944S2 Track Car Project - Spa April 2019

[924Srr27l]

I'm sure you could easily lose rear grip at Oulton by planting the throttle just after the apex (if you were cornering fast enough). All you have to do is exceed the maximum grip that the tyre can offer.

[font="comic sans ms,sans-serif"]No Really, (This Narrow track 924 compared to the wider 944/968's) has never had any oversteer tendancies in road or Race trim[/font]

[font="comic sans ms,sans-serif"]with 3 different sets of Dampers (Spax / Bilstein B6 / Intrax) and Michelin PS3 or R888 Toyo Tyres, instead it's the front axle that slips first (Understeer) , Neither has any of the total of 8 Transaxles I've had (924S / 944 / 968) they all have a natural understeer set up[/font]

[font="comic sans ms,sans-serif"]looking at this whole thread you've had a very common and consistent Oversteer problem with this car for over 6+ years[/font]

[font="comic sans ms,sans-serif"]Many times you mention having "Offs" and that the rear is unstable and loose etc..[/font]

[font="comic sans ms,sans-serif"]I'm keen to help others for free on how to get the best out this classic chassis and would suggest you either back off the rear[/font]

[font="comic sans ms,sans-serif"]anti roll bar (Fit a smaller diameter) and / or the damping and also spring rates and even change tyre pressures all to give the rear axle more compliance and give . Or you could just make the good axle bad, EG Fit a stiffer front ARB or higher rate springs.[/font]

[font="comic sans ms,sans-serif"]The spring rates are not the actual wheel rates which are determined by the suspension design. The Front Struts are .9 and the rear trailing arms .55 of the spring rate so EG a Front Spring of 400lbs gives a wheel rate of 360lbs, and a rear coil spring of 500Lbs an actual rate of 275lbs. So the rear Springs will and should always be a higher amount but you can adjust this with this calculation to obtain a rate less than the front in your case with an oversteering balanced car. [/font]

Removing the torsion bars is a big job (much bigger than swapping the springs anyway) Ride height is just fine at the moment.

[font="comic sans ms,sans-serif"]Yes it's a PITA but well worth it if you want to improve the handling because it makes for very easy ride height and spring changes. [/font]

I don't believe 888's would be much quicker (if at all on 16's) & would certainly cost much more.

[font="comic sans ms,sans-serif"]They would trust me, else all the Race cars in my Series would be buying AD08R's. And they have been tryed and reported to be too hard and not sticky enough.[/font]

I'm not going to do that for ~a second a lap (I'm not racing).

[font="comic sans ms,sans-serif"] True, it would seem you're a Trackday boy and not that competitive which is a good thing for not spending loads of money![/font]

[font="comic sans ms,sans-serif"]Each to their own, some people enjoy driving on roads, some on circuits and others like to be more competitive and pitch[/font]

[font="comic sans ms,sans-serif"]themselves and their vehicle against competition[/font]

Just booked Spa for early April - what a great circuit!

[font="comic sans ms,sans-serif"]I've not been yet, but will be Racing 2 rounds there next year.....[/font]

 

[924Srr27l]

I have seen (a good few years back) photos of a broken rear suspension arm on a track car with torsion bar delete, I don't know what spring rates they were running or how hard they were hitting kerbs, they were going back to running a torsion bar / lighter coil over setup though. Not entirely sure why it should happen but I guess down to leverage as the wheel rises suspension compresses, the weight of the car is acting downwards on the other end of the arm. The break was pretty much midway along the arm.

Oh, this sounds bizarre ! I don't understand this, only if you imagine removing a Damper and then attempting to move the trailing

arm up and down (Car on ramp) you'll have resistance from the torsion bar, if you fit the damper back on and with a coil spring fitted you'll have even more resistance.

Which if this resistance is made up with either 1 or 2 springs in any combination the arm will not be under any more stresses

Even if a car with a 140lbs torsion bar is replaced with a coil at 800lbs the spring does not put additional stresses into the middle of the trailing arm?

I'd say over 75% of the worldwide Transaxle dedicated Race cars all use Rear Coil Springs and with a T bar delete.

I've never seen, heard or are aware of a universal issue that fitting coil springs to a 24/44/68 chassis has issues with the trailing arms braking in half !

The only reported issue from Porsche was when fitting 18" Wheels (The Excessive Weight) and from a racing point that the top damper chassis / bolt mounting is not that strong and could be braced / welded.

Also the bottom bolt is not strong enough and several manufacturers offer stronger versions (Racers Edge & Intrax etc..)

R

 

[edh]

I'm sure you could easily lose rear grip at Oulton by planting the throttle just after the apex (if you were cornering fast enough). All you have to do is exceed the maximum grip that the tyre can offer.

