Tire Pressure - How Low Do You Go

[Jay]

I went low today and it was comfy and offered a lot of traction.  The Wolf Tooth / Silca calculators on my phone recommended 30 psi or a bit higher, I used around 21-23.

RH Hurricane Ridge (measure 40mm) on Quill rims, TPU tubes, 90% gravel/dirt (though very few roots/rocks, and I avoid them easily as these my hometown trails I know very well).  I'm around 160lbs, and on trails I'm standing a lot and generally I don't sit heavy on the bike. I did go off a few curbs but eased the rear tire down as best as I could.  While it worked out very well, I was thinking I may be pushing my luck.

Do you often go lower than recommended?  For anyone running 40mm tires or thereabouts, every go down to low 20's?

[Guy Jett]

Rene Herse recently came out with a revised tire pressure calculator giving similar results to what you used if you use the new "Simple" calculator (for what it's worth):

• 44 psi for "smooth asphalt";
• 36 psi for "rough asphalt", "smooth gravel", and "mixed paved / gravel";
• 37 psi for "rough gravel / large rocks"; and 
• 34 psi for "rough gravel".
  (I'm using you're weight as given at 160# and assuming a bike weight of 35#.)

The new "Pro" version gets more complicated with riding position, front and rear luggage weights, chainstay length, rim widths, stiffness of the sidewalls, etc.

Note also that Jan Heine also states that these are "suggested starting pressures" to find your ideal pressures.

I, too, "ride light".  And I use the Pro Version for both my bikes:

Hilsen with 650B x 38 Loup Loup Pass 35.4mm actual front/rear, 40psi front / 46 psi rear.

On my old Raleigh Competition with Soma Shikoro's 700C x 38 front / 33 rear, actual measurements 41.3 / 39.6, 36 / 42 psi.

After riding some I am also thinking about dropping my pressures a bit but would probably do so in 2 psi increments. And I probably wouldn't go below a 6 psi total drop.  In your case, if you feel you need to "ease the rear tire down", you're probably too low, should come up a bit more, and stop worrying.  And remember, if you crush the tube with the rim, you may have as many as 4 holes to patch!

G.A.Jett

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[Nick Payne]

I find that for riding on sealed roads, which is where most of my riding happens, if the front tyre pressure gets too low it adversely affects the handling, as the lower the pressure, the further forward the front of the contact point between tyre and road, changing the trail. For the 40mm Pari-Moto I'm presently running on my Bleriot, I find somewhere between 35-40psi is about right. I can definitely notice the handling start to get get squirrelly when the pressure gets down to around 30psi. I weigh about 140.

Nick Payne

[Steve]

I've been running 24-25psi with 48mm RH knobbies with TPU tubes on my off-road Ritchey. 

On my Platy with 48mm RH slicks and butyl tubes I tend to pump it up to about 38psi for pavement, though I'll bleed them down to around 28-32 for mixed terrain.. 

My Hillborne with 42mm GK slicks and butyl tubes (26" tubes in 650b tires) generally gets inflated to about 28psi for mixed surface riding.

Never experienced a pinch flat with any of these setups - though I do find the tires feel a bit too boggy for my taste if I go much lower.   For reference, I weigh about 166lbs, the Richey is at 24lbs with bags and the two Riv's each weigh in a bit over 29lbs, both with fenders  and rando racks.

Steve n AVL

[Patrick Moore]

I’m also 160 and use pretty low pressures by the standards of the official charts, but I find that my 42 mm (actual) extralight RH Naches Passes start to wallow much below 30 psi, this on pavement. I daresay that on our sandy soil I’d not notice the wallow as much, but I also think that I’d draw the line at the upper 20s. Note that these tires have onionskin-supple sidewalls. I usually put in 35 front and 40 rear.

28 mm actual Elk Pass (extralight to the max: 175 grams new in the labeled 559X32 mm size): 55/60 f/r.

22 mm actual 559x23 mm Michelin Pro Race and Conti Grand Prix (this was >10 years ago, don’t know if these are still made): 80/90 f/r.

32 mm actual EL Stamped Pass: 50/55 f/r.

45 mm actual EL RH Snoqualmie Pass: 30/35 f/r.

48 mm very light Furious Freds and Supple Vitesse SLs, both at 360 grams: about 20 psi.

54 mm actual lightest model Thunderburts: 18 -19 f and r

61 mm actual lightest Big Ones: ~17  f and r.

72 mm actual WTB Rangers: 12 psi.

I’ve ridden stiff-walled 60+ mm Big Apples down to 12 psi by mistake and didn’t notice this on our sandy dirt, only discovering the underinflation when I returned to pavement and they started to wallow.

I’m a light rider, and haven’t gotten a pinch flat in 30 years except for the one time I deliberately rode 22 mm Michelin Pro Races at 80/90 into a pile of large gravel at speed; yep, pinch-flatted the front tube.

OTOH, I recall, 55 years ago, discovering how delightfully fast my 27 x 1 1/4” cheapos felt when pumped to an amazingly firm 70 psi!

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Patrick Moore

Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum

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