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View Full Version : 8.50x6.00 vs. 8.00x6.00 static diameter



cubscout
03-22-2007, 10:45 PM
I know there's some related discussion on another thread, but don't want to hijack that. Here's the deal:

After some runway "improvements", lots of small rocks. Picking up quite a few divots on the Propguard (q.v.) Currently running McCreary (Specialty Tyres) 8.50x6.00 6-ply, nearing end of service life.

Using a framing square on the sidewall, and level, measured 19-1/2" static diameter on one side, and 19-7/8" on the other, at ~16psig.

What are you friends with 8.00x6.00 measuring? 8.00's are legal with our prop/airframe combination.

I'm trying to balance the relative costs here: 8.50's are quite a bit more cost than the 8.00's, but if they help save the prop, maybe worth it? Or not?

Gonna start another thread on Propguard, which has been consPICuously absent.

And the good news, 8.50x6.00 tubes now available again (Husky Rant deferred...). The bad news, ~$60USD at Desser, and ~$68USD at Univair; haven't checked other sources. Not available at this time in "Leakguard" tubes. Guess where I WON'T buy them this time.

Thanks. cubscout

KiwiCub
03-23-2007, 04:21 AM
Down here in New Zealand where everything costs double there is no way I can afford even the old 26" "tundra tyres" let alone the bushwheels that everyone is talking about. I've been running 8.50x6 for years and like them a lot over the 8.00x6 or 8.00x4 because of the way it keeps the prop out of the stones. The 8.50x6 is standard fit on the Fletcher topdressing planes here and tyres gone unserviceable on the Fletcher are fine for the Super Cub. I've got two pair of these will keep me going for ever; all I land on is grass. The plane lands a bit slower in the three point and rolls over a bit of rough stuff easier. Nothing like the bushwheels but does me fine.

d.grimm
03-23-2007, 07:29 AM
I was able to get all the measurements from the Goodyear website when I was checking tire sizes.

mvivion
03-23-2007, 08:35 AM
cubscout,

We found that McCreary tires can be somewhat different diameter, as you note. Goodyear 8.50's seem to be a little more consistent. I've been told that the Goodyear 8.50's are also slightly larger in diameter, but haven't verified that. I don't like having different size tires on an airplane. Got enough demerits in my skill levels without introducing that kind of stuff :lol:.

The 8.50's will protect your prop a lot better than the 8.00's, though, whichever brand you buy. One spring, I put a set of 8.00's on a Husky to save weight and drag, compared to the 26 inch Goodyears. I saw a lot more stone damage with those small tires, and the Husky has really good prop clearance. I was operating strictly from gravel runways with those tires.

I'd stick with the 8.50's, unless the budget just won't tolerate the difference in cost. The Goodyears are more expensive, by the way.

MTV

WWhunter
03-23-2007, 11:48 AM
Mike is correct in the statement that Goodyears are larger in diameter. On the Champ I bought recently I noticed the plane seemed to be leaning to one side and thought the oleo was in need of repair. My son told me it looked more like a tire was different. I had to laugh.....I hadn't noticed but he was right. There was one McCreary and one Goodyear 8.50 on the plane. I had checked air pressure several time and had never noticed they were different. Sure enough, I measured the height and the McCreary was nearly an inch and a half shorter. So, if you need the extra height get the Goodyears.
Keith

WWhunter
03-23-2007, 12:19 PM
Opps, double post.

cubscout
03-23-2007, 10:12 PM
Thanks for all the constructive comments.

I'd heard the rumour about diameter difference between McCreary and GoodJeer, and was offering up my empirical measurements to try to quantify this discussion, and hoping for similar from others. And yes, I actually did pass sophomore geometry, and understand the difference between diameter and radius, and have a sense of the "squished out" bottom of real-world tyres, and how all that impacts prop clearance.

When you add up the total of tyres times two, and tubes times two, there's a BIG cost swing among the different options. When I change out tyres, I want to make sure there's a rational basis, not just some respected opinions I read somewhere on the internet.

