This is the third in a series of technical articles covering some of e-bikes complexities in quite full detail so that all aspects of the subject can be appreciated.
The background to the suspension issue.
Suspension has been around for hundreds of years since carriages and stagecoaches, and cars adopted it very quickly. Bikes as we know them have been around for 150 years or so, but never had suspension until about the last twenty years. When I was a youngster, the whole country rode bikes, few could even afford bus fares and cycling to and from work was the norm as it had been for more than half a century, so most of the population knew far more about bicycles than is true now. Bikes could have had suspension then very easily, but customers didn't ask for it or feel they wanted it, simply because the bikes were correctly designed and didn't need it. And that was on post World War II roads that were in the worst condition possible after a decade and a half of total neglect due to the war effort.
It was the mountain bike that changed all that from it's first showing in 1979, people liked the macho look and started riding them on the road, putting up with the huge extra effort needed to propel them for the sake of the style. That's fine for them, but I dislike the way in which that fashion has virtually eliminated good utility bike design, to the point where shops don't have them and few people even know what a good efficient bike is. As a result the majority considering a bike purchase mistakenly think suspension is essential.
Not so in mainland Europe though where there's huge numbers of utility cyclists. They are people who ride for every purpose throughout their lives so can be regarded as knowledgeable and professional, but they haven't followed the mountain bike fashion and ride unsuspended well designed bikes. That's because as very experienced cyclists, they know better.
The technical and efficiency aspects.
The implementation of suspension forks on bicycles is generally rather poor, and they fall far short of the standards of motor cycle ones since the weight that can be added to a bicycle is limited. They generally fall into two groups, the ones with slack which are a bit imprecise in handling but spring ok and last, and those that are more taut but which can often seize up after a while due to inadequate clearances combined with poor sealing of the legs.
Suspension on bikes is inefficient, and is universally accepted as such by cycle designers worthy of the title, and they only include it in designs for marketing reasons because customers knowing no better demand it. Of the forms of suspension, rear suspension is the worst and most inefficient, then front suspension follows which is not quite as bad, next down is a sprung seat post, and finally fat low pressure tyres which are not terribly inefficient in the suspension sense at least. However, there are various groupings to consider when judging the relevance and effects of springing systems, Road Bikes, Mountain Bikes in competition, and Electric Bikes.
Unassisted road bikes should never have suspension and no knowledgeable cyclist or designer will think they need it, since they suffer the most from it's inefficiency. Suspension adds comfort but creates more work for the rider in direct proportion, the more protection from road bumps, the higher the penalty paid in pedalling effort. As far as possible, here should be a rigid connection between rider, pedals, and road to ensure that no effort is wasted. Think of hammering a nail into wood. Which is more effective, hitting the nail with a bare steel hammer, or having a block of rubber between the two? Clearly the rubber would absorb the energy and be ineffective at driving in the nail.
In practice when cycling, pedal downthrust effort is absorbed by the springs, a small proportion is lost as heat, and the rest is then returned in useless modes. Half is sent down into the road at the forward sloping angle of the forks and slowing the bike as it's in the opposite to the direction of travel, the other half is sent back up into the bike. The only time that second half has no effect is when the pedal cranks are vertical, at all other points the upwards rebound force directly opposes the rider's pedal effort and has an ill effect on cycling rhythm and muscle action. Therefore, the suspension having lost some of the original pedal effort into the spring, almost half of the lost portion returns to have a second go at wasting the rider's effort. Added to these, insufficient damping of the spring motion which is common on bike suspension causes excess rebound bounce, and this multiplies the forward energy loss.
Mountain Bikes in Competition on severe surfaces can benefit from suspension forks with very limited spring movement to prevent wheel or frame breakage, but with no excess movement beyond that reducing the rider's competitiveness.
Electric bikes are a more complex case with three aspects. The three aspects are the proportional relevance of suspension in e-bikes, e-bikes with front hub motor, and e-bikes with other motors. As you've seen, the major objection to suspension is the way it saps pedal effort. The importance of this to e-bikers is often lower if the motor power means less pedal effort, and especially lower if a powerful bike is used and the rider doesn't intend very much input. Conversely, with a sporty bike like the eZee Torq which requires the rider to make a very real contribution to the effort, springing would cause a large loss of rider input, and that's why eZee wisely made this their only full size model without it. (Unfortunately they've given in to the market now with the latest Torq Trekking which has sprung forks.)
E-bikes with a front hub motor have the potential to be uncomfortable to ride. The high unsprung weight of the motor in the wheel when bounced up by poor roads has considerable force, and this can cause hard jarring shocks into the handlebars, especially bad if a rider suffers RSI or a wrist condition. Therefore, unless it's a sporty model where efficiency is important, sprung forks are advisable for the extra comfort they give.
E-bikes with motors in other positions do not need suspension as they are like road bikes in character, but as said above, much depends on the degree of rider input. With high intended rider input, avoid suspension, but if the motor is being relied on for most of the motive power, having springing doesn't really matter much.
For a second opinion on some aspects of suspension, see
this post by Ian in the main forum.
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