Been reading all I can on clutching and gearing. For Low hp low torque engines can there be benefits to gearing lower for acceleration? I figure 0 to 30mph acceleration will benefit from lower gearing with low hp and low torque engines to help get them going out the hole assuming no traction issues and help turn the track better in deep snow too. At speed I figure the clutches compensate for gearing differences so probably no change to acceleration at speed but have read there can be some effects from gearing on clutching with how it loads the engine from a change in feedback to secondary and from weight position in the primary. Can anyone explain what benefits there are to lower gearing and the potential impacts on clutch operation and tuning?
keysersoze
What a great question and a difficult question to answer.
For me, when I lowered my ratio I felt as if my power band came much quicker than stock. I felt as if I had more of a steady track speed through the trees and my rpm’s held a more consistent rpm when going uphill due to my weight and gear on the sled. Now, these are my interpretations of how I felt the sled responded, but it’s abit more in depth than I could ever explain. Dynamo Joe has done a great job and the world a favor by feeding his knowledge to us. You should read the “technical” section of his website at www.ibackshift.com Just head to the upper right corner where the menu is located and the technical section is under there. 🍻 Happy reading
For me, when I lowered my ratio I felt as if my power band came much quicker than stock. I felt as if I had more of a steady track speed through the trees and my rpm’s held a more consistent rpm when going uphill due to my weight and gear on the sled. Now, these are my interpretations of how I felt the sled responded, but it’s abit more in depth than I could ever explain. Dynamo Joe has done a great job and the world a favor by feeding his knowledge to us. You should read the “technical” section of his website at www.ibackshift.com Just head to the upper right corner where the menu is located and the technical section is under there. 🍻 Happy reading
To put it extremely simply.
yes lowering the gearing will give you more low end torque as expected but if you don’t adjust the clutches by changing the springs, weights and or ramp you will over rev at wide open.
similarly if you raise the gearing and don’t adjust clutching to accommodate you often will under rev at WOT and be out of the peak HP range.
yes lowering the gearing will give you more low end torque as expected but if you don’t adjust the clutches by changing the springs, weights and or ramp you will over rev at wide open.
similarly if you raise the gearing and don’t adjust clutching to accommodate you often will under rev at WOT and be out of the peak HP range.
2022 back country sport oem gearing is 23/51 with 2022 renegade sport gearing at 23/45 so BRP has the b/c already geared lower for that sled. A quick clutch parts check shows different cam and springs for the clutches so yes they do compensate for the lower gearing by changing shift parameters.
Gearing lower gives track speed staying power, maintaining track speed at full throttle
Gearing lower gives more abrupt ski lift when off and on the throttle.
Gearing lower gives ski lift at slight higher track speeds when off and on the throttle.
Gearing lower may give more engine speed at steady part throttle. Example; for lack of better numbers, lets say a 21-53 makes 6000 rpms at 28mph. 20-53 makes 6000 rpms at 26mph. 19-53 makes 6000 rpms at 24mph.
Gearing lower will run the belt farther out to the rim of the primary. IF run out the clutch full stroke, THEN the engine will flare into overrev.
When I was making my 440 fast trail kit, as I geared lower from 21-43 to 19-43, I geared to 19-47 was the most low gears available. When running hard through deep bumps at 50mph, the engine speed would be slow to recover. I ended up going from a xxx/420 to a xxx/460 finish on the primary spring, and, lowering the finish angle of the helix. Once i geared back to stock 21-43, the engine speed was higher and I could trim the flyweight grams to make it pull 8600 again.
Aaen 2015 book. Pg 76 Clutch component influence on a tuning objective.
IF the shift speed [revs pull lower than power peak rpm], THEN...
combine two of those options, or
combine all three of those options.
You dont give up. You keep trying to solve you issue.
Gearing lower gives more abrupt ski lift when off and on the throttle.
Gearing lower gives ski lift at slight higher track speeds when off and on the throttle.
Gearing lower may give more engine speed at steady part throttle. Example; for lack of better numbers, lets say a 21-53 makes 6000 rpms at 28mph. 20-53 makes 6000 rpms at 26mph. 19-53 makes 6000 rpms at 24mph.
Gearing lower will run the belt farther out to the rim of the primary. IF run out the clutch full stroke, THEN the engine will flare into overrev.
You betcha, that can happen.
When I was making my 440 fast trail kit, as I geared lower from 21-43 to 19-43, I geared to 19-47 was the most low gears available. When running hard through deep bumps at 50mph, the engine speed would be slow to recover. I ended up going from a xxx/420 to a xxx/460 finish on the primary spring, and, lowering the finish angle of the helix. Once i geared back to stock 21-43, the engine speed was higher and I could trim the flyweight grams to make it pull 8600 again.
Aaen 2015 book. Pg 76 Clutch component influence on a tuning objective.
IF the shift speed [revs pull lower than power peak rpm], THEN...
- increase the finish force of the primary clutch spring, or
- lower the finish angle on the helix, or,
- increase the finish force of the secondary clutch spring, or
combine two of those options, or
combine all three of those options.
You dont give up. You keep trying to solve you issue.
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