Differences

This shows you the differences between two versions of the page.

--- techtalk:ref:svcproc11k [2023/10/29 00:54]
hippysmack [Torque vs Speed]
+++ techtalk:ref:svcproc11k [2024/01/21 21:01] (current)
hippysmack
@@ Line 26: / Line 26: @@
 {{:techtalk:ref:svcproc:gear_ratio_and_internal_torque_ratio_chart_by_hippysmack.png?direct&450|}} {{:techtalk:ref:svcproc:gear_ratio_and_overall_torque_ratio_chart_by_hippysmack.png?direct&450|}} \\
+The internal gear ratio chart shows the rate of how the transmission gears reduce speed and increase torque to the transmission sprocket (accept 5th GEAR). \\
+Changes to the internal ratios (1st-4th GEAR) affect final drive ratios and thus rear wheel torque and speed. \\
+The overall gear ratio chart shows the rate of how the (combined) ratios change engine sprocket torque and speed to the rear wheel. A lower gear provides a greater torque multiplication (drive ratio) between the engine and the rear wheel. Our motorcycles accelerate harder, the lower the gear they are in. Downshifting to a lower gear has the effect of increasing drive ratio and thus increasing the torque multiplication between the engine and the rear wheel. ((AC2W of the XLFORUM https://www.xlforum.net/forum/sportster-buell-motorcycle-racing/sportster-motorcycle-drag-racing/36229-when-to-shift-peak-hp-or-tq/page3?t=70371&page=3)) \\
+The values are ONLY ratios. They do not show how much torque is produced. They do show at what (rate) torque is multiplied through the different gear teeth changes. \\
+More rpm equals more torque in any transmission GEAR and given at the (rate) shown. \\
 ====== General Terminology ======
@@ Line 51: / Line 59: @@
 {{:techtalk:ref:svcproc:gear_ratio_-_driver_and_driven_gears_in_neutral_by_hippysmack.png?direct&450|}} {{:techtalk:ref:svcproc:gear_ratio_-_driver_and_driven_gears_in_1st_by_hippysmack.png?direct&450|}} \\
-===== Torque vs Speed =====
+===== Torque vs Speed (ratios) =====
-The gear ratio shows the trade-off between torque and speed. Speed is RPM and Torque is PUSH. ((https://motorcycleinfo.calsci.com/Horsepower.html)) RPM is what is needed on the highway and Torque is the ability to move the bike faster from a stand still. Progressively through the upper gear changes, torque is lowered and speed is gained through gear ratio changes. As with the 2 gear train mentioned above; \\
+The gear ratio shows the trade-off between torque and speed. Speed is RPM and Torque is PUSH. ((https://motorcycleinfo.calsci.com/Horsepower.html)) RPM is what is needed on the highway and Torque is the ability to move the bike faster from a stand still. Progressively through the upper gear changes, torque is lowered and speed is gained through gear ratio changes. As with the 2 gear train mentioned below; \\
 If the driving gear is smaller than the driven gear, the result is the driven gear turns slower (less speed) but with (more torque) applied downstream of it. \\
 If the driving gear is larger than the driven gear, the result is the driven gear turns faster (more speed) but with (less torque) downstream of it. \\
 Example: A 20 teeth gear is driving a 40 teeth gear. The input speed is 1000 RPM and the input torque is 50 ft/lbs. \\
 Using the gear ratio (20/40 = 0.5:1), the output speed was reduced to 500 RPM (1000 x 0.5 = 500). \\
-Using the inverse gear ratio, (40/20 = 2:1) then multiplying the known input torque (50 ft/lbs) by the result, (50 x 2 = 100 ft/lbs). \\
+Using the inverse gear ratio, (40/20 = 2:1) then multiplying the example input torque (50 ft/lbs) by the result, (50 x 2 = 100 ft/lbs). \\
 So the output speed was cut in half by this gearset but the output torque doubled (this does not take into account efficiency loss).
 However adding gear efficiency, ex. 99% for a spur gears, the formula changes to (40/20) x 50 x .99 = 99 ft/lbs of output torque.
 The same mathing applies if the driver gear has more teeth than the driven gear. The results are just in reverse. \\
-{{:techtalk:ref:svcproc:gear_ratio_and_torque.png?direct&400|}} ((drawing by Hippysmack)) \\
+{{:techtalk:ref:svcproc:gear_ratio_and_torque_by_hippysmack.png?direct&400|}} ((drawing by Hippysmack)) \\
+===== Torque vs Speed (horsepower) =====
+Below is a compilation of quotes from aswracing of the XLFORUM; \\
+Torque essentially comes from two things: cylinder pressure and the mechanical advantage it has on the crank. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-buell-motorcycle-racing/sportster-motorcycle-drag-racing/36229-when-to-shift-peak-hp-or-tq/page3?t=70371&page=3)) Mechanical advantage on the crank comes from both the bore and the stroke. This is easy to visualize when you think of the stroke as a function of how far the crankpin is from the center of the crank. The stroke is essentially the size of the lever. More stroke means the rod has more leverage to turn the crank. But bore size also gives more leverage. Pressure is described in pounds per square inch. Well, with a bigger bore, you've got more square inches to push on. So the bottom line is that both the bore and the stroke contribute to the torque. \\
+The other ingredient of torque is the pressure you build. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-buell-motorcycle-racing/sportster-motorcycle-drag-racing/36229-when-to-shift-peak-hp-or-tq/page3?t=70371&page=3)) That pressure is a function of a whole bunch of things, including things like how well you filled the cylinder and how hard you compressed it on the compression stroke. The piston moving out of the way regulates the pressure. Ever wonder why a motor pings at high load? It's harder to move the piston out of the way at high load, hence the pressure gets too high. So cylinder pressure has a close relationship to the torque.  Horsepower is and always will be torque times rpm (divided by 5252, but conceptually, you can ignore that part, all it really does is scale the number to what Watt's horse could do).
+Downshifting to a lower gear has the effect of increasing drive ratio and thus increasing the torque multiplication between engine and rear wheel. ((AC2W of the XLFORUM https://www.xlforum.net/forum/sportster-buell-motorcycle-racing/sportster-motorcycle-drag-racing/36229-when-to-shift-peak-hp-or-tq/page3?t=70371&page=3)) However, not everyone understands that.
+Some people latch on to this notion that "torque accelerates the bike" and argue emotionally around that. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-buell-motorcycle-racing/sportster-motorcycle-drag-racing/36229-when-to-shift-peak-hp-or-tq/page3?t=70371&page=3)) What they fail to understand is that torque at the rear wheel is what accelerates the bike, not torque at the engine. And the torque shown on a dyno sheet is torque at the engine, i.e. upstream from the gearing. But that gear reduction in the primary, transmission, and secondary changes everything. It can take less torque and make it more. The more rpm you have, the more gear reduction you can apply for a given rear wheel speed. So engine rpm ends up being every bit as important as engine torque when it comes to accelerating the bike. Hence when we talk performance, we don't talk in terms of torque, nor do we talk in terms of rpm, we talk in terms of their combination. What matters is the total combination of torque and rpm you can make, which is better known as "horsepower". \\
+The torque peak means absolutely nothing for maximum acceleration. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-buell-motorcycle-racing/sportster-motorcycle-drag-racing/36229-when-to-shift-peak-hp-or-tq?t=70371)) \\
+Get two identical bikes going side by side, with both at the engine's torque peak. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-buell-motorcycle-racing/sportster-motorcycle-drag-racing/36229-when-to-shift-peak-hp-or-tq?t=70371)) Whack one of them wide open. At the same time, downshift the other bike to put the motor at the power peak instead and whack it wide open. It won't even be close. The bike at it's power peak will run away from the other bike. Why? Because when you downshift, you multiply the torque. That means that even though the motor is making less torque, since you have more gear reduction in the lower gear, you end up with more torque at the rear wheel, and that's what accelerates the bike. \\
+This is exactly what a horsepower curve (on a dyno chart) is all about. It takes into account that the rpm the motor is turning is also a component of the performance. The more rpm you're turning, the more gear reduction you can apply at a given speed, and hence the more you can multiply the motor's torque. Horsepower is a complete description of performance, torque is not. At any given speed, maximum torque at the rear wheel occurs at the power peak, not the torque peak. \\
