# The ratio of e-bike power output to rider weight.



## plummet (Jul 8, 2005)

Ok team, 

I'm trying to get my head around the ratio of rider weight to power output for ebiking.

If an 80kg rider uses a 80nm torque ebike. Would a 50kg rider using a 50nm torque engine have similar assistance performance?

Can lighter riders use the lighter weight ebike and get similar performance to a heavier rider using a standard ebike.


----------



## minimusprime (May 26, 2009)

yes power to weight ratios matter in cycling, the math is easy. 105kg rider/bike (80kg + 25kg) / 80nm toque = 1.31 kg/nm would technically be comparable power to weight to a 75kg rider/bike combo running at 57nm. This of course is not quite as simple on the trail as power/weight ratios matter most when climbing and not so much on the flats. This is the same thing that happens in road/xc racing as well where a higher power output rider that weighs more, (peter sagan or one of the other sprinters) can kill on flat ground, but will get murdered on climbs by riders with better or similar power to weight ratios.


----------



## rocwandrer (Oct 19, 2008)

As a single data point, I reprogrammed a BBSHD to make it far less powerful. I set it up so that the first setting was just able to offset the weight of the assist system (about 25 watts peak) and the next 3 assist settings were intended to just slightly offset fitness disparities on a group ride for a 250 lb rider.

I put a 70lb kid on the bike and setting one became turbo and anything over setting one took off so hard it was startling to the rider.


----------



## plummet (Jul 8, 2005)

That's good info.

So I will, do some maths......


----------



## McShred (Oct 4, 2021)

My personal experience is that the difference in power to weight doesnt have a big effect on trail speed but does have a pretty noticeable effect on battery drain. I often ride with people on the same bike as me who weigh 50-60 lbs more, in cases that the motor matters our speed is reasonably matched, but at the end of the ride my battery is much better off. Its never quite as good as simple math says it should be, but its close.


----------

