2 valve stems?


one thought…maybe it’s where the sensor for those -low tire pressure warning,sensor thingy’s mount??
…actually,the nitrogen /air bleader kinda makes some sense…would the nitrogen be lighter?would you bleed from the top or bottom?


I would like to say that the whole Nitrogen explanation will buy you a little street cred on the race track. However, those rusty drum brakes will lower it again. Those rims only look good with disk brakes in my opinion. It looks kind of like a turd decorated with a ribbon.


goin on 9 years in Ohio weather, I’d say they’ve faired well.


It would be more effective to let all (nearly all) the air out and replace it with N2 than try to flush it out that way. If that is what they are for, it is a really dumb ideal unless you need to do an exchange while the vehicle is moving. If that is the case you need a lot more than two valves!


Nitrogen is slightly lighter than air so theoretically you would fill from the top and bleed from the bottom. But since air is 78% Nitrogen, the pure N2 introduced into the tire would infuse into the remaining air very rapidly. I did a plume analysis on a nitrogen leak once. A 1/4" hole and 10 psi only produced a measurable plume about 12" high and 3" wide.


I gotta chime in here. The idea that you put nitrogen in one valve while letting air out the other does not make sense. The nitrogen and the air would mix inside the tire, and you would be pulling some N2 out with the air. (I do not need a CFD simulation to believe that.) From my career experience I know that when you want to backfill a vessel with nitrogen, you first pull a vacuum to take out the air. Our guys used a valve manifold – pretty much like the manifold used to evacuate air from an AC system before putting in the refrigerant gas.

So, I’m still waiting for the real answer to this interesting question.





OK. It says “to make it easy to purge… if you run nitrogen.” “Purge” means sucking out the air, so I guess you remove the stem from the air-purging valve. It’s like having the valve manifold built into the rim.

(BTW, when I posted I was responding at #20. I neglected to notice that there was a second page of posts, many of which addressed my point.)

Back to lurking.


Purging can be performed under positive pressure, or negative pressure.



Purging can mean using a pump to vacuum something out (evacuate an A/C system for example) or removing it from the other end by other means (blowing ballast tanks on a submarine for instance).

One could theoretically purge the A/C system on a car by introducing refrigerant into the low side service valve while depressing the high side valve. This will allow the refrigerant to force, or purge, the air out of the system.


This is an email response from a member of the suspension team at the company which made those wheels. “Most of those other questions are just from people who didn’t believe the right answer. If you’re going to purge the air in the tire and replace it with nitrogen, you need both an in and an out. Simple. It’s more effective than simply letting the tire go flat and refilling it, as that won’t displace all the air.
It’s one of those things that’s useful and effective if you need it and know how to use it, but can be safely ignored otherwise.
Go ahead and pass that along to the forum, I’m not a member there.”
[name removed by Hellokit]
Flyin’ Miata Company
So, there you have it, directly from the source!


cancel this response.


It’s a nice theory but that isn’t going to purge a tire unless, as I said before, you’re able to flow many times the volume of the tire through it. You can bet these places don’t do that, it’s all for show. That is not an efficient means of purging that volume and shape. Too little flow to mitigate mixing and way too much volume for that size inlet and exit. You have no way to force an efficient flow path from inlet to exit. What you have is a slow dilution model and that takes serious volumes of gas to properly purge. Like I said before, sample the gas an hour afterward and PROVE what you claim. Until then, it’s another gimmick only slightly better than deflating and refilling with pure N2.


Wouldn’t it be cool to fill the tire really fast with 2 air hoses at once? You could win bets on how fast you can pump up a tire. Kind of like a hot dog eating contest - how many tires can you pump up in 60 seconds?


That wouldn’t be easy to answer. It is true that the rims with two stems makes it easier than one stem especially if you don’t have another option to increase the ratio. Though, not sure whether it is appropriate calling it “effective and useful”. As I say, more than “slightly better” but less than “useful and effective”.

As for flow path, you could make de-swirl vanes by pinching the sidewall for directing the air to the exit.


I totally agree it’s a gimmick.
The only way I could see this working, and one does not need 2 valve stems to do it, would be if a vacuum was pulled on the tire; much like pulling one on an A/C system before recharging.

Of course, one wonders if the tire bead would stay in place when 20" of vacuum hits… :slight_smile: