Wednesday, September 4, 2013

Nitrogen Fill into Q50 Tires

#1 Myth about filling Nitrogen in Tires: It does not expand and contract as much, and does not leak out of tires, so there will be no low tire pressure warning light.


Air is about 78% nitrogen, 21% oxygen, 0.9% argon, 0.1% carbon dioxide.

Specific Heat Capacity is the amount of heat that is needed to raise the temperature of volume of a substance without changing state (Remember you Chem-101 class?)

Air has a specific heat capacity of 1.01 kJ/kg K 
Oxygen has a specific heat capacity of 0.91 kJ/kg K 
Nitrogen has a specific heat capacity of 1.03 kJ/kg K 

Since air has only about 21% oxygen, by using the just nitrogen, the change in capacities are only 0.02 kJ/kg K. Thus Nitrogen fill tires will still expand and contract almost as much as air filled, just a slight difference, immeasurable really. 

Generally, 10 degree F in temperature change results in 1 PSI change in tire pressure -  Air or Nitrogen.

So why put in Nitrogen?

My reasons for using Nitrogen:

1. Convenience: Faster and easier than a 12V pump for me, I am lazy on cold winter days. I have a 2200psi scuba-sized Nitrogen tank in the garage. The tank refill costs me $7 to refill and lasts about 2 years of toping off all cars throughout winter. The temperature here varies from 100F in summer to -10F in winter and that means 10-12 PSI variance in pressure easily, not counting moisture. This way, I can top off in the morning before the car is driven and have equal pressure on all tires for the correct season.

2. Cost: Dealerships charge $6-8 to fill a tires and $2 to top off each tire. Costco is free. But going anywhere means the pressure will be wrong as one side of the car maybe exposed to sunlight, and driving will raise the temperature, thus pressures.

3. Moisture: The Nitrogen source is guaranteed 99.99% dehumidified. This means no moisture in the tires. This is a concern because when the temperature hits 32F (freezing point) or below, the moisture turns to ice in the tires and then pressure drops quicker as that volume is gone. Moisture also introduces variances, for example filling a tire on a 95% humidity day with air will introduce a variance in its expansion. This is the main reason planes and race cars run Nitrogen. Really dehumidified air will work just as well, but no one sells that.

4. Oxidation: While only 21% is oxygen, but the oxygen can react with tires rubber compound inside and reduces their life-span. Having an inert gas like Nitrogen prevents any oxidation, corrosion of TPMS, etc. Though I suspect that the run-flat tire threads will wear out long before oxidation kicks in.

5. Fun: I get to use my cool N2 labeled chrome caps.

How to Put Nitrogen into the Q50 Tires:

Step 1: Put a safety chuck on the back wheel of the Q50.

Step 2: Jack up Each Wheel, one at a time. We do not want to deflate the tire with the weight of the car on the tire. This will cause the rim to cut the tire completely and damage the rim.

For the front wheels, since the Q50 does not have a jack that it comes with, I used my floor jack, against this the frame. Do not use the Factory Jack Points with a flat floor jack and do not jack up against the body, only the frame. Be careful as some body panels hold 480V Hybrid battery cables.
Front Jacking Point with Floor Jack

For the rear wheels, I normally go against the differential or suspension member, but the Q50's rear suspension is very different and does not have a good point, therefore I ended up using a 2-by-2 piece of wood flush behind the rear factory jack point and against the frame as below. Lots of aero panels under the rear part of the car.
Rear Jack Point using a solid 2x2 block of wood
This discovery of multiple plastic panels and aero plastic parts under the Q50 has me a little weary about allowing just any shop to jack up  the Q50. If they do it wrong, they could break, bend or damage a part and probably won't even know it.

Step 3: Using a Tire Valve Tool, remove the tire valve carefully making sure not to let it shoot out. This will let out all the air.
Easy Tools for the Job.

Step 4: After the air is completely out. Put the valve back, fill in a little bit of Nitrogen. Repeat Step 3, this will purge out any of the remaining air and then screw the value back into the stem completely.

Step 5: Set the regulator on the Nitrogen tank to about 35 Psi and let it fill up. Don't use higher pressures, it may go quicker, but you may blow up the tires quicker.
Filling up N2.
Step 6: Using an accurate tire pressure gauge, set the pressure to 35 PSI but adding or removing N2 as needed.

Step 7: Put a little soapy water (or saliva) on your finger and run it over the tire valve to form a little film across the valve stem opening, if it bubbles up then the value is not tight enough. Re-tighten it.  

Step 8:  Let the car down from the Jack and repeat for the remaining Tires.

I had a new tank refill, and to flush and fill all four of the Q50's tires it took about 1400 PSI. So that leave me a good 800 PSI of Nitrogen for top offs.

Little tank goes a long way.
My Nitrogen Tank comprises:
- 22cu Ft tank which is filled at 2216psi.
- Regulator with 4000 PSI inlet and 125 PSI outlet
- Hose with Brass fitting and clamps
- Tire Air Chuck with Lock on Clamp.

I have had Nitrogen for 5 years now in on all my cars, motorcycles and bikes. The consistency in pressures and cease are worth it.

Interesting Q50 Rear Suspension, will require further study.