Are heavy tire valve caps bad?

BenI · 09:47 AM

Do fancy metal valve caps have any downsides? I received a set of Porsche decorative valve caps for Christmas, and am not sure if I should use them. I have basic rubber valve stems and have heard that heavy caps can lead to stem failure-is there truth behind this? I would like to use the caps but they are much heavier than my current plastic caps. Any opinions/experiences would be appreciated.

Ben

Rouser · Rouser's Garage

I haven't heard of metal valve caps being so heavy that they effect the valve stem or rim/tire balance. Anything is possible; I just haven't come across anyone where this happened.

The only major disadvantage to decorative valve caps is that guaranteed they'll grow legs, regardless of how much you tighten them. No sense rewarding your friendly neighborhood juvenile delinquent.

Germain · 02-11-2002, 12:35 PM

Well, considering that the sticker that comes on a tire can throw off the balance by 2 ounces, I'd guess the heavy valve stem caps could too. I'd just get them rebalanced if I cared enough, but I'm me and I wouldn't care enough.

BenI · 02-11-2002, 01:45 PM

I heard that the added weight stresses the valve stem and it developes cracks or breaks off.

rdupre@houston.rr.com · 02-11-2002, 02:00 PM

The heavier valve stem caps stressing the valve stem makes a little sense since theoretically the centrifugal force would cause it to try and bend out and back. It would be constantly flexing with the normal driving you do.

On the other hand, valve stems are made pretty sturdy and I would bet that you would wear out a set of tires before the stem.

Come to think of it, I've seen valve stems of all sorts of lengths which would in effect create the same flexing/stress problem as a heavier cap. (something about fulcrum & lever length, you engineers help out) Doesn't seem to be a big problem on those cars though.

Check with your local tire dealer and see what he has to say.

Zeke · 02-11-2002, 06:19 PM

With a short stubby valve stem there should be no problem this side of 150mph. I agree though that the balancing should be considered. While we're on the subject of tires and buying new tires, if you can find a tire shop w/ a bubble balancer, have the rim checked for balance w/o a tire but w/ a stem. Then mount the tire but do not inflate. On the balancer, rotate the heavy spot of the tire opposite the heavy spot on the rim. Now inflate and it's ready for the computer dynamic balancer. Uses less weights. Works really good on larger tires/rims.

Jim Smolka · 02-12-2002, 02:02 AM

Rdupre,

Sorry, but the engineer inside of me cannot let you get away with 'Centrifugal force'. There is no such thing (Newton's Laws). There is only lateral acceleration.

rdupre@houston.rr.com · 02-12-2002, 11:14 AM

OK fine, be literal. I knew someone would take me to task

I was relying on what I remember from high school science. And, that was a long time ago.

Whatever force it is, it will cause some stress on the valve stem, causing constant flexing as the wheel turns faster or slower. I believe that valve stems are designed to take this into consideration.

jmcleod · 02-13-2002, 08:22 AM

interesting thread, i'll add a bit of info that on 911 Fuchs, there is a little valve support "bracket"???? thingy that i guess keeps the valve stem from flexing too much and breaking. and anyway, centrifugal force is in the eye of the beholder, viewed as if located on the rotating rim in an accelerating frame of reference, but that's all fictious anyway