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

[Polar Express]

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.

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?

 

[AKSNOWRIDER]

doug danger on here changed to the xtreme on his 700 last year..what a difference....before he changed, his ported twin pipe 700 was neck and neck with my piped D8, a well modded vertical escape, and several 08-09 cats....one hill one would out mark the other..since doug did kurts drop and roll and the xtreme..none of us have been able to come close to where doug climbs..it is silly how big of a diference it made....a good part of it I think came from kurts drop and roll...you can see how much better the sled works when it is almost stuck...it just keeps climbing back up on the snow vrs just making a hole..thats what made me decide to do both the extreme and kurts drop and roll...........................

 

[duramaxdan]

drop and roll

whos this kurts guy?

 

[AKSNOWRIDER]

whos this kurts guy?

the owner of Fastrax motorsports..one of the best polaris mod shops around.........
http://www.ftxmotorsports.com/

 

[Polar Express]

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?

 

[AKSNOWRIDER]

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?

I havent changed mine yet..getting ready to order it all from kurt....I am running stock drivers with the 2.5 camo extreme in 2.86 pitch..you can do a 3.0 pitch extreme but then you need to change drivers..the 2.86 camo is designed to work with the stock 3 drivers(has the center window)..I could change drivers but I dont see any reason to..never had a problem with the stock drivers..and the track is about 2pds lighter with the center windows....

 

[Polar Express]

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!

 

[craigvansickle]

doug danger on here changed to the xtreme on his 700 last year..what a difference....before he changed, his ported twin pipe 700 was neck and neck with my piped D8, a well modded vertical escape, and several 08-09 cats....one hill one would out mark the other..since doug did kurts drop and roll and the xtreme..none of us have been able to come close to where doug climbs..it is silly how big of a diference it made....a good part of it I think came from kurts drop and roll...you can see how much better the sled works when it is almost stuck...it just keeps climbing back up on the snow vrs just making a hole..thats what made me decide to do both the extreme and kurts drop and roll...........................

The kit your talking about moves the driveshaft down 3/4" and back 1"? I can see the 3/4 inch down reducing the approach angle, it seems like moving it back 1" would just negate the reduced approach angle gained by the 3/4" drop. Is the benefit then in the increased track clearance?

 

[AKSNOWRIDER]

The kit your talking about moves the driveshaft down 3/4" and back 1"? I can see the 3/4 inch down reducing the approach angle, it seems like moving it back 1" would just negate the reduced approach angle gained by the 3/4" drop. Is the benefit then in the increased track clearance?

I have wondered the same thing craig, but after riding dougs..it rips....kurt says the drop and roll really helps with both tunnel evac. and with aproach angle..(I am thinking it moves the skid back as well if you look at the pics it looks like new tunnel brackets for the skid are included)

 

[mountainhorse]

Davy,

I can see where you are coming from...And I never take offense to a good discussion.

In fact... researching is before pulling the trigger on something is the best way to go.!

Here my view on the topic... expanded.

It is not the snow that is "packed up" inside... which, with the full length coolers on the Dragons is very minimal... it is the snow that you physically have to get pumped thru the tunnel...

Snow is pumped thru the tunnel like water down a river... you may get some minor buildup of ice in the nooks and crannies... but it doesnt get packed up there and stay. If it did...you're sled would stop.. Were talking tons of snow per minute here.

The smaller the opening... the harder the "pump" (read engines and clutches) have to work to get the same fwd motion. This amount of extra work grows exponentialy with the reduction in size.
This could account for upwards of 10- 20 HP worth of parsitic drag when you are ... I dont know of a pipe that give you that much hp.

For an example of this "pumping thru"... have a look at this Youtube video... in particular at :57 seconds into the clip.... you will see huge amounts of snow getting pumped out of the tunnel opening. This is typical of deep snow operation.
http://www.youtube.com/watch?v=eiuzQVlKDvM

On the Polaris sleds this is the weak suit in the design.... lack of clearance.

More material, (weather that is snow, water, dirt, yogurt or electrons) thruough a fixed opening takes more energy to move through that opening.

If you take the same amount of material and move it thru a smaller opening... it takes more engergy (HP) to move it at the same speed.

Opening up the clearance will take less HP run the sled thru the powder.... even more evident in high moisture content snow like we get in the Coastal states.

The ONLY reason. IMO, to switch to a 3" pitch track of the same type would be to be able to run 7 tooth drivers which have the smallest diameter (read tunnel clearance) of any of the drivers out there... there are no 7 tooth drivers for the Polaris shaft other than the Combo drivers. There are no 2.86" pitch 7 tooth drivers either. The additional clearance compared to an 8 tooth 2.86" driver (stock or Combo) is .28"... which would take the clearance from about .15 with the 8tooth drivers & a 2.5" lug to to about 5/8"...

Does the Camo Extreme perform better in most conditions, yes... It could be better if it had more clearance...

I'm running the Arctic Cat Power Claw HCR 153 on my sled this year... We'll see how it compares to the 155 Camo X, 2.86" pitch that I pulled off...it is 9 lbs lighter than the 155" Camo Ext 2.86 P

Point 2.... The RAW chassis with the 2.4" track has the least clearance of the production RMK's... mostly at the fwd roof of the tunnel is where it gets choked off.

