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Thread: Big tires; what size and why

  1. #1
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    Default Big tires; what size and why

    No doubt if I dug I'd find multiple threads on Tundra tires, but I'm lazy, so figured I'd just write it out. The plane is a Cessna 170. She's on Lady Legs, slightly taller than standard gear, and is pulled by an O-320 w/Constant Speed prop. I've talked w/ folks that have mounted both 29" and 31" on the C-170, and each loved their respective choices.
    So, what say you? If you had a choice, what Make, Style, and size of tire would you choose for your C-170 weight class aircraft? Just pretend for a moment that money is not a problem. Yeah, a little bit of fantasy, but a guy has to dream. Without knowing a thing, I'd guess (and maybe be wrong) that there is more than one choice of manufacturer, at least for 26" to 29".
    What issues might a guy run into by going to the bigger 31" tires? Again, some guys use them and love them, then I hear that the 31" might roll off of the rim in tight ground handling. For AK BW, weight is only about 1lb different on paper, not sure about the others.
    So, let's compare and have some fun dreaming about getting into the back country.
    ARR

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    Your C-170 already wears longer (higher) landing gear legs. Forward views from the driver's seat are already restricted somewhat. Larger wheels will make that restriction even more noticeable, and with 31" tires and tubes that difference will be a whole lot. For that reason, my personal recommendation is that you move to 29" tundra tires rather than the 31" jobbies. Braking is a consideration as well, by the way, and with the larger 31" tires it will be even more noticeable. My opinion, for what it's worth . . .

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    Great perspective Grizzly. Thx. Right now on 8.50 forward visibility is good, but I can see what you are saying. I've heard about braking problems, but don't quite get it. Some say braking is more touchy, i.e. the wheels stop easier, possibly causing tip over? But then some say to get heavy brake rotors/discs for better braking. Hmm, still trying to learn, and see all of you as a valuable resource.
    ARR

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    Quote Originally Posted by Ak River Rat View Post
    Great perspective Grizzly. Thx. Right now on 8.50 forward visibility is good, but I can see what you are saying. I've heard about braking problems, but don't quite get it. Some say braking is more touchy, i.e. the wheels stop easier, possibly causing tip over? But then some say to get heavy brake rotors/discs for better braking. Hmm, still trying to learn, and see all of you as a valuable resource.
    ARR
    In all my Alaska bush hours, I've never noticed an advanced overturning tendencies with bigger tires. Perhaps some have. I can tell you that I flew a lot of bush hours in a C-170A model (165 heavy case Franklin engine and climb prop) with 8.50x6 tires and tubes and never had any trouble on sandbars, gravel bars, or mountain slopes and ridges. Used C-180's for lots and lots of beach work, but was careful to stay out of really dry sand . . .

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    As far as braking problems it boils down to not enough brake to stop the tire from turning IE large tire, single pucks, or poorly maintained brakes. The other side of the problem is brakes working too well and locking the tire. IE double pucks. Having too much brake is not a bad thing and can be controlled by how hard you apply them. Not having enough will be controlled by what you run into. The bigger the tire the more braking power is needed to stop them. Most problems with going on your nose are generated by the yoke controller not the tire or brakes.
    DENNY

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    I have ABW 31's on a 170b with an 0360 180 legs. With that said I have friends or know of other pilots up here with 29's and 26's on 170's and if you put the same pilot in each plane I don't know that you would see a noticeable performance difference. I was concerned about visibility issues as well however I still have excellent over the nose visibility during ground ops (I am 5' 11"). For brakes the Cleveland double pucks are fine, I am often more concerned about enough braking authority rather than nosing over however there are cases where nosing over could occur if you stomped on em at the wrong time, but I would say that is less likely in these planes than say a cub with brake boosters. Honestly in my case money wasn't an issue and I wanted 31's however if I had been constrained to 26's I wouldn't have cared as I have experienced/witnessed the tradeoffs to be minimal at best in the hands of a skilled pilot, of which I am not yet. Also in regards to 31's coming off the rim I was told it was more of an issue with 180's but to make sure I was conservative on tire pressure in conjunction with soft surface ops to avoid it happening FWIW.

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    Big tires are the best thing you can do to IMPROVE braking authority on surfaces that you'll want big tires for. If you nose over in a Cessna you screwed up. It isn't easy to do. I'm a fan of 31s on Cubs and 29s on Cessnas. Sidewall flex increases a lot with the 31s and under a heavy plane it can be a problem. The softer the tires the more true that is. You can tuck 29s, too, but unless you're flying side slopes it's not much of a factor. Guys who fly Cessnas on beaches prefer big AirHawks for the stiffer sidewalls. I don't know anyone who needs bigger than 29s for where they take Cessnas. Most of us aren't landing on wet swamps or in basketball size rocks with a metal airplane. To each their own.

    I've used 29s for almost 15 years on my 180. Not so much for where I can operate but more to protect the prop on surfaces I use. Easier rolling makes less prop dings in rocks and gravel. Another big advantage of 29s over 26s or 850s is AOA. I can take off and land shorter without bumping my tail when I use 29s.

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    Once again, Mr. Pid is pretty much on track, IMO. I'll only add that, when operating C-170s, C-180s and C-185s on gravel, be sure to keep the tail wheel air pressure well up.....

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    Though I don't want to get away from the focus of which tire/wheel choice, Grizzly brings up a point about air pressure, a topic that seems to come up quite a bit. As little as 3lbs more or less in the big tires seem to make a difference on how they react, or work, on rough surfaces, under load, and under turns. Feel free to add air pressure in the discussion too, as maybe there is more to learn there also. Thx folks,
    ARR

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    Been flying 180/185s for awhile.... Mrpid is right on. C-185 29 gar aero 10-16 psi baby bush wheel on the tail at max psi ( whatever it says on the side wall)

  11. #11

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    I am no expert by any means, but I have flown 185's for almost twenty years in Western Alaska. My tires of choice are 29 inch Bushwheels on the mains and a baby Bushwheel on the tail. All tires are pumped up pretty hard.

  12. #12
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    Well, I pulled the trigger on a set of 31" tires. For 1 pound per tire added weight, little added frontal area for drag, and only a little added cost, I decided to go for it. I'll add the baby bushwheel that I picked up used also. Before I put them on the plane I'll be practicing wheel landings a bit more, then practice some more after they are mounted. I'm excited. Great conversation folks.
    ARR

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