Come hear about KSP 1.1, straight from Squad!

[LostOblivion]

One reason big SRBs (like the ones in KW) are hard to use is that we can't give them thrust curves. I've tried building low-cost lifters out of the KW 2.5-meter SRBs but the problem is if I set their thrust so they just barely get off the launch pad, by the time they burn out the TWR is up to 6 or 7. If we could have even a simple, linear thrust curve, big SRBs would be a lot more useful.

This, thrust-curves, is what stops Squad and any modder from making something reasonable out of SRBs. Like Hotaru says, the SRBs as they are now cannot be used essentially as a core stage without having very little TWR at launch and very high TWR before separation. IRL, most solid rocket boosters give linearly or exponentially less thrust, by design, as they continue to burn. Simply giving the SRBs more fuel and thrust will only increase this TWR difference to the point where they become unusable. No, if Squad wants to implement proper solid rocket boosters, they need to implement thrust-curves, tweakeable or static.

[Kuu Lightwing]

Ariane V doesn't seem to have any problems with exponential TWR of SRBs according to this graph:

[Jouni]

This, thrust-curves, is what stops Squad and any modder from making something reasonable out of SRBs. Like Hotaru says, the SRBs as they are now cannot be used essentially as a core stage without having very little TWR at launch and very high TWR before separation. IRL, most solid rocket boosters give linearly or exponentially less thrust, by design, as they continue to burn. Simply giving the SRBs more fuel and thrust will only increase this TWR difference to the point where they become unusable. No, if Squad wants to implement proper solid rocket boosters, they need to implement thrust-curves, tweakeable or static.

I don't see the problem. Large SRBs are no different from small ones. If you multiply thrust, fuel mass, and dry mass by the same constant, you get a larger version of the same booster with the same performance characteristics.

The most efficient SRB in the game has mass ratio 5.33, which means that the final TWR is 5.33x higher than the initial TWR. A Skipper with an orange tank has mass ratio 5.57, while a Mammoth with three large fuel tanks has mass ratio 6.14. The TWR of liquid stages increases more than the TWR of SRBs, but we still don't throttle them down, except in badly designed rockets.