|Given my weight plus the bicycle|
weight and riding conditions,
what is the optimal
I have a bicycle tire pressure gage but evidently any gage's reading can vary by 15% (see discussion, August 22, 2016, at Compass Bicycles). So 40 psi could be 40 psi +/- 6 psi, which could be a very meaningful difference but, hopefully, any error in accuracy is consistent. I suppose I should seek to calibrate the gage.
Also of great interest: Given the supple casings of the Bon Jon Pass tire, 40 psi was probably too low of a tire pressure - a little higher, perhaps 45-50 psi, is probably better (see discussion, March 9, 2016, at Compass Bicycles). That is quite high given my experience with Specialized Trigger tires in the Gran Fondos. But, that said, the Bon Jon Pass tires are likely more supple and so perhaps require more air pressure.
The simple approach would be to pump some tubes up to 50 psi, ride conservatively on fast downhills, and be done with it. However, I've made it tricky because I want to get good performance (speed, reliability, and safety) out of the combination of rim, tire, and riding conditions. The big challenge is the riding conditions, which I assume to be 100 miles of 1/2 gravel and 1/2 road, with very, very fast descents, which expose you to pinch flats, and quite varied kinds of gravel (nice bits and deadly chunks).
In the five Gran Fondos that I've done, I've had three flats - one flat on the road for unknown reasons (back tire), one pitch flat at high speed when I went over an unexpected creek bed too quickly (back tire), and a "burp" when I hit an evidently ordinary rock at very high speed (front tire). In 1/3 rides with tubeless setups I've not had problems; in 2/2 rides with tubes I've had problems.
|Compass Bon Jon Pass tires. Note|
those black lines after about 50 hr of
riding. Have I damaged the tire by
riding low tire pressure?
The Compass Bon Jon Pass tires seem to fit the rims superbly. As I inflate the tubes, the tires make a sharp popping sound as they seat with the rim groove, and the tire shape with the rim looks, to me, really good. So, I'm hopeful I'll get them to work tubeless. But, alas, I do worry, since experts have reported frustrations and challenges - and I'm not, dah, an expert.
Attempt #1 - Failure. I check my rim tape on my front tire and it looks pretty good to me. This tape worked in the autumn with Specialized Triggers 38 mm. Just in case, I put another piece of tape over the valve hole, seeking to get a good seal with the valve. I used Stans Sealant and, since I don't have a compressor, I used a handy compressed air cylinder that I carry on my rides. This method for putting a lot of air into the tire fast did not work - just a lot of sealant on the garage floor and a mess to clean up. The tire did not even get close to seating with the rim. I have found this method to work with the Specialized Trigger tires but no luck here. So, onward .
Attempt #2 - Success! I ordered some Orange Seal Tubeless Tire Sealant, and headed off to one of my favorite bicycle shops, Counterbalance Bicycles, which has an outside air compressor. The Orange Seal sealant is evidently better for these tires (see review and discussion, August 22, 2016 at Compass Bicycles). No need for soapy water. Instead I took the tube out while carefully keeping one of the tire beads on the rim. Once the tube was out, I put in the valve. Then, keeping the wheel horizontal, I put some sealant into the tire and brushed it around the bead and slobbered it around on the inside rim edge. Then, I put the tire back on the rim. I blasted it with air while jiggling the sealant around near the valve, and sure enough the tire filled with air and the bead made a sharp snapping sound as it popped into place on the rim. Magical. That worked on both wheels, quite easily, in pretty much the same manner. I inflated the tires to 50 psi and rode home. Three hours later the tires seem to be holding air just fine. Tomorrow, I'll lower the pressure and give them a whirl on my weekly long ride.
Update, April 15, 2017 - I filled the front and back tires to about 43 psi and I rode hard today on nice gravel. The Compass Bon Jon Pass tires are beautiful. They felt really good, both on gravel and then on road and vice versa. I noted that sensations on the transitions - seemingly, fast on the road, fast on gravel.
The only problem, and its a big one, is that after 4 hours I needed to stop and blast the back tire with air. It went from about 43 psi to less than I suppose 15 psi (I couldn't quite see my gauge which I carried along with me). The front tire was great - I don't think it lost air or at least it was minimal.
Hmmmm. From magical, to disappointed. I'm not sure where the tire is leaking - no obvious signs. I can press the tire inward and cause sealant leaks but that doesn't seem to be what is going on. I guess the next step is to watch it carefully and determine if it leaks when not being ridden. And, then, perhaps add more sealant and see if that makes a difference. Or, perhaps I should swap the tires and see if that makes a difference -- perhaps its the tape or valve?
As it stands, because of the loss of air, the tires are probably not viable for GFL, which is a real bummer given how nice they are to ride. However, because they ride so well, perhaps I should simply stop every two hours and pump them with air. Ha! Or, perhaps I should ride with tubes at a fairly high tire pressure and ride very conservatively on the downhills to avoid high speed pinch flats. Neither of these solutions is very appealing.
Update, April 16, 2017 - Anyway, the next day, after about 18 hours, the tire is dead flat. So, with my stand-up pump, I easily bump it up to 50 psi. And then I checked the pressure every hour. Here's the sequence of readings, in psi, hour-by-hour for six hours: 50 - 42 - 33 - 28 - 22 - 15 - 10. So, during yesterday's ride, I started at 45 psi. Therefore, after about 4 hours, one would expect the tire would be down to less that 20 psi. This prediction seems to be about right, although I would imagine that air would leave the tire more quickly when riding than when stationary.
I retrospect, I should have also recorded the pressure on the front time, which seems okay. I can say, however, that the front tire has gone from about 45 psi to 20 psi in 30 hours. So there is a lot of leakage but it is slower leakage.
So, I think the next question is: Where is the air escaping? I see no obvious places. Is there a way of correcting the problem or have I somehow irreparably damaged the tire? (Note: The tire held air the first night.) If I have irreparably damaged the tire, how exactly did I do that? What should I learn for the next time? Could I have done anything differently? Was it an issue of tire pressure? I don't think so and I don't think my riding was out of the ordinary.
I think the next step is to dump a bunch more sealant into the tire, pump it up, and see what happens. But, that will have to wait, alas, a couple of days ...
Main conclusions: Tubeless tires are great; Tubeless tires are a pain in the ass; I want to make the Bon Jon Pass tires tubeless because they feel fast both on gravel and on the road.
Attempt #3 - Success!!! I contacted Compass and asked for some help diagnosing my troubles. We exchanged some e-mail and they generously considered my observations to be a "warrantee issue," and sent me a new tire. I though that was extremely nice, since I really didn't have clear evidence that it was a problem with the tire casing.
Anyway, I re-taped the back wheel and dumped 2 solid ounces of sealant into the tire. The tire inflated beautifully. I pumped it up to about 50 psi and the tire held air all night. Then, the next morning I lowered the pressure to about 43 psi and did a long ride and the tire held air just fine - perhaps losing 1-2 pounds over 24 hours.
The tires feel very, very good. They feel fast and quite solid - if a little squirely at high speeds - on both gravel and road surfaces. So, with 4 weeks until Gran Fondo Leavenworth I believe I have an good tire set-up. Here's to hoping that I don't cut or otherwise wear out the tires in the next 4 weeks. Ha!