We often receive the questions, "Should I go with a 12" or 13" shock?" or, "I want to maintain my stock ride height, which length shock do you recommend?"
As far as the first question, we generally steer people to the 13" shock. Why? You're basically getting more shock (travel) for the same amount of money, and your seat height isn't going to change a whole lot. Our 12" shocks are designed to be ridden with one 1/2" of sag, meaning they will sit at an 11.5" bolt to bolt length when the sag has been set properly for the rider/passenger and the rider/passenger is sitting on the bike. Our 13" and shocks are designed to be ridden with 1" of sag, meaning our 13" shocks will measure 12" bolt to bolt when the rider/passenger is sitting on the bike and they are setup properly.
What does this mean? Our 12" shocks are only going to sit about 1/2" lower than our 13" shocks when installed and adjusted properly.
Because a stock shock doesn't have very much sag or "give" when your sitting on the bike, your 12" shock may not be sitting much lower than 12" when your weight is on the bike. For example, you may have a 12" shock on your bike, and that shock may only sag 1/4" or not sag at all meaning, with you sitting on the bike, you may have an 11.75" or 12" bolt to bolt measurement. In this scenario, if you were to go with our 13" shock, your seat height would remain relatively unchanged, once you have adjusted the sag to 1" and you would ultimately end up with more travel.
This leads us to the second question of "I want to maintain my stock ride height, which length shock do you recommend?" We usually receive this question from our shorter customers, or customers who just don't want to increase their seat height at all, and want a shock that is going to sit them as close as possible to their stock ride height. In these situations, the best thing that can be done, is to measure the shocks your currently have on your bike between the upper and lower mounting bolts with with your weight sitting on the bike. You can then compare the measurement you get to either 11.5" or 12", which is target shock length (after setting sag) for our shocks with them properly adjusted and your weight on the bike.
Keep in mind their are some FL Touring models out there that do come stock with a 13" shock, and in most cases you will want to run our 13" shock on these models.
In conclusion, if you have a stock 12" shock and can tolerate, at the most, about 1/2" of seat height increase, we recommend you go with the 13" shock to get the most bang for your buck!