Fat Bike Tubeless Conversion

While I have done a ton of tubeless conversions on 29"ers and even on some gravel grinder set ups, I had not considered doing a tubeless fat bike tire set up. I just did not see the benefit for the tires I had been running, which weren't puncturing on me, nor having issues with ride quality or traction.

The new tires I have, the Fatback Sterlings, they are a completely different feeling tire. No punctures as of yet, but they seemed harsh and not very damped. Not to mention the fact that they are undersized for their rated width. Tubeless conversion may help all of that, is what I was thinking, plus the Sterlings are tubeless ready tires.

So, I talked with my good buddy, MG, and he gave me the lowdown on how much sealant to use. I took another cue from fat biking aficionado, Adam Blake, and along with a discovery I made myself, I have a successful tubeless conversion on my Fatback Sterling tires. Note: These tires are tubeless rated and the rims I used are Fatback Uma II 70mm wide rims. Your mileage with other rims and tires may vary.

How To: The first thing you have to do is to get something to seal off the rim's drillings and spoke holes. I had already used a rim strip consisting of two wraps of Chrome colored duct tape backed with a single wrap of clear shipping tape to keep the adhesive of the duct tape from sticking to my tubes. When I pulled the tubes, I left this basic rim tape in there.

I had Mrs.Guitar Ted pick me up the widest roll of Gorilla tape she could find, and you know what? It measured exactly 70mm wide, just like my Uma rims! Gorilla tape has been used successfully in tubeless conversions for a couple years or more by a lot of folks in a lot of different combinations, so I felt confident in choosing it as a rim sealer/strip. Basically, Gorilla tape is ultra-strong duct tape. It is sticky where it needs to be and strong enough to withstand air pressure. 

Here (right) we see what my original rim strip looks like. It has been in there since I built the bike up in late 2011. Amazingly, my too long spokes did not eat their way through this strip and damage my toobs!

It is also worth noting that my Fatback Uma 70's have vent holes in the rim extrusion right in the bead seat. Obviously, whatever rim sealing tape one chooses must cover these little land mines of leakage, or you'll be unsuccessful in your tubeless attempt. Fortunately, as mentioned, the Gorilla tape was the same dimension as the outside rim width.

Once I stretched on the Gorilla tape carefully, making only one round, I had what you see to the left here. The keys to success here are to start with laying in the tape as squarely as possible, then concentrate on getting it pulled fairly tight while you use your free hand's fingers to press down the tape alongside each bead seat and just alongside the holes drilled in the rim. This gives the tape something to grip on to as you stretch the tape coming off the roll slightly with your other hand. Do not worry about getting the tape to lay completely down on the rim just yet.

After making one complete round, (I would go around twice if there were no underlying rim strip), I overlapped the tape by about two inches and cut it off the roll. Then I carefully pushed the tape down into the rim well, always focusing on using my thumbs and pushing slightly towards the outside of the rim as I worked my way around. I did not focus any pressure at all in the center where the rim cutouts and spoke nipples are.

After getting the inner rim well pressed down and looking smooth, I focused pressure on the tape in the rim bead area, pressing it down with the tip of my thumb nail. I worked both edges until they were laying flat. Then I cleaned up the residual talc powder left from the tubed set up, ran a clean rag over everything to make sure there was no dirt or talc powder left, and then I laid in a layer of Uncle Dick's Bead Slip right on the rim bead seat area to aid in tubeless set up.

Then I needed to puncture the tape at the valve hole with an awl to allow for the installation of my tubeless valve stem. I have several valve stems I could use, but in this case, I chose the durable, ultra reliable Bontrager stems. These fit well on the single wall rim's inner well and with the "O" ring seal, it keeps the air where it belongs here.

Note that the threading on the valve stem does not go all the way to the base of the valve stem. Due to the thin, single wall extrusion of the Uma 70mm rim, I could not thread a nut on the stem down far enough to secure it. Then I needed to come up with a solution. I used several Avid brake caliper convex and concave washers to make up for the unthreaded portion of the valve stem. I ended up needing three to account for that, and the presta valve nut on top of that to tighten everything up.

Once the valve stems were secured, I removed the cores to make airing up the tires to seat the beads easier. Do this before mounting up the tires, because if you haven't gotten the Presta valve nut tight enough, it is easier to rectify without a tire on there! Now you are ready to mix your sealant, (if you make your own, like I do), or get your favorite sealant handy, because now it is time to mount those tires!

