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After just 50 miles on my 07 Little Red Bomber, I had to replace the stock 14t sprocket with a 15t JT sprocket. Wow, what a difference. First gear is no longer a “granny gear” and the entire rpm band is reduced which should increase mileage along with less wear on the engine.

So far all of my riding has taken place in town with a few 60 mph stretches on a nice and straight county road.
 

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I doubt you will see much, if any, difference in mileage or engine wear. A 15 up front, or 30 in the rear does drop rpms a little, but there is a corresponding loss of top speed.
 

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Not to mention an increased need for downshifting when you encounter hills. I have a few steep grades I hit in town here and can keep it in top gear as long as I'm maintaining 45-50mph (or higher). A taller gear ratio would certainly mandate dropping down a notch or two on such hills.
 
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I added a 30 tooth rear. I still like it better than the stock 33 tooth, but I do down shift more now. Most every time I climb the hill I live atop of I drop two gears. One for most of the average hills and to climb up out of the low hollows abundant around South-Central Tennessee. I can't say that I can tell my gas mileage improved, but nor can I say it's dropped noticeably either. I can say engine heat went way up. The Rebel's best torque range is not when she is stretching out and running as hard as she can. She makes heat there. I learned that not only did I need to let mine breathe, She needs it fairly frequently especially in the humid heat of dog days in Dixie or I would have quickly scorched my engine. I asked a mechanic friend of mine what temperature conventional oil started to quickly break down. He told me his best guess was 280 there abouts. Makes it a bit scary when I regularly bump 260 before dropping back to let her breathe and cool off. So after my highway gearing mod on my Rebel I went from changing oil every 1K to every 500 Miles. And neighbors, that oil (Havoline 10w40 conventional) comes out of that crankcase black as sin and thin as water.

I still like the higher gear ratio over the specs she rolled off the line having. But I would not recommend it to others that are not very aware of the downsides. Especially not to novice riders living in areas that see 80+ temps even if they have modded their Rebel to keep up with Crankcase temps like I have. I have no doubt that I am thermally stressing my engine more than Honda would consider responsible. Likely the Honda 250 Rebel needed to have been engineered for water cooling for highway gear ratios.
 

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Did you have the oil temperature guage before putting on the 30 tooth rear sprocket? If yes, what was the average temperature at highway speeds?

I've been told that engine temperature should go down the faster the bike is going, but your experience indicates that may not be accurate.
 

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The Rebel's best torque range is not when she is stretching out and running as hard as she can.
True, but it does happen at about 2/3 that range:

 

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I threw a 15 tooth front sprocket on while I had it on the lift working on other things. I ride at 55 mph on mainly flat roads for commuting, which is what I'm using this ride for. I should be buying gas sometime today and will be checking the fuel economy, which I really don't expect to change from the 75 mpg I have been averaging. It does seem to 'wind out' the gears a tad more, but not that much more. I just wanted to try it out and see if it would be better than the 14 tooth. All I need now is to add a super charger and maybe I can get a little scratch off the rear tire lol.
 

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Wouldn't be the first:
Actually, if he finished it and it worked, it most definitely would be a first. ;)

FWIW in the 16 years I've been on Rebel boards that is the ONLY turbo I saw that was completed. Alas it failed on the working part. Then again I suppose "If u do ur research u will b fine" should have been a clue. :D
 

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After just 50 miles on my 07 Little Red Bomber, I had to replace the stock 14t sprocket with a 15t JT sprocket. Wow, what a difference. First gear is no longer a “granny gear” and the entire rpm band is reduced which should increase mileage along with less wear on the engine.

So far all of my riding has taken place in town with a few 60 mph stretches on a nice and straight county road.
Any updates on how the 15T is working out for you?

.
 

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I threw a 15 tooth front sprocket on while I had it on the lift working on other things. I ride at 55 mph on mainly flat roads for commuting, which is what I'm using this ride for. I should be buying gas sometime today and will be checking the fuel economy, which I really don't expect to change from the 75 mpg I have been averaging. It does seem to 'wind out' the gears a tad more, but not that much more. I just wanted to try it out and see if it would be better than the 14 tooth. All I need now is to add a super charger and maybe I can get a little scratch off the rear tire lol.
Or, any updates from you on how the 15T is working out?
 

