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Xtra-12 How do you fine tune it?

This is a discussion on Xtra-12 How do you fine tune it? within the The Performance Tuning Shop forums, part of the Snowmobiles category; I have been going over my Polaris service manual for my 98 XLT LTD and trying to figure out the suspension adjustments. My sled has ...

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Thread: Xtra-12 How do you fine tune it?

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    Scott S's Avatar
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    I have been going over my Polaris service manual for my 98 XLT LTD and trying to figure out the suspension adjustments.

    My sled has 4 inch carbides on EZ steers, no studs. Suspension is set as follows. IFS 1 inch pre-load and 1 turn in on dampening. Front track shock 1-1/2" pre-load and 1 turn in on dampening. Torsion spring on medium. FRSS is set to high. I weigh about 205lbs.

    This set up has been awsome all year in powder and hard pack up until the new carbides as the old ones were worn down. They were a different configuration than the SPX and had carbides, about 2 inches at the very back only. The SPX has 4 inch of 90 degree in the middle

    I just replaced my carbides with 4" SPX 90 degree and this last ride out the rear was very loose. It was all over the trail even at constant speed. The trails were drifting and fairly soft. It felt as if the ski's were plowing under the snow and the rear was barely getting traction. It got worse with speed or deceleration and was even present while cruising. And by loose I mean all over the place in the rear. I touch the brake and around she would try and go. Same thing with acceleration. It was like a constant fishtail. After 138 miles of screwing around I was pooped. The front tracked straight and true. When in the bush on hardpacked she ran perfect. My buddy's sled tracked near perfect in all conditions.

    I dropped the front IFS springs pre-load to 1 inch, down 1 1/4 turns in 1/4 trun increments. I couldn't adjust the track anyways as it was iced over. It was still loose in the rear. My thought was to drop ski pressure.

    The factory manual describes how to do the adjustments but not what effect they have on the sled. It does say the limiter strap does not control ski-pressure as in a conventional set up. It is the FRSS which is set high - as light as possible. The limiter is all the way out anyways.

    I think maybe the front track shock preload might be related to ski pressure. When resting the front of the skid is solid on the floor and the rear is lifted about 1/8 of an inch off the floor. When you sit down the rear settles down.

    Does anyone know what each adjustment effects and to what extent?

    Due to poor snow I have to adjust while the skid is thawed and then trailer 2 hrs to ride. Once there I can't get any adjustments due to icing.

    Any suggestions or set ups I could try before heading out again.

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    Your Carbides are too agressive and do not match the traction in the back. Go back to using the same carbide as before or stud the track. I would recommend studding as the control of the machine is greatly enhanced in all conditions. Studs make for a safer snowmobile.

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    Scott S's Avatar
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    Thanks for the reply,

    The Polaris dealer is where I got the carbides. He said these were the correct ones for no studs. They are only 4 inch 90 degree SPX lites. The ones for studded sleds were 7 inch and up with 60 degrees. I don't know exactly what the old ones were as they were on the sled when I bought it used. I run 5.5 90 degree on the doo with a .91 non studded and they are great. I just reduced the ski pressure to offset the new carbides. Same thing as the carbides wore out I added ski pressure. Once changed I lightened it up and all was good. I just can't figure this one out.

    I am going ot stud it with 120 up the middle. I'm just not sure of the size. I was thinking of changing the .88 for a 1 inch track and going from there. It's just that the .88 is in perfect condition. I was thinking of doing it after the season.

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    keep reducing ski pressure either by softening ski shocks or increasing front skid pressure.

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    If the track is good, just leave her and stud. 96 is all you need for the xlt. Friend we ride with has a 97 sp with the 12 and 12. His rear shock needs some lovin, as she sits now, he gets no darting. He's running 6" of carbide.We did find before studding it was a spinner, with the .88. Thing was on rails after 96.
    Would have thought with 4 you would be fine. I know until they get worn a bit the rear will want to come around on you.
    That rear squat sounds simliar to his. Rear idlers are a inch or two off the ground before the front will loose contact.
    I've never played with the 12. My bet is you could stiffen your front shock to get less ski pressure. Yuor limter strap will decide how far down the front will go. Try letting them out just a bit in 1/4 inch adjustments.

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    I would stud the .88 track with 120 1" studs. Personally I don't think 96 is enough for the power your making. Studs will completely end your fish-tailing problem, they worked for me.

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    cnc
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    I was about to post asking for help but you just discribed to t exactly what is happening to my wifes 1999 500xc that we just bought. Deep snow or plowed road on the lake it goes fine, but on the trail with loose snow and small bumps it's constantly fishtailing even at steady speeds. I followed her and the track does not seem to spin before breaking loose to one side or the other. The guy who sold it to us just put new 6" carbides on with no studding on the track. We played with most of the suspention ajustments with no inprovement. I think I will put on a new pair of 3" ez steer carbides that I have for my classic touring. By the way can anyone tell me the proper set up for the both the front and rear limiter straps on the 500xc? I don't think they were set up right when we got the machine and I screwed around with them more trying to solve the fish tailing.
    Thanks

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    It does sound like too much carbide, but my '99 500XC just has steel skags, and it does the same thing, backing off the preload on the ski springs really helped though.
    Also, check the ski alignment, i know they say to toe them in...but try adjusting them dead even.

    Saw a great tip on Snowtraxx, set the skags into 4 - 6 foot long U channel that is snug enough not to move, measuements can be taken more accurately further ahead and behind the ski this way.

    cnc...my xc's limiters are set up as stock, I can check what they are set at if you like.

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    cnc
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    A buddy of my seems to think that if there is too much pre load on the front track shock then we are riding mostly on the front of the track and the skis and not getting even weight distribution and traction over the whole length of the track.

    500fasenuf, that would be great.

    cnc

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    Scott S's Avatar
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    CNC, that's what I was thinking also. The sled seems to pivot on the front of the skid. If I set it down lightly the front of the skid contacts the ground but the back is still 2-3 inches off. If I just get off it the rear is about 1/8 to 1/4 off the ground.

    Traditionally the front track shock preload is increased to reduce ski pressure, but the Xtra-12 has no shock on the front arm. It actually ties in to the center of the sled. It is reverse of most others including the Xtra-10 and the edge.Maybe this is the problem, I was thinking increasing the front pre-load would reduce the ski presure but in fact what is likely happening is the front of the skid is like a rocker and causing the sled to tip the center back and forth causing the loose feel. Maybe if I loosen the preload on the front track shock and flatten out the skid this will put more track to the snow and reduce this effect. It makes sence that when you slow or hit powder the sled tips forward loosing traction and causing excessive ski pressure. The rest of the time the ski pressure is likely too light. That would also explain the limited efect of the IFS spring pre-load.

    This would explain alot if it is in fact true.

    Given this that is why they said the limiter strap had nothing to do with the transfer as it was being over ridden by hte fron track shock mounted to the center arm instead of the front.

    With my doo and my new skid a quick spin of the limiter knob and she goes from wheelies to tracking hard and flat. The doo track shock is conventional and lays forward like the edge and is impacted by the limiter length which inturn affects the track angle and transfer.

    Hmmm.

    Any comments out there?

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