This is a trick I had to invent!

In my case, the Sterling tires had been run with tubes for a bit, and this stretched out the tires enough that when I mounted them for this tubeless installation, they were very loose fitting. I was afraid I would not get them to seat up properly, since I have a very small capacity air compressor to aid in mounting up tubeless tires.

I knew that the Uma 70's have a pretty deep drop in the rim well for a single wall extrusion. This makes things quite difficult. So, I figured out that by inverting the casing of the tire in the center of the tread, it pushes the side wall and bead to the outer parts of the rim. Now a short blast of air and I had the beads set easy-peasy! By the way, I introduced my sealant before airing up. My good buddy, MG, advised me to use 8oz. per tire, or 237ml each. That's a lot of sealant, but these are pretty big volume tires, so, they need a lot of sealant!That part done, I screwed in the valve cores and aired the tires back up.

Now is the time to take the tire and rim to inspect how your bead seated. You may need to air up those tires to a slightly higher pressure to fully seat the beads. I ended up taking my set up to 20psi. I would be very careful not to go a whole lot higher with this combo since the tires fit so loosely. Again, your mileage may vary here. I would maybe think about what Stan's advises here as they do not recommend going above 40psi with mountain bike tires.

Next- Take the wheel in hand and lay it nearly sideways while holding it on one side. Now tap the tire on the floor while turning the wheel in your hands after every tap slightly. I learned this trick from MG. Go all the way around tapping on the floor with the wheel nearly flat to the floor about three revolutions, then flip the wheel and repeat. This has the effect of splashing your sealant up around the bead area and will help to seal up the bead to the rim in a quick and efficient way.

The next thing I would recommend doing is to ride the set up right away for 20-30 minutes at least. This will ensure that the casing seals up and should allow you to know whether or not you have any leakage issues. In my case, everything came out rock solid. After 12 hours, the pressures were still where I had originally set them. If you notice leak down, I would suggest spraying the tires down with a solution of dish soap and water to identify exactly where you are losing air and address the situation accordingly. In my past experience, if you do everything above, the issue is usually a poor seal around the valve stem.

Now for some numbers: 

Wheel Weight:

• Rear before conversion = 8.03lbs
• Rear after conversion = 8.01lbs
• Front before conversion = 7.15lbs
• Front after conversion = 7.00lbs
• Tube Weight: 210gm/240gm
• Surly Standard "Toob" weight for reference = 490 grams each. 
• Sealant used: "MG" formula. 16 ounces between two tires. (Probably lost a small amount during set up) 

I haven't tried measuring the width yet. That will happen today when I get my hands on the calipers at work. I will update that here after I get that done.UPDATE: I measured the tires at 97mm wide w/tubes, now at 101mm wide tubeless.

All set up to go, sans toobage!

Impressions: My initial feeling by way of observing the tire casings is that going tubeless, (which removes the support of a tube), allowed the sidewalls to "pooch" out some more and if anything, it slightly flattened out the casings a bit more. Otherwise I did not immediately note any stretch. Again- I will make measurements today to ascertain if the tires have stretched at all.

On my ride to check out the set up, I did not adjust the air pressure from the 20psi I used to seat up the tires. I did this to compare the ride feel I had with tubes at 20psi, which I was familiar with. In my opinion, the harshness of the ride with tubes was completely removed. These tires with tubes were really harsh on sharp impacts. No more! The ride feel was far more damped and comfortable. I did also note that the tread area was hitting the snowpack all the way across the casing, so I do not feel that lowering the pressures way down will benefit this set up. That said, I probably will drop these down to 15psi and see how that goes.

So, overall my initial impressions are that by going tubeless I saved a miniscule amount of weight. In that sense, it was not worth doing it. (If you are coming off Surly tubes though, you could potentially save a lot of weight!)  However; the ride feel is 100% better and I sense that the rolling resistance has been lowered somewhat. In this view, going tubeless was totally worth doing. It made the Sterling a completely different experience. Stay tuned for updates...

Note: Using components not designed to be used as tubeless is a risk to the rider and may result in severe injury or death. I do not condone, nor recommend that anyone do what I have done with the components they possess. If you decide to set up your fat bike tires tubeless, you do so at you own risk and assume all responsibilities for any consequences from doing so and using them as such.