19 Tooth Front Sprocket

Maersk

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Can I get a sanity check, please. Just added a British customs 19 tooth front sprocket to my 2012 T100. RPMs at 70 mph were exactly the same as the 18 tooth. Would have assumed a reduction in revs?
 

Red Dog

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They would be correct.

The difference is in the fuel efficiency of the bike. Increasing the front sprocket raises the final drive ratio. No gain speed, but gain in gas mileage.

I, like many other Suzuki DR650 riders, will run a 16 or 17 tooth front sprocket while riding pavement, then in the campground or hotel parking lot go back to 15 tooth for the next day's ride with Little Rabbit Fufu down the bunny trail.
 

Maersk

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They would be correct.

The difference is in the fuel efficiency of the bike. Increasing the front sprocket raises the final drive ratio. No gain speed, but gain in gas mileage.

I, like many other Suzuki DR650 riders, will run a 16 or 17 tooth front sprocket while riding pavement, then in the campground or hotel parking lot go back to 15 tooth for the next day's ride with Little Rabbit Fufu down the bunny trail.
Thanks, Red Dog, for the reply. Not sure I totally follow you. Is your suggestion there would be no reduction in revs by moving from an 18T to a 19T?
 

Philois

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Yes I’m confused too, I was incorrectly given a 17 tooth front sprocket instead of an 18 tooth for my America (2015, I believe earlier models were a 17 tooth) difference of around ( not exact) 250 revs at 100kph. And around 40km less out of a tank of fuel. Not sure how your revs remain the same for the same speed. For info I am going to refit a 18 tooth sprocket.
 

Red Dog

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I'm attaching a couple of *.pdf's showing the difference between how a 15t stock front sprocket vs. a 14t off-road front sprocket affects the the gearing and speed of the bike. Also, attached is the worksheet itself - not my creation.

The differences are subtle, are noticeable.

Apparently, I can't attache Microsoft spreadsheet files. If you want to play with your own numbers, let me know, we'll figure something out.
 

Attachments

  • Gearing-14t Off-Road DR.pdf
    56.3 KB · Views: 4
  • Gearing-15t Stock DR.pdf
    56.3 KB · Views: 3

Rolandrat

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I have a 19t and a 40t at 3k revs gives 90kph with speedo corrected.
 

Red Dog

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Pulled out the service manual this morning and did new gearing charts for the Bonneville.

The up/down shift rpm's are a bit of guess work. Everything else should pretty well spot on.

Enjoy!
 

Attachments

  • Gearing-19t Front Sprocket Bonneville.pdf
    56.5 KB · Views: 4
  • Gearing-Stock Bonneville.pdf
    56.1 KB · Views: 5

Red Dog

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Okay guys, I messed up the gearing charts I posted yesterday.

I've corrected the charts. It's the front wheel size I should have used. Speedo connected to the front wheel - duh. Someone also mentioned they got a 17t front sprocket with their America, so I'm including a chart it. From playing games with the numbers, it looks like the 19t front sprocket wins in terms of getting the best gas mileage and speed out of the Bonneville. Now, I would suppose it would apply to some of the other Modern Classics. As I mentioned before, I'm not able to attach spread sheet files. If you want the file, make contact and we'll figure out something.
 

Attachments

  • Gearing-17t Front Sprocket Bonneville.pdf
    56.1 KB · Views: 0
  • Gearing-18t Front Sprocket (stock) Bonneville, rev 01.pdf
    56.5 KB · Views: 1
  • Gearing-19t Front Sprocket Bonneville, rev 01.pdf
    56.2 KB · Views: 1

Maersk

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Thank you, Red Dog for all the replies. At the end of the day, I’m still not sure why the additional 19th tooth on the cog yields the same RPMs, but fully appreciate all of your analysis.
 

Rolandrat

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Thank you, Red Dog for all the replies. At the end of the day, I’m still not sure why the additional 19th tooth on the cog yields the same RPMs, but fully appreciate all of your analysis.
Did you correct the speedometer.
 

blacklav

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Only careful riding style will increase your mpg, not the gearing. The motor still needs a certain amount of energy ( ie fuel ) to overcome all the elements acting against it. Wind, tyre pressure, internal resistance, road elevation, riders weight etc etc.
Your throttle might 60% open at 4000 rpm for 70mph , it'll still be 60% open at 2000rpm for 70 mph. Or something like that.
 

Rolandrat

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Rolandrat

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I did not. Is that done with an external tool tied into the ECU?
Yes google tunecu.full instruction on how to set up,it gives diagnostic, sync throttle bodies,re-map and other useful information
 

Maersk

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Yes google tunecu.full instruction on how to set up,it gives diagnostic, sync throttle bodies,re-map and other useful information
Thank you, sir.
 

Red Dog

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Okay, I forgot to give the "Your mileage may vary" disclaimer.

We must remember that these charts are premised on the idea of all things being equal. Final drive ratios need to be considered. Under all things being equal, which final drive ratio should get better mileage, a 2.389 or a 2.263? Looking at the charts for a 18t vs 19t, the final drive ratio also affects the total ratio of all gears, 1st through 5th.

We've also not discussed re-mapping ECU. Re-mapping will allow you to map for better fuel economy or for better performance.

And once again, I screwed up. The chart that's suppose to be for the 19t front sprocket shows the 18t front sprocket. I'll get it right here at some point.

19t front sprocket, rev. 02 is attached. I checked it after I attached it and it is correct.
 

Attachments

  • Gearing-19t Front Sprocket Bonneville, rev 02.pdf
    56.5 KB · Views: 1

Maersk

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Okay, I forgot to give the "Your mileage may vary" disclaimer.

We must remember that these charts are premised on the idea of all things being equal. Final drive ratios need to be considered. Under all things being equal, which final drive ratio should get better mileage, a 2.389 or a 2.263? Looking at the charts for a 18t vs 19t, the final drive ratio also affects the total ratio of all gears, 1st through 5th.

We've also not discussed re-mapping ECU. Re-mapping will allow you to map for better fuel economy or for better performance.

And once again, I screwed up. The chart that's suppose to be for the 19t front sprocket shows the 18t front sprocket. I'll get it right here at some point.

19t front sprocket, rev. 02 is attached. I checked it after I attached it and it is correct.
Great stuff. Thanks, very much, Red Dog.
 
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