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Not to pick on boater Al or Marathon I am not surprised the setting needs to be at max firm. A coach that has less weight on the front may find that setting unacceptable. What is your front axle weight Al, not what Marathon says, but what the scales say?
Jon,
I went with the setting that I heard from other owners. Asking the question of Marathon on weight, around 16 K. When I get some extra time I'll take your suggestion to the scales. Just for grins has anyone weighed the front end of an '05-'07 Marathon XLII double slide with or with out the family dog ?
AL
05 Marathon 2s
When in Spearfish we saw one that topped the charts at somewhere around 19,000.
There you go, was that porker an XL II or HS-45 ? At that weight there speaks for the setting for full firm or you will be prematurely wearing out your front end parts. I did notice that the up and down seemed a little excessive on the trip to Omaha. I had 2 sets of Koni's on my Affinity with the setting oppox 1 turn off max firm. That seemed to work best. Concern was the heavy weight of the XL II and with input from members was confirmed max firm was probably be the setting. After about 500 miles I'll know for sure about this current setting.
TIRES....I also had that minor pulling problem on the Affinity. Seemed to be aggravated by excess road crown. I decided to cross the tires before driving on to the alignment rack. There were 20 K miles on new Michelins , no visible wear, no cupping. On Country Coach the problem tire is the right front. That solved the issue immediately.
AL
05 Marathon XLII 2S
The Marathon weighed in Spearfish was an XLII.
I'm curious. My coach really hates the cross-cut cement roads that we have here in CA. I feel every separation, and at times it can be really annoying to almost bone jarring.
I get a little (but not a lot) of what I would consider to be bouncing type of motion that I would associate with bad shocks. I've asked, and have been told that 45'ers tend to oscillate a bit more than the 40s (my 40ft didn't bounce at all).
So, I'm curious if new shocks might help with this cross-cut type of roads?
Ray
Al,What is the Koni part number?
The correct tire pressure combined with a shock set for the particular coach or driver's needs will do what can be done, but I don't think our suspensions can make all roads feel like a magic carpet.
If our coach requires a lot of air pressure for its air bags, by its nature the ride is going to be compromised and if the shocks are bad the coach is going to have very little dampening.
I am not sure what you mean by cross-cut, but there is a stretch of I-59 from the northern AL state line towards Birmingham that has expansion joints or some variations in the slab heights at the joints and my coach just gets hammered going down that road. I do not experience anything like that anywhere else. But I won't look to make any changes in my bus because of that road. It is just the way that road feels and I suspect all vehicles are affected.
You are correct about the stretch of I-59 in AL. One of the worst sections I have traveled too. I ride the left lane and you do not get beat up quite so bad.
I do ride the left lane and let everyone pass on the right. I-10 west through Louisiana used to be like that many years ago, but last time we were on it it wasn't bad.
The last time we had the POG at Kerrville, I-10 was terrible. After bouncing all the way there and back; I changed my shocks on our 40' Marathon as soon as I got back home, and I didn't really see any diference. It was just a bad road.
Koni part number for XLII is 90-2574. Does anyone have any suggestions for cold tire pressure? I have heard 105-95-85 from several sources.
AL
05 Marathon XLII
Pressures are based solely on weght.
http://www.michelintruck.com/micheli...ion-tables.jsp
AL,Thanks for the part #,I had a non slide 2001 Marathon and it weighed about 17,000 on the steering axle,Jon is right,go weigh your coach and then you know from the chart what air pressure to run.I bet that 16,000 is not even close.
OK ...currently what pressure are you carrying in an XLII ...2 slide ? I just want to have a starting point as a referance from you more experienced Prevost owners. What do you think of 105-95-85 Lbs. (cold). Where is this chart your speaking of Jack ? I'am the new kid on the block.
AL
05 Marathon 2 S
010 GMC Arcada AWD
Jon,,quick question ....how did I become a senior member when I just joined the group ?
AL
05 Marathon 2 S
Well you look old so that makes you a senior. Just like the rest of us. Just kidding.
The number of posts it takes to become a senior is a setting the webmaster controls. Apparently he got some complaints in the past about how many posts it takes to reach senior status, so he set the number so low everybody gets there with their first post.
Al,Jon's post # 53 has the Michelin chart website,just click on it.I have 115,100,100.I like a little extra and I am not concerned about the ride.
Drove my bus across some CAT scales last summer so the State of TX could decide what to charge me for registration. 2000 Marathon XLV full of fuel, full of fresh water, 20% full on black and gray tanks.
Front axle: 14,420
Drive axle: 19,260
Tag axle: 11,960
Total: 45,960
GVWR: 48,900
Today was weigh in at the CAT scale. Our 2005 Marathon XL II 2/slide...fuel under !/2 tank, water at 50%. Front axle 17740.... Rear 34140 for a grand total 51880 lbs. I was thinking it would be in the low 16000 range and was surprised. Jack 14r you were correct in your post that 16000 wouldn't even be close. Maybe it was the extra weight of that clear shield bolted on the front cap ...Jon.
Cost of weight at Flying J $ 9.00.
AL
2005 Marathon XLII 2/slide
That is great,at least you are under on the front axle.Most weigh with waste tanks empty and fuel and fresh water full,also most Flying J scales can weigh 3 axles,that way you know how to adjust air in the drive and tag.
Jack,
Adjust air in the tag and drive? No understand Kimosabe..
I should have said drive tires,tag tires.
I know, I was just pulling your chain!:)
a couple of tidbits ,i never see age of tires,brought up when we talk weights ,pressures,u can have proper air ,old tires and still be setting on the side of the road,it is extremely important to get the date codes off of your tires(most of the time on the inside of the tires)because of the intro of slides and the addition of all the acc.the coaches got heavier ,the the axle uprating that was done by putting 125lbs of air in the 315s,and raising chassis air pressure,for the brakes,to get to a 17200 lbs axle,and many coaches were over this so if you have a old set of tires with over 90 % air(130lbs max) on a hot road ,the tire rating will not be the same as when the tire was new,they did,nt upgrade any steering componants,so that puts stress on the components,and shortens there life this thread is talking about this now so the shock that is factory may need upgraded with this in mind ,there are 06 xl2 out there with 03 365 tires on them,i,ve had cust. lose a tire with proper air pressure(the tread came off without losing air pressure) it does,nt matter steer or tag ,one both ,it seems this year tire if you can have too much air he had ck,d tires before leaving (he,d already lost one on pryor trip)115 to 120 lbs he drove from naples thru jacksonville at 67 mph and it was 87 degree at the time ,he lost the tread i had him ck air pressure it ,135lbs so ck your year of tire,weight of coach ,and put speed rating,and watch tag pressure,with your tag down it put about 1500lbs to your front axle(when weighing front axle dump tag to find out)so the more air in your tag tire the more front axle can weigh,so if you are heavy on your front axle,you can make it worst
Rick,I am going to try this when I get home next week,I have 100 Lbs in the tag,if I reduce it to 85 do you think that it will show on the scales?What you are saying does make sense.
Just to stir the pot I'll bet it makes no difference. If you could change the air pressure in the tag axle air bags it would make a very big difference. I am not advocating that or suggesting anyone modify their coach to do that because when that is done it affects other things.
Post the change Jack, but try to hit the exact same points on the scales, or better yet, pull on them with 100 PSI in the tag, and without moving drop the pressure to 85 and see if it shows up. The reason I bet against it is because while the rolling radius may change by a fraction of an inch, the tag axle air bags will adjust for that fractional change because the ride height valves are sensed ahead of the drive axle and not at the tag.
What about ride height, and I'm thinking with the front axle as it take most of the abuse. If this is in specs which should be about 11 3/4 front and 11 5/8-11 3/4 rear, how will that effect the ride and air pressure ? With my weights as determined on the scale a few days ago (17770 frt and 34700 rear) what should my tires pressure be ? Presently at 105-95-85
That is my next project to check ride height and I already know the front bag is a fraction under 11 inch and of course this does effect the overall ride of the bus.
After playing around with ride height,shocks, air pressure on the Country Coach Affinity what really worked was dropping the overall ride height of the coach 1 inch. I realized this when investigating the shock extension travel. When set to max bag CC factory specs there was a possibility of breaking a tower bolt. The long and short of this story was a better ride and nearly elimination of rear end wine. IMHO I think the specs were wrong on the coach from the get go. I never had any more ride issues with that coach. Even the buyer remarked how different my Affinity road, steered compared to another he was considering to buy. Many CC owners wear out the right frt tire at an alarming low mile point. I know why.
Got a little of tract and probably more useless info
AL
2005 Marathon XLII 2/s
Jon,I know from race cars that air pressure front to rear will not change the weight,at the place I weigh you must exit the scales to be re-weighed.I will change the weight and then weigh it again,I know that the air bags would change it but I hope the tire pressure will also,I will report the results next week,I am in France now.
Al, the alignment on our coaches is done at the ride height and if we adjust afterwards it "MAY" impact the alignment. I do know that as the coach is raised towards its high position in the front the steering and handling are considerably compromised. I do not know at what increase in height the changes begin to be felt. I am sure fractions of an inch will have no measurable impact.
If you are looking for a "softer" ride you are getting into an engineering issue. For example, the valving in our shocks and the diameter of the air bags control how harsh a bump feels. Lowering the bus ride height in essence reduces air bag pressure so the bumps will be less harsh, but in doing so the risk of the bus bottoming increases. Conversely, raising the ride height increases the air bag pressure making bumps feel more harsh and risking a rebound to the full extension of the suspension and as you surmise damaging the shock eyes or the attach bolts.
The way our air bags are engineered, by setting the bus at the correct height we have presumably equal up and down travel and the steering geometry is optimised for that position. When we adjust heights (actually by lowering or increasing air bag pressure) we depart from that ideal. I would make sure the bus is set within specs and use adjustable shocks that you can play with to dial in the ride that suits your needs.
