Bilstien Shock Discussion


Hi Folks,

I’ve been seeing a lot of discussion lately about our shocks, the lack of availability, and ideas to change. This is a thread to get the ideas and issues going. After the new spring change, I think it would be a good idea that we have a healthy discussion before any drastic measures are taken.

What we learned in NorCal on the first weekend with new springs:
The first thing we discovered is that matching ride height from the previous setup was much too low. We saw bottoming out on both the front and the rear. The rear height adjusters were hitting the white spring retainer cones. Check your cones to see if you have marks from the red adjuster screw.

We then learned that even with ride heights an inch higher than previous, we were very short on shock travel. We used zip ties on the struts to help determine that we are spending most of our time riding on the bump stops. We also did the test on a car with the old setup and discovered we’ve been riding bump stops the entire time. In the old setup, it is not as noticeable, and it looks as though “setting the car” in a corner meant leaning onto the bump stops. It wasn’t good, but the system worked together, and we raced our trashcans full of water. :grin:
With the new setup we have the same issue, although with the different spring rates, it is much more noticeable, and causing much more instability.
We have about 1/2"-1" of shock travel at most before hitting the internal bump stops.
Has anyone looked into there shock travel and noticed the same thing?

We talked about possible solutions to the shock travel issue.
1- The cheap fix would be mandating a minimum ride height, but the cars would have to be back to stock height to possibly get off the bump stops.

2- New shock and hacking up the shock tube. This would be a good solution, but not in a spec class. We would need new, shorter bodied shocks, and shortening the shock tube by 2" or so. This would be a very expensive solution, especially for those of us who can’t do our own labor. This could mean people need to spend several thousand dollars to get the setup done. This is a low budget spec class, and a change this costly could see many people leave the series. It would also be much more difficult for newbie builds.

3- Working with someone to create a camber plate with the bearing on top of the strut tower, giving us the extra 1.5" of travel the plate takes up now under the shock tower. This may be the best solution as far as cost and ease go, if we want to retain a lower ride height. This idea would need some help from vendors to create something that works.

There may be other solutions to this problem, I’d love to see what everyone thinks. Has anyone else noticed the shock travel issue?

This is just some of the discovery we’ve had after our first weekend, so I’m sure there’s much more we can learn over time. My biggest is worry from here is rule creep and cost increases, as I know many of us run SpecE30 because it is a simple, “affordable”, series. The last thing we need is more adjustment in the car, causing a ton of expensive testing. The best part about the E30 is not having to turn a wrench on it. Pull it off the trailer and go racing. I really do like the new spring setup. It is a lot more predictable, until the shock bottoms out. If we can fix that issue affordably, it could be perfect.

Nick Thiemann
#3 FNTECH SpecE30
Nasa Norcal


But does number 2 definitely require shortening the strut body? My understanding is that the Koni Yellows are either shorter, or have different internals that allow them to run lower before hitting the bump stop.


Also, I don’t see number 3 really saving costs, based on the very thing mentioned in number 2. Those that can’t do the work will have to pay someone to swap camber plates, if a company could/would even develop a very specific one off part. Nobody else in the e30 world is asking for a special camber plate, so it would likely be a limited run part, and likely not inexpensive. So already expensive camber plates get even more expensive, and then what happens a few years down the road and someone wants to buy another set and they aren’t available? We can’t depend on custom parts.


Idea #2- If that is the case, that could work. Koni Yellows did great for 944 Spec, and the adjustability was very limited, which would be okay for the class. It looks as though there just isn’t enough space between the top off the shock tube and the spring perch, minus the depth of the bump stop, at our current ride height. We have to find a way to grow that space in order to get more shock travel. The machining and welding is my main concern. Is there somewhere we can confirm details on the Koni’s?

#3 If someone like GC where to make a plate, it may not take a lot of design or parts changes. We were looking at a new plate, and it may be possible to just flip their current plate, with a few adjustments on their end. If the plate cost ~$350-400, that would be much cheaper than new shocks all around. It would be the same thing as them making a special spring kit for us. The spring kit for newbies would be more expensive, but include the plates. It’s also something that most garage DIY guys can install, versus, machining/welding/removing ball joints.

