Changed Final Drive Gearing 2013

[ClassicVW_imp]

Bob's physics statements can't be merely called an opinion, just as you can't call belief in gravity an "opinion".

[rboe]

Yup. Physics is pretty much just measurements; no room for opinions. Advance a hypothesis based on facts (more the merrier); adjust the hypothesis until it fits the facts then you have a theory. Keep testing the theory until the facts don't back it up.

Lower gearing will let a motor spin up faster since you have given it better mechanical advantage for the given load, than a taller gearing. Which means at the top rpm you'll have to shift sooner. Unless you have geared it so low (think 4 wheel drive low) your speed advantage is nought (and don't think this is the case with the CB but if your times hold up, it could be).

[AzBob_imp]

I think they are both right depending on circumstances and expected outcome. When I raced motocross I raced against a friend that geared his bike down a tooth because he never got to top gear in 5 th, whereas I geared mine taller because 2 nd, 3 rd and 4 th were all I needed to negotiate the course. I always beat him to the first turn because I took off in second and could wind it a long way before shifting to 3 rd . He on the other hand had his bike geared low, took off also in second, but could only go a shorter distance in each respective gear. On the start I shifted once, while he shifted twice.

Not sure what physics would say but in our case taller gearing made it easier to get into the first turn first....that or I had better reflexes and a better line lol

Hows that for convoluted logic?

Thanks for posting Mickey::

Motocross riders change gearing all the time to suit track conditions. Long straights require taller gearing even in the dirt. If shorter gears where faster they wouldn't change. The only time they go to shorter gears is on a tight loose track where torque is required. forward momentum is more important than torque. Here's a good read.

http://twostrokemotocross.com/2010/12/sp...ould-know/

You have a fundamental misunderstanding of physics (which is not uncommon, so please don't be offended). If taller gears are "faster," why not just put in the tallest gears one can reasonably fit? Because taller gears reduce torque, lowering the rate of acceleration...

We can use physics/mathematics to prove this: The formula for acceleration is a = f/m (from f=m/a, which is Newton's second law of motion). In other words, the rate of acceleration is the force applied to an object, divided by the object's mass. If the mass is constant (as is the case when considering two identical bikes/riders), increasing the force (torque) will result in a linear increase in acceleration. You can see an example of this for yourself: drop a rock of any size to the ground. Now, throw the same rock at the ground, releasing from the same height. The thrown rock will get there a hell of a lot faster because you applied more torque to it. Gearing is the same thing. It gives you the ability to apply more force (torque) to the same mass. Lowering the gear ratio increases the torque, as we all agree, which will increase the acceleration, since we know that increasing the torque will linearly increase the acceleration of the object.

An example using motorcycles: take two identical motorcycles of identical loaded weight, with riders of identical skill in standing start races. Gear one lower and one higher. Start out in first gear, and don't shift at the top of first and both riders will go to full throttle as soon as is practically possible. The race will be over for the bike when it hits redline and the rider will stop the bike. The lower geared bike will out accelerate the higher geared bike until it hits redline, but the higher geared bike will pass and travel further before hitting redline.

This example can be expanded to cover the situation we're talking about here: the fact that the lower-geared bike will out-accelerate the higher-geared bike will remain true regardless of the speed the bikes start off at, as long as both bikes start in the same transmission gear. So, if both bikes start off doing 50mph in 3rd gear, the lower geared bike will again out-accelerate the higher-geared bike, and the higher geared bike will again travel further before hitting redline in 3rd.

So, let's talk about a race between these two, identical (other than the final drive ratios) bikes and riders. As can be deduced from the example above, in a race between these two people then, the outcome, or winner, comes down to the rider with the lower-geared bike's ability to shift quickly and accurately (since he will likely have to shift more, or at least, sooner), and how far the race is (i.e. length, 1/4 mile, 1/8 mile, between stop lights, etc.).

(if the race is of a length that causes the lower-geared bike to hit top speed in top gear, the winner will then be a function of how long it takes the still-accelerating higher-geared bike to catch up to the now constant-speed lower-geared bike, and whether or not he can catch up before the end of the track/race course -- in its most simplistic, this is the situation called out in the dirt bike track, above, and is of primary concern when setting up a vehicle for any particular racing venue).

[Randy B]

I am sensing a spinning effect taking control.....

[CIP57_imp]

Bob, if two bikes with the same rider, same weight and same road conditions go head to head, from what you are saying the lowered gear bike should be faster 0-60 correct.

There is a sweet spot in gearing, you are assuming this situation or bike has that sweet spot. I'll give you the video, look at the 0-60 times what really matters here, the 19-38 gear ratio will outrun the stock gearing. I know i could have run a tenth or two better but I had a bad start off the line. The 0-100 times are faster as well, once i hit 3rd at 100 I'm long gone. Listen to the motor with the 19-38's it sounds sweet.

Bob, you seem like a nice guy and very knowledgeable, please take a look and give me your unbiased thoughts.

I have a 3.57 19-38's and 3.79 stock 0-60

Stock Gearing

http://vid1034.photobucket.com/albums/a4...50902b.mp4

19-38

http://vid1034.photobucket.com/albums/a4...qleggr.mp4

[CB4ME_imp]

A touch above 3600 RPM at 70mph and about 3050 rpm at 60 mph in 5th with 19-38 gearing.

[808_rider_imp]

I have no personal experience as to the effects of changing the final gear on motorcycles but my experience from riding multispeed street/mountain bicycles is in agreement with Bob. From a standing start, the lower the gearing, the quicker I can accelerate. On the rear wheel of my bicycle, if the chain is on a sprocket with 17 teeth, my bicycle will accelerate quicker than if the chain was on a sprocket with 12 teeth.

Not sure if my experience on bicycles translates over to motorcycles, but I just wanted to throw that out.

[the Ferret]

Same vid isn't it?

[CIP57_imp]

Same vid isn't it?

No different vid's

[rboe]

In physics, to cover your butt and to make sure other folks can do the same experiment to see if they get similar results you need a measure coarse, accurate clocks/timers, a means of accurately weighing the bike and a record of atmospherics. All variables have to be taken into account and the more runs you can do so you can average the results the better.

Unfortunately, and I don't want to sound mean here, but those videos are no better than hearsay. No attempt to show a measured distance nor any timing device. They neither support nor dispute your claim or Bob's.

Now it you two could meet at a drag strip, make several passes, swap sprockets and repeat more runs, then we'd have some real data. Plus the opportunity to sling mud in person. In good jest of course.