Help Understanding Rear Suspension in Deep Snow

craigvansickle · Sep 15, 2009

I am trying to understand the mysteries of the rear suspension and would appreciate some help. I have a good grasp on the actual mechanical function of the stock/timbersled/holz. What I am trying to understand is how these various setups react to the conditions presented to them and how that affects real world performance. I understand that there are many variables at play. To start with: I took a side view of a 600rmk 155" and put it on a 30 deg slope. In the current position the track is at a 13 deg angle from the surface of the snow. I would assume in this situation the front of the rails would be in the full down position. The rear would be moved up towards the tunnel due to weight transfer and the track being under full power. My question is what angle in reference to the surface of the snow is optimal. Lets say in standard powder. Not to fluffy and not to wet and dense. I hope this makes sense. It is my understanding that in this situation much of the weight of the whole rider machine combination is transfered to the rear of the skid frame. How well does the stock suspension operate in this condition vs quality aftermarket units?

akrevrider · Sep 15, 2009

Timberlsled review & Tech video

Craig,

My decision to purchase a Mountain Tamer came down to a leading edge design and at a price that I could still afford to do other mods to my sled.

With a maintenance background I recognized that the TS products are engineered very well with many new design changes for 2010.

Good luck in your research.

http://www.boondockersmovie.com/timbersled-suspension-review/

http://www.timbersled.com/MtnTamerTechVideo.htm

akrevrider

Jkinzer · Sep 15, 2009

watch the timbersled tech video and it will help explain the way rear suspensions work in reference to the sled

craigvansickle · Sep 16, 2009

Ok. I watched and read everything on the timbersled site. Including the installation instructions and tuning guide. So far this is what I understand regarding the stock suspension:

The back arm/coil spring/shock of the rear suspension has enough internal friction that it sags even when adjusted to the correct spring setting for the rider.

The back arm/coil spring/shock of the rear suspension does not have enough of a progressive travel to handle the the transfer of weight to the rear.

Do I have that correct?

KAWGRN · Sep 16, 2009

yes and if you put extra heavy springs in the rear rear it still colapses as the whole weight of the sled slides on to the rear arm, the timbersled does this too untill it hits the coupling stops then both arms are in time c onnected so the whole rail moves together and the spring forces also couple. I was going to try to make sisors stops for the stock lower arm like on the fAB CRAFT REAR BUT THE TIMBERSLED VID CONVINCED ME TO QUIT SCREWING AROUND

craigvansickle · Sep 16, 2009

KAWGRN said:
the whole rail moves together and the spring forces also couple.

Is the advantage of the coupling just in the increasing spring force required to move the rear or is there also an advantage to having the front and rear coupled together higher in there travel in the deep snow?

akrevrider · Sep 16, 2009

craigvansickle said:
Is the advantage of the coupling just in the increasing spring force required to move the rear or is there also an advantage to having the front and rear coupled together higher in there travel in the deep snow?

Craig,

There is an advantage to having the front & rear coupled together as the sled is at an incline during travel in deep snow.

The angle of the Mountain Tamer coupled skid allows for a better climbing position: thus pulling the sled up and over instead of clawing a tunnel through the snow.

Simply put the first couple of times I hit the steep & deep clawing through snow ridges, I could see where the stock IQ suspension was lacking.

IMO this is where the Mountain Tamer will allow me to work my way up a hill in/out of the throttle instead of blasting wide open hoping I'll make it over the top....:face-icon-small-hap

akrevrider

craigvansickle · Sep 16, 2009

akrevrider said:
Craig,

There is an advantage to having the front & rear coupled together as the sled is at an incline during travel in deep snow.

The angle of the Mountain Tamer coupled skid allows for a better climbing position: thus pulling the sled up and over instead of clawing a tunnel through the snow.

Simply put the first couple of times I hit the steep & deep clawing through snow ridges, I could see where the stock IQ suspension was lacking.

