Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Topic: Larger tires - reasons and caveats? (split from Re: Tire clearance issue) (Read 1043 times) previous topic - next topic

Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

March 17, 2013, 12:25:21 pm

I guess I just do not get it, Why would we need to re-engineer a vehicle that has had such a good life for the last 10-20 years, to now think it needs re-engineered for the next 5-10 years of expected life ?
Yes some folks just have to change something just to make a change, me I think the engineers at Foretravel have done a good job of it so far and I am not bright enough to want to change tire size, bump stops and other changes just tring to prove the larger tires will work just fine.
Where have I missed the point ?
Dave M

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #1 – March 17, 2013, 02:45:53 pm

Dave you have a point to a degree, and with that I wonder why you have changed all the wonderful things that the Techs at Foretravel put into yours??? I know why, 'cause you wanted something different or better or the original just simply broke!!!
This is not an issue to try and better those Techs it is more an issue of simple day to day things that crop up and peoples ideas on how to fix/change.
If Foretravel say it is not a problem to let coach floor sit on the tyres, then to me that means that they knew it was happening from day one, but, did not think it was going to be an issue. Neal and others (me included) think otherwise.
I guess also they thought the Bulkhead Rolocks would not be an issue either?? or the loading put on that area.
Have Tyre sizes changed by manufacturers since the original ones used-I do not know ?
These things/changes are normal in ones life and when the time comes to fix or improve we do the best we can, and if it really does improve something we post it to hopefully help the next one.
IMHO
John H

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #2 – March 17, 2013, 04:11:46 pm

Hi John H,
Yup, I have indeed upgraded a few items, LED Lites, paint job, head lites, rear door so I could open it, house type refrig and the 500 HP ISM.
I have not nor see at this point the need to install larger tires nor white walls

My question is why the burning desire to HAVE TO change the bump stops just so the larger tires can clear, that is what I do not get. Maybe you can inform me what I am missing ? eh!
Cheers
Dave M

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #3 – March 17, 2013, 04:41:11 pm

Dave, my comment was not about installing bigger tyres it was that there seems to have been a problem from day one of a coaches life on the tyres hitting the underneath of floor. Neal mentioned people who have had pressure problems with their floors and do not want it to continue, hence different ideas on how possibly to correct this.
My coach had marks on all wheel positions and the PO said it was from new but he had not thought about correcting it and that is why I think FT knew about it, or, found out about it once it had been mentioned and as John S said raised it away.
Cheers Dave

John H

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #4 – March 17, 2013, 04:44:49 pm

I think one thing that must be remembered when changing tire brands it that tire sizes do not always measure the same between the many brands out there. This is especially true with Michelin from what I've read.

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #5 – March 17, 2013, 09:34:58 pm

Quote from: Dave M – March 17, 2013, 12:25:21 pm

I guess I just do not get it, Why would we need to re-engineer a vehicle that has had such a good life for the last 10-20 years, to now think it needs re-engineered for the next 5-10 years of expected life ?
Yes some folks just have to change something just to make a change, me I think the engineers at Foretravel have done a good job of it so far and I am not bright enough to want to change tire size, bump stops and other changes just tring to prove the larger tires will work just fine.
Where have I missed the point ?
Dave M

Quote from: Dave M – March 17, 2013, 12:36:10 pm

.......................................why would we change size to a larger size knowing the limits that exist that now require makeing bump stops to prevent the larger tire from rubbing.
Is it a cost issue or just hating the 275/80R22.5 ?...........................................
Dave M

Quote from: Dave M – March 17, 2013, 04:11:46 pm

Hi John H,
Yup, I have indeed upgraded a few items, LED Lites, paint job, head lites, rear door so I could open it, house type refrig and the 500 HP ISM.
I have not nor see at this point the need to install larger tires nor white walls
My question is why the burning desire to HAVE TO change the bump stops just so the larger tires can clear, that is what I do not get. Maybe you can inform me what I am missing ? eh!
Cheers
Dave M

Dave,
What you may not understand is that John and I (and many others) are not trying to increase tire size.
We are not trying to make "Vanity" changes.
We are only trying to help others think through and implement "corrective" and "preventative" changes to correct a known design issue.

From all that I can gather, many (if not all) 1996 to 2000 model year FT coach tires contact and deform the undersides of the floors when all air is dumped from the airbags.
Also, when leveling, uneven ground can make the problem worse as the "high ground" tire(s) can exert even greater pressure on the sub flooring due to the exaggerated suspension geometry caused by the off level condition.