Keep the ideas coming!


I think we’re missing something. Back when I looked into coilovers for us a couple years ago, I had careful conversations with Bilstein re. their struts being compatible with coilovers. They expressed no reservations re. the range of movement of their strut in our coilover application.

It’s hard for me to buy the idea that we’ve been routinely on the strut’s bumpstop all these years. I’ve been doing this a long time. I’m not a gifted driver so my “feel” for what is going on is not that terrific. But I think that if I’d been routinely hitting the front bump stops, I’d know it.

Our front springs are now ~45% more stout. So a given whack makes them compress 45% less distace than last week with the old springs. 45% is a lot. So I’m struggling to figure out a theory where suddenly we’re pushing the strut rod as deep as we always have. If you look at old pics of the car heeled over in a turn, vs with the new springs, the car heels over only about half as much. The strut rod should be pushing less deep into the strut body.

I’ll try to set up an experiment tonight where I see how far up I can push a front wheel.


I have yet to test this, but one bit of warning about rising the bearing point of the camber plate.

If the point is too high, you will end up with tires bottoming out inside the wheel well. I would trade for bump-stop stops any day. You will lock both on hard cornering and hard braking.

From past experience, some cars are just designed in a way where shock travel is already optimal and any more you would just bottom the wheel out. I would not be able to speak for the E30, I forgot to test this while installing the kit this sunday.

For the rear, we could add bump stops to the shock, but I don’t know how strong are our shock towers, but that is a easy and convectional place. Also could we be allowed to cut 1 in off the adjuster? I adjusted to the bottom and the car is sitting higher then the H&R. Most adjustments will be a adding a little I assume.


We thought this was only an issue on the new setup, since the top hat on the old system places the top of the spring above the bottom edge of the camber plate, giving us back the 1" of travel. That’s why we also did the zip tie test on the old system. I think the bump stop “spring rate” was fairly similar to the old progressive spring rate, which made it much less noticeable. We would have to test if there is tire clearance, but I think that wouldn’t be an issue, especially if the car is raised up like it currently seems to be without completely removing the old spring perch weld and moving the collar down an inch or two.

Ranger- I’m as surprised as you are in what we found. I’m very intrigued to see what your experiments turn up. If the car is sitting on its wheels, I’d love to see what kind of travel is left on your car.
Here’s what we did:
We put a zip tie around the shock, and then set the car down. That showed us where it sat sitting still. There was very little travel left before hitting the bump stop. Then we sent out the cars around the track to see where they ended up. The zip ties either ended up around the very top of the shock, or blown completely off. We did this for both setups. The new setup seems to have to be about 1" above the previous ride height to get the same amount of shock travel.


Slight hitch in that logic:


You do understand that picture means nothing regarding spring rate, right?


Nick (@YetiPaws) , to clarify, you identifying bumpstop position by removing the spring, and letting the suspension settle onto the bump stops with a ziptie marking the max compressed position? Then reinstalling the spring and checking the gap to the ziptie?


To be honest I’m not quite sure. We pushed a shock down until we felt the bump stop. From what I could tell, it looks like we only have 1-2” of total travel, including the bumpstop. I’m just a diy guy tinkering in my garage. This was a discovery we found trying to work out ride heights during the weekend. Folks much smarter than I figured this out. I’m just trying to see what the rest of the class thinks, and what we can do for a solution.


Well, get the smarter guys to come here and join the conversation. :wink:


I think the point is that just because the springs are stiffer doesn’t mean they won’t bottom out. The new springs are shorter, so it’s not an apples-to-apples comparison.


Bottom line up front. Raise your front end.

Details. Using a lift and then setting the car down on a stack of boards under a wheel I simulated a front tire under different degrees of compression. I managed to do this w/o crashing the car down or encouraging the car to roll out thru the closed garage door. I took a bunch of measurements and pics. I made drawings and spent an entire beer just staring at it.

A longer spring wouldn’t help. We’re already pretty close to the bottom of the adjuster range.

