dyi front camber mod - 986 Forum

baxster · 05-01-2011, 11:18 PM

I've already adjusted my front camber by moving the strut tower bolts. When I look from underneath I can see that the top of the strut can move about another 1/4 inch if the bolt holes were a bit longer. That might give another .25 to .5 of negative camber.

Has anyone tried to make the bolt holes any longer? What do you think of the idea?

harryrcb · 05-02-2011, 07:01 PM

Yes it works great, although I would recommend getting larger type cupped washers for better grip.

baxster · 05-02-2011, 07:13 PM

What did you use to make the bolt holes longer or should I say wider? How much longer did you make the holes? How much of a difference did it make?

Sorry for all the questions but I'm curious if the work is worth it.

harryrcb · 05-03-2011, 05:11 PM

You can use a dremel or die grinder and I did it so long ago I don't remember the specs but it was worth it. don't know if you want to wait (have a lot of fires burninig right now) but eventually I can did into it and give you the specs. I do remember you need a lot of careful measurments sos that you don't screw up the caster by moving the strut forward or backward, you want to go straight in.

baxster · 05-03-2011, 08:52 PM

thx... I'll put this on my mod list.

insite · 05-04-2011, 11:48 AM

keep in mind that when you change the camber, you are also changin the toe.

with our cars, the tie rods attach ahead of the axle, so when you add negative camber, you toe out. when you add positive camber, you toe in.

the cars are set from the factory with some toe-in, but if you add enough camber to cause toe-out, be aware that the car will become darty when trying to drive straight. it will get a bit squirrely under braking. it will also tend to understeer a LOT in the rain. oh yeah, and it can DESTROY your tires.

better to be sure you understand what you're doing. the best alternative is to have an alignment shop add neg camber while doing a full alignment. this way, you can be sure your toe is proper.

baxster · 05-04-2011, 08:23 PM

Thank you insite for your insight

. You sound like an expert on the topic.

Once I extend the bolt holes, I will have a professional alignment done with zero toe and camber maxed in the front, and 1/2 degree greater camber in the rear with slight toe-in.

insite · 05-05-2011, 05:46 AM

bax -

what are you using your car for? street, auto-x, track, combiniation? what kind of tires do you have? maxing out your front camber isn't necessarily a good thing.

the boxster has a LOT of caster built into its design. that means that as you turn the steering wheel, the suspension geometry actually adds camber. the further you turn the wheel, the more camber is added.

more front camber GENERALLY helps with understeer, and can increase lateral g capability. this comes at the expense of braking distance and straight line stability. in effect, you are trading straight line contact patch for a larger contact patch during corners.

the right amount of camber really depends on a lot of factors. give me some insight & i'll give you some insite.

baxster · 05-05-2011, 09:52 PM

The box is mostly for street, then some auto-x, and hopefully some DE days. It has 17" S-02A's.

From what I've read, maxing the front camber will get you something like .5 to .7 of neg camber, and that's with about 1/2 inch of movement of the strut tower bolts. If I can get 1/4 inch more movement of the bolts, I might be able to get up to 1 degree negative camber.

Are you saying that -1 deg of front camber will make my braking noticeably worse?

insite · 05-06-2011, 04:52 AM

-1 up front is too much for street tires. -0.8 is about perfect. aim for -1.8 to -2.0 in back. the amount of neg up you can get up front will depend on whether your car is lowered or not. when you lower your car, neg camber increases.

and yes, more neg camber reduces braking distances. you are trading straight line traction for turning traction. always a trade off......nothing is free.

Pat · 05-06-2011, 07:30 AM

The nice thing is, with increased camber you don't have to slow down as much for corners, so loss of braking isn't such a big deal.

j.fro · 05-07-2011, 06:39 AM

Just some information, FWIW.
I use aftermarket struts with mounts that give me a lot of camber adjustment. Camber is set to -2.3 degrees up front with zero toe.
In a typical year, I'll put 12,000 miles on the car and do 12-14 auto crosses. The car eats two sets of tires: a set of r-comps for the AXes and a set of street tires for the rest of the driving. Every spring my tax return goes straight to a tire purchase.
Is it sensible? no way!
Is it fun? HELL YEAH!!!

baxster · 05-08-2011, 08:35 PM

Quote:

Originally Posted by insite

-1 up front is too much for street tires.

With the mod I'm talking about, I'll probably be lucky tp get up to -1. Why is -1 too much for street tires?

baxster · 05-08-2011, 08:40 PM

Quote:

Originally Posted by j.fro

Just some information, FWIW.
I use aftermarket struts with mounts that give me a lot of camber adjustment. Camber is set to -2.3 degrees up front with zero toe.
In a typical year, I'll put 12,000 miles on the car and do 12-14 auto crosses. The car eats two sets of tires: a set of r-comps for the AXes and a set of street tires for the rest of the driving. Every spring my tax return goes straight to a tire purchase.
Is it sensible? no way!
Is it fun? HELL YEAH!!!