This tire-to-subfloor-contact occurs with the original Michelin XZA1-A's, as well as all of the evolution series of tires, XZA2-A's, XZA3's and XZA3+'s. Size by size, the evolving tire series all have the same physical dimensions as the FT OEM "as-built" Michelin tires. We are not trying to install larger tires.

I don't know that all coaches behave identically in the 1996 to 2000 models, but some coaches seem to be capable of deforming the underside of the floor enough (and compressing the insulation sufficiently) to deform and delaminate the upper plywood layer of the floor. That delamination presents itself as a "spongy" hump in the floor, under the carpet, that changes as humidity changes.

Adding 3/8" or 1/2" to the existing frame-to-suspension-travel-stop buttons, seems to take care of some, if not all, coaches. I've tried to get a better answer from FT to no avail. I do know that tolerances must be tight because, I have a travel height gauge, I check and ensure proper travel height a couple of times a year, and yet I have experienced "bottoming" of the suspension under lightly loaded conditions. Lightly loaded, air bag pressures are lower, so that explains why suspension handling improves under increased loading.

I think that 2001 and newer FT coaches do not have the same issue due to frame dimension redesign, but that may be only because I have never encountered a 2000 or newer FT owner with the issue.

I hope that helps to clarify what you have supposed are "Vanity" vs. "Corrective" and "Preventative" changes. Your thoughts are influential on the Forum and by dismissing the issue, some members may be misled.

I have found that many owners are not aware of this suspension behavior, until they either read about it or someone directly demonstrates it to them. Owners deserve to know that there is at least the potential of doing damage on these model year coaches. It can be easily prevented through inexpensive frame-to-suspension-travel-stop button modifications or by just not dumping or auto-leveling suspensions into high pressure tire-to-floor-contact situations.
Neal

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #6 – March 18, 2013, 06:47:48 am

I see we got off track from my origional comments, concerning why install larger tires, when there is this clearance issue

So I am back to the ?? is it a cost factor or just the hate of the 275/80R22.5 tire .
There must be a reason for installing the larger tire, knowing there is the rubbing issue ?
Dave M

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #7 – March 18, 2013, 07:36:57 am

Quote from: Dave M – March 18, 2013, 06:47:48 am

I see we got off track from my origional comments, concerning why install larger tires, when there is this clearance issue
So I am back to the ?? is it a cost factor or just the hate of the 275/80R22.5 tire .
There must be a reason for installing the larger tire, knowing there is the rubbing issue ?
Dave M

Dave,

What size is the larger tire you are referring too?

Rudy

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #8 – March 18, 2013, 04:27:59 pm

Availability is the main reason people go to a 295

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #9 – March 18, 2013, 04:38:47 pm

Dave,

The 295/75R 22.5 tire is one tenth of an inch in diameter different than a 275/80R 22.5. How can 0.05 of an inch (1.27 mm) closer to the coach make much difference?

Rudy

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #10 – March 18, 2013, 05:22:12 pm

Dave,

I like the 295/75R 22.5 because it is a common large truck tire on almost every street corner made by most truck tire manufactures. So they are less expensive due to volume and competition.

275/80R 22.5 and 295/80R 22.5 are limited in the number of manufactures that make that particular size tire.

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #11 – March 18, 2013, 06:49:47 pm

275/80 and 295/75 are both almost exactly the same diameter. Larger difference found between different brands than the sizes. I have 295/75s all the way around with a 275/80 for a spare.

Pierce

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #12 – March 19, 2013, 05:44:52 pm

I'm guessing the 295/75R 22.5 would not be Michelin? I don't see that tire size on their website.

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #13 – March 19, 2013, 07:49:45 pm

Quote from: Michelle – March 19, 2013, 05:44:52 pm

I'm guessing the 295/75R 22.5 would not be Michelin? I don't see that tire size on their website.

Michelle,

Don't see that tire on their website either. The only difference is a slight difference in aspect ratio. The wider aspect ratio will result in a slightly larger footprint on the road. The 295/75 is 0.1" more in diameter (501 vs 502 revolutions per mile). The difference is so small that different brands vary more than that. The 295/75 would also (might) have a very slightly firmer ride, but again, a very small difference. The 295/75 rear have about the same amount of clearance between the "bulges" so they don't touch each other above the road contact area.

I have seen the sizes used interchangeably on some tire dealer sites with an asterisk used after the 275/80 to indicate a "European" designation for the Michelin.

The other option would be to go from G load rating to H. This would increase the load capacity but usually has at least one more ply which will stiffen the tire resulting in a firmer ride.

