Is there a difference?

Oscar Aguilera · Joined: 18 Jul 2001 Posts: 1614

OK last one and then I'm through with this one. You take what MG typed.

40/80 and a 20/40 same ratio.

And bsed on what MG typed the front in each case is spining twice as fast. Compare the two ratios and the 20 front is spining twice as fast as the 40 front.

They are hooked to the same motor, but the motor can only rev at one rate. The smaller will reach one rpm sooner than the larger. That's it I'm done.

One beer please. I don't even drink but maybe 3 times a year, but I need a beer after this.

Oh ya, on dyno runs the motor builder only reads what the motor does (max rpm) at a given load, not how long it took to reach rpm with a load.

I will read what you guys type however.

[ October 18, 2001: Message edited by: Oscar Aguilera ]

Rick Blood · Posted: Thu Oct 18, 2001 9:11 pm Post subject: Is there a difference?

Oscar, Oscar, Oscar

Keith Archambeau · Posted: Thu Oct 18, 2001 10:19 pm Post subject: Is there a difference?

Yea, but the 100 tooth driver has a bunch of holes in it and is made from carbonunobtainiumfiber and is lighter than the 10 tooth.
RACE!

John Learmonth · Posted: Fri Oct 19, 2001 1:13 pm Post subject: Is there a difference?

quote:
Originally posted by Oscar Aguilera:

And to further explain, this change will alter the place on the track at which the motor reaches that magical, perfect rpm when you should BANG to the next gear.

So when you used to up shift at 2 feet from the corner, you will now shift at a different spot closer or further depending on which way you go with your SAME RATIO gear change be it a larger CSS or smaller CSS.
.

Oscar, I'm not meaning to be deliberately sceptical, but I think the effect you're experiencing is called the 'placebo' effect.

When you make an adjustment in the expectation or hope of a change its all too easy to experience what you hope for even if it doesn't actually occur. Been there!

Pete Muller · Posted: Fri Oct 19, 2001 4:56 pm Post subject: Is there a difference?

quote:
Originally posted by Oscar Aguilera:
So another analogy: This one most pepole can do at home without testing at the track.

Take your average mountain bike and find the front gear that is 42 and shift to the gear that is 20 in the rear. From a dead stop see how long it takes you to pedal to 5 MPH cranking normally. Then take the same bike and change to the front gear that is 32 and change to the rear gear that is 16 and do the same. Stay sitting down for maximum effect. You should exert less energy and reach 5 mph faster with the smaller front driver.
The final gear ratio is close enough to say they are the same and still see the differnce.

Sorry Oscar, but in cycling terms... "close enough" doesn't work.

Not only are the ratios [you use] different (one is 2.1/1, the other is 2.0/1... which is a BIG difference on a bicycle), but there's a very good chance that the 42/20 is cross-chained significantly, and the 32/16 is probably quite straight.

PM

Pete Muller · Posted: Fri Oct 19, 2001 5:01 pm Post subject: Is there a difference?

quote:
Originally posted by Oscar Aguilera:
OK last one and then I'm through with this one.

Compare the two ratios and the 20 front is spining twice as fast as the 40 front.

They are hooked to the same motor, but the motor can only rev at one rate. The smaller will reach one rpm sooner than the larger.

Surely you're kidding!?

The reason the motor revs at "one rate" (I'd have to assume you mean: accelerates at a given rate) is because there is a given load, which.... is dictated by the gear ratio.

PM

Chuck Bunnell · Posted: Mon Oct 22, 2001 8:00 am Post subject: Is there a difference?

Oscar, you really need to spend some serious time with a first year physics book. Go back to my first post and re-read it. It answered the question you've posted. You've since changed your question but with vague terms and mixed nomenclature which is half wrong. If anyone should be buying beers, it is you for us. I fear you are the one giving new karters bad advice.

If you have the same ratio with two different sets of gears for the axle and countershaft, (or PTO for clutch karts), there will be negligible difference in performance in all respects. The smaller gearset will have slightly less rotational inertia and mass, and as a result will allow a faster acceleration. Accleration is the rate of velocity change with units of distance per time squared. Peak engine rpm, (top speed), will still be dictated by gear ratio and load. Nothing will change that. I rambled on about the other changes earlier, go back and read it again. We're definitely picking the fly **** out of the pepper here. Driver error and inconsistancy will account for larger changes than what we're talking about here.

It seems you are changing your question to be about just changing one half of the gearset at a time. First the countershaft and then the axle making each one smaller. But you didn't say what the changes were and what the different ratios were. Say you started with a 17-23 which is a ratio of 1.353 and then changed to a 16-23, (made the front smaller), and now have a ratio of 1.438, a fairly big change. The kart will accelerate quicker but top speed will be reduced. So now you make the back smaller to "make up for it". Now we have a 16-22 which is a ratio of 1.375. To select your gear ratio properly you really need to use a ratio chart to be able select a gearset that is the next step one way or the other. Most times you will need to replace both gears on a shifter to make the smaller step. Do the math.

I'm a little grumpy today. Sorry if it shows.

Larry Ferguson · Posted: Mon Oct 22, 2001 2:20 pm Post subject: Is there a difference?

A Pepsi? Why you...
Just what I thought. You've just been settin' us up to see who would be found in the gutter first. Shame on you!!!

IMO, as many have stated, ratio is ratio. However, the larger the dia. of the sprocket the better. Remember, these poor little chains were designed to rotate around sprockets that are considerably larger in diameter than those on a shifterKart (100cc excluded). The only difference being that they both share simular drive gears. I dunno, sounds good to me.

David Tallant · Joined: 18 Jul 2001 Posts: 35

The 19/28 will have more torque. This is not because it is bigger in diameter, but lower in gear ratio. A 19/28=1.47368 where as a 15/22=1.46666.

Oscar Aguilera · Joined: 18 Jul 2001 Posts: 1614

Alright, I know there really is no difference, and I have hashed it out in my head to try to find one, way before this deal we just did.

Yall came back to saying the same things I cancelled out to myself. There is no difference.

The only thing no one pointed out was that there aren't too many gear ratios that cross over exactly the same to worry about in the first place.

I still think the motor would have more leverage but I can't prove it. Usually when I switch to the smaller set that is close it is a faction of a lower gearing to begin with. This is what changes shift points more than anything and that is because you change gear ratios.

I wasn't instigating I truly was hoping to find a difference.

I'll buy a case, first come first serve.

I didn't mean that anyone's advise was bad, or that mine was better. I only was trying to emphasize that drivers should always do their own testing in the end. When I type it is always sounds so good till I reread it the next day.

PS, In an effort to retain more knowledge I ate my physics book.

Pete Muller · Posted: Mon Oct 22, 2001 7:54 pm Post subject: Is there a difference?

quote:
Originally posted by Oscar Aguilera:
I still think the motor would have more leverage but I can't prove it.

Oscar,

The instantaneous power an engine produces is described with the term "foot pounds".

Your assumption that a smaller gear somehow gives the engine "more leverage" would be akin to say that an engine produces more torque if measured in inch pounds than foot pounds. If an engine produces 10 ft.lbs. of torque... it produces exactly and precisely 120 in.lbs. of torque.

The length of the [measuring] lever... whether it be a gauge of some sort... or your sprocket... is meaningless.

Very, very basic physics.

PM

Oscar Aguilera · Joined: 18 Jul 2001 Posts: 1614

It is still something that erks me. Based on all the write up, if you put a 200 tooth sprocket on the front and the same gear ratio with a 10 tooth in front the second time, the motor would rev up and too the exact same rpm at the same amount of accelleration?

If you had a 2foot long torque wrench and tightened a bolt to 200 ft pounds, how much less energy, force, weigth would you have to use to turn a 4 foot torque wrench to the same foot pounds? The motors work from the coutershaft out as opposed to a wrench where the force is at the outer edge.

As sensitve as these motors are there must be a difference but maybe it is too small. I don't disagree I just want an answer that I can feel better with. These are examples I have dealt with to myself, the torque wrench is new.

take a clock that has a 1 foot face, and take a clock that has a 10 foot face. The gears are just ratios inside. Would the motor that powered the two if they were built exactly the same require the same amount of power? If the larger clock was outside would the wind against the second hand slow the clock motor down given all the gear ratio in a single clock?

I am not a clock maker nor to I pretend to know clocks, just another philisophical view. There are too many in karting you know.

I'm starting to sound like Paul Kish

Pete Muller · Posted: Tue Oct 23, 2001 6:06 am Post subject: Is there a difference?

Oscar,

It appears that your conjecture is a moving target.

Your "clock analogy" does not relate to a kart (or the original intent of this thread) in any way: The forces that would act on your hypothetical second hand are not a "ratio". Your question is akin to asking "if I push on the end of a one foot lever... and push [with the same force] on the end of a ten foot lever... which would require more power to rotate from the far end?"

You asked:
...if you put a 200 tooth sprocket on the front and the same gear ratio with a 10 tooth in front the second time, the motor would rev up and too the exact same rpm at the same amount of accelleration?

The answer is simple:
The difference in acceleration could be precisely calculated based on the moment of inertia of the rotating parts.

As I stated in a previous message: in the context of the size sprockets that we have available to run on a kart (small enough so the rear sprocket clears the ground... and large enough so the front sprocket is larger than the crankshaft), the differences (in moment of inertia) are insignificant.

Rick Blood · Posted: Tue Oct 23, 2001 6:37 am Post subject: Is there a difference?

With your example, the 2 foot torque wrench would need 100 lbs. to tighten the bolt to 200 ft. lbs. and the 4' would need 50 lbs.
The reverse is, a motor developing 200 ft.lbs. of torque would generate 100 ft.lbs. on the short wrench and 50 ft.lbs. on the long one. This energy is then directly transfered to the rear sprocket where it is applied and magnified opposite of the way it was generated. If you had a 1 to 1 ratio, the 100 would become 200 and the 50 would become 200. A 1.5 to 1 ratio would result in 300 ft.lbs. in either case.

The clock example won't work because the hands on the clock are balanced so length does not matter.

I applaud your desire to fully understand the "WHY" in this question but you are driving me crazy in the process.

[ October 23, 2001: Message edited by: Rick Blood ]

Mike Goebel · Posted: Tue Oct 23, 2001 7:36 am Post subject: Is there a difference?

quote:
Originally posted by Rick Blood:

The reverse is, a motor developing 200 ft.lbs. of torque would generate 100 ft.lbs. on the short wrench and 50 ft.lbs. on the long one.

[ October 23, 2001: Message edited by: Rick Blood ]

You mean 100LB and 50LB force at the end of the short and long wrenches respectively. I know you just mistyped the info.

Mike G.