drnick

since replacing the rear tyres with grippier rubber the car just isnt the same! it definitely sticks better to the tarmac but something of its predictability and stability at speed has gone... it ranges from slightly disconcerting to briefer moments whilst changing line or applying breaks at higher speeds, especialy in sweepers. in fact this change is apparent at lower speeds also whilst changing line say with a chicane.

it feels like something loose in the rear suspension, the weissach axle i suspect! any advice regarding an effective mod to stop its self steering tendencies???

Doug Hillary

Hi Nick,

Kiwi's forever?? ( I'm originally from cold windy Dunedin, Brrrrrrrrrrrrrr )

Nick, you don't mention;
tyre brand and type purchased ?,
are all the tyres/wheels as per factory sizes ?,
pressures used front/rear ?,
type, age of front tyres ?,
how many kms have the new tyres have done now ?
was the car re-aligned recently ?

All the relevant data above is needed in order to provide some meaningful suggestions

Sometimes just a simple tyre changes can chnage theway a car feels!

Regards

Regards

drnick

yes doug i agree, dunedin is a cool place..

every thing that i have had done to this car has changed the way it felt to drive, all the way from tyres through to plug leads. sports seats and a momo steering wheel along with jaeger shifter make for enjoyable motoring untill recently.

last week or so i changed the rear tyres from continnentals to brigestone so3's to match the fronts which were changed aprox 1000m before.

to be honest i was never stoked with the amount of grip the continental tyres provided and as a consequence didnt drive with quite the reckless abandon i would have liked, especialy when its wet (like, all the time here in england!).

adding brigestones to the front really made a difference! the car felt solid and planted through the front and really grips either wet or dry, but i still wouldnt push the rear whilst it had contis.

since adding the rear brigestones the levels of grip are much improved (entirely a subjective rating i know, but man you can really feel it) especialy at lower speeds. however the high speed handling has changed!

where before the car was predictable through sweepers it now is not. this is difficult to describe, its not there constantly but now and again theres like a 'fidget' or slight wiggle latterly to one side or other. it can be provoked best by simultaneous braking and cornering or changing line! - not recommended procedure.

its almost over steer but not quite and sometimes it feels like the weight of the car actualy moves in towards the apex, at some delayed time from steering input.

i am convinced its the weissach axle overloaded by the grippier tyres now on the rear. and to confirm this i have tried overinflating the tyres, not massively but to the extent that rear traction was lessened - the car ran more settled through high speed turns!

so now id like to pin or otherwise ajust the rear axle and dispense with its inherent passive steering.

current tyres are brigestone so3's all round - 225/45/17 at front and 255/40/17 at rear . tyre pressures are 37 psi front and 39 psi rear. the car has had three alignements done within the last 12 months following various suspension/steering work.

the whitsundays have to be some of the best sailing around! i was there very briefly last year through the winter months whilst on my way from brisbane to cairns in a campervan. i couldnt believe the number of sea turtles we saw or just how fast they are in the water!

ErnestSw

You don't mention whether your new Bridgestones are the same size as the Contis. If there's a difference your alignment could be off.

Doug Hillary

Hi Nick,
Yes it is a wonderful place here - I have owned a place here for about 8 years - and another in the country near Brisbane. I split my time between

I would suggest that you wait awhile until you have about 2k on the rear tyres. But, experiment with the pressures especially the rears

The wider/lower profile the tyre, the more sensitive the car can be to steering and road "inputs". Are the rim offsets correct ??

I do not think the rear axle "correction" you suggest is advisable

My car on Falkens is a little "sensitive" too on certain road surfaces - I believe this is a 928 characteristic. Both my two - '81 928 ( sadly sold ) and now '89 S4 where very similar in that regard

It raining here today and 24C as we approach winter

Regards

Mike LaBranche

Could someone please explain why pinning the Weissach axle helps? What worked with 225's doesn't with 255's? or 310's for that matter. WTF? Is the force generated by the tires really 'overwhelming' it?

Nick, I'd let the tires 'break-in' a bit. Play with the pressure. Give it an objective review after a few hundred miles and some heat cycles. I always make my best effort to replace all 4 tires at the same time, even if I have to buy cheaper tires to do so. Switching the balance at one end by doing 2 tires will feel different. And the alignment suggestion is also valid. I'd pursue reasonable adjustments before resorting to modifying the rear suspension.

drnick

yes, id really like to hear from someone who has pinned the rear axle and specificaly whether it improved their higher speed handling.

people are doing this and i know devek recomend it for tyres above a certain size. i am hoping to find out whether it is a better thing to do and if so the best way of achieving it.

ive just been out for a drive and sure im happy to keep driving, ajusting tyre pressures, fine tuning suspension settings and so on. furthermore the car really does go well and it sticks to the road. but handling is an individual thing and for myself id like the rear suspension to be more directly connected with the rest of the car, especialy at higher speed!

its been over 1000m, there is no change in the tyre sizes going from the rear continentals to brigestones and the car is aligned correctly. i dont neccesarily agree about matched tyre sets, i think the moment you put varying widths of wheel on your 928 from front to back you are acnowledging the inherintly different requirements of each end, front to back.

