Cobra Trailer Spare Tire mount failure

Anyone have any experience with the option offered by Cobra of mounting the spare under the trailer behind the axial?


On Sunday, September 20, 2009 at 3:44:45 PM UTC-7, JJ Sinclair wrote:

I never did like suspending all that weight with no part of the tire
resting on the floor, ala Komet.
JJ

On Friday, July 17, 2015 at 8:43:15 PM UTC+1, Jonathan St. Cloud wrote:
Anyone have any experience with the option offered by Cobra of mounting the spare under the trailer behind the axial?



I don't have experience of that Cobra option and don't know how it is designed. I have, however, been under a trailer that needed to be jacked up by the roadside to unbolt an under-mounted spare and it was a very worrying experience as passing vehicles blew the trailer about. I would only have an under trailer spare if the the design is such that the spare is in a cradle so that, no matter how flat the tyre, the wheel could be slid out from the side without any need to go or reach underneath.

John Galloway

I have that option, I put a plate on the inside of the trailer to help carry the load. The real problem with the initial installment is the bolts are too short and it is a real tussle to get the wheel off the bolts because as soon as one or two are loose the tire shifts against the remaining bolt and this can cause the threads to be damaged. Additionally, it is almost impossible to get the flat tire back on the bolts because of weight and short bolts. BUT, better than having the tire break off the original mount and fall on the nose of the glider.
Boise, ID

I have an early (1983) Cobra trailer originally built for a Ventus. It is the smallest (width and height) clamshell I have ever seen. It has been retrofitted for my Pegasus, and if it was 1/4 inch smaller in any dimension, the glider would not fit inside. So, I can't keep a spare inside due to space limitations.

As a result, I built a spare tire carrier that is mounted on the side of the trailer just behind the right fender. I keep a dedicated screw jack with handle and a lug wrench and handle inside the front hatch. The last time I had a flat (actually a tread separation) on the road, it took eight minutes to swap the tire.

I didn't have to unload the fuselage or anything else. I keep a vinyl cover over the spare, but they only last a couple of years. So I spend $20 for a new one when it deteriorates.

Your best insurance concerning flat tires is to not let them get over a few years old. The tread depth may be (and probably is) just fine. What kills tires is age, oxidation (ozone) and ultraviolet exposure. A hundred bucks on a cheap set of radial tires every two or three years is cheap insurance for your $50,000 investment. I also don't bother with "ST" or trailer tires, as they are more expensive and (in my opinion) don't offer any more protection, reliability or longevity.

A lot of this comes from my own experience, as well as from airshow pilot Bob Carlton, who has been dragging glider trailers to airshows around the country for twenty years, logging as many as 30,000 miles or more every year.

Anybody want to buy a slightly used enclosed trailer for a 13 meter glider? Only 650,000 miles. Good tires.

One time some years back when this fatigue failure mode came up on RAS I asked Mark Mocho about it. He created an external spare wheel mount on the side of the trailer, just in front of or closely behind the wheel (can't recall which). Put on a cover to keep the sun off the tire. Worked well.
Don't have it on present Cobra, though perhaps should.
Ask Mocho at M&M Fabrication.
HL.





On Sunday, September 20, 2009 at 11:56:12 AM UTC-6, Barny wrote:
Just a warning to check your trailer spare before a trip and along the
way at gas stops. My 1998 trailer spare tire mount broke on a highway
trip. The wheel is mounted on the frame that holds the glider nose in
place. Two 8mm bolts welded to the nose cone frame hold the wheel to
the frame. One bolt sheared and the other broke away at one of the
welds. I was extremely lucky that the wheel didn't go through the
canopy or damage a wing. The wheel was dangling on the remaining bolt
with the broken weld, the tire tread was 5mm from the wing. It didn't
touch the wing or canopy, so I was "spared" a horrific tragedy.
I had a small shop weld two new 8mm bolts in place. I then added a
third mount to the Cobra design to keep the wheel from rocking on the
existing mount. I suspect the wheel weight rocking caused the
failure. The third leg is very easy to make and install yourself.
Use a small metal bar from a home improvement store, two bolts,
washers and nuts. Photos of the broken mount and new third leg can be
seen he
http://www.flickr.com/photos/brucebarnard/

The tire is in front of the axle not behind in that option.

I am in awe of the marketing penetration of M&M candies. My business is "MM Fabrication." 95% of the people who write checks, offer references or email me always write "M&M."

Wish I had thought of it first.

As a result, I built a spare tire carrier that is mounted on the side of the trailer just behind the right fender.

Mark, have you had any wear or bending of the cobra trailer wall?

Also, kits, pics, do you sell????

I also have a 85 cobra with spare under the fuselage inside. Would like to go outside.

Kevin
92

Harbor Freight has a spare tire bracket that looks like it will bolt to the side of the trailer. If I built a kit, it would look a lot like this and cost more, so you might as well try this one:

http://www.harborfreight.com/trailer...ier-93341.html

Be sure to locate it where the bolt heads on the inside of the trailer wall will not interfere with the wing dollies or the wing itself. I recommend using round head carriage bolts. It may be obvious to most people, but do not drill through the trailer side without taking your wing out first.

Mine is located just in front of the right fender. I have not seen any evidence of bending, but try to support the tire in such a way that it is not cantilevered. There are other types Like this one:

http://www.etrailer.com/Trailer-Carg...ne/413200.html

It can be mounted vertically, so the load is spread over a larger area of the sidewall.

On Friday, July 17, 2015 at 9:25:10 PM UTC-4, Mark628CA wrote:
I have an early (1983) Cobra trailer originally built for a Ventus. It is the smallest (width and height) clamshell I have ever seen. It has been retrofitted for my Pegasus, and if it was 1/4 inch smaller in any dimension, the glider would not fit inside. So, I can't keep a spare inside due to space limitations.

As a result, I built a spare tire carrier that is mounted on the side of the trailer just behind the right fender. I keep a dedicated screw jack with handle and a lug wrench and handle inside the front hatch. The last time I had a flat (actually a tread separation) on the road, it took eight minutes to swap the tire.

I didn't have to unload the fuselage or anything else. I keep a vinyl cover over the spare, but they only last a couple of years. So I spend $20 for a new one when it deteriorates.

Your best insurance concerning flat tires is to not let them get over a few years old. The tread depth may be (and probably is) just fine. What kills tires is age, oxidation (ozone) and ultraviolet exposure. A hundred bucks on a cheap set of radial tires every two or three years is cheap insurance for your $50,000 investment. I also don't bother with "ST" or trailer tires, as they are more expensive and (in my opinion) don't offer any more protection, reliability or longevity.

A lot of this comes from my own experience, as well as from airshow pilot Bob Carlton, who has been dragging glider trailers to airshows around the country for twenty years, logging as many as 30,000 miles or more every year.