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Hi folks. What is the recommended process to do nitrogen fills on tires ? I see some people vacuum out the air, etc.

Hi Racer D,

Apart from just using only dry nitrogen to fill/adjust tyre pressures, what you're referring to is what usually called purging the tyres. When you get a new set of tyres fitted, you won't always be able to trust/always know what the tyres were filled with and how dry the air/nitrogen they used was.

The normal process is to first, before the tyre is fitted to the bare rim, make sure there is no moisture/condensation on the inner surface of either the rim or tyre. Then once the tyre is fitted and delivered to you you can start purging. This normally means removing the valve core and releasing the pressure. Then fill the tyre with dry nitrogen and then release all the pressure again. You repeat this filling/releasing process, usually 3 times. At this point you can consider the tyre purged and ready to fill with nitrogen for the final time and have the cold pressure set.

We go to all this trouble as we're trying to evacuate any moisture that might be left within the tyre. We want to get rid of this moisture as otherwise it leads to more pressure growth as the temperature changes. We usually want to minimise this, but more importantly, we want it to be consistent between sets/tyres so we can hit our hot targets properly.

What about all these guys who use evac type pumps to suck air out of the tire ?

You can certainly do that instead, if you have the equipment, but it would be a good idea to also do this multiple cycles, as you probably won't be able to fully vacuum out the air in the tyre because the pressure differential on the sidewall will tend to unseat the beads.

As Tim said, the most important thing is removing the moisture content - remember, air is already 78% nitrogen, so that's a deminishing return on increasing the percentage - and learning what the tyre's pressure changes are.

An additional benefit, if you're using magnesium wheels, is the removal, or at least reduction, of the moisture will reduce the oxidation of the wheel's inner surface.

Using an evacuation pump is the same principle, it's just about trying to draw out the existing gas/moisture within the tyre. You see all sorts of different setups used by teams, all different levels of complexity, all with a similar idea.

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