Originally Posted by
prj71
What I've been trying to say along along is that 25 psi is good starting point that works for most of the general public all the time. But some people try to dissect it too much when all I was doing was making a generalization. Start there than go out and experiment and fine tune. Optimum for 29er tires is between 18 and 28. 30+ is way too much unless you are riding gravel trails or smooth machine built single track with little to no features.
In the end the reality of the situation is that whatever pressure is chosen you are choosing a trade off between rolling resistance and grip.
I understand what you are saying, and what I am saying is that it is not true. You are giving out bad advice, based on bad assumptions. Without knowing someones weight and tire size, you have NO IDEA what the optimum tire pressure is, and you had absolutely no basis to say that 30 was too high for the OP. You were shooting blindfolded in the dark. The range that "most people" run (which are numbers you are just making up based on almost no data), regardless of weight or tire size is utterly meaningless to any individual trying to get an of what pressure to run or even where to start. 30 PSI is ABSOLUTELY withing the range that some people end up. You just heard from a several in this thread. Were I running 2.1-2.2 tubed, I would be around 30, if not a little more.
And you are wrong about what the trade-off is. In mountain biking, it is not rolling resistance vs traction: The primary drivers are traction vs pinch flats and loss of stability, which means that you may need to run higher pressure in rougher terrain and for more aggressive riding. Look at what most DH or Enduro racers are running: 2.3-2.5 tubeless tires, with sturdy sidewall. Visit some forums and look at the pressures they are running: mid 20s to low 30s is typical. Some higher.
The proper advice was given elsewhere in this thread: start high, and slowly lower until you find where you are either getting pinch flats or tires squirming.