I have since checked the Donvel site; it is a different product than Brock's. The Donvel setup acts more to stabilize than to soften the ride like Brock's does.
On Brock's setup the rear of the front spring is disconnected and an airspring is installed between the rear of the spring and the frame, thereby relying on the airspring to fully support the load and apparently really smoothing the ride.
The Donvel system on the other hand is installed WITHOUT disconnecting any part of the existing spring, but instead uses an airspring to help stabilize the ride rather than soften it.
Each company is attacking a different issue:
Donvel- instability
Brock's- Rough or stiff ride
I hope this helps to explain things a little. It looks like either product should do what it is designed to do.
Gary
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