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Hello so I have a question for those who have switched the front sprocket from the stock 14t to 15t. What is your rpm at going 75mph on the 14t it is almost exactly 8000 for me and i would like to get that down if its worth it. Im concerned the high rpms aren't good on the bike?

Also does switching to a 15t make the bike struggle more? is it noticeable? Thanks!
 

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Hey Brenden, I'm running +1/-2 and pulling a shade over 7000rpm at 75mph so I reckon you will be looking at 7500rpm with the +1 set up.
Naturally you wont have quite the same rate of acceleration in top gear but if you do notice it initially you will soon forget how it felt beforehand.
Then you can enjoy the more relaxed cruising and better fuel consumption. :)
 

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Just to be clear Brenden..+1/-2 from Kiwi means ....+1 on the front sprocket (one extra tooth from stock ) and -2 on the rear sprocket (2 less teeth from stock). Just making sure you understand.

Kiwi..with the gearing on your 300 on a long uphill grade at highway speed do you need to shift down one gear to 5th to maintain your speed?
 

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Kiwi..with the gearing on your 300 on a long uphill grade at highway speed do you need to shift down one gear to 5th to maintain your speed?
Sure, but with the standard gearing and only 30 HP I often had to do that before as well! It doesn't turn your bike into an instant gutless wonder :laugh:

One thing I would say is that fifth becomes a more usable proposition in a lot more scenarios now where you are battling a killer head wind or maybe a long steep gradient. Dropping back to fifth is now not such a big deal or drop in road speed.
 

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Thanks again kind Sir...You are a wealth of information...


Got my +1 front sprocket today. Guess what it is Made in Indonesia...who would have guessed! :)
 
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I'm sure it's not even necessary, as at 15/34t, the bike still has plenty of power to go 70+MPH up a long bridge in final gear...

For RPM calculation here's the formula:

Stock: 14/36t

Modified RPM = Stock RPM * Stock Front Sprocket teeth * Modified rear sprocket teeth / Modified front sprocket teeth / Stock rear sprocket teeth

Eg:
If modified sprockets are 15/34t, and stock RPM=8000, then:
RPM = 8000 * 14 * 34 / 15 / 36 = ~7050 RPM.


Since just modifying the front sprocket, you can scrap the rear sprocket out of the formula, and it'll look like this:
RPM = Stock RPM * Stock front sprocket / Modified front sprocket = 8000 * 14 / 15 = ~7466RPM

Your RPM will drop by 533RPM at 8000RPM, or it will drop by ~266RPM @ 4k RPM.

Upping 1 tooth on the front means round about 7% higher MPH, or 7% better MPG (at lower speeds), and 7%lower RPM.


Looking at the HP graph, you'll drop 1HP, but gain 0.5 lb ft of torque:



With just a 15t, your powerband (HP peak @ 8500rpm) will be at 89MPH instead of 83MPH.
That means if you want to go faster than 85MPH, the new gearing will be better.
 

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HMMM Interesting..if an engine makes a specific amount of Horse Power AFAIK changing gearing in the drive line does not change the out put (H.P. wise) of said engine. What changes is the torque peak produced at certain RPM's. Changing gearing will change RPM's where peak torque is developed. This is what I understand.....however I could very well be wrong (I probably am! :))
 

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HMMM Interesting..if an engine makes a specific amount of Horse Power AFAIK changing gearing in the drive line does not change the out put (H.P. wise) of said engine. What changes is the torque peak produced at certain RPM's. Changing gearing will change RPM's where peak torque is developed. This is what I understand.....however I could very well be wrong (I probably am! :))
I think what MeeLee was meaning was that by dropping the revs 500RPM from 8000 to 7500 at 75MPH (by fitting the 15T) you are now in a different part of the HP/Torque curves.
At 7500RPM the motor is producing 1HP less than at 8000RPM as the power curve is still ascending to its peak at 8500RPM. However you are gaining half a ft-lb more of torque as peak torque was earlier at 6800RPM and is now descending as revs rise.
Correct MeeLee??
 
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Yup! Got ya...!:) Thanks
 

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I think what MeeLee was meaning was that by dropping the revs 500RPM from 8000 to 7500 at 75MPH (by fitting the 15T) you are now in a different part of the HP/Torque curves.
At 7500RPM the motor is producing 1HP less than at 8000RPM as the power curve is still ascending to its peak at 8500RPM. However you are gaining half a ft-lb more of torque as peak torque was earlier at 6800RPM and is now descending as revs rise.
Correct MeeLee??
Difficult subject.
The more I think about it, the more I wonder if the HP/Torque curve of a bike is affected by a sprocket change, or not?

At the engine, there will be the same HP and torque curve, regardless of sprocket size, that's for sure.
But the torque on the rear wheel lowers when increasing the front or decreasing the rear sprocket size.

Most of the time, the torque and HP curve, intersect at 5200RPM,
That means I'm struggling with the idea if the Torque curve is affected, the HP curve must be affected as well.
It would be interesting to see someone do a dyno run with stock sprockets, and a gear change (preferably a large one, to see the difference); or compare 5th gear and 6th gear on a dyno run, to see if the curves both are affected by the gearing difference or not.

Another idea is that it might be possible, that with the lowering of RPMs, the torque gained on the curve, is compensated, by the one lost due to the sprocket change...

Not sure if that makes any sense, but I'm playing around with these thoughts right now...

For best top speed (eg: if the bike can run 95MPH stock), I'd say you could gain about 5MPH, if the bike would be doing 8500RPM @ 100MPH; that would mean that the best sprocket setup for this bike would be a 16/34T or a 15/32T. Unfortunately neither one of them is possible on this bike.
 
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