[flatthump]

K im confused here. On a stock STi.......At normal rideheight...there is only 2.5 inches of jounce before the bump stops! Thats insane. Or is it 3.5"

If thats true, then im definetly resting on my bump stops under braking with my pinks.
So should I cut another ring off the front bump stops?

[Mykl]

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.

This is where choosing the appropriate spring rate for the tires you intend to use comes into play. Also, with some coilovers, if you find that you're bottoming out you can adjust the travel so that you can gain some compression travel in exchange for some droop travel.

If the tire is actually coming into contact with the fender, you can either raise the car, or adjust the suspension so that it bottoms out before that happens.

Originally Posted by Splash

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.

Mike

That car has Megan Racing coilovers. More specifically, their "race" model with the 12k/10k springs. A buddy of mine here in town owns that car. The difference in droop travel between his car and mine is silly.

Originally Posted by stretch

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.

That's not true for all coilovers. It's definitely *not* true for mine.... which are ZZYZX. I can run whatever spring I want and maintain full droop travel.

I can take pictures if you would like to see how this is possible.

[stretch]

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

Hey, that comes out perfect with my measurements! However, the previous misconception was that those bump numbers were for prior to the bump stops, when in fact they include the bump stop (and the bump stop is about 65mm long).

The car rides 95mm into the strut travel, right where the 65mm long bump stop starts. Apparently 2004 models do not ride on the bump stops unless they have longer bump stops.

Originally Posted by Mykl

That's not true for all coilovers. It's definitely *not* true for mine.... which are ZZYZX. I can run whatever spring I want and maintain full droop travel.

But there's no point, you cannot prevent the tire from becoming unloaded simply by adding droop travel beyond the unloaded spring. Are the springs very progressive to avoid unloading quickly?

[Mykl]

Originally Posted by stretch

But there's no point, you cannot prevent the tire from becoming unloaded simply by adding droop travel beyond the unloaded spring. Are the rears very progressive to avoid unloading quickly?

Then why do people add helper springs? They don't offer enough pressure to actually keep the tire loaded. But they do help extend travel a bit while keeping the main spring seated.

[stretch]

Originally Posted by Mykl

Then why do people add helper springs? They don't offer enough pressure to actually keep the tire loaded.

Firm(ish) helper springs are a way to add a progressive spring rate to a linear spring. Soft helper springs are there to hold the spring in place during an overextension of the strut and don't do anything meaningful. You don't want the spring to dangle. But that's why strut manufacturers use less droop travel; adding it forces you to buy a helper spring.

[Mykl]

Originally Posted by stretch

Firm(ish) helper springs are a way to add a progressive spring rate to a linear spring. Soft helper springs are there to hold the spring in place during an overextension of the strut and don't do anything meaningful. You don't want the spring to dangle. But that's why strut manufacturers use less droop travel; adding it forces you to buy a helper spring.

That's a point that I had not considered... despite the fact that it now seems to be somewhat obvious.

[flatthump]

Hmmm, Prodrives bumpstops are longer than a CUT stock bumpstop. And their spring rates are pretty soft compared to others. Im glad I didnt use the prodrive bumpstops....

So you guys recommend cutting one more ring off the bump stop?

[DuckStu]

Most cars today are designed with the bumpstop as part of the suspension. In other words, they are intending for the car to hit them often and to act like a progressive spring.

I was floored when I heard this. I first noticed it on a BMW I was modifying. I saw t again on an H3 Hummer I currently lease. It's front bumpstops are 1/2" away from the control arm when the car is empty. That means that 3/4" compression of the wheel and the front bumpstops are already contacting the front control arms.

I should think that when we lower one of our cars by an inch, that we should be trimming the stiffer (upper) end of our bumpstops by something like 1/2 - 3/4"

[Splash]

Originally Posted by stretch

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.

Yeah, see I have two setups... I use OEM struts and springs for winter, and I have a set of Ohlins fixed-perch struts and RCE springs for everything else.

A racing buddy of mine has an '05 with RCE springs on OEM struts.

RCE's lower about 20mmF and 15mmR and have about 300/280 rates

The OEM struts are overdamped for the OEM springs. A STi Pink is probably closer to the optimal rate for them. The RCE's were designed to be the max spring a OEM STi strut could handle.

I can't feel the bumpstops on either OEM or RCE springs, definitely not like I could with the S-techs on the OEM struts.

The Ohlins are on a different planet as far as feel is concerned. They're single adjustable and have 25-clicks worth. I autocross on them at anywhere from 9 to 2 from full stiff. I drive daily on them at about 17 or 18 from full soft. Any less and they will be underdamped for the RCE's. In the street setting they ride like buttah and I have not ever felt the stops.

Originally Posted by stretch

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.

Ah, good.. Then you know how much a role camber plays into that as our cars have HORRIBLE camber curves. You can add a HUGE amount of spring into the front via a HUGE front swaybar, and get better grip by doing that since you're actually using the whole front tire.

Now, back when I had the S-techs, I also had the stock bars. I felt exactly what you describe, even without braking, by entering a corner. It would feel fine for a split second, then it would hit the stops and go into terminal understeer.

With the OEM package or the Ohlins/RCE package, I don't get that any more. The common denominator is that my huge bars stay on the car. During race season, I run -2.8 camber up front. I don't have much understeer problems.

Originally Posted by stretch

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.

