Honda Rebel 250 (2013 model, 70 to 90mpg US, 108MPG IMP )

[ProDigit]

Although the Rebel 250 already has pretty good gas mileage, it's an reasy bike to mod, to get more out of it!

Stock sprockets are 14/33t, makes the little rebby rev in the 4-6k range for normal riding.
Unfortunately this also is right in the engine vibration range.
Engineers had to rubber damp mount the handlebars, for them not to vibrate out of the hands.

Top speed on this bike, 83-85mph can be gotten at the end of the HP band, where HP decreases due to high engine RPM and friction (9k+ rpm).

Also, stock oil works very bad on it.
The Rebel loves a mix of 5W30 and 10W40.
Depending on which region you live in, hot S Florida needs more 10W40 (in between a 50/50 mix, and a 25/75) than 5W30, but colder regions might need 50/50 to 75/25 for 5W30 over 10W40 oil.
The engine will vibrate less doing this, than filling it with either 5W30, or 10W40, or heavier motor oils.


There are 3 mods one can do that I did on the reby, that will improve performance and MPG from stock. Each one of the mods, targets a different desired outcome, explained below. Since the Reby comes super undergeared, and 1st gear is pretty much useless (when you do use 1st gear, you'd shift 1st, 3rd, 5th, and skip 2nd and 4th gear, due to insanely short gearing, essentially owning a 3 speed geared bike), all mods are to make gears taller, not shorter.
Taller gears spread out the gears, and make them more effective in the right rev range. It helps double or triple shifting, where eg: one slows down to 20mph in 5th, and downshifts 3 gears to get into the right gear to accelerate again. Taller gears address this issue, aleviate or eliminate it, by forcing you to already be in 4th or 3rd to get to 20mph, and by allowing 1 to 2 gears downshift to actually make enough difference in engine RPM, to depart again from a slowdown.

the 1st:
Change the sprocket setup from 14/33t to 15/30t
This I would say is a stock upgrade, with a very neutral gearing, which I recommend anyone to do. Both sprockets can be found on the cheap on amazon or ebay, both steel as well, taiwan made, not china made; and are of better quality as The aluminum sprockets found mostly on custom sizes.
They're also a tad cheaper!

Departure from 1st gear happens still very smooth (with the flick of the clutch), you still don't need to master riding with clutch very well, as the bike pretty much flicks into gear. Stalling from a red light won't happen very easily, unless you want it to.
Not too short, nor too long acceleration through the gears,
and pretty much top speed at a lowered peak RPM, while still maintaining nearly 100% acceleration from stock.
MPG up by as much as 10MPG.
Few MPH more top speed

The rebel vibrates a lot around 4k rpm, so riding speed outside of vibration rpm range goes up from 20-30mph to 25-35mph.
Sadly, most roads around here are 40mph, so doing 40-45mph brings you right in the vibration range (where handlebars and frame vibrate under the buzzing ptwin engine) Vibration peaks at 50mph with these gears, and can make the hands and feet feel numb after a while.

2:
15/28t.
Harder departure from a stop. You need to be able to ride with clutch, but a novice rider sould have no trouble departing uphill, 2 up and with luggage without problems.
A beginner might end up stalling the bike from a dead stop from time to time.
Benefits of this gearing:
Bike's top speed reached spot on in the lower part of the HP band, meaning this is the most optimal gearing you can give the Rebel when you want to go as fast as the bike possibly can, on a windstill day. Also brings lots of benefits when being on the highway, or interstate riding in other car or truck's wakes, or when riding with a back wind, the bike could reach 90+mph ! (Been there, done that, but it takes a while to get there, and requires an optimal environment ).
This means, that the bike will go a tad faster as with stock gearing, but with the added benefit when ducking forward, and/or a back wind one can reach speeds in excess of 87MPH, where as with stock the bike would be rev limited (due to internal engine resistance, not wind resistance ).
Another benefit:
This puts the bike right out of engine vibrations range riding from 25-40mph.
Past 40mph, the bike will vibrate again, peaking around 55mph, but the vibrations are somewhat reduced over using the stock gears.
85mpg consistent tanks are possible.
5th gear is optimized to ride from 30-40mph, as cruising gear, as well as top speed when no wind, or wind in the back.
Great for most city and suburb riding.

4th gear is very close to stock 5th gear, so top speed in 4th will be around 80mph, but the bike will feel like you're squeezing out the last of it's juice to get there.

A very good compromising gear, acceleration still faster than most cars from a red light.

