Hi, back in the old days when a couple of mates of mine raced t140,s
they fitted 3.60 front and 4.25 rear. they said the 3.60 on the front made the bike handle better.
This is sizes i used on both the commandos I owned the T150v and my wifes T140e( I changed the rear wheel rim size on the Trident and commando to 18").
The T140es I own now has a 4.10 on the front but it's brand new when it wears out I'll fit a 3.60 if I can find one.
I fit where possible TT100's if Malcolm uphill can lap the Isle of Man at 100mph on them, then it's good enough for me.