Although I am sure everyone is tired of talking about rear shocks I would like to throw out a couple thoughts and questions to the experts who will hopefully correct any misconceptions. This relates to a Roadster.
I do not know what it is about the stock rear shocks but they sure doe not instill confidence in me on a bumpy or washboard road.
I would think progressive spring rates front and rear should provide a smother more stable ride.
The valving on the Progressive rear shocks seem to be a big step up from stock and they come with a progressive spring rate.
The Progressive 444 is available in a couple of different lengths 11.5” – 12” – 12.5” - 13”.
Stock height being 12.5”
Changing the rear and or front height will change the bike's geometry. Wheelbase, rake angle, ground clearance, etc. and thus handling.
I believe Claviger has suggested that using a smaller front tire and lowering the front makes the bike more responsive. I would suspect that raising the rear will have a similar effect to geometry but also increase ground clearance. This has been suggested by Ishrub.
Further reading suggests that this will make the bike more responsive but less stable.
I would guess that Triumph would lean toward making the Rocket 3 more stable than responsive so adding a 1/2” rear height should be fine.
Being tall and around 200 lbs. and only having a passenger around 10% of the time the standard spring rate with the 13” shocks should work well. No problem flat footing for me. I could preload the rear for the passenger.
As a side note the Rocket seems to be sensitive to small changes, Just adding a few pounds pressure to front tire to help with low speed handling made a big difference.
Rick