Originally Posted by
daihard
I'm a novice, but I wonder about the accuracy of the chart. I weigh 140 lbs (fully clothed). Even with a 20-pound luggage, I only give approximately 80 lbs to each wheel. I have 700x28 tyres, which means according to the chart, my tyre should have no higher than 60 psi. Does that really make sense? The pressure numbers written on the tyre are 100-120 (min-max) psi.
Chart doesn't take into consideration the tires, the rider, the road.
At your weight, riding most 28c tires at 60 would not be a big deal.
Ideally one wants the tire firm enough to not have too much flexing (hysterisis) which builds up internal heat, and not so firm that the tire boucnes thru road irregularities. The 'irregularities come into play even on seeemingly smooth road surfaces. SO pumping until the tire is rock hard is counterproductive and slow. You can do it by 'feel' if you have enough comparison to other wheels/tires or you can be very pragmatic and do coast-down tests at different pressures. And then makes decisions on speed VS comfort.
A 28 ridden at 70 lbs will feel very much like a 23 ridden at 90, given the same level of tire construction.
AT 160 lbs, I find th best balance on the 28 is 70frt75rr for me.
Pinch flats at normal pressures for a size can mostly be attributed to rider inattention. Not lightening when going over surface joints or other edges is all on the rider. If a rider is hitting an edge hard enough to cause a pinch flat, there's a good chance they;re also doing damage to the rim.