Figures
 

As y'all know, I just picked up that BMC Time Machine. But I only picked it up a couple weeks ago, far too soon to get it dialed in for my Santa Barbara race this Saturday. No problem, I was planning on riding the Shiv anyway.

But I have been having problems with the front wheel on the Shiv holding air. Crap. I added sealant and a couple other things but just couldn't get it to hold air for more than a day. So last week I took it down, pulled the old rim tape and put on new rim tape. Mounted the tire and loaded it up with sealant. I aired it up and it seemed to hold air overnight pretty well but I added just a smidge more sealant just to be sure, and on Saturday I took it for a short ride to make sure sealant was everywhere it should be. Bike felt good and I thought it was solved. Checked it on Sunday and still had air. We're in business.

I checked it throughout the week and it did feel like it was getting softer but still felt like enough air to ride. But I get home from work tonight and I'm getting ready to load up the car so I can leave right after work tomorrow. I check the tire and it's really soft now. Double crap. I top it off and set the bike to the side. I keep putting my gear together and check the tire about 30 minutes later. Not flat but definitely softer than it should be. WTH???

I take the wheel back off and rotate it at different angles to make sure I give the sealant a chance to get wherever it needs to go to stop the leak. I air it back up and 30 minutes later it's soft again. So here I am the night before I need to leave with a tire that won't seal. As much as I hate it, I pulled that tire and the valve stem, cleaned out the sealant and just popped in a TPU tube.

I've gotten so comfortable running tubeless that now I have anxiety. I have a lot of punctures out here when I run tubes, hence my conversion to tubeless. I rarely have any issues elsewhere, but that doesn't really ease my mind that much. I've pulled thorns out of my tire while stopped at a traffic light and the tire seals right back up and I finish my ride no problem. That's a major benefit to going tubeless. But I'm going to have to roll the dice on Saturday and hope I don't have any unfortunate incidents out on the course. I do have a spare TPU tube just in case.

But it only has to make it 34 miles. Wish me luck.

Tubeless with sealant sounds good on paper...

When you get back, you should get to the bottom of this, to have any reliability. Doesn't sound like a hole in the tire, so must be at the tire beads, or rim tape, or valve. Submerged wheel and tire section in water in basin should show a valve leak, or bead leak. Rim tape, I guess would show a leak through the spoke holes, but with a double-wall rim, that leak could go to ALL spoke holes, so you don't know exactly where, only that it's the rim tape and you need better stuff.

This is my concern. If you're doing a sprint, no big deal. But if you're rding for an hour or so, how much air are you losing along the way?

I didn't see anything about checking if the valve core was tight.

I moved to the Vitorria Multiway valve stems and reduced the air leakage, substantially. There are VERY expensive, but worth it. They have the traditional cone shaped rubber stopper, which I find to be far superior to the stems with the hammer shaped stopper. I do give them a good tightening. I have them paired with Pirellis, a discontinued tire that was notorious for fast air leakage, and the stems have helped a lot.

One of the reasons I just bought a pair of Rovals for my new Time Machine is I wanted to try another brand with tubeless. Because of the puncture risks where I live, I am a tubeless convert. It absolutely makes sense (and cents) out here. But the only wheels I have had so far that are tubeless capable are Reynolds. I have all but given up on getting the rear wheel of my AR80 set to seal and now I'm having difficulty with the front wheel on this AR41 set.

I find that once they seal, they are good for months. I'm OK with doing routine maintenance 2-3 times a year but I really don't like the rim tape thing. Tubeless wheels come from the factory with some kind of heat formed sealing tape that seems to work really well. I don't know why anyone would remove it, but it happens. I just wish there was a way to apply that by the end user.

Ah, didn't know that, thanks. One would think a factory seal is best... but how does one replace a broken spoke, without exposing the nipple head inside the wheel to hold it in place? I suppose if you have really long nipples with a bit shorter spoke, you could easily unscrew the nipple and hold it while lacing and threading on the new spoke.

A good while back I saw some Shimano road race wheels (I think possibly from the LeMond era, not certain), with spokes that had a Z/S bend that inserted easily into the rim side, then crossed over to the hub flange on the opposite side, which had nipples in a straight-pull configuration. That setup looked brilliant, because it put the rim spoke holes on the neutral axis in bending of the rim, loaded in shear instead of tension normal to the surface like most spokes, so should be more durable. But I mention because it would solve the problem above.

Sure it was Shimano? In the early '80's, Harlan Meyer/Hi-E experimented with the use of double-ended aluminum spokes that had an S-bend where they passed through the hub. Each spoke threaded into nipples placed 180 degrees apart in the rim.

Nope, S-bend was into rim sidewalls. Quick search brought up a pic from past sale, says wheels from 2002, zoom into rim to see better:

https://cimg0.ibsrv.net/gimg/bikefor...1f96b1cbe9.jpg
The rim looks stronger to me, but the tight space at the hub for the nipples means fewer spokes which I don't like.