A Little Arithmetic To Determine If I am In Top (6th) Gear.

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May 10, 2005
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Toronto, Canada
On my CBR300R, in 6th gear, my road speed in km/hr is exactly 16 times engine rpm in thousands. At 5K engine rpm, the bike is doing 80 km/hr.

The bike is geared so low that I am constantly trying to shift into 7th. Now I just look at the tach to see if I am already in 6th gear.

Also the gear box is very close ratio. Would love to have a much lower 1st gear for crawling in traffic and a higher top gear for more relaxed riding on the highway.
 
You can change the sprocket and make it better at one end but worse at the other. So I'd leave that alone with your current mix of city and highway.
 
On my CBR300R, in 6th gear, my road speed in km/hr is exactly 16 times engine rpm in thousands. At 5K engine rpm, the bike is doing 80 km/hr.

The bike is geared so low that I am constantly trying to shift into 7th. Now I just look at the tach to see if I am already in 6th gear.

Also the gear box is very close ratio. Would love to have a much lower 1st gear for crawling in traffic and a higher top gear for more relaxed riding on the highway.

What’s your maximum sustained speed? Do you regularly go much faster than 80 km/h? Redline is 10,500 rpm, you are running half that and from what I’ve read, the bike will top out at just over 100 mph (160 km/h) at almost the rev limit in top gear. To me, that seems about right for a 285cc single cylinder that is called a 300. Reality is, it’s a small engine and has to spin at higher rpm to do the work. Maybe you have the “wrong” bike for what you need since it doesn’t work for you at either end of the rpm scale like you would prefer.

The issue you speak of, can’t be solved as has been mentioned. Which side of the problem is most helpful for you to address? Shorter gearing in town or taller gearing on the road?

My other thought is trade up for a larger small bike, Ninja 400 with 399cc would eliminate your dilemma in terms of being able to change the gearing (sprockets) and not have a bike that’s unlikeable at either end of the RPM scale. There is enough torque and hp to do what you want.
 
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The bike has ridiculously close ratio gearing. Great if you are on the track racing and wanting to keep the engine rpms up for max power. Not so great if you do not want to race through city streets.

The gear ratios are 1st 3.416, 2nd 2.25, 3rd 1.65, 4th 1.35, 5th 1.166, 6th 1.038. Ratio of 1st gear/6th gear = 3.416/1.038 = 3.29. The 5 spd NV3500 in my Sierra pickup has the ratio at 4.02/0.73 = 5.51

I will keep the CBR300R.
 
LOL I have the same NV3500 in my Truck!! I had 3:23 gearing and now have 3:73 and a TruTrac diff. It's a 05 GMC Sierra 1500 standard cab base model 4.3 V6.

I recommend just getting used to the gearing you have if 1st is already high. If not, experiment by raising the countershaft a tooth and see if you can use the friction zone in 1st gear to keep the speeds lower.
 
The bike has ridiculously close ratio gearing. Great if you are on the track racing and wanting to keep the engine rpms up for max power. Not so great if you do not want to race through city streets.

The gear ratios are 1st 3.416, 2nd 2.25, 3rd 1.65, 4th 1.35, 5th 1.166, 6th 1.038. Ratio of 1st gear/6th gear = 3.416/1.038 = 3.29. The 5 spd NV3500 in my Sierra pickup has the ratio at 4.02/0.73 = 5.51

I will keep the CBR300R.

Bummer you didn’t find those things out until after you got the bike.
 
Here is something that can help you in case you have not tried. Simply punch in the size sprockets you want to use. If you want to be super duper accurate, roll your bike 3 complete revolutions of the rear tire with you on it. Measure and divide inches by 3.

Your bike data is already in the system:

 
Not out much, and you can always down shift if needed.
Downshifting from 6th to 5th does not accomplish much, it gets you from 1.038 to 1.166 gearing, not much of a change and hardly worth the effort. I frequently shift twice, say from 6th to 4th, to see a useful change in gearing.
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My thought, since the initial post says a need /want is a shorter first gear as well, (thus the conundrum) one tooth bigger on the counter shaft is going to take that the wrong direction and make it less desireable. Depending on the chain length, I’d go a tooth or two larger on the rear. That will help down low and with 5th and 6th so close already, won’t make too much difference up top.
 
