[stretch]

I snapped this picture today while trimming my front bump stops. I'm running stock springs, but wanted to trim my stops anyway because the car felt to me like it was frequently hitting them (see here for reasoning). As seen in the picture, I measured roughly 3.5 inches of travel before the struts hit the bump stops. The bump stops are just under 2.5 inches long.

Now, the stock springs compress an inch for each 224lbs of load on them. Each front spring has to support a little over 1000lbs and more if you're driving with passengers. That means each spring has to compress about 4.5 inches before it'll support the load it needs to at normal ride height.

About an inch of that is preloaded into the spring when the tophats go on, but the remaining 3.5 inches are using up the available strut travel. Since I measure 3.5 inches of travel before the car hits the bump stops, that means all STI's ride exactly where the bump stops- even on a totally stock car.

The monotube gas struts add a little to the spring rate, and probably amounting to a nearly static 50lbs- not drastic.

I haven't reinstalled my struts yet (ran out of time), so I can't yet comment on the improvements that trimming the bump stops will make. I cut off the firmest progression only. I also installed Group-N tops and Koni struts in the rear, so it'll be hard for me to comment on how this individual change feels.

Still, the size of the bump stop is pretty alarming to me. Unless I'm missing something, this data implies that all lowering springs lower well onto the bump stops. It also implies that the stock spring rates are very progressive because they're always hitting the bump tops (increasing the spring rate 50lb/in, then 150lb/in, then more). Could this be to blame the horrible turn-in of a stock car? Braking and turning would put you waaaaaay onto the stops.

[jasv11]

I think that as the spring compresses it takes more weight to squish it further then the first inch.

Say for instance../
1st inch 224lbs
2nd inch 224 + 350lbs
3rd inch 224+ 350+525lbs
and so on....

just guessing here on the values but you get the picture

I have swifts lowered about 1.1 inches Back and front with one bump of bumpstops removed and have never hit them yet.
Car handles awesome as well.

Or Ive completely misunderstood your question

[wdb]

Originally Posted by jasv11

I have swifts lowered about 1.1 inches Back and front with one bump of bumpstops removed and have never hit them yet.

How do you know? The bumpstops are progressive, you may not feel a jolt when they first come into play.

[stretch]

Yeah, the first progression of the bump stops is especially soft. You don't ever feel an impact from them.

I'm beginning to second-guess the amount of preload in the springs. I'll measure the wheels at full droop, then at ride height, and calculate used strut travel from that.

[jasv11]

In sportbike racing we use a zip tie around the front fork to see how far the fork compresses during a practice/race. Maybe this can be done to our strut to find how far it compresses.

[Cadence]

Originally Posted by stretch

Still, the size of the bump stop is pretty alarming to me. Unless I'm missing something, this data implies that all lowering springs lower well onto the bump stops. It also implies that the stock spring rates are very progressive because they're always hitting the bump tops (increasing the spring rate 50lb/in, then 150lb/in, then more). Could this be to blame the horrible turn-in of a stock car? Braking and turning would put you waaaaaay onto the stops.

My guess is your are correct and lowered STis are always on the stops. Being on the stops would also add to the "bobble" effect". There are many Mac strut cars that are designed this way and the only real cure is to get new springs and dampers.

Has anyone measured the stock STi springs to see how the rate changes as it compresses?

[stretch]

OK, I just measured 3.5" of wheel travel when lifting the car from rest (no driver). That should correspond to 3.3 inches of strut travel, which is close enough to my original statement. Once a driver and passenger get in the car, a stock STI will be sitting on the first, softest progression of the bump stops before even starting the car. Incredible.

My car feels downright squishy with the trimmed stops, but I just switched to winter tires, a smaller front sway, Group-N tops, and Koni rear shocks, too. As I said earlier, I'm not going to be able to comment on the effects of trimming just the stops because I did a lot of work yesterday. I can say that large bumps such as speed breakers get partially absorbed now, rather than just catapulting the car upwards. It feels great having more usable suspension travel, but now I want firmer, linear springs to get some immediacy back.

Even moderate-drop springs like Pinks or RCE's are going to put you passed the softest progression of the bump stops. I guess if people like the way that feels (and the positive testimonials are numerous), then good for them, but geez, that's really not allowing much bump travel.

