Gear down 850 RMK

[FlynHigh]

Not stock belt. The TKI has a tensioner. The tensioner allows multple gearing choices but it does much more than that. As the tensioner pushes in, the belt is forced to wrap 3/4 the around the top gear. This makes for much more teeth contacting than the stock set up. When there is more contact a smaller top gear is adequate without slipping or stripping the belt. Now the top gear is smaller, a smaller lower gear is also possible without compromising ratio. this smaller bottom gear helps avoid contact with the belly pan. I have seen several broken lower gears and going larger on the lower is worse for clearance.

Keep in mind Doo and Cat traditionally run 2.5:1 or even lower gearing(higher ratio) and why do you think they chose that when Polaris went with 2.27? Polaris has been limited due to physical size and no tensioner. But you can see the trend has been toward lower gearing over the past couple years. For those gearing up I will argue all day that there is zero advantages for mountain riding. Now that Polaris uses the P22 clutch that is wider around the center bearing, these sleds start out in a higher gear than the P85. This is a huge disadvantage, especially for the turbos that lack bottom end compared to the NA's.

Kurt’s has a modification to eliminate the P22 center bearing so the belt rides lower in the primary like a P85 and hence lower “ratio” when starting out. Does require adding the adjuster set screw back to the secondary. Which I would then recommend rebalancing the secondary.

 

[madmax]

The 50t Polaris QD2 gear fits right on any other QD driveshaft. You’ll also need the longer Polaris QD2 belt.
You have to be careful with Kurt’s, they have a couple different ratios available. One is the 2.08 (pro ride) ratio that they have had forever. They have a newer kit that has an actual QD 2.38 ratio. Don’t confuse “final drive ratio” with actual QD gear ratio, it’s very misleading on Kurt’s website.

 

[Fat_Tones]

The 50t Polaris QD2 gear fits right on any other QD driveshaft. You’ll also need the longer Polaris QD2 belt.
You have to be careful with Kurt’s, they have a couple different ratios available. One is the 2.08 (pro ride) ratio that they have had forever. They have a newer kit that has an actual QD 2.38 ratio. Don’t confuse “final drive ratio” with actual QD gear ratio, it’s very misleading on Kurt’s website.

I got confused by this…lol. Kurt’s has 32/67 and 29/69. They publish the final drive ratio of the former as 2.37, meanwhile the pulley ratio of the latter (not factoring drivers) is 2.38. I think in their product description they state both pulley and final drive ratios, but not sprocket count.

The day after interacting with Scott in this thread I had a phone conversation with Curt himself. He advocates very strongly that QD2 is too low (for mountain riding) and he really pushes the 32/67 kit (2.09 pulley ratio). Meanwhile other very credible tuners advocate strongly to gear down from QD2 with the 29/69 kit (2.38 pulley ratio) and are claiming quicker off idle response and higher track speeds. So as a layman it sure can be difficult to figure out what one needs to do. Curt said he will be testing in Revelstoke soon so I can’t wait for the results!

 

[Nolimits]

NapaMatt did you have to change clutching at all between the two setups? Or did your same clutching work well for both gearing options?

 

[armey37]

I recently made the switch on my 22 850 165 with a 3” track from qd2 to Kurt gear down “gear up”. Only mountain riding for me. What I noticed is I lost a little bottom end when going slow through the trees (heavy wet snow) is the only negative, once past 1/4 throttle she pulls hard. The positive is it pulls more track speed on top. Overall I like it. The belt is quite too. My clutching is also dialed in from TRS and I run a slp head.

 

[Kylep]

Maybe im way off here but is it not better to clutch around the lower gearing? Seems like the new tracks dont like more than 70 mph so why gear them up past that? Different weight profile/primary spring and a good secondary setup seems like a better idea. Or is it easier to throw on a couple gears and a belt to compliment the stock clutching?

 

[BeartoothBaron]

Kurt’s has a modification to eliminate the P22 center bearing so the belt rides lower in the primary like a P85 and hence lower “ratio” when starting out. Does require adding the adjuster set screw back to the secondary. Which I would then recommend rebalancing the secondary.

That should help the low end, but if you're losing the advantage of now having to adjust belt deflection, why not swap to the P-85? Other than price, I guess... It is true this would give you the same benefit as a gear down on engagement and off idle though.

The 50t Polaris QD2 gear fits right on any other QD driveshaft. You’ll also need the longer Polaris QD2 belt.
You have to be careful with Kurt’s, they have a couple different ratios available. One is the 2.08 (pro ride) ratio that they have had forever. They have a newer kit that has an actual QD 2.38 ratio. Don’t confuse “final drive ratio” with actual QD gear ratio, it’s very misleading on Kurt’s website.

It's frustrating when companies use final drive ratios to muddy the waters. You're probably just buying the gear setup, not changing drivers too, so you care about the gear ratio. Polaris did a back-and-forth with the AXYS, gearing up while going to a smaller driver - hence a "gear down." Not ideal because you gain rolling resistance and a higher approach angle. Putting aside final drive, my thought is it's hard to gear down too much for low-speed riding. The benefit in a quicker track spin-up is can make the difference between popping out of a situation and trenching in. You probably need lower than QD2 if that's your priority. On the other hand, QD2 is probably a bit low for wide open pulling, and being geared down from there will definitely lose peak track speed. It's kind of like a race car geared for a road course on a big oval - or vice versa - it's a pretty individual and situational choice.

