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Hi guys and gals :)

Did any of you, who have switched the rear sprocket out with a 30 tooth sprocket, experience a higher mpg?
I know there is a lot of variables like : weight, road type and gasoline quality.

But what is your general experience ?
Is it more a comfort upgrade?
 

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1985, 86 CMX250C, 81 CM200T, 74 CL360, Invisible to cages, treat them accordingly. Avoids Road RAGE!
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I have the 15T front and the 30T rear on both of my 1st generation Rebels. They do seem to give a slight Improvement in gas mileage due to the fact the engine is not spinning around at great speed just chasing its own tail. Kind of like when you're peddling a bicycle in a low gear trying to go fast. A better gear ratio does improve your economy slightly. But this varies on your driving and weight load and such. I normally ride with two people on my Rebel. That means that loaded as it is with all the extra gear I've got as well, I average 70 to 80 mpg this way, & 1 time hit 100 mpg! But... that was using 100% gasoline not ethanol blends, riding through hilly, curvy terrain, & not exceeding 50 mph.
That being said, the 2nd generation doesn't handle this as well, due to its reduced power.
 

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I saw no increase in mpg. More downshifting on hills, slightly reduced rpms, and top speed.
 

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mpg is more a function of driving behavior than rpms

for example - let's say you ride from point A to point B twice, everything is the same except in one trip you use 4th gear and the other trip you use 5th gear - assuming the speed is the same in both trips and it is an appropriate speed for both 4th and 5th gear, the mileage will be exactly the same - the same amount of work has been done in both trips - physics
 

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I have a 30T on my '07 for a good number of years and compare it to my stock sprocket '00 Reb. On average I got 10 more miles per tank of gas versus the stock. However, the stock sprockets are better for highway travel. Since most of my riding doesn't have any highways, I'm okay with it.
 

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Added the 15/30 to my 2009. My mileage didn't really change to a noticeable degree, even after over 7000 miles worth of testing. Why? The engine is already running full tilt on stock gearing most the time anyways, so there's no more torque to try to take advantage of with longer gearing. Unless you cruise going 50mph in 5th, you don't save any gas with the longer gearing it seems like. If you do cruise at 50- you save, at most I could get it to do, 8% better mileage? That I'm not 100% on, since, it's hard to both consistently fill up the tank to the same exact spot, and trust a fuel pump to accurately measure dispensing such small amounts of gas (usually around 1.25 gallons between fill-ups/top offs for me). Your riding style will make a much larger determination in mileage it seems.

I average 56mpg on my rebel 250 both before and after the swap. For comparison, my rebel 500 SE, averaged around 47mpg, but holding 80mph instead of the 250's 70-ish. Dropping down to the 250's cruise speed, got it around 54mpg on stock gearing.

However-
This gearing is substantially better. Even on my "weaker" later model US market bike. As for "it being too weak to take it"- your gearing is longer, and our power band is up top. The stock gear map on the speedo is now useless (or well, even more useless)- stop following it. 3rd now goes up to a GPS 65mph, 4th GPS 75mph, and 5th has wound all the way out to a GPS measured 90mph (down hill, 20mph tail wind). 1st is actually usable now, and 2nd usually spools out to around with 3rd would normally end before.

The new gearing, I'd argue, is substantially better for 70mph highway use. As it puts 70-75, at the top of 4ths power band, instead of a weird middle ground between the peak of 4th and start of 5ths that it has a hard time holding on stock gearing. 60mph, is also now a speed it pretty much never drops below, even up hill into a 15mph head wind, as the top of 3rd handles it well. I'd constantly find myself searching for 6th on stock sprockets, but the new ratio matches the peak of what the bike can do better.
 

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Added the 15/30 to my 2009. My mileage didn't really change to a noticeable degree, even after over 7000 miles worth of testing. Why? The engine is already running full tilt on stock gearing most the time anyways, so there's no more torque to try to take advantage of with longer gearing. Unless you cruise going 50mph in 5th, you don't save any gas with the longer gearing it seems like. If you do cruise at 50- you save, at most I could get it to do, 8% better mileage? That I'm not 100% on, since, it's hard to both consistently fill up the tank to the same exact spot, and trust a fuel pump to accurately measure dispensing such small amounts of gas (usually around 1.25 gallons between fill-ups/top offs for me). Your riding style will make a much larger determination in mileage it seems.

I average 56mpg on my rebel 250 both before and after the swap. For comparison, my rebel 500 SE, averaged around 47mpg, but holding 80mph instead of the 250's 70-ish. Dropping down to the 250's cruise speed, got it around 54mpg on stock gearing.

However-
This gearing is substantially better. Even on my "weaker" later model US market bike. As for "it being too weak to take it"- your gearing is longer, and our power band is up top. The stock gear map on the speedo is now useless (or well, even more useless)- stop following it. 3rd now goes up to a GPS 65mph, 4th GPS 75mph, and 5th has wound all the way out to a GPS measured 90mph (down hill, 20mph tail wind). 1st is actually usable now, and 2nd usually spools out to around with 3rd would normally end before.

The new gearing, I'd argue, is substantially better for 70mph highway use. As it puts 70-75, at the top of 4ths power band, instead of a weird middle ground between the peak of 4th and start of 5ths that it has a hard time holding on stock gearing. 60mph, is also now a speed it pretty much never drops below, even up hill into a 15mph head wind, as the top of 3rd handles it well. I'd constantly find myself searching for 6th on stock sprockets, but the new ratio matches the peak of what the bike can do better.
Well put! My apologies to all of those that I may've offended by saying that the 2nd generation couldn't handle it. It really does depend upon your riding style & speed.
The mpg that you're getting is extremely low! Even at 75 mph & above, I still get 65-70 mpg & that's riding VERY heavy. Even with, now, my very leaky carb, which I'll soon be rebuilding, I just got 75 mpg on my last tankfull.
But... hmmm... that was 100% gasoline with a 110 octane rating. I normally fill up with 90 octane 100% gas. I was just trying out for the 1st time the $9.50/gallon stuff! And it definitely makes a difference in fuel economy & power. But not really worth it, at a $6/gallon increase in cost.
But even using 86 octane 10% ethanol blends I get an average of 70 mpg on both of my Rebels. One of them has 49,000 miles on it, the other is nearing 10,000. Are your brakes dragging? Is the exaust black? Something isn't right. You should be able to get better milage than the 54-56 mpg that you're getting.
 

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Added the 15/30 to my 2009. My mileage didn't really change to a noticeable degree, even after over 7000 miles worth of testing. Why? The engine is already running full tilt on stock gearing most the time anyways, so there's no more torque to try to take advantage of with longer gearing. Unless you cruise going 50mph in 5th, you don't save any gas with the longer gearing it seems like. If you do cruise at 50- you save, at most I could get it to do, 8% better mileage? That I'm not 100% on, since, it's hard to both consistently fill up the tank to the same exact spot, and trust a fuel pump to accurately measure dispensing such small amounts of gas (usually around 1.25 gallons between fill-ups/top offs for me). Your riding style will make a much larger determination in mileage it seems.

I average 56mpg on my rebel 250 both before and after the swap. For comparison, my rebel 500 SE, averaged around 47mpg, but holding 80mph instead of the 250's 70-ish. Dropping down to the 250's cruise speed, got it around 54mpg on stock gearing.

However-
This gearing is substantially better. Even on my "weaker" later model US market bike. As for "it being too weak to take it"- your gearing is longer, and our power band is up top. The stock gear map on the speedo is now useless (or well, even more useless)- stop following it. 3rd now goes up to a GPS 65mph, 4th GPS 75mph, and 5th has wound all the way out to a GPS measured 90mph (down hill, 20mph tail wind). 1st is actually usable now, and 2nd usually spools out to around with 3rd would normally end before.

The new gearing, I'd argue, is substantially better for 70mph highway use. As it puts 70-75, at the top of 4ths power band, instead of a weird middle ground between the peak of 4th and start of 5ths that it has a hard time holding on stock gearing. 60mph, is also now a speed it pretty much never drops below, even up hill into a 15mph head wind, as the top of 3rd handles it well. I'd constantly find myself searching for 6th on stock sprockets, but the new ratio matches the peak of what the bike can do better.
The "gear map" is the maximum speed for each gear. It isn't the recommended shift speed, and I know zero Rebel 250 riders who normally wait until reaching those speeds to shift.

Well put! My apologies to all of those that I may've offended by saying that the 2nd generation couldn't handle it. It really does depend upon your riding style & speed.
The mpg that you're getting is extremely low! Even at 75 mph & above, I still get 65-70 mpg & that's riding VERY heavy. Even with, now, my very leaky carb, which I'll soon be rebuilding, I just got 75 mpg on my last tankfull.
But... hmmm... that was 100% gasoline with a 110 octane rating. I normally fill up with 90 octane 100% gas. I was just trying out for the 1st time the $9.50/gallon stuff! And it definitely makes a difference in fuel economy & power. But not really worth it, at a $6/gallon increase in cost.
But even using 86 octane 10% ethanol blends I get an average of 70 mpg on both of my Rebels. One of them has 49,000 miles on it, the other is nearing 10,000. Are your brakes dragging? Is the exaust black? Something isn't right. You should be able to get better milage than the 54-56 mpg that you're getting.
Riding at WOT for extended periods, my mileage is similar to SEANIA's at "70-ish". At lesser speeds, it goes up considerably.

Regarding octane, this from the U.S. Department of Energy:
Will using a higher octane fuel than required improve fuel economy or performance?
It depends. For most vehicles, higher octane fuel may improve performance and gas mileage and reduce carbon dioxide (CO2) emissions by a few percent during severe duty operation, such as towing a trailer or carrying heavy loads, especially in hot weather. However, under normal driving conditions, you may get little to no benefit.


"
 

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Interesting! For me, riding 2 up, completely loaded, running WOT, 70-85 mph, the worst that I've ever gotten was around 65 mpg on either of my Rebels. That's why I say that it sounds like something else is wrong as well.
 

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Well put! My apologies to all of those that I may've offended by saying that the 2nd generation couldn't handle it. It really does depend upon your riding style & speed.
The mpg that you're getting is extremely low! Even at 75 mph & above, I still get 65-70 mpg & that's riding VERY heavy. Even with, now, my very leaky carb, which I'll soon be rebuilding, I just got 75 mpg on my last tankfull.
But... hmmm... that was 100% gasoline with a 110 octane rating. I normally fill up with 90 octane 100% gas. I was just trying out for the 1st time the $9.50/gallon stuff! And it definitely makes a difference in fuel economy & power. But not really worth it, at a $6/gallon increase in cost.
But even using 86 octane 10% ethanol blends I get an average of 70 mpg on both of my Rebels. One of them has 49,000 miles on it, the other is nearing 10,000. Are your brakes dragging? Is the exaust black? Something isn't right. You should be able to get better milage than the 54-56 mpg that you're getting.

To be fair, it really doesn't "handle it"-5th is entirely a hyper-mile/overdrive gear now. Rarely do I need it, I just want it sometimes.

I run 93 10% blend, even though "it runs on 87 just fine", because I don't ever re-jet for the weather, ride in all weather, and rarely clean the carb. The 93 is both to compensate for it running lean in colder weather, running lean from potential carb issues, and for the added cleaning packages most pump 93 brands add in to prevent me having to clean the carb as much.

70mpg, is, maybe doable- at 50-55 mph, in 5th, in good weather, on flat terrain- but I ride in all weather, and the highway speed is 70-80mph in my state- so hypermile opportunities never really pop up.

Oh, running higher octane can lower your power output past a point. It becomes so resistant to ignition, that, it has trouble burning fully on anything that isn't using higher compression to help force it to ignite when it should. Maybe not from 87 to 93, but putting 110 (of the same fuel type) in a 87 designed engine/jetting will definitely cause some power loss, and maybe even some misfires. If that doesn't make sense, keep in mind that water can technically be used (and occasionally is) as anti-knock- "but water would prevent it from wanting to ignite!!" yeah that's kinda the point, and is why running way too high of a octane rating can be detrimental.
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Interesting! For me, riding 2 up, completely loaded, running WOT, 70-85 mph, the worst that I've ever gotten was around 65 mpg on either of my Rebels. That's why I say that it sounds like something else is wrong as well.
70-85mph on speedo, or GPS speed? That's a huge difference. A more worn front stock tire size, when reading 85mph, will actually only be 75mph GPS. A brand new stock size tire, will still read, at a minimum, 5mph over what the bike is actually going past 45 mph. This is intended from factory, and the odometer is set separately to be accurate, even though the speedo isn't.

Also, if you have a earlier pre-2003-ish(?) model that'd make a large difference as well. As the pre-ethanol models will be running a leaner jet meant for ethanol free fuel.

Running ethanol free fuel on top of that, will also net you even more gains, since, the rebel 250 being a lower-compression (9.2:1) high-temperature (aircooled) engine, will help to prevent recondensing. Plain gas, has more potential chemical energy, and the rebel 250 is setup to take advantage of that. Honestly high octane pure gas doesn't make much sense to me, since, at the compression levels you'd use to need that octane rating- you'd recondense the fuel and loose more power then if you had just run ethanol instead.

If we'd all rejet our bikes for ethanol free fuel, and ran it, we could probably hit 70mpg too, but as it stands on 10% ethanol jetting and fuel- doesn't look like it? Rejetting leaner for 93 10%, instead of 87 ethanol free, might get the desired 70mpg too though.
 

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I have NEW tires on my '86 Rebel (mfd 10/85). And when I say my mph, I do mean 'speedometer milage' which as you've stated, with worn tires, can be off by as much as 2%.
These older engines are indeed cammed & timed differently than those made after 1996. And they have a larger exaust & larger jets in the carbs than their 'progeny'. The Rebels made in 1985 had the largest factory installed jets, they just get smaller from there.
The racing fuel (110 octane) that I used did improve my mileage, this I know. But the fact that it was specifically racing fuel, it may be formulated differently from other high octane fuels.
My milage drops to 65-70 mpg only if I ride hard or exceed 65 mph, otherwise it's normally above that. I've never gotten lower than 65 mpg. Perhaps the lower powered, more EPA friendly, 2nd generation Rebels are far less capable in the milage department, at higher speeds, than the pre-EPA mandate bikes.
 
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