I think if you look at the OE bump stop, you can get an idea if it was designed to be a 'stop' or auxiliary spring + stop. You prob know more than I so I'd like you opinion on the following. All bump stops have individual coil rings or sections, most are progressive (upside down trapezoid shaped) while others are linear (cylinder shaped, often comes with aftermarket shocks). Some OE bump stops are short, some are longer. Mazda, in general, uses pretty long ones, which I assume they intend on using it as more than just bump stops b/c they engage very early. Shorter bump stops allow the shocks to do the majority of the dampening. This topic and suspension tuning really interests me so I'd like to understand more, where I can. Thanks.
Ah, I knew this discussion gave me a sense of dj vu
http://www.mazdas247.com/forum/show...our-Bump-Stop-With-Lowering-Spring&highlight=
Don't know if I actually know more than anyone else, but I'd like to think I have a good understanding of how cars work
So while your car shouldn't need to depend on the bump stops for every day driving, every single car manufacturer HAS to model the behavior of the entire suspension system in all environments/situations possible that the suspension would experience- to do otherwise would leave the door open for unexpected failures, lawsuits etc. As an engineer, I try to account for EVERYTHING. The shape and composition of the bump stop still matters quite a bit, and depending on how the suspension guys wanted to set up their car, they could add the stop in at any point in the suspension's travel to play with the overall effective spring/damping rate that the wheel will see. I imagine that it's a lot more economical to use a cone/trapezoid shaped piece of rubber and have it ramp up the overall spring rate against the wheel as compression pushes the wheel up rather than have a shock with complex valving that would do the same thing- a chunk of rubber is a hell of a lot cheaper to mold into different shapes to give a progressive rate than a shock. I personally would prefer to do everything in the shocks and not have to worry about the bump stops, but that doesn't make large/long bump stops a bad thing at all.
I didn't touch the bump stops on my 5 when I lowered it, but on cars that I have messed with them, I replaced them completely with stiffer/shorter ones that were just meant to stop motion and not provide a progressive buildup of force into the suspension system. You go shorter to increase the amount of bump-stop free suspension travel, but too short and you're going to run into hard interference. I went too short on my Nissan Hardbody, and as a result, when I went over REALLY hard bumps/dips (like coming down from being airborne), the tops of the tires would contact the inner upper surface of the fenders. It was rare though, and I didn't worry about it too much since only the tread hit, and nothing sharp was cutting up the tires. Up until I got to the hard contact though, the travel was nice and smooth with a lot more control than hitting the factory bump stops much earlier in the suspension stroke.
So I didn't worry about the 5's bump stops since I was more than tripling (I think) the stock spring rate and providing damping to match, while definitely NOT taking out anywhere near a third of the travel. I think the way the BC coilovers are set up though, the shocks will hit their internal bump stops before engaging the factory ones anyway- but I've never checked, and I haven't noticed any abrupt transitions from locking up the suspension when I'm really flogging the car through the twisties. In any case, I should be hitting my factory bump stops less than with the OE setup.
Now if you really like to dump your car and lay it low while getting springs that aren't that much stiffer than stock, you'll definitely want to get harder and shorter bump stops to get some of your suspension travel back and keep the hard points of the car from hitting and damaging themselves. Ideally you'd measure the motion ratio of your suspension between the bump stop location(s) and the wheel, and figure out the shortest height you could get away with (while adding some back in for bump stop squish) and not have the tire stuff itself into any steel under the car during full compression.
So enough blabbing, here are some old photos illustrating what I had done on my old truck:
Rear stops:
Front stops:
So you can see how close the factory stops were in the back after lowering the truck 2" in the rear. All the shorter stop is doing is preventing hard axle to frame contact, but it took away the progressive rubber stop that helped to increase spring rate during compression. I got a lot of travel back, and on hard turns the axle would float instead of slamming against the rubber stop and locking up the axle. On the front, you can see where the factory stop wore off a clean spot on the lower control arm- even before lowering, there was only about a half inch of space between the factory stop and the LCA. The cone shape was clearly meant to act as a progressive spring. The low profile stop I bought was NOT for the location I put it in (too thin) and so was totally useless- the tire became the bump stop against the fender. Oops. The correct aftermarket front stop was quite a bit taller than mine, but still a cone shaped progressive stop, just shorter than factory and made out of stiffer polyurethane. Oh well, that truck's long gone, and I'm not lowering any more vehicles while still keeping factory spring rates, so I really don't need to worry about my bump stops that much.
Hope that's not too wordy.
