19 Tooth Front Sprocket
- Thread starter 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.
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
Well-Known Member
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.
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.
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.
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.
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.
Did you correct the speedometer.
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.
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.
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
Thank you, sir.
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.
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.
Maersk,
While I have a cable-driven Speedo on my ‘09 Bonnie, I believe I can answer your original question (as long as you DO have an electronic Speedo):
For simplicity’s sake, let’s presume that your Speedo gets its info based on the rate of rotation of the countershaft to which your front sprocket is attached. Let’s further presume it reports 60 mph at 3,000 rpm in 5th gear.
While a larger front sprocket will make the rear wheel turn at a greater rate than the one it replaced, your Speedo is being fed the same info regardless of the size of the sprocket up front.
Regardless of how fast you are actually going with a different sized sprocket in 5th at 3K rpm, your Speedo will always report the same speed. If you had a cable-driven Speedo, it would definitely show the speed increase with a larger front sprocket.
Hopefully this performs your sought-after sanity check. You can prove this to yourself by running a smartphone app such as Waze or Riser, which uses GPS to quite accurately report your current speed. If so inclined, take a 5th gear/3K rpm speed reading with the 19 tooth, put the 18 back in, take the 5th/3K speed reading, and compare. I promise they will differ with the 19 tooth giving more mph at 3K.
I want to say that while Red Dog may be mistaken in stating that an increase in final drive ratio will not affect speed, his opinions regarding MPG have merit. Also kudos for the efforts in his analyses.
Hope this helps!
-Sparky
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