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I want to know more about KERS for bicycles... I have a question. What will happen if we attach the flywheel on front wheel? Does it make any difference? Please reply me.. I preparing this as my minor project of M.E 6th sem... Please provide some guidence...


2 Answers 2


I take it KERS is "Kinetic Energy Recovery System" which takes energy from your momentum and stores it temporarily, also offering a braking effect. With the intention to use this stored energy for subsequent acceleration.

A spinning flywheel on the front wheel may have significant precession effects when spun up. If the rider tries to turn left or right, and the flywheel is co-planar with the rim, then the wheel will experience a rotational force around the long axis of the bike.

In short the front wheel will try and lie on its side.

This would prove dangerous if unexpected by the rider, and the scale of the force would vary with how much rotational energy the flywheel has stored.

A flywheel on the back wheel would experience similar forces on cornering, but the back wheel follows the turn rather than being moved to create the turn.

Downsides to a rear KERS, the wheel is already busy with drive, and often has disk brakes too. Adding something inside the rear wheel will increase the weight where we don't want it, and rear wheel braking is the least useful sort of braking.

So, added weight, added complexity, added adrenaline when the bike kicks sideways, and minimal benefit.

  • 1
    A KERS would also be EXCELLENT on a rubbish truck, because they're consistently starting and stopping at each bin. Or a milk float, if you still have them.
    – Criggie
    Jan 24, 2017 at 10:08
  • 3
    You should also do a back of the envelope calculation on how much energy you can recover with KERS. If you google search for "E-bike regenerative braking" or something, you'll find people's arguments on how much energy you'd recover. The general upshot is that at best, the system will get you 5-10% of what you put in, but in a decent number of cases may cost you more energy.
    – Batman
    Jan 24, 2017 at 12:03
  • 3
    @Criggie Milk floats in the UK were traditionally electric, so regenerative braking would be very natural and not involve much extra equipment. Jan 24, 2017 at 12:58
  • 1
    I'd think that an electrical KERS system wouldn't suffer from the precession effects. Whether or not that would be practical, I don't know; I suspect the added weight would overwhelm the benefit of the recovered energy for a human-powered bike. Building one would be an interesting project though! KERS for an e-bike might be practical though...
    – rclocher3
    Jan 24, 2017 at 18:55
  • 1
    @PankajNegi maybe two opposing flywheels that spin in opposite directions ? Adds to the weight though.
    – Criggie
    Jan 24, 2017 at 19:42

As implemented by Audi, the trick isn't to depend on mass so much as speed. Both are input variables. A faster flywheel requires better bearings so the cost goes up. Also, I would expect precession to remain a factor, but if it's in near the center-of-rotation of the bicycle, then the effect would more predictable at least no?

  • Does Audi manufacture bikes now??
    – ojs
    Mar 15 at 13:12
  • @ojs to my surprise, yes audi-technology-portal.de/en/mobility-for-the-future/… But they don't have KERS - likely that part comes from the Audi F1 team's efforts to include KERS in their race cars where higher speeds would be more common.
    – Criggie
    Mar 15 at 21:27
  • This appears to be more of a response to the existing answer than a direct answer to the question. "I would expect precession to remain a factor" makes little sense in the context of the question, which doesn't mention precession. Please write answers that stand on their own and don't require incorporation of another post to answer the question.
    – DavidW
    Mar 16 at 15:04

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