FIRE UP
Ramona, CA. USA
Senior Member
Joined: 03/08/2004
View Profile
Good Sam RV Club Member
 Offline
|
Gents,
There's a been a zillion posts on rough ride, swaying, porpoising, wandering, and many, many more signs and symptoms of chassis handling problems. It seems the one answer that always appears, whether it's a diesel pusher, Class A Gasser, whatever, is PUT KONI FSDs on it! And in some cases, throw a set of BILSTEINS at it.
I, like many other F-53 pilots out there, have a fairly rough ride. But it doesn't just have to be an F-53, I've seen questions of the same nature coming from Monaco, Discovery and other Diesel drivers. There's a ton, as most of you experienced DIYs know, of other things that contribute to a harsh or rough ride, swaying etc etc. Load, springs, tires, tire pressure, sway bar bushings, sway bars themselves, panhard bars, air bags, etc etc.
OK, enough lead in. Since shocks seam to the the "do-all" answer for problematic front ends, I need someone with real technical expertise to explain to me, how a shock, which can be designed many ways, can soften a ride that, what has been logically explained to me, is caused by an over sprung front end. That is, for example, my front end is a 7000 lb front axle and, I assume the springs are rated for 7000 lbs. But, in actuality, the front end of my coach, with us in the front seats and ready for trip, only weighs in at just over 5300 lbs. That's roughly 1600-1700 lbs under weight for the capacity of the front springs.
Now, here's where I get confused. IF, you've got a set of springs that are strong enough to support 7000 lbs of weight, but, you've only got 5300 sitting on them, wouldn't that mean the spring is TOO STRONG for a normally soft ride?????? So, if the spring IS too strong, and you put a shock, ANY SHOCK, under it that has any portion of it's "compression dampening" at even 5%, WOULD THAT NOT ADD TO THE ALREADY HARSH RESISTANCE CREATED BY A TOO STRONG SPRING?? I guess what I'm asking here is, "How can a shock soften the compression of a TOO STRONG spring"?
I mean, you're already trying to compress a spring that although maybe rated for the coach and chassis, is too strong and or improperly loaded, and adding MORE resistance to that, therefore making the ride even more harsh. I have no idea how Konis for motor homes are designed, what kind of valving in the high speed vs slow speed circuits, and for that matter, Bilsteins either. To put is simpler, if you put a very small leaf spring from a tiny little trailer upside down on the concrete and, it's rated for two hundred pounds, and, you weigh two hundred pounds and stood on the arc, you would compress that spring, correct?
But, if the spring was rated for 400 lbs, and you stood on it, I'm pretty sure you wouldn't even change the arc at all. If you were to add a shock that has even 5% of compression dampening, it surely wouldn't compress.
So, am I way off in all my theory here? I don't profess to be any type of design engineer, I'm just trying to logically understand some of the reasoning some give for correcting problematic front ends of these beasts. Thanks for any tech help here.
Scott
Scott and Karla
San Diego Fire Department RETIRED
2004 Itasca Horizon, 36GD Slate Blue 330 CAT
2011 White Honda CRV EX-L,4WD w/NAV Toad
2008 Caliente Red LVL II GL 1800 Goldwing
KI60ND
|
Cloud Dancer
San Antonio and Livingston TX USA
Senior Member
Joined: 06/08/2001
View Profile
|
First of all, the amount of total weight that the spring can support has nothing to do with it. You might have that confused with spring rate(how much weight it takes to compress the spring ONE inch). THEN, you need to know whether the spring is linear or non-linear.
YES, a shock absorber is NOT the part of the suspension design that is FIRST looked at whenever one is designing a "soft-ride" suspension.
A "soft" spring can support as much total weight as a "hard" spring, (ALL WITHIN REASON, of course). The difference is that the soft spring will require more vertical 'travel' to be designed into the suspension, due to the fact that it's going to compress MORE. If your total design does NOT allow ample/sufficient vertical 'travel', you simply can NOT end up with an optimized 'soft' suspension.
* This post was
edited 09/08/10 11:59am by Cloud Dancer *
Willie & Betty Sue
Miko & Sparky
2003 41 ft Dutch Star Diesel Pusher/Spartan
Floorplan 4010
Blazer toad & Ranger bassboat
|
jauguston
Bellingham, WA
Senior Member
Joined: 07/03/2005
View Profile
Offline
|
You specify springs in your question. Many motorhomes have air ride. My last coach was a 32' Gulfstream Sun Voyager DP. The problem with the ride and it came new with Bilstein shocks was the front end porpoised something terrible on uneven roads. I put a set of Koni FSD shocks on the front only and it made a totally different coach out of it. FSD's are expensive but worth every nickel. I don't have enough miles on the Sportscoach Elite to be sure yet but I am betting it will get FSD's on the front also.
Jim
2005 Coachman Sportscoach Elite 402 40'
350hp Cat C-7 w/MP-8
7500w Onan quiet diesel generator
6-Kyocera 130w solar panels SB3024i MPPT controller
Pressure Pro TPMS
1987 Suzuki Samurai tintop Toad w/VW 1.6 turbo diesel power
|
JIH
Roseville, CA
Senior Member
Joined: 09/30/2007
View Profile
|
FIRE UP wrote:Gents,
There's a been a zillion posts on rough ride, swaying, porpoising, wandering, and many, many more signs and symptoms of chassis handling problems. It seems the one answer that always appears, whether it's a diesel pusher, Class A Gasser, whatever, is PUT KONI FSDs on it! And in some cases, throw a set of BILSTEINS at it.
Boy do you have guts!! I have always wanted someone to explain how a set of shocks can soften a ride at the same time help to control sway. By the specs Koni's have slightly more compression resistance than my stock Monroes, so I can not bring myself to believe that the Koni's will do anything for my very rough riding front suspension. I have just been reading up on the Kelderman (?) system which replaces the front leaf springs with ones with a lower spring rate and then adds an air bag. I believe this whould help, but the cost is about 15% of my motorhomes value. Can't justify it at this time. By the way, I drove my motorhome with the shocks removed and it porpoised (bounced) very badly. It is what shocks are designed to eliminate.
With new $47 Monroes it totally eliminated that condition.
* This post was
edited 09/08/10 12:23pm by JIH *
2000 Southwind 36Z
2004 GMC Canyon, Toad
|
rgatijnet1
Florida
Senior Member
Joined: 06/22/2009
View Profile
Good Sam RV Club Member
|
You can still drive your coach down the road with no shocks at all. The shocks will not change the carrying capacity of the springs, etc. What you will find out is that at every bump, the coach will continue to bounce up and down. The shocks are installed to dampen that movement so that after a bump, the spring reacts to absorb the bump and the shock reacts to dampen the spring movement both up and down.
I had Bilsteen shocks, and being gas charged, they tend to resist spring movement on a small bump, like a road joint. The FSD shocks are not gas charged and handled the small road joints better. On large bumps, I did not notice any difference between the two shocks. Both Bilsteens and Koni's were a big improvement over the worn out OEM shocks that I replaced. I did not compare the Billsteens or Konis to a new set of OEM shocks so I cannot say that the more expensive shocks are a lot better, or even any better, than the OEM shocks that come from the factory.
|
|
|
Cloud Dancer
San Antonio and Livingston TX USA
Senior Member
Joined: 06/08/2001
View Profile
|
I've also noticed that people confuse the "quality" of a brand of shock absorber with the owner's selection of the quality of the "match"(shock piston diameter and valving and travel to the application).
|
LVJ58
Las Vegas, Nevada
Senior Member
Joined: 02/26/2001
View Profile
Good Sam RV Club Member
Offline
|
Don't understand it, can't explain it, but the FSD shocks sure enhanced the ride quality of our 2000 F53 and that's basically all I cared about.
Fun & Safe travels to all,
Jim & Sherry Seward
Las Vegas, NV
2000 Residency 3790 V-10 w/tags & Banks System
2003 Suzuki XL/7 toad
|
StevenH
Michigan
Senior Member
Joined: 02/20/2008
View Profile
Offline
|
What Cloud Dancer is saying using your simplified example of a spring rated at 400 lbs with a 200 lb load. The spring may be compressed 50% or some other number for example 75%. The 50% would represent a somewhat linear compression the 75% a non-linear. The loads are not static (you standing on the spring) but dynamic (you jumping up and down). The more travel the spring has the easier to get a good ride but then you start getting bounce (porposing) and other non desirable issues. The shock will dampen the spring so you don't keep bouncing up and down after hitting a bump. This is what solved jauguston's issue.
Susspensions are very complex and the more weight variation from empty to full the tougher the job to get a good ride. Compare an old pickup truck to the more current ones. The difference in ride is amazing. Auto makers have invested considerable sums of cash in improving ride. More expensive variable rate springs and other things.
Most people "throw" a set of shocks at the problem because it is the simplest and cheapest attempt at solving the problem. If the springs are getting soft the vehicle may start bottoming out against the bump stops. Your looking at a larger investment replacing these.
Hope this helps.
Steve
97 Beaver Patriot 40'
3126 CAT, Allison 3060
Aqua Hot
|
wolfe10
Texas
Senior Member
Joined: 10/08/2000
View Profile
Offline
|
OK, the information in the original post is absolutely valid. Boiled down, if the axle does not deflect relative to the chassis (i.e. no movement between them) a shock does NOT do any work. Said another way, a shock only works when there is suspension travel.
I can remember back 5 years ago, discussing this with the owner of a leaf spring DP whose front axle weight was WAY under front GAWR. His conversation started-- what shocks will..... Well my first suggestion (after the basics like tire pressure) was to totally remove the front shocks and go for a drive. Indeed, he proved that his old shocks were NOT the cause of the harsh ride, as ride quality did not change (though of course handling over bumps did).
Once the spring and actual weight are in-line (i.e. the spring allows the axle to deflect over bumps, THEN shocks come into play.
Shocks can/do dampen movement on extension and on compression. And the rate/amount of dampening can vary a lot between the two directions.
Simplistically, dampening on compression adds to the effective spring rate (making the ride harsher). So if you have a choice, you want the majority of the dampening done on extension.
For the most part shocks are a compromise. The best shock over a tar strip or bridge joint is NONE. The suspension is not deflecting enough that you need control. And dampening just adds to ride harshness. Now, go over a big dip and you need a lot of control to keep from porpoising. So, chassis engineers and shock designers for the most part have to compromise between too stiff and too soft.
Let's take it to the next level-- many mention the Koni FSD's. The beauty of these shocks is the designer did not have to choose A valving-- they can choose one set of valves/dampening control over those tar strips and a very different one over the large dips. Generally, for a given application, the Koni FSD's are softer over small bumps and yet stiffer over the big ones. Much less compromises. But, of course at a cost!
Brett Wolfe
1993 Foretravel 36' U-240
Cat 3116, Allison 3060
FMCA Forum: www.community.fmca.com/index
Caterpillar RV Engine Owner's Club: www.catrvclub.org
|
Gsmitty77
San Diego
Senior Member
Joined: 10/09/2006
View Profile
Offline
|
Oh Boy - A shock thread!!!
One comment I think I learned back when researching FSD's, and how they help some on stiffness.
Most shocks 'dampen' (add resistance) during the compression stroke. FSD's 'dampen' on the 'rebound', or up stroke.
So, no compression stroke add to the feel of a stiff ride. Porpose/Dampen/Shock control, during the rebound upstroke, does the duty of the shock.
Other comments:
-Liked Kelderman, except for the costs
-Most F53's on the road, are way underloaded on the front end. More so with many Fleetwood products, that have the water tank on the very back end of the rig. (Full tank of gas, full tank of water, and the wife's shoe collection under the bed = Smitty popping a wheely!)
-Linear or progressive, are key questions to consider when talking springs.
So, why all the questions on shocks for your Bounder, you know you want a DP to carry your bike on the back of !
Best to all. And Scott, my best to your fire brother's in Colorado, fighting a fire as we all type...
Smitty
(Ex Bounder F53 Owner - Roo, she was a fine rig!
|
|
|
|
