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Old 03-02-2014, 10:35 PM   #29
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Spinn I wonder if you could leave your tmp's on both tires and just hook up the crossfire to them.
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Old 03-02-2014, 10:49 PM   #30
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Originally Posted by stan5711 View Post
Spinn I wonder if you could leave your tmp's on both tires and just hook up the crossfire to them.
Yes! If you are using flow-thru sensors they can sit between the cross fire and the tire. Or if you have internal sensors then, of course, the individual tire measurements would be available to you. Unfortunately not all external tpm sensor manufactures have flow-thru models.
Of course the ultimate authority on this is the manufacturer.

Steve

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Old 03-02-2014, 11:49 PM   #31
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If I was to purchase Dually Valve stems and go to tire shop for install what is an estimated cost on MH with 19" wheels? I'm talking about install using current tires. Is it also correct that TPMS will fit on the dually valve stems?

Thanks
I paid $40 to have them installed on our coach with 19.5" wheels here in GA.

And yes it is correct that the TPMS units will fit on the dually valve stems.

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Old 03-03-2014, 01:33 PM   #32
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Your scenario is wrong. The crossfires close a valve once the tire pressure is 10 psi below design in either tire. So only one tire goes flat while the other tire stays at 10 psi below normal. A black flag is viewed through the window to let you know.
Thanks for the clarification.
So does this mean a TPMS will not work if attached to the Cross Fire valve?
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Old 03-03-2014, 03:54 PM   #33
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Thanks for the clarification.
So does this mean a TPMS will not work if attached to the Cross Fire valve?
If the TPMS sensor is attached to the Crossfire valve stem and the tires are at the inflation reading of the Crossfire(c.f.) then the tires should both be at the set pressure. If one tire begins to leak then the cf well try and balance the pressure until both tires are about 10psi low, your tpms will alarm (depending on settings). The bad tire may continue to lose air but the good tire will not lose any more air pressure.

So worse case (if all works the way it is published) the bad tire losses air, the cf balances until the good tire losses 10psi, the tpms should have alarmed by now giving you hopefully enough warning.

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Old 03-04-2014, 10:39 AM   #34
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If the TPMS sensor is attached to the Crossfire valve stem and the tires are at the inflation reading of the Crossfire(c.f.) then the tires should both be at the set pressure. If one tire begins to leak then the cf well try and balance the pressure until both tires are about 10psi low, your tpms will alarm (depending on settings). The bad tire may continue to lose air but the good tire will not lose any more air pressure.

So worse case (if all works the way it is published) the bad tire losses air, the cf balances until the good tire losses 10psi, the tpms should have alarmed by now giving you hopefully enough warning.

Steve
Thanks for info.
Is the 10 psi trigger based on cold setting pressure?
If cold is 65psi then the hot pressure may be 70 to 80 psi depending on speed & load and ambient temperature. Will the cross fire trigger and stop the air transfer at 10psi below the hot pressure or 10 below the cold press.
If the trigger is 55 i.e. 10 below cold pressure, then both tires can loose 15 to 20psi down from hot pressure before the trigger based on above pressures.
Some TPMS only warn based on the cold set pressure while better systems also warn when there is a rapid loss of pressure from the hot pressure.

Given that many TPM warn with a 15% air loss it sounds like there needs to be special instructions to Cross Fire users of the need to adjust the "standard" cold pressure to be high enough so that 10 psi loss would be at least 15% of the cold pressure.
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Old 03-04-2014, 10:43 AM   #35
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If I was to purchase Dually Valve stems and go to tire shop for install what is an estimated cost on MH with 19" wheels? I'm talking about install using current tires. Is it also correct that TPMS will fit on the dually valve stems?

Thanks
Did you ever ask your RV dealer to show you how to set tire pressure on your inner dual tires with the valve stems they provided originally?

Dual wheels are supposed to have "hand holes" large enough to get your hans in to remove the valve cap. If you can do that you can easily screw on a TPM sensor.
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Old 03-04-2014, 10:44 AM   #36
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Both of my RVs came with extensions on the inside rear tires... my current coach points the outside tire inward, and that's a real P.I.T.A. for filling, checking, and even my TMPS. So don't forget to consider how you want the OUTSIDE tire valve stem to operate. I would certainly have mine turned around to face outward if it didn't cost an arm and leg to do that...
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Old 03-04-2014, 11:37 AM   #37
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Originally Posted by Tireman9 View Post

Thanks for info.
Is the 10 psi trigger based on cold setting pressure?
If cold is 65psi then the hot pressure may be 70 to 80 psi depending on speed & load and ambient temperature. Will the cross fire trigger and stop the air transfer at 10psi below the hot pressure or 10 below the cold press.
If the trigger is 55 i.e. 10 below cold pressure, then both tires can loose 15 to 20psi down from hot pressure before the trigger based on above pressures.
Some TPMS only warn based on the cold set pressure while better systems also warn when there is a rapid loss of pressure from the hot pressure.

Given that many TPM warn with a 15% air loss it sounds like there needs to be special instructions to Cross Fire users of the need to adjust the "standard" cold pressure to be high enough so that 10 psi loss would be at least 15% of the cold pressure.
Great point Tireman
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Old 03-05-2014, 11:35 AM   #38
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Both of my RVs came with extensions on the inside rear tires... my current coach points the outside tire inward, and that's a real P.I.T.A. for filling, checking, and even my TMPS. So don't forget to consider how you want the OUTSIDE tire valve stem to operate. I would certainly have mine turned around to face outward if it didn't cost an arm and leg to do that...
I assume you do not have a "dual foot" pressure gauge which is designed to connect to both inward & outward facing valve stems. The outer rim does have a stem that points to the inside. This is industry standard as the wheels need to be interchangeable (mount on the front, inside rear and outside rear).

There are metal extenders that have a 180 degree bend to point to the outside. If you were to get some special bolt in 180 degree stems you could never use those wheels on the front or inner dual position.

I personally believe that most/all the problems people with extenders or hoses are the result of just pushing the air chuck on the end of the extender or hose. This puts side loading on the hose or extender which can result in loosening of the extender or hose.

I mounted my hoses so the ends are bolted down.

When I check inflation or add air I hold the hose end rather than just jab the air chuck on it. I have 17,000 miles on this set-up since 2008 with zero leaks.
I am not impressed with the big rubber donuts that fit in the hand holes that are supposed to support the hoses.

Yes I do have TPMS but they are internal to the tire in this picture.
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Old 03-05-2014, 01:45 PM   #39
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I have been using these for years with no problems. It is peace of mind to look at them when every time we stop and know that both dually's are inflated properly. You purchase them for the desired PSI. They use braided lines, not solid. One fill for both tires.

Amazon.com: Crossfire Dual Tire Pressure Equalization System, 100 PSI, one per pkg. (CF100STABT): Automotive
I've used these for 12 years, (88k miles): Link Cat's EyeŽ - Innovative Products for the Transporation Industry, with NO problems

They're similar to Crossfires.

Mine have the braid covered hoses.
BTW, I have no TPSM,
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Old 03-05-2014, 01:54 PM   #40
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Both of my RVs came with extensions on the inside rear tires... my current coach points the outside tire inward, and that's a real P.I.T.A. for filling, checking, and even my TMPS. So don't forget to consider how you want the OUTSIDE tire valve stem to operate. I would certainly have mine turned around to face outward if it didn't cost an arm and leg to do that...
I just let my jacks down to take the load off, dropped the pressure to near zero, loosened the nut on the valve stem, rotated it to the position I wanted, tightened the nut and re-pressurized. Very simple
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Old 03-05-2014, 03:57 PM   #41
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There are metal extenders that have a 180 degree bend to point to the outside. If you were to get some special bolt in 180 degree stems you could never use those wheels on the front or inner dual position.
My coach, on Spartan chassis, came with outer dual stems that point outward. Aluminum wheels are not normally usable in all positions due to only one side being polished. Of course they could be used in another position temporarily, and the valve stem would not normally prevent that.

As for reaching a hand through the wheel holes, the "hand" holes are smaller on aluminum wheels than on the traditional steel wheels (and the Chevy wheels pictured above). Most aluminum wheel holes, round or triangle, are small enough to make it difficult even to remove a valve cap, much less a TMPS sensor.

Quote:
I mounted my hoses so the ends are bolted down. I am not impressed with the big rubber donuts that fit in the hand holes that are supposed to support the hoses.
Flexible hose type extenders MUST be bolted down or secured in some way. The rubber donuts are NOT designed for use with flexible hose type extensions. They are used with long metal valve stems or solid metal extensions only. And on aluminum wheels, the donuts, like the holes, are relatively small.

One caution on the hose type extensions ...they are pretty vulnerable to damage by anything that gets into the wheel area. We went to an RV chapter meeting in December and one coach with hose type extensions bolted to the wheel can ventured into soft ground. By the time he called a tow truck, the hoses on one wheel had been ripped apart at the valve stem by mud, and one tire popped loose from the rim. It was quite a mess, with a good bit of mud inside the tire.
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Old 03-06-2014, 01:27 PM   #42
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Thanks Tireman for the explanation!!

And to the other member who recommended letting the air out and spinning the valve stem manually. I have read of others doing that but I'm afraid of running into trouble (my luck) that would require a tow, plus repair.

Alas, my TPMS flow thru sensors still give me grief. I get unexplained failures from them (TST brand). The fine guys at TST always send me a replacement for problematic sensors but it seems that at least half the time I get sensors that don't register on my reader. I am using the signal boost too, so I can't explain it.

So I guess I am now asking if anyone out there had direct experience with TST's or another brand that sells INTERNAL sensors? I worry about battery life in those things...and just ...will they work?
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