the reserve wont register on the gauge you should get about 20 + miles easy from the reserve
http://www.ebay.co.uk/itm/BIKE-BICYCLE-CYCLE-MIRROR-GLASS-FLEXIBLE-FITTINGS-1-PCS-/130526873391?pt=UK_SportGoods_CyclAcces_RL&hash=item1e6402072f
there flexible so when you hit things they don't break easy moll and only a £5 posted to you