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Difference: Alignment and Geometry

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PolarExpress

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Alignment checks that the L-R wheels are facing the right way and consistent with each other in symmetry. Effectively a 2-dimensional check easily done at KwikFit... with appropriate effectiveness.

Geometry normally refers to a 3D check of:


  • caster (from above, the fore/aft tilt)
    [list:IOGSqQIloa]toe (from above, point your toes in/out to get the idea)
    [list:IOGSqQIloa]camber (looking from the front/back of the car, the tilt of the wheels)
In addition, a proper geometry check will check the ride heights of the car and the car should also be corner weighted at the same time to ensure correct ride heights with a passenger and [half tank of] fuel.

A proper geometry will be setup for the abilities of the driver, the type of tyres used, and the type of roads/circuits the car will be used on. Geo can be the single biggest factor in determining a "good handling" car... it will determine the physical capabilities of the car too. ie, the same car can go faster over the same circuit/road with the same driver with a revised geometry.


Migration info. Legacy thread was 74607
 
Uneven tyre wear is almost certainly a sign of out-of-kilter geometry. Where abouts are you based? A reputable indie can do the geo as long as they have the required Beissbarth equipment. They will also be able to set it to a bespoke setup based on your driving, whereas an OPC can only set it back to factory settings.

I use JZM in Kings Langley, Herts for all my geos, although I'm sure others here could chime in with where they have had their geo done. Deffo a must do before the 'Ring!!!!! :)


Migration info. Legacy thread was 74616
 
Guys,

I wanted to just check what is best for me, given cash constraints: I use the 996 c2 Cab sparingly (6k p.a.) mostly for motorway journeys. I track it once per year.

Would I really notice getting full geometry done if it is just the standard setup?

Or is laser alignment enough to keep me happy?

Pls bear in mind geo is £220 at OPC, Laser is considerably less (£85?). If I was loaded I would get geo, but I aint (full house refurb underway).

Thanks, Josh


Migration info. Legacy thread was 139860
 
The problem with OPCs and non-Porsche specialists is they will only give you a setup straight out of the book. Whilst fine for most people there is considerable difference between the min/max values they work with. For instance I think there's nearly 0.5 degree of camber difference on the standard setup that would still return 'green' on the OPC's check. That small amount of camber, castor, toe can make the world of difference. From a car that understeers and feels unsteady to a neutral handling fun car.

It's the Porsche specialists that have this information to hand that allows them to precisely give you the best setup not a compromised one.

Migration info. Legacy thread was 139861
 
Whoah - thats v useful to know. In that case if I want Geo I have to go to an Indy specialist. Anyone got any recs for SW London? I know JZ are recommended, but its a day out of my life to get them to do it! SW, anyone?

Migration info. Legacy thread was 139866
 
There's a number of specialists around, a vast number in and around the Heathrow/Windsor/Guildford area, there's always Parr down in Crawley who have a similar reputation to JZM.

I've used Tognola in Datchet (Windsor) in the past.

Migration info. Legacy thread was 139870
 
Regardless of the settings you will always get uneven tyre wear - to what degree is down to how the car is setup. Weight shift in the car under load from braking and acceleration causes the camber and toe to change purely with suspension movement and is linked to the geometric centres of the suspension design.

Natural inner tyre wear on a 911 is unavoidable.


Migration info. Legacy thread was 139884
 
Previous poster said:
Quote: Originally posted by stats007 on 08 May 2007

Regardless of the settings you will always get uneven tyre wear - to what degree is down to how the car is setup. Weight shift in the car under load from braking and acceleration causes the camber and toe to change purely with suspension movement and is linked to the geometric centres of the suspension design.

Natural inner tyre wear on a 911 is unavoidable.
Click to expand...
I disagree. If a car is geo'd correctly for the kind of use it will be subject to, and the pressures inflated to the correct matching pressures, there is no reason why tyres will not wear at an even rate (ie, left-right across the same tyre).

