One of the easiest ways to modify your car’s handling is by adjusting air pressure in the tires. It’s also one of the easiest ways to screw up your car’s handling. The problem with air pressure is it changes during a race. As air gets hot, it expands, thus while racing, as a tire becomes hotter from road-surface friction, the air in the tire also becomes hotter, increasing pressure. I have seen upward of 8 pounds of tire pressure change from static in the pits to hot off of the track — and 8 psi can seriously change the handling of the car.
To battle this problem and foster more stable tire pressures (resulting in more stable handling) I use nitrogen gas inside my tires. Nitrogen is less affected by temperature change than air. This is not a new secret to the world of motorsports, but the trick to making nitrogen gas work to your advantage is by getting a larger percentage of the gas into the tires. Nitrogen isn’t some exotic gas. In fact, 78 percent of the air you are breathing right now is nitrogen and about 20 percent oxygen. Many tire shops now have nitrogen machines that fill and refill a car’s tire with atmospheric air after filtering out oxygen particles, putting a purer nitrogen gas into a car’s tire. I have found through testing that these machines don’t get anywhere near the purity of nitrogen into the tires that evacuating the tire and placing pure nitrogen into it does.
To evacuate a tire and replace the space with nitrogen, I built a tire- evacuation/nitrogen-fill system with a $19 tool from Harbor Freight and a bunch of brass fittings from Orchard Supply Hardware. I started with an “Air Vac” box from Harbor Freight, which is used to evacuate home heating and air-conditioning systems. The design is simple: air pressure is attached to one side of the box (I use a garage air compressor) and that air goes through a venturi tube, which creates a vacuum on the other side of the box.
I attach that side of the box to a tire’s valve stem. I found that evacuating the tire was easy, but pulling the chuck off of the valve stem, then replacing that chuck with a line from a nitrogen tank allowed air to get back into the tire. To combat this, I built a small manifold with a “T” and attached two gate valves. The manifold is attached to the tire, the vacuum, and the nitrogen. By switching the valves on or off I can chose to vacuum the tire or fill it with nitrogen.
For it all to come together, you need to have your own nitrogen supply. I bought a small nitrogen tank from a welding supply store and added a regulator to it. When the tank is empty, I just trade the empty tank for a full one. My small tank can fill about 12 205/50/R15 tires and leave me enough gas to make adjustments at the track. I use a regulator safety cage from Capitol City Motorsports so nobody gets hurt if the bottle falls over. The nitrogen tank is also a portable power supply for air tools if you need them at the track. Tudor and NASCAR teams use these same nitrogen tanks to run their over-the-pit-wall air tools.
Once the contraption is completed, simply evacuate the air in the tire until it looks like it is going to turn itself inside out and about one moment before the bead is about to pop, switch off the vacuum and fill the tire with the nitrogen. The first time you evacuate a tire, you will swear it will be damaged from the deformity it sustains. I have spoken with tire engineers at Toyo, and they have told me I am not damaging the tire or harming the belts.
Once we fill our tires with nitrogen, we use a marker to write “NIT” on the sidewall so nobody on the crew accidentally fills the tire from an air compressor. At the track, tire pressure should only be increased by adding nitrogen from the tank to keep the purity inside the tire as high as possible.
I have found evacuating and filling the tire twice helps increase nitrogen purity, but you will never get all of the oxygen out, even with the tire completely deformed. I also have read that water (or humidity in a tire) is even worse than the 20 percent of oxygen (which is why Intercomp sells an expensive tire-drying system for $1,699). So what is not helping racers and their tire pressure issues is tire shops that wet the beads of the tire with soapy water to help them easily mount it onto the rims. That water remains in the tire, providing more humidity inside and more changing pressure. I forbid my local tire shop from using any lubricant to mount my tires (not surprisingly the guys at the tire shop aren’t happy to see me show up with twelve rims and twelve tires).
There have been naysayers on the nitrogen issue and some who argue nitrogen still expands. However, my testing has shown that using dry, clean wheels and tires, purged of humid air two times, and filled with the purest nitrogen possible through my trick manifold equaled a change of about 1.5 to 2 psi from cold to hot race conditions. That is a big change from the earlier 8 psi. The whole air evacuation system cost me about $40 to build — if you don’t count the $300 nitrogen bottle, $100 regulator and $60 regulator cage. It costs me $18 to replace an empty nitrogen bottle with a full one.
To me, nitrogen is a no-brainer and a cheap way to make a car consistent. The benefit of this DIY system is using a purer nitrogen gas to take advantage of its benefits. And remember kids: Buy the nitrogen tank. The nitrous tank is a whole different party.