Handling Comparison:36' U270/42' U320

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Handling Comparison:36' U270/42' U320

November 06, 2014, 01:29:43 am

Having just spent several 500 mile (+) days, back to back, driving our 16 year old, 36' U270 from NH to Nacogdoches and then Phil's (still hard to adjust to "our, new to us") 12 year old, 42', tag axle U320 back to NH, we encountered a number of comparison details that will fade over time. So I thought that it might be of help, or interest, to members to have some insights into what we felt.

Although we have owned the U270 since brand new, we have ridden in and driven a number of Prevost conversions, Newells and other Foretravels over long distances, so we already knew what to expect, but the NH to Nac to NH distances, over a short 16 day span, made for a comparison that was more sharply focused and I'll try to capture some of it, while it's still fresh.

First, the U270 (mechanical, 8.3 Cummins) starts instantly. Not the best of designs regarding ultimate diesel engine treatment, but very reassuring.

The U320 (ISM-450) starts when the computer is darned good and ready. It gives a good feeling that the parameters for an acceptable start have been evaluated and approved, but it gives one pause to consider all those electrons racing out of batteries for so long, even under idea conditions. On my own analysis and the sage advice of FOT and Cummins, I believe in minimizing unnecessary wear and tear so we always use the boost switch, except for periodic verifications of start batteries performance. Even more important on the U320.

Second, the U270 doesn't strain at the leash when the transmission is engaged. With the U270, the sequence of mirrors, seatbelts, gauge check, service brakes on, parking brakes released, shift pad, service brakes released don't seem to be all that important, as long as they all get done prior to moving.

The U320 is more demanding. One does all of the above in strict sequence, because once you shift to drive (or reverse), you need to be paying strict attention to whether you are moving or not and where you are pointed, regardless of whether the parking brake is still set or whether you think you have enough service brake applied or not. Don't think that the parking brake or absent minded use of service brakes is going to hold the coach. The (ISM-450) idle torque is high and more than enough to cause "creep" until the transmission is taken out of gear, even when on level ground and the idle speed and brakes have just been adjusted to spec. Cold fluids and temperatures amplify the need to be attentive.

Third, the U270, even without a toad, requires varying degrees of forethought when it comes to grades in heavy traffic. Generally, it is not difficult to drive the U270 with the empty trucks and not at all difficult to pace with the heavy truck traffic, but one does have to sort the groups out and one learns to use truck traffic behavior and the bulge of the truck tire sidewalls to monitor one's options, often yielding position so as not to inconvenience much slower truck traffic or blocking "4 wheelers".

The U320 is much easier to drive, in that respect. One watches the "overtaking 4 wheeler traffic" more than the trucks. Set the speed control on your preferred cruise setting, when a long grade appears, get into the passing lane (your will only drop 1 or 2 MPH, if at all, on the upgrade), cruise on by a high percentage of the truck traffic, tuck back into the slow lane after you top the grade.

Fourth, the U270 is very light in it's steering effort and the road feedback is nearly instantaneous. The steering has a "floating" feeling and those unaccustomed or inattentive to how light the steering is, tend to over-steer, which causes the coach to "wag the toad". My DW is particularly insensitive to this and says that I nag her way too much about over-steering.

As soon as it moves, the U320 gives the impression of having VERY heavy steering. At slow speeds in parking lots, it is heavy and at all speeds it is heavy. The good part of that is that it runs true with almost no attention when the road is not crowned. The bad part is that when the road is crowned (like a lot of them are between Nac and NH), it takes considerable attention and turning pressure on the steering wheel to overcome gravity's insistent pull toward the low side of the crown. It all becomes second nature and one becomes accustomed to the additional effort. But a good example is that I don't think that I buzzed a rumble strip once with the U270 on this recent trip, all the way from NH to FL to Nac. The first day out with the U320, from Nac to NH, I probably buzzed rumble strips, on the low side of the crown, 15 or more times. Enough so that the DW thought I was "losing it." Then she did the same thing dozens of times in getting used to the heavier steering herself (requires more steering pressure to stay lane-centered -- proportional to how much the road is crowned). Another way to think of this is as a light sports car that is easy to over-steer, if you are not being precise with your steering input versus a massive vehicle that wants to "plow" straight ahead, unless given (seemingly, at first) over-abundant steering input. That leads to another observation, after a 500 (+) mile day; the additional work expended in one's arms and shoulders. On the positive side, there is NO tendency to absentmindedly over-steer and the DW loves not being nagged about "wagging the dog".