Originally Posted by jasv11

In sportbike racing we use a zip tie around the front fork to see how far the fork compresses during a practice/race. Maybe this can be done to our strut to find how far it compresses.

The bump stops are rather time-consuming to get at and if my data is correct, the zip tie would probably explode at the first hard bump. It's a good idea, but I'm not going to volunteer to do this.

[Cadence]

STi owners seeking a well engineered package have no real solution other than a good coil-overs system and here is why...

With the stock springs we are already riding on or very near to the bumpstops and the car is equipped with progressive rate springs. If want our cars to handle better we need to retain as much suspension travel as possible while increasing the spring rates and hopefully getting linear rate springs.

If the front suspension (struts) starts out with 3" (75mm) of bump travel and we install a set of Pink or Swift springs that are approx 15% stiffer (224# stock to approx 257#) but sit 1" lower (25mm...or 33% of the available travel)....guess what.....we are more likely to use up all of the available suspension travel (this is a very bad situation) during aggressive driving than when the car was stock. Can you say bumpstop lover? Who in their right mind would want this set up Maybe RCE could do a limited run of their new springs with a zero drop? The carshow crowd wouldn't buy them but I sure would!

The ideal combo, IMO, for a street/track/daily do-it-all package would be Ohlins struts with linear 350# front and 300# rear springs and a drop of no more than 20mm from the stock STi ride height (Group N tops and mid-sized bars too). If this combo was available my wallet would swing open and I would let 2500 greenies go to the lucky vendor

[Mykl]

This thread has inspired me to take some travel measurements for my coilovers. I may even go so far as to do the zip tie thing just to see how much I can compress them. Although, I have managed to find the "bump stops" a couple of times while autocrossing.... which is basically the coilover housing crashing into the upper spring perch, you definitely notice it.

[Splash]

Of course, you are forgetting just a couple things....

You would SO feel a bumpstop... Even the soft section has an internal spring rate that makes the mainspring seem downright flimsy. However, not only does the bumpstop have a MUCH higher rate, it gets COMBINED with the mainspring's rate when you get into the stops.

Also, the stock mainsprings are progressive, so your rate at stock height might not be 224lb/in, it could be less, throwing your measurements off more.

Then, ask yourself... If the advertised drop of a Tein S-tech is 2.0 inches, and the car is already sitting at the top of the stops with stockers, then not only must the car's new drop overcome the spring rate, but it must also compress that bumpstop to about 1/5 it's total length....

I don't know about you, but I don't think ANY density of foam rubber can compress by 4/5, and since my car came with S-techs on it, I can vouch for the almost EXACT 2.0" drop they provide.

Now, drop the car 2.0 inches, and THEN it felt like they were right off the stops. Any rise followed by a dip would cause the car to rise over it normal height, then drop back down. During that trip down, it would feel ok, until just past normal height when it would get into the bumpstops, severely increasing the effective spring rate, and making the resulting abnormal firmness, but no clunk or bang.... (at least the stops were working)

This sudden increase in firmness on the way back down doesn't happen for me on the OEM springs, which tells me I am not hitting the stops.

Mike

[stretch]

Originally Posted by Splash

Of course, you are forgetting just a couple things....

You would SO feel a bumpstop... Even the soft section has an internal spring rate that makes the mainspring seem downright flimsy. However, not only does the bumpstop have a MUCH higher rate, it gets COMBINED with the mainspring's rate when you get into the stops.

I've talked with one a guy who makes bump stops. He always called them "urethane jounce bumpers", but whatever. I'm pretty sure he said jounce bumpers start out around 50lbs/in in the first (hollow) progression, quickly shooting to around 150lb/in before running out of travel and going to infinity. The STI bumpers may differ, dunno.

I don't think you'd feel this unless one did a direct comparison. Heck, I used to think all the STI's firmness came from the stock struts. What feels like harshness is (at least partially) a lack of suspension travel and sky-high actual spring rates, but it's not obvious that the car is hitting the stops.

I went though with this because of understeer during braking. That told me the front spring rates were skyrocketing under braking. I could not tell the car was hitting the stops due to anything ride-quality related.