Uneven wear across a tyre occurs because either tyre pressures are incorrect and/or the geo is optimised for a different kind of driving the car has been subject to.


Migration info. Legacy thread was 139887
 
Well no offence but you're wrong I'm afraid. The car would have to have no suspension travel or body roll at all for wear rate to be even on a 911 - even if you did return the standard negative camber to be zero.

Migration info. Legacy thread was 139888
 
Previous poster said:
Quote: Originally posted by stats007 on 08 May 2007
Well no offence but you're wrong I'm afraid. The car would have to have no suspension travel or body roll at all for wear rate to be even on a 911 - even if you did return the standard negative camber to be zero.
Click to expand...

Please explain as I'm puzzled. 
All cars have suspension that travels (although some less than others) allowing a tyre to be loaded up on the inside/centre/outside in different states of motion. 
A 911 is no different.  Over the lifetime of a tyre and the millions of different loads exerted on a tyre, it is possible for the tyre to be evenly worn across the tread if it has a geo and inflated pressure to match the average of all the motions/loads exerted.  ie, the net effect is zero imbalance/even wear across a tyre.


Migration info. Legacy thread was 139922
 
Chris, have a look at this, He came out to give a talk to the club

http://www.cofg.co.uk/


Migration info. Legacy thread was 139931
 
Previous poster said:
Quote: Originally posted by oceancarrera on 08 May 2007

Please explain as I'm puzzled.

All cars have suspension that travels (although some less than others) allowing a tyre to be loaded up on the inside/centre/outside in different states of motion.

A 911 is no different. Over the lifetime of a tyre and the millions of different loads exerted on a tyre, it is possible for the tyre to be evenly worn across the tread if it has a geo and inflated pressure to match the average of all the motions/loads exerted. ie, the net effect is zero imbalance/even wear across a tyre.



This is what Fearnsport told me..

They said as long a I dont just drive her on the motorway all the time, when corning the weight is shiffed to the outer side of the tyre.. and they will wear even..

For long non corning trips the inner edge may wear more !!

But the pressure of the tyres is very important ! And I was given what they should be with the Geo that has been done !
Click to expand...

Migration info. Legacy thread was 139933
 
Dan,
I was asking Stats about his conjecture that all tyres will wear unevenly on a 911...

Migration info. Legacy thread was 139984
 
It's to do with the fundamental design of the suspension. As the suspension moves under compression and rebound the geometry changes accordingly. This movement is engineered into the suspension design with differing axis and roll centres - hence why you get different behaviour from double wishbones, trailing arms, multi-link suspension etc. It also enables things like anti-dive and squat forces to be generated. The design aims to keep the tyre as flat as possible on the road throughout suspension travel - running alot of negative camber means this will happen through corners but has an adverse affect in a straight line.

In normal use the design and setup of a 911 means the insides of the tyres will always wear more than the rest unless you drive in circles all day :wink:
.

If you're interested there are some links below:

http://autopedia.com/stuttgart-west/Physics/StuttPhysics01.html


http://www.carbibles.com/suspension_bible.html


http://www.ae-plus.com/Key%20topics/kt-brakes.htm




Migration info. Legacy thread was 140027
 
I agree with Ade in so much as that if the geo setup is done for the correct type of driving them you "should" get even tyre wear.

The tyre wear is at the end of the day an "average" wear on the rubber. When you corner hard on a setup with min camber, you'll get excess wear on the outer edge. On the other hand, driving on motorway/slow traffic most days with massive camber then you'll have no inner edge before you can say geo!

If you're lucky enough to find a setup that allows for the amount of road/track driving and the varying ability and style of your driving, then you should have even tyre wear. But that can mean less than optimum traction either on track or on road.

Moral of the story:

Get 2 911s, one setup for road, one setup for track, in order to maximise tyre life, and save the planet! :lol:


Migration info. Legacy thread was 140099
 
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