Drive ratio upgrade HOW TO: Belt Pulleys, Primary sprockets, improve TQ up to 13%
#41
01-22-2016, 11:22 AM
Road Warrior
Man you guys sucked me into this one LOL
I guess I should have said "at the crankshaft" IOW the output of the engine does not change. The point at which it is applied does.
I fully understand this, I applaud you for your efforts. I believe gearing changes like yours can be very useful. I'll take my bike for an example: I'm looking to change my gearing because at 60-65 mph I feel stuck somewhere between 5th and 6th, and depending on how fast of a rate I want to accelerate at I may or may not downshift. My goal is to tighten up the gearing a little so I can just roll on the throttle instead of down shift so much. By changing the gearing I'm moving the point at which the torque is applied. At the same 60-65 mph my engine will be running at a higher rpm and I will be farther into my torque curve.
I guess how I see it is: If mph remains constant and a gearing change is made the "increased Torque" felt is because the engine rpm is increased and it is running at a different point in the torque curve
Yep it's still a TQ increase mechanically- let me try to explain it, sorry if this gets long.
I'm going to present this in terms of gears and levers as it might simplify things. Below is a link to an excellent source of info on this topic, and I've provided the math calcs to back this up.
The purpose of the final drive pulleys ("gears") is to multiply the torque delivered by the engine and transmission to the wheel. Your F/R drive pulley combo ("gears") can be thought of as complex levers. In other words they provide mechanical advantage that multiplies work- in this case, torque, to help the engine's power move the bike.
Lower (shorter ratio) gears are like a longer lever: They provide more mechanical advantage.
Higher (taller ratio) gears are like a shorter lever: They provide less mechanical advantage.
It's similar to when you use a long breaker bar instead of a short ratchet handle to remove tight bolts. Just like a long bar puts more torque on a bolt or nut, lower ratio pulley combos (say 30/70 instead of stock 32/66) provide more torque to the wheel. This is quantifiable physics and it's right on the money.
So all that said, it's sort of easy to calculate the torque multiplication provided by your belt pulley combo at the wheel- just multiply:
(primary ratio) * (selected gear) * (final drive ratio) = overall ratio
(overall ratio) * (max crank TQ) = actual wheel TQ
Which is going to be a lot more at the wheel than the motor's TQ max due to force multiplication by the drive ratios. you'd be surprised!
So I'm not going to do the math but you can if you plug in the numbers from my charts on page 1.
But don't take it from me - please. Go to the expert source and read this short article on ratios and wheel torque.http://www.nrhsperformance.com/tech_power.shtml
It is a very good read and pretty easy to grasp. You'll then see how pulley ratio changes directly add to or subtract the amount of applied torque at the wheel. You'll also see why it is a verifiable fact that shorter drive ratio = faster acceleration and greater wheel torque. There is a limit to this benefit of course, and that is also outlined on the page. Hope this helps!
I'm going to present this in terms of gears and levers as it might simplify things. Below is a link to an excellent source of info on this topic, and I've provided the math calcs to back this up.
The purpose of the final drive pulleys ("gears") is to multiply the torque delivered by the engine and transmission to the wheel. Your F/R drive pulley combo ("gears") can be thought of as complex levers. In other words they provide mechanical advantage that multiplies work- in this case, torque, to help the engine's power move the bike.
Lower (shorter ratio) gears are like a longer lever: They provide more mechanical advantage.
Higher (taller ratio) gears are like a shorter lever: They provide less mechanical advantage.
It's similar to when you use a long breaker bar instead of a short ratchet handle to remove tight bolts. Just like a long bar puts more torque on a bolt or nut, lower ratio pulley combos (say 30/70 instead of stock 32/66) provide more torque to the wheel. This is quantifiable physics and it's right on the money.
So all that said, it's sort of easy to calculate the torque multiplication provided by your belt pulley combo at the wheel- just multiply:
(primary ratio) * (selected gear) * (final drive ratio) = overall ratio
(overall ratio) * (max crank TQ) = actual wheel TQ
Which is going to be a lot more at the wheel than the motor's TQ max due to force multiplication by the drive ratios. you'd be surprised!
