Does anyone know if you can get supermax sprockets exchange in the UK or do you need to send to the US?

No UK exchange that I am aware of. You have to send an alloy one to the USA for conversion but I am told they are pretty quick returning it.

Supermax or steel?
You will get charged £90 by customs on return.
John.

Give Krazy Horse a call as they were thinking about offering their own supermax type conversion

I would guess that shipping both ways might be well north of £120, plus Duty/VAT, so buying from the US bears quite a price premium.

I had mine done about 3 years ago and had to send it to the US, turn around was about 3 weeks they do pulleys in batches so it just depends where you fall in the production cycle as to the actual timescale. Cost if I remember correctly was £450, shipping £60 return and import duty £90.

I was the first customer to order one and It lasted quite well until it failed! I have since bought the steel one with no regrets. The way the SuperMax is built makes it vulnerable. The neoprene wrap is not only bonded to the aluminum wheel but bolted as well in many places. The bolts are tiny as they must fit in the depressions (valleys) of the sprocket and not make contact with the belt. When we removed the wheel to replace the sprocket with the steel one, the neoprene had slipped and had caused some of the bolts to deform the aluminum as well as missing a few. The neoprene was spinning around the wheel so no movement.

I think I racked up about 19,000 miles before failure. I think that the amount of torque reaching the wheel as well as potholes and other obstacles took their toll.

This will never happen with the one piece steel sprocket.

Yes, I caught the 'tiny bolts' coming loose on my Supermax so refitted them with adhesive on the threads. So far so good, but it's only done around 6K miles... If I had to replace it, I'd probably go for a Fabian steel one (if they're still available at the time).

I've got over 22k miles on my MMC steel sprocket, no problems whatsoever.

It may be heavier that the original alloy (or Supermax) but to be honest I couldn't tell the difference in the way it drives.