[hstudent]

Can anyone explain why First Group designed 175s and 185s when neither seem to have advantages over 170s?

They all have a top speed of 100mph. Using TP Express' diagrams of 170s and 185s a driving coach without a first class section has practically the same number of seats (62 on a 170, 64 on a 185)

I've only been on 170s operated by Central Trains, but I personally found those ones more comfortable than 175s or 185s.

Also there were problems with 185s on the Leeds-Hull line, in that they were having to run at 70mph rather than 90mph due to their weight, which was one reason why Transpennine Express opted to use 170s on that route.