Fifth, the U270 is riding on the same air bags but, the bags have less air pressure in them, even when both coaches are loaded with exactly the same cargo/payload. That's because the body shells, the later year (1998 to 2002) heavier frame components, engine, transmission, gen sets and trim levels all add weight to the U320, 4200. The additional wheelbase, the added tag axle, the higher pressure air bags all combine to provide a sailboat versus ship behavior in various sea states. When the road is straight and smooth and calm and there is no truck traffic turbulence at play, both coaches feel remarkably calm, quiet and massive. Add turbulence and poor road conditions and the U270 begins to feel more buoyant (not to mean "darting about" or poorly behaved at all, just that while still going straight, the turbulence induced buffeting is begun to be perceived as a "wiggle in your seat" and the compressions/rebounds, caused by poor road conditions, become evident in the degree of up/down suspension travel (buoyancy).

Under duress, the U320 acts much more like a ship. I liken it to a ship in heavy seas, where under heavy turbulence and bad surface conditions, the vessel just shudders as it encounters heavy seas, maybe flexes a bit, but only sluggishly moves up or down and never deviates from its directed course. The driver's Knoedler air seat contributes even more to that feeling/impression in that while the harder air bags flex less and the coach shudders under heavy surface condition abuse, the air seat is remarkable at softening bad surface conditions, through its several inches of travel, on (at least the more dramatic) roadway insults.

There is likely more that I will think of, but enough for now:
Neal

Re: Handling Comparison:36' U270/42' U320

Reply #1 – November 06, 2014, 02:41:08 am

Excellent report. Any idea of the tire pressures versus axle loadings?

Sounds like you are fairly close on the 320.

The 500 mile reference was similar to mine as received.

Wheel bearings tightened during seal replacement made a major difference as did weighing the coach as did adjusting the tire pressure exactly proportional to the load.

Replaced the drag link ends also.

Reduced the work load by a large percentage.

May or may not be any help but I set up a lot of coaches long ago.

The 276" WB to the drive axle smoothes out things a lot.

1/2 inch steering wheel corrections.

Re: Handling Comparison:36' U270/42' U320

Reply #2 – November 06, 2014, 07:42:17 am

Yes, I run 110psi in steers, 85psi everything else. Also check alignment. We don't experience any of the road crown steering pressure described.

Re: Handling Comparison:36' U270/42' U320

Reply #3 – November 06, 2014, 11:30:30 am

I too have the 42 foot and do not have the road issues you mentioned. You need to get it aligned again. I run 115 in my front but I have a slide. As to hard starting, there were 28 upgrades to my ECM when I took it into cummins and few of them were for long start times. It is something you need to have looked at.

Finally, the M11 is bigger to turn over and I added a second cable directly to the starter fromthe batteries and also replaced the ground wire star washer. Made a huge difference and I no longer need the boost switch. The boost switch is only carrying 100 extra amps but it is more direct then the start batteries that go through a splitter box.

If you look at all these you might find it a bit different.

Re: Handling Comparison:36' U270/42' U320

Reply #4 – November 06, 2014, 11:51:42 am

The calculated weight tire pressure on our coach is 108/98.

One of the biggest boosts for my Foretravel stores business was to have every skeptic adjust their tire pressure correctly. Every single owner mentioned how much better it steered and rode.

Not as safe driving on the center ribs of the tires in weather conditions.

Glad you others on this thread posted on your driving differences.

The wheel bearings were the key on ours.

My normal steering wheel adjustment at the edge are 1/2 inch? No play is the key.

Driven a lot that make you work at it.

Good news it's fixable.

Figured out the steering wander was a big factor in a lot of sales of coaches.

Customers would come back later to look at their trade in and mention poor handling and/or ride compliance.

Adjust up the Koni's also. Third or fourth setting to compensate for the wear. Less body roll also.

Re: Handling Comparison:36' U270/42' U320

Reply #5 – November 06, 2014, 12:01:49 pm

Quote from: Caflashbob – November 06, 2014, 11:51:42 am

The calculated weight tire pressure on our coach is 108/98.

Bob, is this calculated per the tire mfg. pressure recommendations for weight?

Re: Handling Comparison:36' U270/42' U320

Reply #6 – November 06, 2014, 12:03:20 pm

My coach is only 38', and a U295 with one slide. It is much heavier than that U270, and a little lighter than the 40' U320. Being that I have no tag axle, I need relatively high tire pressures to handle the weight. I run 110 front and 95 rear. Absolutely no handling issues. Tracks straight and true, needs only a small of steering bias to keep centered on a crowned road, passing big rigs only slightly push it to the side while passing. Now it only I had another 100-200 horsepower for the hills, but who wouldn't want that. As it is, I still pass all but the empty trucks and some cars on the Grapevine.

