# LSA/UL "Tundra" Tire request for advice

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#### Victor Bravo

I have a Kolb Firestar that I'm trying to get set up for off-airport fun, "extreme STOL" as they call it now. NOT "real" bush flying, which involves carrying people and/or cargo. Just "dirt bike in the desert" stuff for fun. I want to do all that fun stuff the guys with Super Cubs do in those wild youtube videos, but I don't have $250K to do it. Didn't even have 10% of that money to play with I just put a much taller landing gear on it to get the nose up for better AoA. It will have VG's, and it has a 60HP HKS engine with a ground adjustable propeller. Will be operated as a single seat aircraft, no need to use the laughable "rear seat" that would barely fit my Dachshund. The airplane came with Azusa Tri-Star aluminum wheels 6 inch by 4 inches wide. I just got a set of Tracy O'Brien hydraulic brakes for it. I had planned to put the new Desser Tire light aircraft "tundra" tire on it, which is an 8.00 x 6 tire with an oversize outside diameter of 21 inches. One or two of the guys on the Kolb list mentioned that they had problems with this tire and wheel combination, the tire spinning on the rim, shearing off the valve stem, etc. The subject of "rim screws" or "tire screws" came up. Apparently you drill holes in the wheel, and put in sheet metal screws so that the sharp point goes into the thick part of the tire "bead", which resists the shear loads when the tire tries to rotate on the wheel. Now drilling a hole through an aircraft wheel rim... creating stress risers and crack initiators... then continuing to drill right into your !*#&*% tire... sounds crazy to me. But JEGS sells a kit for this, and other automotive and off-road people appear to be doing this all the time. My instinct as a mechanic tells me that if you did want to run a screw through your aluminum wheel you'd at least want to use a tapped hole and a machine screw instead of just gorilla-twisting a sharp sheet metal screw through it. Does anyone on HBA have experience and wisdom with this? Can I do this with confidence, or do I create a high probability of cracking my wheels? How does this affect changing your tires, or servicing the wheels, bearings, etc? #### Mcmark ##### Well-Known Member Bill, I have done it automotive/racing applications, but never for aircraft. I have broken off one in a wheel slick combo. Might be better off using a short self tapping screw with the "drill" portion just into the tire. I don't think it will take much to keep them in place, if they have enough air in them. That's the "rub" isn't it? Puns, the lowest form of humor! YMMV Mark #### blane.c ##### Well-Known Member HBA Supporter I have a Kolb Firestar that I'm trying to get set up for off-airport fun, "extreme STOL" as they call it now. NOT "real" bush flying, which involves carrying people and/or cargo. Just "dirt bike in the desert" stuff for fun. I want to do all that fun stuff the guys with Super Cubs do in those wild youtube videos, but I don't have$250K to do it. Didn't even have 10% of that money to play with

I just put a much taller landing gear on it to get the nose up for better AoA. It will have VG's, and it has a 60HP HKS engine with a ground adjustable propeller. Will be operated as a single seat aircraft, no need to use the laughable "rear seat" that would barely fit my Dachshund.

The airplane came with Azusa Tri-Star aluminum wheels 6 inch by 4 inches wide. I just got a set of Tracy O'Brien hydraulic brakes for it.

I had planned to put the new Desser Tire light aircraft "tundra" tire on it, which is an 8.00 x 6 tire with an oversize outside diameter of 21 inches. One or two of the guys on the Kolb list mentioned that they had problems with this tire and wheel combination, the tire spinning on the rim, shearing off the valve stem, etc.

The subject of "rim screws" or "tire screws" came up. Apparently you drill holes in the wheel, and put in sheet metal screws so that the sharp point goes into the thick part of the tire "bead", which resists the shear loads when the tire tries to rotate on the wheel.

Now drilling a hole through an aircraft wheel rim... creating stress risers and crack initiators... then continuing to drill right into your !*#&*% tire... sounds crazy to me. But JEGS sells a kit for this, and other automotive and off-road people appear to be doing this all the time.

My instinct as a mechanic tells me that if you did want to run a screw through your aluminum wheel you'd at least want to use a tapped hole and a machine screw instead of just gorilla-twisting a sharp sheet metal screw through it.

Does anyone on HBA have experience and wisdom with this? Can I do this with confidence, or do I create a high probability of cracking my wheels? How does this affect changing your tires, or servicing the wheels, bearings, etc?
"TUNDRA TIRES" do not use inner tubes. The valve stem is in the sidewall of the tire. The belly of the tire is "rubber-ed" from sidewall to sidewall. This is so it can rotate around the rim without losing air pressure.

#### Victor Bravo

##### Well-Known Member
"TUNDRA TIRES" do not use inner tubes. The valve stem is in the sidewall of the tire. The belly of the tire is "rubber-ed" from sidewall to sidewall. This is so it can rotate around the rim without losing air pressure.
Uhhh, well... yes, uhhh, but upholding the technically correct definition of "Tundra Tire" is not quite important enough to pay 10 times as much as an incorrectly labeled tube type tire of similar diameter

Desser's 21 inch tire is \$110, and the Airstreak is a grand, and I do need two of them but I don't need the TSO.

I did not know that the tire was airtight by itself without even be ing installed on a wheel. Wow!

#### blane.c

##### Well-Known Member
HBA Supporter
I am having trouble choking on the price of them. I remember when I ran them on the cub I was shocked then to (it is starting to come back to me)
We talked about it back then. It is not a big deal how it is done really, and felt you could modify any tire you wanted to do the same thing, just vulcanize in a belly and a valve stem. It helps if you have seen a real one first. The man who originally made them did them in his garage I believe I was told. And having had a pair I believe it. They are big not high tech.

The screws in the sidewall trick works to a limited degree then they just score the tire bead as it rotates and shears off the valve stem.

#### Victor Bravo

##### Well-Known Member
If the screws are really not that good, what do you think I can do to not spin the valve stem off while running low pressure on larger tires?

#### Daleandee

##### Well-Known Member
I had planned to put the new Desser Tire light aircraft "tundra" tire on it, which is an 8.00 x 6 tire with an oversize outside diameter of 21 inches. One or two of the guys on the Kolb list mentioned that they had problems with this tire and wheel combination, the tire spinning on the rim, shearing off the valve stem, etc.
You may be solving a problem you don't have. If it's a concern for "one or two of the guys" it may be their technique rather than the combination itself. Still I get that you want to do all you can to avoid that scenario. Perhaps a bit higher pressure and some bead sealer will do the trick. Some suggest using something like Gorilla Glue but I can't go there as at some point you have to remove them. :ermm:

Dunno if this helps at all ...

Dale
N319WF

#### Victor Bravo

##### Well-Known Member
No, it's hard enough to separate the tire from the wheel without glue. I tried removing the small tire from my Azusa wheel, and I realized I could not do it by hand. Next stop... wooden block and sledgehammer

#### Daleandee

##### Well-Known Member
No, it's hard enough to separate the tire from the wheel without glue. I tried removing the small tire from my Azusa wheel, and I realized I could not do it by hand. Next stop... wooden block and sledgehammer
Yep ... sometimes a "C" clamp will find its way onto the work bench when changing tires ...

Dale
N319WF

#### TFF

##### Well-Known Member
Racing classes, where screws are not allowed, glue the bead. Low pressure, you will either have to glue or screw the bead and still be ready with some way to inflate it if you knock it off like CO2 cartriges or pump and rachet strap. Not umless you got some bead lock rims. Ouch for one piece rims. Valve stem a whole different problem. I would have thought proper Cub tires would give you similar performance at you weight. Those big wheels are not light.

#### pictsidhe

##### Well-Known Member
If I was going to tundra an ultralight, I'd have a look at cheap riding mower tyres, usually tubeless and fairly light for the size. ATV tires are usually heavier. Some off road motorcycles use tyre bolts. These are basically clamps to firmly hold tyre beads to the rim. Sometimes several are used.

#### blane.c

##### Well-Known Member
HBA Supporter
If the screws are really not that good, what do you think I can do to not spin the valve stem off while running low pressure on larger tires?
The Super Cubs operating "light" were going in and out of around 100 feet and weighed around 1200lbs all up (pilot, fuel, fishing equipment, etc.) and the ones working heavy into 300 to 400 feet were 2200lbs or more. When you are trying to stop over a ton in 300 feet and stand on the brakes if the tire slides around the rim a bit, it is like a low tech. computer assisted braking in a sense and worked empirically. A lot of ideas were tried over several decades and so some things were hit on over time that just worked. In order to not slip the tires, you have to have less force acting on them, so the way to make screws in the the rim work is to not try to land as much weight as short.

#### Victor Bravo

##### Well-Known Member
you have to have less force acting on them, so the way to make screws in the the rim work is to not try to land as much weight as short.
Well, that's precisely the law of physics that I'm trying to outfox

Going on a diet would be too... simple... and just too ordinary for a man of my intellect :whistle:

#### blane.c

##### Well-Known Member
HBA Supporter
Well, that's precisely the law of physics that I'm trying to outfox

Going on a diet would be too... simple... and just too ordinary for a man of my intellect :whistle:
There was some experimentation ... with replacing the wheel with a yoke on the axle. The yoke had a minimum of three arms and each arm had a small diameter wheel, when the lead wheel hit something the top wheel rotated into lead. I am not sure if they had brakes or how.

I know people have had success with the screw in the rim thing they went about it scientific. They calculated were to put the holes and they did not use screws they threaded the holes and they used little machine screws/bolts. They may have pre-drilled the tire as well for all the little machine screws I would have, just prep everything and mount the tire after drilling the pilot holes for tapping the threads in the rim and put a stop on the drill bit for how deep you want to go in the bead and go to it, then you can tap the tire bead too. This will work until the tire slips on the wheel once, which may be never depending on how well it is done and what abuse is actually put on it. Some red locktite is a good idea until you have to heat the wheel/tire to 500 degrees to get the screws out, but they probably won't move until then.

#### pictsidhe

##### Well-Known Member
Drilling the bead seems a bad idea to me. Why not rim locks? Well proven to stop tyres spinning on rims, not going to damage the bead. The bad is they can be a royal PITA to get in place.

#### Battson

##### Well-Known Member
Yes, I've done what you describe in the OP with my Goodyear tires and flown hundreds of hours off-airport. It works 100% and it's a fairly common solution to this problem.

Carefully drill the holes right through without damaging the existing threads. Tap them right through, remember proper cutting fluid is your friend with small delicate taps, and don't rush - back out the tap a 1/2 turn often, to break the swarf clear. Remove all sharp edges and burrs afterwards. Measure the bead thickness. Sharpen the necessary screws and check the length is right for your tires / bead thickness, don't go too deep into the bead. Even just 1/4" is deep enough. Assemble and enjoy. You also want to paint some lines on your tires, so you can see if things DO move; trust but verify.

More details and instructional photos here: