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Tire Stem Caps

Discussion in 'Model S: Driving Dynamics' started by jdesmo, Feb 18, 2013.

  1. jdesmo

    jdesmo Member

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    Don't replace those 'cheesy' plastic wheel stem caps!!!!!!!!. they are designed to blow out in case of a major pothole, failure of the valve, instead of the tire blowing thru the side wall. BEWARE
     
  2. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Do you have a reference for this?

    I've played and worked in and around garages since I was 7, and I can say that this is the first time I've ever read/heard that. First, that would imply the valve core is also designed to blow out, and then it would implicate those manufacturers that make metal caps.
     
  3. steve841

    steve841 Active Member

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    Yeah, I'm not buying that one.

    Unfortunately ..someone here already experienced that exact issue and the tire was DOA
     
  4. Kaivball

    Kaivball Member

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    I don't think so
     
  5. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Nonsense. The valve core will more than keep the pressure in during a pothole situation--and you don't want to lose air in a pothole situation because that will ruin the tire immediately. Generally speaking, the higher the pressure you have the lower will be the damage will be from potholes.

    The cheesy soft plastic caps are designed to be easy to install in a factory because they don't have to be careful not to strip the threads--they can just be pushed on. They also keep dirt and water out, so they are not 100% useless. However, best practice is to replace them with either metal or bakelite caps that seal the air. Although many people use the valve core as the main way to keep air in the tire, the cores are really designed to be a convenience to allow you to check the pressure without letting all the air out. Metal or bakelite valve caps should be your primary air seal, not the valve core.
     
  6. jdesmo

    jdesmo Member

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    #6 jdesmo, Feb 18, 2013
    Last edited: Feb 18, 2013
    Absolutely yes, reference is my Jaguar dealer and our forums. my XF supercharged has those plastic caps, and on the Jag forum it was discussed at length by the technicians who explains the mechanics of these failures on super low profile tires.
    Also, the plastic caps should not be too tight on the stems.

    (But since experts here insist, it must be just 'nonsense')

    Here below is some of that Jaguar forum thread:

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    There have been a number of reports of failure of the TPMS valve stem. Jaguar warns against use of metal valve caps. If you use metal valve caps there is a serious risk the valve stem will fracture at the point on the stem where the cap ends, the valve body flies out andvthe tire pressure goes to zero extremely quickly as if for a blow out.

    Did you have metal valve caps by any chance?

    Although the tires are not warranted by Jaguar the TPMS is. There is no way the TPMS should part company with the rim as the valve stem secures it. Is the valve stem still there?

    __________________
    09 Azure XF Lux, dove grey interior
     
  7. Babylonfive

    Babylonfive Power12

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    Jerry, do you recommend a set of chrome or bakelite caps? Amazon?
     
  8. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I don't purport to be the expert, but I'd like to see it published in a manufacturer's note or similar documentation, not as just the word of a particular person. If the stem is fracturing because the cap can't blow off, you've already reached a serious failure anyway as the valve stem is going to shoot out through the plastic cap, or blow it off anyway, resulting in a complete loss of pressure.
     
  9. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    There are any number of sources. Where it's cold the bakelite ones are a bit better because they are easier to get off, the metal ones are sometimes slippery to your fingers. The bakelite ones have thicker walls so your fingers don't slip as much.

    I guess Jaguar has a problem with their valve stems, because the way I read the letter is that the metal valve caps will cause the valve stems to crack. I wouldn't generalize this.

    Note that the "nonsense" part is that the flexible caps will somehow let out the air when hitting a large pothole (if they did somehow let out the air when hitting a pothole the tire would be ruined instantly with a pinch shock). However, there is no way that is going to ever happen because the valve core will seal the air. That's totally different than the post about the Jaguar and it's valve stem cracking problem.
     
  10. montgom626

    montgom626 Active Member

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    Not buying it either.
     
  11. woof

    woof Model S #P683 Blue 85 kWh

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    I always thought metal caps were a no-no in an environment with salt on the roads. Disimilar metals (metal valve stem + metal cap) doused with a salty aqueous solution (salty winter road slush) creates galvanic corrosion. Not enough to charge the car, but enough to create a mess of the caps that may become difficult to remove.

    Acura once sent me replacement plastic caps to exchange for the stock metal ones for this exact reason.
     
  12. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I'll take plastic ones as long as they'll coat it with a metallic finish. The flat plastic is just... blech.
     
  13. jdesmo

    jdesmo Member

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    I choose to live and learn:

    It is not Jaguar specific. Ford has experienced issues. The relevant statistic would be accidents caused by tire blowout. One poster on this board experienced a sudden loss of tire pressure but the TPMS unit was destroyed in the incident. The remains did show a broken valve stem. UK posters have reported failure while adding air to the tire.

    Jaguar has updated the part and declares that only plastic valve caps are to be used.
    The is a real hazard, potentially very dangerous. You would be extremely foolhardy to ignore this problem, especially relying upon anecdotal evidence or personal unskilled observation. Comparison to other makes, particularly predating TPMS use is also suspect.
    __________________
    09 Azure XF Lux, dove grey interior

    Here is the text of a communication from Jaguar:

    Concern:
    Jaguar has received Warranty claims for TPMS valves/sensors which have been broken whilst
    attempting to remove metal valve dust caps from the tyre valves.
    Cause:
    Metal valve dust caps corrode onto the aluminum TPMS valve stem and become difficult to remove
    without breaking the tyre valve.
    Action:
    Jaguar engineering do not recommend the fitment of metal dust caps to vehicles fitted with TPMS and
    warranty claims will not be accepted. Any vehicle found with metal/chrome valve dust caps on TPMS
    tyre valves must be removed and replaced with the Factory fitted grey plastic valve dust caps, part
    number XR8 51652.

    Owners must be informed of the consequences of putting metal valve
    caps on Aluminum TPMS tyre valves.

    (Note: It's not only steel. Can be also aluminum due to different alloys. Hence they say METAL)
     
  14. ElSupreme

    ElSupreme Model S 03182

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    What you reference above and what you posted first are two entirely separate things. This reference says that metal caps will cause the stems to fail and the tire to lose pressure during a pothole attack. You said the plastic ones should fail during a pothole effect. You do NOT want air escaping when you hit a pothole (or at all really).

    The reason not to use metal, is that some metals will cause the tire valve stem to corrode, weaken, and possibly fail. Most likely with a tire pressure spike caused by hitting a bump or pothole.

    Basically it is a corrosion problem. Nothing to do with the mechanical bits. I use the cheap plastic ones because, who really cares?

    Having better stronger valve caps (that don't induce a failure point) would only help the car. You said the worst thing that could happen was helped by the plastic caps. You had the complete opposite understanding of the problem. That is why no one believed you. If you put Al caps can cause galvanic corrosion of the valve stem and have it shear off, there would have been a 100% different reaction.
     
  15. childressmd

    childressmd Member

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    Unsprung weight!

    :)
     
  16. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    What you posted here was not what you said before. You said something about plastic caps needing to be there to relieve pressure so the tire stem didn't explode on potholes.

    The Jaguar communication you pasted has to do with bimetallic corrosion. And yes, that can be a real issue if you insist upon torquing a stuck cap off the stem. Personally, if I had to apply such force to the cap that I needed to twist off the entire valve stem, I'm probably using the wrong tool.

    Personally, I think plastic caps are ugly as sin and are the rough equivalent of putting lineolum in your car... but that's me, I guess.
     
  17. aaronw

    aaronw Member

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  18. Kaivball

    Kaivball Member

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    How long do you have to go not ever checking your tire pressure for binding corrosion to occur????

    If you check your tire pressure at least once a month I can hardly imagine corrosion to occur unscrewing and screwing the metal cap. How could it possibly bind that you break the valve stem?
     
  19. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    These will work - plastic underneath, chromed surface. They're likely to scratch easily, but they will work.
     

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