Tire Delimma: 8.50 or 8.00 ?

N3243A · Post by **N3243A** » Sun Oct 30, 2005 9:15 pm

It bears repeating in this thread regarding braking capability of large diameter tires that installation of Gar Aero 8:50x10 tires and any of the Alaska Bushwheels require (by their STC) the use of Cleveland double puck brakes most typically in the form of Cleveland wheel and brake kit 199-62.

Bruce

Post by **GAHorn** » Mon Oct 31, 2005 6:34 pm

It was indeed difficult to not join Ol' Gar when he poured a round during lunch...but I managed to force myself.
The downwind/x-wind taxying illustration was merely an example of how braking efficiency can be minimal in some situations. Increasing tire diameter will make it worse (if the same brakes are used.)
The take-off scenario using the tic-tac-toe (#) layout is not something I made up on my own. I plagiarized it from W.D. Davies's (Master Test Pilot) book. He's a well-known British test pilot/author/aeronautical engineer.
If an airplane begins a takeoff roll already "rotated" (like all taildraggers do), even if at the most advantageous angle of rotation, ...then it's takeoff roll will be lengthened over optimum (for that airplane) as opposed to the tri-cycle airplane. (This assumes a hard, dry runway. The taildragger has other advantages on soft, wet, or rough surfaces that may be off-setting.)
It's another matter, difficult to prove one way or the other, as to whether a standard 170 might benefit from a higher angle-of-rotation for takeoff (which is what the "theory" of the larger diameter tires pre-supposes.) IMHO
As regards the possibility of an airplane using larger tires to achieve a higher angle of rotation earlier in the takeoff roll than an airplane with standard tires.... and theoretically achieving flight sooner than the standard airplane... I believe it's also possible to imagine that the standard airplane, with less drag being introduced early in the takeoff, might find it's wings developing sufficient lift to do exactly as you've observed ARDave,... namely being able to lift the airplane off the ground with it's tailwheel still rolling. As opposed to the larger-tired airplane still rolling with all it's wheels on the ground attempting to overcome the excessive drag imposed by it's too-early/too-high stance. (Yes, it'll also eventually be able to lift it's mains off the ground with the tailwheel still on the runway. So what?)
Still just theory. "In theory, we're sittin' here on two million dollars..."

CraigH · Post by **CraigH** » Mon Oct 31, 2005 9:06 pm

Got the Goodyear 800x6x6 tires in today. I was relieved to see that they have the rounded footprint similar to the McCreary's, not the flat footprint of the smaller Goodyear tires.

For those of you with 6 ply 800s, what pressures are you running? Based on prior experience I was thinking somwhere between the 18-20psi range?

Post by **Bruce Fenstermacher** » Mon Oct 31, 2005 9:45 pm

The owners manual gives a pressure for 6.00 x 6 tires but I've never found on for 8.00 tires. Goodrich 8.00x6 6 ply tires are at 26 pounds right know which seems about right for me.

N170BP · Post by **N170BP** » Mon Oct 31, 2005 9:59 pm

If I'm going to be playing around at rough fields, I'll
reduce the pressure to 18-20 lbs, but run my 850s @
24 lbs otherwise (gets too hard to push the thing around
on the ground, even on smooth pavement if you let
the pressure drop much below 24 psi).

Post by **GAHorn** » Mon Oct 31, 2005 10:25 pm

Did you buy the Goodyear Flight Custom or Flight Specials? (The Flight Customs are their premium tire. It has a more "squared" tread not only because of the mould, but also because it's a belted tread which needs the flat tread to realize maximum benefit of a belted tire. Belted treads are more stabil, do not "squirm" under heavy braking, and wear longer.)
The idea of proper tire pressure has to do with the weight of the aircraft and the amount of air pressure necessary to expose the maximum amount of tire "footprint". If you put too much air in, the tire will be overinflated and the tread near the sidewalls will begin to lift off the ground. The tire will also wear excessively in the middle of the tread as a result.
If you put in too little tire pressure the tire will not support the weight of the airplane without exposing the sidewalls to excessive flexing, heat build-up, and sidewall bruising/cuts. The tire will also hydroplane on wet pavement more readily, and under heavy braking the tire may slip on the wheel, which can tear the tube's valve stem from the tube on touchdown.
All three approved tire sizes on the 170 should be inflated to 24 psi.

AR Dave · Post by **AR Dave** » Tue Nov 01, 2005 12:32 am

George I'm not really sure what all you said about plagiarizing British Engineers and all. To tell the truth I don't even know what that is! But it looks like you were theorizing incorrect information again! Guess we should let it go after I have the last word

It's another matter, difficult to prove one way or the other

It's not a hard concept and it's been proven over and over by American Bush Pilots, who aren't even Plagiarized. You really ought to give this one up and stick to your own experience, not foriegn engineers theories. I have a feeling that you're not going to be able to put your theory aside to understand real, so I guess we're at a dead end.
What are you talking about the tailwheel staying on the ground for?
You underestimate our slow flying 170's and using angle of attack for STO. What's the shortest distance that you've ever seen a 170 get off the ground at? Was it on 6.00's? Feel free to take your and my post, about STO, to the proper subject. btw - I supported you when you were trying to win the youngest girl pilot award!

To the public - after meeting and talking with George on several occasions, I've decided to call him my friend - A very strange type friend and btw a whole lot different than me (for the record) but a friend to say the least!

Actually, I've got to stay his friend long enough to figure out how in the world he landed Jamie! I've got this theory that he theorized her into it!

CraigH · Post by **CraigH** » Tue Nov 01, 2005 1:13 am

Went with the Flight Specials. I'm partial to the rounded look on older taildraggers.

Post by **GAHorn** » Tue Nov 01, 2005 2:01 am

The shortest takeoff I've ever witnessed a 170 make was a B-model with fixed pitch prop, standard tires (with wheel pants) and a TCM IO-360 engine. It used no flaps, rolled about the distance of two runway lights (about 400 feet) and went up like an elevator. I have no idea of his takeoff weight, but he was the only one aboard. (His tail came up slightly before the mains left the ground.)

AR Dave · Post by **AR Dave** » Tue Nov 01, 2005 2:43 am

Thanks for being honest George -
With the 8.50's I'm sure he could have done a lot better, even with a cruise prop. Probably a Hot Tex day!
Night -

CraigH · Post by **CraigH** » Sun Nov 13, 2005 10:50 pm

Finally got everything wrapped up. Real happy with the results, and think I like the look of the 800 tires with no panties much better.

Post by **Bruce Fenstermacher** » Mon Nov 14, 2005 2:17 am

Yep sure do like the looks alright. Not sure I would have sold the pants though. I also must complement you Craig on the ease you seem to have posting pictures.

doug8082a · Post by **doug8082a** » Mon Nov 14, 2005 2:36 am

It's funny, with all the things that "we" have strong opinions about, I never would have guessed that wheel pants would have been such a polarizing topic. I think they look good either way. Although I am partial to wheel pants myself, I have to admit it does look good with the 800s on it.

blueldr · Post by **blueldr** » Mon Nov 14, 2005 3:42 am

My airplane is equipped with six inch Cleveland wheels and double puck brakes. I have found that most 800X6 tires will come in contact with the brake caliper unless a 1/8" shim is installed between the wheel and the brake rotor.

kloz · Post by **kloz** » Mon Nov 14, 2005 1:58 pm

I read somewhere that you can go with a different rotor to use the bigger tires. Might be worth looking into.

Craig

Put some red tips on your prop to set things off real nice.