Snowmobile Fanatics banner
1 - 13 of 13 Posts

·
Registered
Joined
·
94 Posts
Discussion Starter · #1 ·
I plan on running a dual rate setup on my ProX and on my dads 04 XC SP.
Deycore used to sell a kit that came with a 4 inch spring and a 9 inch spring. For these particular applications a 13 inch total is perfect. My question is why not run a 6 inch and a 7 inch spring ?
For this discussion let's use a 100/180 set up in a ProX which has 5.7 inches of shock stroke. This combo has a 64.3lb initial spring rate.
If using a 4 " and a 9" spring the 4" spring will coil bind (if no tuning rings are used) after 2.65" of shock stroke then crossing over onto the 9" spring for the remaining 3.05" of shock stroke.
same scenario but using a 6" and a 7" spring.
the 6" spring will coil bind (if no tuning rings are used) after 3.5" of shock stroke then crossing over onto the 7" spring for the remainder of 2.2" of shock stroke.
If you where trying to tune so the sled eats up the small washboard then still has enough to handle some big moguls wouldn't you want to use the majority of your suspension up on the lighter spring then save the last part of your travel for the occasional big bump ? Or would you split it evenly by using the 4" spring ?

Next part. What is too much rate and to little rate ? I know too much will be stiff as hell and not enough will not have enough ski pressure and can bottom out.
I was thinking for my Prox I would try 120/160 which has an initial rate of 68lbs. So if I was using a 4" & 9" set up the soft spring would take 180.2lbs to compress 2.65" then crossing over to the 160 which would take a additional 488lbs (total of 668.2) to fully use the remaining 3.05" of shock stroke.
Does this sound like it would be okay ?
 

·
Registered
Joined
·
3,729 Posts
Let me clarify, that we are talking front suspension, correct? Overall, I think the 6/7-inch combo would work. Also, an inch of shock travel at the top of the stroke makes for less ski travel than an inch of shock travel at the bottom of the stroke. So even more reason to go with the 6/7-inch setup. It sounds like you are meaning for this to be a trail setup, not a racing setup, which is maybe what the 4/9-inch setup was for.

A couple questions though. You said we were talking about a 100/180 lb setup. Why do you say the initial spring rate is 64.3 lb? Are the springs variable rate by themselves?

How did you figure the amount of shock stroke at the point of the initial spring bind? Do you have the bound spring length for the lighter spring? Your numbers do not make sense to me.
 

·
Registered
Joined
·
94 Posts
Discussion Starter · #3 ·
Yes we are talking front suspensions and for a trail setup.

Using a 100/180 the initial rate number comes from (spring rate #1)x(spring rate #2) divided by (spring rate #1)+ (spring rate #2)= initial rate. Plus I have a dual rate spring chart. Basically two springs working together have a lighter rate than each spring has seperately, until the lighter spring coilbinds (or hits the tuning ring) then the rate is that of the heavier spring.
Yes I have a chart showing spring lengths and what there solid length (coilbind) is , the difference between the two is your length of stroke.
 

·
Registered
Joined
·
3,729 Posts
Okay then. At 2.65 inches on the 4/9, 120/160 combo, the force would not be 180.2 lb. 68 lb may be the INITIAL rate, but it is not the rate for all of the first 2.65 inches. Therefore, you cannot just take 2.65*68 to get the force at 2.65 inches.

What is the solid length of the first spring?
 

·
Registered
Joined
·
94 Posts
Discussion Starter · #5 ·
Okay that answers another question I had. When the lighter spring compresses which rate do you use, the initial or the rate of that particular spring ? Sounds like the rate of the spring correct ?

