Technical FAQ: Suspension maintenance, the basics of road tubeless

Lennard Zinn explains the fundamentals of road tubeless tire mounting and set-up. Plus a reader troubleshoots his road disc brakes.

Dear Lennard,
When going through your full suspension mountain bike (i.e., removing and cleaning all the pivots) what is the best way to know if they are tightened properly when reassembling?
— Jeff

Dear Jeff,
Tighten the pivot bolts to the manufacturer’s specs. Then remove or completely deflate your rear shock and lift your swingarm and drop it, checking for binding. Also push and pull on the swingarm from the side to check the pivots for lateral play.
― Lennard

Dear Lennard,
A German friend mistakenly ordered a tubeless road tire, as in the description it said it could also be used with a tube. Never ever have I seen a tire so ridiculous to mount. We did actually get it on sans tube, just to see if it would stretch a bit, but I guessed it would not, since that’s the point of the carbon bead. I’m actually amazed we were able to get it off to return it. It was a Cube branded wheelset, which looked like a Mavic design, so it was not designed as a tubeless rim.

But this got me wondering — what do road tubeless folks do when they get a flat? Are tubeless rims easier for mounting? I would not personally be able to get a tube in a tire like this. Is the assumption that the latex will seal up any holes? What would one do if the tire needed a boot patch? This experience certainly did not inspire me to ever try road tubeless.
— Steve

Dear Steve,
Relative ease or difficulty of mounting/removal of tubeless road tires is highly dependent on the rim, as well as on mounting/removal technique. It depends on both the external diameter of the rim walls and the depth of the rim bed. If you have the wrong rim, it’s very difficult to remove the tire to fix a flat on the road. Even with the proper rim, it can be a bear to mount and dismount road tubeless tires.

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I do frequently mount and dismount road tubeless tires here in my shop and don’t have much problem with it, but there are a couple of caveats. I believe that you can generally count on the accuracy of the diameter of the tire bead, because the liability issues can be big for the tire manufacturer if they make it too loose, so it is generally the rim is the issue.

First of all, I am a bit leery of mounting road tubeless tires on a rim not specifically designed for them. That is because, with a Mavic or Shimano UST tubeless rim, I can not only count on an accurate outer rim diameter, bead-seat diameter, and deep enough channel in the center of the rim bed, but also on the bead-lock ridge (the “hump”) on the medial edge of each bead-seat shelf. This key feature keeps the tire from coming off the bead-seat shelf and allows it to run for a while when flat. It also reduces the biggest danger: burping the tire at high speed on a sharp switchback while descending along the edge of a cliff. If you burp either tire, especially the front, under these conditions, and it could be very dangerous. I am fine with using tubeless-ready MTB tires, cyclocross tires, and fat, gravel-road tires on non-tubeless rims with slick, tubeless rim strips, because a burp on those tires is an inconvenience, not a great danger. I have burped tubeless MTB and cyclocross tires many times without crashing. But with a tubeless road tire, the high speeds, tire grip on the asphalt, and hardness of asphalt to land on, greatly increase the risk, and the possibility of controlling the bike in the middle of a hard turn if the pressure suddenly drops precipitously is slim.

The deep rim-bed channel on a tubeless road rim allows you to mount and remove the tire without snapping off your tire levers. Both beads have to be able to drop down into it while mounting; this is another reason for the carbon beads, since carbon’s high tensile strength allows the beads to be thinner than Kevlar beads. Even if the rim valley is deep enough, if it is a non-tubeless rim, when you put on the tight, airtight rim strip, the valley then can become too shallow to easily mount the tire.

It also critical to finish mounting the tire at the valve stem after ensuring that the bead on the opposite side is sitting in the rim valley. Similarly, on removal, you have to start at the valve stem. Unseat the tire beads by pushing inward on them after deflation, push the bead opposite the valve stem into the rim channel, and begin prying the tire off near the valve. This is what minimizes the circumference the bead is surrounding.

Mavic claims its new tubeless wheel/tire system is easier to mount and has a Kevlar tire bead, as opposed to the carbon one that all tubeless road tires I know of have employed in the past. I can see how the slight stretch of Kevlar would make mounting easier, but I’m not sure how that doesn’t also increase the possibility of blowing off of the rim.
― Lennard

Revisiting road disc-brake issue

Dear Lennard,
While holed up with a broken collarbone, I figure now’s a good time to update you on this. I found a solution: new pads. What I didn’t mention to you originally was that I took the OLD pads — that to me seemed to still have 50% life left — and put them on the brand new brakes (saving the new pads for a later date). Had I thought this mattered, I would have mentioned it in the original story. When I finally put back on the brand-new pads on the brand new brakes, everything seems to work fine. (Note: this is my CX bike, and I haven’t ridden it yet. I’m assuming the fix continues to work after a few miles are put in.)

So it is fixed, but a new question arises: Why does the change of pads matter? If the used pads are a little thinner, wouldn’t hydraulic brakes just move the pistons out a little further? If not, we’d all have to change our pads every 100 miles! Or is this not about the thickness (or slight lack thereof) of the used pads, but rather their contamination? As in, they could no longer provide the needed friction on the rotor, and therefore I needed to squeeze the lever so hard it bottomed out on the handlebar? It didn’t feel like I was squeezing hard though … It felt like — and as I recall it looked like — the pads were just not touching the rotor till the lever was fully pulled.

This recently popped up for another rider on a forum, which reminded me to write you back.

Thanks for your initial help, and sharing the issue/response in your column.
— David

Dear David,
I’m sorry to hear about your collarbone break.

You’re right; the brake should work as well with thin pads as with thick ones. The fact that the hydraulic fluid fills behind the piston so that the spacing from the pads to the rotor stays constant is one of the benefits of hydraulic brakes vs. cable-actuated ones. Piston retraction is a fixed distance, as it is performed by a square-cross-section piston seal sitting in a groove in the cylinder and twisting and untwisting on itself as the piston moves out and back.

I suspect your pads are contaminated. A good test would be to thoroughly clean the old pads and put them back on the bike.

The best way to clean the pads is to sand them, face down, on a flat piece of drywall-sanding screen lying on a flat surface so that the material removed from the surface of the pad falls through the screen, rather than being rubbed back onto the face of the pad.
― Lennard