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Discussion Starter #1 (Edited)
Hey all, I just bought a Speed Twin and I’m considering swapping the front sprocket to a 17t. I’m posting here because the Speed share most in common with the Thruxton so I figured I’d get better info here. I went back about 15 pages and didn’t see much info.

I’m just curious about how people who have done the mod feel about it. It’s easy enough to go back but I figured I’d get some opinions on how it elongated the gears and how much if changed the ride.

Thanks!
 

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Ive not ridden the 900 but will assume it is smooth like the 1200.
We sometimes gear old bikes higher just to reduce vibration. That's not really necessary with the 1200, there is no appreciable vibration at any RPM. There is a power pulse when it's pulling, but we like that, wouldn't want to lose that!
So another reason to gear a bike up would be to increase top speed. It doesn't always work that way, sometimes they go slower. With my 1200 I've had it to 220 kmph on the speedo, lots of speed there.
The last reason I can think of is to increase top speed in the intermediate gears. Gearing it up 7% with the sprocket change will do that for you.
You will also lose 7% of the available torque at the rear wheel in each gear.
Gearing always is a compromise and it's also a bit specific to the individual rider's preferences.
I feel that the Triumph engineers got the gearing right with the bike, but you might like your 900 geared up a little.
Are you ok with 7% less torque in each gear?

7% less on the 1200 still leaves a good amount, but it won't pull as hard as with stock gearing.

Glen
 

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Discussion Starter #5
Ive not ridden the 900 but will assume it is smooth like the 1200.
We sometimes gear old bikes higher just to reduce vibration. That's not really necessary with the 1200, there is no appreciable vibration at any RPM. There is a power pulse when it's pulling, but we like that, wouldn't want to lose that!
So another reason to gear a bike up would be to increase top speed. It doesn't always work that way, sometimes they go slower. With my 1200 I've had it to 220 kmph on the speedo, lots of speed there.
The last reason I can think of is to increase top speed in the intermediate gears. Gearing it up 7% with the sprocket change will do that for you.
You will also lose 7% of the available torque at the rear wheel in each gear.
Gearing always is a compromise and it's also a bit specific to the individual rider's preferences.
I feel that the Triumph engineers got the gearing right with the bike, but you might like your 900 geared up a little.
Are you ok with 7% less torque in each gear?

7% less on the 1200 still leaves a good amount, but it won't pull as hard as with stock gearing.

Glen
Thanks for the informative post. I actually have a Speed Twin so it’s a 1200. Pretty much an upright Thruxton. I did the same mod when I had a Street Twin and liked the result so I assume I’ll like it on the Speed Twin as well, I was just trying to get some opinions.

Thanks again for your well thought out reply.
 

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Discussion Starter #6
Silly question: if it’s a 7% loss in torque per gear, is that cumulative? Meaning 36% less torque overall? That’d be a big loss...
 

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Hey all, I just bought a Speed Twin and I’m considering swapping the front sprocket to a 17t. I’m posting here because the Speed share most in common with the Thruxton so I figured I’d get better info here. I went back about 15 pages and didn’t see much info.

I’m just curious about how people who have done the mod feel about it. It’s easy enough to go back but I figured I’d get some opinions on how it elongated the gears and how much if changed the ride.

Thanks!
I've done the counter shaft and rear sprocket changes a dozen times are or so on the Thruxton R, same motor as the Speed Twin.


I've run 16,17 and 18 on the front as well as three other combinations on the back. The motor will handle them all from your current 16/42 to 18/37. The 17/42 your considering is a minor change that will make cruising a little more relaxed but you won't notice any decrease in acceleration.

The one tooth larger in the front might cause a problem if your chain is brand new and has not stretched enough. Check your chain adjusters. If the 17 won't fit because your chain is not long enough (not likely) you could drop two teeth in the back to a 16/40 combination.
 

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17t/42t will fit a brand new setup just fine.i just did it on my Thruxton about a month back. Third best mod I've done after a Quickshifter and the low clip-ons.

Sent from my SM-G955U using Tapatalk
 

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Not cumulative but Torque is a function of the gear ratio, in direct proportion.
If you gear a given motor to a load at 1 to 1and have 10 ft lbs available then lower gearing by 10% (1.1 motor rev to 1 load rev) , you will have 11 ft lbs available, or 10% more torque available.
Gear ratio is determined by dividing sprocket sizes.
You can use diameters or radii, or the most common, number of teeth, it doesn't matter which, as long as you are consistent ( r/r or d/d or t/t)
Changing the number of teeth of one sprocket 7% changes the diameter of one sprocket by 7% and also changes the radius by 7%, so it changes the gear ratio and torque at wheel in each gear by same.

To be precise, changing to a 17 tooth from a 16 tooth will give a 6.25% increase in gear ratio.
 

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Hey all, I just bought a Speed Twin and I’m considering swapping the front sprocket to a 17t...

I’m just curious about how people who have done the mod feel about it.
Thanks!
I haven't regretted this mod.

Cons: Bike feels less hyper. You give up a little off the line pop. Not as wheelie-happy.