Again, I solicit your actual measurements.

Thanks. cubscout

willyb
03-24-2007, 12:44 PM
Does anyone know what tire Goodyear makes in 8.50x6.00.I searched Goodyear's site with no luck.Desser's site does not list a 8.50x6.00 in Goodyear.Thinking about using an 8.50 and it sounds like the Goodyear is the one to use. Thanks, Bill

Speedo
03-24-2007, 02:46 PM
Here's the Goodyear p/n: 856C61-3

I couldn't find a p/n for Michelin.

willyb
03-24-2007, 08:05 PM
thanks for the part # I will see if I can track some down. Bill

redrooster
03-24-2007, 11:02 PM
The latest Chief catalog lists 850-6 Goodyear Flight Special II tires at 196.50 each, and tubes at 102.50 each.
Also lists 850-6 McCreary Airtrac's at 129.95, with tubes at 63.95.

Rooster

cubscout
03-29-2007, 01:56 PM
A couple more data points:

8.00x6.00 6 ply SpecialtyTyres (f.k.a. McCreary), 17-1/2"; 8" to centre of axle at ~15psig; ~200 landings, mostly asphalt, lots of tread left (PA-18)

8.00x6.00 6 ply Goodyear Flight Special II, 17-1/18"; at ~30psig, almost worn out (C-185)

8.00x6.00 6 ply new Desser recap on Goodyear core, unmounted, 18"; rib grooves ~1/8" deep

Still looking for actual measurement of Goodyear and new Specialty Tyres 8.50x6.00 6 ply, and maybe recaps if available, too.

Thanks. cubscout

Crash
03-29-2007, 09:48 PM
Goodyear 8.50 x 6" on my C-180 measure 21 3/4" with 30 psi in them. This was taken with two squares laid across the sidewall measuring the front to rear crown of the tire, not from the flat spot (floor). Tires are fairly new.

Crash

Bill Rusk
03-29-2007, 10:07 PM
I know it is not really the 8.00 Vs 8.50 debate but you might be interested. Here is a picture of the Goodyear 26 on Mark Rusche's PA-12 with an Alaska Bushwheel 26 next to it for comparison. Both are listed as 26 inch tires.

Bill

http://www.supercub.org/photopost/data//500/medium/Rusche_tires.jpg

Champdriver
03-30-2007, 07:54 AM
Cubscout, one other issue to take into account is the weight difference between the 8.50x6, 6 ply and the 8.00x6, 4 Ply. If my memory and notes serve me correctly, the 8.50x6 are available in 6 ply only, and weigh in at 15.0 pounds each. The 8.00x6 are 4 ply and weigh 10 pounds each. That's only a 10 pound difference, but in an old J-3, PA-11, Champ or others, this can be a significant weight. If you are one of those Monster engine guys (160 or 180 Hp), then it probably won't be much of an issue. Good luck with your Tire search.
Champdriver

Snert
03-31-2007, 03:57 AM
My 800-6 4 plys are going on today. I made the decision based on weight. I don't plan on crawling over rocks with them. I just wanted an edge over the 600-6 in case of an unscheduled off field landing. It may make a difference, it may not. I appreciate the guys that stick to the 800-4 to keep the plane as original as possible. My L-4 has taken a serious deviation from original so who cares.

cubscout
04-02-2007, 11:22 PM
Thanks all, for the additional input. And Crash, thanks for the data point: Looks like tyre pressure has a big input on diameter.

A couple more data points:

8.50x6.00 Desser recaps on Goodyear cores, fairly new: one side 19-1/2" o.d., ~9" floor to middle of axle; other side 20" and 9-1/4"; low side ~15psig, high probably ~18psig, on C-185.

Goodyear 26x10.50x6.00, smooth tread, ~23"o.d., ~11-1/4" floor to middle of axle, ~16psig, on Supercub. Supposedly "unobtanium" new for now; wish't I'd taken up Jr. on his kind offer :cry:

The other thing which came up in the personal discussions is that sometimes small rocks become lodged in the grooves, and then fling themselves onto the prop back side as they spool up on takeoff. Kinda like bug strikes on the TRAILING edge of a Supercub.... This makes sense based on what I've observed. So apparently careful taxiing and throttle management on small rocks isn't a total solution, though very important.

GoodJeers have fewer, and narrower grooves than Specialty Tyres (f.k.a. McCreary); and according to Desser experts, are lighter too, ~12# each in 8.50x6.00, plus tube. Anecdotally fewer problems with rocks in the grooves.

"Leakguard" tubes available in 8.00x6.00, but not 8.50x6.00.

And HUGE price swing with different combinations.

Lots of stuff to plug into my decision spreadsheet.

Stay tuned.

Thanks. cubscout

SpainCub
04-29-2009, 07:47 AM
Great info on this thread. I am still undecided on the 8.50 vs 26" but since my major problem now is EU (EASA) STC approvals, and on top of that I can get anyone form CC to help me out :( and they are the STC holders....

mvivion
04-29-2009, 08:36 AM
Cubscout,

If prop damage is AT ALL an issue, consider the cost of a new prop, damaged by rocks. Taller tires, offering more prop clearance, can make a difference. Normally, picking up rocks with the prop just causes some leading edge damage, which can be filed out. BUT, rock damage can also cause more serious prop damage.

So, while the price point between the larger Goodyear 8.50 and the McReary 8.50 is indeed higher, the larger diameter of the Goodyear affords another inch or so of ground clearance.

Treaded tires do pick up stones and throw them, but that sort of damage is generally done to the tail of the airplane. The major exception to that is if you're on wet, or freezing surface, where the small stones actually stick to the tires more. Some prop damage will occur from treaded tires in any case, but it's especially bad during freeze/thaw periods in spring and fall. What happens there is not that the rocks are being thrown into the back of the prop, but rather they are being lobbed up into the air and forward, then traveling THROUGH the prop arc, and striking either the leading edge or the back of the prop.

If you are operating largely off gravel, buy the biggest diameter tires you can afford.

MTV

AntiCub
04-29-2009, 03:47 PM
Here's another consideration. I watched a Cub with bushwheels nearly slide sideways into the trees at taxi speed last night. There was about an inch of slush left on the grass runway in the shady areas and when he got a little off the crown those bushwheels acted like one of those old round sleds and gravity took over. He was a skilled pilot and with a little power and rudder he managed to slide sideways down the runway till he hit some dry grass. But I have to wonder if those little groves in standard tires might not have kept him out of that situation in the first place? Anyone have experience with that kind of situation?

Phil

aviationinfo
04-30-2009, 10:32 AM
Is there any reason you'd have to use Goodyear tubes with Goodyear 8.50's? Would it be a bad idea to use the McCrearys?

mvivion
04-30-2009, 10:59 AM
McReary tubes should work fine.

Phil,

There comes a time when whatever you've got isn't going to work well. Considering all the potentials (gopher holes, ruts, rocks, banks, etc), I'd almost always opt for the biggest tire you can afford. If you don't have to do a lot of pavement work, bushwheels are king, no doubt.

MTV

AntiCub
04-30-2009, 07:36 PM
Phil,

There comes a time when whatever you've got isn't going to work well. Considering all the potentials (gopher holes, ruts, rocks, banks, etc), I'd almost always opt for the biggest tire you can afford. If you don't have to do a lot of pavement work, bushwheels are king, no doubt.

MTV

Actually Mike, I was wondering if the little grooves would have helped at all, or if they're too shallow to make much difference.

Phil

capav8
05-03-2009, 10:42 AM
A customer came into the shop to have us mount his tires for his champ rebuild. After the mounting I checked the overall height of the tire at 21 1/2" inflated to 30psi. I called Wag Aero to check on tires for my v6 stol and got this info.

