Bilstien Shock Discussion


If he set the car at it’s old height, I would raise the front (and probably the rear) by 10mm to compensate for sag. I think 10mm is about 2 turns of the collar. I’m gonna raise mine at least an additional 5mm.

Have fun at Sebring. Bummer I missed you guys at East Coast Champs.


How sure are you that the old springs were progressive? I did a bunch of research on springs back when I tried to start a debate on coilovers some years ago. I just went back thru my notes and thru the original forum thread. Then I went to H&R’s website to see how their marketing dept talked up their springs. No mention of progressive anywhere.

I would think that the stouter nature of our new front springs would make the transition to the bumps more gentle, shock travel being the same. But shock travel isn’t the same because intentionally or not, we’re lowering our cars.

In my experiments last night, I measured 20mm of available shock travel before “I think” I was hitting the bump stops. Then I realized that spring sag had really hosed me. Measuring my car height the same way I did prior to the spring install showed that the springs had sagged 10mm. So I’d gone from 30mm to 20mm, fully a 1/3rd of my available travel, just due to sag. Obviously, with our much stouter springs, we don’t need as much spring travel as we used to. So we’re fixing a problem that we’d learned to “live with”, because we didn’t understand it (hitting the bumpstops) was happening, nor did we realize the cause. I’m thinking that this is all good news. We’ve finally ID’d a problem that has caused our cars to suck, and because our height is now adjustable, we now can control of this problem.

Consider that. The same week we figure out a long standing problem, we are also handed the tools to fix it. That’s pretty cool.

I’m gonna raise my front end prob another 5mm and I’m going to use the zip tie trick that you guys mentioned, and for the first time ever, I’m gonna stay off my bumpstops.

It occurs to me that us figuring this out and getting our cars off of the bumpstops ought to significantly reduce the pounding our front ends take. That’s cool. Same for the rear because no more bound up springs.


Fixed it.


I realize that my experience isn’t as an SE30 racer, only as an ITS car now, but I do run the same spring rates and the same kit as you all do.

E30’s do have a problem running too low. There is an optimal ride height which is optimal due to suspension geometry. I know people will disagree, but I know this by talking to an Ex-Firehawk Series car builder and racer and a guy named Ben who’s a friend of mine.

It reduced lap times enough to realize instantly this was the correct analysis .


I’m glad to see I’m not crazy. Hopefully this will be solvable with raising the ride heights and going racing. It would be great to learn how much travel we actually need on track with the new setup. I’ve heard the same rumor about raising ride height on the old setup for a nationals win… It would be great if we could pool our collective brains to figure out the perfect ride height/shock travel. I like the idea that we can all work together to set up our cars, and make it the best driver to win. That’s what makes a spec class great!

@Ranger As for the old springs being progressive, that’s just what I’ve heard from other people, so I have no data whatsoever to back that up. Were you able to determine how tall the bump stop is? It would be great if someone had a blown shock they could take apart and measure to be sure. Then we can measure using zip ties on track how much travel we need, telling us how high we have to be before hitting the bump stop. Hopefully the guys going to Sebring will be able to gather some data for the collective…

Rear: the only issue dictating ride height we saw was if the red height adjuster on the bottom was hitting the white spring retaining cone on the top, then it was setup too low. I went from 2 full turns from bottom and it hitting, to 4 full turns and no more bottoming out. This could also be solved by a skinnier, longer top cone, that would go inside the red adjuster instead of hitting it. Beyond that, I think it’s just finding a height that works well with the front to corner balance the car.

Hopefully some more NorCal peeps chime in. I moved to this region a couple years ago and found that they take things much more serious than the Rocky Mountain folk. I’ve been trying to install a little Colorado laid back fun attitude in everyone, and hopefully bridge some gaps between regions. I’m really looking forward to meeting y’all at COTA. I’ll bring the Whiskey to match your Tequila!

@kgobey- Would happen to have any ride height or shock travel data you would be willing to share with us to give us a idea where to start?


I think the bumpstop limits the last ~23mm of strut travel. It was a little tricky to get the calipers in place to measure. That # is within 2mm of what I was seeing. The pics below show how I was using a lift and setting the car down with a corner on a stack of wood in order to replicate full compression of the strut. The second pic shows what the spring and shock look like at full compression. As you can see, the spring would be perfectly happy to compress more. Eyeball hard the amount of strut still visible. That’s the 23mm.

I’ll try to look at the rear tonight. I’m in the middle of a work crisis so doing long hours. Last night I had to tear out the ceiling of the kitchen because a 2nd floor bathtub was suddenly pouring water thru the ceiling. Sigh.

Re. COTA. It is my responsibility that the COTA is a total blast for SpecE30. Any more fun, and we’d end up in jail.

Setting bump travel

Scott does your wheel touch anywhere? How much space is left?

About the old spring being progressive. Look at the coils. The distance between the coil change with height. A linear spring would have the same distance, just like our new spring.


I’d estimate 2" of space at the bumpstop. I didn’t focus on that issue, and I had the wheel turned sharply the whole time so I could see behind it.

I’m not too worried about tire-fender clearance. We had to be hitting the bumps before, so the only folks using a bit more of the available clearance are the non-GC camber plate owners that ended up with a couple mm more available bump travel before hitting the bumpstop. So their wheel can go a little higher.


Certainly appreciate the info here. I think that sharing all this information between groups and with everyone will assuage the fear that a few (maybe “some” or even "many) of us had that changing the suspension would lead to real advantage to those with time/desire/$ to tinker, test and tune. I’d love to do that but am busy concentrating on getting my driving to the point where any of this will matter. Again, much thanks to those doing this testing and sharing.


Sim racing can do that for you. You can practice at home as much as you want!


Agreed, but a race car on track is better than a sim set-up in our home and I was offered a choice… :wink:


Ok, so I looked hard at the rear. Bottom line, I think we’re fine. We’ve got more travel than we used to.

Details. With the car at rest, I measured the distance from rear spring perch to hat 5.25". Then I used the lift and some some stuff to jack a rear wheel 14" up into the air. Much to the surprise of the car. See pic. Then I got under and looked at spring compression and the distance was 4.25" so 1" of spring compression. The spring seemed happy to compress a bit more if I put my weight on the fender. See pic.

This was at my left rear. The adjuster shows 2 threads from the bottom.

With the corner being compressed, the narroww tip of the white plastic centering piece was a little bit into the red threaded tube. I figure that the spring would need to compress >1" more before there’d be any mark on the white plastic centering piece, but lateral movement could certainly bang the threaded tube into the centering piece prematurely. It looks to me like there is a second inch of available compression before the white centering piece went deep enough into the red threaded tube before the white centering piece got jammed hard.

At 1" of compression plenty of space remained between coils. I’d guess that the white plastic retainer would bang hard into the red threaded tube before the coils bound.

Recall that the H&R Race springs were almost bound up at rest. Can someone that still has the old springs lift up a corner and see how far apart spring perch and tower are when the springs bind up? I looked up old posts and found #'s all over the map. I recall about 1-1.5" of travel before the H&R Race springs bound.

Looking at the #'s to compare spring compression before and after. Depending on what #'s you use, our rear springs are 14-19% more stiff. Lets say 15%. Lets say our Race springs had 1.5" of travel before binding. Because our new springs are 15% stiffer, the bump that caused 1.5" of compression last month would cause 1.275" today. I have a helova lot more travel then 1.275" available. I bet I have 2" easy. So a bump that would have completely bound up the old springs would prob only take up 60% of the available travel of the new springs. For rear bump travel, we are clearly much better off with the new springs.

Sagging. I’m a little fuzzy on this. I’d be interested to see other people’s #'s. I think I’m looking at about 5mm of sag. That is to say, I put my springs on, carefully set my car to it’s original height, came back a week later to find that the car was now lower. It’s hard to ID an exact # tho, because after installing my springs, I dicked around in the rear fixing corner weights. My estimate of the situation is that I had to raise my rear end 5mm to get back to old height.

Anyone else have #'s on rear sag?

Pic shows how I shoved the rear end up. Even with 14" of lift, I only consumed about half of the available travel (1 of >2").

Pic of spring compressed 1" due to corner sitting on 14" of stuff.


@bedmonds, is that the “RA Turn 3 gators” package?


Victor Tate wrote something in fb re. this issue that I though would be best replied here. Saying anything useful on fb is such a waste of time because in a couple hours it’s gone forever. Victor suggested that this is a spring length issue.

I don’t think it’s spring length. It’s hard to puzzle thru the geometry of this with someone because the both of us really need to be looking at a front strut. One should take a pic of their front strut/spring assembly with the car at rest, and then do it again when the front corner is compressed. The limiting factor is actually the height of the strut housing. In a perfect world, it would be about 2-3"" shorter.

Take a look at the front strut pics in the forum thread. That’s the only way this is going to make any sense.

On top of the front strut is the strut retention collar, . The strut shaft emerges from that and goes up to the spring top hat. But because our cars are lowered so much, the strut shaft doesn’t poke up very far. That “doesn’t poke up very far” means a pretty limited range of motion for the strut shaft.

By raising the car using the adjustable perch, one can move the top hat farther away from the strut retention collar. This gives you more “bump travel”. That is to say, the strut shaft will happily compress more. Lower the car, by turning the adjustable perch down a few threads, and the top hat comes down closer to the retention collar and you lose bump travel. This is because lowering the perch lowers the spring which lowers the tophat.

The strut shaft seems to bottom out with about 23mm of it peaking out above the adjusting collar. So if your car is really low, say you’ve set the adjustable perch down low on the red threaded cylinder so that the top hat is only 43mm above the strut retention collar, you’re now only allowing the strut shaft to compress down 20mm. Sure, you’ve got 43mm of strut shaft visible, but it only goes down to 23mm before hitting the bump stop. 20mm of bump travel probably isn’t enough.

If you use the adjustable perch to raise the car 10mm, you end up with 53mm of strut shaft showing. Now you have 30mm of bump travel.

The taller spring idea. We can replicate the impact of a taller spring by putting some turns into the adjustable perch and threading it up the red threaded cylinder. This raises the car. There’s lots of available threads there so we could replicate a much taller spring if we wanted. So all a taller spring would do is limit how low we can drop the car.

Re. car height should be adjusted with control arms parallel to ground. That’s a weakness of turning a DD into a race car. Our suspension just wasn’t designed for what we’re doing.

Back to the issue of bump travel, new vs. old. I’ve been thinking about the geometry of all of this and looking hard at the design of the OEM spring hat vs. GC spring hat.

The CA guys figured out that with our old springs we were banging on our bumpstops a lot. Based on my car’s old ride height, and having screwed with the struts now night after night, it’s pretty clear to me that we had about 30mm of bumptravel. Not a way in shit we have more than 35mm. Folks that get bigger #s are probably measuring the amount of strut shaft sticking up at rest, and not spotting the fact that the strut will not go all the way down. In compression the strut shafts stops at about 23mm (measured from gland nut to the top hat) still showing. So in order to get 30mm of bump travel, the top hat needs to be 53mm above the gland nut. We have 40-47% (depending on who you believe) stouter springs now, so we end up in the same situation, in terms of how often we hit the bumpstops, if we set our car to 18mm of bump…totally not enough bump travel. That is to say, imagine a bump that would use up all 30mm of bump travel with our old springs. Because our new springs are so much stouter, that same bump would use up only 18mm of bump travel. So there is just no way we are worse off for bump travel with our new springs.

I’m thinking that 30mm of bump travel is about as low as you’d want to put your car. If you’re going to a track that is tough on suspensions, maybe go with 40mm of bump travel.

We really need more data points tho. I found 10mm of front sag and about half that in the rear. But we can’t rely on that until we get corroborating #'s.

Last night I found that I had 30mm of bump travel at one front corner and 20mm on the other. The delta was due to some cornerweighting efforts a couple weeks ago where I had to drop a corner to take some weight off of it. In order to compensate for perceived spring sag, I added 10mm to both sides. So now I have 40mm and 30mm of bump travel.


maybe some Sebring people could get a suspension camera going this weekend?? that could be really interesting


I bet that folks put a zip tie on their strut and use that to measure how much bump travel the tracks in their region are causing. 95% of folks will be like me and just set up for enough bump travel for all their tracks. The 5% will lower their fronts for some tracks in their region and raise them for others.

I wonder what kind of bump causes the most compression. A fast bump, like hitting a gator, gets resisted by the strut, but the slower the bump, the less the strut resists. I wonder to what extent changes in elevation (a slow bump?) cause bump travel vs. banging over a gator. Is it possible that elevation changes cause more suspension compression then a gator?


this was my orig facebook reply–
interesting. firstly i think H&R springs are terrible…the company wont even release their true spring rates. generally they are weaker than stock and just shorter. lame. back on topic…this seems like a spring length issue. your car height should be adjusted so your control arms are parallel to the ground…from that position you can determine a proper spring height and spring rate and how much preload is best. it seems strange to me to lower and raise the car to suit the springs…its the opposite…the springs should be proper length and lb rate to suit the correct height. and for your shocks to do a proper job dampening they need a decent amount of travel per their design. there seems to be a lot of things wrong with these setups and with the combined design of the suspensions…? i am a bit confused…am i understanding what the issues are…??? why do you think raising the front end will solve something…WHAT are you trying to solve rather? if you are bottoming out when hard braking maybe you need stiffer/stronger spring rates? there are a lot of variables at play but to diagnose this i feel like certain things need to be addressed to eliminate some variables (set the car height so control arms are parallel is a start basis). let me know if i am way off here in understanding the issue…! #becauseracecar


i just feel like you should level the control arms to start. this IS a street car that we are racing…not a purpose built race car. start there…then determine your spring length, your spring rates, your preload, your shock travel/length…etc. to diagnose an issue any other way i feel like you are going to run into problems on both ends and create too many variable issues and contradictions. start with proper geometry and go in one direction so there is a flow to the fix. if you test a product and setup that we find isn’t designed right you are going to create more problems and run down too many other wrong roads before you find a solution. you will often find a lot of poorly engineered products for a popular car like this…designed to make money and look cool in today’s hipster trends…but not designed for functionality and then on top of that the extra specific intensity of racing. this isnt even bringing in to the conversation that different drivers have different preferences towards balance in a car setup (not gonna over complicate this and go there…its irrelevant now but should be considered later).
-Victor Tate


FYI, I just got off the phone with Ground Control to see if any of their non_Spec E30 camber plates had a shorter stack height than the Spec E30 plates. The answer was not really, maybe 5mm.


5mm is 50lbs of force…