Grantmac said:
On the street you shouldn't be going through maximum travel. Likewise higher rebound and possibly compression will have handling benefits compared to offroad.
Bingo.
flat tire said:
Start by installing the lighter spring.
With all due respect, that is not correct.
Consider what is the fundamental purpose of suspension: to ensure maximum grip between the tyre and road surface, while maintaining control and balance. Comfort is usually a secondary function, and is a compromise on handling.
A road bike doesn't need 200mm of travel to achieve maximum grip. Using the full 200mm of travel of a fox 40 fork is going to cause excessive geomety changes during weight transfer (and also increase weight transfer = less grip), that will negatively impact balance, response and overall control. The wheel rate (natural frequency) will be far too low. But it will be very comfortable. You will be riding in a big boat. And we will call you captain.
Consider this situation: offroad bike, long travel suspension, riding on the road, braking hard before a corner, weight transfers forwards, forks almost fully compressed, rear almost fully decompressed. Major geometry change. You progressively release the brakes, and turn in to the corner. What is the attitude of the bike ? Pitched forwards like a mofo. How long does it take to return to neutral position ? Far too long. Is this ideal for weight distribution and front/rear balance for cornering ? No.
Take a look at suspension figures for offroad vs road motorcycles. Typical offroad "race sag" (sag with rider) for rear wheel will be around 100mm. Road bike will be around 40mm. Track bike will be more like 25mm. Seeing a pattern ? Smoother surface = less suspension travel, stiffer springs. Yes, there are differences between the types of bike (geometry, weight, loads), however, the fundamental theory is the same.
Also, higher speeds, and higher braking/accelerating loads = more load transfer, which again, requires stiffer suspension.
TLDR: Everything else being equal: smaller bumps -> less suspension travel required -> stiffer springs. And stiffer springs means more rebound damping required to react to the higher forces.