Redding struggled to a lowly 11th on the timesheets on the second day of running at Aragon on Tuesday, ending up almost 1.4 seconds slower than Kawasaki's pacesetter Jonathan Rea.
The Briton was only second-quickest among the BMW contingent, with Loris Baz a strong fifth-fastest on the satellite Bonovo bike.
After praising BMW for the improvements it had made it to its M1000RR challenger over the winter in last month's Misano test, Redding admitted that the Aragon test proved tougher, not helped by two crashes on Tuesday.
"We didn't really find a solution for the rear grip, which was my weakest point and something we were trying to improve," he said. "It was a busy day with the sessions, they go by so fast, we didn't manage to make a long run, we had to try qualifying tyres and I had two crashes, which cost us time.
"We learned a couple of things today, but it didn't really help us make the big step we needed.
"[The main problems are] is rear grip on the edge and trying to make the engine more calm. The rest is not too bad - braking and [corner] entry are ok. We could improve the mid-corner, but we have bigger issues at the moment."
On his crashes, Redding added: "I was trying to find the limit more. We tried new front tyres, the feeling was better but when I pushed more I crashed. It was tricking me, like [telling me], 'you can go harder'."
Conditions for this weekend's opening round at Aragon are expected to be warmer than they were during testing, something Redding hopes will help the BMW to be more competitive.
The 29-year-old maintains that finishing inside the top six remains his target despite a tougher-than-expected test.
"Before the [test] I was saying if I could be top six in the races I would be happy," said Redding. "I'll stick by that. It's going to be a little bit more difficult than I expected, but that's my goal, it's reasonable and we have to try."
Baz was by some distance the fastest BMW rider on Tuesday, trailing only Rea, the Yamaha of reigning champion Toprak Razgatlioglu, Ducati's Alvaro Bautista and GRT Yamaha's Garrett Gerloff.
But the French rider admitted his best lap came while he was getting a tow from Rea, and that his race pace is not comparable to that of the Kawasaki rider.
"At the moment we are faster on one lap than on the [race] pace," Baz told Motorsport.com. "The pace is worse compared to him [Rea], we have more drop on the rear [tyre] and the bike is harder to ride after a couple of laps.
"It was good to compare with him because the target is to be as fast as them, but at the moment we know that Johnny and Toprak [Razgatlioglu] are ahead of everyone on pace. They are the references and we have to catch up."