IMO this is where the Mountain Tamer will allow me to work my way up a hill in/out of the throttle instead of blasting wide open hoping I'll make it over the top....:face-icon-small-hap

akrevrider

OK so if you are in a climb (with mtn tamer) and the skid is floating around the point where the front and rear couple - you hit a variation in the snow - the suspension will compress evenly rather than just the soft, overloaded rear rear on the stock sled - keeping your skis down and the weight of sled more forward?

akrevrider · Sep 16, 2009

craigvansickle said:
OK so if you are in a climb (with mtn tamer) and the skid is floating around the point where the front and rear couple - you hit a variation in the snow - the suspension will compress evenly rather than just the soft, overloaded rear rear on the stock sled - keeping your skis down and the weight of sled more forward?

Craig,

You are correct on the design & operation statement. The paragraph below is from the thread Kawgrn started on his D-8T which also has a Mtn Tmr. There are also some good pics of the 2010 Mtn Tamer skid installed in "Kinzer's Mod" that he has posted up.

How the Mtn. Tamer Suspension Works:

"The biggest benefits of the Mtn. Tamer design is that it puts even pressure on the snow between the front and back portion of the suspension. This is achieved by our rear arm slide mechanism and the mounting position of the shocks. The slide mechanism couples the back portion of the suspension to the front at a specific spot in the range of travel. At this point the suspension will travel straight up into the tunnel, reduce the track angle, and applying the sleds weight toward the front, pulling it on top of the snow."

akrevrider

craigvansickle · Sep 17, 2009

Alright, that makes a lot of sense to me.

When I look at the photo I posted above a couple things jump out at me:

a steep ramp angle(where the track exits the driver and descends to meet the rails) would possibly increase the tendancy to claw at the snow rather than climb on top.

A steep ramp angle may also cause the sled have more of a tendancy to rotate backwards under high power on a slope in deep snow.

Are these statements accurate?

thefullmonte · Sep 17, 2009

craigvansickle said:
Alright, that makes a lot of sense to me.

When I look at the photo I posted above a couple things jump out at me:

a steep ramp angle(where the track exits the driver and descends to meet the rails) would possibly increase the tendancy to claw at the snow rather than climb on top.

A steep ramp angle may also cause the sled have more of a tendancy to rotate backwards under high power on a slope in deep snow.

Are these statements accurate?

Great thread buddy! :beer; I believe your statement is again correct. It has always been my understanding (removing all suspension variables) that a steep approach angle will want to dig and plow forward as you are saying rather than getting on top of the snow. In essence each paddle is going in the same spot the prior one did.
With less approach angle each paddle has the opportunity to dig further into into fresh snow. In a perfect world think of the belly pan parallel to the snow and your track making a nice gradual angle down in the powder. Each lug from your drivers to the very rear of your suspension digging further in the snow if necessary.
I don't think I explained that very well.

POLZIN · Sep 17, 2009

CV this is an awsome thread ! This is the kind of discussion I would love to see/ read more often on this site. keep it coming fellas !

without having revisited the Tsled video and assuming I understand what I have read above the tsled skid and specifically the adjustment on the rear torque arm allow for a geometric change affecting transfer rather than just a change in transfer due to changes in shock dampening /rebound/ spring tension etc. like most othe skids ?

akrevrider · Sep 17, 2009

craigvansickle said:
Alright, that makes a lot of sense to me.

When I look at the photo I posted above a couple things jump out at me:

a steep ramp angle(where the track exits the driver and descends to meet the rails) would possibly increase the tendancy to claw at the snow rather than climb on top.

A steep ramp angle may also cause the sled have more of a tendancy to rotate backwards under high power on a slope in deep snow.

Are these statements accurate?

A flatter track angle from the front of the track to the snow allows a sled to pull itself easier through the snow. Some riders install a drop & roll kit that allows for a flatter angle on their sled to obtain an optimum geometry.