3:15/25t:
This is the max. gear change one can do on the rebel, without major modifications.
The front sprocket has no more space to fit any larger, and the chain would be cutting the rear sprocket bolts when trying to go smaller in the rear; and thus it would be the recommended upgrade for max mpg, without any major modifications.

And although the other setup 15/28t can use stock chain (110 link), a 108 link would fit better.
the 15/25t needs a new chain; a 106 link is what'll fit best, 108link being too large.

Like with the 28t, the 25t sprocket needs to be custom made. Rebelgears does that for you, and is only available in hardened aluminum.
My 28t has about 6-8k highway mile life on it, as well as about 4k city, and little more to go.
I suspect it lasts 20-25k miles of city riding, and 12-15k miles highway; or more...
So the aluminum sprockets exceed their reputation.

4th gear in 15/25t is very much like 15/30t 5th gear and feels really nice as final gear upto 40mph, to stay out of the vibe-zone.
5th gear does feel like an overdrive, used only between 35mph and 60mph ideally.
It can be used between 25 and 75mph, but the engine is stressed much harder at top speed, and also at such low RPM, that I would not recommend to use it that way.
It's a bit overgeared, when you won't do past 45mph on most roads anyway, a 15/26 or 15/27t might be more what you need.
But if you have 45mph roads where people do 50mph, the rebel will be buzzing buttersmooth, without much of any vibes at those speeds!
between 30-50mph is pretty much vibration free, and it buzzes really nice at 5k rpm 60mph on the highway as well, not overtly like from the stock gears.
Much milder! 60-65mph is vibe peak.
MPGs of 90-95mpg are attainable, which gives you the pleasure of going cross state for only a few bucks, same gas mileage as a 50-100cc scooter, but the added benefits of being a much faster bike, when it needs to be, both in acceleration as in top speed!

Top speed in 4th gear on the 15/25t is where the engine revs a bit higher than its optimal range, but speeds of 85mph aren't uncommon to get.
It's a small tradeoff, of revving too high in 4th, yet too low in 5th to make the bike's optimal peak speeds, but 4th still makes for a decent highway gear.

Cons of this 15/25t gearing:
Most urban and city roads are 30-45mph.
the vibration free rev range in 5th is between 35 and 50mph.
That means the bike is a little over geared for most slower (city) riding; though I like it, as I finally am using 4th gear more (25-40mph).
Also, very low acceleration in 5th, if any (Mostly between 40-60mph it accelerates ok, outside that, very slow, and downshifting is recommended to actually accelerate).

Departure from a dead stop is ok for a novice, but harder with passenger and luggage, and feathering is needed to go uphill.
Then again, there aren't many uphill starts here in FL for me, so for me that's a non issue.
Acceleration from a stop is about even with most cars, when you stay below 4k RPM.
If you need to accelerate faster, you'd need to rev it up in the HP band, and in 1st that means you'd be doing 20mph, before shifting to 2nd (about 3 seconds), but the bike does still pull away from most cars like that.

If you plan on using the bike mainly in city and suburbs, and will never go above 65mph, I will recommend +1t up in the rear, to 15/26t.
You'll lose a few MPH top speed in 4th, as it will rev higher than optimal revs, and 5th gear won't have the power to sustain above 75mph either for longer rides, unless with backwind or slipstreaming.
15/25t is a compromise between rideability and MPG at low speeds, while still being able to maintain close to top speed figures in 4th.
15/26t or 15/27t would give you a tad better acceleration and departure from a dead stop, while having the vibe free zone just below 45mph, which is where you'll find yourself riding the rebel most of the time.


===============

Best MPG figures mentioned on each gearing, are gotten from riding between 30 to 50mph.
Wind resistance increases exponentially above 45mph, so MPG does go down a lot when going faster than 50mph.
It also goes down when going in any gear other than final drive.
That means, in most cases, below 30mph usually you'd downshift to 4th or 3rd, and MPG will be negatively effected there.

Mpg numbers are for urban riding, not city, meaning with a moderately low amount of start-stops, doing mostly riding between 25-55mph.

City riding might not benefit from a 15/25t at all, if the bike never reaches speeds high enough to cruise in 5th gear.

The above results are gotten over a testing period of 1.5 years, and 13+k miles.
They are done on an almost stock, 2013 Honda Rebel 250, (save for installed sissy bars, and crash bars).

Tests are done by a 180lbs rider, 6'4", and occasionally with a 130lbs passenger of 5'8".
mpg numbers are mixed results with and without passenger.

