PSI amount question
 

Kind of a stupid question here; I didn't want to hijack the other person's thread, but I saw that several of you mentioned pumping up to what seems like really high PSI levels. I have a hardtail MTB and my listed PSI is 40-60, and I keep them at 55. My tires are 26 X 1.75. Do I need to get tires with a higher capacity and/or that are wider, or is the idea just that you pump to the upper end of your tires' recommendations?

Every rider needs enough tire pressure that the bike handles securely, feels right, and the tire doesn’t bottom out against the rim on typical impacts. All of that has to happen within the designated pressure range on tires, and where indicated, the pressure range of the rims.

There are various online charts which cross-reference rider weight and tire size to give suggested tire pressures, but depending on your needs, it may suffice to simply inflate to max indicated tire pressure, check when seated on the bike that there’s a bit of sidewall deformation (or sag, or tire drop), and if not, release pressure until there is.

If you’re experiencing handling issues, pinch flats, sidewall abrasion, or other issues like front wheel scrub in turns or heavy, sluggish acceleration, add air pressure to reduce sag, being mindful not to exceed indicated max pressure.

No idea what mine is rated at but I run at around 6 bar / 90 psi. I would probably run wider tyres at a lower pressure but I like the ones that came on my Trek.

I weigh 260
When riding an MTB on the street I always pump them to the max pressure listed on the sidewall, or even +5 on top of that.
They roll so much easier when at the top!.
When riding on trails I drop them down to 30-40 or so.
But know that the lower you go the more you risk pinch-flatting the tubes.

Also take into account that some pressures mentioned look exceedingly high because they are different tyres. On another forum I see a lot of guys tell people 90psi is the pressure to be at without even asking what sort of tyre people are running, some even do it without asking where the bike is ridden. I run 29 x 2.15 and they are rated between 30-50psi, someone running 60 or more is not running the same tyre as me.I find 40ish works for me and when I've asked anyone from the bike shop to seasoned riders what they recommend it's always 'whatever you feel comfortable with between the low and high rating on the tyre'. For a while I thought that was just a cop out but then I think back to the days of driving the truck and having 60 tonnes on a few bags of rubber. The ratings are there for reason, the wheels wont stop turning because you have a little more or a little less in them, but if trouble strikes they might also not do what they are designed to do.

I just read this from the WTB website for their Nano 700x40c gravel tires (I looked these up because these were on my bike when I received it)

"*WTB's tire pressure recommendations have changed over time due to further developments in technology. Riders may always reference the markings on their tires for allowed pressures ranges, but may also consult wtb.com for the most up-to-date tire pressure recommendations from WTB. We calculate pressure recommendations based on an average rider weight of 160-180 lbs and suggest increasing our minimum recommended pressure on WTB.com by 2-3psi for every additional 10 lbs of rider weight. Never exceed the maximum tire pressure marked on a tire."

So the minimum pressure is adjusted due to weight and max pressure is the max pressure.
I just thought this is interesting.

fwiw, for all 3 of my bikes:

• trial & error to get what I like
• I never go over the max on the sidewall
• the front always has less than the rear, maybe 5 or 10psi
• Wifey like hers softer, in general, plus she doesn't weight much
• the lowest I've gone is with my MTB on sandy trails, 21psi front 25psi rear. mostly it's more like 25psi front 35psi rear (for trails, not pavement)

just put the summer tires on. this is what 21-5ish psi looks like on a WTB 700x2.25" tire w/o rider weight
https://cimg1.ibsrv.net/gimg/bikefor...f962971064.jpg

:thumb:

You may be seeing people referencing much smaller road bike tires that can be pumped to above 100PSI (pounds per square inch of area). Bigger tires, like your 1.75's, have a LOT more surface area inside the tire, so for an equal tire pressure the number of pounds of force exerted on the inside of your tire is higher than for a skinny tire. If you pumped your tire up to 100PSI you would either explode the tire or split your wheel's rim (both very dangerous).

FWIW I think you're probably already doing it exactly right. If I recall correctly you're a heavier person, so yeah pump it up to 55-60 and ride it.

I'm repeating others a bit but:
- Don't go above the max rating for the tire.
- Having some "squish out" or widening at the bottom of the tire is normal and desirable.
- You can go as low as you want on pressure; you'll know it's too low when it gets significantly harder to ride, and if you get anywhere close to "bottoming out" over bumps (causes pinch flats and bent rims).
- If you're at the max pressure for the tire, and you can tell it's not enough pressure to prevent pinch flats/bottoming out, you can get a tire of the same size with a higher pressure rating. Just don't go down a size, or you won't be improving anything. I'm simplifying a bit, but a tire of half the size with double the pressure rating is going to act the same as what you have now.

