Bid Change Speed is the limit of bid adjustments (increase or decrease) on your keyword or targets to reach your best bid.
The default value for bid change speed is 20%. Why? ZonTools has factored in that there are delays in syncing with Amazon. This value ensures that before we reach your best bid/optimal bid, we have enough and the most accurate data from Amazon.
Bid Change Speed is a rule/threshold that guides the system to know how much more than the average you want to add to your bid in order to maintain your average.
Bid Change Speed is a rule/threshold that guides the system to know how much needs to be added to your bid to maintain your average cost per click (CPC).
If you think that $1 is a good bid for a keyword that is performing the way you want and is reaching the target ACoS you want.
If your bid is $2 with an average CPC of $1, and we adjust the bid to $1, the resulting new average will be 0.7.
If we keep updating your bid based on the average, the next average is going to be always below 0.7, or most probably around 0.5. Eventually, this will drive your bid to 0.
Driving the bid to 0 is not a good idea because your products lose on: