Tire Pressure Gauge; Tire Air

[Jeff Field]

I’ve been using a gauge I got at a motorcycle shop for $30. It compares well to a few nicer gauges that I’ve used “back to back.” It reads 0-15 psi in .5 increments. With the needle between 2 marks, I’d say you have .25 psi resolution. If you know there is more that 15 psi in that tire, don’t put the gauge on it. Looking at other gauges, I’d pick one now that does 0-20.

I have a compressor at home, but rarely bring it to the track. I’d only need it to bead new rubber. Making pressure adjustments is easily done with a bicycle pump. I’m considering one of those 2 gallon air tanks that I can fill at home and bring along. Way less hassle than the whole compressor.

[Troy Smith]

sjp:

Couple of thoughts for you…

The gauge sensitivity is not the utmost important feature, what is, however, is consistency. Get a gauge and go with it. I’d say you’re fine w/ a 30 lb. gauge and one that allows you to read in 1/4 lb. increments.

The optimal operating zone for MG Yellows (TTAC/IMI & CSC Tire) is 13 lbs of pressure. People use Nitrogen because it is more predictble than air. If you are using air, you never quite know what you’re going to get unless you measure the temperature, relative humidity and adjusted altitude of the air at the time you fill the bottle/compressor/tire. Make sense? Nitrogen is preferred because the moisture content is controlled (those in the ‘know’ will tell you that the air we breathe is like 74% Nitrogen) and moisture is what makes the gas inside the tire expand w/ heat and contract w/ cold. Air is perfectly acceptable BUT you will struggle to find the best operating window for the tire as you improve your driving and can ‘tune in’ to issues like that. We have an advantage here as it is quite dry so our ‘moisture content’ in the air is much less than say, Florida.

Now, how to find that operating window…test, test, test.

Basic rules of thumb for finding the optimum tire operating window are:
Your typical Qualifying Session is 10 minutes or about 10 laps: test for getting your tires to come in ‘early’ (read in 3 laps or less assuming you will at some point go out for a race with new shoes and want to take advantage of that new sticky coat on the outside of the tire to let you run your fastest lap). This means, on a typical CO summer day of about 90 degrees, you may go out at 12 psi on MG’s knowing that the tires will quickly (one lap or two) come up to 13 psi and you better be on it as they will then go over to 14 – 15 psi and you will start to slide (little bit, not like a drifter or anything) which means slower times.

Your typical Heat Race is 10 laps also. As a driver, you need to figure out (again…test, test, test) if you want your tires to come in early race or late race. By testing, you will know how the tires react to your kart, your driving style and the weather conditions.

Your typical Main Race is 20 laps. Same scenario, more laps.

Food for thought stuff:
– The gas inside the tires will expand if your kart sits in the sun even if you are not driving it. They’re black, they attract the sun, they will heat up sitting on the stand. Keep your kart in the shade for the most accurate results and set your tire pressure last thing before you go out on the track. Easy way to remember this…keep your tire gauge in your seat.
– Different tracks and different direcations will put extreme pressure on one particular tire (typically this is the outside front but it can vary by track.
– You need to go out with different tire settings, run about 10 laps, come in and immediately check your pressure. Same w/ 20 lap sessions. Build a data base and the knowledge will come.

Send me your e-mail if you want and I’ll copy you on a test-n-tune form I use which you can modify to your liking. Also, Doug, Greg, and Jeff are really the experts when it comes to tires and especially with their chassis. I’m sure they’ll give you much better advice!

Best,

Troy

[Garrick Mitchell]

Get an air tank from Harbor Freight… You fill it via a Schrader valve (same as car tires), so you can charge it at any gas station. A bike-tire pump works in a pinch.

My pressure gauge is 0-30 psi and has 1/2-psi increments. The cool feature you won’t find on garden-variety gauges is the bleed valve. It’s a small button you press to release air from the tire a little bit at a time. You over-fill the tires a bit and then bleed them down to the desired pressure. I don’t remember the brand, but I got it for $30-ish at IMI.

Ditto what Troy said about testing in order to hit the optimum pressure (13 psi for MG Yellows) at the right time.

[Joe Rosse]

I’d agree with all the prior comments. Consistency is far more important than dead-on accuracy. Make sure the dial face is easy to read (seems obvious, but I have one brand-name gauge that’s a pain to read.) I’d suggest a 30 pound range, because you may need to go more than 15 pounds, especially in the rain. And you can break a 15 pound gauge if you attach it to a tire that heats up and comes in with 20+ pounds of air in it (ask me how I know–and, BTW, this is a good reason to get a good brand that will do warranty repairs!) Finally, the air tank is probably much more practical than trying to lug along an air compressor, and they’re cheap enough you won’t regret buying it if you later go with nitrogen. (I recently heard of a person who converted a fire extinguisher to be a real compact air tank for last minute adjustments on the grid–sounds interesting, but I rather doubt it would get you by if you have a leaking tire.)

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