Re: Handling Comparison:36' U270/42' U320

Reply #7 – November 06, 2014, 12:09:19 pm

Quote from: Chuck Pearson – November 06, 2014, 12:01:49 pm

Bob, is this calculated per the tire mfg. pressure recommendations for weight?

The numbers are on the tires sidewalls. 6,500@110 psi as an example.

Lower the tire pressure the same percentage as you are of the max load.

Cost myself a certain amount of biz as some owners would come up to me later and mention they no longer needed a new coach as theirs drove great now......

Re: Handling Comparison:36' U270/42' U320

Reply #8 – November 06, 2014, 12:13:17 pm

Bob,

Why not use the tire manufacturers Inflation Table to determine the correct minimum PSI and then add a 5 PSI or so safety cushion to that minimum? That is why they publish the tables. Also, all tires do have a minimum PSI, irrespective of how light the load.

Re: Handling Comparison:36' U270/42' U320

Reply #9 – November 06, 2014, 12:14:23 pm

Quote from: Tom Lang – November 06, 2014, 12:03:20 pm

My coach is only 38', and a U295 with one slide. It is much heavier than that U270, and a little lighter than the 40' U320. Being that I have no tag axle, I need relatively high tire pressures to handle the weight. I run 110 front and 95 rear. Absolutely no handling issues. Tracks straight and true, needs only a small of steering bias to keep centered on a crowned road, passing big rigs only slightly push it to the side while passing. Now it only I had another 100-200 horsepower for the hills, but who wouldn't want that. As it is, I still pass all but the empty trucks and some cars on the Grapevine.

I think my m11 is still down on power after fixing an air leak in the fuel filter but from the Bakersfield side with a Honda tow car never got below 52 on the hill.

More is better and need to invest more coach bucks at the cummins dealer with a Dyno I think....

Re: Handling Comparison:36' U270/42' U320

Reply #10 – November 06, 2014, 12:25:20 pm

Quote from: wolfe10 – November 06, 2014, 12:13:17 pm

Bob,

Why not use the tire manufacturers Inflation Table to determine the correct minimum PSI and then add a 5 PSI or so safety cushion to that minimum? That is why they publish the tables. Also, all tires do have a minimum PSI, irrespective of how light the load.

Yes 85 is the minumum if memory serves me.

If everything else was perfect two pounds difference in tire pressure was noticeable per my testers(customers)

Do they still weigh the coaches axles at the FMCA rallys like long ago.

Big support and an air jack and an electronic scale in between.

Foretravel left to right weight distribution was so good both tires were normslly the same.

Adjusted many SOB's tires different left to right as they varied considerably.

Gave the boys something to do. They loved it. Especially if the correct adjustements made a noticeable difference which it did in most cases.

Yes filling all the tanks was required. As noted under was not recommended. A bit over was less problems.

I keep my coach basically full weight all the time. Only real variable is fuel weight.

I assume the chart is the same weight/pressure calculations as doing it yourself just predone?

Re: Handling Comparison:36' U270/42' U320

Reply #11 – November 06, 2014, 12:31:24 pm

I had mine weighed at the fmca rally in Indio last winter.

Re: Handling Comparison:36' U270/42' U320

Reply #12 – November 06, 2014, 12:35:38 pm

Quote from: Caflashbob – November 06, 2014, 12:25:20 pm

Do they still weigh the coaches axles at the FMCA rallys like long ago.

YES. And many other locations: Weighing Schedule

Re: Handling Comparison:36' U270/42' U320

Reply #13 – November 06, 2014, 12:37:56 pm

If you know the weights, Michelin website has pressure charts

Re: Handling Comparison:36' U270/42' U320

Reply #14 – November 06, 2014, 12:59:32 pm

If you are concerned about handling issues, I would suggest you have someone that operates heavy transport equipment drive your MH & get it repaired/adjusted no matter what the length and weight. pc

Re: Handling Comparison:36' U270/42' U320

Reply #15 – November 06, 2014, 03:52:27 pm

Guys, guys,
I was just offering some observations on the differences in handling/driving experience between U270, 36' and U320, 42' coaches.
Many newbies, as well as long term owners, do not have the opportunity to drive both coaches over long distances and I, for one know that when we were shopping for our 1998 U270, I wondered how the driving experiences might differ.
I don't/didn't have handling problems with either of them. The alignments are neutral on both (no compensation for road crown -- which I prefer) and I have personally checked wheel bearing play (zero), steer tire run-outs, steering center and steering gear box end stop relief clearances during my PDI.
I did not "6-corner" weigh the coach before leaving Nac, because I do not have things organized as I intend to for the long term and we didn't take the trailer on this speed run to Nac. Both will change final tire values.

