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First time owners of run-flat equipped cars are almost always caught off guard when they arrive at their dealership to have one of those tires repaired due to a nail or puncture. What they expect is the prompt repair or patch, but what they get is an estimate for a replacement tire. If they are lucky, they will only need to purchase a single tire, but more often or not, if their vehicle is of the all-wheel drive variety, they will be pushed to replace the tires in pairs. So much for a simple tire fix. Adding further insult to injury, the cost for run-flats in some cases is as much as 30 per cent more than a conventional tire.

Run-flats, or zero pressure tires, have one distinct advantage. If you ever do get a flat, they can be driven on with zero tire pressure or for approximately 50-100 kilometres, which should be more than enough time for you to get to an auto repair shop. Vehicles from BMW, Mercedes-Benz, Mini and many Cadillacs come standard with run-flat tires, which accounts for about 14 per cent of the tire market. These auto manufacturers save on weight, which boosts fuel economy due to the lack of spare tire, jack and tool kits. This fuel economy boost may be minimal, but the engineers at these car companies know that most of their customers don’t change their own tires and instead opt for roadside assistance, so why not take the weight savings?

In addition to the added cost as mentioned above, reduced tread wear is a common complaint for run-flat tires; in other words, they wear out faster. The sidewall does all the work in any zero-pressure situation and must therefore be reinforced and made of heat-resistant rubber, making them far less pliable than a conventional tire. This thicker sidewall produces a noticeably harsher ride, forcing the tire manufacturer to seek a solution to soften the driving experience. Using a softer tread compound achieves that and offsets the roughness, but unfortunately does so at the price of tread life.

Indicators that your run-flat tires are indeed flat are difficult to manage for inattentive drivers as there is no obviously flattened tire to catch one’s attention when walking up to your parked car. Drivers must depend on the Tire Pressure Monitoring System (TPMS) to detect any problems. Blowouts still do occur when the driver misses the fact that their tire is flat and drives well past the manufacturers run-flat distance limitations.

So, can you repair a run-flat? The answer is a firm maybe. If the sidewall indicates “do not repair,” then obviously the answer is no. Alternatively, the tire manufacturer Bridgestone’s FAQ section writes “some punctures may be repaired under certain restrictions.” Finding a tire professional and having them inspect the tire to see if it meets the criteria necessary for repair is mandatory. However, I highly doubt that your dealer service department is going to offer you that service, as most auto manufacturer literature prohibits run-flat repair. You are free to go outside the car dealer environment and visit a recognized tire dealer for the brand in question and ask them for a second opinion.

Can you replace your run-flats with conventional tires? There is no law saying you can’t, but it is rarely recommended. Most run-flats-equipped vehicles are typically heavier European sport sedans that specify extra load (XL) rated tires. Matching tire sizing with proper load and speed ratings usually limits available tires to a select few, which of course, are mostly run-flats. There may be a couple of manufactures of conventional tires that meet all the specific criteria, and you are free to install them on your car, but you probably shouldn’t. To me, it’s kind of like people who buy vehicles that require premium fuel but always try and get away with regular. I just don’t get it.


Your automotive questions, answered

I recently purchased a 2017 Mercedes C300 4matic that has about 17,000 km on the odometer. The car has the Eco start/stop feature that stops the engine when at a light or when stopping for more than a few seconds, only to start it up again when you depress the accelerator. We live in a smaller town with many stoplights and it occurs to me that the frequent stopping and starting must create significant stress and wear on the engine through drop in coolant, battery drain, ignition stress, etc. (It’s a 4cyl.) Looking at the gas usage/carbon saving aspects, the feature does not appear significantly valuable enough to retain, and the stopping and starting is just mildly annoying.

I can disable the feature each time I start the car for the length of the immediate trip by switching to Sport+ drive, but I’m thinking of disabling it on a more permanent basis so that I don’t have to drive in Sport+. Do you have an opinion or thoughts on doing this?

Ron M, Burlington

I’m with you on the annoying aspect. I have not gotten used to it either. But it’s not going away. Disabling it on a more permanent basis requires you to hack the vehicle software, similar to jail breaking a cellphone. Doing this may lead to unforeseen ramifications. Mercedes-Benz will know that you have tampered with the factory programming and may deny recalls, computer-based warranty claims and possible future warranty extensions. Even if you try and reverse the software hack at a later date, all manufacturers now have the ability to detect tampering even if you have had it reversed.

Yes, the frequent starting affects starter motor longevity, but manufacturers have worked hard at designing starters that are up to the task, and premature failure rates are decreasing. In the end, is it worth the trouble? It might just be like the airplanes that go over my house every 10 minutes for a few hours a day. Somehow, I don’t hear them any longer.


I have a 2014 Nissan Rogue with the CVT. The maintenance schedule says that the transmission fluid should be checked at 60,000 kilometres. Is this something I can do myself, and if so, what should I look for? Am I just checking if there is enough, or is it more involved than that?

Jan, Vancouver

CVT transmission fluid is quite different from that which is used on conventional transmissions. Topping up with the wrong fluid will lead to catastrophic results. Also, CVT transmission fluid requires replacement at an elevated frequency when compared to conventional transmission fluid. Therefore, just checking to see how much is there, or what colour the fluid is, won’t be enough. In the case of CVT transmissions, unless you are reasonably competent at deciphering detailed fluid specifications, you should probably rely on professional services.


Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.

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