[font="comic sans ms,sans-serif"]No Really, (This Narrow track 924 compared to the wider 944/968's) has never had any oversteer tendancies in road or Race trim[/font]

[font="comic sans ms,sans-serif"]with 3 different sets of Dampers (Spax / Bilstein B6 / Intrax) and Michelin PS3 or R888 Toyo Tyres, instead it's the front axle that slips first (Understeer) , Neither has any of the total of 8 Transaxles I've had (924S / 944 / 968) they all have a natural understeer set up[/font]

......

I don't believe you are unable to provoke the rear tyres into oversteer in your car...whatever the underlying bias of the chassis. You seem to be wilfully ignoring this.

Your characterisation is inaccurate.

It's true to say the current setup has a slight oversteer bias, as opposed to understeer. I rather like that, particularly on turn-in as the car rotates quite eagerly.

The roll-oversteer on the original softer springs was fixed.

In the cold & damp, as the suspension is stiff & there is plenty of torque, you need to be careful with power on corner exit, particularly on slower corners. I CBA with faffing around with a wet setup so just try and drive round it. Occasionally it will break traction.

I may try 50N rear springs this year but don't want to push the balance too far the other way. I understand about effective spring rates etc..

Driver errors (inattention, red mist, lead foot etc..) are the cause of any off-track excursions - better drivers/driving would have avoided them. I will try not to mention my (and others) failings again on this thread in case people draw the wrong conclusions and blame the car....

 

[924Srr27l]

......

I don't believe you are unable to provoke the rear tyres into oversteer in your car...whatever the underlying bias of the chassis. You seem to be wilfully ignoring this.

[font="comic sans ms,sans-serif"]Not in the dry on R888's unless I do a standing start, 5000rpm and dump the clutch in 1st gear but even then the LSD works brilliantly with great traction. Because of the flexibilty of the 2.7 8V engine I don't need to change down to 2nd gear anywhere on any track (so far) because the engine with it's 9Kg less spinning parts (Knife egde crank / Forged Rods & Pistons / Aluminium Flywheel) whips up fast so even from as low as 2000rpm in 3rd gear any chicane or the slowest bend can be used without having excessive power on corner exits that could wheelspin the car if too much throttle was applied. [/font]

[font="comic sans ms,sans-serif"]To Spin in your case (1) wheel in 4 th gear at 70mph? in the dry? at Donington just sounds a tall order unless you had a light car and a lot more power? I could understand if it was an abrupt power delivery (forced induction engine) but not an N/A with 153bhp per ton?[/font]

[font="comic sans ms,sans-serif"]How was the balance on the 924S and 44 turbo you had? [/font]

Driver errors (inattention, red mist, lead foot etc..) are the cause of any off-track excursions - better drivers/driving would have avoided them. I will try not to mention my (and others) failings again on this thread in case people draw the wrong conclusions and blame the car....

[font="comic sans ms,sans-serif"]It could be the car? (as above) you've not enough power to weight to be spinning a wheel at this speed unless you've poor tyres, a faulty damper? or incorrect geometry (Toe Out?) unless the oversteer balance started to break the rear of the car away first then you either kept your foot on the gas (As opposed to lifting off some to correct the slide with opposite lock) as the rear girated? or you had lift off oversteer? where the pendulum effect took over.........[/font]

[font="comic sans ms,sans-serif"] [/font]

[font="comic sans ms,sans-serif"]R [/font]

[font="comic sans ms,sans-serif"] [/font]

[/quote]

 

[blade7]

I have seen (a good few years back) photos of a broken rear suspension arm on a track car with torsion bar delete, I don't know what spring rates they were running or how hard they were hitting kerbs, they were going back to running a torsion bar / lighter coil over setup though. Not entirely sure why it should happen but I guess down to leverage as the wheel rises suspension compresses, the weight of the car is acting downwards on the other end of the arm. The break was pretty much midway along the arm.

Tony

I thought the bottom damper mounting was the weak point when running TBD? AFAIK some race series rules insist the TB remains for this reason.

 

[944Turbo]

The contact patch of a tyre will provide a finite amount of grip, if they are on the point of slipping from a turning induced load, then very little extra load in the form of power is required to make them break traction and slide. In a softly sprung rolling car with an open diff the power will probably spin away on the inside wheel as it would have little grip with the road, however if the outside wheel is already loaded to the point of slipping the diff might decide the outside wheel has the least resistance.

