track clearance issues for IQ RAW (AND PRO CHASSIS RMK & ASSAULTS)

Mountainhorse note 10-17-2010: I have copied this from the IQ section as it applies to the Pro Chassis which has the same dimensions to the roof of the tunnel from the drive shaft center.

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I recently bought a D8. I'm brand new to Polaris and in my quest to learn more about my new (used) sled, its limits, and benefits, a topic has surfaced. Some friends of mine and I were discussing this last night over some beer and wine, and I'm curious if others out there have experinece with this, and maybe others have thought of things we have not.

I have heard that there is a windage drag developed in that tunnel between the track and tunnel/bulkhead, and a snow drag as well, so switching from the 5.1 to say, a Chal-Extreme creates more drag, both snow and wind. I was informed of this concern from a polaris guy who is well regarded, and he was very kind to me when he shared his advice. But, with all do respect to him, after thinking about this for a couple days, I'm not convinced, and here's why:
1) when we are out riding, that tunnel gets packed full of snow all the way up inside. So, weather there is 4" or clearance, or 1/2" of clearance (between the paddles and tunnel/bulkhead) when sitting in our garage at home, when we're riding, all that 'clearance' is now packed full of snow. Sure, there is HP that is robbed with that process, but I can't see how we can get away from that with any design, or amount of spacing; It's just part of what happens when you run a track on snow at high speed. Even if you powdercoat it and run heat exchangers up there to 'melt' the snow off, when we're on the throttle, the rate the track brings snow up there will vastly overcome any hot surfaces' ability to melt/repel built up snow until you come to a stop.
2) Like I wrote earlier, I'm BRAND new to Polaris (just bought my first one, a D8 & never ridden one yet) but from what I hear, the new IQ RAW chassis in stock form has a lot more room in there than the older RMK chassis did AFTER a drop/roll kit. If this is true, (I trust the source) it pretty much confirms the theory. But if you wanted more room in there, rather than buying $$$ new drivers to switch to a 3.0 pitch, and 7-tooth, (thereby decreacing the radius/dia of the drivers) and adding a anti-stab kit, you could just do a drop/roll kit (Fastrax has them for $340), and you get even more clearance, and you'd have the added benefits of the improved track angle, and not have to change gearing.

What are your thoughts?

so Doug Danger, and AK, you guys have switched to the CamoCh-Ex, what did you do for your driver setup? will the stock config. work with the Ch Ex, or did you have to do something different?

Thanks! that answered my question. (I did a lousy job of phrasing it) I kinda wanted to go with the 3.0 pitch track, just cuz I'm coming off of A/C, and they seem more common, but the Pol is a totally different animal, so there's no real 'reason' to swap to the 3.0 just for the sake of swapping. If, down the road, I want to switch to two, extrovert-type drivers, and get rid of the third, I can find 2.86 8-tooth extrovert-type drivers, and be just fine.

This way, I can do the drop & roll, track and drivers a little at a time if I want. ($) Thanks again!

I had this reply all written out, and before I could finish, the bell hit for a fire. When I got back, someone had shut down the computer, and my post was lost. I'm to tired to write it out again tonite. I'll be back tomorrow. :beer;

Now that I'm home, and got caught up on sleep, a big thanks to everyone for the great replies so far.

Mountainhorse, one of the things I wanted to do was make sure I was very respectful of you taking the time to share your experience/expertise with me. And rather than listing it was you that shared a concept that I wasn’t on board with, I chose to leave your name out in a sincere effort to show both respect and gratitude. I certainly hope it came across that way. My deepest apologies if it did not.

So back to the track and driver issue:

It seems that folks around here (W. WA) have really liked the idea of dropping a tooth in the drive gear in the chaincase. A local dealer does this as part of their set-up, and lots of folks love it. But, by going down a tooth in the driver, (not the driven gear, but the track driver) you effectively gear-down. I haven’t done the math to see if it’s the same, but I’ll bet it’s close. I need to find out if that has been done to my sled already. The dealer didn’t mention gearing, but he had an open house when I was there, and while he was very patient with me, I didn’t want to take up too much time.

With regards to this track and tunnel spatial relationships…

Going to a 7-tooth driver does a couple things: it gears you down a bit; it gives you a little more clearance between the track and tunnel (if the track is the same). But, it also takes more energy to pull a track around a smaller pulley than a larger one – the energy required goes up with track thickness. So, in theory, for efficiency of power transmission, you’d want the largest driver you could put in there (and still have enough clearance) and do your effective gearing with your gears in the chaincase.

What I didn’t know until I saw a different thread, is that the 2.86 pitch Ch-Ex for the Polaris has the center window cut out for the lone extrovert driver in the center. So, there’s really no reason to switch to the 3.0 pitch track, right? Oh, and I spoke to Dave @ Wahl today, and he confirmed they will have 2.86 extrovert style 8-tooth drivers coming, he expects them ready by December.

Thanks for the pic of the inside of the tunnel. Seeing those rub-marks on the coolers makes it clear that track was rubbing on that tunnel. Talk about parasitic loss! That is significant friction there. And if I remember correctly, that was a stock series 5.1 with 2.4” paddles, so to me, it’s pretty darn clear even with a stock track it would benefit from a drop/roll procedure. Using those figures you posted earlier, and someone else re-posted, you did all the math for diameters and radii’s of the various driver sizes. Taking into account the thicker belting of the Ch-Ex 2.5 vs. the 5.1, with a drop/roll, there is a net gain of ~4 tenths of an inch of clearance to the rear, and 1.5 tenth down over stock with stock track.

You are absolutely correct that snow will not stick to polyethylene. So, a little sheet of it in the right places can be a good idea. Frankly, you could probably get some of those super-flexy cutting board sheets and rivet them in places you wanted that material, it’d be super light, cheap, and probably last a long time.

Now back to the tunnel and the parasitic power loss. I watched that video you sent me. (I actually casually know Emily, the rider just after the segment you referenced) And, it’s very clear the track is pumping a lot of snow out that opening. But I’ll bet you a cold beer, that when we are on the throttle, and our tracks are moving at even a moderate speed, every nook of the front of the tunnel is filled with compacted snow. The only spaces in that tunnel that DON’T have snow compacted in them (at that time) is the space that is carved out by the track as it rotates. So, weather there is ½” or 4” of compact snow in the front of the tunnel by the bulkhead, the parasitic lost from drag and aerodynamic resistance is essentially the same. I accept this is all just my opinion and theory, but it does follow what I know about drive-train efficiency and aerodynamics. I’d love to find a way to test it.

So, IF (and it’s certainly an ‘if’ at this juncture) my summary of the different parts is correct, then efficiency dictates the following:
1) we should use the biggest driver we can
2) adjust for the desired gearing in the chaincase,
3) installing a drop and roll kit to make room for the track paddles do they don’t contact the inside of the tunnel.

What do you think?

On a separate subject, thanks for the suggestion on the RSI grips, but I stumbled across ODI grips a couple years ago, and I love them. They come very long, so if one wants, they can put the bar hooks on, and the grips will slide up and over the entire length. They are a low-duro rubber, and seem to hold up quite well. My wife and I are very happy with them, if you haven’t seen/felt them, check them out next time you need grips.

Davy

Eric,

Thanks again for taking the time!