Negative camber
I was nearly going to ask this in a general chat thread, lucky I didnt or I would have had to move it and give myself an infraction
The thread was talking about excessive negative camber on cars. I have a 97 BMW Z3 Roadster 2.8 6 cyl which has noticable negative camber. By noticeable I dont a ridiculous amount but you can see the rear wheels tilting in at the top.
Presumably this has been done by the previous owner and I havent seen any other Z3 on the road that has a similar camber tilt. As the Z3 suposedly handles reasonably well stock, why would someone do this to the car ? Due to injury/disability I cant get under the car and look to see if there is a specific modification as to why the camber is that great. I have been pulled over for speeding before and the cop asked me what was in the boot that was weighing the car down. I told him there was nothing in the boot and it was just the cars negative camber and he looked at me stupidly and made me open the boot to prove it.
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On rally cars negetive camber on the front is good for cornering and grip, but not as good for straight line and high speed grip. Im also not sure if it's the same for the back wheels as it is the front.
Id have a look for worn suspension parts or lowered/different shock and springs. Maybe try a pedders or similar that do free or cheap tests. Then get some other quotes on what needs fixing/replacing.
Last edited by Gerbertron; 07-07-10 at 04:59 PM.
At a guess I would say its been lowered. I have to get 2 slow leaking tyres fixed soon so I might ask them to have a look while its up in the air.Originally Posted by Gerbertron
G'day,
There's a plethora of info out there on various forums, however this may indicate that the rear trailing arm suspension was lowered, resulting in the negative camber as noted.
Quote:
Originally Posted by Ian McCloghrie
The other disadvantage to a pure trailing arm is that it doesn't add camber to the wheel as the suspension compresses, like a double A-arm or strut can. Semi-trailing arms can add camber, but you get toe changes at the same time, which generally isn't desirable.
A good footnote to this comment... the toe of a semi-trailing arm will be fairly constant in a relatively small portion of the suspension's travel, but will go further and further out of whack as the suspension moves further up or down. Therefore, the designer of a semi-trailing arm suspension has to position the trailing arms so that they will be in the "sweet spot" of the toe curve when the car is at normal ride height.
This creates a problem if you try to lower the suspension of a trailing arm car. If the suspension is lowered significantly, the trailing arms may move out of their ride height "sweet spot" and create dynamic camber and toe problems that can make the car handle poorly, particularly on bumpy pavement. When a trailing arm car is lowered, the suspension mounting points often need to be moved to correct the camber/toe geometry. This can be very difficult to do on some cars.
FWIW the FC RX-7, Datsun 280ZX, and 1st-gen Nissan 300ZX are three other popular sports cars with semi-trailing arms.
I have the same car and have the same issue.
I have replaced all the springs and shocks struts etc to current M series and i still feel that i have too much negative camber in the rear now, but it is defiantly better than it was before.
There is a guy on eBay that sells a camber kit for the Z3..Or replace your springs
Interesting you should bring this topic up....
Was looking at the wife's Diahatsu Rocky the other night noting the camber on the front wheels - wondering if this would cause excessive tyre wear on the tyre!
I gather this was positive camber (looking from front of car, top of wheels would measure closer than the bottom of the wheels).
Raises an interesting question of what is too much camber?
Waiting for someone like Godzilla to put a mechanical persective on this
We cannot solve our problems with the same thinking we used when we created them - Albert Einstein
Basically if the car has been lowered is will suffer from Negative Camber, this applies to some cars like most BMW's, Commodores.
if you look it up on google it will explain why
but you'll need a camber adjusting kit, pretty cheap and well worth it to save on tire wear if you don't plan on driving it like a race car
I'd go into more detail but I'm sure GZ will explain better
Godzilla (07-07-10)
OK, ill try to be as brief and clear as possible.
@Sanity, if your springs sag (and they can with time) or someone has replaced your springs with lowered ones, the suspension geometry has been thrown out of whack and the car is not griping to its potential on those wheels under all situations (braking, accelerating and cornering) due to the uneven footprint on the tyres.
When the body is lowered on older independent suspension designs, the arms holding your wheel upright and that are connected to the suspension subframe which is bolted to the underbody need to be lengthened to compensate for the extra distance needed to keep your wheel up right.
In other words when the body is dropped, the arms holding the wheels are drawn down with the body. As the arms are drawn down they pull the wheel in with it.
Other side effects can be the drive shafts could pop out or do the opposite and bind depending on the suspension design.
How do you fix it?
1/Get your ride height back to the correct factory setting.
2/All IRS (Independent rear suspension) manufacturers have some adjustment in the arm joints, but be warned its only a small amount if its done with offset bolts, more if its adjusted with shims.
3/Once you have used all you adjustment, the next step is adjustable arms that replace your original ones and have more adjustment.
My money is on the springs need to be changed, they are either lowered or have sagged.
On a side note, about lowering cars....
When lowering a car, the vehicles suspension geometry needs to be maintained at the optimal position taking into consideration the type of tyres and what the car is used for.
Its all good to lower a vehicles center of gravity to increase cornering speeds, however, if the wheels are not at the ideal angle, cornering grip will be lost.
Generally speaking, a street car with early IRS ideally needs no negative camber in the rear, one used for draging prefers a little positive camber as when accelerating the rear drops bring the tyre to a perfectly upright position, and a track car on slicks prefers more negative camber to counter g forces when cornering.
As an example a R32 GTR has a ideal ride height of 355 mm front and 345mm rear measured from the wheel center to the body above it.
At this height the suspension geometry is at its optimal for performance driving.
Any lower may help lowering the center of gravity but the tyres will not be at maximum grip levels and therefore defeating any gains.
Yes adjustable suspension arms will fix the suspension geometry problems when lowering, however they are groaned upon by police and roadworthy testers.
Note even the Bathurst GTR's which were not allowed modified suspension arms sat quite high.
I kept it short, lucky you didnt ask about spring and shocker rebound rates. LOL
Edit ; one thing i forgot to also mention was if you suspension bushes are worn it may also cause your camber to be thrown out and the car to sit a little lower because the wear in the joins allows some of the arms to be longer and others shorter due to wear.
The best way to confirm your problem is to remove your springs and have their lengths checked.
Last edited by Godzilla; 08-07-10 at 12:30 AM.
Mgoldbe1 (08-07-10)
Well said Godzilla.
I love seeing excessively lowered Commodores with totally scrubbed out tyres....clowns
HSV sell their cars with different arms or camber bolts etc so the original suspension geometry is correct at the lower ride height...
Different cars are affected differently....I remember old cars like VW Beetles and Datto 1600s / 180Bs etc had terrible camber change with suspension height change (atleast these cars has IRS all those years ago!!)....where as Falcon BA onwards isn't affected much at all...
Interesting topic anyways....As GZ said, there is far more in it then just lowering your car...
Last edited by Mgoldbe1; 08-07-10 at 08:59 AM.
Godzilla (08-07-10)
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