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post #1 of 8 (permalink) Old 05-15-2019, 09:50 AM Thread Starter
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Gear ratio / final drive - Street Twin 2016

Hello all, my first post because I couldn't find the answer. I really searched.

I read everything about the tea, raisch cam, de-cat etcetera and know some people on here changed the rear sprocket too.

Because I want my Street Twin to accelerate quicker (top speed is not interesting to me) I want to change the rear 41 tooth to 44 (Raisch sells the sprocket). I went to a local motorcycle mechanic because I don't have the right tools to do this. He asked me a few questions: what will happen to the gear ratio and what influence does it have on the RPM's, what will be the longterm effect for the engine. Couldn't answer the question so I went home to do some research and called a Triumph dealer. He figured it couldn't be bad for the motorcycle as long as I don't drive at full revs for a long time. Ok... who does that?

Thats why I am on here asking the same question to you guys.

On Gearingcommander.com I found out that changing the rear to 44 will have the following effect on the RPM's (first numeber is stock, second number is 44 tooth):

- 50 km/h - 1st gear - 4385 to 4706
- 50 km/h - 5th gear - 1624 to 1743
- 100 km/h - 3rd gear - 4636 to 4975
- 100 km/h - 5th gear - 3248 to 3486
- 110 km/h - 5th gear - 3573 to 3835
- 120 km/h - 5th gear - 3898 to 4183
- 135 km/h - 5th gear - 4385 to 4706
- 150 km/h - 5th gear - 4873 to 5229

I have no intend in cruising at 150 km/h but I will be driving that speed sometimes. Cruising speed on highways will be between 110 and 140 km/h. The increased RPM will be somewhere between 262+ at 110 km/h and 356+ at 150 km/h.

- Will the engine manage this kind of increase of RPM on long term?
- Is there some way to calculate the increase in acceleration with the sprocket change?
- Is there some way to say what fuel consumption will be?
- will I have to remap of do something to the ECU?
- Maybe you have some other interesting things for me to know when changing the sprocket.

I intend to do a cam change in the future as well. Any new insights on that after a year of use?

Edit:

The final drive will change from 2.41 to 2.59

Thanks guys!

Last edited by MaartenR; 05-15-2019 at 09:51 AM. Reason: Additional information
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post #2 of 8 (permalink) Old 05-17-2019, 11:17 AM
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- Will the engine manage this kind of increase of RPM on long term? I don't see why not, its a marginal increase in wear and tear if anything. Ride more, worry less.

- Is there some way to calculate the increase in acceleration with the sprocket change? Probably, but I couldn't tell you how. It will be quicker, but it wont be a huge change.

- Is there some way to say what fuel consumption will be? Not really, will you be mostly riding at motorway speeds 60mph and up? In which case it will probably be a bit lower mpg, however if most riding is around town it will likely be marginally better.

- will I have to remap of do something to the ECU? No

- Maybe you have some other interesting things for me to know when changing the sprocket. You might wear out you back tyre a bit quicker. The bike will feel more responsive in every gear.
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post #3 of 8 (permalink) Old 05-18-2019, 03:01 AM Thread Starter
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Thanks for taking the time to answer my questions Bobber101.

[QUOTE=Bobber101;2003932530]- Will the engine manage this kind of increase of RPM on long term? I don't see why not, its a marginal increase in wear and tear if anything. Ride more, worry less.

Ok will do


- Is there some way to say what fuel consumption will be? Not really, will you be mostly riding at motorway speeds 60mph and up? In which case it will probably be a bit lower mpg, however if most riding is around town it will likely be marginally better.

Mostly I will be driving on country roads - that would be mostly around max 50 mph. I will be driving motorways but not that regular. And living in the Netherlands within 1,5 hours I would have reached my destination anyways. Its a small country after all.
On lesser occasion I will do a longer trip on motorways to reach a destination abroad. I guess it wouldn't make that of a difference to me for fuel. I would be most worried about engine wear and tear on higher revs. But seen your earlier answer you figure it wouldn't cause any problems.
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post #4 of 8 (permalink) Old 05-18-2019, 05:46 AM
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I have the 44 tooth Raisch sprocket on my Street Twin, a cheap and effective mod for your goals. It will not knock you off your seat, it is a subtle mod, and you will barely know the difference after a few miles, the surprise is the overall smoothness of a larger sprocket.
Go for it. don't listen to anyone who spouts theory with no experience with this sprocket. Visit my you tube channel for some testing with an X pipe and stock mufflers as well as after market slip ons. my zero to 60 went from 5 plus seconds to around 4 seconds, and I am no drag racer. I rarely cruise over 120 KPH, and never ride much faster than 140, with that in mind you won't know you decreased your top end. I have data logged the rpms and there is less difference from gearing commander.



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post #5 of 8 (permalink) Old 05-19-2019, 03:30 AM Thread Starter
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Thanks RHB! Nice vids. I indeed found your vids and topics before I posted my first post. Thanks for added info. Did you notice any difference in the speedometer? I understand the speedometer gets its info from the drivetrain and not the front wheel.

There was another video showing your custom exhaust. The look very nice! What kind of exhausts are these?

I will proceed with the sprocket and replace it in the upcoming days/ week.
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post #6 of 8 (permalink) Old 05-19-2019, 05:37 AM
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Quote:
Originally Posted by MaartenR View Post
Thanks RHB! Nice vids. I indeed found your vids and topics before I posted my first post. Thanks for added info. Did you notice any difference in the speedometer? I understand the speedometer gets its info from the drivetrain and not the front wheel.

There was another video showing your custom exhaust. The look very nice! What kind of exhausts are these?

I will proceed with the sprocket and replace it in the upcoming days/ week.
I did some data logging with Torque pro, very little speedometer error, and very little, a couple MPH or so differences in redline (rev limiter) /MPH speed. you will barely if at all notice it in normal driving.
My stainless steel slip ons were self designed and made.

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post #7 of 8 (permalink) Old 05-20-2019, 07:08 AM
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The speed is detected from the rear ABS sensor, so gearing changes make no difference at all.

Changing sprockets is always an interesting experience. If you change the rear sprocket then in first gear you get (new/old)*100 percent more power (as power = torque*rpm) but you run out of gear the same percentage sooner quicker.
As a ridiculous example, if you fitted a 57 tooth rear (or a 13 tooth front sprocket) you would have a new gear. 2nd would be the same as 1st was, 3rd the same as second was, etc. From this you can see that you can't possibly gain any power from changing sprockets, but your new first gear would have loads of torque but very little speed, so you'd have to change up a gear 30% sooner.
That means if your bike can pop a wheelie when leaving the line there's no point gearing it down in 1st. But, if you find you're having to slip the clutch too much then you should gear it down. When you gear it down you will get poorer fuel economy, as you increase the revs in every gear, but it only really effects freeway cruising as your revs will be higher for any given speed.

It's a relatively cheap mod, and easily reversed, so go for it Just be aware of what's happening, and make sure it's the effect you want.

Bike with a few things added, such as... me. I prefer riding my bike to bragging about the chromed rear foot-pegs. Does that make me strange?
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post #8 of 8 (permalink) Old 05-20-2019, 08:57 AM
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Quote:
Originally Posted by jsobell View Post
The speed is detected from the rear ABS sensor, so gearing changes make no difference at all.

Changing sprockets is always an interesting experience. If you change the rear sprocket then in first gear you get (new/old)*100 percent more power (as power = torque*rpm) but you run out of gear the same percentage sooner quicker.
As a ridiculous example, if you fitted a 57 tooth rear (or a 13 tooth front sprocket) you would have a new gear. 2nd would be the same as 1st was, 3rd the same as second was, etc. From this you can see that you can't possibly gain any power from changing sprockets, but your new first gear would have loads of torque but very little speed, so you'd have to change up a gear 30% sooner.
That means if your bike can pop a wheelie when leaving the line there's no point gearing it down in 1st. But, if you find you're having to slip the clutch too much then you should gear it down. When you gear it down you will get poorer fuel economy, as you increase the revs in every gear, but it only really effects freeway cruising as your revs will be higher for any given speed.

It's a relatively cheap mod, and easily reversed, so go for it Just be aware of what's happening, and make sure it's the effect you want.
Absolutely correct academically stated and using an exaggerated example. no one said there would be an increase in power, A gear change is a finite change, that increases leverage but not in any way engine power. If you riding on roads or in conditions where tall gears are not serving your needs or goals the gearing down makes sense. Remember Street twins are only 5 speeds and are geared rather tall to begin with. All the negatives add up to almost no difference in fuel economy, or cruising around the kind of roads the OP was indicating he had. Data logging is a wonderful tool and it is a great way to blow holes in academic theories. My experience with the 44 tooth was that I was cruising on average around town and secondary roads at a little over 3000 rpm. average speeds of about 50KPH. There is not a significant difference from the stock gearing regarding fuel economy or rpm . Fuel economy depends more on you right wrist than anything else. I would suggest to anyone, try it before passing judgement on a specific application. This gear change is not a profound change, in no way hobbles the bike in any gear. If one is worried about losing top speed, 5 MPH at over a hundred mph on a street twin when you are getting blown off the bike anyway is academic. I would agree, and not the case here, that if you spend all your time on 4 lane highways this is not for you.
Charts below are rpm and speed graphs taken fro a PID log file, peak rpms are when labeled, rev limiter second and third gear. I don't have before logs but was using Gearing commander to guesstimate the difference, there are obvious short comings with gearing comander as a base line because they are math calculations in a vacuum, not real world conditions so the value differences are likely less. But you can get the after picture, speeds are GPS, not the speedo which reads higher.
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