With the suspension arm, it was rennlist so you do have to wonder what else went on - was the front end of the suspension arm twisting and binding for instance? (the other bits in the photo did look well prepared though).

having just looked for it - couldn't find it yet - but refreshing my memory looking at other pictures I think the crack originated around the damper mounting,

Tony

 

[944Turbo]

I thought the bottom damper mounting was the weak point when running TBD? AFAIK some race series rules insist the TB remains for this reason.

I think you are correct and my memory was playing tricks!

 

[edh]

I have seen (a good few years back) photos of a broken rear suspension arm on a track car with torsion bar delete, I don't know what spring rates they were running or how hard they were hitting kerbs, they were going back to running a torsion bar / lighter coil over setup though. Not entirely sure why it should happen but I guess down to leverage as the wheel rises suspension compresses, the weight of the car is acting downwards on the other end of the arm. The break was pretty much midway along the arm.

Tony

I thought the bottom damper mounting was the weak point when running TBD? AFAIK some race series rules insist the TB remains for this reason.

Possibly - I had a Leda damper fail on me like that in my turbo. The "loop" seemed to come apart

 

[924Srr27l]

I have seen (a good few years back) photos of a broken rear suspension arm on a track car with torsion bar delete, I don't know what spring rates they were running or how hard they were hitting kerbs, they were going back to running a torsion bar / lighter coil over setup though. Not entirely sure why it should happen but I guess down to leverage as the wheel rises suspension compresses, the weight of the car is acting downwards on the other end of the arm. The break was pretty much midway along the arm.

Tony

I thought the bottom damper mounting was the weak point when running TBD? AFAIK some race series rules insist the TB remains for this reason.

Yes the OE bottom Trailing arm Bolt is not strong enough to take the load of a damper and spring for Racing and a stronger grade material is required as is a longer section or spacer for a Coil over damper to fit without the spring fowling on the trailing arm.

Talking of OE parts that are not up to Racing on Circuits the front wishbone Ball pin is notoriously weak and will shear quite easily

especially on cars that have been lowered as the wishbone then sits at an angle (Upwards at the wheel) which wears out the balljoint

rapidly from which a Failure on track (or the road) is not ideal.

Corrected Geometry wishbones are available for about a Grand a pair from the states, also somebody else in the USA a bit cheaper I can't remember who, or make your own. They sit the car's wishbone correctly (Flat) on lowered cars and not only rid bumpsteer

and making the roll less but are also are a lot stronger for the job in hand using a higher grade Steel Pin.

R

 

[944Turbo]

Possibly - I had a Leda damper fail on me like that in my turbo. The "loop" seemed to come apart

Me too, the loop snapped off, I think the ledas were too short at full extension, Mine happened exiting the M5 onto the A417 (J11a). The image i am looking for had cracked the suspension arm, the shock was still bolted to the bit of arm,

Tony

 

[edh]

The contact patch of a tyre will provide a finite amount of grip, if they are on the point of slipping from a turning induced load, then very little extra load in the form of power is required to make them break traction and slide. In a softly sprung rolling car with an open diff the power will probably spin away on the inside wheel as it would have little grip with the road, however if the outside wheel is already loaded to the point of slipping the diff might decide the outside wheel has the least resistance.

That's my point, that Roger keeps ignoring. If you ask the rear wheel(s) for more longitudinal forces when they are maxed out with lateral grip, something has to give.. I don't really care whether or not he can spin his wheels from a standing start, in a straight line, it's irrelevant.

 

[944Turbo]

[link=https://rennlist.com/forums/944-and-944s2-forum/306955-broken-trailing-arm.html]https://rennlist.com/forums/944-and-944s2-forum/306955-broken-trailing-arm.html[/link] no t-bars & snapped in middle - not the one I was thinking off which snapped around the mounting and towards the centre, I suspect this was weakened by an impact

Tony

 

[blade7]

I thought the bottom damper mounting was the weak point when running TBD? AFAIK some race series rules insist the TB remains for this reason.

I think you are correct and my memory was playing tricks!

I only remember it because I was toying with running without the TB when I fitted KW's. I seem to remember talk of the arm failing around the lower shock mounting because that area wasn't designed for the load.

 

[blade7]

Corrected Geometry wishbones are available for about a Grand a pair from the states, also somebody else in the USA a bit cheaper I can't remember who, or make your own. They sit the car's wishbone correctly (Flat) on lowered cars.

R

A lot cheaper to raise the inner pick up point on the cross member....

 

[924Srr27l]

Corrected Geometry wishbones are available for about a Grand a pair from the states, also somebody else in the USA a bit cheaper I can't remember who, or make your own. They sit the car's wishbone correctly (Flat) on lowered cars.

R

A lot cheaper to raise the inner pick up point on the cross member....

