How much do 26/27/29/31 inch tires slow you down

[little rocket 16]

Just wondering how much the big tires would slow a guy down.

If a guys was flying on say 600 or 850 tires and went to 26/27/29/or 31 inch tires how much speed will be lost.

THANKS

[skypics 89]

Of course, the more stuff you hand out in the wind stream the more drag.

 

That said, I went from 600/6 tires to 800 21" mini tundra tires and could not detect a significant change in TAS.

My Avid MK4 has fairings on everything that could cause extra drag, Wing struts, Jury struts, horiz lift struts, bush gear springs and I have fabricated wing strut cuffs at the forward strut/wing junction. This helped a LOT. 

Those flying Avids and especially with the under-chamber STOL wing will notice the fabric behind the strut wing junction flexing. This is because there is severe turbulence created at this point. 

If you put yarn telltalles be hing the strut/wing junction you will notice that the yarn flows streamlined on climb out, but turns 180 degrees toward the direction of flight when you level off. The proper wing cuff design eliminates this.

John M

[lv2plyguitar 172]

Where can a guy pick up the wing cuff's?

[akflyer 1427]

When I went from 22" nanco tires to 30" airstreaks and there was not a huge difference in cruise.  Maybe 5 MPH or so.  There was a HUGE difference in climb!  Like I was lucky to be able to get 500 FPM solo on a good day. 

Unless you are running a 912 or something with lots of power in it I say use the smallest tire you can safely use for your mission.  I went to the 21" aero classic "tundra tire" and for 99% of the flying I do they work great.  If I truly wanted to play in the bigger rocky rivers I would go with the 26" bushwheels.  I think a lot of guys get hung up thinking that big tires will make the plane a great off airport bird.  It is the guy with the stick in his hand that makes the airplane capable, big tires alone don't do it.

That being said.  Big tires can save lives and airplanes in certain off airport emergency landings.  I know of quite a few that ended up upside down and balled up that had they been on bigger tires they would have walked away with an airplane still in flyable condition.

 

[C5Engineer 1170]

As Leni mentioned it's not about the cruise speed loss it's about the loss of peformance in every aspect of flight. I admit I got bit by the big tire craze myself and went with the 27's. While I only noticed 3-4 mph difference in cruise it killed my climb performance especially at higher Density Altitudes. I have not been up to 10K with my camp gear and full fuel yet with these tires but I suspect I'd be lucky if I could even get up there and I used to cruise that high frequently to cross the Sierra mountains enroute to Idaho. I've considered going back to 21's several times.

You really need to ask yourself if you "need" big tires or "want" big tires. I can't tell you the amount of times I've flown all day with guys on 8.50's or the Desser 21's and they were easily able to land every strip I did I with my 27's. You don't need bushwheels for grass and dirt strips! You do need them for true off airport operations where you don't know what's lurking in the grass and brush or if you are landing gravel bars alongside rivers on a regular basis.

[little rocket 16]

When I went from 22" nanco tires to 30" airstreaks and there was not a huge difference in cruise.  Maybe 5 MPH or so.  There was a HUGE difference in climb!  Like I was lucky to be able to get 500 FPM solo on a good day. 

Unless you are running a 912 or something with lots of power in it I say use the smallest tire you can safely use for your mission.  I went to the 21" aero classic "tundra tire" and for 99% of the flying I do they work great.  If I truly wanted to play in the bigger rocky rivers I would go with the 26" bushwheels.  I think a lot of guys get hung up thinking that big tires will make the plane a great off airport bird.  It is the guy with the stick in his hand that makes the airplane capable, big tires alone don't do it.

That being said.  Big tires can save lives and airplanes in certain off airport emergency landings.  I know of quite a few that ended up upside down and balled up that had they been on bigger tires they would have walked away with an airplane still in flyable condition.

 

So next question is what kind of cruise speeds are you seeing and with what engine /prop combo ,at what RPM on what model of avid or kitfox ,just out of interest.
I have 31 inch bushwheels on my Model 4/1200 with Rotax 912UL 80 hp and the IVO inflight adjustable prop,also have 12 inch tailwheel and yesterday was my first flight with this setup and cruise at 2500 ft at 5400 RPM on GPS was 97 MPH which I was very happy with. Climb rate at 2000 ft elevation was around 1000 ft per minute myself [150 lbs] just over 1/2 tanks and 30 pounds baggage OAT 60 f.

[Av8r3400 1179]

Specs:

Classic IV-1200
105 hp Zipper 912
78" x 48" Prince fixed pitch prop
26" Airstreaks
700# empty weight

I cruise about 100 mph at 5200 rpm.  I can get 115 at 5800.

With the large tires I can sustain climb at 1700+ FPM, solo with half fuel.


With my 21x800-6 tires I am seeing about 3-5 mph more speed at the given power settings and 200 FPM more climb.
 

 

My old plane, IV-1050, 650#, with 80 hp 912 and 68" 3-blade Warp taper tip, would easily see 15 mph more speed across the board, with a max of 1200 FPM climb when very light.  Takeoff distance was substantially longer.