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When I had a 30T rear sprocket what I found was this.

Power was plenty for any riding in the 55 MPH and lower speeds. I got around 10 more miles per tank of gas. On the highway doing 70 MPH it just seemed to bog down. At 35 MPH I got my best gas mileage at 102 MPG. All my statements are backed by the gas receipts, which I still continue to collect today.

15T front wouldn't be far off from this.
 

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Discussion Starter #14
Sorry for the delay, but I wanted to run as many tanks of gas with the 15t gear as a I did with the 14t stock gear for more conclusive results.

Average MPG was 68.96 with the 14t gear.
Average MPG was 76.38 with the 15t gear.

I only use the Rebel as an economical form of transportation in town and work.

The farthest that I have rode the Rebel in one day was 130 miles. That will never happen again. I have a 2000 BMW 1200 for long distance and interstate riding.

The one negative that I experienced with the 15t gear was that my top speed in a strong head wind was only 65mph. The 15t gear will lower your top end torque curve. So if you are wanting a 15t gear for higher top speed, that will not happen when you are on the road.
 

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Thanks for the follow-up.

It sounds like your experience is consistent with what others have already reported, and the 15T front sprocket is a good choice for local around town riding, but not optimal for highway cruising.

In other words, there’s no free lunch. The Honda engineers must have chosen the stock configuration for good reason!
 

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For what it's worth the top speed loss is not a Rebel specific issue with such sprocket mods. My 600 Shadow at twice the power and triple the torque (with said torque peaking at half the RPMs that the Rebel peaks at, so let's just call it six times the torque ;) ) also saw a noticeable loss. Stock cogs on that bike got me up to 112mph as clocked by a CBR whereas the taller gear ratio cut that down significantly, it took me two miles to accelerate from 80 to 90mph on a long flat road whereas the stock gears got me up to pinning the needle (105 on the gauge) in no time.
 
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This is interesting discussion, especially about the fuel economy. I am from upstate New York and use my bikes year round (I don't have a car). So my Rebel got 48 MPG during Dec/Jan month, with below freezing temps and riding with half open choke (engine never warmed up to close it completely). Then as weather got warmer, I started to see 50, 54, 57, 67, 76, and now in the summer months a consistent 75+ MPG on mixed trips with stops and 91 MPG on a straight 130 mile trip averaging 45-55 MPH. My bike is 100% stock 1987 Rebel 8000 miles on it.
My point is that the sprocket test that someone makes and mileage that he gets may not be the same that someone else with different temperature settings and elevation would get.
As for the sprocket change, I thought about it, but had some road situations where I was glad I had the stock setting. Then again, in my case it may work and someone else's not. I am only 115 lb heavy and my take-off acceleration is more than adequate for traffic, even if it's 50+ MPH traffic. Just my 2 cents.
 

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^ That's probably a slower 80-90 time than a Ninja 250. Pretty pathetic, that was definitely bogging the engine down.


You can't screw up 100 ft/lbs and 160 HP too much though...with taller gearing on my cbr1000rr you could still pull the front end up in 6th if you wanted to. :p I regeared it because the front end came up way too much in 2nd/3rd gear, and I wasn't even anywhere near the redline. At 6,500 the second set of injectors kicked in and things got scary. And nowadays they're advertising 1k's with over 200HP....yeah, good luck using all that power on 2 wheels. I could barely use half of 160. No wonder all these fancy electronics are put on the 200HP bikes now. (Just wait til one fails, $$$)




Anyway, I tried 15/33 on my 250 and ended up going back to stock 14/33. I loved how relaxed the engine was at 55, but as soon as the wind blows you can barely hang in 5th. All it did was bog down the engine which will wear it out quicker....so stock it stays. When I need a new chain I'll probably go with a 35 or 36 tooth rear and put the 15 with it so I don't waste the money for the sprocket.
 
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