Mountain Biking - Running Different Tire Pressures on 29er's

I'm new to MTB and am used to running roughly full pressure on road tires. I have just put CST Caballero tires on my 29er and am running 5psi below it 65 psi rating. I can see some advantage to running a little lower for more grip but I have seen people talking about running close to 30 psi with these and other tires. Is this doable on a "normal" setup and is there much advantage to it?

It depends on the tread of the tire, and where you ride. Pavement and pavement-like hardpack give you more results with more psi. Softer terrain, bumpier terrain, etc., does better with less pressure to better deal with 'erratic' surfaces.

I ride my MTB a lot on pavement (commuting); for that, I'm near the tire's limit. For sketchy surfaces, I'll drop 15-20 psi (I weigh 230+, btw).

I'm new to MTB and am used to running roughly full pressure on road tires. I have just put CST Caballero tires on my 29er and am running 5psi below it 65 psi rating. I can see some advantage to running a little lower for more grip but I have seen people talking about running close to 30 psi with these and other tires. Is this doable on a "normal" setup and is there much advantage to it?

For off-road use, people typically run much lower pressure, even below 30 psi. Lower pressures give you a larger contact patch between the tire and the trail for better traction, and allow the tire to flex more easily to absorb bumps. This is one of the big reasons people run tubeless tires -- tubeless tires allow you to run extremely low pressures without pinch flatting.

I don't run over 40 psi. I also don't ride mine on the road.

The OP running 60psi on a 29er tire seems hella high to me unless he's going for low rolling resistance solely on road. In the dirt is a different story.

I run between 22-26 psi on my tires, 26/650b/29er with most tubeless. I have run the same on tubed wheels but I don't bash into obstacles. I weigh a max of 150 lbs (winter weight) and down to 144 lbs in the summer. Obviously adjust if you're lighter or heavier or if you plow into trail obstacles or pick clean lines.

. . . or if you pick around the trail obstacles or plow direct, clean lines.Fixed. :D

Fixed. :D
Hahaha nice!!!

I have slowly started to experiment with lower pressures. Mine are at about 40PSI (started at 60) but I haven't ridden enough with the new pressure to have been able to see the difference :( .

The best tire pressure will depend on the tire and riders weight.

I ALWAYS run as low as I can without sacrificing handling. With 2.4 racing ralphs I run 20-21, with 2.25 Racing ralphs I run 19-20 and with 2.0 Furious Freds I run 18-19. All are 29er tires and setup tubeless.

I have known for a while that lower psi helps with traction and is faster for rough terrain and recently found out that low pressure is also faster for anything other than smooth roads.

This past fall while training for a 30 mile race that is run mainly on smooth fire roads I decided to do a tire test. I used a hard packed very smooth dirt road that had a reasonable grade. I coasted the entire .6 of a mile so that the only variable was the tires. I tested all three tires at 20 psi and 40 psi. I made 3 runs on each tire/pressure combo to make sure that the numbers were accurate. All 3 runs were almost identical. As I suspected the thinner less aggressive tread was the fastest but much to my surprise the lower psi was faster than higher psi for every tire.

Here are some of the numbers from my Garmin the RR were the 2.4":
Tire psi-----Time-----Distance----Avg spd----Max spd
RR 40 psi----2:04-----0.6---------17.4--------27.5
RR 20 psi----2:01-----0.59--------17.7--------26.2
FF 20 psi----1:51-----0.6---------19.5--------27.9
FF 40 psi----1:55-----0.6---------18.9--------27.4

Try the 25 -35 range depending on rider weight and riding style/ terrain. You want your tire to grip and conform to the ground/ rocks, not bounce off of them.