Setting motor max volts.
I just advised the same exact thing to a freinds chair as I advised Expresso, (and Snaker did it too). And he is pleased with some extra speed!
Only this time I took note of the actual figures.
A powerchair on typical lead bricks, using R-net has the max motor volts set to 21.4 to 22.4 volts typically. I looked at a few peoples saved settings. The reason for this is to have a constant maximum speed so that as battery volts sag under load theres enough left to steer. Esp when battery is partly discharged. This is essential using lead batteries, and the motors are usually rated for X RPM at 22V. So lets use 22V as the average figure.
A lithium battery does not sag. Its voltage is typically 26V most of the day. You can set the max motor volts to 26.0 in the R-net programming software. Thats 22V up to 26V. 19% higher. Or 19 percent faster! I did the maths several times as it surprised me.
So this means an 8.5mph chair will now go at 10.1mph
A 13kph/8mph chair will go 9.52mph
A 10kph/6.2mph chair, with all this extra torque still intact, will go 7.4mph. (Or almost 8 with slightly bigger tyres).