 

[Reddragon800]

Do not use the 32/67 ratio. The QD2 is lower then that. Kurts website really needs to be updated. He is using the "final drive" ratio taking into account the 6 tooth 3.5 pitch drivers. He's using a reduction compared to the old pro days (2013) when lots of people would switch to the 3"pitch 7 tooth dirvers. But now all the sleds come stock with the 6 tooth 3.5 pitch drivers so there is no need to calculate a change in driver size. The only ratio that should be used is the 29/69 (2.38). Even with this ratio, 1-1 shift is still 114kmph. For reference, the skdioo gearing is 2.52. They get much closer to 1-1 shift then the cats and polaris.

FYI - anyone gearing up a mountain sled is doing it wrong. Its only applicable if your 240hp and up.

 

[Reddragon800]

I got confused by this…lol. Kurt’s has 32/67 and 29/69. They publish the final drive ratio of the former as 2.37, meanwhile the pulley ratio of the latter (not factoring drivers) is 2.38. I think in their product description they state both pulley and final drive ratios, but not sprocket count.

The day after interacting with Scott in this thread I had a phone conversation with Curt himself. He advocates very strongly that QD2 is too low (for mountain riding) and he really pushes the 32/67 kit (2.09 pulley ratio). Meanwhile other very credible tuners advocate strongly to gear down from QD2 with the 29/69 kit (2.38 pulley ratio) and are claiming quicker off idle response and higher track speeds. So as a layman it sure can be difficult to figure out what one needs to do. Curt said he will be testing in Revelstoke soon so I can’t wait for the results!

This has already been tested all over BC, see my FB and IG page. @Seinen Racing Products. A lower ratio will ALWAYS beat a higher ratio for mountain sleds.

 

[Fat_Tones]

Do not use the 32/67 ratio. The QD2 is lower then that. Kurts website really needs to be updated. He is using the "final drive" ratio taking into account the 6 tooth 3.5 pitch drivers. He's using a reduction compared to the old pro days (2013) when lots of people would switch to the 3"pitch 7 tooth dirvers. But now all the sleds come stock with the 6 tooth 3.5 pitch drivers so there is no need to calculate a change in driver size. The only ratio that should be used is the 29/69 (2.38). Even with this ratio, 1-1 shift is still 114kmph. For reference, the skdioo gearing is 2.52. They get much closer to 1-1 shift then the cats and polaris.

FYI - anyone gearing up a mountain sled is doing it wrong. Its only applicable if your 240hp and up.

I have a very hard time imagining my 850 NA with QD2 getting even anywhere close to 1:1 shift out when settled into a climb. Currently in break-in getting 8150rpm and 66km/h track speed (6500ft). What rpm do you target on the 850NA?

 

[FlynHigh]

Polaris manual recommend 8100-8250 RPM range for 850 NA. SLP recommends 8200-8300 for their 850 NA clutch kits. From my experiencer riding at 6-9,000 feet 8200-8300RPM works best. 8100 RPM just seemed a bit doggy to me, amazing what that extra 100 RPM does. I believe the Boost guys spin them up to 8400 RPM.

Below is a chart I put together outlining all the gear ratios available for sleds that came with a factory belt drive . Note TKI does make some other ratios but that applies to sleds that were converted from a chain case to a belt drive. I did not list any of those.

 

[volcano buster]

Polaris manual recommend 8100-8250 RPM range for 850 NA. SLP recommends 8200-8300 for their 850 NA clutch kits. From my experiencer riding at 6-9,000 feet 8200-8300RPM works best. 8100 RPM just seemed a bit doggy to me, amazing what that extra 100 RPM does. I believe the Boost guys spin them up to 8400 RPM.

Below is a chart I put together outlining all the gear ratios available for sleds that came with a factory belt drive . Note TKI does make some other ratios but that applies to sleds that were converted from a chain case to a belt drive. I did not list any of those.

View attachment 432105


You list ARP bolts for Bottom Pulley on both columns. Is this in error?

 

[AssaultUP]

So I have run QD1 and QD2 on a 2020 khoas 850 155 2.6. You need the 50t bottom sprocket and the belt for qd2. Parts are interchangeable. Takes less than 5 mns once you know what you are doing. I would gear down to QD2 if I was mountain riding and gear back up to the QD1 if I was going to be with people doing more trail riding.

It’s a huge change and I absolutely loved the QD2 gearing. Works so much better off trail for the sled and you don’t burn your belt in tight trees. Really puts the power where you want. For trail riding it just takes some top end off if you are trying to keep up with trail sleds.

I left the clutching alone and just changed the gearing. Never had an issue keeping her at 8200-8300rpms. I totaled that sled and now have a 9r with QD2. I kept the spare QD 2 sprocket if you are interested in buying it let me know.

