I have 3ft radius curves on my layout, which had been fine for 8 coaxh trains for me

Truth be known - quite tight.. under 2ft. Kids have run trains at well over realistic speeds for decades on 6x4 baseboards.

Whether that LOOKS right, is a different question, but it will run just fine.

Having trialed with airfix coaches at break neck speeds I got 10 behind a Patriot go around a second radius with no issues at all. It just doesnt look at all right, but my second and third radius curves are to bring trains around to the fiddle yard area

I've done it using an 18" radius, but the question is does it look right?

Lisa

thankyou for your comments.

I forgot to mention this is for a hidden fiddle yard so looks do not matter.

My little railway uses old Hornby-Dublo track with 15" radius curves.  My son used to hurl 'Golden Fleece', with a few coaches, round it at break-neck speed - no problem!

You may have a problem with more modern stock - especially long coupled-drivers locos, as they are not designed for such tight curves.  Small flanges on modern wheels also hold the curves less well.  If your coaches are all bogies and your wagons short 4-wheelers, then these should be fine.

50 Wagon goods train and in 00 what a layout this will be, can wait to see future posts

The layout will be 37ft x 14ft but the end were the fiddle yard is only 7ft 4in wide for 8 tracks.