Geometry
Author
Discussion

doneitnow

Original Poster:

663 posts

178 months

Tuesday 3rd April 2012
quotequote all
Not quite sure how to explain this but here goes.

In my Gen 1 Cayman S, when I go around a long sweeping bend/tight-ish doing 70mph the car feels like it is fighting against its self, ie back going out front going in,is this normal due to taking a bend to fast or would you suspect the geometry is out? The bend where I notice it most for those of you who know it is the slip road when coming from the Dartford bridge on to the A2 towards Kent.

wemorgan

3,583 posts

208 months

Tuesday 3rd April 2012
quotequote all
I don't think there's enough information to conclusively say whether the geometry is out or not.

Either way, if it's not been done for a couple of years it's worth having it checked at a specialist.
Sports cars are worth having this done on a regular basis to allow you to enjoy them as much as possible.

gsewell

724 posts

313 months

Tuesday 3rd April 2012
quotequote all
It sounds like that slip road may be like the one from the M25 southbound onto the M40 westbound. I have yet to find a car that feels planted at speeds that should be doable. My guess is that the road camber is such that the car gets unsettled with exactly the symptoms you mention.

By contrast, the M25 Eastbound onto the M11 Southbound (and the reverse slip) are a pleasure to drive fast.

Trev450

6,770 posts

202 months

Tuesday 3rd April 2012
quotequote all
If its only that bend that you experience this feeling and you are happy that your tyre pressures are correct and tyre wear is even, then I would put it down to the camber or road surface on that particular corner.

MadMark911

1,755 posts

179 months

Tuesday 3rd April 2012
quotequote all
Could be loads of things - but the older it is and the higher mileage it's done - the more likely it is that it needs new bushes to feel 100% tight!

That particular sliproad is both tight, goes downhill, is bumpy and heavily cambered, so if you're taking it fast (as I have done numerous times); the car will start to feel unstable as it approaches the limit ....

MM.

doneitnow

Original Poster:

663 posts

178 months

Tuesday 3rd April 2012
quotequote all
wemorgan said:
I don't think there's enough information to conclusively say whether the geometry is out or not.

Either way, if it's not been done for a couple of years it's worth having it checked at a specialist.
Sports cars are worth having this done on a regular basis to allow you to enjoy them as much as possible.
It is 31/2 years old, but I have only had it for 31/2 months so would not know if the geometry has ever been done. I know it came from the factory with 19's but has 18's on it now but would not think that would make a difference but don't know.

doneitnow

Original Poster:

663 posts

178 months

Tuesday 3rd April 2012
quotequote all
gsewell said:
It sounds like that slip road may be like the one from the M25 southbound onto the M40 westbound. I have yet to find a car that feels planted at speeds that should be doable. My guess is that the road camber is such that the car gets unsettled with exactly the symptoms you mention.

By contrast, the M25 Eastbound onto the M11 Southbound (and the reverse slip) are a pleasure to drive fast.
I know the M11 one and would not say it is as tight as that.

doneitnow

Original Poster:

663 posts

178 months

Tuesday 3rd April 2012
quotequote all
MadMark911 said:
Could be loads of things - but the older it is and the higher mileage it's done - the more likely it is that it needs new bushes to feel 100% tight!

That particular sliproad is both tight, goes downhill, is bumpy and heavily cambered, so if you're taking it fast (as I have done numerous times); the car will start to feel unstable as it approaches the limit ....

MM.
Never over 70biggrin. As mentioned the car is 3/12 years old, done 19k, would the bushes be worn a this mileage?

wemorgan

3,583 posts

208 months

Tuesday 3rd April 2012
quotequote all
Treat the car to a proper geometry alignment. What's your location? Maybe someone can recommend a nearby specialist.

doneitnow

Original Poster:

663 posts

178 months

Tuesday 3rd April 2012
quotequote all
wemorgan said:
Treat the car to a proper geometry alignment. What's your location? Maybe someone can recommend a nearby specialist.
I am based in Kent, near Bluewater, who do people recommend?

wemorgan

3,583 posts

208 months

Tuesday 3rd April 2012
quotequote all
Wheels in Motion who are well regarded, have a list of 'approved' tyre centres
http://www.blackboots.co.uk/tyre-fitting-centres.p...

From that list Dixon Motorsport look to be the closest.

Unit 3c Europa Trading Estate
Fraser Road
Erith
Kent
DA8 1QL

I'd give WiM a call to see what an approved centre really means.

MadMark911

1,755 posts

179 months

Tuesday 3rd April 2012
quotequote all
doneitnow said:
Never over 70biggrin. As mentioned the car is 3/12 years old, done 19k, would the bushes be worn a this mileage?
Ahem! A few Leptons more and it gets interesting! Well I'm about to have the bushes (certainly the "coffin arms") checked / changed when the geometry is done on my 911 (at 38K / 4 years old), but I've been told that the rubber ages even when you're not doing any miles and much faster when you subject the car to high G-forces on a regular basis!

