[Pparana]

Originally Posted by rwalker

How can too much front grip cause understeer? We agree that understeer means front sliding/pushing?


Not always, I mean anything that is making the turn in sluggish, or unresponsive.

Interesting examples. Note that I'm running stock camber rear (around 2?, dunno) and more than -3deg front. My car really seems to like it.

.5 or so additional camber is not so far off the mark, that will also reduce under steer, which may be what you like. I did not want to go past 3 deg for tire wear and temps did not call for it. I guess a way to describe it is BBQ, Lots of ways to cook the meat, but in the end you get the same results.


HPDE or track days is not racing, If you like the way the car feels than run that setup. Unless you are chasing 10ths of seconds its kind of a moot point. My main setup goals are safety, feel, consumables, then time in that order.

[rwalker]

Originally Posted by Pparana

.5 or so additional camber is not so far off the mark, that will also reduce under steer, which may be what you like. I did not want to go past 3 deg for tire wear and temps did not call for it. I guess a way to describe it is BBQ, Lots of ways to cook the meat, but in the end you get the same results.

fair enough, but you were making it sound like good, safe recipes were only in this 1deg range...

Originally Posted by Pparana

HPDE or track days is not racing

fair enough, but most of us out there in A and B groups are trying to go as fast as possible

autocross is racing

in both cases (and on the street) my car feels great

[Pparana]

Originally Posted by rwalker

fair enough, but you were making it sound like good, safe recipes were only in this 1deg range...


fair enough, but most of us out there in A and B groups are trying to go as fast as possible

Its not as if it is unsafe, its just out of normal parameters. I geuss a good place to start would be with a tyre pyrometer. You would run a few laps to warm up, then a few hot laps, then pit in. Ideally someone else can grab the temps very quick. You then adjust the camber based on the readings. (I have not seen or heard of many applications where the camber delta is more than 1 degree).

This is a good article on tire temps:

http://www.longacreracing.com/techni...meter%20Tips#D


Once that is sorted, then you would move on to other parts of the suspension for tuning.

A good book that covers most theory and application on suspension and chassis would be:

http://www.amazon.com/Chassis-Engine...car+suspension


autocross is racing

in both cases (and on the street) my car feels great

Not sure on auto cross, not my thing, but I believe it is one car on track. Not much race craft involved there. More like a Time trials. DEs with run groups usually employ point bys, again no real racing there.

In any event all I am trying to say is if your car feels great to you and your happy with your times, performance, consumable use than why change it. there are no HPDE medals to win. It is a sport strictly for enjoyment of the driver.


I will not even consider setup changes until I am running laps within 1/2 a second consistently for at least a few days, and that is only at my baseline track where I have the most time.

[bgregg]

After any suspension changes, you usually have to do additional fine tuning. I'll assume on BMW M235i most everybody would have the common problem on getting it "just right", since you'd be very lucky indeed on the first try!

And from my figure 8 driving test, which is a pretty good low-speed way of feeling the handling, I would say that most people are trying to tackle the problem of understeer. That is what my first impressions of what my own fine tuning will be addressing.

Here is the list of possible "cures":

Ways to Correct Understeer

Raise front tire pressure
Lower rear tire pressure
Soften front shocks and stiffen bump
Stiffen rear shocks
Lower front end
Raise rear end
Install wider front tires
Install narrower rear tires
Soften front sway bar
Stiffen rear sway bar
Increase front negative camber
Increase positive caster
Soften front springs
Stiffen rear springs

Oversteer and understeer are more common problems in racing than in street driving. As such, weather and track conditions, as well as varying driving styles and abilities will also play a role.

Source: Oversteer and Understeer corrections courtesy of Roger Kraus Racing.

[Pparana]

Originally Posted by bgregg

After any suspension changes, you usually have to do additional fine tuning. I'll assume on BMW M235i most everybody would have the common problem on getting it "just right", since you'd be very lucky indeed on the first try!

And from my figure 8 driving test, which is a pretty good low-speed way of feeling the handling, I would say that most people are trying to tackle the problem of understeer. That is what my first impressions of what my own fine tuning will be addressing.

Here is the list of possible "cures":

Ways to Correct Understeer

Raise front tire pressure
Lower rear tire pressure
Soften front shocks and stiffen bump
Stiffen rear shocks
Lower front end
Raise rear end
Install wider front tires
Install narrower rear tires
Soften front sway bar
Stiffen rear sway bar
Increase front negative camber
Increase positive caster
Soften front springs
Stiffen rear springs

Oversteer and understeer are more common problems in racing than in street driving. As such, weather and track conditions, as well as varying driving styles and abilities will also play a role.

Source: Oversteer and Understeer corrections courtesy of Roger Kraus Racing.

I would start with ride height and spring rate (rear). If symptoms are showing under the conditions described, sounds like too much weight is transferring to the rear under acceleration causing the front end to wash out. I think if I read correctly your ride height has you raked to the rear?

Best bet would be some track time to get more input at various speeds and conditions so you can decide what changes would suit you best.

[bgregg]

Have a tiny amount of suspension settling after having it a couple of days, and jacking the car up a couple of times now to change tires back and forth from street to track, and vice versa.

Currently at 25.5" front and 25.25" rear on the street tires/wheels. So as Pparana suggests, I will try getting the rear a little bit higher than the front for understeer correction. Maybe the rear I'll try 25.75, which is a half-inch change in height. Recall that I am as low as I can go in front, but have tons of height adjustment in the rear!

Will also be trying narrower rear track tires, as mentioned previously and that also counts toward understeer correction.

For the obvious reasons of preserving street comfort, I'll avoid trying the next step up in rear springs (which would be 700 lb/bin), for now. I value the street comfort too highly!

On most cars, I would just do the rear swaybar only. But since this car is so labor expensive on swaybars, try other options first. I could try even more negative camber in front since I can now do that pretty easily.

[Pparana]

Originally Posted by bgregg

I have a tiny amount of suspension settling after having it a couple of days, and jacking the car up a couple of times now to change tires back and forth from street to track, and vice versa.

I am currently at 25.5" front and 25.25" rear on the street tires/wheels. So as Pparana suggests, I will try getting the rear a little bit higher than the front for understeer correction. Maybe the rear I'll try 25.75, which is a half-inch change in height. Recall that I am as low as I can go in front, but have tons of height adjustment in the rear!

I will also be trying narrower rear track tires, as mentioned previously and that also counts toward understeer correction.

For the obvious reasons of preserving street comfort, I'll avoid trying the next step up in rear springs (which would be 700 lb/bin), for now. I value the street comfort too highly!

On most cars, I would just do the rear swaybar only. But since this car is so labor expensive on swaybars, try other options first. I could try even more negative camber in front since I can now do that pretty easily.

What's the height w the track tires? I would start there and try to get at least neutral or slight rake with front being lower. Rear sway is pretty easy. Actually shame you did not put it in w the diff, About 80 percent of the work was done. Rear bar should be no more than 2.5-3 Hours of labor if you decide to go that route. You will have to figure out if the tires are washing out, rolling over or if the steering is just sluggish to respond. Some track time and a pyrometer would be a good start to base lining the car. From there you can make some better assumptions on what you might want to do.

[bgregg]

During my figure 8 testing my observation/complaint was not about body roll at all. I think the guys with Dinan or H&R spring setups do benefit from swaybars, so that is a smart decision for them. But, since I have dealt with body roll already primarily through the Eibach race springs I may be able to use a smaller hammer solution.

I am thinking I need about 3 or 4 smaller hammers simultaneously in NASCAR pit stop style. And I am motivated to try all the inexpensive ones first. So I am thinking of doing the following ones:

1. increase rear ride height
2. increase front tire pressures
3. decrease rear tire widths (not cheap, wanted to do that anyway for safety reasons and rotation reasons)
4. increase front negative camber and maybe decrease rear negative camber and get a 1.0 difference between front and rear. Something like -2.8 front and -1.8 rear?

With the limited slip, the rear end is gripping in an awesome way. So rear is dominant right now. What sounds optimal to me is just enough negative rear camber to prevent tire wear, but not so much as to lose the acceleration capabilities of the rear down the straights. During my figure 8's the front always lost grip a lot sooner than the rear.

What I am looking for is more equal grip front and rear so that they lose grip about the same point. Then the rest is up to me as the driver to adjust my driving style to the car.

The compromise solution is usually this: corner entry (understeer), mid-corner (neutral), corner exit (power on oversteer).

[bgregg]

Got a few more days in of regular driving:
I am quite happy for a "street" car with the 440 lb/in front springs and 650 lb/in rear springs. The ride is still comfortable to me, as in firm but not at all harsh. A trackrat might like to experiment with the 475 lb/in front springs and 700 lb/in rear springs that are a step up from where I am at.

With my current spring rates, the car is much stiffer than the Dinan (10% stiffer than stock) and H&R lowering springs. I also had a brief experience with the Eibach Pro-Kit springs before the Eibach Race springs. EDC was being called upon much more to perform anti-dive control with the soft springs. I have a lot more built-in anti-dive with this setup. Similarly, a lot of anti-roll built in.

The main spring observation I can make is to skip over the 5" 425 lb/in front springs, because they did not hit the target. Mainly due to the 5" length rather than the 425 lb/in rating. It was just inadequate spring travel range. 6" length is just right.

Relative to stock, am I about 2X the spring rate in front over stock? It definitely doesn't feel like that much, but maybe numbers are deceiving to feel. It may be too complicated a question to answer, since Ground Control carefully avoided comparing progressive and linear. So I am presumably 2X stiffer in the soft/progressive range of the stock spring, but then as it ramps up I am only 1.5X stiffer, and so on.

On track, a progressive spring will eventually take a "set" as it gets past the soft range and into the firmer range. So the driver has to get used to the idea of some non-linear performance in roll (and in dive). Hence why linear springs are easier to drive on a track, and why I said that I liked them. Also, explains why people like adding swaybar upgrades to the progressive spring setups (both front and rear) to take some of that effect back out.

I have not noticed any problems with using a fairly comfortable linear spring set. No unwanted oscillations or bouncy or floating behavior. On a cost basis, the coilover conversion kit without damper upgrades or swaybar upgrades compares to doing lowering springs+pair of swaybars+camber plates, to put that in some perspective. Both solutions would probably be using camber plates so that is just a small difference, however my camber plates seem to be better off in fitment to a 2.5" coilover spring and staying in compression even with the car off the ground.

That said, I think a Dinan spring+complete swaybar+camber plate setup would drive quite well. I did have a Dinan setup on a previous BMW. And I had an AC Schnitzer setup on another BMW. This is my first Ground Control setup. Today after driving my car, I got out of it and smiled-this is good!

[Pparana]

Glad you got it sorted, let us know how you like it on track.

[bgregg]

Adjusted my rear suspension up to equal the front height, so have everything at 25.5" on all corners. By jacking the car up in the air to take all load off the swaybar, I was able to do the rear height adjustment. Since the height adjusters were not under spring load, I was able to turn them by hand to bring them into contact with the spring and get the desired height. Way easier than I was expecting, actually.

Then took the car out on street tires to re-run the figure 8 test one more time. On street tires I felt that the rear did want to be playful. So the handling to me is like throttle steering. A little bit different than the feel on race tires. The handling is almost optimized already for street tires the way I have it.

Proceeded after that to do one of my favorite mountain drives, which really tests the suspension ability to keep tires on the road, with the crests and falls. And also test the suspension travel from some pretty hard dips. This type of driving I do more often than racetrack driving. Got to give it high marks of praise!

[ocN55]

How much did this kit run you? Can't find it listed on the site.

[x233]

bgregg, excellent work. glad you sorted it out so well. thanks for the detailed writeup. this may be very helpful.

[Ace604]

Originally Posted by ocN55

How much did this kit run you? Can't find it listed on the site.

+1

Which vendors are currently selling the kit?

[bgregg]

Originally Posted by Ace604

+1

Which vendors are currently selling the kit?

Only available directly from Ground Control, and I don't think they have updated their website to mention the kit for F22 availability. I found out about it just by E-mailing them to ask what they had. It was around $1075 with tax+shipping. The springs would be available from any Eibach reseller/authorized distributor (which Ground Control is in N. California). The camber plates and height adjusters were custom items from Ground Control.

[Ace604]

Any updates on this? Been looking more and more into this setup lately. Since I have a set of Koni yellows laying around, thought I'd put it to use with this kit. I've already emailed GC and they said they are able to adapt their kit for the Koni's.

So did the 440 lb 6 inch springs end up being the best fit? My goal for the car is quite similar to yours as well.. the odd autox/track day, spirited backroad runs, and dd.

[bgregg]

Yes, the kit is holding up well for me still. No real changes in noise or anything since I first installed it. I would say 6 inches for front springs is best, since you'll actually be able to go over a speedbump or uneven pavement without cringing. You'll still cringe on a major pothole though, so I try to avoid those!

[HP Autosport]

Originally Posted by M-terkait

Same as my case, cant be arsed to post pics again.

That is the weakest link in the GC plates. Have some of these bearing on hand when doing front suspension work with GC plates is a must.