Re-gearing the Honda Rebel 250

1985-honda-rebel20250-motorcycle-motorcycle-200340244-c1cc6fd3eedb17179808dd529af6caeeMy input on the Rebel 250 is always the same,

The bike is hopelessly undergeared!
With a stock 14/33t sprockets, it is jerky in first gear, you don’t even go half of an intersection before needing to shift into second gear, and fifth gear cruises nicely at 25-30mph. (so what about the other 50mph?)

The gears are so close together, because it’s made to shift incorrectly, here’s what I mean with that:
Because the rebel is a 360 degree ptwin, the whole engine/transmission system vibrates quite a lot; as one piston fires at exactly the opposite time as the other, having them fire evenly timed every other rotation of the crankshaft.
It vibrates, except in ‘resonant vibrations’, where the engine is canceling out its own vibrations, by rotating in a specific RPM range.
The Rebel has 3 such ranges.
1- somewhere between 2500 and 3666rpm (around 3k centered)
2- between 6k and 6666rpm,
3- between 7750 and 8500rpm range.

Also, it has odd vibrations, where the engine would vibrate and ‘add’ to the chassis vibrations.
These ranges would be:
1- around 4200 to 5200 rpm
2- 7-7.2k rpm
3-8.5+ k rpm.

Because of that, you will want to run the engine at around either 3, 6, or 8k rpm, where handlebar and chassis vibrations lessen.
These ranges on stock gears are not very nice riding ranges for Florida, where the minimum speed is generally 35mph, to 55mph.
Makingbthe stock gearing larger, from 14/33t where it cruises fine at 25-30mph, to 15/25t raises that ‘vibration free zone’ to 35-45mph, which is much closer to the speeds I usually ride at here in FL.

The rebel’s gears are tuned to run in that 8k range, where the gear spacing makes sense, not at 3-6k rpm, where double or triple shifting happens quite a lot, and city riding is bugged with more shifting than riding.
At this 8k range the bike is quite peppy, and has good engine brake-ability, but also wears out a lot faster. MPG is also a lot lower there, than in the lower rpm range.
The engine also surpassed it’s hp band (at 6.6k rpm to 7.5k rpm), and though a lower gear will give you higher torque to the rear wheel at those rpms, the lower engine hp and torque will make the rebel not accelerate faster than when trying to ride it at below 7k rpm in higher gear.

Same acceleration at 6k rpm, as in lower gear at 8k rpm, really makes no sense to even go beyond 7.5k rpm!

For those reasons, the rebel needs a sprocket change from the stock 14/33t.

I’ve ran quite a few sprocket combinations on it, and my advise is highly subjective, so you might feel different about it than I do.

Changing from 14/33 to 15/33 (or 14/30, about the same gearing), does little, but is a step in the right direction.
Running a 15/30t, I found the Rebel had quite a neutral gearing, quite perfect for normal riding on it.
The gears weren’t long, neither short. I found the bike’s response quite bland with this.
Further lowering the rear to 28t, I found the sprocket setup most suited for fast acceleration, and the gears to be quite tall. Big bike feel for under $75, without the torque nor danger!
At this setup 4th gear equals stock 5th gear, which means that in 3 gearshifts from first, you’ll be going just as fast as 4 gearshifts with the stock gearing, essentially saving you the time for one gear to shift.
I also found at this gearing you could rev it up to the end of the hp band (around 7k rpm), and when upshifting, the next gear would be in the befinning of the hp band, meaning I’d be shifting that bike in the rpm ranges where the engine makes most power, all the way from second to fifth gear!
I also found that the bike reaches highest top speed in this gear!
Instead of reaching 83mph at 9k rpm, now it does 87mph at about 8.5k rpm, much closer to its horsepower peak.
First gear also rides much smoother, and i can shift into second gear, well after I reached the other side of the intersection.
There are 3 more benefits from upgearing the bike:
1- For some reason, every upgear, made the bike vibrate less, to the point of at 15/25t it vibrates at 4k rpm, but not too bad.
2- Every upgear to 15/28t, and under conditions upto 15/25, would increase MPG on the bike. With a 15/25t it would lug below 2.5k rpm (30mph), and above 70 mph with a headwind. But on my 15/25t, I honestly never had a tank below 66mpg US. Most of the time I get between 72mpg (100% interstate riding, with about 25-50% of WOT) to 115mpg us at a continuous 30-40mph.
3- the engine runs cooler, wears less, and there’s a theory stating concerning opening the throttle a bit more under a heavier load, that the already lean running Honda bike, runs much closer at the ‘perfect’ 14.5:1 air/fuel ratio. Worse for pollution, but much better for performance.

The only gearing higher than a 15/28 I’ve tried, is a 15/25t gearing. This is about 50% higher geared than stock.
This type of gearing is harder on the clutch from a standstill, especially uphill with 2, but any novice knowing how to use a clutch properly, could start it.
It has another disadvantage, that the top speed lowers considerably in 5th gear, and 4th.
In 4th gear, the revs are still a bit too high, and it would rev at 8k rpm to do 75mph. Far above the hp band.
In 5th, it would reach 6k rpm at 80mph, but won’t have enough torque to maintain this speed unless someone is pulling the wind in front of you, or you have a backwind.
4th gear does get it up to about 85mph, wind still, no hills, but barely.
I’ve reached 90mph with some backwind on a few occasions.
Bit most benefit of the 15/25t lies in higher mpg at low speeds (80-110mpg US, which is what you usually get from a fuel injected 250, or 150cc scooter not going over 40mph).
And the lower vibrations.
15/28t feel like long gears, much like the Chevrolet Spark has, long gears, slow acceleration, a more big bike feel if you keep it around the 3k rpm range.
At 6k rpm it still outaccelerates most economy cars from a stoplight riding rather peppy!

After all said and done, I like my 15/25t much much better than stock gears, but if I ever where to do it over again, would have equipped an old rebel (before 2008) with a 15/28t, and a new one of the past year or two, with a 15/27 or 15/26t.

So how does the stock 300 do compared to the Rebel on the interstate?


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