Quote from: Sumskat on August 22, 2025, 09:13:59 AM

Hi, just checking back in with this forum.

In terms of frame sizes, I’ve posted the serial numbers below

Both are ‘L’ according to the SNs (Green = 587L08025, Red = 487L07005).

Effective toptubes: 40cm (Red), 42 (Green)

Stand over heights (tyres are flat so I’ve given a range): 70-71cm (Red), 72-73 (Green)

It’s not very clear in the photo of the frame number for the green bike. Are you sure it’s 587L. The reason I ask is that frame size is a large and the virtual top tube according to Thorn literature is 630mm but the bike looks more like a medium/small. Could it be 537L, I wonder?

Looking at the frame and your own height I’d say it is a 537L.  I’m a tad taller and that is the size I’d ride.  Nice bikes.

Also forgot the (less?) obvious. Looks more like an XTC - pump mounts behind the seat tube / shot in seat stays.

My errand bike is a 1994 Bridgestone MB-6.  It has a lot of breather holes.  It was stored outside for over a decade before I bought it.  I took everything off the frame to try to make it a functional bike again.  There was a lot of rust inside the frame, but the frame was still sound.  I sprayed a lot of Frame Saver into the frame to try to stop any further rusting.  Put it back together again with some new parts and expendables.

And proceeded to store it outside for another half decade.  But now it is stored inside. 

It has not seen any lasting damage.

That said, I have seen on this forum photos of rust perforations in some of the older UK made frames.  And I recall one person had a rusted out downtube on an S&S coupled Thorn where water got into the downtube but only flowed down to the coupler where it accumulated until a rust perforation allowed it to drain.  When I saw that on this forum, I was quite happy that I had put the frame saver into that particular tube on my Nomad Mk II. 

I do question the logic of a breather hole up high, not down low on a seatstay. 

Breather holes have the advantage that you can treat the insides of more tubes with an anti-corrosion product. This probably isn't necessary on most Thorn frames, which are usually treated before delivery.

And, if you wish, you can "seal" them afterwards to slow/stop water entry. I generally use window sealant, as I have this around for other jobs.

I currently treat frames I acquire (usually second-hand) with AC50 spray, then block the holes in small tubes with window sealant after leaving the frame/forks to dry for several days.

Seat tubes and head tubes/steerers need occasional checking, as water can get in around the seatpost or stem (in my experience, more often with Aheadset type steerers), but these two areas are relatively easy to access and treat.

Rather similar to the Sherpa I recently sold, which was all set up and running well, which went at £350…….

The XTC was lighter and had shorter geometry, it was always intended as a drop bar sporty bike.  I wanted one for years, then I rode one and wasn't that keen.  Maybe a combination of geometry and wheel size, the handling was a bit too sensitive for my liking. Thorn long held that commitment that 26" was the best size wheel for anything except racing, kudos for putting their money where there mouth was, but IMO larger wheels have always been best suited to larger frames for anything other than rough stuff.