They are available for £20 per tyre from Spa Cycles, the best price I found after a bit of searching (post free if order is over £50).
Having read about them on this site, I ordered a pair for my non-electric bike, which had a puncture needing attention. I fitted them and pumped up to about 60psi. I was amazed at how much less resistance they gave compared to the factory-fitted tyres on my Marin bike; on a very moderate but smooth uphill path, I kept rolling a long time after I stopped pedalling. Highly recommended - just ordered another set for electric bike!
Frank
Having read about them on this site, I ordered a pair for my non-electric bike, which had a puncture needing attention. I fitted them and pumped up to about 60psi. I was amazed at how much less resistance they gave compared to the factory-fitted tyres on my Marin bike; on a very moderate but smooth uphill path, I kept rolling a long time after I stopped pedalling. Highly recommended - just ordered another set for electric bike!
Frank