Now to some of your points:
@Bob:
Placard (calculated) pressures are 115 Steer, 95 Drive and 70 Tag at GVWR
I think that Phil was using 100 Steer, 90 Drive and 90 Tag, at least "As Found in Nac"
This morning 98 Steer, 88/90 drive and 87/88 Tag
I didn't change what I found in Nac, because the tires looked good and, as already stated, because I intend to weigh later, before leaving NH, fully loaded for FL. Based on the Michelin sidewall info and the placard info, I'm sure that I 'm running too soft, which I don't believe in, but the current pressures should have given us a "soft" ride home without inducing inappropriate wear or handling anomalies.
The U320 steering corrections have excellent dead spot, absent road crown influences, requiring only about 1/2" corrections from neutral. That's better than the U270. As previously stated in my first post, neutral steering, wander and dead spot are all better in the U320.
Not that I think there is a need to, but the Koni Gold FSD's, that Phil upgraded to, are not adjustable, correct? Shock behavior is optimal and there is NO body roll, as far as I can detect -- big ship, dead ahead, no bottoming, no porpoising, a little shudder on bad surface conditions, no roll or pitch, Knoedler air seat shock is amazing.

@ John S:
I'm not sure your basis for recommending an alignment. Just as a good men's tailor asks a gentleman if he "dresses right" or "dresses left", a good alignment shop asks if the primary operator "drives right" or "drives left" (or does the operator prefer neutral)? Most shops don't care or do not wish to explore the depth of understanding with the operator. These are road crown compensation questions. Josam's in Orlando has always asked me that and I appreciate their professionalism in asking. I understand the difference and I want neutral, not a pre-set bias to accommodate right or left road crown "average" conditions.
All highway engineers crown roads to accommodate water runoff and to preserve traffic forward momentum without scrubbing pavement off (bank the roads). Phil's coach seems to be set up perfectly neutral, which I much prefer. Left of the crown, it falls to the left as gravity pulls it that way. Right of the crown it falls to the right. The steering compensation (EFFORT in your arms) is the same amount, left or right. It's just that the amount of steering effort is HEAVIER (requires more exertion) than the U270. That seems to be weight or mass driven, probably some significant steering components differences as well. One quickly becomes accustomed to it, but it is definitely heavier and is not alignment related.
In the "tramways" (road compression ruts worn into the road surface), the U320 is as straight as a die, whereas the lighter U270 seems to wallow (up one side of the rut a bit, then absent steering input, it falls back to center rut and then up the other side a bit, "wallowing" back and forth).
If the U320 is starting hard, I'm not aware of it. My only point is that the U320 ECM computer decides when it is appropriate to start and that is very different than the U270. Therefore using the boost (and keeping the boost circuit connections/function optimized) becomes more important, just as keeping all of the battery terminations optimized becomes more important.
John, how do you measure the boost switch 100amp extra supply to the starter and how does that compare with the start battery bank contribution to the starter? I need to find the shunts to measure that.

@ amos.harrison:
Brett, you say: "..........Also check alignment. We don't experience any of the road crown steering pressure described."
I don't know how an alignment can compensate for BOTH right and left crowned roadways. Setting an alignment to compensate for an "average right lane crown", is going to make a coach pull harder to the left in left lane driving. That's why I prefer neutral. I have never driven a vehicle that doesn't respond to gravity and compensating right crown over left crown (through alignment offset from neutral), doesn't lighten steering effort in both directions. It may make it less in one lane but it will make it greater, if not double, in the other lane.

@pc:
I don't believe that I have "handling issues".
I do believe that a U270 36' and a u320 42' handle quite differently and many Foreforum members might be interested in knowing how and why. And, having grown up on a very large dairy farm, I have operated heavy transport equipment ever since I could reach the pedals, highway and off road. Sort of akin to:
"If one wants to operate a large touring motorcycle safely and well, start with many years of off road motorcycle experience, in all kinds of terrain and conditions. Then, if you are at all perceptive, you will intuitively understand the basic mechanics and geometries better."

