It you like practical math/physics stuff...

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

Sometimes I answer question for high school students about physics, below is my response about a question involved changing the gearing on a CBR600. This was one of the more interesting questions I got and I know some of you like this stuff. The bike comes with a 16 tooth front sprocket and a 42 tooth rear sprocket, they were asking about the difference in 0-60 if they changed to a 15 front and 45 rear.

Nick
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Let's say your stock bike went from 0-60 in 3 seconds. Make some assumptions, no slipping, uniform acceleration, no air resistance, etc...

Well, 60 MPH is 26.8 m/sec, so you accelerated at 8.94 m/sec^2. Let's say you and your bike and you are 250 kg (551 lb). The force used to accelerate you was 250*8.94=2235.2 N (502.5lb). This would be the force your tire is pushing with. So, your rear wheel torque is 502.5lb times the radius of your rear tire, 12.4 inches (1.03 ft), which is 502.5*1.03=519.14 ft-lbs. If you measured your sprockets radius you could then determine the force in you chain, my guess is it's about 6 inches (.5 foot). So, the force in your chain is 519.14/.5=1038.29 lbs. Finally, your stock ratio is 16/42, so the torque at the sprocket is (16/42)*519.14=197.77 ft-lbs. Using a first gear ratio of 2.666 and a primary ratio of 2.111, gives 2.666*2.111=5.63, so the torque at engine is 197.77/5.63=35.14 ft-lbs. If you look at the torque curve of a CBR600, this number makes sense. Also, remember the real 0-60 is less than 3 seconds for a stock CBR600.

Now, when you changed the gears it didn't affect the torque the engine put out, so the torque at the front sprocket is the same. The torque at the rear wheel is now (45/15)*197.77=593.31 ft-lbs. So, the force of your rear wheel is 593.31/1.03=574.28 lbs (2554.5 N). You new acceleration would be 2554.5/250=10.22 m/sec^2 and your new 0-60 time would be 26.8/10.22=2.625 seconds.

Finally, when you get a 0-60 around 2.7 seconds the tires begin to play a large role, normal street tires begin slipping. You need a tire with more grip...
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Avandia Law

J_DOGG · Posted: Apr 16, 2003 7:45 am Post subject:

Good stuff. my brain is in overload right now.....

From my rice rockets dayz I always just told people, dropping a tooth makes you get there faster but you lose top end speed. I'm simple like that.

PEACE

NAW · Posted: Apr 16, 2003 7:57 am Post subject:

That's right JDogg, kinda like changing a prop on a boat......Good work Otto, you're definetly an educated mofo... Cool

arlanj · Newbie Joined: 07 Apr 2003 Posts: 31 City: The Plains

I had a recent application similar. Had to slow down the speed of a meat grinder. The grinder already had a 15" pully and the 1/2 hp motor had a 3 inch pully. Tried a couple of smaller pulleys and finally went down to a 1 1/2 inch pulley on the motor and the grinder speed was just right.

Education pays off.

criminally_minded · Posted: Apr 16, 2003 10:38 pm Post subject:

Nick: Please don't do that to me again. Wink

Mariognarly · Addict Joined: 14 Jan 2003 Posts: 853

Wow, that brings back memories from physics classes. That makes a ton of sense, seriously it does. Good job on the explanation Otto.

Jester · Posted: Apr 17, 2003 1:55 pm Post subject:

To quote Ogre: (ahem) NEEEEEEEEEEEEEEEEEEEERDS!!!!!!!!!!! Laughing

Tig · Newbie Joined: 02 Mar 2003 Posts: 27 City: Mt. Airy, MD

My teachers were much more basic/applied.

1. when a big object smashes into a little object, the little object loses.

2. You can't push with a rope.

Maestro · Posted: Apr 18, 2003 1:02 pm Post subject:

That's why I didn't take physics this year... I hate school...

Dragonlady8 · Guest

I like physics. Especially when applied to Biomechanics. All I can say if I can understand physics anyone can! Shocked

salmon_tacos · Posted: Apr 18, 2003 4:32 pm Post subject:

Did I actually just read a post about the gearing of a meat grinder?

There's just something surreal about that.

So what happens when a meat grinder goes too fast?

criminally_minded · Posted: Apr 20, 2003 9:45 pm Post subject:

Splatterfest. Very Happy

Mister C · Posted: Apr 20, 2003 10:09 pm Post subject:

It was a motorcycle, but why would you want a CBR600? Personally, that bike is too uncomfortable for me, and the insurance you gotta pay for that is astronomical.

wake152 · Posted: Apr 20, 2003 10:12 pm Post subject:

im a senior in college and can proudly say ive never taken physics and from that equation i never will.

Mister C · Posted: Apr 21, 2003 6:11 pm Post subject:

Personally, physics looks interesting, but i dont wanna have to put the time and effort in to learn it.

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

Insurance is actually pretty cheap, about 315 or so a year for full coverage on a 25 year old...if you only get liability it's like 150. If you don't shop around you can get a bad deal...

criminally_minded · Posted: Apr 22, 2003 4:42 am Post subject:

Otto: I have a challenge/question for you, if you're up for it... Very Happy

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

Bring it on...
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Coach handbags

criminally_minded · Posted: Apr 22, 2003 6:00 am Post subject:

Ok, this is a fairly simple concept, but I might have some trouble explaining it, bear with me.

I was traveling up a steep road the other day, and it started me thinking. I can't answer this, so I hope you can.

Generally if you are traveling up an incline which is a set angle (say, 15 degrees) and you travel a set distance, (1 mile for example), then you can also figure out the distance you have travelled vertically (risen).

It is also true that, if you were to travel at this same angle (15 degrees) for 1.1 miles, you would have travelled further vertically as well.

Now, imagine a conical shaped mountain. Carved into the side of this mountain is a 2 lane highway, sloped at a 15 degree angle and spiraling up the mountain from the bottom to the top.

Both lanes travel the same distance vertically (the rise), and both are on a 15 degree incline, but if you were to drive 2 cars up the highway, side by side, the car on the outer lane would have covered more distance at its wheels than the car on the inner lane by the time they both reached the top.

How can this be? If they are both traveling at 15 degrees, and one car drives a greater distance than the other, how is it that they can end up at the same point vertically (same height).

It has me stumped.

Ok, I have just finished work, and I have tomorrow off (no net access), so that gives you 'till thursday to explain it to me! (It's gotta be something really simple... I just can't wrap my head around it) Have fun!

criminally_minded · Posted: Apr 22, 2003 6:03 am Post subject:

Nevermind, I just read through what I wrote and I figured it out by myself.

I am such a dumbarse, a very tired one.

Catch you Thursday.

Mister C · Posted: Apr 22, 2003 4:32 pm Post subject:

The reason this is because the outer lane has to travel a slightly farther distance.

salmon_tacos · Posted: Apr 22, 2003 5:07 pm Post subject:

He said that already. That was one of the things he was correct about. Since his description seemed impossible, obviously one of his assumptions was wrong. It turned out to be the assumption that the incline on the inside was the same as the incline on the outside. In fact, the incline on the inside is greater than the incline on the outside.

Of course, he figured that out already so whatever.

ohsix · Posted: Apr 22, 2003 5:12 pm Post subject:

i'll try to explain it. the further outside you get on the road the less the angle so the whole road isnt actually a 15 degree incline. i guess you already figured that out though. if you were walking up the inside of the road (closest side to the mountain) you would be walking up a more steep grade or angle than if you walking up the outside of the road.

ohsix · Posted: Apr 22, 2003 5:12 pm Post subject:

damnit. salmon beat me to it.

criminally_minded · Posted: Apr 23, 2003 10:00 pm Post subject:

Yeah I figured it out about 10 seconds after I hit 'reply'. I was going to delete it, but then I though, what the hell, maybe someone equally as stupid will also be stumped for all of 5 minutes Laughing

Mister C · Posted: Apr 24, 2003 9:51 pm Post subject:

But too bad someone isnt as equally stupid as you are Very Happy