Gearing Question: Front vs Rear...

sixpack577

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Also, keep in mind that when doing low speed balance point wheelies your chain pull is almost nothing so the difference in loads perpendicular to the swing arm is also almost nothing.

Low speed to upwards of 120mph+.
I can't see the speedometer riding a standup:laugh:
Only measured against a car beside me, or seated with the front wheel roughly a foot/ foot and a half high passing 140mph on the speedo.
 

Dennis

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Low speed to upwards of 120mph+.
I can't see the speedometer riding a standup:laugh:
Only measured against a car beside me, or seated with the front wheel roughly a foot/ foot and a half high passing 140mph on the speedo.

Ok, rather than low speed I'll say less than full throttle wheelies. Swing arm forces are relative to torque.

You can give your dad my calculation explanation in my earlier post, along with the gear diameters. I'll measure some in a bit. I may be missing something but hopefully he catches it. I've looked on the internet for some suspension calculators but haven't found any yet.
 

sixpack577

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Ok, rather than low speed I'll say less than full throttle wheelies. Swing arm forces are relative to torque.

You can give your dad my calculation explanation in my earlier post, along with the gear diameters. I'll measure some in a bit. I may be missing something but hopefully he catches it. I've looked on the internet for some suspension calculators but haven't found any yet.

Most of them are near or at the rev limiter.
If I can catch perfect balance in too high of a gear for the speed I'm running, then I can keep them at a much lower rpm.
I'll read back through your posts and see what I can come up with.
 

Dennis

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Most of them are near or at the rev limiter.
If I can catch perfect balance in too high of a gear for the speed I'm running, then I can keep them at a much lower rpm.
I'll read back through your posts and see what I can come up with.

Post 37

The torque you are producing (and resultant chain pull) is dependent upon throttle opening and rpm. You can be at 11k rpms and not producing much torque if you are at 1/3 throttle opening and steady engine speed. If you are on the limiter you aren't making much torque at all. You won't see maximum swing arm forces unless you are at full throttle and not on the limiter.
 

sixpack577

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You post the front sprocket diameters then.
I have a 17t I need to find, but I don't have the time now to pull the sprocket cover and chain, especially if you can find the diameter of the 18t.
Please excuse my tired brain, but be more specific as to what I need to ask(I did re-read the posts).
I can give gear ratios, sprocket diameters(wheelbases will slightly vary depending on chain tension), but what specifics do you want to know...I'm not an engineer, you and him are.
I don't want to get into the conversation and then he asks for a factor that I do not have to give.
I think this is going to turn into a .000001" debate:laugh:, wait, it already is:laugh:

I was typing when you were, post 37
 

sixpack577

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Post 37

The torque you are producing (and resultant chain pull) is dependent upon throttle opening and rpm. You can be at 11k rpms and not producing much torque if you are at 1/3 throttle opening and steady engine speed. If you are on the limiter you aren't making much torque at all. You won't see maximum swing arm forces unless you are at full throttle and not on the limiter.

Ok, that I can agree with, as the engine's powercurve and peak tq/hp would have to be considered(right?).

The swingarm part I simply do not know, as I would think that rider weight and body position(standing wheelie)would somehow contribute to that?
 

sixpack577

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I'll be back tommorrow to see if you have the sprocket diameters(all I really need is the 18t).
I'll then run it all by my Dad over the weekend or hopefully friday evening. Then I'll wait a few days for a verdict, or else get more numbers than we agree to disagree that can or can't be felt:laugh:
Goodnight:beerchug:
 

Dennis

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Yes, there are endless numbers of mathmatical answers that could be calculated. For me, the one that matters is the one you can relate to. For example, in stock conditions at max torque, calculate bike squat at the seat and you could have one value you can relate to. Change to the other two gear ratios and see what the difference is in squat. I predict the difference between the two new ratios will be less than the difference between either new ratio and the original. I predict the difference in total squat between the two new ratios will be a tiny fraction of the total. I would then question that you could tell the difference. In the end it still is a subjective result if the differences are small, less so if I'm wrong.

Gears:
Really we should be able to calculate these from chain specs, but I didn't think to measure a chain. I have a 16 tooth, 18 tooth and several 43 tooth gears in my toolbox. 17, 18, 45 and 46 are in use. I think it is better to calculate sizes based on one measurement so a consistant measuring error goes into each size.

I tried to measure "effective" dia, essentially the center of the pin if it were on the gear. Your dad will need some other measurements like center distance between drive and driven sprockets, angle of shock, etc but you can get that. Maybe 700 pounds/in spring rate is a good number?

Tooth Measured Dia Calculated Dia
43 8.375 8.375
46 8.959

16 3.111
17 3.306
18 3.500 3.500
 

Dennis

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Well I can't get my columns to line up in the above post but you should be able to figure out three columns. I only have measured dia for 18 and 43 tooth, the others are calculated.

