Coilover adjustment question?

[ddub]

I just installed some Megan racing coilovers and they ride great. I adjusted the ride height and measured it from the ride height adjustment clamp to the spring adjustment clamp. I did not touch the spring adjustment clamp. Now when the car is put down on the ground, it looks like the left front wheel is a little lower than the right front wheel. Measureing from the wheel hub to the fender lip, there is about an 1/16 to an 1/8 of an inch differance from each side. I don't know why this is though because I made sure they were set at the same place, measureing on the coilover. I can see that there is a lot more camber on the left front than there is on the right front. I am taking it in for alignment tommorow at les schwab. Maybe they can make sure everything is good. Any suggestions?

[AtomicLabMonkey]

Production tolerances on the car can easily throw off measurements taken from a fender. If you want to set ride heights correctly, measure to the control arm chassis pivot bolts instead of the fenders. Also make sure the car is on a flat, level surface.

[sperry]

Also, drive or roll the car around a bit to make sure everything is settled.

[Dean]

What the Monkey said. eveness of corner ride height is mostly meaningless in terms of eveness of handling. If you want the car to handle evenly, cornerbalencing for "even" cross-corner weights is what you want to do.

[Kevin M]

Take it to C&C Fuel Injectiuon instead of Les Schwab, unless there's somebody there that knows a lot more about McStrut coilover setups than I'm expecting. LS and Big-O and places like that are going to give you the lame ass factory alignment specs, unless there happens to be a specific individual there who knows what he's doing. And a lot of SECCS folk have gone to C&C now for cornerweighting and performance alignments.

[M3n2c3]

Originally Posted by BAN SUVS

Take it to C&C Fuel Injectiuon instead of Les Schwab, unless there's somebody there that knows a lot more about McStrut coilover setups than I'm expecting. LS and Big-O and places like that are going to give you the lame ass factory alignment specs, unless there happens to be a specific individual there who knows what he's doing. And a lot of SECCS folk have gone to C&C now for cornerweighting and performance alignments.

How much would a cornerweighting and alignment cost?

And I concur on the suggestion to stay away from Les Schwab.

[sperry]

Originally Posted by M3n2c3

How much would a cornerweighting and alignment cost?

And I concur on the suggestion to stay away from Les Schwab.

Probably around $100 including a performance alignment.

[M3n2c3]

That's not so bad. I may have to get that done before the season starts. [/thread hijack]

[Kevin M]

Yeah I'm pretty sure that's what Matt paid for his alignment, but I'm not positive so YMMV.

[ddub]

thanks for the info. I took it to les scwhab today and they said my car was too low. It wasn't that low though. I am going to call C and C tomorrow and find out the details.

[Dean]

Take a look at this thread, and take some measurements. You probably don't want to be much lower than the tarmac/race ones, or you enter the dreaded "Positive Camber Zone".

http://www.seccs.org/forums/showthread.php?t=3283

[ddub]

My spring rates are 8kg front and 6kg rear. Are the recommended ride heights ment for softer springs than what i have. Right now I feel like my car handles great. I have it at about 13.25in in the front and 13in in the rear. It takes corners much better now than it did before. With stiffer springs, the less the spring compresses through corners, meaning less body roll. I also really like the way it looks now, but definitly need alignment. I was reading some other threads and saw other people who had it at the height I have it now.

[Dean]

Ride heights on the Impreza chassis are largely determined due to suspension geometry. Once the front control arms go past level, the front suspension design causes camber to go positive very quickly which is very bad for handling.

It is so bad that in stock Autocross class where you can only change the front sway bar, not rear, they put massive 32mm bars on and have had great results.

The improvement in contact patch and enhanced turn in far outweighs the reduced suspension complieance and does not induce additional understeer as you would normally expect.

[MattR]

Originally Posted by M3n2c3

How much would a cornerweighting and alignment cost?

C&C quotes $300 for full custom alignment and corner balancing, because they bill it out as 3 hours of labor. If it goes incredibly quick they adjust the price as needed, but it is a time consuming process, and as you can see, not cheap.

Alignment only there is like $100.

[AtomicLabMonkey]

Originally Posted by Dean

Once the front control arms go past level, the front suspension design causes camber to go positive very quickly...

This is a bit of a misleading statement; angling the LCA's down towards the chassis is typically bad for handling, but not for the reason you're describing. The negative camber gain in bump does get smaller as you angle the LCA's down, but it is not an on/off switch like you make it sound. The wheel will still have negative camber gain in bump up to point where the LCA is perpendicular to the steering axis.

The dominant effect is the change in front view swing arm length, instant center locations and corresponding changes in roll center location & stability. These parameters are very sensitive to LCA angle. Changing the chassis pivot height even 1/2" can mean the difference between a stable roll center as the suspension articulates, and a roll center that swings wildly around outside the car as the instant centers pass through asymptotes.

[ddub]

I just talked to C and C, $300 is kinda steep. They said they could do an alignment and make sure that all the wheels are at the same height for $100. When I take it in, I will ask them if they think my car is to low. I actually raised it up a little after the les swhab visit. I may just leave it where it is now and raise it up if C and C thinks I should.
Judging by the feel of my car yesterday, I think it handles great. I was taking corners and it felt like I was on rails, no understeer either.

[MattR]

Cool, good deal.

[Dean]

Originally Posted by AtomicLabMonkey

This is a bit of a misleading statement; angling the LCA's down towards the chassis is typically bad for handling, but not for the reason you're describing. The negative camber gain in bump does get smaller as you angle the LCA's down, but it is not an on/off switch like you make it sound. The wheel will still have negative camber gain in bump up to point where the LCA is perpendicular to the steering axis.

The dominant effect is the change in front view swing arm length, instant center locations and corresponding changes in roll center location & stability. These parameters are very sensitive to LCA angle. Changing the chassis pivot height even 1/2" can mean the difference between a stable roll center as the suspension articulates, and a roll center that swings wildly around outside the car as the instant centers pass through asymptotes.

I don't believe what I am describing is misleading at all, or incorrect for the macpherson strut front suspension on the Impreza, and the way the attachment points are configured. I am not discussing the chassis pivot at all, as it cannot be adjusted, and am focused solely on dynamic camber as it relates to ride height.

Due to the fixed top connection point on strut type suspensions, and the relatively short front LCAs on the Impreza; as they travel thought their arc from

_
  \
to
_ _

to
_ /

Under compression, they go from gaining negative camber quickly at the bottom to neutral to gaining positive camber quickly at the top. Ride heights controlled by the strut adjustments determine where in this range the LCA operates.

The ride heights I linked to in general keep the LCA out of the extrmely high positive gain area near the top that people get into when they over lower the Imprezza front suspension, especially on soft springs.

Because they cannot change springs, or ride height The A Stock autocrossers have done a bunch of imperical testing, using ever larger front sway bars on the front of the stock STI up to the current huge 32mm bars with no rear changes to keep the stock front suspension from going into the bad positive range. On a car that already understeers, that sounds like lunacy, but the gains in/maintenance of front traction due keeping a properly negative camber and thus good contact patch while cornering far outweighs the negative effects of the stiffer roll characteristics on that end of the car.

[ddub]

The Key point that I see from your description is SOFTER springs. So it seems like you should be able to go lower with stiffer springs because there is less of a compression distance under cornering.

[AtomicLabMonkey]

Originally Posted by Dean

I don't believe what I am describing is misleading at all, or incorrect for the macpherson strut front suspension on the Impreza, and the way the attachment points are configured. I am not discussing the chassis pivot at all, as it cannot be adjusted, and am focused solely on dynamic camber as it relates to ride height.

Dean, I'm not debating the relative merits of larger swaybars on Imprezas to cure the low amount of designed negative camber gain. I know what you're talking about there, that's fine, but it's not what I was correcting you on.

My point was that the change in camber gain as you lower the car an inch or two is not a huge effect - the change in front view geometry, and subsequent effects on roll center, roll couple & dynamic weight transfer, is.