| Author |
Message |
    
Mike Carino (Mikec)
| | Posted on Wednesday, January 15, 2003 - 04:20 pm: | 
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Hi everyone, getting ready to put a 3in lift on the disco and I'm going to use Bilstein 7100 series shocks. I was wondering if anyone out there has them mounted on their rig and what valving did you go with front and rear. If anyone would like to make a suggestion or reference to valving to choose, I would appreciate that as well. I was looking at going with 360-80 on the front and 255-70 on the rear.
Thanks
Mike |
Peter Matusov (Pmatusov)
| | Posted on Wednesday, January 15, 2003 - 06:51 pm: |
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never thought about it, but it sounds like since a Disco has more weight in the back (about 60% on the rear axle), i'd use stiffer valved shocks in the rear.
peter |
perroneford
| | Posted on Wednesday, January 15, 2003 - 08:45 pm: |
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What springs are you using? You need to do the math on your springs and then pick the valvng to match. You want shocks that slightly overdamp the power of the spring uncompressing.
Both the springs force and the damping force of the shock are measureable and known values so it shouldn't be too hard...
-P |
James Gall (Jimmyg)
| | Posted on Thursday, January 16, 2003 - 12:43 am: |
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7100's....OVERKILL! Do you race or have sick Articulation? |
Mike Carino (Mikec)
| | Posted on Thursday, January 16, 2003 - 09:20 am: |
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Hey Perrone, I am going with Rovertym springs. If I remember correctly John does have that information on his site, so I'll look into it. The valving that I provided was given to me by the place I getting them from. I think the 360-80 for the front is probably right on, since you figure in the weight of the bumper and winch. 255-70 is middle of the road and was not sure how the laden/unladen cycle would affect driving manners. I think I should be able to fine tune the ride by adjusting the nitrogen pressure.
I'm going with the 7100's because they are fully rebuildable and you can adjust the valving on them. Also I like the build quality (heim joint mounting points, etc.). Plus I should have them for a very long time.
I was just looking to see if anyone else had experience with them and what valving they went with. Anymore advice or help is really appreciated.
Mike |
perroneford
| | Posted on Thursday, January 16, 2003 - 09:55 am: |
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Shock valving has absolutely NOTHING to do with how much weight is on the truck or how much your truck weighs. It's only relationship is to the spring rate, and length of travel of that spring.
Take note that the 7100s will be quite a bit louder than other more common shocks due to the lack of the rubber bushings.
Yes, John at RTE does run 7100s. I will be too sometime this summer, but I'm trying to figure if I want to modify my 3.5" lift first.
Good luck to you.
-P |
Peter Matusov (Pmatusov)
| | Posted on Thursday, January 16, 2003 - 07:21 pm: |
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Mike, adjusting nitrogen pressure doesn't change the valving.
Even with the bumper and winch your disco's front will be lighter than the rear, and, normally, disco front springs are softer than rears. Putting soft-valved shocks in the rear will make your rear passengers sick, and result in some really funky handling.
just like Perrone said, the shock valving should be at least proportional to the spring rate.
Also, I don't know how did you figure out that the 360/80 or whatever shocks match your front springs' rate. The shock valving (measured in something like Newtons per meter/s) is a totally different value than the spring rate (in, say, pounds per inch). The coincidence of the numbers does not mean anything.
peter |
perroneford
| | Posted on Thursday, January 16, 2003 - 08:42 pm: |
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Peter,
The spring rate determines how much force a spring can exert. When you mate this to the the length of excursion of the spring, (from fully compressed to unloaded), and you know the weight each spring is burdened with, you can calculate the speed and force with which the spring will uncompress.
When you know the force and rate the spring is compressing with (pounds per inch) you can convert that into metric numbers used for shock valving. You choose a shock with 10-15% more damping than normally required to compensate for ballistic movement of the spring (such as taking the spring to coil bind) and you have a balanced system.
-P |
Peter Matusov (Pmatusov)
| | Posted on Thursday, January 16, 2003 - 09:38 pm: |
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Perrone,
the spring rate and geometry, with the weight on this spring, are not enough to calculate the speed of compression/extension of the spring.
You're on the right track. The idea of a shock absorber (simple linear shock) is to keep the vehicle from bouncing repeatedly about its steady-state. Engineers have a term - Q-factor - which is proportional to the number of times something will pass its equilibrium point before settling. a Q-factor of 1 corresponds to ~3 oscillations. If you make the vehicle over-damped, with less than 1 cycle to rest, it will be rather harsh-riding. The optimum is Q~0.5-0.7. To keep the Q-factor constant (a task when choosing the right shock, besides word-of-mouth thing), the following relationship must be kept constant:
damper rate / sqrt(mass x spring rate).
note the nonlinear dependence here. If you get springs that are twice as stiff, you need a damper that's only ~40% stiffer, for the same vehicle. I mentioned "at least proportional" as a guide to get a shock that will produce the ride a hair stiffer than a stock shock with stock spring.
peter |
Mike Carino (Mikec)
| | Posted on Friday, January 17, 2003 - 11:44 am: |
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Thanks for the information guys and all the discussion. It has been very informative. I got an e-mail from Darrel Mauzy. He is running the same shock on his Disco and actually has a friend that works @ Bilstein in their off-road R&D. Darrel is running the 360-80's in the front as I would have suspected, but had the valving in the rear done at 400-100. I've e-mailed him back to see how the ride is.
Peter, I know that nitrogen pressure won't affect the valving, just how consistent the shock will perform.
Thanks for the help Perrone and Peter.
Mike C |
PerroneFord
| | Posted on Friday, January 17, 2003 - 11:57 am: |
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Good stuff Peter. I've been a bit slack on the Physics for some time. But both of our point's hold true. Determinig ride quality can be done "off the truck" but you need to know some important constants. People are always taken aback when they ask me about buying springs and I ask them what their truck weighs. How the hell are you going to choose proper springs when you don't know what you are asking them to hold up?
And as you pointed out, once you know what spring you need, finding the proper shock is not so difficult. The rate is non-linear because you are only changing one part of the system. Mass is being held constant. It also accounts for failure of damping when you put 50% more mass into the truck and try to drive 80 mph down the freeway.
-P |
Peter Matusov (Pmatusov)
| | Posted on Friday, January 17, 2003 - 12:07 pm: |
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I'd suggest to call Bilstein's shop in Poway with any questions. These guys make a zillion very custom shocks for desert racers, and they go into a very fine detail on valving and choice of shocks.
They can also revalve any shock for you to any setting you want (although i suspect it'll double the cost of the shock). It was an awesome thing to watch - how a shock gets taken apart, revalved, put back together, and the valving curve measured at the machine - all within 15 minutes.
peter |
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