An inner tube which has correct dimensions for the Blockley 28x3 tyre size.

This inner tube is fitted with a TR6 valve stem. The TR6 is a metal valve stem that has a diameter of 8 mm. Blockley is in the process of manufacturing a tube to fit the 28x3 tyre size correctly, with a decent quality butyl tube having a decent 3mm wall thickness, but unfortunately these will not be available until July / August 2026 time.  

So what to do in the meantime? The quality of the tubes available elsewhere is poor, which is not unsurprising. There are brands that really need to be avoided - we have looked at various samples brands, so if you can't wait for the Blockley tubes which we will have in August, we would suggest the better of what can be used would be the Kenda brand which has a better wall thickness - we usually have a few of these, but perhaps customers can find their own sources for less - the cost of what we have delivered to Blockley ranges in the £20 - £21 bracket, around what our own tubes will no doubt retail for.

Please note that the Michelin 21MDR or a 710x90 tube sizes as recommended by the usual tyre wholesalers are wholly unsuitable and have the wrong dimensions (Blockley makes these dimensioned tubes which we have in stock). The Redwing brand of tube they offer is something we are not impressed with.