How eMTB Suspension Kinematics and Pivot Placement Are Different (And How They’re Not)

Images courtesy of Giant Bicycles.

Riders who are excited by electric assistance know all about the differences between battery and muscle-powered mountain bikes. Some standout characteristics are power output, weight, drivetrain and tire wear, traction, larger chainrings, and a notably longer chainstay measurement. How do those variables affect suspension kinematics and pivot placement? We asked Giant Bicycles engineer Fedde Taekema, who was hired four years ago specifically to work on e-bikes, and he was happy to clear up some questions.

First up, there’s a motor where a lot of pivots might typically be, and the engine body takes up some space where the shock would normally mount. Engineers also strive to fit a water bottle inside every front triangle and keep the seat tube short with a deep dropper-insertion length so riders can size up their frames if they like and still run the dropper travel they’re accustomed to. Some frames also need space for a Fox Live Valve switchboard and a range-extender battery inside the front triangle.

That’s a load of parameters to cram into a small space, and Taekema said this is likely the most challenging factor. The space is so tight that on some frames it’s not possible to fit a shock with an external reservoir (piggyback) and a water bottle — even given Giant’s vertical shock orientation and the use of shorter Trunnion-mount shocks. Liv and Giant’s Maestro suspension system uses a pair of co-rotating links, placing the lower shock mount on the same axis point as the forward-most pivot of the lower suspension link, and this rotating point is typically quite low on their bikes.

With newer e-bikes like the Trance X Advanced E+ the lower shock mount and pivot have to be a little higher, and the engineers pay extra attention to ensure the bike still rides the way you expect from a Liv or Giant frame. Taekema said that their main focus with e-bikes is to make them ride as similarly as possible to their “acoustic” platforms. To that tune, they conduct all of their acoustic MTB and e-bike testing in the same place, learning what the electrified platforms need in order to perform with similar pop and plow that their lighter counterparts offer.

We had a hunch that the heavier sprung mass of e-bikes would require higher anti-rise and anti-squat values than that of the muscle-powered frames that sometimes weigh half as much. While those values do differ slightly from Giant’s muscle machines, the variation isn’t super noteworthy. Additionally, when we asked Taekema if the motor’s torque affects anti-rise he said, “not so much. It adds power, but it’s quite a constant power. Our motor system is programmed to feel natural, so the power is also going up and down, but it’s [the anti-rise value] quite similar.”

Despite the massive 473mm chainstay length on the Trance X Advanced E+, compared to the 439mm stays on the analog Trance X, the bikes’ suspension also has a similar leverage curve. We would have guessed that the longer lever might require additional resistance to offer a similar ride character, but those assumptions were thwarted once more. Giant wants riders to be able to fit up to 2.6″ tires behind the motor and lower link, sliding that rear axle out significantly. The Trance e-bike has 20mm of additional travel out back to play with, and some of that travel helps support the longer lever while keeping this hefty steed stable. On the leverage curve specifically, he notes “maybe one is a little bit steeper than the other, but overall it’s pretty similar. That also has to do with the Maestro layout.”

Surprisingly, Taekema also mentioned that the e-bike shock tune isn’t all that far off from a muscle-powered tune. We didn’t ask for the secret ingredients, but he said that the shim stacks aren’t wildly different from one another. The battery bikes receive a little firmer compression tune and different volume spacers to deal with their weight, and that’s about it.

Often when we chase a story that leads to a null hypothesis like this one it will be tossed in the bin, but the fact that e-bike suspension kinematics are not significantly different from muscle-bikes for Liv/Giant is intriguing in itself.

Do you have questions about suspension that you would like us to research and report on? Please ask them in the comments section.