Rich9928p

My '79 Euro hybrid track beast has pinned Weissach arms. It came that way from the PO.

The theory is that the Weissach "active" rear alignment change is calibrated for a "normal" street driving environment (stock power, stock tyre size, stock tyre grip). If you increase power, increase tyre size (mine are 275 mm wide in the rear), have more grip (i.e. DOT track tyres or racing slicks) then it may be desirable to pin the Weissach so you don't get the alignment change since it wasn't designed for these new circumstances.

I've never driven my car without the axle pinned, so I can't say if it helps or not. I can say that the car is very predictable, neutral, and is a pleasure to drive on the track.

Marc Thomas has the "white" car pinned. Don Hanson has his mighty stroker pinned. Mark Kibbort says it isn't necessary for his car.

Your "underpinnings" may vary.

Erik - Denmark

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by drnick:
<strong>...... this is difficult to describe, its not there constantly but now and again theres like a 'fidget' or slight wiggle latterly to one side or other.........i am convinced its the weissach axle overloaded by the grippier tyres now on the rear. </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Hello,
I have Good-Year Eagle F1 225/50-16 all around and have the same feeling as Nick describe.

I was wondering has anyone experience by renewing the Weissach links and eventual other rubber bushes in the rear suspension - This units are all more than 20 years old and cannot be like new.

drnick

rich, thanks for posting! it seems that pinning or disabling the weissach axle may not produce much difference in the cars character. i hear what your saying as regards performance enhancements and the view that the standard set up wasnt designed for these ie larger rear tyres etc. also, it would seem as you push the car harder you can approach and exceed the usefull limits of the weissach system.

erik - i have a set of replacement bushes on order and plan to have them installed in due course! it seems our thinking runs along similar lines, kind of reasuring to know. how are you coping with rear bilstein shocks? i had these replaced all around and it transformed the cars handling, i dont mind the extra firmness and im thinking off uprating the springs at some point also.

Erik - Denmark

Nick,
I am very interested to hear the result of your new bushes in the rear suspension - Please inform when finished!
No doubt the Billstein shock are extremely good for fast driving, the reason I only have them at the rear is that was step 1 - In step 2 I will also have Billstein them in the front (together with the appropriate springs) - I am working in steps due to pocket money and spare time - And there shall also be something to do 'tomorrow'
The only irritating issue with the Billstein shocks, are the bumping when driving slow, but on the other hand, I do not want 'a limo' <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

Mrmerlin

Diggin the Archives. Dr Nick did you ever replace the front bushes in the rear lower control arms? What was the result

RKD in OKC

Hmm,
I have Koni adj, springs, and swaybars on my GTS. Understand the suspension on my car was setup by Devek. The car was very loose with throttle with stock 17s and pilot sports 225/255 when I got it. On the track it felt like it spun the rears when I just thought about giving it more throttle.

Went to new pilot sports on 18s 225/285 and did a ride height and alignment with the new rims and rubber. Lost the loose on throttle, and don't notice any wiggling like you describe in the rear. And I would say the grip is a lot higher with the 285s over the 255s.

What you might be feeling with those new Bridgestones is a softer sidewall and the tires taking a set as you load them. You may need to run more than 39 in the rear, my 90 GT really liked 44 in the back.

mark kibort

so many factors, so little time.

you can see from nearly all of my videos that my car is very stable under all conditions it can get itself into. That ranges from off line passes, trail braking, and in the rain! I have all factory rubber and run up to 335s in the rear! the pinning doesnt allow for the flex of the rear lower control arm to give the additional toe in which counteracts the forces that want to kick out the rear end (oversteer) thats all.

if your car is feeling nervous, you might have too much toe out in front, or too much brake bias in the rear. I have very little brake bias in the rear. so little, that i run through pagid orange pads (literally destroyed) in 3 weekends and Im only half way through the rears after 3 full competitive race seasons running near 12 race per year.

Ive also driven several race 928s with pinning and they have a little bit more oversteer than mine, but also have much bigger rubber in front.

The only issue i have with mine is a little too much body roll for the tight tracks and a lot of push in the medium speed turns. high speed turns with braking, is excellent.

Pinning might only create a looser car.

check out some of my videos for what its doing at high and medium speed turns.

by the way, explain your set up in detail and Ill make some comments.
alignment , ride hight, spring rates, swaybars, shocks, weight , tires, pressures, etc.


mk

mark kibort

scot's racer, by the way, runs 305s in the rear, runs near my old times at laguna as I ran with my old part euro 5 liter, and has bilstiens and cut off (one coil) eibach springs. Ive driven it,and it runs like any other 928 that is reasonably well set up.

mk