I don't know about you, but I don't think ANY density of foam rubber can compress by 4/5, and since my car came with S-techs on it, I can vouch for the almost EXACT 2.0" drop they provide.

This is a good point, but let me share a previous experience with you. On my previous car, I ran Eibach springs. They were too soft, too low springs (like S-techs) that put the car on its bump stops, albiet just barely (not nearly as bad as S-techs on the STI). When I later switched to coilovers, my bump stops had split down the seam for the first two progressions. This made those progressions much, much softer- almost useless.

Furthermore, I couldn't get the car to stop snap-oversteering until I trimmed the rear stops. It was quite the learning experience!

Originally Posted by Cadence

STi owners seeking a well engineered package have no real solution other than a good coil-overs system and here is why...

I wonder if coilovers are much better. Some coilovers allow more bump travel, but actually using that bump travel with the wheels turned left or right puts the tire into the fender. Been there, done that! The stock struts are probably designed to run out of travel just before this happens.

Can you say bumpstop lover? Who in their right mind would want this set up Maybe RCE could do a limited run of their new springs with a zero drop? The carshow crowd wouldn't buy them but I sure would!

I agree. But I think our solution is simpler than that: Ground Control. Set your own spring rates, set your own height. Springs just aren't in my budget yet, though.

I think Prodrive is the only company to really get the ride height thing down, using both a minimal drop and including shorter bump stops. RCE camber plates and stock-height, firmer springs are really the ideal solution here because then you get the slight drop (better aerodynamics, lower center of gravity) while retaining suspension travel.

[Cadence]

I don't think you'd feel this unless one did a direct comparison. Heck, I used to think all the STI's firmness came from the stock struts. What feels like harshness is (at least partially) a lack of suspension travel and sky-high actual spring rates, but it's not obvious that the car is hitting the stops.

There is no question, IMO, that stock STis are riding on the front bumpstops most of the time and STis lowered on stock struts are on the bumpstops all of the time. It is important to keep in mind that this 'feature' was not a mistake by the guys in Japan after too many sakes and due to the design of the strut, spring and bumpstop it isn't like comparing a Ferrari F430 riding on the bumpstops. Lots of Mac strut cars use the bumpstop as part of the designed effective spring rate. Having said that I don't want my car riding on the bumpstops so I need to find a solution that gets me more travel or at least stiffer springs without a loss of travel.

I wonder if coilovers are much better. Some coilovers allow more bump travel, but actually using that bump travel with the wheels turned left or right puts the tire into the fender. Been there, done that! The stock struts are probably designed to run out of travel just before this happens.

Good point but this should only apply to oversized wheel and tire combos. Also with stiffer than stock spring rates and near stock ride height I would think a properly designed coil over should work very well and you would only rub during an Auto X or wild driving.

I agree. But I think our solution is simpler than that: Ground Control. Set your own spring rates, set your own height. Springs just aren't in my budget yet, though.

I would go with Ground Controls on the stock struts for a budget solution but I don't want to run unprotected struts. As you probably know the 2.5" Ground Control springs require the removal of the stock dust boots which leave the piston exposed to the elements. This is fine for a track car or anyone who lives south of the snow-belt but it won't work for me.

I think Prodrive is the only company to really get the ride height thing down, using both a minimal drop and including shorter bump stops.

I don't know much about the Prodrive springs. Are they still progressive? What are the rates?

The search for a solution continues

[Splash]

Originally Posted by stretch

I've talked with one a guy who makes bump stops. He always called them "urethane jounce bumpers", but whatever. I'm pretty sure he said jounce bumpers start out around 50lbs/in in the first (hollow) progression, quickly shooting to around 150lb/in before running out of travel and going to infinity. The STI bumpers may differ, dunno.

I don't think you'd feel this unless one did a direct comparison. Heck, I used to think all the STI's firmness came from the stock struts. What feels like harshness is (at least partially) a lack of suspension travel and sky-high actual spring rates, but it's not obvious that the car is hitting the stops.

I went though with this because of understeer during braking. That told me the front spring rates were skyrocketing under braking. I could not tell the car was hitting the stops due to anything ride-quality related.

The stock STi firmness is from the aggressively high compression setting in the stock struts. If you went from them to Japanese coilovers, you would likely see no improvement. However, a Bilstein, Ohlins, AST, G4, etc.. ride totally different.

You could be getting understeer during braking because you are asking the tire to turn and brake at the same time. Tires are not good multitaskers. You will get better turning if you don't ask yout tires to slow you down too.

FWIW, I could decidedly tell when the S-techs allowed me to hit the stops. While I know the stops are progressive themselves, I don't feel anything like that on my OEM's.

Originally Posted by stretch

This is a good point, but let me share a previous experience with you. On my previous car, I ran Eibach springs. They were too soft, too low springs (like S-techs) that put the car on its bump stops, albiet just barely (not nearly as bad as S-techs on the STI). When I later switched to coilovers, my bump stops had split down the seam for the first two progressions. This made those progressions much, much softer- almost useless.

Furthermore, I couldn't get the car to stop snap-oversteering until I trimmed the rear stops. It was quite the learning experience!

Ok, after what you just typed you really need to re-examine what you said earlier... If your Eibachs put your car "just barely on the stops", how can you assert that the stock height is also just above the stops? If I am right, the Eibachs lower almost 2". That 2" is a significant part of the total front travel.

Trimming the rear stops should really be totally unnecessary. There is SO much travel back there that if you are in the rear stops, your tire is into your fender. Assuming your car is an STi, it's likely that your snap oversteer is caused by the DCCD in Auto catching up with you in on-throttle corner exits. If you set the DCCD to the most forward, you'd be surprised how pushy they get. Or, you can drive an '06... The DCCD is faster-reacting and uses the steering angle to kinda pre-guess what you are doing.

Originally Posted by stretch

I wonder if coilovers are much better. Some coilovers allow more bump travel, but actually using that bump travel with the wheels turned left or right puts the tire into the fender. Been there, done that! The stock struts are probably designed to run out of travel just before this happens.

Other than the ZZYZX coilovers, I haven't seen one yet that didn't have LESS total travel than the stock struts. Not only are the bodies shorter, but the droop travel has been almost eliminated in some cases...

Check this link out...

http://forums.nasioc.com/forums/show...highlight=17x9

The pics show a WRX up on stands, and on the ground. Between the two, the wheels gap up front only changes about an inch and the rear doesn't look like it changed at all. This is an autocross car on either Tein or Cusco coilovers.

Originally Posted by stretch

I agree. But I think our solution is simpler than that: Ground Control. Set your own spring rates, set your own height. Springs just aren't in my budget yet, though.

I think Prodrive is the only company to really get the ride height thing down, using both a minimal drop and including shorter bump stops. RCE camber plates and stock-height, firmer springs are really the ideal solution here because then you get the slight drop (better aerodynamics, lower center of gravity) while retaining suspension travel.

If I were to use your measurements, even the Prodrive solution isn't good. If you say the stockers are just above the stops, and the Prodrives lower 15mm, and their bumpstops are 1/2" shorter... Sounds like you'd be in the same spot.

I had read where a Subaru engineer said an '04 STi has 65mm bump travel until it hits the stops ('05/'06 have 10mm more because they have 10mm taller springs). My old S-techs lowered 2" (~50mm), leaving me with ~15mm of bump before I hit the stops... In practice, that's about what it felt like.

Mike

[stretch]

Originally Posted by Cadence

I would go with Ground Controls on the stock struts for a budget solution but I don't want to run unprotected struts. As you probably know the 2.5" Ground Control springs require the removal of the stock dust boots which leave the piston exposed to the elements. This is fine for a track car or anyone who lives south of the snow-belt but it won't work for me.

I'd probably just use a sock. Water isn't a big deal so long as sand and dirt stay off the shaft.

Good point but this should only apply to oversized wheel and tire combos. Also with stiffer than stock spring rates and near stock ride height I would think a properly designed coil over should work very well and you would only rub during an Auto X or wild driving.

I think suspension geometry plays a big role here. I *think* suspensions with a big kingpin offset and kingpin inclination should tuck into the fender as they turn.

