Composite question from multiple members:
While at the Fly-in I noticed that most of the planes had the larger size 17.50×6.00×6 tires on the Main gear. Some had the smaller 15×6.00×6 on the nose. My plane, a 1980 Sundowner, has the smaller tires on both the main and nose. When it was delivered from the factory, it had the larger tires. The POH says either size is approved. Checking the Log Books it appears that the plane has had the 3 small tire arrangement for several years, while it was an Instrument Trainer for Executive Beech in St. Kanasas City.
My question is, what are the advantages and disadvantages of the two sizes? What changes do you see? Landing differences, ground stance different, cruise speed change due to drag, etc.? It seems to me that the larger tire with its lower air pressure spec would be a little more cushioned. I looked at the new Spruce Catalog given out at the Fly-in, and do not see a tire listed as 17.50×6.00×6. They are just “6.00×6”. What about retreads? (Search strings: tire sizes, size tire, larger tires, smaller tires, 6-ply, 4-ply)
You won’t find reference to the height of the “standard 6-inch” size tires. Watch out for the Ply Rating. When we did Brad’s tire at the Fly-in, I found that someone had previously put the wrong ply rating (PR) tire on his plane. Tires are available in 4 PR, 6 PR and 8 PR in the sizes we commonly use. Most Musketeer series use 4 PR.
I prefer the 15/600×6 tires because the low profile reduces drag in flight, the lower sidewall makes for easier step up onto the wing, and I really can’t tell any difference in the “cushion” effect at landing. There is a theoretical difference in the drag, but it’s down in the noise of the measurement, and won’t show up in performance. It is easier to step up to the wing with the smaller tires on the mains. And the taller tire does give better prop clearance on the nose. Though I prefer to have all the same size on the plane, I guess it’s in theory legal to have 2 different profiles at the same time, even side to side on the mains… but it might feel funny landing on one main first all the time, unless you bank to bring them down together.
The standard size 6.00×6 does not include the height as part of its size. All you want to look for is the 6.00×6 and the “PR” or Ply Rating. The optional 15x6x6 (sometimes written 15/600×6) is always written with the “15” in front, because it’s the reduced profile tire and its height is how we identify it.
I prefer to buy from Desser Tire (www.desser.com) as they have excellent prices, ship FedEx at no extra charge and have given me great service over the years. I’ve also bought several tires from Spruce, especially when I was going to be there in person anyway or when I had an order already being shipped. I bought 3 tires from them just 2 weeks ago.
I have personally had only marginal experience with re-treads. On trainers where some frightened student is going to land with the toe brakes on and flat spot the tires 0.7 hours after maintenance puts a new one on, it can make sense to use the cheapest tire. On a “personal aircraft” where the owner/pilot is going to lavish attention on the airplane and treat it like it was intended to be used, I prefer the Goodyear Flight Custom IIIs. I’ve found that they last for YEARS on my own planes and the Macs were always in need of replacement. The difference in cost at initial purchase was quickly lost when the second and third cheap tire was installed. I rarely charge myself shop labor, so it’s got to be even MORE cost effective to run the Goodyears, when changing a tire also includes an hour or more of shop labor at the outrageous rates mechanics charge these days.
Here are some numbers from Desser Tire’s online site:
(17.5) 600×6: 17.5″ OD; 5.2″ wide;
4-ply rating max load 1,150 pounds, max inflation to 29 PSI
6-ply rating max load 1,750 pounds, max inflation to 42 PSI
Cross-sectional area comes to approximately 91 square inches, if it had a rectangular profile; slightly less due to tread curvature.
15/600×6: 15.2″ OD; 5.55″ wide;
6-ply rating max load 1,950 pounds, max inflation to 68 PSI
Cross-sectional area comes to approximately 83.25 square inches, if it had a rectangular profile; slightly less due to tread curvature, though the lower profile usually has a bit more squared shoulder.
These inflation numbers are for unloaded tires. How many of you jack your plane to check your tire pressures? You don’t need to, I’m just illustrating that you have to understand what the numbers represent. You can follow your POH and shop manual instructions for tire pressures. You can also go by tire wear patterns and ride quality. If your tires wear out the center ribs first, add pressure, and vice versa. You have more leeway for this with the 6-ply tires; but if both are aired to the same pressure, the 6-ply will give a harsher taxi ride, imparting more vibration to the airframe. The 6-PR usually have a more stable contact patch, which can help extend tread life.
Please take notice of the load ratings. You taxi on three tires, but usually land on two (or try to). The rated load of two 4-ply tires in the 600×6 size is 2,300 pounds. What is your max gross weight? The breaking load of one 4-PR is 1,670 pounds, versus 2,540 for the 6-PR, for the standard 600×6 tires; it is 2,830 for the 15/600×6 6-PR. Ever touch down hard on one wheel? This is just food for thought, for your particular application. My Sierra has a max gross of 2,750 pounds; I run 600×6 6-PR tires.
If you do a search on BAC for “recapped tires”, you will find a thorough posting that addresses them. The Monster Recaps from Desser Tire have received very good ratings from Aviation Consumer, due to their deeper tread (deeper than most new tires).