Gearing Question: Front vs Rear...

[saygbye]

think it has more to do with what your gonna do with the bike. if you want to drag race(without extensions) you want to change the front sprocket to set the rear wheel back as far as possible to try and prevent wheelies.

however, you you want the front to carve corners and wheelie and stuff you probably want to change the rear to bring the rear wheel foreward to shorten the wheelbase.

one does make a diffrence over the other. imho

 

[Tufbusa]

I think what Sixpack feels is the difference in chain pull. Altering the agle of the chain has an effect on how the swingarm responds to throttle.

Whomever decided that going up 3 in the rear shortens the wheelbase by 2 inches needs a new measuring stick. I've never actually measured it but I'd be surprised if it's much more than a half inch with a stock chain.

 

[SoCal Blur]

Undoubtedly wheelbase is a factor. Note I stated buying a new chain, that is to keep the wheelbase the same. If that is the only "feel" factor we are discussing then we agree. If you are going to tell me you can feel the extra friction of the chain wrapping tighter on a -1 gear or the extra friction of 4 more total teeth with a +3 gear on the back I won't believe you. I also don't believe a +3 gear shortens the wheelbase by at least 2".

Well I bought a new chain, the stock length (112 links) and I measured and the wheelbase was almost exactly 2 inches shorter going from the stock gearing. I'm sure my original chain was stretched a bit so I have to summarize that going from a -1 front sprocket to a standard front sprocket and a +3 rear sprocket will shorten the wheelbase at least as much as it did for me, if not more.

This has certainly turned into a fascinating discussion. Much more so than I had with my coworker.

 

[JGGUNS]

Undoubtedly wheelbase is a factor. Note I stated buying a new chain, that is to keep the wheelbase the same. If that is the only "feel" factor we are discussing then we agree. If you are going to tell me you can feel the extra friction of the chain wrapping tighter on a -1 gear or the extra friction of 4 more total teeth with a +3 gear on the back I won't believe you. I also don't believe a +3 gear shortens the wheelbase by at least 2".

More like 2 centimeters.

 

[jethro52185]

There have been a few other threads on this same topic. Let me start by saying that I'm very familiar with gears and ratios. I'm a machinist by trade, and there is "more than one way to skin a cat". As far as -1 equaling +3, well that is highly unlikely to add up exactly. Maybe jgguns can actually tell the difference in the seat of his pants. But in a perfect world if -1 equalled +3 and there was zero difference in wheelbase, the difference between the two would be zero. Final drive ratio is final drive ratio, I don't care how it is divided up. It is true that the chain may have to make a tighter turn around a -1 gear, but the horsepower or torque loss of this is negligible. Personally I have a -1 because I like the "thought" of having a longer wheelbase. Can I tell the difference in the half inch or so that I gained in wheelbase length? Probably not, but that's ok, my brain/placebo feels it, and after its all said and done, that's all anyone is trying to please in the end anyway.

 

[jethro52185]

This conversation reminds me of a similar situation in my garage the other day. I helped install hid's in my buddys r6. After the install, he complained for a week that the bike didn't seem as fast. He brought it back to my house and after some searching we found a plug that we had forgotten to plug back in. We plugged it back in and I told him to go test ride it and see if it was any faster than it had been. After the test ride, he came back all smiles, and explained that it felt much faster now, even faster than it was before the hid install. He was wondering if that plug had been unplugged the whole time he owned the bike, and if he had been robbed of time at the drag strip because of it. He was already making plans of picking up a half second in the quarter mile. I was sitting back laughing to myself this whole time, because apparently I was the only one that followed the unplugged plug back to the source.......it was the plug for his electric fan blades. It was 40 degrees, so I highly doubt that he even missed them the entire week he had been riding. My point is, never ever underestimate how much you "think" you can feel when it comes to seat of the pants differences in performance.

Has any one ever dynoed different gearing options and are willing to post the results? Very interested about this.