I don't know much about the Prodrive springs. Are they still progressive? What are the rates?

Very mildly progressive and not very firm. My point was only that the chosen ride height seems appropriate, the springs barely lower the car yet use shorter, softer bump stops. Splash is right, though, they seem to lower by as much as the shorter bump stops allow, so you probably don't gain any more travel. However, the springs are firmer and bump stops softer, both of which should contribute to a less severe spring rate spike.

Originally Posted by Splash

The stock STi firmness is from the aggressively high compression setting in the stock struts. If you went from them to Japanese coilovers, you would likely see no improvement. However, a Bilstein, Ohlins, AST, G4, etc.. ride totally different.

But... my car rides nicely now, even over the speed breakers in my neighborhood. I'll admit, it may be from the softer tires, but I'd only expect softer tires to decrease the immediacy of a deflection, not the total amount of deflection. I've tried a fair bit of suspension products before, and it feels to me like I have more suspension travel. I'll be perfectly honest, the front struts (coupled with Koni's in the rear) feels really close to some premium coilover sets I've ridden on, and way better than the too-much-bump-resistance Japanese coilovers.

You could be getting understeer during braking because you are asking the tire to turn and brake at the same time. Tires are not good multitaskers. You will get better turning if you don't ask yout tires to slow you down too.

I'm a seasoned autocrosser and I know the traction circle. A stock STI understeers even under mild braking and minor turning when the tire should have grip left. I know steering grip is shared with braking grip, but it's a very disproportionate amount of steering grip lost when braking.

If your Eibachs put your car "just barely on the stops", how can you assert that the stock height is also just above the stops?

Re-read what I wrote, I was talking about the previous car I had- a Mazda6.

Trimming the rear stops should really be totally unnecessary. There is SO much travel back there that if you are in the rear stops, your tire is into your fender.

Again, you're responding to something I had done on my Mazda6, but I'd like to mention the rear bump stops anyway. I did take apart a stock rear STI strut, and strut travel is not as long as the standard WRX strut. Furthermore, the bump stops are rather long. I did not take any measurements (though can if people are interested), but I'd bet the rear is much closer to riding on the stops than you'd expect.

Other than the ZZYZX coilovers, I haven't seen one yet that didn't have LESS total travel than the stock struts. Not only are the bodies shorter, but the droop travel has been almost eliminated in some cases...

With firmer springs, the struts have to have less travel. An 500lb/in spring settles to its ride height in just two inches, so it cannot have more than two inches of droop travel (unless running a progressive spring). Any more travel would be useless because that tire would be completely unloaded. However, coilovers can still add (or at least retain) bump travel versus stock, which is what I was referring to by increased travel. It's true that total strut travel almost always decreases.

I had read where a Subaru engineer said an '04 STi has 65mm bump travel until it hits the stops

I had read that too- any idea where that information originated? It's plainly obvious that there is not 65mm (~2.5 inches) of bump travel before the bump stops unless you're starting that measurement from a droop situation.

[Cadence]

I had read where a Subaru engineer said an '04 STi has 65mm bump travel until it hits the stops ('05/'06 have 10mm more because they have 10mm taller springs). My old S-techs lowered 2" (~50mm), leaving me with ~15mm of bump before I hit the stops... In practice, that's about what it felt like.

Are you sure about this info? According to SOA, via nhluhr =

2004 STI
Front:
Rate is 39.2 N/mm (224 lbf/in)
Bump Travel: 75mm
Rebound Travel: 95mm
Swaybar: 19mm
Rear:
Rate is 34.0 N/mm (194 lbf/in)
Bump Travel: 100mm
Rebound Travel: 100mm
Swaybar: 20mm

2005 STI
Front:
Rate is 39.2 N/mm (224 lbf/in)
Bump Travel: 65mm
Rebound Travel: 95mm
Swaybar: 20mm
Rear:
Rate is 34.0 N/mm (194 lbf/in)
Bump Travel: 85mm
Rebound Travel: 100mm
Swaybar: 20mm

This makes it look like the '04 has 10mm morefront travel compared to the '05. I had never heard that the '05 springs were taller Can the '05 front springs be used on the '04 struts?