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Discussion Starter #1
what are the options here?
and if anyone can do a little lesson on how changing sprockets affect speed, etc would be appreciated

can you change just the front sprocket or do you need to change both?

more teeth from standard =?

less teeth from standard =?

looking for a bit more zip in acceleration, as i tend to find myself pottering along in 4th gear as it "sounds right" , then look and then change up
 

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Should that say back sprocket as in rear sprocket, or you want a black coloured sprocket?

You can change the front or rear separately if you like or both together, to gear your bike down and staying with triumph parts you could fit a 16 tooth front sprocket or a 42 tooth rear sprocket separately or both together.
Changing the front would make a 6.25% difference and the rear would be 13.5%, obviously add them if you change both.
Bear in mind if you change the rear to a 42 to it will shorten your sprocket distance by approximately 1 inch, you need to check whether you have enough adjustment on the rear wheel to compensate.
Hard to quantify the changes in acceleration but if you use the same gears as you do presently it will obviously accelerate harder.
No doubt somebody else will reply and say you could just use a lower gear on your existing setup, which is partly true but I think we tend to ride in a certain way and use the gears we're used to, so if you do a sprocket change you'll probably use the same gears as before but the bike will feel faster.

The Bonneville is obviously setup for cruising at lower revs as 6th is geared for 158 mph top speed which it won't get anywhere near, so you will notice the increase in engine revs when you're cruising which you may or may not feel is worth the increased acceleration.

All the data is on this site if you can follow it, looks a bit busy at first glance.
https://www.gearingcommander.com/
 

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I believe you are asking about a T120 Black motorcycle and any sprocket change. In general it is considered better to increase the rear sprocket size rather than go down on the front sprocket if you have options. Many people have increased from the stock 37 tooth rear sprocket to a 39 tooth. I went to a 40 tooth rear on my T120. Either of those work without chain modification and in fact place the adjusters more in the middle of travel (assuming a good chain). This made the gearing much better for the way I use my bike and will definitely help acceleration. On my bike with a 40 tooth rear and stock 17 tooth front the bike is turning 3250rpm at 70 mph.

Chuck
 

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Discussion Starter #4
Yes. Back sprocket. And front sprocket. Pretty much answered the question between the two replies. Many thanks! Think I'll do a rear first then decide.
It's the rev speed that catches me out. I'm sat there happy then realise I'm in 4th . Too used to triples for the past 7 years
 

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I also am running the Thruxton 42 tooth rear sprocket.
Moves the rear wheel to the center of the adjustment slot.
Gas mileage is still in the low sixties per US gallon.
60 mph is 3000 rpm in sixth.
 

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Hookalatch: Just curious where you found the 40 tooth rear sprocket. Steel or aluminum?
I read about a french company but no US supplier.
Thanks for any info.
 

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Hookalatch: Just curious where you found the 40 tooth rear sprocket. Steel or aluminum?
I read about a french company but no US supplier.
Thanks for any info.
Sprocket Specialist 1800 782 8200 have 40T aluminum rears for Triumph watercooled twins. I sent them my rear sprocket for the pattern in 2017. I've run my 40T several times.
 

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I fitted the 39 tooth steel supersprox on my T120. I like it much better than the stock 37 tooth. It allows easier cruising in the traffic we have around here and hasn't really changed the top end much. I'm not an interstate rider with this bike anyway. Got mine for 42.00$ from amazon shipped to my door. It just makes 1st, 2nd and 3rd more rideable. One of the best improvements I've done to the bike so far.
 

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I also replaced the rear sprocket with 39t. On paper the difference should be subtle. Subjectively it feels like a huge improvement. Even though you can shift where you want, and I had gotten used to the original gearing on my 2017 t120, it always felt kind of slow revving and the gearing felt wide (tall?). Now all the shifts feel like they are where they should be, zippier launch, and I feel like I’m getting a lot more of my money’s worth out of 5th and 6th. Still plenty relaxed at highway speeds.

That, and replacing the stock tires (Pirelli Scorpion Trail 2, but anything will do) made big improvements to an already great motorcycle.


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