Structural Rigidity...

M

Maniac

Elite
It still really surprises me... how much the roof, given its foldable, adds structure to the car. I always note, such as today, on a roofless drive back from the office to home, that there's a shimmy I can feel in the steering over rough ground, it was always there on the e85, a slight vibration I could just about see in my hands, coming through the steering wheel horizontally due to the lack of fixed top chassis stiffness. When the top is up, there's none of that, the whole car really is (nearly) as good as a fixed top when its in place.
 
It's surprising how much a front strut brace elimates body shudder. After fitting one to the Z3 it made a big difference so might eliminate it all together on the E89 with roof down.

Tim.
 
Hmm that's an interesting thought. I only get the feeling through the steering at certain speeds and certain roads, like a high frequency side to side. Nothing wrong with the car (for a change) as I always remember it from the e85 too. But a strut brace might be an interesting DIY ;)

Oh god slippery slope approaching...

http://www.orange-tuning.de/shop/wiechers-35i35is-strut-racingline-carbon-p-171163.html?language=en&sort=1a

http://www.motorsportworld.co.uk/framefixsbc.asp?page=3&make=BMW&model=Z4&ProdGroup=Performance%20Suspension&ProdSubGroup=Strut%20Braces
 
I had a strut brace on my e85 but I could still feel what Maniac is describing & I would guess with the lid up the e89 does feel solid it is the best of both worlds I would have thought.
 
Perhaps its too rigid. I've not noticed that on the 23i.
Strange though i mounted a camera via a bolt to the centre speaker blank plate behind the seats just in front of the wind stop.
On replay there is a strange panning effect every so often.
Can only put that down to the rear deck twisting.
Probably what causes the only roof noise i have now, which disappears when the rear quarter lights have moved down a touch or more.
 
The official word on this is 'scuttle shake' or 'cowl shake' in the US.

Happens on almost all convertibles. That's why I love the roof up time as the car is solid.

Interestingly it's discussed on the odd jag f type review too. A good reason to consider the f type coupe when it arrives.
 
Seems Merc can't get rid of it entirely either...

http://www.youtube.com/watch?v=0ON7iDGdsvo

Interestingly I'm beginning to wonder if its not the road/speed, but the new wheels or tyres I have on.. I don't recall this much scuttle shake before, so either something needs a good old tighten up, or something that's changed on the car has increased it. Can't see it being the lighter 313s? More likely the 'wish I'd never bought them' Pirelli P Zero run flats. The more I drive, the more I think I want rid of run flats.
 
Everthing has a natural frequency that it will oscillate at when disturrbed and a car will react just like the big undamped spring that it is when it hits a bump(s)
This will be different with roof up to roof down or full loaded or driver only.
Maybe this explains different behaviour, roof up and down??
 
Sure, I get that. I'm just wondering if I can help minimise it somehow. Its not there all the time, rough tarmac sets it off, but still, if I can minimise it, I'd be happy to try. I might try that section of road with different adaptive damper settings to see what effect that has. But now I'm running it around my head, I do wonder about those new wheels and tyres and the impact of their dampening properties against road surfaces... I do like a good mystery.
 
i first noticed this in my S2K, thought it was the wheel balancing/ tracking.. learnt to live with it.

Then got the Z, and it was still there but less.

Drove the SLK which seemed fine to me though - with the roof down.. or maybe its just not as noticeable.
 
I think it probably depends on the roads, speeds, the car etc... Given the really really poor roads I have to drive on here in Manchester, I'm surprised the car hasn't shaken itself to pieces by now. I know I'm being shaken to pieces! lol
 
Maniac said:
Hmm that's an interesting thought. I only get the feeling through the steering at certain speeds and certain roads, like a high frequency side to side. Nothing wrong with the car (for a change) as I always remember it from the e85 too. But a strut brace might be an interesting DIY ;)

Oh god slippery slope approaching...

http://www.orange-tuning.de/shop/wiechers-35i35is-strut-racingline-carbon-p-171163.html?language=en&sort=1a

http://www.motorsportworld.co.uk/framefixsbc.asp?page=3&make=BMW&model=Z4&ProdGroup=Performance%20Suspension&ProdSubGroup=Strut%20Braces[/quot
Another strut brace to consider here.
http://www.wiechers-sport.de/shop/dom-fahrwerkstreben/produkte/df--bmw-z4-e89---n54-sdrive35i---sdrive35is-domstrebe-alu-racingline-vorne-oben-detail
Click to expand...
 
Problem is if the car is too stiff it won't hold the road. Guy i know that works JLR said the MGTF was too stiff and a lot of metal was taken out.

If all this after market stuff makes a difference, why wasn't it fitted in the first place?
 
So, I've revisited this and the adaptive suspension settings make no effort to reduce it. Its roof down only, over a stretch of 50mph motorway road. Oddly I do also feel a general wobble from the wheels around this speed, its minor but I feel it come and go so perhaps its wheel balance that's setting off some sort of reverb causing the cowl/scuttle shake. Not to worry, we've six months of top up weather coming before I try it again :(
 
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