We recently tried taking the train from Rüsselsheim with a heavy electric-assist oversized semirecumbent tandem bicycle. Unfortunately, we found that the lift was just a little too small (at most 0.1 meter / 4"). We lacked the tools and time to take enough off the bicycle to enable us to lift it up and down the stairs and there were no ramps, so we did not manage to get on our intended train.
Although the presence of lifts (or ramps) can be easily gained from public sources such as bahnhof.de, sizes vary, and we find that some lifts are large enough whereas others are not. Is there any (publicly available) dataset on the dimensions of railway station lifts in Germany, so we can estimate in advance whether our tandem would fit?
I'm guessing that the answer is "no", but one never knows!
(Of course, another question is that many trains have no or limited capacity for such large bikes, but at quiet times in regional trains, I've found it's usually fine.)
Older model of Hase Pino to illustrate the length. Eva Kröcher via Wikimedia Commons, GFDL 1.2 / Free Art License / CC-BY-NC-ND 3.0
NB: Tandems are allowed on DB regional trains:
You can only take a tandem, recumbent bike or tricycle on trains with a larger storage capacity.
Source in German additional states it's regional trains only:
Ein Tandem, Liegerad oder Dreirad kann nur in Nahverkehrszügen mit größerer Stellplatzkapazität mitgenommen werden.
Die Mitnahme von Tandems, Liegerädern und großen Dreirädern (> 120 cm) ist in den Fernverkehrszügen nicht erlaubt.