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It's a well known problem statement that fat rims and fat tires are lose fitting. More so with different tire / wheel combinations. This makes even Ghetto / Split tube tubeless susceptible to two issues. Burping and trouble getting tires mounted.
Here is a picture of my Moto Boris with its Vee Mission (folding) tires hanging slack of its Weinmann HL-80 rims. After one of its tubes went flat overnight. The bead pulls back and you can practically shake the tire off the rim.
So, filling the valley of the rim with a light weight filler like foam is used with both tape and split tube to avoid this. Its easier to seat the bead and is somewhat reported to reduce burping.
My solution was to use some Filter Floss. It's sold in bulk for aquariums and ponds. Mine is the two sided blue / white in 1" thick. Mine was off of a bulk role available in lengths longer than 80". Below is just an example of the product. Again, I tried 1" it can be had thicker or thinner.
Amazon.com: Puro-Kleen Kleen-Guard Pond & Aquarium Filter Media, 16" x 72", Pack of 2 (12 Feet Total): Patio, Lawn & Garden
This was then cut into a strip that fit the rim edge to edge. It's easy to cut with scissors, the challenge is a nice neat strait line.
My preference is for Schrader. Was easy to drill these single walled rims. So, I selected Schwalbe AV10 (24") because they have fully threaded Schrader stems.
Below you can see a long strip and a short strip that I cut. The short one is notched for the valve stem. I found it easy to put the long piece in first, then slip the shorter one in around the stem. No overlap was needed as the edges of floss matched up and created no gap under the split tube later.
Insert the stem with the lock ring only about half threaded on. Inflate the tube a little. This makes it stand out from the rim. It's now easy to tuck in the filter floss strip between rim and small tube. Let the air out of the tube keeping the tube aligned strait as it comes down to put pressure on the floss. You can now tighten the stem lock nut.
Carefully split the tube down the middle like any other split tube setup. Clean the powder out of the tube with soapy water. The AV10's were perfectly sized to overlap the rim just enough. No circumcision needed to be performed afterwards. Laid ontop of the floss the tube now sets about level with the rim edge.
Mounting the tire required a tire lever now. Keep the bead more or less centered in the valley and manipulate the split tube to center it again. I left the Schrader core in and used an air compressor. Bead popped into place without use of soapy water or sealant as lube. No strap or cord was needed to pinch the tire down. I believe a track pump could have been used, I just did not try.
Tire held air for 30 minutes before I pulled the core and added sealant though the stem. The bead held when core was pulled on both front and back. I used 3 cups of Stans in each.
It's been a week, still holds the original 10 lbs of pressure. I've rode maybe 15 miles on these some rocky trail and some intentionally jumping on / off curbs trying to make them burp. Have been unable to do so.
Initially I experimented with them at 5 lbs of pressure, could not make them burp but self steer was horrible. Went to 10 and stayed there. I would expect 7 or 8 lbs to be fine, thats just too low for my Clydesdale but.
I also tried to make them burp with the "c clamp test". I tightened the clamp as far as I thought safe then pulled / pushed on it. Was unable to make it burp. Ran this test at 20 and then again at 10 lbs. USE CAUTION if you try this, you can hurt yourself I wore a leather glove and eye protection.
Would be glad to hear if anyone else tried filter floss. So far I'm very happy with this method and was the easiest tubeless setup I've ever done. The benefits of tubeless have already been proven to me in ride quality and weight savings.
I do have the concern that the floss will eventually lose its thickness due to pressure unlike a closed cell foam. This could allow burping to happen. It would also then be hard to reseat in the field if needed. I intend to change out the original rim strip once I obtain a new one I want to try. But quite a few more test miles need to be logged first. Will report back here after more long term testing.
Weights measured on my digital kitchen scale.
Removed Vee Ruber tube : 460 gm
Installed 24" AV10 tube : 163 gm
Aprox 80 " of 80 mm Filter Floss at 1.0" : 44 gm
Here is a picture of my Moto Boris with its Vee Mission (folding) tires hanging slack of its Weinmann HL-80 rims. After one of its tubes went flat overnight. The bead pulls back and you can practically shake the tire off the rim.

So, filling the valley of the rim with a light weight filler like foam is used with both tape and split tube to avoid this. Its easier to seat the bead and is somewhat reported to reduce burping.
My solution was to use some Filter Floss. It's sold in bulk for aquariums and ponds. Mine is the two sided blue / white in 1" thick. Mine was off of a bulk role available in lengths longer than 80". Below is just an example of the product. Again, I tried 1" it can be had thicker or thinner.
Amazon.com: Puro-Kleen Kleen-Guard Pond & Aquarium Filter Media, 16" x 72", Pack of 2 (12 Feet Total): Patio, Lawn & Garden
This was then cut into a strip that fit the rim edge to edge. It's easy to cut with scissors, the challenge is a nice neat strait line.
My preference is for Schrader. Was easy to drill these single walled rims. So, I selected Schwalbe AV10 (24") because they have fully threaded Schrader stems.
Below you can see a long strip and a short strip that I cut. The short one is notched for the valve stem. I found it easy to put the long piece in first, then slip the shorter one in around the stem. No overlap was needed as the edges of floss matched up and created no gap under the split tube later.
Insert the stem with the lock ring only about half threaded on. Inflate the tube a little. This makes it stand out from the rim. It's now easy to tuck in the filter floss strip between rim and small tube. Let the air out of the tube keeping the tube aligned strait as it comes down to put pressure on the floss. You can now tighten the stem lock nut.
Carefully split the tube down the middle like any other split tube setup. Clean the powder out of the tube with soapy water. The AV10's were perfectly sized to overlap the rim just enough. No circumcision needed to be performed afterwards. Laid ontop of the floss the tube now sets about level with the rim edge.

Mounting the tire required a tire lever now. Keep the bead more or less centered in the valley and manipulate the split tube to center it again. I left the Schrader core in and used an air compressor. Bead popped into place without use of soapy water or sealant as lube. No strap or cord was needed to pinch the tire down. I believe a track pump could have been used, I just did not try.

Tire held air for 30 minutes before I pulled the core and added sealant though the stem. The bead held when core was pulled on both front and back. I used 3 cups of Stans in each.
It's been a week, still holds the original 10 lbs of pressure. I've rode maybe 15 miles on these some rocky trail and some intentionally jumping on / off curbs trying to make them burp. Have been unable to do so.
Initially I experimented with them at 5 lbs of pressure, could not make them burp but self steer was horrible. Went to 10 and stayed there. I would expect 7 or 8 lbs to be fine, thats just too low for my Clydesdale but.
I also tried to make them burp with the "c clamp test". I tightened the clamp as far as I thought safe then pulled / pushed on it. Was unable to make it burp. Ran this test at 20 and then again at 10 lbs. USE CAUTION if you try this, you can hurt yourself I wore a leather glove and eye protection.

Would be glad to hear if anyone else tried filter floss. So far I'm very happy with this method and was the easiest tubeless setup I've ever done. The benefits of tubeless have already been proven to me in ride quality and weight savings.
I do have the concern that the floss will eventually lose its thickness due to pressure unlike a closed cell foam. This could allow burping to happen. It would also then be hard to reseat in the field if needed. I intend to change out the original rim strip once I obtain a new one I want to try. But quite a few more test miles need to be logged first. Will report back here after more long term testing.
Weights measured on my digital kitchen scale.
Removed Vee Ruber tube : 460 gm
Installed 24" AV10 tube : 163 gm
Aprox 80 " of 80 mm Filter Floss at 1.0" : 44 gm