As to tire pressures they are totally dependent upon the tire size and the weights they carry. This chart should help you find the right settings:
http://www.michelintruck.com/micheli...ion-tables.jsp
Jon,Quote:
Originally Posted by Jon Wehrenberg
I'm far from an expert but I think your quote above needs a bit of clarification. The air pressure in an air bag (air-spring) is essentially the load on the bag divided by the cross sectional area of the air-spring piston. This psi doesn't change as you add or remove air from the bag (assuming a cylindrical piston profile) because neither the load nor the cross section change. When you add or remove air from an air-spring you're simply raising or lowering the bus. The pressure stays the same, but there will be some ride stiffness change in exactly the opposite way as was quoted above. Long air-springs (lots of air above the piston) makes the spring rate softer; short air-springs (less air) makes the spring rate firmer. The ride stiffness (spring rate) is directly proportional to the cross sectional area of the air-spring piston and inversely proportional to the air-spring length (the column of air above the piston); i.e., increase the spring diameter and you've stiffened the ride, increase the spring length and you've softened the ride. Of course, a real air-spring is far more complex than my simple explanation, but the fundamental principles remain the same. Please correct me if I'm wrong.
David,
It has been my observation that as my air pressure in the auxiliary system builds (and feeds the air bags) the bus begins to rise.
I can bring my air bags on my present coach up to ride height in the front with about 105 PSI. To increase the height to full extension I have to increase the pressure. Having said that you may be correct in that the internal pressure remains the same, but the volume of air increases until the bag reaches its limits in height and then the pressure internally increases.
I may have my foot firmly implanted in my mouth and the only way to verify this is to put a gauge on the air bags and see what happens to the pressure as the air bag rises or drops.
Has anybody done this?
John,
That's right. Say your coach is at ride height equilibrium with 100 psi in the air-springs. You crank open the auxiliary tanks and shove 125 psi into the air-springs. The air-spring then rises, increasing it's internal volume, until the pressure in the spring is restored to 100 psi. If you continue to shove 125 psi into the spring, it will continue to rise.
The thing is, when you increase the height of the spring, the spring rate has gone down and the ride has become softer. When you decrease the height of the spring, the ride becomes firmer. This is easier to grasp when you realize that regardless of the height of the vehicle, the air pressure in the air-spring is the same. It's at the 100 psi equilibrium required to carry the load. What's changed is the quantity of air in the bag. More air, softer ride; less air, firmer. A simplified spring rate formula looks something like this:
Spring Rate (K) = (internal Pressure) * (piston cross section area) / (height of air column above piston)
Jon,Truk,jack,Rick.and travelite....Your comments are well taken and I appreciate everyones impute in this ride handling issue. Lots to be learned on getting the best ride as we already have the best built. Simply put minor adjustments make a big difference. I have an appointment at the shop tomorrow with a Prevost tech which will check the ride height. Bag height as per specs doing this on a level surface. The tech does the adj from a pit and rechecks at least 4 times deflate and recharge. I believe the front is low by about an inch and I've only said the coach does not sit level appearing low in the front. Normal inspection of front end parts, shocks,(new Koni's installed air) air bags and any signs front end damage will also be looked at. The way you have put "equal up and down travel and the steering geometry is optimized" well put and I would take that one step further as ideal ride ability.
Next stop the air pressure site.
Thanks
AL
2005 Marathon XL II
Al,
If you're really an inch low up front, which is a lot considering that compression travel is only around 3 to 4 inches, then you're in for a treat. Your ride will almost certainly be better, softer, more compliant. Please keep us informed. Good luck!
This is the continuing adventure on ride height of an XLII......lets get it right. The air bag measured in at an height of 10 1/2 in the front and was adjusted to 11 3/4 by the tech. The rear was checked and that was OK at 11 3/4, both sides. Road test and recheck and all is OK, the coach sits level now. On the way back to storage there is a remarkable improve meant on the ride.
Did a very close inspection of the front end and found no problems, air pressure was checked and adjusted per the scale weighing last week. Also gave me a good tip on the unfortunate chance of a flat tire in the front on where "not" to put the jack... hollow suspension tubes. Bet the tech tell what the XL II weighed in his opinion on the front axle and was within 100 lbs. The bus is "more better".
AL
2005 Marathon XLII
Is anyone riding on Road King shocks on front of an XLII ? I was reading the bru-ha-ha on there claims of bigger better best.
AL
2005 Marathon XLII ....with clear shield,... Koni shocks..., ride height adjusted,... air pressure adjusted to weight,
Is anyone riding on Road King shocks ? I posted this message and then it disappeared. This is one thing I don't understand .....the midday wash of the messages.
AL
2005 Marathon XLII
I weighed the coach today with 110 LBS in the tag and then re-weighed with 80 LBS. in the tag and as Jon said nothing would change,he is right.
Good news on that item. Did the bus weigh in close to mine ? My front was at 17770.
AL
2005 Marathon XLII