The modifications where done to improve gas mileage, driving comfort and top speed of the bike, not to have better acceleration, although one can argue that with a 15/30t setup one might have best acceleration, as 1st gear actually becomes useable, unlike with stock gears where some users prefer to depart from 2nd gear instead, or 1st gear barely gets one 50ft forward before shifting.

[user removed]

Bought an 06 with 1800 miles not running for $600. New battery, clean the carbs,air up tires and lube chain. Sold it a few Kmiles later for $1400. It would easily do 80on the Interstate and 80plus mpg when driven conservatively. These days I have a Suzuki GZ250, 2004 model, I paid $650 for in running condition.

I generally stay off the Interstate these days. Love the simplicity of a single cylinder bike, but the Rebel has slightly better performance and top end.

regards
mech

[ProDigit]

Yup, you're right.
The rebel has a small performance edge over eg: the Suzuki TU250X;
I find the Rebel slightly underpowered for the interstate, when having a bit of headwind, but with a 10MPH tailwind, it performs more than admirably, even on the interstate!

A Rebel with a 249-300cc BBK, or the Rebel with direct fuel injection would probably be all you need to have sufficient speed (direct fuel injection adds HP over port fuel injection or with a carburetor).

For a thumper you'd probably be better off with a 350-400cc one.
Thumpers are better MPG wise, but they vibrate a lot, and usually give good torque, but less good top speeds.

I bet a 400cc thumper could do 90MPH tops, which is what a 249-275cc PTwin does as well.
One can then argue which one will give the better fuel mileage.

CC over CC, there's no argument over which wins what.
A thumper wins in MPG, and a Ptwin in performance.

But when comparing MPG based on performance numbers; a ptwin is both smaller, lighter, has higher performance, and therefor, if top speed are matched on both engines, the PTwin would have better MPG as the same performance can be gotten with a smaller engine. (eg: 250cc PTwin vs 350cc Thumper have both about the same top speed, and similar torque in the torque/HP band, but the thumper gets it's torque at the lower revs 2-4k rpm, while the ptwin gets it at usually 7.5k RPM.

For that reason, I believe thumpers are good upto 200cc.
They would make great and affordable small city bikes, but lousy highway bikes.
Too large thumpers are heavy, require more oil, and vibrate a lot more than a Ptwin engine (which needs a way smaller counterbalance).



To get 80MPG out of the Rebel stock, is quite an achievement.
I got 60-66MPG out of it riding it hard, and 75MPG riding it like it was made out of porcelain, stock gear.
Perhaps you're talking about 80MPG IMP instead of US?
80 MPG IMP equals 66MPG US, which is what I got stock out of my bike as well.
My current numbers of 88MPG US equal 105MPG IMP.
That'd be a 20MPG raise.

The Rebel fuelups so far have been:
1st tank 107MPG (US), might be because the next tank wasn't completely filled up, so some off reading there, as well as a bit of carb cleaner in the fuel might offset the value a bit).
2nd tank 88MPG, (tank wasn't fully filled); 50% highway and interstate riding with headwind probably the cause of lower reading
3rd tank 87MPG (was because the tank was completely filled to the brim; with some highway riding, and lots of start stop traffic.

Because the tank was filled a lot more than previous (I tried to squeeze $6 on fuel in it, the last $0.5 was overfilling it a bit), I might see an increase in MPG on my next tank.

I'm expecting 95+MPG on my next readout (that is 115+MPG IMP).
I'm expecting to have an average of around 90MPG US, or 108MPG IMP on my Rebel, riding it lightly.

[user removed]

I've owned a TU25X,a couple of Rebels, a Vulcan 500, two Suzuki GS500s, a CBR 250R and a long time ago a Harley and a Kawasaki 900 (1973).

You can see the mpg numbers in my garage, all are US gallons. I usually ride locally around Willimasburg, Va, probably no more than 50 miles max from my house.

regards
mech

[ProDigit]

Seems like I hit with some trouble on the bike.
Though I usually never take the bike in 5th gear above 65MPH, last week I did about 60 miles at Wot (80MPH) in 5th.
I wanted to test how much my MPG was, doing 6k RPM over doing 7 or 8k.
My clutch started slipping on the way back.
On my way to, I didn't go all out; I had wind in the back, and going to 80 was a breeze.
On my way back I had about a 10-15MPH headwind, and after 10 miles on my way back (30 miles to, 30miles back), I experienced a controlled clutch slip; where the engine slowly started increasing RPM, while my speed stayed at 80MPH.
I immediately rolled off the throttle, and continued my journey in 4th gear, doing 70MPH.