Yes body weight, position, etc all play into what happens but we are holding them constant and only looking at the effects of chain pull as a result of chain angle and rear sprocket tangency point change.
 

SoCal Blur

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Alright,

As promised I was able to get some measurements of the amount of wheelbase shortening that took place when I went from a 40 tooth stock rear sprocket to a 43 tooth rear sprocket. Also a new stock length chain (112 links).

First, I was incorrect with my previously stated 2 inches. When I measured again, I suddenly remembered exactly what I did. My first measurement was actually not the amount of movement forward but simply the distance the axle was from the end of the swing arm which is about 2 inches. Guess I my memory failed me that day.

2inch.jpg



Before I replaced the rear sprocket and chain, the flat side of the adjuster was even with the end of the swing arm. After I replaced the rear sprocket and chain, the flat side of the adjuster had moved forward about 1 inch from the end of the swing arm. So the the wheelbase actually shortened by about 1 inch, not 2 inches as previously stated. My apologies for the inaccuracy.

1inch.jpg


Even at 1 inch instead of 2 inches, I believe that the difference is still noticeable with the tendency of the front end to rise under power.
 

sixpack577

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Alright,

As promised I was able to get some measurements of the amount of wheelbase shortening that took place when I went from a 40 tooth stock rear sprocket to a 43 tooth rear sprocket. Also a new stock length chain (112 links).

First, I was incorrect with my previously stated 2 inches. When I measured again, I suddenly remembered exactly what I did. My first measurement was actually not the amount of movement forward but simply the distance the axle was from the end of the swing arm which is about 2 inches. Guess I my memory failed me that day.

2inch.jpg



Before I replaced the rear sprocket and chain, the flat side of the adjuster was even with the end of the swing arm. After I replaced the rear sprocket and chain, the flat side of the adjuster had moved forward about 1 inch from the end of the swing arm. So the the wheelbase actually shortened by about 1 inch, not 2 inches as previously stated. My apologies for the inaccuracy.

1inch.jpg


Even at 1 inch instead of 2 inches, I believe that the difference is still noticeable with the tendency of the front end to rise under power.

I belive that a wheelbase shortened by an inch can make a difference in wheelies, as it can in curves.
 

sixpack577

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Yes, there are endless numbers of mathmatical answers that could be calculated. For me, the one that matters is the one you can relate to. For example, in stock conditions at max torque, calculate bike squat at the seat and you could have one value you can relate to. Change to the other two gear ratios and see what the difference is in squat. I predict the difference between the two new ratios will be less than the difference between either new ratio and the original. I predict the difference in total squat between the two new ratios will be a tiny fraction of the total. I would then question that you could tell the difference. In the end it still is a subjective result if the differences are small, less so if I'm wrong.

Gears:
Really we should be able to calculate these from chain specs, but I didn't think to measure a chain. I have a 16 tooth, 18 tooth and several 43 tooth gears in my toolbox. 17, 18, 45 and 46 are in use. I think it is better to calculate sizes based on one measurement so a consistant measuring error goes into each size.

I tried to measure "effective" dia, essentially the center of the pin if it were on the gear. Your dad will need some other measurements like center distance between drive and driven sprockets, angle of shock, etc but you can get that. Maybe 700 pounds/in spring rate is a good number?

Tooth Measured Dia Calculated Dia
43 8.375 8.375
46 8.959

16 3.111
17 3.306
18 3.500 3.500



I had assumed that the length from center to center of front to rear sprockets would be needed.
I honestly have no time this weekend to switch sprockets and measure each.
Is that a distance you can calculate?(surely somehow it's possible).
I also see the direction this is heading.
There are many variables that will change the exact numbers.
Rider weight, chain tension, engine powercurve, rpm of peak hp/tq, ect.
All of which will effect final numbers, but still probably not enough on paper to make a convincing argument(on my end).
If you can calculate the sprocket distances, great. If not, I'll have to try to make time in the next week to do so.
If it does have to wait I would seriously like to continue this.
It's educational if nothing else.
In my defense I stand by my opinion.
I also AM NOT that guy who always feels the big power gain. I'm actually the opposite, and expect little to no noticeable gains from modifications. I'm suprised when I really do.
I will discuss it more with my Dad(as said he doesn't ride), but his opinion will probably closely follow yours.:laugh:
It's been another long day, so goodnight.
I am enjoying this thread though.:beerchug:
 

JGGUNS

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Boy, this thread has gone south!! Who really gives a crap? As long as everyone likes the gear they are running then the debate over mathematical calculations really don't matter. I happen to think that that +3 feels and behaves differently than a-1 front, as does Marty. No .00005 calculation difference that can be done will change the way we feel about that so I ask again, who cares?
 

