what are pros and cons for extroverts driver

[mountainhorse]

First off... no one here is being an A-Hole.. Just a good discussion.
( though I've been one at different points in my life.. LOL.)

frisco... have a look at the inside fwd roof of your tunnel...You will probably find rub marks from the track if you are running 8 tooth drivers and the stock or 2.5" track like most sleds I've looked at with this mod running a loose track (even bone stock sleds have this because of the small clearance)

Here is my take on the whole tension thing from some other posts (cut/paste)

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... don't take my word for it.... Call Bruce Dashnaw at Camoplast or Jack Struthers at Carls cycles. Also, a loose track will further choke off the tunnel opening as the track "balloons" 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 their original hyfax... and that is running stock everything, less bogies add scratchers. Our snow is pretty darn hard and lubrication is less than ideal.

The rolling resistance between an 8 tooth and 7 tooth is not that big.... there is a big difference 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 boundary 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 through 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.

even with the Avid Combo drivers... Keep the track tension stock on the track... a loose track allows the track to distort, the paddles to fold over a bit more than normal and gives poor performance.

I believe that loose tracks that distort under load are the major reason for "stabbing" NOT the fact that the rails are trimmed or the teeth are "sucking" the track up between the the driver and rail... a tight track cant get "sucked up" in that gap. Early M-Cats had crappy rear suspension geometry that HAD to run the track loose... those are the ones that gave rise to the phenomena of stabbing...loose tracks to follow suit... stock Doos don't have stabbing problems, they have short rail tips and no issues with stabbing on a wholesale level.

The new single ply tracks will stretch more quickly than previous models and need to be checked for proper tension quite often (tension instructions in your Owners manual)

Proper tension = better performance than a loose (out of spec) track.

Mountainhorse:Looser tracks allow the paddles to fold over easier... a part of the equation that most dont think of and is the MAIN reason why (I think) Jack Struthers says that a tight track works better than a loose one...it hooks up better, expecially in more setup conditions like on a track or hill-drags, or spring time climbing (or our average Sierra cement)

The people with Extrovert (AKA combo) drivers seem to want to run the track real loose and feel it frees up HP...a loose track allows for distortion of the track as it leaves the driver and makes the track more suceptable to "stabbing"... With the extros, I dont look at them as a way to allow a track to be run looser... I look at it as a prevention of ratcheting in the high-demand situations.

I think the "combo" drivers are the best option, but run almost as tight as the stock drivers AND run the more slippery hyperfax as well as popping back on some idlers for spring conditions as well.

Extros, IMO, are mandatory on high hp sleds... BUT they should be run at the correct, not loose, tension... similar to normal tracks/stock-drivers.

When they are running normally, not ratcheting, the teeth of the extro are not even contacting the track or the clips and only drive from the involute portion on the inside of the track.
The first of the M-series cats had poor geometry that tightended up the track when it worked thru the travel and caused all kinds of problems that was the big factory push to extros and the one that gave the extros and stabbing a bad rap


Do NOT run the track too loose.... many people do with extros and end up stabbing the rails thru the windows... IMO, too loose of tracks by people with Extrovert drivers is the main cause of stabbing track windows with the rails ("stabbing")... most sleds do not, IMO, need anti stabbing kits...

There is a difference between an extrovert and a combo driver... unless it is ratcheting, the teeth on a combo driver never touch the track.

Mountainhorse:Loose tracks may "pull" easier with the sled off the ground... but that is not the case with the sled in motion, with the weight of the sled on the track and drivers turning the track... rippling as it is pushed down the hyfax.

You can't compare the power required to turn track being pulled by hand on a stand and one that is in use, under power with traction... these are two completely different scenarios.

Also, with the Combos on ANY Polaris RMK>....Run STOCK tension specs if you want the track to perform well...especially on the lightweight single ply tracks....The myth that a loose track will turn easier and use less hp is just that... a myth... Loose tracks are more prone to stabbing, the paddles lay down easier, the track balloons out and rubs on the tunnel or decreases clearance, and there is more friction along the hyfax when the sled is in motion with the wieght of the rider and sled on it....Turning it on a stand with the track off the ground is NOT representative of what is happening with a sled on the snow and in motion.

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[mountainhorse]

The stock drivers (3 driver setup with the toothed center driver) DO ratchet from time to time.

Once the track starts to ratchet and the teeth are driving the track.. if it does ratchet... the track teeth ride up on the track, stretching the track like crazy flexing the fiberglass rods in the track rubber and "crash" the track into the tunnel surface until the teeth settle back into the driver window.

If you have had your track ratchet on a stock driver setup... this is what is happening.