+Torque is twisting force, without any regard for speed. But speed is enormously important. For example, if you have 80 ft-lbs at 3000 rpm, you can get twice as much done as if you had 80 ft-lbs at 1500 rpm. You're making the same torque, but you're making it twice as fast. In fact, you could take that 80 ft-lbs at 3000 rpm, gear it down 2:1, and have 160ft-lbs at 1500 rpm. In other words, you have the option of making twice the torque, but doing it at the same speed as the weaker motor. So you see, having more rpm is a huge advantage. You can make small torque into big torque if you have more rpm. That's what gear reduction is all about. It's also exactly why a 600 race rep with 40 ft-lbs at 15,000 rpm will beat up on a Sportster making 80 ft-lbs at 5000 rpm. It may only have half the torque, but it's turning three times the rpm. So for any given rear wheel speed, it can have three times the gear reduction through the primary & tranny & final drive, which multiplies it's torque three additional times over that of the Sportster. Hence more torque reaches the rear wheel at any given rear wheel speed. Three times 40 is 120, and that's more than the 80 that the Sportster has. That's exactly why you talk horsepower when you're talking about performance. Horsepower is literally torque times rpm. It combines the twisting force (torque) with the speed of twisting (rpm). Both are equally important when you're talking about performance. They're also totally interchangeable. Gear something down, you decrease rpm and increase torque. Gear something up, you increase rpm and decrease torque. \\
+Here's a motor we built for a guy several years ago. \\
+The torque peak is 109.4 ft-lbs at 4600 rpm. The power peak is 117.6 hp at 6700 rpm. Pick a rear wheel speed. Let's just say 500rpm. If we have the motor at 4600rpm, and we're in a gear, that gives us 500rpm rear wheel speed, that means we have 9.2 of overall gear reduction (4600 divided by 500 is 9.2). Well, if the motor is making 109.4 ft-lbs, and you've got 9.2 of gear reduction between the crank and the rear wheel, you've got 109.4 times 9.2 equals 1006.48 ft-lbs of torque at the rear wheel. Okay, now let's see what happens at the power peak instead. If we have the bike at 6700rpm, and it's got 117.6 horsepower, that means it's making 92.2 ft-lbs of torque (torque = (hp times 5252) divided by rpm). If you work that out, you'll get 92.2 ft-lbs, and you can see on the chart that's about right. \\
+If we have the motor at 6700rpm, and we're in a gear that gives us 500rpm rear wheel speed, that means we have 13.4 of overall gear reduction (6700 divided by 500 is 13.4). Well, if the motor is making 92.2 ft-lbs, and you've got 13.4 of gear reduction between the crank an the rear wheel, you've got (92.2 times 13.4 equals 1235.48 ft-lbs) of torque at the rear wheel. 1235.48 is more than 1006.48. The power peak wins. \\
+So as you can see, at the same rear wheel speed, you put more torque to the rear wheel when the motor is at the horsepower peak, not when the motor is at the torque peak. This is exactly why horsepower is the meaningful number. It takes the engine's rpm into consideration. The engine's rpm is every bit as important as the engine's torque, because the more engine rpm we have, the more gear reduction we can apply for a given rear wheel speed. And the more gear reduction we can apply, the more we multiply the engine's torque. There's a much more direct way to do that calculation, I did it the long way just to illustrate the concept. But the short way is just to calculate rear wheel torque directly, knowing rear wheel rpm and rear wheel horsepower. Remember, any time you know any two of the three components (torque, rpm, or power), you can calculate the third. \\
 ====== Formulas ======
@@ Line 73: / Line 103: @@
   * **Output Torque ratio** for 4 gears = (number of teeth on driven gear x number of teeth on driven gear) / (number of teeth on driving gear x number of teeth on driving gear)
   * **Output Torque** = (input torque) x (output torque ratio)
+  * **Power[hp]** = torque[lb-ft] x RPM ÷ 5252
+====== Examples of Gear Ratio Calculations ======
+===== Ratios for 2 Gears Only =====
+The information below shows how to calculate the numbers for a gear train using only 2 gears. \\
+Instead, you can find a gear ratio calculator online to do the math for you. \\
+[[https://www.omnicalculator.com/physics/gear-ratio|Click Here]] to link to one that gives you gear ratio, mechanical advantage, output speed and torque by inputting known values.