So I'm not going to do the math but you can if you plug in the numbers from my charts on page 1.
But don't take it from me - please. Go to the expert source and read this short article on ratios and wheel torque.http://www.nrhsperformance.com/tech_power.shtml
It is a very good read and pretty easy to grasp. You'll then see how pulley ratio changes directly add to or subtract the amount of applied torque at the wheel. You'll also see why it is a verifiable fact that shorter drive ratio = faster acceleration and greater wheel torque. There is a limit to this benefit of course, and that is also outlined on the page. Hope this helps!
I guess how I see it is: If mph remains constant and a gearing change is made the "increased Torque" felt is because the engine rpm is increased and it is running at a different point in the torque curve
#42
01-22-2016, 12:36 PM
Road Warrior
For example, plug in a 15% increase in rear wheel torque due a change in gearing (which carries with it a 15% reduction in rear-wheel rpm, so you need to plug that in too), and one can see that power at the wheel stays about the same, with the various gear ratio changes.
In the most simple way I can think of "All the gear ratios do is determine where the engine output appears on the speedometer"
Last edited by Fat11Lo; 01-22-2016 at 12:51 PM.
#43
01-22-2016, 12:38 PM
Man you guys sucked me into this one LOL
I guess I should have said "at the crankshaft" IOW the output of the engine does not change. The point at which it is applied does.
I fully understand this, I applaud you for your efforts. I believe gearing changes like yours can be very useful. I'll take my bike for an example: I'm looking to change my gearing because at 60-65 mph I feel stuck somewhere between 5th and 6th, and depending on how fast of a rate I want to accelerate at I may or may not downshift. My goal is to tighten up the gearing a little so I can just roll on the throttle instead of down shift so much. By changing the gearing I'm moving the point at which the torque is applied. At the same 60-65 mph my engine will be running at a higher rpm and I will be farther into my torque curve.
I guess how I see it is: If mph remains constant and a gearing change is made the "increased Torque" felt is because the engine rpm is increased and it is running at a different point in the torque curve
I guess I should have said "at the crankshaft" IOW the output of the engine does not change. The point at which it is applied does.
I fully understand this, I applaud you for your efforts. I believe gearing changes like yours can be very useful. I'll take my bike for an example: I'm looking to change my gearing because at 60-65 mph I feel stuck somewhere between 5th and 6th, and depending on how fast of a rate I want to accelerate at I may or may not downshift. My goal is to tighten up the gearing a little so I can just roll on the throttle instead of down shift so much. By changing the gearing I'm moving the point at which the torque is applied. At the same 60-65 mph my engine will be running at a higher rpm and I will be farther into my torque curve.
I guess how I see it is: If mph remains constant and a gearing change is made the "increased Torque" felt is because the engine rpm is increased and it is running at a different point in the torque curve
With the shorter final drive ratio, your engine is turning more rpm for each more forceful wheel rotation, and this does result in some loss of top end speed per gear before hitting rpm redline than before (as per charts on page 1) - but - and this is most important - in our case it is not any loss because the bike came from the factory geared too tall to begin with. That loss of top mph per gear is no loss because the motor is well outside of its max TQ/ HP band anyway. Hence the reason you feel your bike is pokey at 60-65 mph. Stock, the bike is geared in 6th to not redline until 150mph+ - that is crazy town on the too tall side of gearing
We are shortening the max top speed of each gear, but the range of speed per gear you end up with is more optimal for our specific bikes (not other bikes or cars, our bikes only) and always feels powerful -sort of like how HD used to set them up pre 2006 and early sportsters. And now the bike will revv out faster / speed up faster because you have x% more torque going to the wheel via the drivetrain than before, and you're keeping each gear's speed range more within the optimal HP/TQ output range of the motor.
Hope I explained this ok and I think you already get it. This is not my info, it is a culmination of already existing info put into one place and in a hopefully easier to understand method.
Last edited by LA_Dog; 01-22-2016 at 12:55 PM.
