Due to a back problem of many years, I have to ride in a different position than most. I can't sit straight up on the bike even with a back rest due to increase prssure on the spine. I have to be leaning back to a certain degree then have my back puttting pressure on the back rest. After measuring last night in order to achieve this, I will need a +5 pull back on the bar. Does anyone know of a place that I can order this........or the measurements I would need in order to achieve this? TIA.