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Rob MacGregor (LAURA LEYSHON/LAURA LEYSHON/THE GLOBE AND MAIL)
Rob MacGregor (LAURA LEYSHON/LAURA LEYSHON/THE GLOBE AND MAIL)

Rob's Garage

Should I fill my tires with nitrogen? Add to ...

Hi Rob,

I live in Prince George, B.C. and I want to put a pair of studded tires on the back of my pickup.

I'm driving a 2008 Silverado 4WD automatic. I would like to buy a pair of steel rims and mount studded winters only on the rear. The tire shops are all trying to sell me a full set of four. My questions to you: are they just trying to sell me two tires I don't really need, or is this really necessary? Is this unsafe, and or liable to cause vehicle damage? One tire man told me it may damage my transfer case if the tires are slightly different. Back in the day before all-season radials, with a two wheel drive, two studs on the back worked just fine for me.

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Also, is there any advantage to nitrogen over good old-fashioned air?

Thank you, Bill

Great question Bill. I'll start with the easy stuff first. In a perfect world, you should replace all tires at the same time with the same size, brand, tread design and speed rating. That's easier said than done because unless you are buying all four tires at the same time, it's impossible to match up different tires from different suppliers. That said, consumers need to consider the application and how much driving will be done on the "temporary" winter tires.

The key to this is the circumference of the tires and the importance of the manufacturers' recommendations with respect to transfer cases. It's important that the rolling distance of each corner is as close to identical as possible due to the mechanical and electronic controls that are in place on your truck.

An argument could be made that if you have a transfer case that "free wheels" the front axles when in two wheel drive mode, you are good to put on a slightly different sized rear tires. However, I would strongly suggest that you follow the recommendations outlined in your owner's manual as I'm going to make the assumption that your Silverado has the new Autotrac NVG246 transfer case. This is extremely sensitive to tire circumference differences.

As for the nitrogen (or just plain old N if you wear a lab coat) versus old-fashioned air (I love your term to describe air) the jury is still out.

I hate to sound like a fence-sitter but because this technology is new, it's difficult to commit to a firm statement one way or the other.

The theory behind using N is that the molecules are slightly larger than air, which is really a makeup of 78 per cent nitrogen and 22 per cent oxygen. That small concentration of oxygen molecules is just enough to create a dilution of the overall mix, allowing for a greater chance of the air molecule to literally leak between the rubber molecules. This is the norm with tires. Many of you will have experienced this when leaving a vehicle or a boat trailer unattended for more than a month. The tire pressures will drop off noticeably through this process.

Another advantage to N is the fact that it is non-corrosive, unlike air or more importantly, the oxygen in the air. Oxygen has been blamed for the rust that forms on the inside of a mounted tire and wheel assembly, because as everyone knows, rust is simply the combination of oxygen and iron, or iron-oxide. With only nitrogen inside the tire/wheel combination, there is no way for rust to form.

But the downside of nitrogen is that there is not much in the way of infrastructure support for refilling your tires. This is the biggest push back on this issue and it's a strong case, not to mention that there is usually an added cost by installing N.

I actually had a set of new tires installed on my car and was asked if I wanted to use nitrogen. Based on the info above I elected to go with good old-fashioned air.

The case is getting stronger and stronger in favour of N, especially when you get front men like Jay Leno advocating for you. His video is on this web site: http://www.getnitrogen.org/

So Bill, install your two studded tires as long as they are the same diameter or circumference as your original tires and as for inflating with nitrogen, that's going to be a philosophical decision you will have to make.

Send Rob your maintenance questions at globedrive@globeandmail.com

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