UST 101 - A Lesson in Tubeless Tire Tech
It's the rare occasion these days that we build someone's new mountain bike and install tubes in their tires. We're huge fans of tubeless as the benefits are plentiful -- greater traction, generally lighter weight, and fewer flat tires. Most of the time, our customers request that their new bike gets setup with some sort of tubeless system. There are numerous ways to go about it. That's the beauty, that's also where the nightmare begins for some. UST approved tires and rims are the ultimate for ease of installation and reliability. Using non-UST rims and/or tires can make installation vary from tricky to difficult. In our experience, ease of installation has a direct correlation to on-trail performance and reliability.
First, let's say that some rim and tire combinations just don't work tubeless for a variety of reasons – the tire bead/bead seat diameter is off and a primary seal is hard to gain, or the tire carcass leaks incessantly, or worse – the tire seats and seems fine only to blow off unexpectedly. That is not the kind of performance you're looking to get when bombing off the backside of your favorite switchback climb. We'll warn you now that tubeless conversion is mostly science with a little artisanship mixed in, though it is not without cultish allegiance to certain products or misinformation either. We are always amazed at how much time some people spend dicking with their tires to keep air in them. For most people with bad habits, improper knowledge, or junky gear, they would be much better off putting tubes back in their tires and just going riding. We hate to hurt anyone's feelings, but if you don't have problems with pinch-flats, then going tubeless may not offer any practical advantage and the time spent on the conversion and maintenance may not be worth it. If you do ride hard trails regularly, and have to run high air pressures to avoid pinch-flats, or ride in areas where thorns are a problem, then a tubeless conversion would probably make sense.
For the ultimate in tubeless tire reliability it is always a good idea to use UST or tubeless ready equipment. Mavic and Hutchison worked together to create UST, or Universal System for Tubeless, to solve problems associated with leaving tubes behind and set standards for other rim and tire manufacturers to work towards. UST compatible systems should allow the user to install the tires by hand and inflate with a standard floor pump. The tires will have an extra layer of rubber inside the carcass to seal against leaks. They do not have to be used with a liquid sealant.
Stan's No Tubes has become a key figure in the tubeless movement, taking some of the ghetto out of ghetto tubeless conversions with their simple, yet effective conversion systems. Most any standard rim can be converted to a tubeless system with a Stan's No Tubes Rim strip kit or the combination of fiberglass strapping tape and their yellow rim tape. Both options will seal the spoke holes. The former will work best with tires that are a bit "loose" on the rim and the latter for "tighter" tires. This conversion is a little bit more work than slamming a tire on a UST rim, but it can work great. We've used both Stan's rim strips and their tape kits with great success.
Valve stem choice must be made according to rim cross section. Mavic and Shimano rims really need their own proprietary valve because of the channel shape in the center of the rim. Stan's valves work fine in their rims and most other kinds, but make sure that the valve hole in the rim isn't drilled so big that the small rubber end of the valve stem can easily pull through. We buy cheapy presta tubes and cut the valve stem out of them, leaving a small disc of rubber at the base. We trim it just narrow enough not to impede sealing at the bead seat and the extra rubber that remains ensures that the valve will not pull through the rim when we are mid-race and desperate.
Everybody has their favorites and we know we'll catch hell for voicing ours, but from our standpoint, Mavic has the best rim profile for tubeless riding. Their UST compatible rims differ quite a bit from their regular tube-type rims for good reason. Quite frankly, their rim cross section looks more like what you'd find on a car or motorcycle – tubeless applications we drive and ride all the time and don't give any thought too. The channel, shown with the yellow arrow, allows room for the stiffer UST tires to be installed by hand, mostly eliminating the use of tire levers and reducing the risk that the bead becomes damaged during installation. The second feature is the ridge that sits inboard of the seated tire bead, shown with the red arrow. This ridge makes for the audible pop when a tire is seated, but our experience shows that it keeps the tire from pulling away from the bead seat at lower pressures and almost eliminates "burping" tires over bumps and around corners. Mavic UST rims don't have spoke holes either, so only the valve stem hole needs to be addressed.
Tire choice can make or break the success of the conversion. Obviously, UST tires are going to work well. They have a properly shaped and consistent bead to seal against the rim seat. The tire bead is also stiffer and is designed to avoid the dreaded and inexplicable sudden blowout where the tire simply leaves the rim. UST tires also have an extra layer of butyl rubber inside the tire carcass to hold in air and this offers a slightly stiffer and more puncture resistant sidewall. For this reason, UST tires are heavier than their non-UST counterparts. Tubeless Ready tires are designed to be run tubeless, so they have a stiffer bead for safety, but they lack the extra layer of rubber inside. They are a good choice for those wanting lighter tubeless systems and don't mind pumping their tires up more often.
