To ID how much bump travel you have, lift up your front end and put a zip tie on each strut shaft. Don’t put them too high, you’re going to want your gland nut, the thing that holds the strut body into the strut housing, to push your zip tie up the shaft. Clip the end of your zip tie so a spring coil doesn’t hit it and mess up your reading.
The pic below, if you look carefully, has a zip tie that was pushed up into it’s current location when I dropped the car back down on it’s wheels.
With a zip tie on each shaft, set the car back down. This will allow the gland nuts to move the zip ties so you’ll be able to ID the rest location of the gland nuts. Don’t shove on the front corners, like one would do when corner-weighting, because that will move the zip ties. Now lift the car back up and measure the distance from the bottom of the zip tie to the bottom of the top hat…the surface that the spring pushes up on. We’ll call that # “shaft compression at rest”.
The link below is to a post where I measured how much the strut shaft will compress. If you measure the shaft length the same way I did, from gland nut to the underside of the top hat where the spring pushes on it, my #'s should work for you…23mm of shaft showing when the shaft wouldn’t compress any more. So if you have 53mm of shaft showing(gland nut to top hat), you’ve 30mm of available bump travel. Note that I heard a rumor that old struts have thicker bump stops then newer struts, but that is not confirmed. My struts are prob 10yrs old. So if you have newish struts, you might want to measure your own bumpstop thickness like I did.
Ok, so you have a # for “shaft compression at rest” and you have my 23mm # for how much shaft is sticking out when the shaft won’t compress anymore. Just subtract the two. If you’ve got 63mm of shaft sticking up, measuring it like I did, and 23mm is as low as the shaft will compress, then you have 40mm of bump travel.
I have 37mm of bump travel. I figure that with our 40-47% (depending on who you talk to) stouter springs, 37mm is a reasonable place to start.