Sky Bet Championship club County won 2-0 at the iPro Stadium on Saturday with two goals from Scotland international Chris Martin.
But keeper Bell reckons the trip to the East Midlands was a useful exercise ahead of their Petrofac Training Cup match with Hibs at Ibrox tomorrow night.
He said: "Derby are obviously a very good team. They came close to getting into the Premier League last year, so we knew it was going to be a tough challenge for us.
"It was a great work-out for us and I think it really got us up to speed. I am sure Derby will go on and do well in the new season.
"The fans came down in their numbers. It was really their first opportunity to see us. We were disappointed with how we lost the goals and lost the game, but we can take positives out of it as well.
"We had our mind on Tuesday. We are ready for it. We have been training for six weeks now. It was good to have a test like we did on Saturday before the season starts."
Bell gave Rangers manager Ally McCoist a scare when he went down hurt in the second half and needed treatment at the side of the pitch, but the former Scotland player said he will be fine for the Hibs game.
He said: "I have had knee problems previously. I went too far back, into a position I can't really go into, but there is no major damage. It will just be sore and stiff.
"Getting a bang on my left knee always worries me. But the physio came on and looked at me and it was fine."