Jim’s Tech Talk
Jim Langley
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 Thoughts
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.
Tire Squirm
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.
I remembered getting some Vittorias that had these high minimum pressure (I haven’t see that on other tires) and so I pumped them up to the 115 minimum and found myself bouncing all over the place. At my weight of 130 this was way too much and so I backed it down to what I put into other brands of tires. Given that the trend is for lower pressures than in the past, it’s hard to figure out why Vittoria continues to label their tires this way.
Jan Heine at Bicycle Quarterly has been advocating wider tires and lower pressures for several years now, and he has the data to back-up his claims. I weigh 160, and am running 28mm Rene Herse tires at 65psi. They’re light and supple, and the ride quality is wonderful. It’s long past time to ditch the skinny high-pressure tires.
Agree with Michael. Jan Heine is a hard core cyclists and is scrupulous in his testing methods. I am using a pair of his tires on my bike right now. They are “perfect”…until the next set, of course.
I am a convert to Jan’s philosophy. Now run Rene Herse 650×48 tires on pavement and trails. Wonderful ride. Usually pump up to 35 front and 40 rear for pavement (5 psi less for trails) and don’t add air for several weeks when pressures are in lower 20s. No pinch flats. I am running Tubolito tubes which may have less air loss that typical tubes. I weigh 175. I tried running their 35mm tires and was pleased with them, but the 48s don’t seem any slower and offer even better ride and more grip off pavement.
I LOVE that tire. So smooth/quiet on pavement, such nice footing on trails. The one place where it doesn’t excel is deeper mud … but riding in deeper mud is bad for the trails, so I try not to do that anyway.
Isn’t the degree of suppleness in the sidewalls an important factor? I can run my Rene Herse tires down to ridiculously ‘low’ pressures without problem (180lb, 35mm, 35psi). But doing the same with my ‘squarer’ Ultra Gatorskins or my Hakkapellita 32mm studded snow tires would leave me unstable.
t wegh 255 lbs and i run vittoria rubino pros 700×25 at 95 rear and 90 front on campy scirocco c-17 wheels. i have never had a problem of any kind, albeit the roads i ride on here in eastern nc are pretty good. same for conti gp’s with same results.
Been riding since the 80s and there’s a theory about pinch flats that I wonder if you have encountered? It goes : when you hit a big hole the wheel itself deforms slightly and is not perfectly round anymore and of course the spokes stay the same length and the nipple pokes up and pinches the tube. In recent years I’ve hardly ever see pinch flats anymore. For a decade or so I ran mavic wheels that had the nipples screwed into the trims and the inside was smooth and didn’t even need rim tape. I had ZERO pinch flats. I know I didn’t conduct a double blind study but I think there’s some validity to the theory. Of course today’s rim’s are lightyears ahead of what we had ” back in the day”. BTH…I run 700×32 tube continental 5000 with 50-60 lbs…any thoughts?
While what you describe can happen, it has nothing to do with pinch flats and is pretty rare on a modern wheel with a quality rim strip. If the spoke nipple had caused the flat, you wouldn’t have the characteristic “snake bite” double puncture that results from the tube being pinched at the two rim sidewalls.
Per the original question about minimum pressures on the tire sidewall, these numbers come largely from the marketing department. Surely we all know that a tire with higher pressure ratings is a better tire, right? Not! While tire sidewall stiffness has a slight impact on the pressures you need to run, the primary driver is rider weight and tire width. If you need to run more than 100 psi (6.9 bar) to prevent pinch flats, you should ride wider tires or learn to ride more carefully.
I interpreted Jack’s question not to be about speed, wear, or pinch flats, but about safety. That is, does running so far below the manufacturer’s stated pressure range run the risk of having the tire come off the rim (tubed or tubeless)?
For the last 3 years, I’ve been running what is now normal but what used to be considered low pressure (mostly tubeless) on a handful of different tires with zero issue. But, all it takes is one issue for things to go sideways in a hurry.
When people talk about tire pressure I bring up my unscientific theory. Take 2 balloons, inflate one to the max pressure it will hold, take the 2nd and inflate to a decent pressure. Take a dull screwdriver and see which balloon is easier to puncture. I weigh 190 lbs and run 80psi x 90psi in my Conti 25mm tires. Haven’t punctured in 5 yrs, “knock on wood!”
This IMO is a flawed analogy, as when you increase the inflation of a balloon, it gets bigger and the rubber expands and gets thinner…as opposed to when you increase the pressure of a tube in an enclosed tire, where the tube wall thickness doesn’t change nearly that drastically . . .
try vittoria run-flat inserts
you can go very low and then you are saved by the inserts
be careful, go ower and consider wearing body armor
you can use tire pressure apps too
Geoffrey P. Radoff ,M.D.
I’m curious as to why Jack wants to run such low pressures. Using the online Silca Pro Tire Pressure Calculator and assuming Jack plus his clothing and bike weigh 170 lbs total, running 25mm tires width on brand new recently paved roads, the calculator recommends 98 psi rear and 96 front and on rough roads like chip seal, it recommends 86psi rear and 83 front. Both are well higher than what Jack is running. Jim pointed out several reasons not to run that low. A pinch flat will lose air almost immediately, and on a front tire, the risk of losing control at speed seems high. Damaging the rim is a high price for sure, and damaging the tire sidewall seems a good way to wear out a $50 tire prematurely.
If the benefit to Jack is the perceived comfort of a softer ride, I’d think moving up to 28 mm tires would be the better choice. The Silca calculator recommends for 28mm tires for Jack, 82psi rear and 80 front on new pavement and 72psi rear and 70 front on chip seal.