Again, a STi rides 10mm lower than a WRX, so I'd expect the struts to be a tick shorter.

I just know that the total full extension to full compression length difference on the rears is HUGE compared to the front.

Originally Posted by stretch

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.

Firstly, springs do not alter a struts travel. A strut that has 6-inches of travel will have that no matter what spring you use (short of coilbind). If you do something to gain bump travel you will lose droop travel. You must be careful though because topping out a strut is just as hard on them as bottoming out. The only way to increase travel is to have longer strut body and shaft (and more ground clearance to allow it) like the Rally DMS 50 coilover. Our struts are already down as far as they can be, so there is no way to increase travel without raising the car, or raising the hoodline.

2ndly, even with the amount of travel we have, we either MUST use progressive springs or Linears with tender springs. If we use a main spring long enough on its own to handle full droop, it will go into coilbind at full bump. The coilovers you see with linear mains and without tenders are the ones that have the most compromised total travel.

Originally Posted by cadence

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.

The info from Nuluhr is what I read, though I think he is backwards on the '04 vs '05 numbers... The '05/'06 sits 10mm higher than an '04. By default, this means the '04 has 10mm less bump travel.

However, you have to combine bump and droop travel to get the total. To say you can't have 2.5" bump travel without starting at full droop isn't paying attention to the actual numbers.

Mike

Mike

[flatthump]

Originally Posted by Splash

The info from Nuluhr is what I read, though I think he is backwards on the '04 vs '05 numbers... The '05/'06 sits 10mm higher than an '04. By default, this means the '04 has 10mm less bump travel.

.

Mike

Mike

I wish someone could clarify this as I thought of it too.

[thrlskr]

Great discussion! I'm in for non lowering linear springs as well.

[Cadence]

The info from Nuluhr is what I read, though I think he is backwards on the '04 vs '05 numbers... The '05/'06 sits 10mm higher than an '04. By default, this means the '04 has 10mm less bump travel.

However, you have to combine bump and droop travel to get the total. To say you can't have 2.5" bump travel without starting at full droop isn't paying attention to the actual numbers.

Are you sure? The numbers came directly from someone at SOA and nhluhr just posted them. AFAIK the '04 and '05> struts are different so it is possible that the '05> cars sit 10mm higher due to different springs (this is still news to me but I'll take your word for it) but that the '04 cars in fact have more bump travel due to the strut design.

Did you measure the travel on your Ohlins?

[stretch]

Originally Posted by Splash

Firstly, springs do not alter a struts travel.

Right, but a matched spring/strut set should not have droop travel that extends passed the length of the spring. Sorry if I was unclear of the point I was trying to make.

2ndly, even with the amount of travel we have, we either MUST use progressive springs or Linears with tender springs. If we use a main spring long enough on its own to handle full droop, it will go into coilbind at full bump. The coilovers you see with linear mains and without tenders are the ones that have the most compromised total travel.

I agree that we must use progressive or tender springs on stock or stock-length struts, but not at all for the reason you state.

The reason lowering springs must be progressive is because firmer-than-stock springs would run out of extension before the strut does and would become unseated. The problem is worst in the rear, where each spring supports roughly 685lbs. A 250lb/in linear spring will support its 685lbs with 2.75 inches of compression. However, the car has more droop travel than that even at stock ride height, and more if lowered. Thus, the spring would not stay in place without a helper spring.

The solution is to either run a shortened strut (of which none are available off the shelf), run a helper spring, or run a progressive spring rate and avoid the problem. I, however, do not like progressive springs- if I did, I'd just let the car ride on its bump stops! I don't even like having to use helper springs because they make a linear spring slightly progressive, even if their impact is minimal. A shortened strut is the preferred solution here, but currently one must buy coilovers to get that.

Bilstein often makes two versions of their struts for cars, one OE size and one shortened for use with lower springs. They offer the shortened strut for the above reason. Too much droop travel is not good if you're springs can't use it.

Coil bind shouldn't be an issue unless running tightly wound, short springs. The stock front springs, for example, only make four winds. Fully compressed (in a vice), the entire spring would be about two inches! In fact, coil bind is more of an issue with progressive springs because they typically have much more winds in them.

[drees]

stretch, you're right on the money here and while you're looking at the STi, on my WRX I also found that once you throw lowering springs into the picture, you will either be slightly engaging the bumpstops or very close to them depending on how much the springs have lowered the car. I found the situation to be the same on the front and rear of my wagon.

With stiffer springs you don't notice the transition to the bumpstops as much because you don't use as much of the bumpstop and the higher rates transition better into the added rate of the bump stops. With a soft, low spring like Tein S-techs, it's a lot easier to notice the car running out of travel and running into the bumpstops.

Ideally, whenever you lower the car, you'd increase the bump travel and reduce the droop travel by the same amount you lowered the car.

As others have mentioned, using a tie-wrap it's easy to find out how much suspension travel you are using. Another fairly easy way is to pull the spring out and then measure the shock travel with the wheel off by measuring from hub to fender. Best time to do this is in the middle of spring swap. It would be nice to get some hard numbers from someone who has done this.

[stretch]

Yeah, I think most cars will hit the stops with lowering springs. The huge surprise here (at least to me) is that even the stock springs are riding on them, and as DuckStu points out, that's becoming normal! I just can't understand why that would be done on a performance vehicle. Ah well, at least it's an easy fix.