 

[SoCal Blur]

I think you may be overlooking two important points. 1) the wheelbase will be shorter with a +3 rear arrangement vs. a -1 front arrangement. 2) as Tuff mentioned, the difference in chain pull - altering the chain angle relative to the swingarm. Both of these result in geometry changes. If you are familiar with how your bike feels and behaves before these geometry changes, you WILL notice (i.e., feel) the changes. I think this supports what sixpack was saying about feeling the difference because, physically, there really is a difference between the two set ups even if the gear ratios are similar.

 

[jethro52185]

I think you may be overlooking two important points. 1) the wheelbase will be shorter with a +3 rear arrangement vs. a -1 front arrangement. 2) as Tuff mentioned, the difference in chain pull - altering the chain angle relative to the swingarm. Both of these result in geometry changes. If you are familiar with how your bike feels and behaves before these geometry changes, you WILL notice (i.e., feel) the changes. I think this supports what sixpack was saying about feeling the difference because, physically, there really is a difference between the two set ups even if the gear ratios are similar.

I touched on the wheel base length issue, and yes I believe that to be true. Out of curiosity how much bigger is a +3 sprocket in diameter than a stock sprocket? Is the difference in this measurement that much of a difference?

 

[GIXERHP]

Not when you have my tool box!

Rear sprockets are much, much easier to play with.

 

[SoCal Blur]

I touched on the wheel base length issue, and yes I believe that to be true. Out of curiosity how much bigger is a +3 sprocket in diameter than a stock sprocket? Is the difference in this measurement that much of a difference?

I wish I would have measured the diameter and I'm at work so I can't do it now, but it is noticeably larger. Next time I get a chance, I'll measure it and compare it to stock.

 

[The Big Red One]

I think you may be overlooking two important points. 1) the wheelbase will be shorter with a +3 rear arrangement vs. a -1 front arrangement. 2) as Tuff mentioned, the difference in chain pull - altering the chain angle relative to the swingarm. Both of these result in geometry changes. If you are familiar with how your bike feels and behaves before these geometry changes, you WILL notice (i.e., feel) the changes. I think this supports what sixpack was saying about feeling the difference because, physically, there really is a difference between the two set ups even if the gear ratios are similar.

Good points. I was thinking about going up 1 tooth bigger on the rear of my 14, a much heavier rider than me who also owned the same year 14 and had done it said don't waste your time, you won't feel it. I tried it anyway because thats all the room I had with the low mileage stock chain. I felt a very noticeable difference, and so did my even lighter friend There's a lot of small factors that can affect things. -1 down in front on the busa is more like 2 1/2 teeth up in back, so 3 up in back, with the slightly shorter more wheelie prone wheelbase, and the variables of different rider positions/weights on the bike, plus the points mentioned above, I could easily see how there could be a percieved difference between -1 in front and +3 in back. I know that just the -1 in front didn't give me quite what I expected acceleration wise, but when I added the 2 up in back it seemed like just as much or more of a change than just the -1 alone
If I was to do it again I would def try and make the changes on just the back sprocket if possible
And I agree, this has turned into quite an interesting topic

 

[Dennis]

Let's get some facts on record.

For a Gen-2 the stock ratio is 43/18 = 2.388. Front -1 is 43/17 = 2.529. Rear +3 is 46/18 = 2.555.
For Gen-1 the stock ratio is 40/17 = 2.353. Front -1 is 40/16 = 2.500. Rear +3 is 43/17 = 2.529.
The relative difference is about the same between Gen-1 and Gen-2. The -1 or +3 options are pretty close. As previously stated, it is about 2.5 teeth on the rear to equal one on the front. You are splitting some fine hairs to this makes a Busa feel more torquey vs feeling like a 1000. I can't imagine what a +4 tooth gear would do!

As for chain pull, I'd like to lay it out on CAD to see the difference in tangency point but I think my software license was reclaimed. I'll see if I can find someone to do it for me. If someone here who has experience doing this wants to take on the challenge that would simplify things.

A stock Busa arm has a total adjustment range of 1". I use only a small part of the range on a stock arm when changing gears +3". I went +2 from stock on my bike recently and added one link to keep the adjuster in the same place.

 

[SoCal Blur]

Hmmm. I will have to measure again. It's possible I started at the 1" mark instead of 0" as that's an old habit I was taught to not use the end of a ruler. Thanks for posting the pics, Dennis. I'll try to confirm this weekend.

 

[cdhoroho]

Dennis get me measurements of the gear diameters and ill cad them up for you
On prostreet bikes they run 19 or 20 front tooth and 48-50 rear tooth sprockets the larger rear does help in a way with adding traction by adding down force on the rear tire but this is hard to explain

 

[sixpack577]

I've never tried to stunt a motorcycle. I can reliably adjust my 1/4 mile time by .03 seconds when trying to hit an index, can you? The correct answer isn't determined by who has the most motorcycle skills, it's all physics and is independent of the rider.

I explained the last time why it is the same, and I know you are smart enough to calculate the ratios so you understand what I'm talking about. I do not accept subjective "feel" as proof. I'm not saying you don't believe it, but it's all in your head. You really need to explain the physics behind your claim if you want to have any credibility. Normally you give decent advice, but you really are off the mark on this one.

I have drag raced several bikes quite a few times over the years, but do not consider myself a dragracer by any stretch.
I simply don't have the desire or motivation to fight for tenths or even hundredths of a second(more power to you and those who do).
I was not talking about who has the most skill either, but simply what I do and how it feels to me.
A 2.53 vs a 2.56 gear doesn't really seem like it would be noticeable.
You however are wot asap and covering a 1/4 mile as qickly as you can.
You are comparing the miniscule difference you find in the gearing, assumimg every aspect of each run is the same.
I am balancing a bike close to vertical, and right at the rev limiter alot of times(without hitting it...front would drop).
I assure you if we had 2 identical Busas, one 17/43 and the other 18/46. I got on them from the right side unknowing of which I was riding. I would be able to tell you exactly which I was riding.
That may seem like a bs, but I'de put money on it.
I will say that maybe my opinion doesn't apply to the average rider, and I don't think it's in my head.
I tried 18/43, 17/43 and 18/46 on my 08 busa, sevarl times. I went with the 18/46 as it feels better on one wheel.
It's not that a shorter wheelbase makes it easier to get up either. I can ride them just fine bone stock. My wheelbase is roughly 1.25" shorter too, with chain slack in spec.
I respect your professinal opinion as an engineer. My dad is a mechanical engineer, as is one of my best friends, who also owns a busa. My dad doesn't ride, and my friend doesn't wheelie, so they leave the discussion at "they only know what the math says, but maybe it does feel different riding like that."
My uncle and late grandfather are/were physicists, and another good friend is also a mechanical engineer(me, I'm a blue collar joe with a 2yr tech school for mechanics). So if I know anything for certain from experience...it's that it's extremely difficult to persuade the engineering mind away from what the numbers say.
The 1/4 mile and the stunt bike are 2 different animals. I understand how yours works, but I don't think you quite understand how mine does.
I'm open for a good debate.

 

[sixpack577]

A 46t rear is roughly .60" bigger in diameter than a 43t. I have a 43 and 46 in my toolbox and I just measured them with calipers, tooth wear will vary, that's why I said roughly.

I do need to precisely measure the difference in wheelbase with both sprockets also.
I agree guesstimating is bad in that aspect, and I am guilty there.

 

[Dennis]

Dennis get me measurements of the gear diameters and ill cad them up for you
On prostreet bikes they run 19 or 20 front tooth and 48-50 rear tooth sprockets the larger rear does help in a way with adding traction by adding down force on the rear tire but this is hard to explain

I understand the concept. While I was on the treadmill I was thinking about how to calc the difference in spring compression based on the change in gear diameters. My thought process goes like this:

Given 100 ft-lbs engine torque, 1st gear ratio torque multiplication factor and effective drive gear diameter calculate chain pull.

Assume axle center and arm front mount shaft centerlines are level at peak torque

Translate chain pull into horizontal and vertical vectors at the rear sprocket tangency point. Vertical vector is load on arm beneath chain/gear tangency point. (my theory is this is the downforce you speak of).

Translate vertical load to spring mounting point based on ratio of lever arms (tangency point to arm pivot, spring mount to arm pivot).