Greatly saddened though...

I really wanted to record top speed MPGs.

Now the bike will never exceed 65MPH in 5th.
I'm not confident enough to replace the clutch. The new clutch might have the same problems.
I probably would be more comfy replacing clutch springs, if that would help, but I doubt I'd find good springs for that!

[ProDigit]

It seems like gas mileage is well when riding below 40MPH.
But anything above 60MPH, with a little headwind actually is much lower in MPG than with my previous sprocket.
It makes me believe I'm lugging the engine with this setup.

I suppose I could just ride in 4th gear...
I also notice holding open the throttle at a certain position, in 4th gear (say going 65MPH), makes it go slower in 5th gear (55-60MPH).


These results make me think I'm lugging my engine, and should get a bigger rear sprocket next time the sprocket needs a change (probably in a good 5k miles, a 26t).

The engine overall is cool, almost always.
Way cooler, even when ridden hard, than when riding with the stock gears.
I remember the days when I would exit the interstate, and my engine was idling at 1580+ RPM (I have a digital tach installed).
The summers where about 10 degrees hotter as well.
But now it barely idles higher (1440RPM tops, and drops quickly to 1380RPM).
It tells me that the engine is running a lot cooler, when it runs lower RPM.
It's the opposite of what 'another (I shall not name him) person' has been claiming should happen.

If a 26t sprocket works well, I might see if I could increase compression on this bike by a bit; seeing that it runs cooler, therefor it should have lost a bit compression (as compression increases with engine heat)...

Just a thought....

[HighDesertRebel]

Hi thanks for the detail post, it helped a lot. I do have a couple questions. Where did you buy your 28t Sprocket? Also just to confirm, If I go to a 15t and 28T set I will have a faster top speed correct? My last question is just to make sure I can still use my factory chain if I go to a 15t and 28T sprocket set? Thank you again and I hope to hear from you soon.

Trevor

[user removed]

I don't think any sprocket change will increase your top speed. I saw 90 on my Rebel with stock sprockets, probably with a helping wind. 3 stripes a second is 90 mph, not reading the speedometer. I was passing everything since over 80 is reckless in Virginia and only a few dumusses are stupid enough to risk $500, 4 points and vehicle confiscation, even if you still owe money on the vehicle.

I went through the carbs 3 times to get them perfect and the orfices in the jets may have been slightly enlarged. No mods, jet changes or anything else, just taken apart, thoroughly cleaned and every orfice very carefully reamed.

You will not go that fast at altitudes significantly above sea level. While atmospheric density decreases, so does your engines effective compression. Increasing the compression is your best alternative, but if you go to sea level for extended riding you could cause top end engine damage without higher octane fuel.

regards
mech

[ProDigit]

Yes, the engine has most HP and most torque between 6000 and 6600 RPM. More than at 9000RPM.
If you where to go 90MPH on stock sprockets, you'd be doing over 10500RPM or past the redline, very unlikely.

On the 15/28t I often surpassed 87MPH.
I'm currently testing out a 15/27t setup, as the 15/26t setup wasn't favorable top speed wise.
If you have a 2013 Rebel or newer, and are light weight, small in posture, and don't have saddlebags or other stuff on your bike, a 15/27t might be right for you.

Rebelgears.com makes them. There are others that do as well. The stock chain works for upto 15/28t, and need one or two links removed for a 15/25t setup, but will be at the end of the adjustment.

I live in South Florida, a few feet above sea level, and switching to a 15/27 or 15/28t over stock will automatically:
1- Lower engine temps due to lower RPM, resulting in
2- Lower chance of pinging
3- Increase engine life
4- Bring the engine to rev at a 'vibration-less' zone, where the engine vibrates very little.
5- The engine will be running under a higher load, with lower revs, so the carburetor will also run a bit richer than stock, as well as the exhaust pipes will offer less back pressure at lower revs, resulting again in richer riding. The engine will run more at the stoic value of 14.7:1 than at the stock Honda setting of 16:1. It all measures out.

If you want to go even faster, try adding a shot of 2 stroke oil in the gasoline. anywhere between 128:1 to 200:1 is a good ratio. 160:1 seems to be the best ratio for top speed. The piston will slide better on the cylinder walls with the miniscule lubrication; resulting in producing yet less heat.

Just make sure you have Honda GN4 oil in your crankcase, as the modifications stress the clutch, and regular car oil may cause clutch slippage at these peak stresses.

[user removed]

I'm done here.

regards
mech