Pros: Bike feels less hyper (this is not a typo and whether this is a pro or con is entirely subjective). First gear is more useable and as a result bike becomes easier to ride in town. Overall bike becomes more versatile in that it's easier to ride relaxed when the mood suits or traffic dictates. On slower speed twisty roads with short straights and slow to 20 - 30 mph signs before curves, you can leave it in 3rd and just work the throttle and brakes, if you enjoy that kind of thing. Speedo reads more accurately with 17t.

I've gone from the old 5 speed Bonnie where I was continually trying to shift up into a non-existent 6th gear, to a 6 speed Thruxton where I rarely use 6th gear. With the 17t, there's not much point shifting to 6th below 70 mph unless you're on the highway wanting to conserve fuel.
 

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Discussion Starter #12
Hey all, I just bought a Speed Twin and I’m considering swapping the front sprocket to a 17t...

I’m just curious about how people who have done the mod feel about it.
Thanks!
I haven't regretted this mod.

Cons: Bike feels less hyper. You give up a little off the line pop. Not as wheelie-happy.

Pros: Bike feels less hyper (this is not a typo and whether this is a pro or con is entirely subjective). First gear is more useable and as a result bike becomes easier to ride in town. Overall bike becomes more versatile in that it's easier to ride relaxed when the mood suits or traffic dictates. On slower speed twisty roads with short straights and slow to 20 - 30 mph signs before curves, you can leave it in 3rd and just work the throttle and brakes, if you enjoy that kind of thing. Speedo reads more accurately with 17t.
This is kinda what I’m looking for. I can’t gun the bike from a stop without doing wheelies. It’s kinda cool but getting old already. 1st does feel short to me. I’ll see where this goes and potentially go a step further to smooth things out.
 

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With the Traction Control off mine comes up pretty easily, but with control on doesn't do more than a little hop before the TC pulls power away for a nanosecond, then back on smoothly, no wheelie, even in first.
Without the TC on "the tank wants to hit your face" as one tester noted.
So I leave it on.
It works beautifully.
Saved me from myself a couple of weeks ago when getting rambunctious.
Assuming all the settings are the same for both bikes, I can see where the Speed Twin might lift even with TC on whereas the Thruxton doesn't.
The Thruxton riding position puts a fair bit of rider weight on the front end , at least up until 60-70 mph when wheelies aren't happening with 100 HP.
The Speed Twin with its upright rider position doesn't have that rider weight on the front end.
On the subject of front end weighting, as a kid I had an very light and powerful 2 stroke Ossa race bike that had been modded for the Portland track. It flipped on me a couple of times before I learned to use the Ake Johnsson method thru the gears. Ake was a top MX rider back then.
He was a pioneer at finding ways to control the new high powered light weight 2 stroke race bikes.
His method thru the gears was to stand on the pegs then extend his upper body right out over the front end while powershifting thru the gears full throttle with front wheel about 2 feet above the ground. It was quite a sight to see the huge rooster tail coming off his 400 Maico as he left Roger Decoster and the rest of the top US pack behind with that method!!


Glen
 

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Discussion Starter #14
With the Traction Control off mine comes up pretty easily, but with control on doesn't do more than a little hop before the TC pulls power away for a nanosecond, then back on smoothly, no wheelie, even in first.
Without the TC on "the tank wants to hit your face" as one tester noted.
So I leave it on.
It works beautifully.
Saved me from myself a couple of weeks ago when getting rambunctious.

Glen
I guess this is closer to my experience. A little hop most of the time but sometimes closer to a wheelie.

Hoping the sprocket alleviates the hop.
 

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I just changed from the 16T to 17T on my Thruxton S with the ABM handlebar conversion kit. Not too much experience with the swap yet, but finding that the slightly higher gearing seems to make gear changes less frequent. So far, happy with the change.
 

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Discussion Starter #16
17t/42t will fit a brand new setup just fine.i just did it on my Thruxton about a month back. Third best mod I've done after a Quickshifter and the low clip-ons.

Sent from my SM-G955U using Tapatalk
Do you still feel like it’s high powered off the line or has there been a noticeable downgrade in that area?
 

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Discussion Starter #17 (Edited)
Do you still feel like it’s high powered off the line or has there been a noticeable downgrade in that area?
I’ll answer this myself.

No decrease in power. It just feels more refined. Smoother. It’s all still there. The bike is hauling ass, and with a 17t up front you can hit 60 in second before redline, which is a nice little bonus.

I did find myself cruising around town in 3rd a lot today up to about 50. Maybe not the best for fuel efficiency but it’s nice to have the power on command.

So far, happy with the change.

That said, if you really like the hyper aggressive nature of stock sport mode, I’d stay away from this mod. While like liked it at first, I got tired of the front wheel coming off the ground. That didn’t happen at all today.
 

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I see this post was started some time ago. Ive been looking to find a 17 for my speed twin. In all of these posts theres no mention of where you purchased the 17?
Dealer only item? Internet site?
Please advise. Thanks.
 

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I see this post was started some time ago. Ive been looking to find a 17 for my speed twin. In all of these posts theres no mention of where you purchased the 17?
Dealer only item? Internet site?
Please advise. Thanks.
Standard triumph part on the Bonneville t120
You can get aftermarket sprockets but I prefer the OEM type with the rubber cushion.
 
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Now that we can tune the bikes, the 16T sprocket is very appropriate for the HP bikes due to the rev range being extended to 7800 with a tune.
 
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