Johnny G Pipe

Awesome! Ever consider a career teaching physics Alex?

So you are saying that the grip doesnt increase or decrease at any given speed (because that is a function of constants like car weight and contact patch), but the way that the grip is distributed varies.

So, Feral wins, yes?

alexjc4

As the Dodo said "Everybody has won, all shall have prizes"

Grip doesnt change with speed (ignoring aero effects) but it does change with acceleration (which includes cornering) because that transfers the loads front to back or left to right. So the transfer is unavoidable; if you want to accelerate say at 1g in any direction you will see a load transfer dependant on the acceleration , c of g height and track width, you just have to do the best you can to even that load across the tyres (the front tyres sometimes can take less because they steering, the rears sometimes can take less because they are accelerating the car - tyres loaded in one direction car handle less in the perpendicular direction)

jack.pe

I thought that was a small part of it but that the main benefit of negative camber is that it places the tire at a better angle to the road, transmitting the forces through the vertical plane of the tire rather than through a shear force across it. This aspect I guess would also be reduced by more roll but again, since I have H&R reds on the car I am not too worried about roll increasing that significantly.

What worries me more is that having to redo the geometry to take the front bar out would take away the cost benefit and might just make it more worth while to go for a second hand rear C2 bar. Alex said he was unsure if front sub has to be taken out or not, does anyone else know this for sure?

Johnny G Pipe

Good point. If Sunset are still doing rear bars at 150 USD -probably £80 or 90 - I am now thinking that this is the answer in terms of balance of cost versus hassle of fitting, experimenting with the unknown on public roads/kids in car, (not to mention insurance company questions about why the car is missing its factory fitted stabiliser bar)..my rear bar is pretty rusty looking too.

The chat about how it all works is very interesting all the same!

I'll mail sunset (they don't have parts listings) and if they still have a similar price we could maybe ship a few over in one go? Or even better my old man is going to the US this christmas, he could bring 3 or 4 bars back I guess.

Can someone remind me is there a value of goods over which import duty kicks in?

ScottR

What a great discussion; why wasn't learning this fun at school?!

Wish I contribute but sadly I can't. But I'm picking up good bits of knowledge that I can add in to my next man chat down the pub

So, not wanting to belittle any of the points put forwards already (see above) but it would be interesting to hear what some of the specialist shops / race car owners have to say, presuming that they have tried various combos?

kos11-12

Does Sunset sales the 22mm rear bar ?
If they agree to send it with low value you re safe , otherwise be ready to pay the VAT on total invoice INC shipping + custom duty....

Vandit

You don't need to remove the swaybar to take it out of the handling equation. Simply disconnect/remove the drop link from one side and the car will no longer have a front swaybar.

ja78911sc

You guys are a bunch of Nomads

I have had the opportunity to drive a 911 on the track without the front sway bar. This car was set-up for autocross. It was very sensitive to steering input--oversteer. It made me feel real uncomfortable. It is a torsion bar car with 22F and 33R.

ja78911sc

21mm is the largest non adjustable OE rear bar--non turbo. There is a 22mm front OE bar (M030/RSA)

alexjc4

That miata website Feral linked to is awseome! Here's another good thread on roll bars.
http://forum.miata.net/vb/showthread.php?t=459244

boxsey and ja78911sc advise a healthy caution for messing with the balance of a car with a chassis layout known to be unforgiving. And experimenting on the road, even when you've done the maths, could end in tears.

Things are a bit different for the C4 though. We're putting only 70% (50% when things get tricky and PDAS kicks in) of the load from the engine through the rear wheels compared to a C2 and this means you can go to places a C2 can't when you come to also putting lateral load on them. This means the front vs rear roll bar balance needn't necessarily follow the same rules as a C2.

There's a good chart showing the effect of bar thickness on bar stiffness (assuming you don't move the drop link)
http://www.balancemotorsport.co.uk/s...Whiteline.html
Remember though that the distance of the pivot point from the drop link will effect the stiffness of the roll bar, and in the case of a 964 this is significantly shorter on the rear than the front, meaning, by my cigarette packet maths, our 20mm front and 18mm rear bars end up providing about the same spring rate (you might expect the rear would need to be stiffer given the extract weight at that end). On a C2 this gives a nice balance, by giving the overworked rear tyres (all that weight they carry plus driving the car forward) better grip. On a C4 because we are asking less of the rear wheels to propel us forward, and more of the fronts to do the same, the same setup gives understeer. The front of the C4 has less lateral grip available than a C2 and the rear more, when compared to the C2, adjusting the bars to balance this seems reasonable. Of course what you might end up with is a C4 that handles more like a C2 - and you might actually want a nice safe C4...

Apologies for a Skyline related anecdote but... I know of respected racers running 4WD 500bhp+ R32 GTRs who disconnect the front roll bar completely and either leave the stock rear or uprate it. They will of course also be using pretty stiffly sprung coilovers and the chassis layout is different - but the point is you probably wouldn't be able to do that in a RWD car.

Ignoring the front rear balance issue, on the general subject of the choice between big bars + soft springs or soft bars + hard springs. We're talking about hard and soft in "race" terms. I get the impression that the stock springs (and even H&R green or red springs) would be considered "soft". So "big bars + soft springs" is your only option without changing the springs. Soft bars + soft springs = boat. If you have standard KWv3 or PSS9 spring rates you start getting into "medium" so maybe you're in a middle ground and you can go with medium bars, and finally with Cup springs, KW Club Sport or uprated springs for KWv3 or PSS9 might be considered hard (approaching twice the spring rate of the stock springs) so soft bars become an option I guess.

lol, I've gone a bit OCD on this subject and ordered a (really expensive) book of almost biblical authority on the subject:

jack.pe

Alex, good stuff! But since when are H&r reds considered soft? Mine feel plenty hard enough.. The greens are the softer options, are other upgrades really do much stiffer than the reds?

alexjc4

Its all relative, the reds may feel firm for road use, but proper race springs are 2-3 times harder; basically back breaking on normal roads.

Johnny G Pipe

Still waiting for a response to my enquiry for 964 333 701 07 (21mm Stabilizer-Sway Bar) - Qty 1 $149.50 from Sunset Porsche.

Have pretty much taken the car off the road for the winter because of the crazy mud (late harvest after the wet winter) and salt, but if not would be tempted to just disconnect the front bar, but leave it in situ, just to see how it felt. Dare you..

jack.pe

Right chaps,

I am going on the SPA outing next year, will try disconnecting the sway bar linkage then. Will report back around March.

Was looking at it as I changed the wheels yesterday. Seems simple to just disconnect linkage on one side. Are we sure that taking one of side linkages out will not lead to damage? i.e with the bar then being free to hit other parts?

FeralComprehension

Might be better to pull both links and tie the bar up in some way.