tire size and speed

boeing · Post by **boeing** » Thu Mar 22, 2007 00:06

Hi guys, just curious as to what size tires all of you guys are using, and what the associated airspeed is with either smaller or bigger tires.
I currently have 8.50 tires on my 85hp champ. I dont do much off airport landings so i am wondering if these tires may be a bit of over kill.
i few other pilots have said that i will not notice much difference in airspeed gain by switching to a 6.00 tire, but may lose some ability when it comes time to land off strip or on a soft field. In other words it has been suggested to keep the big tires. with the 85hp engine at approx 2250 rpm i am getting airspeeds of approx 85mph.
would there be any advantage worth mentioning by installing the smaller tires? and does the Champ really need bigger tires for off strip take off and landings?

Post by **joea** » Thu Mar 22, 2007 01:01

I have the 7.00 x 6 tires on stock rims and do not lose that much speed with them. Cannot use the stock wheel pants but thats life.

Am getting a bit faster than you are with the same setup on a Chief, but have been told that the Chief is a bit faster than a Champ with all things being the same.

These tires are a bit bigger and should I need to land off airport would help but to tell the truth have not worried about it.

MikeB · Post by **MikeB** » Thu Mar 22, 2007 10:14

I have 8:00's on my 65 horse Champ and I think the speed is about the same as the other Champs on our field with 6:00's. They came with the plane when I bought it and as they had good tread I decided to leave them on, although I have a set of new 6:00's and tubes in the shop. I kind of hate to mess with anything as it handles pretty well on hard surface, although tire size probably doesn't have a lot to do with it. I think my speed runs somewhere between 80 and 85 mph at 2150 rpm. I have been thinking about putting the 6:00s on so I can get wheel pants and keep the mud off the bottom of the wings.

Mike

Nathan K. Hammond · Post by **Nathan K. Hammond** » Thu Mar 22, 2007 11:05

Between 850's and 600's there may be a difference of 2-3 mph. Not really enough to justify the cost of new tires, in my opinion. I've been running 4ply 6.00x6 ever since I've had the airplane, and it took about 10 years before I had to replace a tire. And I operated off pavement for 8 years.

600's are great, and i'll go anywhere with them, except sand; the foot print is just a little too small. 850's or 26"' would be perfect for a Champ and the beach. 850's are also nice because you can run the pressure low if operating off airport, which will make the ride smoother and easier on the airplane. (Big plus there!)

If your buddies are persistant, offer to put on a new set if they're buying!

nkh

Dusty · Post by **Dusty** » Fri Mar 23, 2007 02:55

I've had 8.50s, 26" Goodyears, and now 31" Bushwheels on, and there's next to no difference in speed. I do come down a bit faster when I pull power with the Bushwheels, but cruise is within 1MPH of the 8.50s at the same RPM with the same prop wearing Bushwheels.

7GC · Post by **7GC** » Fri Mar 23, 2007 03:13

Dusty, are you noticing any shorter takeoff roll with the 31 radial BW? They are supposed to have less rolling resistance. One of these days I might replace the 26 Goodyears.

Dusty · Post by **Dusty** » Fri Mar 23, 2007 04:00

GC - yea, a LOT shorter. As you probably know, the Champ wing will fly at a much higher AOA than you can get in 3-point, and the big tires get it up a little higher so it flys off a little sooner. I still fly off with the tail on the ground, but I do it sooner than I used to!

It's easier to push around than it was with the smaller tires, but I don't know that that makes any practical difference on gravel/dirt. It makes a HUGE difference in big rocks - the tires just kinda suck them in one side and spit them out the other - it doesn't climb them, they more go THROUGH the tire. I can taxi on bowling-ball sized stuff without too much problem, but the tail hops around and makes scary noises.

I run them at 3-4PSI if I'm going somewhere really rough, which makes steep sidehills more interesting than you really want. At 8PSI they're a lot taller, easier to handle on sidehills, but REALLY bouncy on these lighter planes. I've made a small bicycle pump a standard part of my toolkit - the big tires are really sensitive to pressure (and temperature), and you just have to continually screw with the pressure.

Goodyears to Bushwheels was a MUCH bigger difference than 8.50s to Goodyears. I love em.