Based on a bit of googling, the balance of opinion seems to be that whether you choose to widen the platform on the carrier or not is a matter of choice, but that some form of ratchet strap is the usual solution.

Would it need to be something like 25mm ratchet strap rated for 250kg loads, or would something like a luggage ratchet from go outdoors be usable? Or in a pinch, a ratchet style jeans belt or two?

I just took the cradles off mine and use a load of toe straps to hold the wheels to the rails. Never had any movement from it.

Deflate tyre first?

Alternatively http://www.arrse.co.uk/wiki/Straps,_Utility

I just replaced the plastic straps with toestraps. Had 4 fatbikes on the rack. Works with 5″ tyres too.

Like these

unrelated but does anyone know if you can move the rear wheel fitment area on a 591, my new bike is too long even with the front wheel holder as far forward as possible.

unrelated but does anyone know if you can move the rear wheel fitment area on a 591, my new bike is too long even with the front wheel holder as far forward as possible

Front & rear wheel fitments move independently, howevere their position will be determined by the clamp – as this will only fix on one point on your frame, and your wheels are fixed in relation to this point (hope that makes sense).

So make sure you get the clamp base in the right position on the rail so your bike fits centrally on teh length of the rail. There’s not so much adjustment on this as it has to be on the upslope of teh rail, and also fixes to the roof bar – which may be restricted if you have set fixing points (ie not roof rails)

Took me bloody ages to get 4 set up so I could fit everything from road bikes to fatbikes with no handlebar/saddle clashes!

Forgot this question was still running round live 🙂

For the record, I bought two 120kg working / 250kg break 25mm straps from Go Outdoors and cut them down substantially. (3m long as supplied) toasting the ends as normal. I removed the plastic straps from one rack and threaded the ratchet straps through. I secured the On One Fatty with the usual down tube clamp and then locked the 4″ Floaters at normal riding pressure with the straps, just positioning the ratchet down the ample sidewalk to avoid scratching the rim. I loosely tied off the excess strap to the spokes to keep it from whipping around. This survived a motorway speed trip of around 100 miles with no concerns. I’ll consider it solved… 🙂