Why do tire gauges not always agree?
Question: I have been working on cars for over 40 years as a hobbyist. I say this to establish that I am not new or inexperienced. My question is this: You have written about and I am a firm believer in maintaining correct tire pressure in vehicles. However, I own at least three tirepressure gauges, one an inexpensive pencil type and two dial type, both made by reputable companies. None of the gauges provide the same reading. How can I determine which one is right and what assurance do I have that buying an expensive gauge will provide any better results?
J.S. Answer: I feel your pain! The spread on my personal tire gauges is about 4 PSI, which is not acceptable. The best, but not so convenient, way to figure out your best one is to see if your local tire shop is willing to check them against their master gauge (if they don’t have one of these, shop elsewhere!). Accuracy of pencil type gauges can be improved by applying a shot of WD-40 or similar to the indicator shaft and manually exercising it in and out perhaps five times prior to use. My take on the research I did was that dial-type analog gauges are usually a better bet than the typical pencil type, with the TireTek premium gauge ($15, calibrated within two per cent) receiving high marks. Digital gauges appear as good or better than dial gauges for consistent accuracy. One digital brand, Accutire, has highly favourable reviews for accuracy, at a reasonable price (around $20).
How big a deal is inflation pressure? Underinflated tires cause sidewall deflection and cause the tire to run at a higher internal temperature. The increased friction also reduces fuel economy by perhaps five per cent (at 6 PSI low) and reduces steering response and vehicle stability. An increased chance of hydroplaning in wet weather is an additional downside. Overinflation is a lesser evil, but should be avoided also as it reduces the tire’s contact patch, leads to a stiff ride and increased tread-centre wear, and increases the chance of a tire injury from an abrupt road surface fault. An upside is a slight increase (3 PSI max) in pressure typically enhances steering response. Studies show that perhaps 40 to 50 per cent of the vehicles on the road have one or more underinflated tires, and about 20 to 30 per cent have tires that are somewhat overinflated.
Q: My starter groans and moans at times, barely starting the engine. I had the battery tested and it was OK. What else could be causing this? Is it the starter? J.L.
A: Possibly, but tests are needed to be sure. Your battery may be suffering from a parasitic drain (glove box light or similar draining it while parked), it’s receiving insufficient charging (a weak or ineffective alternator) or a cable/connection fault at the battery terminals or within the starter circuit. Tests for each of these possibilities are simple and quick for a trained tech to perform.
Condemning a weak or faulty starter is easy; if the voltage delivered to and dropped by the starter, while cranking, is within one volt of that measured at the battery (10.5 volts or higher at the starter, 11.5 volts at the battery) poor performance is the starter’s fault, not the battery or circuit. A tight engine, due to gummy or thick oil or an internal fault, is also a rare possibility. Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, California. Readers can email him at bradbergholdt@gmail.com; he cannot make personal replies.