+The examples below are using a MS-2 (29T) and a CS-2 (34T) gearset (or gear train). Engine RPM at constant 1000 and initial torque of 50 ft/lbs. \\
+In this gearset, M2 is splined to the mainshaft, turns the same speed as the mainshaft and serves as the driving gear of the set. \\
+C2 is sleeved over bearings on the countershaft, has to be coupled to the countershaft by the dogs on C3 gear and serves as the driven gear to M2. \\
+These are arbitrary combinations just for example. \\
+  * **Gear Ratio** = (number of teeth on driving gear) / (number of teeth on driven gear)
+    * Example: A 29 teeth gear is driving a 34 teeth gear at a ratio of 0.85:1 \\ Plug the numbers into the formula (29 / 34) = 0.85294 (or 0.853) \\ The result is expressed in ratio as 0.853:1 (or 0.853 to 1). \\ In this example, CS-2 turns (slower) and at 0.853 times for MS-2 to turn 1 full revolution.  \\ While this setup shows a gear reduction in terms of speed, it creates an output that has more torque when compared to the input torque between these 2 gears.
+  * **Output Speed** = (input speed) x (gear ratio)
+    * Example: Given a mainshaft speed of 1000 rpm using the gear ratio above (0.853), the countershaft speed is 853rpm \\ Plug the numbers in the formula (1000 x 0.853) = 853 \\ In this example and with a constant input rpm, the countershaft (by way of CS-2) has a speed of 853 rpm.
+  * **Mechanical Advantage** = (number of teeth on driven gear / number of teeth on driving gear)
+    * Example: A 34 teeth gear is being driven by a 29 teeth gear at a mechanical advantage of 1.172:1 \\ Plug the numbers into the formula (34 / 29) = 1.172413793103448 \\ In this example, the result is expressed in ratio as 1.172:1 (or 1.172 to 1). \\ This example gives 0.172 times more output torque as compared to the input torque between these 2 gears.
+  * **Output Torque** = (input torque) x (mechanical advantage).
+    * Example: Given an input torque 50 ft/lbs, the output torque will increase to 58.6 ft/lbs @ 1000 RPM between the example gears \\ Plug the numbers into the equation (50 x 1.172) = 58.6 \\ In this example, the torque from the mainshaft was increased on the countershaft by 8.6 ft/lbs (by way of CS-2).
+===== Internal Gear Ratio (4 gears) =====
+Internal ratios are calculated per each transmission GEAR selected. \\
+There are a total of 5 ratios that make up the internal ratio (1st-5th transmission GEAR) and they are calculated individually. \\
+However, Sportster transmissions have an internal ratio of 1:1 in 5th gear so it doesn't need calculating further. \\
+[[techtalk:evo:transfinal01|Click Here]] to see the gearing chart in the Evo section "Primary/Transmission/Final Gear Ratios". The internal ratios are listed for 1986 and up Sportsters. \\
+This section shows how to calculate internal ratios for yourself. \\
+**You must already have gear teeth counts for all the gears in the transmission to calculate the internal ratio**. \\
+You can find a gear ratio calculator online to do the math for you if desired but you still need all teeth counts to use it. \\
+[[https://evolventdesign.com/pages/gear-ratio-calculator|Click Here]] to link to one that gives you internal gear ratio and output speed by inputting known values. \\
+The information below shows how to calculate the numbers for Transmission GEAR 1st-4th. These all use 4 gears (2 drivers and 2 driven) to turn the transmission sprocket. \\
+The engine sprocket and clutch sprocket is not included since they are part of the Primary Drive Ratio which is calculated separately.
+The transmission sprocket and rear wheel sprocket is not included in these calculations since they are part of the Final Drive Ratio which is calculated separately. \\
+**The internal ratio, (AKA, gearbox ratio), includes the mainshaft and countershaft gears that are in the power flow for the transmission GEAR selected**. \\
+The example illustration below shows the gears colored red in the Power Flow for 2nd gear. \\
+**Note**, C3 is in red only because it takes C3 gear dogs to lock C2 gear to the countershaft. \\
+This example uses the stock gears from a 1998 XL1200; M2 (29T) - C2 (34T) gearset and C5 (25T) - M5 (42T) gearset. \\
+M-2 gear is driving C2 gear and C5 gear is driving M5 gear. Use the __inverse gear ratio__ for each gearset. \\
+You may see the word "gear ratio" elsewhere but this article wishes to distinguish the difference for clarity. \\
+Using the inverse ratio, the result will show the amount of torque gained or lost in the listed internal gear ratios per GEAR selected. \\
+  * **Inverse Gear Ratio** = (driven gear teeth x driven gear teeth) / (driver gear teeth x driver gear teeth)
+    * Assemble gear teeth count for each gearset:
+      * Driven Gears: C-2 (34T) and M-5 (42T)
+      * Driver Gears: M-2 (29T) and C-5 (25T)
+    * Plug the numbers in the formula:
+      * (34 x 42) / (29 x 25) or (1,428 / 725) = 1.969655172413793
+      * The result is expressed in ratio form (1.969655172413793:1)
+    * **The Internal Gear Ratio** for a stock 2nd GEAR on a 1998 XL1200 is 1.969655172413793:1 \\ You can round that ratio up to 1.970:1 or use HD's rounded down ratio of 1.969:1 but using the full figure above will be the most accurate for further calculations if needed.
+{{:techtalk:ref:svcproc:gear_ratio_and_internal_ratio_by_hippysmack.png?direct&600|}} ((drawing by Hippysmack)) \\
+\\
+Next, you run the numbers using the same formula for the other 3 gearsets. And of course 5th gear ratio is 1:1. \\
+And you end up with a list of numbers as shown in the chart below (with HD's numbers listed).
+Looking at the chart, you can see the torque decrease as you go up thru the gears. \\
+Higher internal ratios = higher output torque and lower speed. Lower internal ratios = lower output torque and higher speed. \\
+|**Internal Gear Ratio \\ 1998 XL200**|1st GEAR|2nd GEAR|3rd GEAR|4th GEAR|5th GEAR|
+|:::|2.685:1|1.969:1|1.433:1|1.178:1|1:1|
+The above chart shows ADVERTISED RATIOS ONLY (often referred to as Ideal ratios). \\
+The ACTUAL RATIOS WILL BE LOWER (due to efficiency loss). \\
+To quote KHK Gears: \\
+The efficiency shown above is the transmission efficiency of gears without regard to the loss in bearings or agitation of grease. ((https://khkgears.net/new/gear_knowledge/the-first-step-of-mechanism-design-using-gears/know-about-gear-transmission-torque.html)) \\
+You cannot calculate a gear's transmission torque simply as shown above because of the following reasons: \\
+* Heat is produced by meshing teeth and energy is lost. \\
+* Hammering sound is produced by meshing teeth and energy is lost. \\
+Therefore, the torque (turning force) is reduced by as much as the energy is lost. \\
+The ratio of input to output forces of gears is called “machine efficiency” and its approximate value is known according to the gear type. \\
+Based on KHK information ((https://khkgears.net/new/gear_knowledge/the-first-step-of-mechanism-design-using-gears/know-about-gear-transmission-torque.html)) , we'll just use an efficiency rate of 99% for spur gears. \\
+In order to find approximate Actual ratio, the formula needs to be altered. \\
+  * **Inverse Gear Ratio** = 0.99 x (driven gear teeth x driven gear teeth) / (driver gear teeth x driver gear teeth)
+    * Plug the numbers from the example above in the new formula: 0.99 x (1,428 / 725) = 1.949958620689655 (or 1.950:1)
+  * So the actual internal ratio in that instance would be slightly lower than the advertised ratios.
+**Here is why transmission 5th GEAR Internal Ratio is 1:1**. \\
+Any gear that is splined to or locked to a shaft rotates at the same speed the shaft rotates. \\
+Example: In 5th GEAR, if the clutch sprocket is rotating the mainshaft at 1000 RPM, all gears attached to it also rotate at 1000 RPM. \\ (includes M1 and M2 since they are splined to the mainshaft and M5 since M2 dogs lock M5 to the mainshaft). \\
+M5 is splined to the transmission sprocket and these two gears always rotate at the same speed. \\
+So each of these gears rotate at the same speed. \\
+(clutch sprocket RPM / M5 RPM) = 1000 / 1000 or 1, (expressed as 1:1).
