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Q: I took my 2011 Mercedes Benz GLK350 in for its 60,000 km service and was given a new 2012 GLK with 8,000 km on it and 20-inch tires. Mine has the 19-inchers. The 20s rode a lot better. Originally I chose the 19s because I thought I would get a better ride. Was it because the 2012 tires were newer with more rubber, or do the 20s give a better ride? My 17-inch Falken snows give me a smoother ride than my 19-inch Continentals.
A: There are a lot of variables when it comes to ride quality. If we had two identical brands of tire and the same model in 19 and 20 inch versions inflated to the same air pressure, then theoretically the 19 incher would have a better ride; given that the tires were the same age, made in the same factory, and tested on the same vehicle to make sure suspension age was not a factor. Also testing would have to be done on the same day, same route at the same ambient air temperature.
The actual tread depth is not much of a ride quality factor unless one tire is new and one is almost worn out. A millimetre of extra tread depth would be hard to notice. A 20-inch tire from company A can have a better ride that a 19- or 18-inch tire from company B. Comparisons have to be quite exacting to be valid. Your winter tires of course will always have the best ride. The rubber is a softer compound than an all-season. And of course the sidewalls of the winter tires have more flex. So comparing winters to all seasons is apples and oranges.
Q: I need new tires for my 1990 Porsche 928. I am having trouble finding a brand that makes both front and rears (P225/50R16 and P245/45R16). There are just no good choices. I don?t track the car, I just want good street grip.
A:Tires in the OE sizes are a problem. The only set I would consider are the Bridgestone RE-11 summer extreme performance tires. I say that only because there literally is nothing else being made in that combination of sizes that I feel comfortable on. However since you do not track the car these tires are overkill in the extreme. And by today?s trends in car design a 16 inch tire is tiny. How times are changing.
So it might be time for new wheels, not the whole car, just some 17-inch rims. By going to 17 inchers, you open up a big variety of tire choices. The 17-inch tires for your car should be P225/45R17 fronts and P255/40R17 rears. In this tire size combo you can have some excellent all-season tires for three season use, please don?t try winter. These modern high performance all-season tires will have more grip than the OE tires when the car was new.
The three tires to consider are: Bridgestone Potenza RE-960AS Pole Position, Continental ExtremeContact DWS, and the General G-Max AS-03. All are W-Speed rated and have a suitable load index. The Bridgestone is a premium price tire so you won?t save anything there over the RE-11 in terms of cost but you do get longer in the year to drive your 928 with the RE-960. The Conti is a step down in price but still fairly high in price. The bargain here is the General. It is a Continental in disguise at a much lower price point. If you went with these you?d save almost enough to get the new wheels for free.
Should you absolutely want to stick with the OE wheels and tire sizes and some tire shop tells you they can find the tires for you, please check the date codes on the tires before installation. There are warehouses in the U.S. that stock and keep old discontinued tires. You want to make sure you are not getting old inventory that is basically dead dry rubber, before it even gets onto the car.
I would not consider anything older than two years, and that is only because you have an older car and are not going to be pushing it through the corners. Normally my limit is one year, on the car from date of manufacture.