Really.. How ? there's no space on the subframe to have a raised position using the stock wishbones otherwise the Racers would of done this, hence why they extend the outer wishbone pin

or extend the stub axle stem like I did, but I went one further and used stock 944 later wishbones but with a High quality Rod end screwed into an aluminium bush.....

R

 

[924Srr27l]

That's my point, that Roger keeps ignoring. If you ask the rear wheel(s) for more longitudinal forces when they are maxed out with lateral grip, something has to give.. I don't really care whether or not he can spin his wheels from a standing start, in a straight line, it's irrelevant.

I don't care ether as I don't do it (Wheelspin ) I was only answering your claim that you didn't believe that my car doesn't have a wheelspin issue.

It's (The classic pub debate) - "My car can spin it's wheels in 4th gear etc.." in the dry on a Race circuit @ what 70mph? I'm not convinced.

Have a look at this Geezer racing at Donny in an S2 takes the coppice turn in 3rd gear then changes to 4th on the exit, there's not much sign of the wheels spinning but his chassis

looks well dialled in and he'll not be using AD08R's !

[link]https://www.youtube.com/watch?v=rhX5W7GM7ZY[/link]

R

 

[924Srr27l]

The contact patch of a tyre will provide a finite amount of grip, if they are on the point of slipping from a turning induced load, then very little extra load in the form of power is required to make them break traction and slide. In a softly sprung rolling car with an open diff the power will probably spin away on the inside wheel as it would have little grip with the road, however if the outside wheel is already loaded to the point of slipping the diff might decide the outside wheel has the least resistance.

A "open" diff deciding to the loaded outside wheel has the least amount of resistance ??? Nah not possible

The unloaded lighter wheel will always spin up first, and the outer will continue to drive,

If as you suggest the outer tyre has been subjected to too much work, it's slip angle had exceeded the best percentage of slip for the best traction then this is from cornering as more throttle is not applied until near or after the 2nd apex.

So I suspect the rear was getting loose inbetween the 2 apexes and started to slip and slide, but rather than applying less throttle the wheels or (Inside wheel only in this case) did not spin up from more power but the car spun as it was heading in this direction, and the pendulum effect swung the car....

R

 

[924Srr27l]

Racer's Edge Rear shock trailing arm bolts

[link=http://www.racersedge-inc.com/racersedge/rehome.nsf/0/072E27E7E80445B2852571B80046E7CB?open&id=9.3.14]http://www.racersedge-inc.com/racersedge/rehome.nsf/0/072E27E7E80445B2852571B80046E7CB?open&id=9.3.14[/link]

[h2]INTRAX SUSPENSION 924S, 944, 944T, 944S, 944S2 & 968[/h2][link=https://www.lindseyracing.com/LR/Parts/944SUSINTRAX.html]https://www.lindseyracing...arts/944SUSINTRAX.html[/link]

Ground Control Suspension

[link=http://www.ground-control-store.com/products/description.php/II=749/CA=159]http://www.ground-control...tion.php/II=749/CA=159[/link]

R

 

[edh]

If as you suggest the outer tyre has been subjected to too much work, it's slip angle had exceeded the best percentage of slip for the best traction then this is from cornering as more throttle is not applied until near or after the 2nd apex.

You spend all your time second guessing...

As I wrote in my original post

"I was at Coppice, catching a Clio RS at the end of the day & got a bit greedy with the power just after the first apex.. probably a bit tired after ~160 track miles"

It was a driver error. I had been lapping all day without falling off the circuit (and have done so for many days at Donington). Showing me a video of a 944 race car doing exactly that isn't really adding anything.

As you will know, cars on track days run at all sorts of pace, consequently you sometimes find yourself entering corners at lower speeds than are optimal because of cars in front that you cannot pass in braking zones. This sometimes gives you the opportunity to use extra throttle in the turns to try and achieve a better exit speed, & you have a margin to do this because your corner speed is reduced. In this case I made a significant error and was slow to respond to it. I was there - I know what my inputs were.

Please don't post about this any more. We aren't achieving anything.

 

[924Srr27l]

Yes, no probs I can see your not interested.

I often don#t realise some people don't like to learn new things and I was keen to discuss

your comments and find out more, it was Post 257 that caught my attention:

"Yes I can spin the wheels in the dry in 4th if the tyres are using the majority of their available grip to corner"

Watching video clips is very beneficial, as is driver coaching a good idea if you're not keen on making the car faster there's always

time to be gained from the pilot from tuition.

In 1975 my father was in South America working for BRM F1 Team who had Mike Wilds on board for 2 events!

This car like yours was also a 3.0 but a V12 ! Normally aspirated and 420+ BHP ! Now this would spin the wheels up out of Coppice....

R