I think 'insite' would say that your braking will suck at -2.3. What have you noticed with your braking with street tires at -2.3 camber?

j.fro · 05-09-2011, 03:02 AM

The brakes are unreal! I've got Hawk HP Plus pads, stainless brake lines, and use Ate Blue. I can brake very late and still get no understeer in a corner. But that's for AX on the R-comps. I don't push my street tires nearly hard enough, and as a result the inside edges wear fast. I'm lucky to get 10K on a set of front street tires, but that's the price of an aggressive AX set-up. There really is no such thing as a car that does everything well .

insite · 05-09-2011, 05:09 AM

the max camber a given tire can use is proportional to the tire's grip capability. if you use too much camber for the tire, you won't be using the entire contact patch & you'll lose total grip.

imagine zero camber: when you turn, the tire rolls over onto the sidewall. the result is that you're using the outside half of the tire too much & the inside half of the tire not at all.

imagine correct camber: when you turn, the tire rolls, but because of camber, the tire actually rolls ONTO the contact patch, giving you 100% of the tread contact with the road.

too much camber: while straight, the tire rides on the inside shoulder. when you turn, the tire rolls onto SOME contact patch, but the outside half of the tire is still not making good contact with the road.

the result of too much camber will be that the insides of the tires wear too fast. also, ultimate grip in corners will be reduced because you've actually reduced the size of the contact patch.

keep in mind that CASTER affects mid-corner CAMBER, so while you may only have -0.8 dialed in with the wheels straight ahead, when the wheels are turned & the suspension is compressed, you will have significantly more (-2.5 or more). it's easy to go too far w/ front camber on street tires w/ the boxster because the car has a LOT of caster designed into it.

to understand caster, it helps to illustrate extreme scenarios:

zero degrees caster: the rotational axis for the steering is completely vertical. turning the steering wheel ONLY turns the wheels right & left.

90 degrees caster: the rotational axis for the steering is completely HORIZONTAL (i.e. straight out in front of the car). turning the steering wheel tilts the tires left and right, but does not turn them at all.

SOME caster: turning the steering wheel BOTH turns the wheels AND tilts the tires.

as to braking, less camber generally means better braking distances. that's not to say that great braking doesn't exist w/ heavy camber, only that great braking gets even BETTER with less camber.

that having been said, the reason i say -1 may be too much for street tires has more to do with wear & grip than braking sacrifice. you will wear the insides of the tires down.

Pat · 05-09-2011, 05:40 AM

insite~
Would cornering on a road course be different than cornering in AX? One can generate big lateral Gs on a road course around a very long radius corner if driving fast enough. That would mean the caster is almost insignificant, due to minimal steering input. In AX, a LOT of steering input would be required to generate the same lateral load due to the slower speeds, therefore making the caster a much more significant variable.
Thoughts?

insite · 05-09-2011, 05:51 AM

modern porsches are designed with a LOT of caster in order to maximize the effect at smaller steering angles. as a rule of thumb w/ our cars, every degree of steering angle adds almost a tenth of a degree of camber.

keep in mind, though, that this is not the only mechanism through which the suspension geometry adds camber. the car is ALSO designed to gain camber as the suspension compresses. the rates at which this occurs have to do with the inward angle of the struts & the length of the lower control arms. i don't have camber curves plotted for this car, but i CAN say that suspension compression of 1" will result in approximately -.7 degrees of camber gain. therefore, other suspension changes will modify the camber gain w/ certain amounts of weight transfer. example: soft suspension will compress a LOT, & gain significant dynamic camber through kinematic changes to suspension geometry. stiff suspension will move less & gain LESS dynamic camber, therefore more static camber should be dialed in (comparatively) to compensate.

when someone tells you that their camber is set to -1 or some such number, that is the STATIC camber. the measurement, though, is truly a dynamic parameter.

if you hit the track, you'll want to set camber based on pyrometer readings & treadwear, amongst other things. if you auto-x, the tires never really heat up & your tools will be chalk marks and tire wear.

baxster · 05-13-2011, 06:44 PM

I'm surprised there weren't more responses about the actual modification. I'll let you know how much camber I was able to get with the mod.

Thanks again insite and harryrcb!!

Klimo · 05-23-2011, 09:13 AM

This is a great read. Thanks insite. I am in the process of getting my car ready for track days, no auto x. I do about 6 track days in the summer. I am not worried about giving up some street driveablitly or having to go through tires every 10k. I use Michelin PS2s. It sounds like -.8 in the front might be enough to get what we want out of the car, but if it isn't what are my option for increasing camber on the stock suspension. I don't want to be drilling holes or anything into my suspension like what's being talked about on here. Do I need new struts? Can i jsut add camber plates? Thanks.