I am about to buy new springs and shocks, but before doing so want to fill a glaring gap in my knowledge re shock selection.
IIUC I frequently read discussion of shock travel and the ideal being the same up and down travel. But, to be completely honest I am not really sure what is meant by this. Assuming I install my new springs and set the bump stops at a length to just stop the tyre crashing into the wheel arch (is that bit correct?) then the amount of compression in the shock should be greater than the available compression in the spring, other wise the shock will be the limiting factor. Correct? If I test what happens to the passenger side of the axle when the driver side side is compressed to the point it is stopped going further by the bump stop that will tell me how much extension there will be in my shock. Still OK? I can check if the shock will be long enough for my set up in advance based on the expected amount of lift from the longer springs, but other than this what am I trying to achieve to get the shock to have the same up and down travel?
Sorry if I am totally confused, but I don't want to order the wrong parts and want to make sure I have a decent chance of my set up working before buying.
Thanks.
You’re on the right track. I just did this yesterday. This will be a long post, but I can offer my experience. Best thing to do is carefully cycle the suspension up/down with the shocks and springs removed. This can be done using floor jacks and jack stands. You’ll want to determine the limit of up travel and the limit of down travel. Be careful not to over extend your brake lines in the front. Be careful not to damage your rear driveshaft if it binds during droop (go slow and check things).
This testing also allowed me to see when the coils would fall out during droop, and measure what coil length that was happening at. If you’re not already using the coils you want, just measure the distance from coil bucket to coil bucket once you’ve determined full droop. That will give you an idea of how long your new coil needs to be without falling out at full droop.
The up travel will usually be limited by your shocks’ compressed length (unless you have huge tires on a small lift or something, in which case the tires might touch the fenders first).
Determine the limit of up travel by cycling the axle up, measure the distance between the lower shock mount and the upper shock mount. Write it down.
Determine the limit of down travel by cycling the axle down. Measure the distance between shock mounts. Write it down.
If you want to, you can also articulate each side of the axle up while keeping the opposite side at full droop, and retake your measurements. This would be ideal and also allow you to see when the tires would contact the fenders in that scenario.
Use these measurements to determine which shock can maximize your up and down travel. Look through the chart at the compressed and extended lengths of the shocks available.
Ideally you would have the new springs installed before making the decision on shocks. This way you can measure the length of the shocks at ride height. This is how you’ll know what shock will best fit the goal of 50/50 travel, up and down.
At ride height, measure the distance from the lower shock mount to the upper shock mount. The length of the shock at ride height minus the compressed length= available up travel (i.e. how much can the shock compress starting from ride height?)
The extended length of the shock minus the length of the shock at ride height = available down travel (i.e. how much can the shock extend starting from ride height)
You want those as close to equal up/down as possible, with a slight bias towards more up travel if given multiple options. It will ride better that way.
If you don’t know exactly what your ride height will be with the new springs vs the height of your Jeep now… you’ll have to make an educated guess. Ideally, you would have the new springs installed first so you could measure from the exact ride height. If that’s not feasible, you can still get good results if you estimate the new ride height accurately.
Bump stops: set according to whatever the limiting factor is. Most likely it will be shock compressed length.
Tips when cycling your suspension: If your Jeep has stock front lower control arms the down travel will likely be limited by these binding at full droop. If you have a stock rear driveshaft (non Rubicon, no SYE) then your droop will be limited by the driveshaft u joint binding. You can check this by visual inspection and by rotating the driveshaft by hand with transmission in neutral. BE CAREFUL going under the Jeep while it’s raised high in the air on jack stands. Make sure the tires on the ground are chocked. I also like to put a large wheel/tire under the vehicle as a backup if possible, in case it falls for any reason. Safety is #1. I have to say it (for anyone reading this). In the rear your e brake cables and the stock lower control arms would likely be the next things to start binding during droop. The rear panhard bar (trac bar) might contact the exhaust pipe. I do not know if the stock rear sway bar end-links will limit droop before these other things happen. Mine are not stock.
Hope this helps. It’s difficult to explain without visual aid, but not terribly difficult to execute.