Here is a photo of a RAW RMK tunnel (upside down) showing the rubbing of a STOCK 2.4" track on the tunnel... Polaris did not put much clearance for the big tracks in this area. I have seen a lot of Dragons with this rubbing. The Ch Ext 2.5" cuts this already marginal clearance by .10 (actually closer to 1/8" less) on the same drivers.

On sleds with large rear idlers... this rubbing is more apparent as the taller rear idler allows the track to lift off the top idler and go slack when the sled wheelies or comes down hard on the back of the tunnel.

The earlier models had more clearance at the roof of the tunnel... there was no cooler there... it was in the back only.

With D&R's... there is no free lunch as AK pointed out... move it down and back...net change in AOA is not that much... D&R's, IMO, the least amount to gain acceptable track clearance without throwing the balance of the sled off.

My 2 cents

PS... There was a VERY good write by Lane Lindstrom up on the topic of tunnel clearance in the December 2005 issue of SnoWest on page 44. If you still have your old mags.... dig this one out... It has "Saving the 700 class" on the cover with a pic of red 2006 700 RMK wheeling away from the camera. Good imput from some of the best sled builders in the industry.

On the Polaris RAW chassis, ice does not build up of the tunnel like in the days when the coolers did not run full-length. The problem area is at the front of the tunnel on the Dragon models where there is no bulkhead heat exchanger to melt off the snow... The plastic plate on the dragons sheds snow, but the space between that the cooler on the tunnel roof does get ice sticking/building up... I run a 1/16" thick piece of UHMW plastic, full width, in this area... Ice/snow will not stick to UHMW.

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.

 

[craigvansickle]

Is that why people that are trimming there 5.1 tracks down a little aren't noticing much of a change in deep powder? They loose some paddle but gain some track speed?

 

[mountainhorse]

Craig.... that and the shorter lug is stiffer..

IMO... the Camo Ch Ex 2.5" is not one that you really want to trim unless you ca generate a LOT of track speed (AO).... Untrimmed it is already on the brink of being a trencher... trimmed and in soft pow, not what I would call a great idea.

Will the Ch ext 2.5" 155 or 163 work? YES... Would it work much better with proper clearance.... Yes again.

The 2.25 Ext is a softer compound the the 2.5" and does not do as well in coastal snow.

The Cat Power Claw is a 2.25" track, but with an 8 tooth 3" pitch driver... it has a hair LESS clearance than a stock 2.4" series 5.1 track... That is why I'll be running the 7 tooth driver on this.

I think that the Holz 5/8" drop is a good conservative way to go that gives some more clearance where needed and not too much of a departure from the stock geometry of the sled...

 

[rmkboxer]

I put the 2.86 camo extreme on mine with avid drivers and a alpha x suspension. I know the track works great looking forward to testing out the suspension

 

[Polar Express]

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.

 

[Polar Express]

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

 

[rmkboxer]

I switched drivers so I could run my track looser so I don't burn my hi fax up. this is the first sled I have had to replace my hi fax on and it was at 500 miles

 

[mountainhorse]

Loose track = poor track performance...especially on stiff duro tall lug tracks like the Ch ext. if the track is looser than stock... stabbing is more likely, the track will lean over and cause other problems... Correctly tensioned tracks perform better... dont take my word for it.... Call Bruce Dasnaw at Camoplast or Jack Struthers at Carls cycles. Also, a loose track will further choke off the tunnel opening as the track "baloons" out at speed.

Running loose tracks was necessary on the early M series as that was the only way to get the skid to work... Polaris does not suffer from this problem.

I know many California riders that have over 1500 miles on thier original hyfax... and that is running stock everthing, less bogies add scratchers. Our snow is pretty darn hard and lubrication is less than ideal.

Davy... The rollong resistance between an 8 tooth and 7 tooth is not that big.... there is a big difernce between pulling on a track on the stand to judge drag.... and the driver actually driving the track with the weight of the sled/rider on the track. This applies to running big rear idlers, which on the RMK's, if you go larger than 8" you will see more drag and slack track problems.

The boundry layer of water on the coolers keeps the tunnel pretty darn clean, even at slow speeds. The UHMW PE would further add to the snow evacuation... I'll stand firm on my opinion that the snow flows thru the tunnel on the Raw like water down a river.

Personal experience with the 2.5" ch extreme with 7 tooth drivers.... it works well, especially if you have the track at the correct tension.

Would a bigger driver be possible...yes... is it practical, NIMO... I really want as little or no D&R as possible in my sleds....

The tunnel in the photo ran the stock series 5.1 DUAL ply track from 2008.
Tunnel clearance was about 1/4"....

Find that back issue of SnoWest that I talked about and give it a good look-see.

Good luck with your build...I hope to ride with you this year.

MH.

 

[Polar Express]

Eric,

Thanks again for taking the time!

 

[closed]

Davey,

I'm going to jump off the bridge first and go with the D and R from Fastrax with the Challenger Extreme. Great Thread though! Man, you can sure learn allot around here!!

Eric, hope to see you in Puyallup!

 

[coolx2]

Great thread,lots of questions answered that I had in relation to drop and rolls and swapping divers and tracks.Thanks again.