Neal

Re: Handling Comparison:36' U270/42' U320

Reply #16 – November 06, 2014, 04:13:29 pm

Quote from: Neal Pillsbury – November 06, 2014, 01:29:43 am

The bad part is that when the road is crowned (like a lot of them are between Nac and NH), it takes considerable attention and turning pressure on the steering wheel to overcome gravity's insistent pull toward the low side of the crown. It all becomes second nature and one becomes accustomed to the additional effort. But a good example is that I don't think that I buzzed a rumble strip once with the U270 on this recent trip, all the way from NH to FL to Nac. The first day out with the U320, from Nac to NH, I probably buzzed rumble strips, on the low side of the crown, 15 or more times. Enough so that the DW thought I was "losing it."

We've just changed from our 1996 36' U295 to our 2003 40' U320 (with tag). Jim has the same issue -- I say he's "listing" to the passenger side. I think it is just the difference in how the two machines handle; not their setup.

Re: Handling Comparison:36' U270/42' U320

Reply #17 – November 06, 2014, 07:17:47 pm

It is rated at 100 amps continuous duty. I had a friend who lost a post on one of his batteries on his 270. We used the boost switch but with that and the other battery we could not turn over the ISC he has. As to the ECM vs mechanical, I am saying that Cummins programmed a our years requiring more times turning over before it opens the fuel solenoid. It is a TSB and they had 28 different upgrades on my ECM at cummins. It had 7 of them relating to hard start issues.

As to the alignment, I like neutral too. If you have that then you are fine but the question is did Phil ever have it redone. They were doing it originally with a tape and mechanical and now they use laser and when I had Wayne do my coach, I noticed the difference. I found that my 42 foot tracked much better then either my 34 foot 270 or my 36 foot 320. You will not feel the bow wave of the passing truck in the 42 foot that you would have felt in the 270.

I weighed in full for travel with two scooters and two slides at 39K and my max is 42K and the GCVW is 52K. You have no slides so you will be a bit lighter but you still have about 7K or so to fill up and you probably will not be able to put that much weight in. That weight was full water and fuel at A Weigh We Go. I have the 12.5KX generator up front plus the two scooters so I needed 110 lbs and I bumped it up to 115.

Re: Handling Comparison:36' U270/42' U320

Reply #18 – November 06, 2014, 09:34:53 pm

Thanks for the report Neal. Very true that few of us get try different coaches over such distances. Test drives just scratch the surface.
I assume your new coach is the standard solid front axle and not IFS ? (that would be another real good comparison)

Re: Handling Comparison:36' U270/42' U320

Reply #19 – November 06, 2014, 10:11:51 pm

I'm the one that usually starts the coach. And you're right. With the '96, you turned the key to the first click position, waited for the "Wait to Start" light to go out, turned the key the rest of the way, and the coach roared to life.

The '03, there is no "Wait to Start", you just start it but it takes a long time as it checks to make sure it thinks everything is ok and then the start seems a lot harder.

But, once the '03 is started, you better be ready because it wants to GO! I find that sort of disconcerting. The '96 seemed much more "patient".

Re: Handling Comparison:36' U270/42' U320

Reply #20 – November 06, 2014, 10:50:39 pm

Quote from: JohnFitz – November 06, 2014, 09:34:53 pm

Thanks for the report Neal. Very true that few of us get try different coaches over such distances. Test drives just scratch the surface.
I assume your new coach is the standard solid front axle and not IFS ? (that would be another real good comparison)

John,
Thanks. Yes, the 2002 U320 has the standard solid front axle. And yes, a comparison of the two front end designs in FT's would be awesome.
I'm glad that my GOOD comparisons didn't get into anything controversial (being facetious)! I'm waiting to see what Don has to say before I drag out the BAD comparison stuff! After all, he egged me on to share this comparison!
Neal

Re: Handling Comparison:36' U270/42' U320

Reply #21 – November 06, 2014, 11:29:15 pm

The inherent stability of a spread air bag ten bag coach with eight tires is legendary.

Hard to make it handle poorly.

The steering comment is what got my attention.

My coach had a sticking ride height valve that was intermittent requiring periods of steering correction.

Does not take a lot of incorrect ride height. Last thing left

Re: Handling Comparison:36' U270/42' U320

Reply #22 – November 07, 2014, 11:43:30 am

Ah Neal... just looking for a little vicarious "warm glow" as you go cruising down the highway in your new-to-you super land yacht. Like you said, how many of us would have a chance to such an extended "A/B" comparison? Glad to hear you are enjoying the journey!
Don

Quote from: Neal Pillsbury – November 06, 2014, 10:50:39 pm

I'm glad that my GOOD comparisons didn't get into anything controversial (being facetious)! I'm waiting to see what Don has to say before I drag out the BAD comparison stuff! After all, he egged me on to share this comparison!
Neal

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