meb58

What information tells you that 750lb/in springs are better than 550? Springs can add to driver control if the front and rear are balanced...also, heavier springs can cause sudden loss of grip at some point...there is a point where weight transfer and control is optimized and any more spring is just too much. Is this a daily driver?

Beanbag is correct above, you need to calc motion ratios and wheel rates and begin testing rates that converge on good driver control and weight transfer.

I used 400lb front and 600 lb rear Eibachs with koni re-valved double adjustables and the car was very fast on a road course. I never auto crossed it. That ride got a bit much on the highway, however. Stock front bar, 22mm Ground control rear bar, all Mugen bushings, 1.5 deg neg camber up front, .5 deg neg rear 1/8th total toe in rear and a hair toe out up front. If you install an upper rear brace you will notice much of that understeer disappear - I used all four...a roll bar would have been better. This was a 99 Si...GC upper front arms - used stock ball joints - and Mugen rear upper adjustable arm. If you copy this set up and drive at the track you will be quite happy. I put nearly 200,000 miles on this set up. It works but is biased toward track environments. I used FastBrakes Type R kit up front and the only other mod was a CAI.

Check all of your bushings before going too far.

beanbag

That is true if you want to maintain the same natural frequency, a.k.a. bumpiness.
He was asking about the maximum damping available out of a shock, so if you already have the damping maxed out for a given car weight and spring weight, and then you lighten the car, you can go up a little in spring rate and keep the same damper settings.

beanbag

STN, based on what others have told you, you need to check if your understeer is due to a front end "pathology", such as decambering or running out of suspension travel and hitting the bump stops. In either case, increasing the front roll stiffness, increasing the front ride height even, may reduce the understeer.

meb58

Sorry, I missed that.

STN_Pat

No offense, but i'm pretty much already beyond what you're suggesting, and my car is already stripped, track-only and has a welded roll bar. The rear upper bar you're talking about... mine's already a 1.75 DOM steel tube with 0.120 wall thickness on reinforced/boxed shock tower. Busings aren't in the equation as the whole car is bolt cheked and inspected before as well as after every exits. Thanks for posting though.

As stated, i'll be installing the front 26mm bar tonight, shave off some rear negative camber and try the car out next week.

I was just wondering if the more experienced people in here would suggest getting 750lbs front springs now anyway, because 550lbs with 26mm bar will probably still not be enough for my actual rear roll resistance (22mm bar, 600lbs springs, -1.5 or so camber).

Thanks a LOT to all of whom contributed. You have no idea how much you are helping me, and it is immensely appreciated.

CivicSiRacer

Personally I would try one or two changes like others have said. Put the front sway bar on and dial out negative camber. Try to get it to between -2.0 and -1.5. You should notice a difference right away.

meb58

I'll ask again, why do you want to install 750lb/in springs instead of retaining the 550s?

Why not adjust your suspension settings first? Or why not use a larger rear bar instead of a heavier rear spring rate?

I'm not offended...this was a commuter/track car - actually, it was a company car. The boss didn't mind the work but he said no roll bar...the accountant hates cars.

STN_Pat

We're talking front spring rates here. The rear won't be touched.

Main culprit exposed by most who posted is too much roll resistance in the rear vs. the front. Increasing the front roll resistance (and/or decreasing the rear roll resistance by removing rear negative camber) should do the trick.

Increasing rear roll resistance, as you suggest, will only make the problem worst.

meb58

Reducing rear camber will not affect roll resistance but it will reduce rear traction - relative to the front.

Increase front track width = more front roll resistance. If you are inlcined to work out the new motion ratio make sure you also consider the contribution your rubber bushings make to spring rate, especially if you have hard rubber bushings. In fact, these can offset subtle changes in motion ratio; if you calculate the new motion ratio on paper for a wider track and find you have to add 3% more spring rate you may well find that the spring rate in the bushings - almost never accounted for - is greater. There is a fair amount of kinetic energy stored in those bushings at full compression and full droop. If you don't have rubber bushings never mind.

descartesfool

Some of you guys are confused:

1. If you stiffen the front end in any way, it will have more % weight transfer relative to the rear, and you will lose grip at the front, thus tends toward understeer.

2. If you stiffen the rear end in any way, it will have more % weight transfer realtive to the front, and you will lose grip at the rear, thus tends toward oversteer.

TunerN00b

True before inside rear tire lift. Potentially false after.

Before the inside rear lifts, a stiffer front does transfer more weight. After inside rear lift, the rear has already transferred 100% of its weight, and any remaining weight transfer must be up front. If the front end is losing traction after inside rear lift, due to the outside front decambering, then a stiffer front could end up reducing understeer by reducing total roll angle...

slammed_93_hatch

Number 1 rule un suspension running is

There are never ever any absilutes, only guidelines that should be followed until they don't work.

slammed_93_hatch

Number 1 rule un suspension running is

There are never ever any absilutes, only guidelines that should be followed until they don't work.

beanbag

You can say that again!

descartesfool

If the car won't rotate, what can you do?

Reduce rear grip relative to the front. Hopefully without compromising front grip. Simple changes that don't require re-engineering the suspension design, affecting camber and toe curves, Ackerman, etc. Assuming overall roll resistance is high enough to minimize camber change.

1. Move weight toward rear of car to increase weight transfer there and reduce rear grip. Benefit is front tires are less overworked, and rear brakes work harder.

2. Stiffen rear suspension with bars or springs (or dampers for transitions).

3. Soften front suspension with bars or springs (or dampers for transitions).

4. With camber set to maximize grip at the front, run less than optimal camber at rear. Use a pyrometer in combination with a pressure gauge.

5. With tire pressures set to maximize grip at front, run less than optimal pressure at the rear to reduce grip (usually higher pressure at rear than optimal for grip).

