized to make lifting the front wheel easier ;-)

 

Rear tyre size is actually 180/55-17. Let's use 629.8mm diameter or 1.979m circumference.

To calculate engine-revs @ 65mph = 29.06m/sec

rear wheel revs = 29.06m/sec / 1.979m = 14.68 revs/sec

multiply by sprocket ratios 46/16 = 2.875 * 14.68= 42.22 rev/sec for output shaft

multiply by 6th-gear ratio 27/23 = 1.174 * 42.22 = 49.57 revs/sec for input shaft

multiply by primary-reduction ratio 1.822 * 49.57 = 90.32 revs/sec at crankshaft

multiply by 60sec/min * 90.32 revs/sec = 5419 revs/min @ 65mph

Can also use this site to do all calcs for you: https://gearingcommander.com
Entre 4600rpms for starting RPMs and it'll give you 5415rpms @ 65mph

 

Honda did good job with gearing. Typically you want to adjust top-gear to hit theoretical calculated top-speed right at power-peak RPM. On CBR600F4i, that top-speed is 150-155mph with max-power occuring at around 12500rpms.

Gearing is perfect! If it was taller, engine would rev too low and wouldn't have enough power @ 140mph to go faster. It gearing was lower, it would hit power-peak of engine @140mph, but power drops after that and it wouldn't have power go faster. In this case, gearing matches 150mph, right at 12500rpms where power-peak occurs!



Bikes with higher power and higher top-speed with power-peak lower than redline will have taller top-gear. So @ cruising speed on highway, they'll have lower engine-speeds. Compare top-gear of 916 compared to baby brother. I had one way back in '90s.

 

Thanks for the great table! I am, indeed, running the stock 46/16 sprockets, so my RPM at 65mph is right at 5500 (orig. # was from memory, this # is from a ride this morning). My concern was that the bike was revving too high at a sustained speed, but I've talked to a former racer & he assures me that the engine isn't being taxed at 5500 for extended periods, it's designed to be there.
Thanks for the responses.
Dannoxyz- great pic of the 916 at Golden Gate!

 

You're welcome! That's actually my 748.

I was commuting on 2002 Ninja 250 to S.F. for over 10-yrs. It revs 10-11K RPMs on freeway entire way! My 2008 race Ninja 250 has lived its entire 50K-mile lifetime at 12-13K RPMs!

 

I've seen at least 2 F4i that went over 100k so don't worry about the 5500rpm. Honda did pretty much everything right with these bikes... The one exception - cam chain tensioner.

 

Ah, yes, when I zoom in I can see the '7' there in yellow. I'd love to ride a 748 just to feel the difference from the 916.