In my experience, ratcheting is a non-issue with Avid combo drivers.

Now this being said... only a small percentage of riders will experience ratcheting with the stock system... mostly due to not adjusting track tension as they should OR ... if you ride in sticky/wet snow, an ice ball forms around the drivers & Shaft and push the track up and off the drive nubs and teeth on the center driver.















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[pura vida]

i disliked that center extro so much on my d8 that i cut it out with a chisel and hammer (i was too lazy to pull the drive shaft and press the drivers off). i would have done the same on the pro if i would have kept the stock track.

i've really gone back and forth on the whole clearance issue. i could definitely see how the parasitic (that's not the right word...?) drag could be a major HP sap but on the other hand the vast majority of the snow/air is being moved between the paddles of the track negating the overall issue of the drag. to much clearance could be detrimental also as you could create a substantial amount of turbulence in the air and snow. this could be just as bad as the drag. just wish there was a way to measure it. guess you could try a track dyno but that won't take into the effect from snow which my guess tells me would have a much larger effect on the equation than just air would. can you stick a track dyno in water...?

pv

 

[mountainhorse]

Pura...

Yep.. a test of that would be great...but as you say..pretty darn difficult.

If you look at any of the burandt vids or others on PRO RMK's (or any brand for that matter) if they get the front end up and are WFO... look at how much snow snow is flowing out the front of the tunnel... tons and tons.

Restrict any opening and you will have more resistance and take more hp to "pump" that through.

Lots of factors like snow density play a big role in just how much HP will be lost to drag.

I'm not so worried about pumping losses from air.







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[pura vida]

that's actually exactly what i was talking about. you can really see it in some of the turbo vids (thinking of boost) since they are using soooo much hp. plus the turbo vids REALLY highlight the loose/tight track debate/discussion.

yes there is a ton of snow coming from what looks like between the track and front tunnel area but... how much of that snow is actually being moved between the paddles of the track? my guess would be most of it since if you think about how the snow is moving then it will naturally want to continue to move straight down/out as the track continues to curve around the drivers and there is no longer a restriction from the tunnel/bulkhead. it wants to follow the path of least resistance or in this case it is similar to water wanting to take a natural downhill path. compared to that snow actually being snow that is "stuck" between the top of the paddles and the tunnel and being forced out do the the rest of the systems movement. so.... in theory, i would think the "perfect" solution would be to have a system that had zero clearance between the paddle tops and the tunnel/bulkhead (obviously ignoring the real world issue of rubber on metal friction) causing 100% of the snow to be moved at the same rate throughout its path until being dropped out of the system at the front bulkhead.

the only viable real world possible testing would be to have multiple sleds set up exactly the same with only different clearance (d&r) and drivers.

the only time air movement would be an issue would be for top end speed goals which is an entirely different application than what we are discussing.

pv

 

[mountainhorse]

This is the same discussion I had with Davy (PolarExpress) a couple of seasons ago.

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?

And My reply:

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 an (exhaust) 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.

.....

Does the Camo Extreme perform better in most conditions, yes... It could be better if it had (even) 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. (Note Dec 4, 2011... Same is true of the PRO-RMK with nearly identical clearance issues.)

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.

(Note Dec 4, 2011... Same is true of the PRO-RMK I've seen the same rub marks on the tunnels.)

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 (or PRO) 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.

Have a look at this doc... analogous to paddles on a track

http://www.posetech.com/FORUM/finger_spacing.pdf

 

[mountainhorse]

One of the things that DOES help the PRO is that the much smaller capacity coolers have a larger space between them to help with snow movement.

In the end, as Pura pointed out... the only way to tell is in the real world... not me sitting here being a "keyboard" jockey.

Snow conditions, humidity, track speed, track design etc will all factor in...


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[starfire99]

Woody's has a dyno that measures the force required to turn the track only. When the track tension is reduced to the point where a "wave" developes as the track leaves the drivers, it starts to ABSORB MORE HORSEPOWER. The amount of force to move the track by hand is meaningless unless you ride under 30 mph all day.

 

[pura vida]

interesting read for sure, definitely worth some consideration. (where do you find this stuff?? ) i was thinking about the same river analogy but then thought that a jet unit, like you find on an outboard, might be a better comparison. the impeller needs to be tight to the sleeve in order to maintain efficiency and to avoid cavitation. in simple terms, too much space is bad. not sure if it correlates to sleds though. might have to try dropping to 7 tooth drivers if i get a hair up my backside. although i still don't want to run combos right now but decreasing the driver radius could lead to a ratcheting issue. lets see how bored i get later on this winter...

pv