Pierce

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #14 – March 19, 2013, 09:35:12 pm

The leveling system tries to get the front of the coach as low as
possable so you have a small step into the coach.
It will let the front down until one wheel bottoms out (unless the coach becomes level), then the 10psi switch on the HWH manifold will sense the loss of pressure (no weight on that bag) and take the power off the opposite dump valve stopping the front from going down any further. It will then continue leveling the coach from that position.
Sitting on the wheel well never seamed to bother my coach.
When I hear of plywood delaminating I think about moisture getting in there.

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #15 – March 20, 2013, 04:47:14 pm

Quote from: John Duld – March 19, 2013, 09:35:12 pm

The leveling system tries to get the front of the coach as low as
possable so you have a small step into the coach.
It will let the front down until one wheel bottoms out (unless the coach becomes level), then the 10psi switch on the HWH manifold will sense the loss of pressure (no weight on that bag) and take the power off the opposite dump valve stopping the front from going down any further. It will then continue leveling the coach from that position.
Sitting on the wheel well never seamed to bother my coach.
When I hear of plywood delaminating I think about moisture getting in there.

John,
Your first point has more to do with the "Tire Clearance Issue" thread (tires contacting the floor due to suspension travel) than with THIS, the "Why or Why Not to increase tire size" thread. But, a "new-b" pointed out to me today that he didn't know that FT's were designed "to get the front of the coach as low as possible so you have a small step into the coach." In the interest of not misleading readers, then:
In 1998 FT's at least, the HWH doesn't have sensors for and doesn't care whether the step ends up high or low. If your Curb Front tire is the "high ground" tire, the step will be low. But if your Streetside Rear duals are the "high ground" tires, then your step may be at its maximum height, depending upon what the HWH has to do to achieve a level coach, (+,- 1") side to side and (+,- 5.4") fore and aft over a 36' coach.
For 1998's at least, the abbreviated system sequence is;
· HWH first tries to level side to side, by dumping high side air bags.
· Then it tries fore and aft by dumping high end air bags.
· Then it does the same thing by adding air to the low side air bags
· and finally tries adding air to the low end air bags.
The entry step ends up where it may.
The longer version follows:

AUTOMATIC LEVELING
Leave coach engine running:
Set the park brake.
Push the Level "AIR" button one time to turn the system on.
Push the Level "AIR" button a second time. This will start automatic leveling.
The following should occur:
a. The four red warning lights will be on.
b. The indicator light above the "AIR" button will start to flash.
c. The master warning light will be on.
d. The coach will automatically level itself.
The leveling procedure is as follows:
If there are no yellow lights the control box will go directly
into sleep mode.
If there are yellow lights on, leveling will start in a "DOWN"
mode, deflating air bags opposite to lit yellow level indicator
lights, SIDE to SIDE first and FORE and AFT next.
2 minutes after the last "DOWN" leveling solenoid valve is
energized, if the coach is not level, the computer
will switch to the "UP" mode, inflating air bags ac-
cording to lit yellow lights. During any raise (UP) function the
compressor may run. When all the yellow lights are
are out, the control box goes into the sleep mode.
SLEEP MODE:
will remain on but inactive for 30 minutes. After 30 minutes
the control box will wake up and monitor the yellow lights
until leveling is needed. If a light is on or comes on and
remains on for 60 seconds, the control box will re level the
coach using the original leveling procedure. After leveling
the vehicle the control box will return to the sleep mode.
EXCESS SLOPE:
During the leveling mode, either initially
or after a sleep mode, if the coach cannot be leveled
in 15 minutes the control box will stop all operations, and
the "EXCESS SLOPE" indicator will come on. The box will
will remain on until the "OFF" button is pushed, but will not
go into the sleep mode of operation.

The question then becomes, if you want to use automatic leveling, don't want to decrease suspension travel by increasing the elevation of the suspension travel stops and don't want to leave the tires pressing into the floor while parked for longer periods of time, then what can you do?

If I am HWH auto leveling, I leave the coach running,

then I just double tap the level "AIR" button,

then go outside for other "arrival" activities,

then check for tire contact when coach (HWH) is done.
If it is resting on a tire, I have DW go to "OFF" on HWH (takes it out of auto level and places it in travel mode),

then immediately hold "RAISE" until coach is at maximum height all around,

then double tap level "AIR" again to auto level.

Then I watch at the tire that touched and have her stop the auto level process 1/4" before the tire is touched again, if it's getting close. You do this by quickly going "OFF" and then (1) tap of the level "AIR" button (Places HWH in Manual Mode).

Because the HWH levels side to side first, the coach may not be quite level side to side, but that's usually OK. I check it with an "iPhone/iPad on the dash" level app.

Then if the front to back can still be improved, I have her manually let air out of the back air bags (down arrow in back), again stopping her 1/4" before the "high tire" touches, if it's getting close.

When that is done, just turn the ignition key off. The HWH will stay "locked" in that condition until the next time the ignition key is turned on. I have had the system stay suspended that way for weeks with no change in the air bag leveled (or perhaps slightly out of level) condition.

And no, John, to your second point.

For the three instances that I have had experience with and I referred to regarding plywood delamination, none of the three had any evidence of liquids spilled inside (or intruding from outside) to contribute to the delamination of the plywood. (no liquid stains anywhere on the raw plywood).
Best regards,
Neal

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #16 – March 20, 2013, 05:06:32 pm

Quote from: Neal Pillsbury – March 20, 2013, 04:47:14 pm

a "new-b" pointed out to me today that he didn't know that FT's were designed "to get the front of the coach as low as possible so you have a small step into the coach." In the interest of not misleading readers, then:
In 1998 FT's at least, the HWH doesn't have sensors for and doesn't care whether the step ends up high or low.

Neal,

Great job on the description

I've never heard of the system being set up to achieve a low step, either.

Maybe it's a new feature with the "Active Air" HWH suspensions?

As your descriptive algorithm says, the automatic leveling always tries to lower (exhaust air) first. If it can't achieve level by doing that, it will add air to the opposite side/end.

Now, their are those who manually dump all air, then press "level" to force the step to be as low as possible. This may give a more personally desirable step height, but now you're making the system work to add air back in that you just let out.

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #17 – March 20, 2013, 05:07:49 pm

Great info Neal! I'm going to add this information to my Foretravel documentation... Have created a special place in the coaches documentation for resources from the forum and real-world experience.
Don

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #18 – March 20, 2013, 08:19:08 pm

Neal,
Yes I agree, everything you said is in the HWH manual.
The coach will try to level in the down mode, easier to let air out than pump it in,resulting in leveling as low as possable. Depending on the site, yes you may end up with the front all the way up and rear all the way down.
Some one said something about the coach bottoming out on a tire during leveling. That is normal with the Foretravel system.
That's where the 10 psi switches come in,Foretravel put them in not HWH, to try to level with the front as low as possable, stopping the other side ( front) from going lower if one side bottoms out and twisting the coach. No those pressure switches don't sense step height directly but the do know the front isn't going any lower.
The HWH repair manual for the 600 series system listed for Fortravel dated 7 March 2001
still shows those 10 Psi switches in the schematic.
I don't if or when Foretravel changed to something newer than the 600 series system.

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #19 – March 21, 2013, 09:43:54 am

On my '99 U320 I have a small air leak somewhere in the rear air bag loop. (someday I hope to find it) Over time the rear of the coach will slowly drop. Since the HWH system in auto mode releases air from the front to achieve level in this situation, the end result is that the coach will always slowly proceed to lowering itself until one or more tires are in contact with the floor. Personally, I don't feel this is a good situation. I have cracked tiles in the bath area to prove it. My solution is to manually level the coach as high as possible. Then I place a spacer of the appropriate height at each of the front bump stop locations. I use galvanized pipe nipples. Cheap and easy to get in various lengths. Then I put the coach in auto mode. It will slowly settle onto one or more of the front spacers. Once that happens the system will no longer lower itself (it thinks it's as low as possible) and instead will add air to the rear bags. In this mode the coach will stay level and off the tires indefinitely. Obviously, this system won't work if the site is so far off level that the coach can't initially level with all the tires off the body.

Dave VanAmburg

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #20 – March 21, 2013, 09:51:25 pm

It sounds to me like the o rings in the air solenoids on the 6 pack air manifold are leaking. They can be taken off and the o rings inside replaced as well as the o ring between the solenoid and the manifold

Re: Larger tires - reasons and caveats? (split from Re: Tire clearance issue)

Reply #21 – March 21, 2013, 10:03:48 pm

Quote from: red tractor – March 21, 2013, 09:51:25 pm

It sounds to me like the o rings in the air solenoids on the 6 pack air manifold are leaking. They can be taken off and the o rings inside replaced as well as the o ring between the solenoid and the manifold

Photos, part number here Six Pack O Ring Replacement

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