Tires

[Skippydiesel]

I've read a LOT of posts on tires and tire pressures. It's a little contradictory and confusing.
I'd like input on the Cheng Shin 11 4.00X5 tires.

I operate with wheel pants from paved runways in Texas, where pavement temps are hot for several months.

Various forums tout the advantages or disadvantages of various ply ratings.

Aircraft Spruce has Cheng Shin tires in 8 ply, 6 ply, and 2 ply. The 4 ply tire is tubeless.

Do we need 8 ply? Is 6 ply adequate? I've read of someone who is happy with his 2 ply,.

I wouldn't want to trade potential tire failure to save a pound or two per tire, if that.

Only about a dollar price difference between 8 ply and 6 ply.

Thoughts?

Hi John

Small point - Just because a tyre is classed as "tubeless" does not mean you cant use a tube.

As for ply ratings - In my limited experience the criteria for selecting more/less ply's relates to load - more load more ply's AND here in Australia , if you are intending to land/operate in thorn prevalent areas (mostly inland ) higher ply ratings may reduce the number of punctures.

As for wear rate - this is mainly influenced by the tyre compound (hard/soft), the pilots landing technique ( hard braking as apposed to letting aircraft slow under its own inertia), surfaces type (grass/sealed), inflation (over/under pressure will cause accelerated wear) and wheel alignment ("scrubbing" due to misalignment very common)

[JohnBlackstone]

interesting.. i had not considered using a tube with a tubeless "tyre" as you Aussies call a tire. :))

I've heard about those nasty thorns! Ouch. Don't think I'll go barefoot on my next visit, Skippy!

John

[Skippydiesel]

Hi John,

Yep! The the good old Tribulus terrestris L common name Caltrop also known as Cat Head, bindii, etc etc .

Will easily puncture an ordinary bicycle tyres, shoe soles and has been known to do the same to thin (low ply) car /small aircraft tyres. Often lames livestock and unfortunate humans.

Don't know if anyone has actually done any research on the matter but most light sport aircraft pilots (flying in or intending to visit infected areas) seem to try for 6-8 ply tyres, that is if they can find something that will fit their rims, in the hope of having enhanced thorn resistance.

I think that low tyre pressures are likely to contributed to the problem. Pilots will often have lower tyre pressures in the hope of smoother landings and better "flotation" on dirt/grass trips. Low pressure results in bulging tyre walls, the thin side wall (no matter the ply rating) being more susceptible to damage/penetration.

[GraemeSmith]

Ply is a load rating - not a puncture resistance rating. Though higher ply MIGHT have an increased resistance to punctures - it is not what the numbers mean.

Back in the day it literally meant how many plies of woven cotton were in the rubber to increase the load the tire could carry. Modern construction means that is less so and other methods may be employed.

4 ply for load is absolutely enough for the Sonex line. Higher ply tires usually/may be heavier - and you might not want that.

[Skippydiesel]

Graeme's comment:

"Ply is a load rating - not a puncture resistance rating. Though higher ply MIGHT have an increased resistance to punctures - it is not what the numbers mean"

My erlier comment:

"As for ply ratings - In my limited experience the criteria for selecting more/less ply's relates to load - more load more ply's AND here in Australia , if you are intending to land/operate in thorn prevalent areas (mostly inland ) higher ply ratings may reduce the number of punctures."

[jowens]

I went through numerous sets of tires on my sonex due to my home airport concrete having the texture of a cheese grater. I changed to O'keefe 12x4x5 tires had I have been extremely happy with them staying in balance, very low wear, and easy to check tread remaining with rings on the outside edge of the tire. I highly recommend these tires.
http://www.okeefeaero.com/-wheels-tires--axles.html

[Bryan Cotton]

After 42.1 hours and about 128 landings, I rotated my cheng shin tyres as the outside edges were pretty worn. I used the Sonex tooling to set alignment during the build and was pretty meticulous about it. It seems like the gear is set for toe-in which makes it pretty forgiving, but it seems hard on the tires. Also I wonder if this is making the shimmy worse.

For those of you guys who are getting a lot more out of your tires, are you:
1) just better pilots (likely even if this is not the root cause)
2) flying off of grass
3) flying on gear aligned differently than mine

I'd be curious if anybody has thoughts on gear alignment. Not only what they think it should be, but also how to get it.

I am not sure how to change alignment easily. The best I can figure is to measure what I have, level and 3 point attitude, with weight on the seats. Then figure out the geometry so I can calculate how to rotate the axle. That is a pain too because I'll have to match the holes in the existing landing gear. Then I'll have to re-mount the wheel pants so they are streamlined in flight.

[Area 51%]

I'd be curious if anybody has thoughts on gear alignment. Not only what they think it should be, but also how to get it.

I guess you did a better initial alignment than I did. I was eating tires every 30hrs.
I eventually solved that issue as well as most of my shimmy by readjusting the toe-in. How that was accomplished was by reaming the attaching bolt hole up to 3/8in and at the same time moving the centerline of the hole a couple of degrees. Then I used bushing stock to bring the hole back to 1/4in.

I can send you a picture of the process if my description doesn't make any sense.

[Bryan Cotton]

I guess you did a better initial alignment than I did. I was eating tires every 30hrs.
I eventually solved that issue as well as most of my shimmy by readjusting the toe-in. How that was accomplished was by reaming the attaching bolt hole up to 3/8in and at the same time moving the centerline of the hole a couple of degrees. Then I used bushing stock to bring the hole back to 1/4in.

I can send you a picture of the process if my description doesn't make any sense.

I think it makes sense. Pics are always welcome! You have my address.

[daleandee]

I had 195 hours when I replaced my factory tires (and leak guard tubes) with the same. Likely could have gotten a few more hours but a flat tire on a taildragger isn't something I want to happen if I can prevent it. I fly from pavement but have a few turf fields that I love to visit.

I used the plans method (not sure how the Waiex kit plans may vary) but my axles are Tracy O'Briens. They had a spacer on the axle and using that to align the axle with the set up per the plans gave me the 0.7º (IIRC) that is called for. I get even tire wear and zero shimmy. I can't post photos here but I have a couple if you want to PM me ...