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The 15T in front looks like a very tight fit. Any suggestions or tips on installing it and making sure it doesn't rub? Thx.
 

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It is a tight fit, I thought mine was going to rub but when I set the tension on the chain and buttoned everything up it was fine.
 

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The only time mine ever made any noise was when closing the throttle. I would hear a slight clicking noise. It was caused by the chain slack side being transferred to the top of the chain and hitting the case cover, and letting me know the chain needed adjusted. Once adjusted there is no noise. Other than that while a tight fit it causes no problems from my experience.
 

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Some members have reported problems with the chain rubbing the front cover.
turns out it was a cheap chain, which apparently tends to be larger than good quality chain.
 

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so, from reading through this thread seems if you change 1 sprocket the oem chain is fine. i just got my 15t and 30t sprockets in the mail and was wanting to change em out, however was unaware i might need a chain as well. thoughts and tips? 07' cmx 250
 

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It's best to replace the chain and sprockets together. An old chain on new sprockets and vise verse will cause premature wear on the new parts.
 

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Unless the chain has been well taken care of, and doesn't have many miles on it, it should be changed when the sprockets are replaced.

Why are you changing both sprockets? Most folks either go with a 15T up front or a 30T on the rear, not both.
 

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I decided to go with the 15t drive and 30t driven to give me a 2:1 ratio over the stock 2.537:1 if i've done my math correctly, i should be able to go 75 mph with the new sprockets when i'm currently doing 60 mph with the oem set-up. I just installed the 15t at work haha, didnt realize the chain when i ordered them, so im going to use the 30t rear next weekend or so when i can order a chain
 

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I decided to go with the 15t drive and 30t driven to give me a 2:1 ratio over the stock 2.537:1 if i've done my math correctly, i should be able to go 75 mph with the new sprockets when i'm currently doing 60 mph with the oem set-up. I just installed the 15t at work haha, didnt realize the chain when i ordered them, so im going to use the 30t rear next weekend or so when i can order a chain
You will gain less buzzyness at cruising speeds BUT you will loose top end speedwise. I went with just the 15 tooth front spkt and mine tops out with nothing more to give at about 73-74 mph. That was on a flat stretch (1.5 miles) of road with no headwind. If I remember correctly the engine will only pull about 7500-7800 RPM. At 60 mph (speedo reading 65) I'm turning about 6300 RPM.
 

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Don't get your hopes up about increasing top speed with the new sprockets, you might even have less top end with them depending on your weight. The more rider weight there is the more negative affects you'll have at top speed.
 

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I decided to go with the 15t drive and 30t driven to give me a 2:1 ratio over the stock 2.537:1 if i've done my math correctly, i should be able to go 75 mph with the new sprockets when i'm currently doing 60 mph with the oem set-up. I just installed the 15t at work haha, didnt realize the chain when i ordered them, so im going to use the 30t rear next weekend or so when i can order a chain
your math would be fine if the engine could deliver the necessary torque at a reduced speed.

consider that a stock Rebel needs X lb-ft of torque going from the engine crankshaft into the transmission at 75 MPH. With your gear ratio change the required input torque at 75 MPH becomes 2.537X/2 = 1.2685X lb-ft.
You thus need 26% more torque at the crankshaft to overcome the load on the rear wheel at 75 MPH. With the stock setup you will have some reserve torque at 75 mph, but with your modified gearing I doubt if you even have enough to go that fast in 5th gear at the reduced RPM that will be dictated by the gearing. (torque is pretty constant at 11.5 lb-ft from about 5000 RPM on up till it starts to tail off).
Of course, you will really feel this effect on hills and in headwinds as well.
 

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@ firehawk, i currently have the 15/33 installed as i was able to put the 15 on yesterday at work. was waiting for the 30t due to lack of access to a chain-breaker. that being said, I was able to do 85 (speedo that is so 80) no problem at a much easier load to the engine. As far as acceleration from 65-80 i honestly think it was smoother than stock

@duckster, that makes a lot of sense. i hadn't considered how little torque the motor truely has. I'm a rookie mechanic getting my start tinkering with my own horse. so my knowledge is limited i just understand the basics of mechanics and am furthering my knowledge as i progress. im about 135 lbs and around 5' 8". So you suggest against the dual sprocket change? and if so, which of the 2, 15/33 or 14/30 and why? i know that's asking a lot but you guys seems to be a pinnacle of information and i want to make sure i understand WHY one is preferred over the other?
 

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I decided to go with the 15t drive and 30t driven to give me a 2:1 ratio over the stock 2.537:1 if i've done my math correctly, i should be able to go 75 mph with the new sprockets when i'm currently doing 60 mph with the oem set-up. I just installed the 15t at work haha, didnt realize the chain when i ordered them, so im going to use the 30t rear next weekend or so when i can order a chain
The theory and math are correct, but in practice expect about 70-75 MPH. What you end up getting is a bike that has less vibration from the engine.
 

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I have a 14-30 sprocket set up. I just rode the Tail of the Dragon last weekend, my bike climbed the mountains in 3rd gear at 55 MPH just fine. Notice I stated 3rd gear. The bike gets it's torque from engine speed. But I lose torque on the highways at our current 70 MPH speed limit and the bike starts to struggle with a head wind or incline. That said, I do most of my riding at 55MPH speed limits, not because I need to, but because everywhere I need to go is only 55. So I opted for less vibration of the 30T rear sprocket.
 

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HAte to revive a year dead thread but dont want to start a new one for this well read topic.

I just made the 30t rear change last night. I like the sound, it feel smooth but man... it seems like speed is lost and the engine raps out soon in each gear, the acceleration is gone until shifting a gear up.

Didnt expect this. IS this something I should have expected? Not sure I care for it yet.
 

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You're just seeing the trade-off of rear wheel torque for engine RPM. Honda did not under gear the Rebel so that changing sprockets could give lower engine RPM at the speed limit AND a higher top speed. For many riders the trade off for a modest gearing change is a good one. They aren't too worried about top speed or headwinds on the highway. However, as the wise man said. "There's no such thing as a free lunch".
 

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I also fitted a 30T.

Had to machine it myself to fit the 450, because it only came with a 30mm center hole. No problem, I have the needed tools.
Since the 450 has open pipes, the jetting was upgraded too. The mains went from 112 to 135! A Dyno run showed the air/fuel, and it was absolutely perfect! That means, a bit more pull to still have acceleration with the 30T in the back.
The original set up is based on higher revs. Now I can actually ride it on torque instead of revs. What a difference! The first gear now actually has a meaning!
 

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Chain length

Ok. Did you have to shorten your chain at all from 108 links to fit the new configuration or was it ok te way it was. I was looking at a 28 tooth sprocket and maybe a 14 up front or so.

Yes, be careful and only take about an inch and a half of chain off. Mine had a master link so all I had to do is grind off one rivet to make it work.
 

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Going to a 30 tooth rear sprocket on the 250 does not require removing links from the standard length 108 link 520 chain.
 
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