Jim’s Tech Talk
Before we tackle today’s Q & A, I want to make sure you are aware of reader Bruce H’s tip for a deep dive into chain lubricant testing and results.
While we covered a lot of ground in our chain care articles and comments the last couple of Tech Talks (thank you very much!), Bruce recommended two companies that are actually testing lubes, publishing results and selling their own and other favorite lubes. You can also buy chains they’ve fully prepared and optimized – pretty cool if you’re looking for every advantage.
To learn more, visit Zero Friction Cycling zerofrictioncycling.com/au and Ceramic Speed.
Also, Bruce provided a link to a long podcast with two of the head guys talking about their testing. It’s at this link, but you need to scroll to see the player: https://cyclingtips.com/2021/08/nerd-alert-podcast-separating-chain-lube-testing-fact-from-fiction/.
Fascinating stuff, thanks a lot for sharing, Bruce.
How Low is Too Low?
The question for today came from a roadie named Jack who read our column about tire pressure and wrote,
“I like Vittoria tires (25mm width) and at 150 pounds (68kg), I run in the neighborhood of 75 psi front and 90 rear. But this is quite a bit lower than the lowest recommended on the tire sidewall of most of my Vittoria tires. Should I be concerned?”
My quick answer is no. That’s based on my experience with Vittoria tires in sizes from 23 to 28mm. I weigh about the same as Jack and I’ve experimented with a wide range of pressures, including what he’s running. For me 75/90 front/rear did not cause any issues of concern. But keep reading.
In the photo here of a 23mm Vittoria Open Corsa CX tire (the only Vittoria clincher I have right now), the label shows a recommended pressure range of 115-145psi. If that’s the same for Jack’s 25mm tires, he’s about 22% below the minimum on the rear and 35% below for the front. That does sound like a lot but tire performance depends on more than pressure alone.
Signs of Trouble
For example, we don’t know how and where Jack rides. Lighter roadies can still pound aggressively enough to test tires and other components. And, bad roads are harder on rubber than nice ones. The same goes for the weather he rides in.
If the pressure’s too low, I would expect he would suffer from all or some of these issues:
Pinch flatting (the tire bottoming out, pinching and puncturing the tube between the tire and rim) or worse, rim damage from the same bottoming out.
The tire and tube might change position over time. If the tube has a valve nut on it, this won’t happen but if not, it can if the pressure’s too low. You can tell if it’s happening because the valve will go from straight to crooked (not at a right angle to the rim anymore).
The tire might develop sidewall wear. This can be hard to see, but you’d look for signs of the sidewall coming apart or weakening from being flexed more than it was designed for due to being run at less than the company’s prescribed pressure.
What about Tubeless?
Jack didn’t say if he was running tubeless tires, which don’t pinch flat because there’s no tube inside. But, along with the things already mentioned (not related to tubes), what tubeless tires can do if the pressure is too low, is burp and rapidly lose air. This typically happens from a rough transition like a pothole or trying to hop something and coming down a little to one side essentially putting a side load on the tire.
With enough pressure the tire beads will stay put and not allow the tire to shift, “yawn,” and release air. If you’re too low, though, the beads give in to the force and you can lose a significant amount of air in a road tubeless tire. With any luck, you will not lose sealant. And, in that case you can simply stop and pump the tire up – this time a little more than before.
Maybe most noticeable for both types of tires is something called squirm. Too-soft tires can feel mushy and instead of a nice, firm, stable ride, you feel like the bike wants to wander across the road. You know this sketchy feeling if you’ve ridden on a tire going flat.
Hopefully, this gives you enough to go on to judge if I’m correct and your chosen pressures are okay, Jack. And watch for comments from other Vittoria riders here sharing their set-ups and inflation recommendations.
10,242 Daily Rides in a Row
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s cycling streak ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.