The most significant thing I found is that my front end had drooped 10mm. I didn’t check my rear. So altho I thought my front was at the same height as it used to be, in reality, it was a helova lot lower. Shock travel is totally a matter of how high we have our front end. So the fact that my front end was so low, significantly limited my shock travel. Our last race weekend was at Roebling Road, which was probably fine with the limited shock travel of my car being too low. But first chance I get, I’m gonna raise the car up 10mm and regain the shock travel that I lost.

Keep in mind that with our new springs 40-47% (depending on who you talk to) more stout, it takes a lot more bump to compress the shock.

Certainly the old top hat design allowed a little more shock travel, call it 5mm. <later edit…this turned out to be wrong. Old top hat had to be pushed down so the net was that “misalignment spacer” users gained 2.5mm of bump travel. If you didn’t use that spacer, you gained prob 5mm of bump travel> The fact that the spring is taller was meaningless because we all got baselines from our car’s height before the spring change. The old springs were a helova lot weaker. So as hard as it is for me to accept it, there’s no escaping the conclusion that we were banging the shit out of our bumpstops.

I think that we’ll be banging on those bumpstops a lot less now, as long as we don’t put the front of the car too low.

Tonight I talked to a very experienced SpecE30 racer. He told me about a guy, some years ago, that was highly successful at the national level. And that highly successful guy swore, later, that his secret was that he had bent the rules a bit to raise his front end. I bet that he was the only guy that figured out that the rest of us were banging the shit out of our strut bumpstops when the car was heeled over in turns.


Sure. I was taking issue with the “x percent stiffer meaning it travels y percent less total distance”. When both the spring rate and the spring length are different, my contention is that x is not equal to y. If I’m wrong about that, I’m happy to be shown the error of my ways.


@Ranger what do you mean by this? Are you talking about settling from when you first installed the springs? same height = adjuster height?

And to no one in particular:
-if the top of the threaded portion of the strut is at the same height as it was before the spring change at 1G, the relation to the bumpstop is the same as before. However in my Ireland camber plate setup there are actually more threads above the top nut (which is right on top of the bearing of the camber plate, so the nut is a fixed relationship to the ground) than before with the car body at the same height to the ground as before, so overall the strut is actually slightly more extended relative to the ground than before (~5mm). This is due to stackup height change above the shoulder on the shaft of the shock and not needing as much spacing for the OE top hat to clear the camber plate.
-no one has said anything about bottoming the new springs going into coil bind
-as I mentioned already, I believe taking the spring off is the easiest way to accurately know where the bump stop is. I did that for flaring fenders on a car that was going to run 245 wide tires to guarantee clearances when the steering wheel was turned.


@jlucas Adjuster height didn’t change. Springs sagged after initial install. Anyone that hasn’t installed their springs yet, I’d set up the front at least 10mm high. Then the front will, over a couple days(?) to their starting height.

That story about the dude that was kicking ass because he raised his front end is sticking in my mind. It totally fits this new understanding that with the old springs we were on our strut bumpstops all the time. I’m going to raise my front end an additional 5-10mm, and I’m not going to tell anyone. A couple months from now you’ll be hearing “Jesus christ how did Gress get so fast all the sudden”. Don’t tell anyone.

This may be obvious to everyone, but just in case…changing front end height changes steering geometry. Sitting here at work trying to imagine the linkage geometry…I think that raising the car will cause toe-out, and vice versa. This is front only. I wouldn’t worry about rear tow and ride height.

Re. your Ireland camber plates. That’s interesting. I have really old GC camber plates. The top of my strut shafts are in the same place. Maybe that’s why, apparently, those with GC camber plates are reporting the problem disproportionately.

Re. front coil bind. That’s not happening. There’s tons of remaining space for coil compression once the strut bottoms out.

I’ve not yet looked at the rear.


Btw, it’s cool to be talking to you California types. We don’t do enough of that sort of thing.


After the install my mechanic called me about this.

He used grease to measure shock travel. The bottom lines are the car sitting and the top line is under breaking. There is very little travel left for bumps. We are heading to Sebring this weekend. Turn 17 should be interesting.


Yes Eric, It’ll definitely be interesting to see. I’m anticipating almost everyone raising ride height this weekend based on this conversation. Let’s see how it goes. I believe we’re in a good position to provide massive testing feedback to the group after this weekend.