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Discussion Starter #1
Has anyone upgraded the front sprocket? I did this on my 2005 America and it made significant improvement at higher speeds.

If anyone has done this on the new Speedmaster can you tell me where you found it? Thanks.
 

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Upgrade how? Smaller front sprocket? If you are looking to change the gearing it might be easier to replace the rear sprocket. I swapped my stock 37t for a 39t rear.
 

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Discussion Starter #3
A larger front sprocket. Found what I was looking for at spocketcenter.com
 

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smaller sprocket - faster acceleration
larger sprocket - slower acceleration
In theory, yes, but in practice, no. It’s only true for the initial serge from standstill and once the bike’s moving you can hold the gears longer and generally use a lower gear through corners. For real world riding and not just on the drag strip most riders will find slightly taller gearing will be quicker from point to point.
I tested this with my Thruxton. Went up a tooth on the front and although a standard geared bike would get the jump off the line I quite quickly rounded them up. And it was so much better at high speed. Fact.
 

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Got to agree with DtD on this, going up a tooth in front is going to give you a later shift point i.e. a lower gearing and less acceleration. It might work better in certain track scenarios and be faster in a certain gear at X-Z range but straight line acceleration will be lower. Good news is you wont have to shift as often and you'll get some MPG savings.
 

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One of the better explanations of gearing and its effects. Unless your running a track and want 90mph in 3rd gear for the HP1200 engine then it's kinda a wash. Like I said a gearing change can give you better power in a X-Z range for a given scenario but as far as STRAIGHT LINE performance then a smaller number up front gives you acceleration while a larger gives you top end. With a governed engine like many triumphs have then it shifts the powerband but in the same exact way. My bobber will ALWAYS top out at 112 or so but if I drop the tooth count upfront I.E. raise the gearing it will get there faster... so no matter what my bike can get to top speed half way or less through 4th gear if I raise the gearing I always have room up top in 5th and 6th but if if lower it even further I've just reduced my power band and even further reduced my engines ability to put torque to the ground quickly.
 

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Very few people are only interested in off the line acceleration or top speed. There’s a whole world of real, every day riding in between. Smaller front sprocket lowers the gearing, by the way.
 

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Like I said before a gearing change in either direction can increase performance in an X-Z scenario but acceleration and topend are base values in this equation. Unless your running a specific size oval or degree bend repeatedly with a specific number of G's stressing the tire to slip then this is a moot point. Finding the gearing of s bike is VERY simple, you divide the rear sprocket count by the front. Ive got a 16T front and 42T rear resulting in a 2.3125 I'm swapping to a 15T front leaving the rear unchanged resulting in 2.466r! Higher gearing results in faster acceleration while lower equals better top speed .-1 on front equals about +3 on rear just in case... if my bike already is limited before the engine can hit peak power than why cripple it further. Only reason would be to increase fuel economy.
 

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If you dont feelnlike appreciating my 20 or so posts heres another disscussion from your other peers the matter...
 

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Finding the gearing of s bike is VERY simple, you divide the rear sprocket count by the front. Ive got a 16T front and 42T rear resulting in a 2.3125 I'm swapping to a 15T front leaving the rear unchanged resulting in 2.466r! You are in fact quite incorrect, read the link I posted to learn more please. Higher gearing results in faster acceleration while lower equals better top speed .-1 on front equals about +3 on rear just in case...
No need to be insulting or so condescending. The goal here is to help people, not to try to prove how clever you are - especially when you’re not. I suggest you take a look at the very thread you directed us to.

@retjustdad53 (a person whose knowledge is unquestioned and whose opinions I respect) states in that thread: “
Your stock [Thruxton] is 16T/42T. People calculate it a two ways I use the rear divided by the front to get 2.625 in this case, this method means the higher the number the lower (more low end). [sic]

The T120 stock is 17T/37T or 2.1764 which is quite high by comparison.”

It is indeed lower gearing that will make your bike a little faster off the line and in theory give you a lower top speed. But it won’t be faster through the whole rev range of every gear. In the real world people need to choose the gearing that best suits how and where they ride. If that happens to be on a drag strip, lower gearing might be better. If it’s on the salt flat, higher gearing is more likely to get you where you want.

It is “VERY simple” as you say, but it’s no so simplistic that a higher number means higher gearing.
 

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I see that our new contributor @BurgerBobber has edited his posts to remove the insults and some of the condescending comments. I guess that’s something. Unfortunately for him I’d already captured one of them when I quoted him above. And unfortunately for us he’s replaced them with close to the biggest load of drivel I’ve seen on here for a while. Now he’s saying sprocket changes shift the power band (oh dear) and that lower (but he means higher) gearing “cripples” the bike. I’m not sure what he’s done to his bike to change its power output but my Thruxton hit peak torque at around 4100rpm, well short of the redline, and had no problem launching faster than most bikes out there even with a 17T front sprocket.
 
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