Bent front arms

I don't know where Skinz came up with the .7degrees in their 24.7 degrees. Marketing pitch I would think, because if you could tell the difference between 23 and 24.7 you are most likely an alien from another planet with super powers. I have stopped counting the sets of A arms I have built. When it comes to countersteering a powder machine, a certain amount of caster is key to good handling. I proved that with arms that I could adjust and then set each side differently and starting carving up meadows with 2 feet of fresh.
 
Off Trail Mike said:
Mountaintech said:
Is your Skinz front end 4.5" forward?
Click to expand...

Well, its actually a bit more. I measured from my spindle ski bolt to the point where the lower plastic meets the running boards. On my stock XTX, with new Ulmer's and UPBushman bushings (no subframe tweak) I measure 39 inches. On my MTX with skinz, I measure 44 inches, so the ski is closer to 5" forward...maybe 4.5 was measured at the lower a-arm hiem joint?????

Also, the caster is way more on the skinz. I didn't meaure, but I'd bet 5+ degrees more. If I get a chance, I'll measure this too. If I was to sum up the changes, I'd say the forward skis really helps with rolling the sled over on its side, and the increased caster seems to effect the turning radius and turning effort. It would be interesting to hear if you are thinking similar or not, and why you like the stock caster.

Hey Mountiantech, did you ever try any camber changes? I tried a couple of small changes, and didn't see any change in powder performance. Maybe it helps on the trail, but that's not my gig.

OTM
Click to expand...

Hey, could you do me a favor and measure the caster (both sides) on your 2 machines? Also, how do you transport your sleds?
 
Off Trail Mike said:
Mountaintech said:
Is your Skinz front end 4.5" forward?
Click to expand...

Well, its actually a bit more. I measured from my spindle ski bolt to the point where the lower plastic meets the running boards. On my stock XTX, with new Ulmer's and UPBushman bushings (no subframe tweak) I measure 39 inches. On my MTX with skinz, I measure 44 inches, so the ski is closer to 5" forward...maybe 4.5 was measured at the lower a-arm hiem joint?????

Also, the caster is way more on the skinz. I didn't meaure, but I'd bet 5+ degrees more. If I get a chance, I'll measure this too. If I was to sum up the changes, I'd say the forward skis really helps with rolling the sled over on its side, and the increased caster seems to effect the turning radius and turning effort. It would be interesting to hear if you are thinking similar or not, and why you like the stock caster.

Hey Mountiantech, did you ever try any camber changes? I tried a couple of small changes, and didn't see any change in powder performance. Maybe it helps on the trail, but that's not my gig.

OTM
Click to expand...

Hey, could you do me a favor and measure the caster (both sides) on your 2 machines? Also, how do you transport your sleds?
 
So I've got some angles. I used a 10" long adjustable protractor and a 6" level for these, so the angles should be pretty close (+/- 1 degree max).
Angles below are measured down the center line of the hiem joints relative to vertical. Handlebars straight, weight on skis (but no rider). I bounced the suspension a few times first.

XTX has new oillites and UPbushman bushings last season. Hiem joints have slop, but not excessive (maybe contributes to the last 0.5 degrees)
XTX - Stock 42" A-ARMs
LHS Angle: 22
RHS Angle: 21.5

MTX has 2000km's on plastic a-arm bushings with no noticable slop. Hiem joints still very tight.
MTX - Skinz Concept 39"
LHS Angle: 27
RHS Angle: 27

If you measured an imaginary line from the centerline of the spindle ski bolt to the upper ball joint, you can deduct 3 degrees from the above measures.

I don't think either subframe (XTX/MTX) has been "tweaked" yet, but I can't confirm this.

I'm not suprised by the difference in caster, as it was visible the day I put both sleds side by side. I am however suprised that my XTX is actually steeper than supposed "stock". I'll recheck my measures tomorrow, but pretty sure I got them right.

Stranage thing is you'd expect a harder steering sled with the increase in caster, but it simply isn't the case....the skinz turns as easy as the stock front end.

Oh yeah, I trailer my sleds typically or leave directly from home.

OTM
 
Thanks for the taking the time to measure. The problem I have found with a front end that is over 4" forward is that when loading into the back of a truck or onto a sled deck, the sled high centers on the belly pan and tears the lower body panel plastic.
 
I totally agree the subframe do tweak on these brutes, i'm sure most after some solid miles start tweaking.
I also agree, anything more then 4" is too far.
 
I would love a trail version 42" wide 3-4" forward not skinz 5" an adjustable castor/camber. Maybe one that utilizes jre spindle for trail purpose. itruely like the fact that it rocks the front shocks back more inline with the steering post, makes the suspension more in tune with rider I feel. I think the forward adds stability and the shock angle helps the rough trail capability
 
Well testing is done for the season. Spent my last day on the snow last weekend. Got the final designs figured out.
 
Rechecked the caster on my xtx stock a-arms today. 21.5 LHS and 21 RHS, so it's even steeper than Yami's advertized caster.

Not sure how much we need to move skis forward 3-4-5 inches, but bottom line is our modern mountian sleds seem to benefit from a lot of space between the track and the skis...call it a longer wheelbase. The RMK has very forward a-arms as well (likely what Skinz modeled theirs after).

The downside is loading onto sled decks becomes a PITA.

On the subject of Caster, my take on it is the Nytro @ 21 degrees is too steep and my Skinz is too shallow @ 27 so if I were testing, I'd be trying something right in the middle for starters.

Too bad I couldn't mod my skinz upper A-Arm just to see the performance difference with steeper caster.

Looking forward to seeing those new designs coming out of Mountiantech ;)!

OTM
 
Stock caster of 23 degrees decreases over time as front end gets tweaked. It'll go from 23 to 22..21...20...and so on.
 
kennyspec said:
Has anyone measured castor on a pro rmk? Or skidoo or pro limb for comparison?
Click to expand...

The yamaha engineer that is reading this thread can/should chime in on this one....

:)
 
Mountaintech said:
Stock caster of 23 degrees decreases over time as front end gets tweaked. It'll go from 23 to 22..21...20...and so on.
Click to expand...

It gets steeper when you lift the sled off the ground, but I thought when riding it does just the opposite??

As the hiem joints get sloppy, the camber should get shallower since the ski bolt is forward of the lower a-arm hiem joint on the spindle, so every time you hit a bump, it torques (twists) the spindle such that the lower joint goes up an the upper joint moves towards the back of the sled.

TMK50 has it tho, it would be very interesting to see what others sleds have for caster, I'm willing to bet they are very similar in the end.

OTM
 
When comparing Caster to another sled brand you would have to take the spindle design into consideration, maybe comparing the trail aswell.
 
I checked the caster on my Nytro and the RH side is 23deg, while the LH side is 15deg.
Thats with my new CR arms, just wanted to finnish the season.
Now i'm going to replace the subframe, just as mentioned, these subframes do tweak, especialy when you clip a rock and bend the arms.
 
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