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By MikeW
#1700472
I have the standard original tyres which are 20/7.00-8 (i.e 20" dia, 7" wide, 8" wheels) and they need replacing. They are 2 ply lawn tractor tyres buffed smooth and very round cross section. It's all part of the bush flying/STOL image and much as I enjoy Trent Palmer's videos, there's not much opportunity for that in Sussex. Also the only place to get these is Aircraft Spruce at a ludicrous price.
I believe later models - and I think the Eurofox - have more normal 6.00-6 which are about 15-16" dia on 6" wheels.
I can get 16/6.50-8 or 18/6.50-8 lawn tyres for a fraction of the price (10-20%!) and either seems a more sensible size for grass and tarmac strips, the 16 being similar to a 6.00-6, just a bit wider and a full 16" dia.
The 18" has a very thick sparse knobbly tread pattern which I think I'd have to buff off. The 16" has a much smoother, finer pattern which I think might be OK. Both have a rounded cross section rather than flat tread, which should be OK for the swinging arm suspension.
I'll have to measure up for prop clearance but other than that wondered if anyone has any relevant experience and pointers please?
It's tailwheel BTW.
Thanks.
By cockney steve
#1700492
Initial thoughts are that Agricultural tyres are not designed to smack into a stationary- surface at 40+ MPH. _Come to that, they're not designed to run at those sorts of speeds.
Having said that, as with many manufactured items, there's a great deal of a*** covering and the loading on landing will decay very rapidly from initial touchdown. Takeoff, likewise and a 40-mph* spin-up will have a purely centrifugal loading, as the wings will have taken most, if not all, the weight off the carcass.
Why remove the tread? is it really that draggy? I'd have thought that a " bush-tyre " would be more directionally-stable and more damage-resistant with a block- tread.
Not a qualified pilot and never flown in a STOL aircraft, so the above is worth what you paid for it :P
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By Flyin'Dutch'
#1700494
Are you not better off asking on the LAA/BMAA Forum or a KitFox Forum?

Tyres for aeroplanes are a bit of a niche market as they need to cope with high loads and relatively high speeds for their size and patterns determine the resistance/grabbing force which is important to keep in mind as too much grab can cause very high side loads and scrub your undercarriage.
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By seanxair
#1700502
I'll have a look at what is on my aircraft as suspect they will be similar if not the same in terms of size. They do have tread though which I've never found a problem but only fly from grass.
By MikeW
#1700511
@FD @cs
Good points thank you.
I will try the LAA forum but I think this one reaches a lot more people. I'm not BMAA (but happy to see today's announcement of more discussions.) There isn't a UK Kitfox forum AFAIK and the US one is full of people fitting 29" Alaska bush tyres and the like, not smaller ones!
I am not certain why the originals are buffed smooth, I guess it is to allow slip and reduce load, both side load and acceleration grab, and stop them grabbing stones on loose surfaces and let them slip off humps/rocks. Yes in the US people land them on stony river banks, rough hilltops and so on.
The large diameter, width, shape and low pressure (5-10psi) all serve the same purposes I guess.
The large diameter will reduce centrifugal loads too.
Yes it's an abuse of these lawn tyres but they seem to take it. They are surprisingly light, again reducing acceleration force.
Early Kitfoxes were only 950lbs max and landed at about 30mph. Mine is 1050lbs and a bit faster. The change to more normal tyres and 6" wheels came with increase to 1200lbs and more speed.
Maybe I'll have to think again but at 202 Euros each plus shipping from Spruce I shall keep looking!

https://www.aircraftspruce.eu/20x700-8- ... x-tire.htm
https://www.aircraftspruce.com/catalog/ ... oxtire.php amusing to note this says 195lbs max load!
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By seanxair
#1700515
I have Carlisle Turfglide 8.00-6 tyres on mine. A direct replacement for the originals. They appear to be a general golf buggy type but quite deep. Never had any problems with them and run them to the exact pressure that requires two thumbs to make an impression :D
By MikeW
#1700528
Thanks. They offer 8.50-6 as the large option now I have found. They are about 19.5" dia so almost match what I have except on the smaller wheels. Yours I believe will be about 18".
What model is yours?
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By Sooty25
#1700537
ATV or Quad Bike tyres are commonly used, and that sounds like what yours might have been originally. Knobblies with the the nobbles trimmed off with a multi tool, and then buffed flat!.

have a look here, https://www.quadbikeswales.co.uk/quad-tyres.html, you can search by size.

The abuse these regularly get in race environments will probably be a lot worse that your worse landing!
Flyin'Dutch' liked this
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By Sooty25
#1700563
MikeW wrote:@Sooty25 gosh that's the kindest anyone has been about my Kitfox landings! :oops:
Thanks for info.


:lol: :lol: :lol:

Mk1's were 850lb, Mk2's were 950lb, mk3's were 1050lb. 2's and 3's had two wheel options, 6" Matco or 8" ATV. The 8" wheels are straight out off an ATV catalog, hence the use of ATV tyres.

Both run on 0.75" axles but brakes are obviously different so not a simple swap. But you might have 1" axles if your legs have flanged axles rather than the earlier shaft-in-tube type legs.
By MikeW
#1700680
seanxair wrote:
MikeW wrote:What model is yours?


Not a Kitfox but an Easy Raider - similar aircraft that's all


Ah yes I thought the pic looked squashed in! Useful info though thanks.
By MikeW
#1700683
Sooty25 wrote:
MikeW wrote:@Sooty25 gosh that's the kindest anyone has been about my Kitfox landings! :oops:
Thanks for info.


:lol: :lol: :lol:

Mk1's were 850lb, Mk2's were 950lb, mk3's were 1050lb. 2's and 3's had two wheel options, 6" Matco or 8" ATV. The 8" wheels are straight out off an ATV catalog, hence the use of ATV tyres.

Both run on 0.75" axles but brakes are obviously different so not a simple swap. But you might have 1" axles if your legs have flanged axles rather than the earlier shaft-in-tube type legs.


I didn't think the 6" wheels were offered until the Mk4 when they started to move away from the bush image. It was never mentioned as an option for the Mk 2 that I built in early 90s.

So the tyres supplied by Kitfox for 6" wheels were ATV/agricultural ones, not aircraft tyres, is that right? The current spares/accessories catalogue is unclear about it. A handy bit of info from that cat is that the retrofit Grove undercarriage lowers the nose by 2" which suggests no prop clearance problem if I went to 18" or even 16" tyres. Incidentally the tyres I have - which I believe to be original - are clearly marked as 2 ply lawn tyres, they were not tough ATV knobblys. They are cheapos, not Carliles or similar.

My axles are 3/4" push in. I'm certainly not going to change to 6" wheels!

So back to the search, I think 18/6.50-8 with the smoothest tread pattern I can find will be best.
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By Sooty25
#1700713
Hi Mike

this is the exploded drawing for the Matco option. My mk2 has them and details are in the build manual, so I'm assuming they are original, although wheels and calipers have been replaced, the master cylinders appear original so don't think it was an upgrade.

https://static.veracart.com/matco/item_pdfs/2658/document1.pdf

I can't remember the make of tyres on mine, but they are aviation tyres.

For some reason I think the LAA have a Tech doc regarding prop clearance, but it is under changing props rather than undercarriage. There is a prop clearance test. I guess the same applies to shorter cart.