epnnf

My new Kona came w/tubeless tires, 650 x 47, but the shop put tubes in them. Thats ok w/me, since I have yet to make the plunge into the world of tubeless. The tire says max 65 psi; the rim has no marking at all. If there are tubes in there, can the pressure go higher?

DrIsotope

Of tires that have different pressure recommendations for tubed and tubeless use (Panaracer springs to mind,) the variance is usually ~10psi; say 60psi for tubeless, 70psi for tubed.

My question would be why? Bike + rider would have to exceed 300lbs to get past even 60psi in a 47mm tire.

WizardOfBoz

I don't have Dr. Isotope's experience with tubes, but if the tire says 65psi, I'd stick with 65psi or less. As he alludes, you probably have a bit of leeway, but why chance it?

And why would you need it? What is the goal in pumping up 47s to beyond 65? You'd have to weight about 400 lb or more to justify even the 65psi. I'm a big guy myself, but 65psi in a 47mm tire is way, way more than optimal for 99.9% of people.

Regarding the rim, 65 psi in a 47mm tire generates around 10,000 lb of force trying to split the rim in two, down the spoke line. Most rims are built to handle most pressures (they're strong enough for any reasonably size-matched tire and pressure). So you SHOULD be ok with the rim. But again - more than 65 psi is probably suboptimal for ride quality.

Question for all: What pressure do other riders who use the bigger tires use?

redlude97

Yes, you can generally go higher with tubes since you don't have to worry about tire blowoff in a tubeless setup, but anything more than 40psi on a 47mm tire is overkill already

epnnf

just for information only.

I about bout180#.

Yea, tire pressure is a very debatable topic.

FWIW, I got a flat on that bike the other day. Fixed it; rode 4 miles home; checked pressure- about 25psi.

WizardOfBoz

epnnf, when I was a kid, the craze was for really skinny tubular tires inflated to very high pressures. The science has evolved, and it turns out that, in addition to being uncomfortable, super high pressures have some inefficiencies in riding. So lower pressures are now recognized as efficient (perhaps a little more efficient) than tires inflated to mimic the hardness of steel bar. I ride 26mm tires on my fancy CF road bike and use 116psi and 95psi R and F, respectively. But I weigh 245#. On my 27 inch x 1-1/4 classic bikes I will be using 70 and 80 psi for front and rear.

Do a little research and experiment. You might read some of the online articles.

There are a couple of online tire pressure calculators here:
Bicycle tire pressure calculator
and here (its says its for Clydesdales, but you can put in 180lb - I tried)
https://engineeredinsanity.com/clyde...tire-pressure/

I particularly like the latter page.

epnnf

thx for the pressure calculators, wizard.
So, today, I rode my Masi @ around 50, which is lower than the 70 the sidewall suggests, but more than the 45 the calculator suggests. It felt cushy, yes, but slightly out of control. We all know the feeling when you lose air- wheel goes from side to side, etc. I wonder if anybody has actually been on a ride using the pressure the calculator comes up with. Does the calculator consider going over potholes, bumps or just on flat pavement? Some have said lower pressure may actually make you faster, so why do the pros still use skinny high press tires?

Leebo

Pros are racing. At 235 lbs I use 50 f and 55 rear on my 700 x 35's. Less for off road or in the wet. Tires provide comfort and grip, among other things. Do you want to feel every 1/4 " pebble? Slightly softer tires will provide more grip and traction. It is a very personal subject, experiment and take notes. Try this, when you sit on your bike, you want them to squish a bit. Not very scientific, but it works. Trying to go faster? The factory stock tires are probably not the best.

terrymorse 

Really? What feature of a tubeless tire bead keeps it from blowing off the rim hook?

redlude97

Sorry if that was unclear. The tube used keeps the bead pressed against the rim (on a tubeless or nontubeless wire bead) to keep it from blowing off so you can run higher pressures than a tubeless setup

terrymorse 

Ah, that makes sense. Thanks for clarifying.

davidad

The pressure recommendation on the sidewall of a bike tire is one half the pressure needed to blow the tire off of the rim.