+{{:techtalk:ref:susp:gear_ratio_and_internal_ratio_5th_by_hippysmack.png?direct&400|}} ((drawing by Hippysmack)) \\
+===== Primary Drive Ratio =====
+The primary ratio that is quoted in the FSM is actually the primary torque ratio. \\
+It reveals the amount of torque change from the engine sprocket to the clutch sprocket by way of different teeth counts on the two sprockets. \\
+It means that whatever output torque the engine gives at a given RPM is changed to a different torque once that power reaches the transmission mainshaft. \\
+With the clutch sprocket being larger than the engine sprocket, the clutch sprocket will turn slower than the engine sprocket. \\
+And it will, by default, drive the mainshaft at a higher torque rate than what the engine is providing. \\
+The ratio of change, found by using the Inverse Torque Ratio formula, tells the (rate) of how much more torque will be applied to the mainshaft than what the engine is providing. \\
+To find the actual amount of added torque, you'd need to know how much torque the engine is putting out at a given speed and multiply that to the primary ratio. \\
+So the ratio doesn't tell you exact numbers itself but just (at what rate) torque was changed. \\
+The inverse ratio does not tell you how much faster the mainshaft spins either. \\
+The example below shows how to get the numbers that are given in the manuals. \\
+The example numbers are for a 1998 XL1200 with an engine sprocket having 35 teeth and a clutch sprocket having 56 teeth. \\
+  * **Inverse Gear Ratio**: (driven gear) / (driving gear)
+    * Assemble teeth count:
+      * Clutch sprocket (56T)
+      * Engine sprocket (35T)
+    * Plug the numbers in the formula:
+      * 56 / 35 = 1.60
+      * The result is expressed in ratio form (1.60:1)
+  * **The Primary Ratio** for a stock 1998 XL1200 is (1.60:1). \\ This result shows a gain in torque (loss in engine speed) at the clutch sprocket as opposed to current engine torque.
+{{:techtalk:ref:svcproc:gear_ratio_and_primary_ratio_by_hippysmack.png?direct&600|}} ((drawing by Hippysmack)) \\
+===== Final Drive Ratio =====
+The final drive ratio that is quoted in the FSM is actually the final drive torque ratio. \\
+It reveals the amount of torque change from the transmission sprocket to the rear wheel sprocket. \\
+It means that whatever the output torque is on the transmission sprocket is changed to a different torque once that power reaches the rear wheel sprocket. \\
+With the rear wheel sprocket being larger than the transmission sprocket, the rear wheel sprocket will turn slower than the transmission sprocket. \\
+And the transmission sprocket will, by default, drive the rear wheel sprocket at a higher torque rate than what the engine/transmission is providing. \\
+The ratio of change, found by using the Inverse Torque Ratio formula, tells the (rate) of how much more torque will be applied to the rear wheel sprocket than what the engine/transmission is providing. \\
+To find the actual amount of added torque, you'd need to know how much torque the engine and transmission is putting out at a given speed and multiply that to the final drive ratio. \\
+So the ratio doesn't tell you exact numbers itself but just at what rate torque was changed. \\
+The inverse ratio does not tell you how much faster the mainshaft spins either. \\
+The final drive ratio is calculated between the transmission output sprocket and the rear wheel. \\
+The example below shows how to get the numbers that are given in the manuals.
+This example uses a transmission sprocket with 29 teeth and a rear wheel sprocket with 61 teeth on a 1998 XL1200 Sportster. \\
+The formula uses the inverse of the gear ratio formula and the result gives the final drive torque ratio, not speed.
+  * **Inverse Gear Ratio**:  (driven gear) / (driving gear)
+    * Assemble teeth count:
+      * Rear wheel sprocket (61T)
+      * Transmission sprocket (29T)
+    * Plug the numbers in the formula:
+      *  61 / 29 = 2.103448275862069 (or 2.103)
+      * The result is expressed in ratio form (2.103:1)
+  * **The Final Drive Ratio** for a stock 1998 XL1200 is (2.103:1). \\ This result shows a gain in torque (decrease in speed) at the rear wheel as opposed to current engine torque. \\ It is listed as 2.10:1 in the FSM.