 

[FlynHigh]

Volcano Buster,

I intentionally listed two bolt length options for the bottom pulley. I didn’t list bolt length options for the top pulley, but you can match your existing top bolt length using the ARP chart included.

When the belt drive was first released on the PRO chassis in 2013, the bottom pulley had issues with bolts breaking. I can’t remember who, but someone on this forum suggested using a thick spacer (essentially a super thick washer) to allow for a significantly longer bolt. The idea was that a longer bolt would allow more stretch, helping maintain proper clamp load and keep the bolt in the elastic range during use. This is essentially what Polaris ended up doing—except instead of using a thick washer, they ran the bolt deeper into the driveshaft to accommodate a longer bolt.

If you choose to use a slightly longer 45mm bolt instead of the factory 40mm bolt, you might need a thicker Nord-Lock washer added into the stack of washers to prevent the bolt from bottoming out. That setup would allow for the longest possible bolt and slightly more stretch, which could improve reliability. So you would have the factory Belleville type washer against the gear, then the Nord-Lock washer, then the ARP washer under the bolt head. Note the ARP is a “special” washer with one side chamfered to provide clearance for the radius under the bolt head, which helps prevent stress risers so the bolt head doesn't break off.

Note: Since Polaris switched to the longer bolt around 2014–2015, there haven’t been issues with bolts breaking. So, the extra 5mm might be overkill and more hassle than it's worth.

 

[Kylep]

Volcano Buster,

I intentionally listed two bolt length options for the bottom pulley. I didn’t list bolt length options for the top pulley, but you can match your existing top bolt length using the ARP chart included.

When the belt drive was first released on the PRO chassis in 2013, the bottom pulley had issues with bolts breaking. I can’t remember who, but someone on this forum suggested using a thick spacer (essentially a super thick washer) to allow for a significantly longer bolt. The idea was that a longer bolt would allow more stretch, helping maintain proper clamp load and keep the bolt in the elastic range during use. This is essentially what Polaris ended up doing—except instead of using a thick washer, they ran the bolt deeper into the driveshaft to accommodate a longer bolt.

If you choose to use a slightly longer 45mm bolt instead of the factory 40mm bolt, you might need a thicker Nord-Lock washer added into the stack of washers to prevent the bolt from bottoming out. That setup would allow for the longest possible bolt and slightly more stretch, which could improve reliability. So you would have the factory Belleville type washer against the gear, then the Nord-Lock washer, then the ARP washer under the bolt head. Note the ARP is a “special” washer with one side chamfered to provide clearance for the radius under the bolt head, which helps prevent stress risers so the bolt head doesn't break off.

Note: Since Polaris switched to the longer bolt around 2014–2015, there haven’t been issues with bolts breaking. So, the extra 5mm might be overkill and more hassle than it's worth.

All of that is good info, some of the gears on the 13-15 models didnt fit well on the shaft splines, that didnt help the bolts any.

 

[Carramrod]

I have a very hard time imagining my 850 NA with QD2 getting even anywhere close to 1:1 shift out when settled into a climb. Currently in break-in getting 8150rpm and 66km/h track speed (6500ft). What rpm do you target on the 850NA?

8350-8500 rpm

 

[Nolimits]

So I have run QD1 and QD2 on a 2020 khoas 850 155 2.6. You need the 50t bottom sprocket and the belt for qd2. Parts are interchangeable. Takes less than 5 mns once you know what you are doing. I would gear down to QD2 if I was mountain riding and gear back up to the QD1 if I was going to be with people doing more trail riding.

It’s a huge change and I absolutely loved the QD2 gearing. Works so much better off trail for the sled and you don’t burn your belt in tight trees. Really puts the power where you want. For trail riding it just takes some top end off if you are trying to keep up with trail sleds.

I left the clutching alone and just changed the gearing. Never had an issue keeping her at 8200-8300rpms. I totaled that sled and now have a 9r with QD2. I kept the spare QD 2 sprocket if you are interested in buying it let me know.

Thanks for the first hand experience. Thanks for the offer on parts but I have access to a belt and gear. I will keep it in mind if that doesn’t work out.

Thanks to everyone for all the information and charts that have been posted. Good info!

 

[NapaMatt]

NapaMatt did you have to change clutching at all between the two setups? Or did your same clutching work well for both gearing options?

clutching worked well will both gears/ 22/43 and 22/50

 

[Reddragon800]

I have a very hard time imagining my 850 NA with QD2 getting even anywhere close to 1:1 shift out when settled into a climb. Currently in break-in getting 8150rpm and 66km/h track speed (6500ft). What rpm do you target on the 850NA?

8250-8350rpm

 

[FlynHigh]

So I realized that with TKI's larger 66 tooth bottom gear there are more combinations that just the 25 & 26 tooth top gears I listed on the previous chart. I added in 27, 28, 29, and 30 tooth combos for the 66 bottom gear shown on this chart. I am not 100% sure those larger top gears can be used with the larger bottom gear though. You would want to check with TKI that the belt is long enough and that it has proper amount of belt "wrap" around the top gear when using the larger 66 tooth bottom gear.