McCreary Air Hawk 8.50x6 @ 21" diameter
" Air Trac 8.50x6 @ 25" "

As the budget dictates the air tracs are more than 200 bucks less than the air hawks and goodyears. Too me, that's 2 matco master cylinders including shipping.

Just some info I picked up along the way!


Jim

Mark Grubb
05-03-2009, 06:08 PM
Interesting data, indeed. 25" diameter makes them very attractive as does the price. I also note that they require lower pressure than GY et al.
I cannot find tire diameter for Air Trac's anywhere on the web. Anyone have any experience with these tires in moderate off-field settings and static diameter?

Thanks for the resource!

mvivion
05-03-2009, 07:53 PM
The only aircraft tires that McCreary shows on their web site in 8.50 x 6.00 are the Air Tracs.

Desser shows only the Air Trac and SuperHawk in 8.50 X 6.00. The price difference given there is $20 a tire.

Are you sure they didn't quote you a tire diameter for another tire, like maybe the 6.50 X 8.00???

I'm not sure I buy that ANY 8.50 X 6.00 tire is going to be 25 inches in diameter. I have seen a bit of flawed information from Wag before...

More info, por favor...

Also, the Aircraft Spruce catalog gives the weight of the Goodyear 8.50 tire as 12 pounds, and the McCreary's as 16. If that's correct, that's another 8 pounds of weight as well with the McCrearys.

MTV

capav8
05-04-2009, 10:45 PM
I ask the woman if she was sure. She read the info for me again. The difference between 8.50 x6 air tracs and air hawks. AK's would be nice, I simply can't justify to cost. Probably because I'm too practical/frugal/cheap - pick one. However 25" tires will work for me.

mvivion
05-05-2009, 07:04 AM
Let us know what the diameter actually is when you get them. There seems to be a bit of conflicting information on this in catalogs, and I'd bet you'll find they are a lot smaller than 25 inches.

MTV

Mark Grubb
05-05-2009, 10:28 AM
The manufacturer says the diameter of 8:50-6 air tracs is 21.6 inches at 30 psi.

capav8
05-05-2009, 07:10 PM
Yup - - - called wag today to verify the info, got a woman name Dawn. Gave me the 21.6" # for the air trac 8.50x6 and the phone # for specialty tire and rubber. As for this size tire in McCreary, 21.6 is it. I'm glad to hear someone else has received conflicting info from Wag besides me. Lesson learned - - - check and verify!


Jim

jagunson
05-16-2009, 04:35 AM
On green grass strips that may also be quite wet, what would have better breaking ability between 8:50's and AK Bushwheels. The ABW's would have a bigger footprint but it may not necessarily translate into better breaking on green grass. I am also talking about on a bigger airplane such as the 180. Interested to know?

Jamie

mvivion
05-16-2009, 06:44 AM
I'd go with tire chains... :lol: The Bushwheels, chained up, would have awesome BRAKING.

If you're working a place with nice green grass, and absolutely the best possible braking is really NECESSARY, maybe you should pick on drier or longer strips?? :angel:

MTV

skywagon8a
05-16-2009, 06:45 AM
For what it is worth, this is the link to Goodyear's tire chart.

http://www.goodyearaviation.com/resources/pdf/datatires.pdf

jagunson
05-16-2009, 06:57 AM
I think the chains would rattle a tad too much. ATV tires might be the answer.

JAG

cubscout
05-16-2009, 11:12 AM
Hey friends, as has been posted on another thread, I finally bought a set of Goodyear 26x10.50x6.00 tyres. And since they were already attached to a Supercub, the seller threw that in with the deal

:lol:

I'll do some measurements and let you know how they work out.

Thanks. cubscout

BritishCubBloke
05-17-2009, 01:29 PM
Great info on this thread. I am still undecided on the 8.50 vs 26" but since my major problem now is EU (EASA) STC approvals, and on top of that I can get anyone form CC to help me out and they are the STC holders....

Spaincub,

EASA may well be irrelevant. The PA18 is an Annex 2 aircraft. It needs to be approved in Spain. It's all down to the Spanish authorities.

David