My thought, since the initial post says a need /want is a shorter first gear as well, (thus the conundrum) one tooth bigger on the counter shaft is going to take that the wrong direction and make it less desireable. Depending on the chain length, I’d go a tooth or two larger on the rear. That will help down low and with 5th and 6th so close already, won’t make too much difference up top.


Keep in mind that the final drive ratio changes the speed in each gear by percentage, 1 tooth larger on the countershaft sprocket is probably 9%. "IF" you go up 1 tooth on the countershaft sprocket, 1st gear won't be significantly "taller" or faster as 9% of 15mph is just over 1mph. You are unlikely to notice much of a change.

However 6th gear will also be 9% taller, and you will notice a big change and will change the theoretical top speed from 100 to 109. If it were me, I'd go up one size on the countershaft.

The "one tooth up" trick will space out your gears a bit too.
 
Keep in mind that the final drive ratio changes the speed in each gear by percentage, 1 tooth larger on the countershaft sprocket is probably 9%. "IF" you go up 1 tooth on the countershaft sprocket, 1st gear won't be significantly "taller" or faster as 9% of 15mph is just over 1mph. You are unlikely to notice much of a change.

However 6th gear will also be 9% taller, and you will notice a big change and will change the theoretical top speed from 100 to 109. If it were me, I'd go up one size on the countershaft.

The "one tooth up" trick will space out your gears a bit too.

I think both solutions have good merit depending which is the more important goal. If the gearing isn’t short enough to crawl in traffic as it is, like I said it makes that worse by going bigger up front. And lowering the top speed by a handful of mph with a couple teeth bigger on the rear really shouldn’t matter when you consider 95-100 mph is probably 30 mph over most any highway speed he’s gonna run already. He does mention stock gearing not being good for “racing through the city streets“, but “great for the race track”. Ultimately which ever is more useful to him, that is how I would decide. (y)

As an aside, going just one tooth bigger in the rear on my ZRX 1200 makes the difference between a dead heat in a 3rd gear 55 mph roll-on with an FJR1300 to walking away from the the same starting speed. With a small 280cc (300), he may not find the need to downshift two gears when he wants to “move out” with +2 in the rear.
 
If the gearing isn’t short enough to crawl in traffic as it is, like I said it makes that worse by going bigger up front.

That's the thing. The difference in 1st is so small, it won't be noticed. It's not as if going up one tooth will make first gear act like second. It simply raises the top speed of 1st by 1mph. It will give the more relaxed high speed cruise and gear spacing he wants.
 
I hear ya’, don’t disagree. Just trying to understand if it is already too tall in first gear and the lesser of his evils is the higher rpm on the open road, then going just a couple teeth up on the rear will help around town and not be as big of a change as as adding a tooth up front and going the opposite way with respect to making it even taller around town which is already an issue. Granted, it doesn’t make much difference in mph when comparing the sprocket sizes on gearing commander, but it’s a little engine and not a lot of oomph until it gets up there a ways in rpm.

Ok, slow Sunday evening... :) Did a dyno chart check and correlated the rpm/road speed. The engine maxes out about 18.5 ft/lbs at 6,600 rpm. At 4500 rpm that little 280cc tweeter is making 13-14ft/lbs, which is 30 mph with a 15/36 gear combo in 3rd gear. 5100 rpm is up to 16ft/lbs at 30 mph in the same gear with a 14/38 combo. 600 rpm difference (3 ft/lbs) is a 23% difference in torque, if the difference is only 2 ft/lbs, it’s still a 15% difference in output. The bike weighs 315 lbs wet, add a 185 Rider and that is 500 lbs rolling weight. My ZRX1200 for comparison with lighter exhaust and other mods, weighs 495 lbs wet. I am rather tall and weigh 275 lbs. That’s 770 lbs with an engine making 75 ft/lbs at 3500 rpm, 87 ft/lbs max. I can feel a big difference in 1 tooth up on the front compared to 1 tooth up on the rear. It makes a difference in feel with either more relaxed around town or a bit more power via higher rpm in the lower gears. Once on the open road it matters little to the ZRX, but the point being a small 280cc engine will only magnify the differences one way or the other and 600 rpm is a huge difference in output, percentage-wise relative to the weight it has to move around.

I like the more relaxed feel of taller gearing, so I am with you in the grand scheme, but with a litttle engine and not enough power to get out of its own way around town with already too-tall gearing in stock form, I would go up a couple teeth on the rear.
 
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