how much cruise speed loss with 29/31 Bushwheels

[little rocket]

Just wondering how much speed did guys lose switching from 600 or 850 size tires to 29 or 31 inch bushwheel tires?
THANKS

[N981MS]

I lost 1-2 knots with 26s. I was surprised that it was that little.

[PapuaPilot]

I didn't notice any loss of speed going from the 600 to 850.

[AirFox]

1.5 mph going from 26" to 29"

[little rocket]

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 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.

[Av8r3400]

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.

[mattkalin]

Sorry to Revive an old post but is anyone actually running 31" Tires ? I am considering them for my build but probably will just stick to the 29". If you are running 31" can you post a pic and any comments on them?

[redbowen]

31” tires are not made in the airstreak line. The 29” Airstreaks are 25lbs each and the standard 29” are 31lbs each and the standard 31” are 32lbs each, and heavy tread are 36lbs each, so the standard 31” are a total of 14lbs heavier than the Airstreak 29” tires.