Thank you all, but @ EddiePJ, the SUV is an oldie one (mk 2014) with 10 speed cassette (
http://www.tweekscycles.com/bikes/electric-e-bikes/cube-suv-hybrid-29-e-bike-2014). I love (her) so much, nevertheless
I surely don't want to completely mess my current shifting experience, but as RobF said - need my fastest speed to be a little more fast
I had a real tough time counting the existing teeth, and am quite convinced that there are 16 of those buggers (could be 15 though), so, as I am waiting for your kind further answer/enlightment, 18 seems like maybe okay-ish. I found even 17 and 19 ones @ ebay, so even one tooth seems to really make a difference.
I wonder if a bike service guy could change it without that quite expensive spider tool...there aren't many pedelecs (nor hub motor e-bikes) where I come from.