How does BMW do this? Q about ESA II

[dduelin]

From what I have read certain 2010 BMW models that have the Electronic Suspension Adjustment II option ( ESA II ) offer adjustable spring rate in addition to adjustable preload and damping that the prior ESA package included. These adjustments can be made on the fly or when stopped but without having to dismount and manually turn an adjuster device.

How do they change spring rate without changing the spring itself? I thought spring rate was a result of choice of metal characteristics, diameter of wire, and coil pitch and is essentially fixed when the spring is manufactured. I would like to know more.

 

[TPadden]

How do they change spring rate without changing the spring itself?....

On previous suspension units, adjusting the spring rate -- thus providing equal handling no matter the weight carried by the motorcycle -- was only possible by stripping down a shock and replacing its spring for one of a different weight. BMW gets around this by adding a polyurethane bushing to the top of the spring, meaning suspension movement basically passes through two springs; the actual spring and the bushing. By altering the rate at which that polyurethane compresses, BMW is able to alter the effective overall spring rate.

Of course, it's not that simple. In order to precisely control the rate at which the special polyurethane material -- called 'Elastogran' -- compresses and expands, BMW contains it within a sleeve located around the shock's damper unit. An inner collar slides up and down in the space the Elastogran expands into under compression, reducing that space to make the force required to compress it greater or increasing the space to make the required force less. That collar is actuated by ESA II's computer and moves through three positions based on settings chosen by the rider.

Those three settings are: "Solo," "Solo with Luggage" and "With Passenger and Luggage." All three are represented by symbols in the instrument panel rather than awkward phrases and are only adjustable while the machine is stationary. These settings also control the amount of preload, or the amount of force required to initiate spring compression, which effectively alters the ride height.

http://hellforleathermagazine.com/2008/10/details-bmw-esa-ii-electronica.html

 

[dduelin]

Thanks Tom. That is quite understandable.

 

[BamaRider]

And I can vouch the system works quite well. Adjusting on the fly is a good thing and comes in handy. A great option.

 

[cali_rider]

On the BMW forums, ESA gets mixed reviews. It works well when your weight and prefferences match the system. However, if you dont match up well to it then it becomes a PITA. Overall, it seems like most guys on the BMW site would prefer non ESA but with Ohlins. I have used it and its pretty neat but in reality, to me suspension is a set and forget, unless I add luggage. (I ride solo 100% so the 2 up thing isnt an issue)

 

[BamaRider]

On the BMW forums, ESA gets mixed reviews. It works well when your weight and prefferences match the system. However, if you dont match up well to it then it becomes a PITA. Overall, it seems like most guys on the BMW site would prefer non ESA but with Ohlins. I have used it and its pretty neat but in reality, to me suspension is a set and forget, unless I add luggage. (I ride solo 100% so the 2 up thing isnt an issue)

Could it be its set and forget cause it's too much trouble to adust the shocks as the terrain changes? LOL