Solid rate on a 4" 120lb rate spring is 1.350"
 

·
Registered
Joined
·
3,729 Posts
Originally posted by proxrider
[br]Okay that answers another question I had. When the lighter spring compresses which rate do you use, the initial or the rate of that particular spring ?
Actually, both. Remember, as the lighter spring compresses, the heavier spring also compresses, just not as much. Also, remember that there will always be an equal amount of force on each spring. That last sentence is key. So, it is not as simple to say that the smaller spring compresses for 2.65 inches of shock stroke, then the larger spring compresses for the rest of the stroke. Actually, with the 4/9, 120/160 combo the smaller spring compresses for 4.6375 inches of shock stroke. Here, Let's figure the point where the small spring binds, using some math. The small spring binds when there is enough force on it to compress it 2.65 inches. 2.65*120=318 lb. So, if there is 318 lb on the small spring, there is also 318 lb on the big spring. The big spring compresses how far? 318/160=1.9875 inches. So the total shock travel equals 2.65+1.9875=4.6375 inches at the point where the small spring binds. So, if your total shock stroke is 5.7 inches, you are using the lighter spring for 4.6375 inches of the 5.7.

If you went to a 6/7, 100/180 setup, I am guessing you would never even bind the 6 inch spring. If we knew the solid length of the 6 inch, 100 lb spring, we could figure it out.

Conclusion: I would stick with the 4/9 combo. If you could go with a 4/9, 100/180 setup, you would have a softer ride at the beginning, but it would bind faster, causing the heavier spring to be used sooner.

Also, it seems to me that a 100 lb spring should give you plenty of ski pressure for trail conditions.
 

·
Registered
Joined
·
3,729 Posts
Another thing I noticed. Is the solid length of the 100 lb spring the same as the solid length of the 120 lb spring?
 

·
Registered
Joined
·
94 Posts
Discussion Starter · #8 ·
I think I'm getting it now, I don't know why I thought nothing would be happening to the second spring. So it sounds like I was missing a big part of this equation.
So if I decided to add a tuning ring (.5") it would put me into the stiffer spring after 4.1375" of shock stroke ?

Now what about rates ? What is too much and what is not enough ? I'm assuming shock valveing has a lot to do with this. Does the 120/160 combo seem like a good starting point ?

The 4" 100lb spring solid length is 1.310"
 

·
Registered
Joined
·
94 Posts
Discussion Starter · #9 ·
So being that I'm somewhat of an aggresive rider, no jumps but like to ride fast. I also am a pretty heavy guy , around 240lbs. Washboard really irritates me so Im trying to dial the sled in to go thru that but still be able to take a big hit , does the 110/180 sound like a good place to start ?

Now on my dads XCSP, he is 60 and unfortunalty has to keep up with us , he doesn't mind the speed but I can see the bumps really get to him. Washboard is the major thing, when the bumps get REAL big he just slows down. Does a 100/160 set up sound good for this machine ? He is about a 190lb rider. Total shock stroke on his sled is 5.25"
 

·
Registered
Joined
·
3,729 Posts
I am not familiar with tuning rings. Does it just go between the coils to efectively decrease the spring travel? If that is the case, and you add a .5 inch ring, you cannot simply subtract .5 inches from the travel. You have to refigure.

2.15*120=258. 258/160=1.6125. 2.15+1.6125=3.7625. So your smaller spring is effectively bound at 3.7625 inches of shock stroke.

As for the rates you want, hopefully somebody more knowledgeable on the Pro X and XC machine setup will chime in.

For giggles, lets do the 4/9, 100/180 setup. 4-1.310=2.69. 2.69*100=269. 269/180=1.494. 2.69+1.494=4.184. So at 4.184 inches of shock travel, your small spring would be bound.
 

·
Registered
Joined
·
8,108 Posts
I used them for a little while on my 02, they eat up the threaded shock bodies like a mother though.
 

·
Registered
Joined
·
94 Posts
Discussion Starter · #12 ·
JD,
Thanks alot for your help. Now I just have to play around with different rates and stuff.
Rip,
I know they will be wearing the bodies but from what I understand you can not get a better set up .
 

·
Registered
Joined
·
506 Posts
The XC uses a 68 intitial rate and the Prox uses an 80 initial rate. On the XC I would tend to start at the 68 setting. On your pro if you want to soften the stutters a bit think about getting between the 2. When playing with dual springs use the springs to tune and valving for fine tunning.
 
1 - 13 of 13 Posts
Top