The steeper angle will cause the track to trench into the snow instead of pulling itself through the snow. IMO.

akrevrider

craigvansickle · Sep 17, 2009

For the purpose of mountain riding it sounds like the weakest link in the stock IQ RMK is the rear suspensions rear shock/spring/linkage setup. This is something I really noticed while riding mine last year. My old 95 Mountain Cat had pretty much the same rear suspension but with much less travel. I have never cared to that setup. I am sure it is durable and cheap to manufacture, but it seems riding in the mountains asks too much from that dated design. I would love timbersled/float everything, and I could afford that no problem if this was one of a couple hobbies. The problem is that sleds are one of a half dozen expensive hobbies for me.

Each year I want to pick a couple things to improve on my sled. It sounds like this would be a good place to start this season.

Here is a thread I found that had some more good info: http://www.snowest.com/forum/showthread.php?t=151431&referrerid=65999

craigvansickle · Sep 18, 2009

POLZINHUNTER said:
without having revisited the Tsled video and assuming I understand what I have read above the tsled skid and specifically the adjustment on the rear torque arm allow for a geometric change affecting transfer rather than just a change in transfer due to changes in shock dampening /rebound/ spring tension etc. like most othe skids ?

It looks like you can add shims on the TSLED rear arm to adjust how far the rear compresses before coupling with the front.

craigvansickle · Sep 18, 2009

The M sled rails take a sharp turn at the front idler and are pretty much straight from there forward.

RMK rails make a longer gradual arc forward of the front idlers.

It looks like if the RMK rails made a sharper corner at the front idler and ran straight from there forward the approach angle would be almost identical to the M.

Does that variation in rails make a real world difference. It sounds like the rail kicking up in the rear does. How about the front?

polaris dude · Sep 19, 2009

so, if i was going to error on the side of either having it too stiff or too soft which would be better for climbing in powder?

craigvansickle · Sep 19, 2009

polaris dude said:
so, if i was going to error on the side of either having it too stiff or too soft which would be better for climbing in powder?

Hear is what I know with my limited experience with my stock 600. With that long 155" track it is nice to have that rear spring set softer. With those long rails bucking up and down on the bumps it is nice to have a softer setting. When the trail starts climbing up into the mountains I find that setting to be horrible. Especially when you are on a rutted and packed trail climbing up a face. The weight of the sled transfers back leaving your front end light or in the air. In those kind of conditions there is really no soft snow to cut into for steering with your track. I like the rear set much stiffer and weight on my skis. The softer rear spring in powder climbing is bad in another aspect. Even though you can carve side to side no problem the weight transfers far enough back that you have to push your body forward as far as you can to keep the skis down. This puts the rider/sled in an awkward position for maintaining a good line. I addition when you hit a steep section on the slope, even if only a small section, you sled is so rotated so far back and your body is in a bad position to maintain control. I rolled my machine last year in that situation. I had plenty of power and track to keep climbing but I was so far back that when I hit a sudden steep pitch I lost it. I am 200 pounds and I started running my rear spring on the stiffest setting.

Here is the configuration I currently run on my stock sled:
Skis at widest setting.
Sway bar on with shock springs set med-high on the front suspension.
Front track coil over set medium.
Limiter strap on lower or middle hole.
Highest spring setting on rear track spring.

Hope that helps.

never_to_much_powder · Sep 19, 2009

ok so i have more to add here. As far as the rails go i think that the polaris is better they are trying to make less sharp angles for the track to make allowing the track to rotate easier. just my .02 also ive heard that with the polaris's rear part of the rails being kicked up so much tha it also lightens up the front of the sled in deep snow durring climbing. Ive never been on a sled with differnt rails so im not sure about that. But as suspension goes i what about the ezride skid or the Holtz Alfa x so far the only thing im hearin is about the Timbersled skid....

polaris dude · Sep 19, 2009

i see, it makes sense when you think about it, but with my weight at a hefty 140 i might need it a little softer than that. But is it really that hard to control the sled with the skis up? I was hoping this year with the new sled that i would be able to body language it up without needing the skis down

Help Understanding Rear Suspension in Deep Snow

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