Do I need to respect minimum tyre pressures?

johngwheeler

I have a CX bike with Bontrager tyres that are marked 60-80psi. Even the lower limit seems a bit bumpy off-road and I was thinking of lowering pressures. Is this a bad idea?

I do notice on the road that less than 50psi shows noticeable "squashing" when I put my weight over the wheel, which must increase friction, surely?

Any thoughts?

pblakeney

Buy fatter, lower pressure tyres.

imposter2.0

viewtopic.php?f=40114&t=13076775

mr_eddy

Running lower pressure than min on the tyres is not going to cause any tyre damage but the lower pressure will increase your chances of pinch punctures and/or wheel damage. You may find that the tyre could pull off the rim too but that is very unlikely.

I would look at going up a size (i.e if you currently run 35c go for 38c assuming your frame is big enough). Bigger volume tyres are more comfortable at lower pressures and will seem 'harder' at lower pressures due to the size of the tyre. Also worth noting that a larger tyre at lower pressure will be faster than a skinny tyre at lower pressure due to the deformation of the sidewall etc.

HillNo

I am still trying to find the sweet spot in relation to lowest tyre pressure. Sometimes when I go a little too high I find my bike "bouncing" on little tarmac contours. I then assume my pressure is a tad too high. This bouncing doesn't mean my pressure was at the top end. My tyres are from 60 to 100 psi 28mm. So I guess finding that sweet spot for comfort without too much compromise is the best I can hope for. Hopeithelps!

N0bodyOfTheGoat

https://www.youtube.com/watch?v=Clk_LLBYFzA

Expand the description to see the download link to the XLS file, which can be used in Google Sheets. Gives you ballpark pressures for different conditions, depending upon your inputs.

FFT suggests never go lower than minimum pressure on tyre sidewall, but it seems it is quite common to do so.

For me and my Wazoo with 29er wheels and 700x38 Marathon Cross...
Combined weight ~95Kg (kitted out to ride)
Tyre width 40mm (using ETRTO)
Estimated front weight % 40 (as I'm using a 35mm stem)

Suggests ~34.2 PSI front and ~52.2 PSI rear for "mixed road" (we have some quality potholed roads around Southampton)! :shock:

Minimum range on sidewall is 50-85 PSI.

I briefly tried ~55/60 after I wiped out at ~77/83 on a mini-roundabout on 14th Feb, but the low pressure felt really odd on the roads, so I've been using ~60/70 for a few weeks.