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Hot!Negative Camber and Road Crown - Is it necessary to counter steer/compensate

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jameschurchward
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2020/01/23 00:28:32 (permalink)

Negative Camber and Road Crown - Is it necessary to counter steer/compensate

I have Cayman which is running maximum spec negative camber on the front wheels.  The car was set up by a specialist specialising in geometry.
 
I note that on most UK roads (where the road crowns to the left), when driving straight the steering wheel is truned slightly right (say 1-2 degree of counter steer) to compensate.  If the wheel is held level i.e. no counter steering, the car will drifts to the kerb.
 
If I drive in the middle of this same straight road (when safe to do so), the steering wheel is held level and the car drives straight.  If I drive on the opposite side of this same straight road (when safe to do so), the steering wheel is required to be counter-steered 1-2 degrees left to compensate (else, with the wheel level, it will drift to the right and the off-side kerb).
 
In short is a small counter-steering expected when travelling straight to compensate for the crown of the road?
 
What is the experience of other Porche owners.
 
 

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ralphmusic
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 08:24:35 (permalink)
James,
 
I think if you notice it there maybe something not quite right with your settings, or once you notice it you can't un-notice it and so becomes an issue. I ran 3:10 degrees negative on the front and 2:40 rear negative rear and did not have any issue with lorry tramlines nor normal road camber.
 
Do you have a print of your settings you could post here? 
 
Ralph

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jameschurchward
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 09:03:29 (permalink)
Hi Ralph,
 
Here's the printout.
 
Cheers,
 
James

post edited by jameschurchward - 2020/01/23 09:05:57
Hacki
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 09:22:42 (permalink)
Ralph,
 
interesting thread. I know you´re experienced and very sensitive with settings. To me that print out shows nothing special other than that front camber is almost nothing and not "maximum spec", although there´s some camber on the rear. It would also be interesting to read how that car handles - understeer, oversteer, neutral, nervous under hard braking? I guess there´s some understeer.
Can ride height or rake be an issue on a Cayman? Probably yes.
 
I´m impresssed a Cayman with track settings like yours doesn´t cause any trouble when used on roads. (That´s not possible with a 964 Cup or RS, for sure not!)
 
Looking forward to reading more about the modern cars´ suspension issues.
 
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ralphmusic
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 09:52:05 (permalink)
Looking up my last geo settings before it was all replaced with custom parts, the car was a 981 Cayman S, PDK and had PASM -10mm and was on 20" wheels, the settings were:
 
Front
Camber - 1:05
Total Toe 0:02
Castor 8:20
Rear 
Camber - 1:35
Total Toe 0:18
 
The big difference from my settings on my car's stock suspension and from James' setting is (as Hacki observed) the relationship between front and rear camber. Also, as Hacki notes behaviour under hard braking, cornering and acceleration might be issues too but you'd need to be on track to really sense behaviours. You might be surprised at how small a change/difference might make to handling at speed.
 
With my car's later custom suspension, we went with more front camber than rear (as noted on 2nd post above), with total front toe of 0:02 and total rear toe of 0:26 which for me worked well with those cambers.
 
To Hacki's point on road behaviour with my custom suspension, I was very surprised the large cambers did not cause any "camber following" or sticking in lorry tracks, but it just didn't. I needed larger cambers for track use and my "style" of driving.
 
James, I don't know where you are in the UK but you might send your settings to and call Centre Gravity to have a chat through if they see anything that might explain the behaviour. If you call them around 08:30 as they are setting up for the day I am sure they will be happy to spend 10 minutes talking to you.
post edited by ralphmusic - 2020/01/23 09:53:35

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944Turbo
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 10:01:09 (permalink)
My experience is 944 not cayman but when I had my geo done they wanted to set it up staggered to compensate for the crown - how they set up 'normal' cars. I wanted it square to feedback what is going on with the road. If there is pronounced crown the car will want to go down it so on the LHS left, RHS right. I like it as it gives extra feedback, a banked turn (the right way) will give more grip than a flat one.
 
If your front wheels are slightly toed out, which I think they are (with a positive figure) that will create more camber following - especially if those figures are static (when driving the wheels will tend to push back against any compliance in the suspension bushes potentially increasing the toe out   (unless that movement would effectively shorten the steering arms which is dependent on steering rack to hub geometry).  The toe out will improve steering response but toe in will give you more straight line stability.
 
I had my toe set straight for mostly road miles with  5 or 6 trackdays a year, the front camber was at the extreme of the recommended road settings -0.45 castor was also extreme of road settings (very different to cayman 2.5deg) rear toe similar to you for a couple of years and then a bit more (0.17 each side - the rear of the car was very easy to control out of line at this point but had other changes too) rear camber -1.5 degrees.
I was wearing inside of they tyres on the road, outside (much more so especially front) on the track, would have gone for more camber front and rear if my track miles increased and my road miles went down.
 
I think if yours is too twitchy - a small reduction in front toe might help (-0.05) what is the factory figure?

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Lancerlot
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 10:01:42 (permalink)
The NC is not excessive.
 
Caster angle is the main influence on straight line steering. Yours seems OK according to the readout, unless it has been subsequently modified by impact, such as hitting a pothole etc.
 
If all suspension components and tyres pressures etc. are in order, try increasing toe slightly. As a general rule, more toe-in or less toe-out provides for better the directional stability. 
Regards,
 
Clive

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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 10:33:08 (permalink)
James,
 
That looks like a decent set-up to me, with nothing obvious to indicate why the vehicle shouldn't track straight. Basic static mechanics (inclined plane) tells us that there's a component of weight acting towards the kerb, but this should be very small bearing in mind the small road camber angles we're talking about.
 
You don't mention the state of the tyres and it would be worthwhile checking the wear patterns and tread depths for any significant variances side-to-side.
 
I'd agree with Ralph's suggestion that you contact Centre Gravity for advice. Maybe an email containing your printout would be a good first step?
 
Jeff

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jameschurchward
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 10:53:46 (permalink)
My 718 Cayman, to which the print out relates, is on 1300 miles.
 
I wasn't entirely happy with the handling from day-one (October 2019) so took it back to OPC (then 200 miles) who found it was "out of spec".  They adjusted the cambers and toes so it was "per manufactures spec".  Then it really drove strange!  I sent the OPC before+after prints to a specialist who commented that there was no way the before could have been that bad, and he OPC ramps or something must have been wrong.  I took the car to the specialist (now at 600 miles) and their initial evaluation test drive and subsequent inspection and measurement showed the OPC set-up was wildly wrong.  The car was then set-up for fast road use (within Porsche tolerances) and the evaluation drive revealed that the strange handling had been erradicated.  However, it was late by this point (plus dark and wet) and I was driving on unfamiliar B-roads.  It was only on the long drive home, mostly A and M roads that it dawned on me I was having to counter steer right by a degree or so (not much) to compensate for the road crown.  I queried this with said specialist and they said this was normal and more extreme set-ups e.g. on GT Porsches require even greater steering input to compensate for road crowns.  Hence I'm interested in the experieces of other owners.
 
The only person who has driven my car with the exception of me was the specialist who set it up so I'm certain it has not been in a shunt or driven down a pot-hole.   The tyre presures are checked weekly with a hand gauge and on evey drive via TPMS.
post edited by jameschurchward - 2020/01/23 10:55:17
Lancerlot
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 11:11:54 (permalink)
As others above have suggested, discuss the problem with Chris Franklin at Center (sic) Gravity in Atherstone.
It would be worth investing a day there for peace of mind and to get it sorted out.
Regards,
 
Clive
 
 

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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/23 11:39:17 (permalink)
As Ralph said minor changes can cause major effects. So, sorting things out might take a day (as also said before) and the best way is having the chance to test drive the car after every change on a proper road or, even better, on track. It´s really worth the effort. The basic set up has to be done before, of course.
Another thing is to check the calibration of the stand the set up is measured with. Only top equipment will produce correct data. Taking the risk of sounding like an anorak I know that every detail in set up is important and AFAIK Porsches have always been very sensitive to set up changes. And you need a real expert to have a proper set up done. I had a real master do the work on my then track tool (now garage furniture, a 964 Cup), the effects were astonishing - and I also learnt a lot.
 
I wonder how many cars with wrong (OPC) set-ups as described above are out there and the owners have no idea how much more fun they could have.
 
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tscaptain
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/24 09:46:54 (permalink)
Far from being as knowledgeable as the previous contributors I would offer the following.  I have just had my 911 reset to values given by CG, which are very similar to yours but with a bit more negative camber up front.  It drives with the steering wheel perfectly straight on the crown of the road and, indeed, if there is a significant camber on the road, will tend to drift gently left with the wheel held straight when on the left side of the crown. It did this after the original set up at CG too.  The way I see it is that if the road slopes down to the left there is a side force acting on the car - er- gravity.  However, as said before, worth getting it checked out by the best chap.

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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/24 17:01:19 (permalink)
When my car went to Chris at CG he said, 'lets count and see how quick the steering drifts to the kerb'. Iirc it took 1-2secs before his hands were back on the wheel. After it spend 10hrs on his ramp being corner weighed and full geo we went back out on a test drive. With hands off the wheel it took more than a count of 3 before hands went back on. Yes it drifted to the kerb but took far longer. He was happy as the road camber will always drift you from high to low ground.
 
Tyre quality and pressures will also make an impact on the drift as well as geo set up.

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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/01/26 16:53:14 (permalink)
Quote
”The car was then set-up for fast road use (within Porsche tolerances)”
 
no such thing. Because a fast road set up would show red within Porsche tolerances.
you need about -1.2 without parts up front, and make sure the tow at the rear  is ok as that keeps you straight. 
 
I like my cars alive so run zero toe up front, track cars might run a bit of toe out and even more alive But those will tram line. 
 
Geo looks ok to me as is and the car will drift left or right due to the road.
but it’s Not a fast road geo. 

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jameschurchward
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Re: Negative Camber and Road Crown - Is it necessary to counter steer/compensate 2020/07/11 01:14:22 (permalink)
Update (should have posted earlier).
 
I took it back to the specialist.  They agreed with my points - yes it was out of alignment despite the print out and post-adjustment test drive - and re-adjusted free of charge.  But how did they get it wrong in the first instance?
 
Well, they used a bubble level to set the steering wheel level.  Its spring loaded and locates into position on the thumb rests on the inside of the steering wheel.  But on my 718 the right-hand thumb rest is fractionally thicker on the leather/stiching (not much).  Thus when the bubble gauge was level the steering wheel was slightly right-hand down.  So they set it up and we did the post-setup test drive.  However, the mistake was not picked up ... very difficult to spot on the post-setup drive ... in the dark... in the rain... on B-roads ... at rush-hour.  Only later did I begin to question it.

In reality, however, when the wheel was truely level (confirmed by a small spirit level across the spokes ... and by eye), the front wheel were basically pointing to the left!  This was why when travelling on a straight road with normal camber I was having to steer right more that expected.
 
The fix.  Back on the Hunter, and the steering wheel now correctly levelled (based on spokes) ... ~1/8 of a turn on the two track-rods.  Job done.
post edited by jameschurchward - 2020/07/11 10:01:27
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