I have 3mm at the rear seat stay brace. It spins freely enough, but anything other than a smidge of mud and it'll be gathering up with ease.

but anything other than a smidge of mud and it'll be gathering up with ease.

Surely you just answered your own question? There isn't a set value for enough mud clearance. Along as the tyre doesn't touch the frame, then its all down to if you actually ride in mud, and how thick the mud you ride in is.

Stuff it, I'll try it tomorrow and see how it goes. The frame, albeit great, isn't particularly UK-friendly!

Come back in the winter and tell us the answer !

It'll be tucked-up in the garage in winter! 😉

If you can't get a finger between the tyre and the frame then you don't have enough clearance. If you run lowish pressure as well with only 3mm clearance you could well end up rubbing big raw spots on the frame.

If you run lowish pressure as well with only 3mm clearance you could well end up rubbing big raw spots on the frame.

I don't quite follow that conclusion

Surely [as the old joke goes] it's only flat on the bottom

Am I missing something?

Low pressure doesn't make any difference – the tyre only goes fatter where it's touching the ground. If you run high pressures then your more likely to have a problem if the clearance is marginal.
I don't think I've ever had a bike where I could get a finger between tyre and frame. Maybe I've got fat fingers.

you can saw through a frame with a muddy tyre faster than you think…

do you really need tyres that large?

low pressure can cause the tyre to roll more on the rim under hard cornering, not just at the bottom of the tyre hence the frame rub potential, depending on tyre size, sidewall strength and rim width. (read sheldon browns articles on tyres for the full lowdown on tyre physics) speaking from experience as i **** a frame trying the same routine in gritty peak district shite. It's amazing how quickly you can destroy a frame. Do you really need extra fat tyres or is it a fashion "it says so in the magazines" thing?

I have a Coyote Dual with really crap tyre clearance at the back. I had this problem. I put a strip of Gaffa tape on each seat stay. Sticks like shit to a blanket, only reduces tyre clearance by a fraction of a mm but provides good cheap protection for the frame. Check and replace as necessary.

Was expecting the tyre (Larsen) to be the same size as a High Roller. Guess the Larsen is quite a bit bigger.

Fair enough if Sheldon says it, but I have a frame with tight clearance for 2.25s and it only starts to rub if I put higher pressures in. I can't really see how a tyre is going to be deformed that far round the wheel as a result of cornering roll.

Come on then, carbon stays on my Motolite and a tyre with bugger all clearance = problems? Back to the garage me thinks!!

carbon with tight clearance? I'd be a wee bit nervous. If you're wheel is nice and tight and doesn't slur on corners and you stick to recomended tyre pressures it may be worth a go an shorter ride. stick some gaffer/masking tape on the chainstay and if you see any rub marks you know it's too iffy. If it looks ok then YEY it'll be fine until it gets muddy……..so about a week then 😀