+\\
+{{:techtalk:ref:svcproc:gear_ratio_and_final_drive_ratio_by_hippysmack.png?direct&600|}} ((drawing by Hippysmack)) \\
+===== Overall Gear Ratio =====
+This section shows how to calculate overall gear ratio. \\
+Instead, you can find online calculators to do the math for you. \\
+[[https://www.gearingcommander.com/|Click Here]] to link to an online calculator from Gearing Commander.com. \\
+[[techtalk:evo:transfinal01|Click Here]] to see the gearing chart in the Evo section "Primary/Transmission/Final Gear Ratios". The internal ratios are listed for 1986 and up Sportsters. \\
+The overall gear ratio that is quoted in the FSM is actually the overall gear torque ratio. \\
+It reveals the (rate) of torque change from the engine sprocket to the rear wheel sprocket. \\
+It means that whatever the output torque is on the engine sprocket is changed to a different torque once that power runs thru the primary sprocket, transmission gears and final drive sprockets. \\
+Given the changes in the drive path, the overall ratio sums them up into 1 ratio per whatever transmission GEAR is selected. \\
+The overall gear ratio is calculated for the entire gear train in the system including primary, transmission and final drive ratios for each transmission GEAR selected. \\
+Each of those 3 ratios are calculated using the Inverse Gear Ratio to reveal the TORQUE RATIO. \\
+There are a total of 5 ratios needed that make up the overall gear ratio (1st-5th transmission GEAR). \\
+The ratio of change, found by using the Inverse Torque Ratio formula, tells the (rate) of how much more torque will be applied to the rear wheel sprocket than what the engine/transmission is providing. \\
+The example below shows how to get the numbers that are given in the manuals. \\
+The calculations from the examples above for each of those parts of the gear train for a 1998 XL1200 in 2nd GEAR are used. \\
+  * **Overall Gear Ratio**: (primary ratio) x (internal ratio) x (final drive ratio)
+    * Assemble the 3 torque ratios needed:
+      * Primary gear ratio (1.60:1)
+      * Transmission 2nd GEAR Internal Ratio (1.970:1)
+      * Final Drive Ratio (2.10:1)
+    * Plug the numbers into the formula
+      *  1.60 x 1.970 x 2.10 = (6.6192)
+      *  The result is expressed in ratio form (6.6192:1)
+  * **The Overall Gear Ratio ** for a stock 1998 XL1200 2nd GEAR is (6.6192:1). \\ This result shows a gain in torque (decrease in speed) at the rear wheel as opposed to current engine torque. \\ The overall GEAR ratio is listed in the FSM as 6.62:1 for a 1998 1200 Sportster 2nd GEAR.
+\\
+{{:techtalk:ref:svcproc:gear_ratio_and_overall_ratio_by_hippysmack.png?direct&600|}} ((drawing by Hippysmack)) \\
+Next, you run the numbers using the same formula for the other 4 gearsets. And you end up with a list of numbers as shown in the chart below (with HD's numbers listed). \\
+Looking at the chart, you can see the torque decrease as you go up thru the gears (which means speed is increasing). \\
+Higher overall ratios = higher output torque and lower speed. Lower overall ratios = lower output torque and higher speed. \\
+|**Overall Gear Ratio \\ 1998 XL200**|1st GEAR|2nd GEAR|3rd GEAR|4th GEAR|5th GEAR|
+|:::|9.04:1|6.62:1|4.82:1|3.97:1|3.36:1|
+The above chart shows ADVERTISED RATIOS ONLY (often referred to as Ideal ratios). \\
+The ACTUAL RATIOS WILL BE LOWER (due to efficiency loss). \\
+To quote KHK Gears: \\
+The efficiency shown above is the transmission efficiency of gears without regard to the loss in bearings or agitation of grease. ((https://khkgears.net/new/gear_knowledge/the-first-step-of-mechanism-design-using-gears/know-about-gear-transmission-torque.html)) \\
+You cannot calculate a gear's transmission torque simply as shown above because of the following reasons: \\
+* Heat is produced by meshing teeth and energy is lost. \\
+* Hammering sound is produced by meshing teeth and energy is lost. \\
+Therefore, the torque (turning force) is reduced by as much as the energy is lost. \\
+The ratio of input to output forces of gears is called “machine efficiency” and its approximate value is known according to the gear type. \\

Trace:

Differences

Navigation

Search

Toolbox