Here's where it gets sticky, most people will choose to run a liquid sealant anyway because of its puncture sealing properties. So why go UST? Good question. As stated before, UST tires are stiffer, so for extreme terrain they are a great choice. Any other tire will benefit from sealant, as it seals the bead to get started and seals punctures when they happen out on the trail. However, many tire manufacturers do not recommend that tire sealant be used with their tires. Kenda, for example, states that the use of liquid sealants will void their tire warranty. We've seen tires blistered as the carcass can delaminate due to the solvent properties of the ammonia or glycol based latex sealants. Can it happen? Yes indeed. Will your tires become destroyed by the sealant designed to go in them? Be ready. In a worst case scenario, liquid sealants will be messy, unreliable, and rot your tires. For us, they are a godsend. We employ liquid sealants in the tires on our personal bikes and have had, for the most part, excellent luck. And we do this as a no-charge service when building tubeless equipped complete bikes. This is a real world scenario, and we take the good with the occasional bad.
We haven't used tubes on our trail bikes in years, unless we had to install one as an emergency out on the trail. From our perspective, going tubeless offers some advantages that outweigh the work and expense of the conversion. A tubeless conversion will almost always be a wee bit lighter than similar tubed equipment. Potential weight savings aside, the real benefit is performance. We used to run our tires with 20-25 psi more pressure than we do now. Looking back, we suffered a bit to avoid pinch flats on our blocky and sometimes sharp Arkansas rocks. Pinch flats were more often than not, a deciding factor in our hard fought XC races. Now with tubeless wheels systems, it is a thing of the past. We get a much more comfortable ride because of the lower air pressure that we are able to use. Slightly softer tires conform a little more to the trail so our traction is increased. Let's see…better ride, more traction, and far fewer flat tires. This is why we like product development. Do we have flats? Sure, we ride in the real world. That reality however, has us riding more and changing flats with significantly less regularity.
Tubeless tire systems do require a little bit of maintenance. Depending on tire selection, it may be necessary to employ the pump before rides more often than not, as very light tires will likely bleed down faster than normal. This is due to the porous nature of the rubber in the tire carcass and for the same reason, the liquid sealant will eventually dry up. This will happen faster for those folks who hang their bikes up near the ceiling in a hot garage in summer. To add sealant is no big deal, but it must be done to ensure the puncture sealing ability of the system. If a bike sits long enough without tire movement, a literal scab of sealant will form in the bottom of the tire. Depending on the original volume of juice, the scab may contain enough concentrated mass to make the tire feel a little out of balance. It should be pulled free from the tire and taped to a forearm or shin to garner some attention and/or sympathy from co-workers. Then, new sealant will make it as good as new.
While riding on the trail, it is important to remember to do things differently when you hear the inevitable psssst-pssst-pssst as you roll over something nasty. With tubes, you normally stop when that happens. With tubeless, and especially with liquid sealant in your tires, it is important to keep riding. Maintaining momentum will allow sealant to reach the puncture zone and do its work. If the hole is anything but a legitimate gash, liquid sealant does wonders if allowed to form a clot. Of course, if the hole is too big for the sealant to do its work, you can always install a standard tube. Simply remove your tubeless valve stem and install the tube as normal. Don't forget to tuck the extra stem into a jersey pocket or in your tool kit. We have had great luck patching tires once we get back home. Trailside patching has for us, been far less successful. Common sense would dictate that juicy latex goo and dirt make for almost certain patch contamination. It's generally quicker to install a tube and get back to the riding. For smaller punctures, a standard tube patch will work. For linear sidewall cuts, small tubeless car tire patches work great because they are not designed to stretch. Really small ones can be hard to find though. We've found tire patch kits at the hardware store that were fiber reinforced. These would be ideal for tubeless tire patching as they won't stretch either. For any patchwork inside the tire carcass, follow the instructions as you would to patch a tube, but be mindful with the scraper or sanding strip and don't sand into the cords of the tire.
We have gone tubeless and not looked back. Any initial skepticism we may have had when tubeless technology emerged has been completely erased by years of good service. We'll be the first to admit that riding tubeless tires takes a bit more work in maintenance terms, but for us it's all worth it. We ride with more comfort and more confidence, and way fewer flat tires. Pinch flats are a thing of the past, like floorboard mounted dimmer switches or telephones with cords, and for that, we are thankful.