So it sounds like your idea is to get a top hat deeper than you need and then block off the part of the travel that would put the A-arm through the chassis? That's not what you want to do. In that case you've gained 1cm of bump travel at the cost of 4cm of droop.

It looks to me like you don't need deeper top hats at all. If you really wanted that last bit, ISC makes them in whatever size you'd like so you could get a 1-2cm deep top hat. I think you're set with what you've got, though.

You should probably measure the distance between those perches and make sure it's greater than your springs' block height while you've got the chance, that looks pretty close to me.

In my case, it was a matter of the shock hitting the bumpstop before the spring (or upper arm) ran out of travel. This was with old style FM springs & NA tophats. Very jarring to hit those stops. Happened nearly every time I drove the car. Note that old FM springs were known to sag, and mine had, quite severely.

Therefore, by getting new springs and ISC tophats, I was able to get more travel before it bottomed out, keeping me off the bumpstops for most of the time. I can still hit the stops over severe bumps, but that is now pretty rare, so the ride is better.

Edit: ^^^ this harsh bottoming out is what I'm trying to avoid. I managed to fix that issue with my old Racelands, but the shocks themselves still sucked lol.

Yeah, once I started thinking about the 1.5"/4cm hats it seemed like overkill to have all that dead space above the top of the shock body. But, I pulled those thin bumpstops off and installed some random ones in the garage that are about 3cm thick to give it a little more cushion, which of course made the space between the arm and frame more like 4cm at initial contact with the shock body. So having a deeper hat would allow me to run a thicker, progressive bumpstop instead of that super thin bandaid of a bumpstop, yes?

I did have a close look at the springs and there are witness marks on two of the coils, but not on every one up the entire height of the spring, so I'm thinking it is not binding. I'm sure it'll be up in the air again soon, so I'll do some measuring then.

That was exactly my problem. I went with cut-down NA bumps, because I'm cheap, but that's the idea. Several places sell softer/progressive stops, which will also help when you do bottom out.

Longer coils, and having another inch or so of travel eliminated all but the worst of it, and I can live with that.

I just went out and bombed my favorite local canyon, looks like the thicker bumpstops cured the hard hits, but it's a little firm out back :giggle: The springs are 6" eBay specials and on the edge of binding. I can probably live with another inch of height, or half inch if I adjust a bit out out, by going with some 7" springs.

This is why bumpstops exist. If anything else runs out of travel before the shock body, you've got serious problems. You might want to also go under your car and make sure your bumpstop is actually what's stopping bumps and not your UCA.

So this bump stop is 30mm long fully compressed? That doesn't sound right. How long is it with no load? If it's engaged when the car is at rest, you basically just put 100-200# stiffer springs on your car.

Just multiply the number of coils by the wire diameter. As long as the distance between the upper and lower perches never goes below that, you're golden.

1" longer spring and 1" lower perch won't change the ride height as all.

The bumpstop is 3cm-ish free length, maybe a touch longer. It is not engaged when at rest. That drive I took has some seriously deep bumps and I didn't have any hard hits despite my best try at pissing it off. I wonder though if some of the new firmness is due to the bumpstop being engaged quickly.

Probably not, 30mm is a very small bumpstop. What was the free length of the old bumpstop? Was OEM?

Well, this is an NB Bilstein/eBay sleeve setup shoved under an NA, with that super thin bumpstop bandaid on top. So the original bumpstop is long gone.

So that picture was with no load on the bumpstop? I think it's safe to say that not having functional bumpstops was the cause of most of your problems. You still don't want a top hat deeper than 1-2mm though, even with a real bumpstop.

Also, you might want to come up that 1/2" with the longer springs. I just raised my car recently, and dear god it rides like a caddy compared to before and handles way better through the rough corners on some of the backroads around here.

I think i'm around 12.75f 13r or so if you do the hub/fender measurement. My pinch welds aren't the straightest so it's hard to measure there.

https://www.miataturbo.net/attachmen...ine=1400418501

that doesn't make sense; adding tophats would make the springs bottom out quicker. You want the shock to stop on the bumpstop, you dont want the shock to stop because the coils have binded; that will break shit.

oh you got new springs, n/m.

That pic was the skinny bandaid bumpstop, uncompressed, at about 1cm thickness, not the 3cm one I installed in a compressed state. So you can imagine how harsh it was when compressed! It is like night and day with the thicker ones in place. And yeah to the tophat, I may just have some 2cm ones made for the rear and try that out.

You know, I woke up thinking that lol. I really liked the way the 250# spring felt out back on the last setup, so I think going with that 7"/250# and raising up a half inch will be fine. Fender to hub I think I'm at about 12.5f/12.75R right now, and it's not like the roads around here are getting any better.

Exact same situation here as you can imagine. I know there were a few turns I could never "hit" even quickly, as the roughness of the road would cause my rear end to lose traction mid corner and toss me into a slide.

Now with the higher ride height i can hit those same corners much faster with ease, and roll on the throttle to slide out of them if i so choose, which is much better :rofl:

I basically adjusted the ride height so that with the car on the ground the front a arms are parallel to the ground, instead of having to slant slightly upward from the subframe to the hub. I think the suspension is working better at this geometry now.

That makes sense. I just picked up some Eibachs on fleabay, hopefully will have some hats made or ordered in the next couple of weeks.

These seems like they would be terrible. The fact that they're aluminum means the bolt isn't tack welded to the bottom side, so tightening shock mounts will be a two-man job. Fuck that.

I don't have any complaints about my ISCs other than the fact that they used standard hardware instead of metric. If the garage stars use a tack-welded metric bolt, I think they're about as good as it's gonna get.

These are the prototype test parts, the production parts will have 8mm press in studs same as the factory top hats.

I've played with different types of top hats, and one consideration is the width of the shock tube. There probably won't be any problems with thinner body shocks like Koni, but I've found that Bilstein's can top out on the top hat tube corner.

I HAVE NOT TRIED THESE UNITS OR THE ISC's. Checking for marks on the shock and top hat will confirm, but if the top hat tube is a smaller I.D. than the shock O.D., there could be issues.

Thanks for pointing that out, I have thought about similar issues with a lot of these extended hats.