6. Adjust toe front or rear. Too much rear toe out causes instability under straight-line driving and braking. Better to work with front toe angles.

7. Fit rear tires with less grip.

8. Reduce rear track to increase weight transfer there and reduce grip, or increase front track.

9. Increase front downforce relative to rear. Affects high speed turns.

10. Trail brake, and other driving style changes.

STN_Pat

I am adding an maybe important detail.

I am running front and rear elongated top plates to retain good travel.

Could limiting rear droop travel contribute to my problems ?

BTW, the 26mm front bar fits OK on a non-Si chassis. There is an exhaust shield you need to remove from the subframe in order for the bar to fit...and it can't be fitted under the LCA as I thought it would have to be. You have to go the normal route, over the LCA. It is very, very (very) close to the LCA if you use non-SI LCAs (using L shaped end links).

beanbag

only if the spring is still compressed when the shocks are fully extended

meb58

If we're talking springs and swaybars. However, if front track width is increased we still get more roll resistance relative to the back, and more front end grip. The wider track resists roll while also taking more of the weight transfer.

The notion of losing grip comes from swaybars that are too stiff for a given application. Ideally a swaybar is a fine tuning component that should help with balance over-all, but most importantly in my opinion, be an incredible aid to corner exit. If an inside front wheel or inside rear wheel comes off the ground in a corner swaybar contribution begins to fall off and the car begins to corner on three wheels. (inside front = rear wheel drive)

You have to determinehow much traction loss you are willing to sacrifice for driver control - under/oversteer - and exit speed. I should think this is evaluated against all other set up considerations and plenty of track time evaluation. In any event, track width contributions to balance and grip is not the same.

descartesfool

But you can only increase track a very small %, say from 58" to 61", or about 1-3% and changing track screws up things like scrub radius and steering feedback the suspension was designed for. You can change bars and springs by 500% easily, say from 200 lbs/in to 1000 lbs/in, so that avenue has much more range. Obviously a wider track is better if the suspension was designed for it as it reduces overall weigh transfer, but then you have fender rubbing issues, etc.

slammed_93_hatch

While it might be saying the same thing in different ways... I like to look/think about it like this.


"Get the absolute maximum grip you can out of the front of car, then adjust the rear of the car."


Also making the front of the car softer doesn't give you more grip (in and of itself).

You hear people ALL the time say "the car is pushing? soften up the front."

And some times it will help but not all the time, it 100% depends on where you are starting from.

On my car (2330lbs K20a3 EG civic) going stiffer increased front grip.

On another race car (2400lbs b18c EG civic) going stiffer increase front grip.

On another race car (2400lbs 94 Prelude h23/vtec) going MUCH stiffer increased front grip.

Why? The cars where too soft/too much roll to begin with.

It's not a cut and dry answer.

meb58

A front drive car has basically 60% of its static weight over the front axle. So I agree, getting as much out of the front end very impportant.

Back to track width changes...5mm per side will make a noticable difference and up to 15mm per side is fairly sobering...my last track car had a 22mm increase in front track and the difference in grip is quite shocking. Obviously you have to consider everything else...every change should consider everything else.

I was concerned with tie rods for sure, but steering feel in my case was improved because scrub moved to a more effective part of the contct patch - incidentally, camber changes scrub. A wider track may, and did in my case, raise roll centers, an affect I was after.

Comparing 1-3% increase in track with making a swaybar 500% stiffer is not the same. The two control roll in different ways.

...you may find that you actually need less rear bar after increasing front track, but this is a road course evaluation, not an autoX one. An autoX setup requires much more rotation potential than a road car does.

descartesfool

Well I did precede the list with the assumption that suspension was very stiff, which is what you need to minimize camber change

And I also said to maximize front grip.

I have never experimented with track changes voluntarily, except for using spacers to clear suspension arms with Hoosiers.

meb58

A wider track can help, or not, camber curves as well. When track is increased on a Mac Strut for example the camber curve is softened helping this design to maintain some good camber for a larger portion of the bump stroke. Combined with a stiffer suspension we're able to spend most of our time in the camber sweet spot - assuming we get it right while siting still.

There are some aerodynamic trade offs I should think but I can only speculate. Having thr front tires stick way out on tracks with lots of high speed runs may prove to ruin lap times.

raffaelli

STN_Pat

Hey, here is an update.

I installed a 26mm front bar. I lowered the front as I had enough travel to do it. Until I get on the rack, I assume i've got around -2.0 camber up front. I didn't touch the rear as of yet.

I've been on the track today, but it was raining, and it wasn't the track where I do have rotation problems. It's a track I know a lot though, and I did test my changes out. I was running full thread street tires (khumo XS), because of the rain.

I did lower my front tire pressure, too. I didn't run much with these tires yet, so I don't know where their sweet spot is.

It's hard to tell because of the light rain, but the car still rotated OK on some part of the track, and it did pushes are other spot...but I cannot conclude anything yet.

My question is : Let's suppose the upgrade I did was supposed to give the front more roll resistance and since it was too low before, and the result should be better rotation when considering front and rear RR. Supposedly. Would the car automatically be harder to drive in the rain (ie more rotation) ? I don't know if I am clear, but I must say that the car felt more seated, and i'm scared to be going in the wrong direction.

Next step is removing a bit of rear camber. Hopefully that will help some more.

And then...if I don't get the rotation I need, what could I easily do at the track ? I have many big events coming in the next weeks, that's why I am looking at cheap fixes...things I may be able to do at the track.

- Increase rear tire pressure
- Remove even more rear camber
- Increase rear height (i expect a lot from it, as last resort)

Patrick, who still can't figure out why his girlfriend's coupe has got the rotation he would like to have.