I was interested in the idea of the larger Rancho tube but wanted a shock that didn't require driver input. Crawling under there was not for me nor the expense & added complexity of in cab controls, just seems like a waste of money for my needs.
I spoke to Bilstein reps both on the phone and at the 08 SEMA show in Vegas asking specific questions about the difference between the 4600 and 5100. We discussed my use & application- stock truck, unloaded or 2000 lbs in the bed towing, 285 tires on 17" wheels.
5100's will fit on a none lifted Dodge however the valving in the 4600's are valved specifically for the application, both loaded and unloaded where the 5100's are a more universal shock designed for mild lifts such as 2" leveling kits, they just happen to work also on non lifted trucks.
Nothing wrong with the 5100's just not the proper choice for my use which was confirmed by the folks manufacturing & selling both lines.
To sum it up-
5100,s are longer for lifted applications, universally valved for spirited off-road use on trucks that see little work duty (weight in the bed) and to control the additional weight of larger tires & wheels such as 35's running on 20's.
4600's are for non lifted applications specifically valved for the Dodge in both unloaded and loaded daily on road driving. Off road they function well in non spirited driving. 1 or 2 sizes larger on the tires is a none issue.
Either one works well, while one has the ability to out shine the other when it is being used as intended.
Did you see what brods wrote:
having to settle for what a shock engineer thinks is the best compromise for a broad range of vehicle configurations and driving styles
and he is right, thats the way a 5100 is valved, only a bad thing when operated out its intended window otherwise it gets good reviews.