Switching to dropped tuning..

[Chube]

Due to different reasons my band decided to change our instruments' tuning: we're going down one full step (all the strings).
I've been playing 100-40 strings up to now..which gauge should I put on to keep more-less the same strings tension?

[protoz]

I've been running 45-105's for Drop-C tuning for years. plenty of tension.