Stuart Firth
I have found loco’s with Radial and Bissel trucks very intolerant of curves. When I made a couple of N7 chassis for Roy Lowe, who has 2nd radius curves in his fiddle yard, I had to cut off the back end of the chassis and turn it into a pony truck!
The narrowing of the chassis will hopefully do the trick, I was reading Guy Williams’ old book recently and I think I saw it in there.