Me and the bike are only 250 lbs, I would run 26 x 1.75 at 40 psi at the most.

I generally use 80 psi on 700 x 25 road tubeless but never more than 89 psi.

I was researching tires and their rolling resistance, and was surprised to find that to achieve the optimum rolling resistance, tire pressures are a lot lower than I had been using. For example, my 35mm 700c with 230 lb bike/rider/gear optimum pressure is: 53R/52F. For a MTB of the same weight, and 2.3" ideal tire pressure (as far as rolling resistance and speed goes) would be 26.5R/25F.

This was calculated at:
https://silca.cc/pages/sppc-form

I have gone to the lower pressure in my commuter bike with the 35mm ties, and it not only seems as fast or faster, but is also more comfortable.

That is true. That's why so many people are running tubeless tires. When you run lower pressure with tubes you run the risk of pinch flats. I still run tubes so I run my pressure a little higher. But the lower pressure you can get away with the better.

My problems with low tire pressures start to appear long before bottoming out the tire on the rim under impact occurs, namely the handling goes to crap first. I cannot stand mushy tires that can’t carve a crisp line and squirm under hard efforts. I like the bike to feel athletic, which is why I always set pressure by inflating to max indicated and then backing down until the bike starts to lose handling sharpness.

Agreed, But there is a line between comfort and feeling mushy, You just have to find that line and stay on the correct side of it. For me it's a moving target.

I haven't got time for moving targets. I ride my DW to work on a tandem with 2.0" clinchers rated 70psi max. The two of us and all her gear for work weigh 400lb. Going back home after dropping her off and the payload weight drops to just under 200lb! Do you think I should let air out of the tires for the return leg? Due to my eyesight issues I am not going to tell how much deformation there is at the contact patch for a 10psi change in pressure! I'm sorry, but I do think my unique circumstances can inform the wider world of tire users! Obviously, this is FWIW, but I suggest that y'all don't overthink it: inflate to max pressure or 10ish psi less, regardless of what you weigh, and call it good. If a 200lb difference in rider weight does not make for any meaningful difference at or near max pressure, I can't imagine that a 20lb weight difference between two riders means they each need a different tire pressure!!!

I don't know about anyone else but I have not noticed that rolling resistance gets better as my tire pressures get lower! On my roadbike I usually keep the (25mm) tires at 90psi. I can tell when they drop to 80 because I find myself dropping down a gear! Of course off road conditions are different but most of us are not riding off road. Why are we basing what we do commuting in town on what gravel riders or single track riders are doing? On the same roadbike I might be carrying a 40lb backpack or not. I am just not that interested in running calculations for the different pressures I might need running light or carrying a load. It really doesn't matter very much in the end.

I tend to agree with not over thinking it. When I was breaking spokes I tried different pressures thinking it was going to help. I fiddled with PSI differences of only a few. I went out one morning and the tyre was so mushy I could feel it roll the tube on corners. I got advice from all sorts of places, and it was all greatly accepted, but when I finally gave up and accepted my issues was with the light weight wheel the bike came with and got a new wheel, tyre pressures really did become something I stopped worrying about. I do have a figure I inflate to, and I finger check the tyres every few days but I don't check before and after every ride that I have a set PSI in each tyre.

My bike tires say to pump to 50 PSI but when I check my manual it says to reccomend to pump to at least 40, these being 24 x 2.125. Trying to get into the habit of just feeling how firm the tires should be rather then having to bust out a air pressure stick everytime.

It really depends on how calibrated your thumb is. Mine can't tell the difference between 90 and 120 psi. I just use a pump with a pressure gauge on it prior to every ride.

I pump to 5 psi over the rated max because bike tires seem to lose pressure over time and I will finish the day at max pressure, and not have to pump for several days. When I do pump, about once a week, the pressure has dropped a few pounds.

You will get the lowest rolling resistance at max pressure, and this tempts some to over pressurize the tires. Not only does this over stress the tire, it doesn't do as much good as they may think. The physics of it is that there are diminishing returns. Over pressurising the tires minimally decreases the rolling resistance. The more you over pressurise the smaller the gains in decreased rolling resistance get.

For me at 110kg (242lb) on a 44mm (1.75") on gravel, I run 35psi front 42psi rear, for road I run 40psi front 48psi rear.

So to answer the question, I think that you are fine with your tires and the pressure you are using. If you increase the pressure, don't go past the max rating.