Dennis

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Boy, this thread has gone south!! Who really gives a crap? As long as everyone likes the gear they are running then the debate over mathematical calculations really don't matter. I happen to think that that +3 feels and behaves differently than a-1 front, as does Marty. No .00005 calculation difference that can be done will change the way we feel about that so I ask again, who cares?

Apparently you don't.
 

Dennis

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I had assumed that the length from center to center of front to rear sprockets would be needed.
I honestly have no time this weekend to switch sprockets and measure each.
Is that a distance you can calculate?(surely somehow it's possible).
I also see the direction this is heading.
There are many variables that will change the exact numbers.
Rider weight, chain tension, engine powercurve, rpm of peak hp/tq, ect.
All of which will effect final numbers, but still probably not enough on paper to make a convincing argument(on my end).
If you can calculate the sprocket distances, great. If not, I'll have to try to make time in the next week to do so.
If it does have to wait I would seriously like to continue this.
It's educational if nothing else.
In my defense I stand by my opinion.
I also AM NOT that guy who always feels the big power gain. I'm actually the opposite, and expect little to no noticeable gains from modifications. I'm suprised when I really do.
I will discuss it more with my Dad(as said he doesn't ride), but his opinion will probably closely follow yours.:laugh:
It's been another long day, so goodnight.
I am enjoying this thread though.:beerchug:

I can measure approximately the center distance between the sprockets. A method I use a lot is to do quick estimates to see if further work is needed. I think that is all that is needed here, we don't need and won't ever get to the exact ansewr. The important thing is to keep things constant and only vary what we are looking at. We can assume chain tension, engine torque output, rider weight, etc. are the same. We are only trying to see the relative difference compared to the total.

I believe we'll also need to know the angle of the chain on the rear sprocket for all conditions and where the tangency point is. If I had this I could do the calcs myself but I may be missing something in my logic.
 

sixpack577

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I don't know a practical way to get chain angle under all conditions.
Sounds like a good way for the chain to eat a protractor.:laugh:
I also continue to see this growing into yet an even bigger equation...which will be over my head(regardless of whose favor it would be in).
I'll discuss it with my Dad on Sunday. Again though, I think he's going to tell me that there are too many variables to draw a practical conclusion. And, or, predict or conclude numbers with very small variance. Or at least not enough to prove conclusively on paper that there is a big enough difference to actually feel.
I have went over this repeatedly in my mind, and I still come back to my original thoughts. Yes, I can tell.
I do admit that apparently not everyone can, and I was unknowingly making that assumption.
I'll be happy to read any more information you come up with.
If my Dad or myself should have any suprising information, I'll be sure to post it.
In the meantime I'll just let whomever run whatever sprockets they like and draw their own conclusion.
I concur:beerchug:
 

sixpack577

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Boy, this thread has gone south!! Who really gives a crap? As long as everyone likes the gear they are running then the debate over mathematical calculations really don't matter. I happen to think that that +3 feels and behaves differently than a-1 front, as does Marty. No .00005 calculation difference that can be done will change the way we feel about that so I ask again, who cares?

I can agree, but I wanted to know if it was possible to prove on paper.
I think it is, but that the numbers will be small, like the difference in gear ratios between 17/43 and 18/46.
At least not enough to argue as undeniable proof.
I'm happy with my gearing too. I can do the same thing with a stock geared bike as I can with any other gearing(aside from the difference in mph, before anyone points that out).
Guns, you are a hooligan...and I totally respect that!:laugh:
 

Dennis

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I'll measure one tomorrow after I'm done putting nitrous on a buddy's bike. We don't need to measure chain angle, that is easy enough to calculate. What I've been thinking about is how to calculate sprocket center distance for the different combinations. Sort of the chicken or the egg thing. The chain length stays the same so as the center distance changes the angle and engagement length change.
 

sixpack577

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I'll measure one tomorrow after I'm done putting nitrous on a buddy's bike. We don't need to measure chain angle, that is easy enough to calculate. What I've been thinking about is how to calculate sprocket center distance for the different combinations. Sort of the chicken or the egg thing. The chain length stays the same so as the center distance changes the angle and engagement length change.

I was thinking of the chain angle changing with the weight put on the swingarm.
And the weight put on the swingarm changing depending upon several variables; both wheels on the ground with a seated rider, versus a standing wheelie without weight on the seat. The heigth of the wheelie changing the amount of weight applied to the swingarm(different balance points depending on front wheel heigth and counter balance/body weight possibly affecting this?)
 

Dennis

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I'm only going to calculate at one condition and compare the results. The angle will stay the same relative to the arm anyway. The idea is to see if the CHANGE in chain pull is significant compared to the total pull.
 
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