#44
01-22-2016, 12:51 PM
What is the constant in this equation? MPH? At what point is the 15% being measured? If the increased torque applied is done by a higher engine rpm, then how can the wheel speed decrease as well. I would think that one of the variables needs to be held constant. If MPH is held constant and torque was increased by 15% by increasing the multiplier (gear ratio) then the engine RPM would also increase. If engine rpm was held constant the mph would decrease but the torque measured would increase for that particular mph?
Besides we are not discussing every aspect of every type of performance vehicle, which varies widely by type (car, nitro, 1/4 mile, top speed, nascar, etc) - for example with top speed cars, the drive ratio is taller being pushed by major horsepower motors. taller ratio for best top speed in that case is preferred. it does not matter how quickly it takes to get there. You can see then how the entire general subject can go in many different directions and variations. We are only discussing this as it relates specifically to current model HD's and remedying the existing performance issue with factory too tall gearing. Hope this helps.
Last edited by LA_Dog; 01-22-2016 at 01:17 PM.
#45
01-22-2016, 01:18 PM
Road Warrior
For there to be an accurate comparison the point at which the data is used has to be the same. If the engine's output is constant then there has to another constant where the measurement takes place. If the measurement before and after a gear change is taken at the same MPH then the wheel speed is constant. So an increase in the final drive ratio would result in more torque measured at that MPH due to increased engine RPM. IMO this supports the data that you have already posted and your argument. just dumbed down a bit. What I don't understand is how can the torque measured increase and the wheel speed decrease at the same time? This defies everything that I understand about automotive physics
#46
01-22-2016, 01:21 PM
Hey you guys, LA and Warp....I have been following this discussion for quite a while now with growing interest - cause there's so much valuable knowledge in your statements - and with a steadily growing grin....
I don't in any way want to claim to be an expert in drive train engineering, motorcycle performance tuning or track racing....I am just a guy who studied mechanical engineering some decades ago
.... although I've forgotten most of it
Blame it on me not being a native speaker in English but the more I read you guys arguing the more I come to the conclusion that there actually is no real dissent in what both of you are saying...I for my part think (won't prove with any official articles) that both of you are right to a major extent, you're just talking past each other....maybe it's a good idea to consult your pillows and re-read each other's posts tomorrow, perhaps the fog will lift.
I don't in any way want to claim to be an expert in drive train engineering, motorcycle performance tuning or track racing....I am just a guy who studied mechanical engineering some decades ago
.... although I've forgotten most of itBlame it on me not being a native speaker in English but the more I read you guys arguing the more I come to the conclusion that there actually is no real dissent in what both of you are saying...I for my part think (won't prove with any official articles) that both of you are right to a major extent, you're just talking past each other
....maybe it's a good idea to consult your pillows and re-read each other's posts tomorrow, perhaps the fog will lift.
#47
01-22-2016, 01:30 PM
Fat- it's the mechanical ratio leverage and there is math behind it. Erase any thoughts about the engine TQ. that is always the same. the drive train takes that crank TQ and it is multiplied based on the transmission an final drive ratios. Check the charts posted on page 1 for each pulley upgrade in the "Various data by gear" column. Note how the overall ratio of each individual gear is changed with the pulley upgrade. Each gear is shorter ratio and applies more force multiplication to the rear wheel. You are gaining sheer "grunt" brute leverage force, and also are able to wind out the gear faster (accelerate faster, quicker). It does not matter that the rear wheel is going to turn a percentage slower per engine rpm. It would only matter if you went to such a crazy ratio extreme that the rear wheel was turning way way less. but we're far away from doing anything even close to that. Heck even with the 30/70 pulley change, we are still far away from a pure performance overall drive ratio (in the 3.23 and upwards of 4.11 territory).
The formula for figuring the multiplied torque result at the wheel is posted on the last page I think- it's a bit longer formula but does support the data.
The formula for figuring the multiplied torque result at the wheel is posted on the last page I think- it's a bit longer formula but does support the data.
#48
01-22-2016, 01:38 PM
Hey you guys, LA and Warp....I have been following this discussion for quite a while now with growing interest - cause there's so much valuable knowledge in your statements - and with a steadily growing grin....
I don't in any way want to claim to be an expert in drive train engineering, motorcycle performance tuning or track racing....I am just a guy who studied mechanical engineering some decades ago .... although I've forgotten most of it
Blame it on me not being a native speaker in English but the more I read you guys arguing the more I come to the conclusion that there actually is no real dissent in what both of you are saying...I for my part think (won't prove with any official articles) that both of you are right to a major extent, you're just talking past each other....maybe it's a good idea to consult your pillows and re-read each other's posts tomorrow, perhaps the fog will lift.
I don't in any way want to claim to be an expert in drive train engineering, motorcycle performance tuning or track racing....I am just a guy who studied mechanical engineering some decades ago
.... although I've forgotten most of itBlame it on me not being a native speaker in English but the more I read you guys arguing the more I come to the conclusion that there actually is no real dissent in what both of you are saying...I for my part think (won't prove with any official articles) that both of you are right to a major extent, you're just talking past each other
....maybe it's a good idea to consult your pillows and re-read each other's posts tomorrow, perhaps the fog will lift.
#49
01-22-2016, 02:33 PM
Road Warrior
I have done nothing but compliment you and your post, I'm getting real tired of you talking down to me. I ended up in the middle of this because I can see what both of you are saying. Just like Eagle Ray said.
I do believe that's what we're talking about
Hence Final drive ratio, the steps (gears) are multiplied by a constant ratio, changing this ratio changes the overall ratio of all gears
Yes, that is all I'm trying to say. I can not speak for Mr Warp, but that's what I understand his point to be. In order for there to be a true comparison (apples to apples) the data has to be measured at the same point. That's why I'm asking Mr Warp what his constant is. What you say is true because the ratio change will apply more torque if MPH remains constant, what he says is true because the ratio change will decrease the rear wheel speed if engine rpm remains constant. Yes it does not matter because the seat of the pants feel of the bike will improve. The ratio changes that you documented so well are as I said before so subtle that the trade off in top speed is far outweighed by the increased responsiveness of the throttle, through increasing the multiplier of the torque.
All I was trying to do was to add some simplicity to this conversation, there is a wealth of great information here. We are splitting hairs here because it's a very worthwhile modification with a very small percentage trade off. I believe all of the math you have presented more than proves this. I think this info would be very useful to someone who didn't quite get what they wanted out of engine mods or needs help to make a not so ideal cam swap rideable. Hell, a simple pulley change would make a stage one or even stock bike for that matter a much more fun bike to ride I find all of this deep tech talk very entertaining, but I think a large number of forum members may look at the last few pages as pretty draining. IMO we do understand all that is going on here and I think all this effort would be put to better use trying to help others figure out if a gearing change would be in their best interest.
It would only matter if you went to such a crazy ratio extreme that the rear wheel was turning way way less. but we're far away from doing anything even close to that. Heck even with the 30/70 pulley change, we are still far away from a pure performance overall drive ratio (in the 3.23 and upwards of 4.11 territory).
The formula for figuring the multiplied torque result at the wheel is posted on the last page I think- it's a bit longer formula but does support the data.
The formula for figuring the multiplied torque result at the wheel is posted on the last page I think- it's a bit longer formula but does support the data.
#50
01-22-2016, 02:39 PM
Road Warrior
LA Dog, here's a link to the article again, to make it easier for others to read the whole thing and decide for themselves what they think it says.
http://www.nrhsperformance.com/tech_power.shtml
Fat11LO, It's probably easiest and most convenient to use engine rpm as the constant. That will keep engine output (at full throttle) the same for all the gearing ratios you might want to plug in, making it easier to distinguish which changes in wheel rpm and torque are due solely to the gearing changes.
http://www.nrhsperformance.com/tech_power.shtml
Fat11LO, It's probably easiest and most convenient to use engine rpm as the constant. That will keep engine output (at full throttle) the same for all the gearing ratios you might want to plug in, making it easier to distinguish which changes in wheel rpm and torque are due solely to the gearing changes.