Source: http://worldoftanks.com/en/news/17/introducing-the-MT-25/
I don’t usually repost official WG stuff, but US server just published this interesting piece of info by “Yoott, resident US MT-25 expert”:
First Impressions of the MT-25
The first thing a player will notice once they log in will be the sheer size difference in the tank compared to the T-50-2. I would estimate width wise the MT-25 is 20 to 25% wider with much thicker tracks and a much beefier turret and hull design.