When I had my Boxster, I noticed that it was much more stable in fast bends when I changed it from 18" to 19", but at the expense of some ride comfort over rougher surfaces.

A simple thing, but is your car running the right tyre pressures?

MM.

doneitnow

Original Poster:

663 posts

178 months

Tuesday 3rd April 2012
quotequote all
MadMark911 said:
Ahem! A few Leptons more and it gets interesting! Well I'm about to have the bushes (certainly the "coffin arms") checked / changed when the geometry is done on my 911 (at 38K / 4 years old), but I've been told that the rubber ages even when you're not doing any miles and much faster when you subject the car to high G-forces on a regular basis!

When I had my Boxster, I noticed that it was much more stable in fast bends when I changed it from 18" to 19", but at the expense of some ride comfort over rougher surfaces.

A simple thing, but is your car running the right tyre pressures?

MM.
They were at 30 and 37 as per the door but have to admit not checked them in the last two months, what are others running there Caymans at, 235 40 18 Front and 265 40 18 Rear.

Any more suggestions for geometry check/set up in Kent?

MadMark911

1,755 posts

179 months

Tuesday 3rd April 2012
quotequote all
doneitnow said:
They were at 30 and 37 as per the door but have to admit not checked them in the last two months, what are others running there Caymans at, 235 40 18 Front and 265 40 18 Rear.

Any more suggestions for geometry check/set up in Kent?
Cayman might react differently - but on the Boxster I always ran the fronts at 31psi and the rears at 36psi. Small differences, but you get a better turn in and more traction!

2 months? nono Shockingly complacent! You could have lost 2-3 psi in that time .....

doneitnow

Original Poster:

663 posts

178 months

Tuesday 3rd April 2012
quotequote all
MadMark911 said:
Cayman might react differently - but on the Boxster I always ran the fronts at 31psi and the rears at 36psi. Small differences, but you get a better turn in and more traction!

2 months? nono Shockingly complacent! You could have lost 2-3 psi in that time .....
You are quite right, problem is I got used to having pressure monitoring system which this does not have. Will be rectified tomorrow, sorry.smile

thegoose

8,077 posts

240 months

Tuesday 3rd April 2012
quotequote all
doneitnow said:
You are quite right, problem is I got used to having pressure monitoring system which this does not have. Will be rectified tomorrow, sorry.smile
Most monitoring systems won't pick up a consistent loss of pressure over all 4 tyres anyway - imagine the pressure changes between a -30degrees winter day and a +30degrees summer one, the monitoring system wouldn't be expected to indicate anything unless there was a pressure difference across the wheels.

doneitnow

Original Poster:

663 posts

178 months

Tuesday 3rd April 2012
quotequote all
thegoose said:
Most monitoring systems won't pick up a consistent loss of pressure over all 4 tyres anyway - imagine the pressure changes between a -30degrees winter day and a +30degrees summer one, the monitoring system wouldn't be expected to indicate anything unless there was a pressure difference across the wheels.
Not quite sure I understand that, the one on my merc van constantly shows all 4 wheels with the pressure rising and falling as tyres get warm etc!

freedman

6,018 posts

237 months

Tuesday 3rd April 2012
quotequote all
doneitnow said:
I am based in Kent, near Bluewater, who do people recommend?
Project Nine nr Maidstone do full alignment

Rockster

1,515 posts

190 months

Tuesday 3rd April 2012
quotequote all
doneitnow said:
Not quite sure how to explain this but here goes.

In my Gen 1 Cayman S, when I go around a long sweeping bend/tight-ish doing 70mph the car feels like it is fighting against its self, ie back going out front going in,is this normal due to taking a bend to fast or would you suspect the geometry is out? The bend where I notice it most for those of you who know it is the slip road when coming from the Dartford bridge on to the A2 towards Kent.
Just to chime in...

Unlikely alignment the cause of the behavior, but like others have done I recommend you get this done. Unless it was done prior to when you bought the car the odds are it is not right. At this time the alignment specialist can advise you if he finds anything amiss, any bushes/etc. that need replacing. Chances are they'll be fine.

My 02 Boxster is on its orignal bushes and the suspension aligns just fine. The shocks are showing signs of needing replacement. Oh, 10 years old and 253K miles on the clock. Daily driver too, in all kinds of weather.

Tire pressure plays a role in how my cars feel and this applies to your car as well. Generally the tendency is for tire pressures to go down over time.

But road surface condition, camber, and so on also play a role in how the car feels going round a corner.

But you can't do anything about the above, except for tire pressure.

Check the tire pressures. I go by the 'book', but you can experiment. My advise is you do so, at least at first to develop a base line for comparison. Do so in small (one psi) increments and be aware at least with my Boxster going too many (and not that many) psi over the recommended inflation pressure had vibration symptom develop that initially had me suspecting tire imbalance.

Actually, if I had it to do over again, I'd just inflate the tires to the recommended pressure and save the experimentation time for the bedroom.

And tire condition plays a role too. Worn (or just 'old' (heat cycled) tires don't grip well and cold they can be downright dangerous.

Sincerely,

Rockster.