Ignore front sprocket forces for simplicity (my gut says this is a small factor but I don't know this)

At this point we can calculate the spring compression distance based on spring rates and the angle of the spring, or translate that back to vertical motion at the seat, or at the tail, or wherever makes the most sense.

Do this for all three setups and note the difference. The debate then would be if the difference is noticeable so we probably still wouldn't have an answer!

This is just my thoughts, could be some errors, but a fun winter exercise anyway. If anybody is a suspension expert I'd be interested to get their input. I'll measure some gears after dinner.

 

[Dennis]

I have drag raced several bikes quite a few times over the years, but do not consider myself a dragracer by any stretch.
I simply don't have the desire or motivation to fight for tenths or even hundredths of a second(more power to you and those who do).
I was not talking about who has the most skill either, but simply what I do and how it feels to me.
A 2.53 vs a 2.56 gear doesn't really seem like it would be noticeable.
You however are wot asap and covering a 1/4 mile as qickly as you can.
You are comparing the miniscule difference you find in the gearing, assumimg every aspect of each run is the same.
I am balancing a bike close to vertical, and right at the rev limiter alot of times(without hitting it...front would drop).
I assure you if we had 2 identical Busas, one 17/43 and the other 18/46. I got on them from the right side unknowing of which I was riding. I would be able to tell you exactly which I was riding.
That may seem like a bs, but I'de put money on it.
I will say that maybe my opinion doesn't apply to the average rider, and I don't think it's in my head.
I tried 18/43, 17/43 and 18/46 on my 08 busa, sevarl times. I went with the 18/46 as it feels better on one wheel.
It's not that a shorter wheelbase makes it easier to get up either. I can ride them just fine bone stock. My wheelbase is roughly 1.25" shorter too, with chain slack in spec.
I respect your professinal opinion as an engineer. My dad is a mechanical engineer, as is one of my best friends, who also owns a busa. My dad doesn't ride, and my friend doesn't wheelie, so they leave the discussion at "they only know what the math says, but maybe it does feel different riding like that."
My uncle and late grandfather are/were physicists, and another good friend is also a mechanical engineer(me, I'm a blue collar joe with a 2yr tech school for mechanics). So if I know anything for certain from experience...it's that it's extremely difficult to persuade the engineering mind away from what the numbers say.
The 1/4 mile and the stunt bike are 2 different animals. I understand how yours works, but I don't think you quite understand how mine does.
I'm open for a good debate.

Maybe we should have your dad do the calcs. I'm an engineering manager now so I don't know how to do anything anymore.

I recognize there is a difference in chain pull forces. I have never calculated them but my gut feel (opinion) is we are talking about something that is a minor factor. The major factor is the gear ratio change, like 18/47 instead of 18/46. If chain pull were a major player then 17/40 would be notably different from 18/43. But hey, I could be wrong. Your comments relating the difference of 17/43 and 18/46 being similar to Busa vs 1000 would be MORE than major player in my book. This is what I take exception to.

Regarding drag racing, the chain pull load will also change wheelie characteristics.

 

[Dennis]

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.

 

[sixpack577]

Maybe we should have your dad do the calcs. I'm an engineering manager now so I don't know how to do anything anymore.

I recognize there is a difference in chain pull forces. I have never calculated them but my gut feel (opinion) is we are talking about something that is a minor factor. The major factor is the gear ratio change, like 18/47 instead of 18/46. If chain pull were a major player then 17/40 would be notably different from 18/43. But hey, I could be wrong. Your comments relating the difference of 17/43 and 18/46 being similar to Busa vs 1000 would be MORE than major player in my book. This is what I take exception to.

Regarding drag racing, the chain pull load will also change wheelie characteristics.

Fire away!
He likes doing things like this for me.
Give me whatever formula, example, ect. that you would like me to give to him.
Otherwise, with my explanation he's just going to give me gear ratios and say, "They're different, can you tell, I have no idea."
Also expect an answer to probably be a few days, early next week, by the time he gets to it.
He likes to think on things for a while, then he'll do it on paper after he gets time and has thought about it enough.
I would really like to see what we could come up with.