The shuttle liftoff thrust was about 6.78 million lbf (30.16 MN). The SRBs underwent significant throttling over their approx. 120 sec firing time, as can be seen in this graph. This throttling was not dynamic but designed in by controlling propellant surface area:
https://en.wikipedia.org/wiki/Space_...Srbthrust2.svg
Getting the desired time/thrust curve is quite the science for solid rockets. Unlike the simple 'end burning' black powder rockets, most AP based solid rocket motors are 'core burning' and are ignited at the front. The shape of that core cavity determines the time/thrust relationship. IIRC, the Shuttle boosters had a 'star' shaped core to get the desired characteristics.
It would have taken six shuttle launches to deliver to LEO the same useful payload as a single Saturn V.
The shuttle was a tremendous technological achievement, but it failed miserably at it's primary goal of reducing the cost of inserting payload into orbit by at least an order of magnitude. By most measures, even accounting for inflation, the cost of placing a pound of payload into orbit was not meaningfully different between the Space Shuttle and Saturn V. About the only meaningful capability we gained with the shuttle was the ability to bring large objects
back from orbit.
I find it both amusing and pathetic that NASA is now spending billions of dollars to
recreate the capability we already had 45 years ago with the Saturn V
