Discussion
ras62 said:
Possibly worse on track Henry...when braking as the front of the car dips the toe will change causing instability, in cornering toe again changes with one corner compressed and one lightly loaded.
For example we did some tests today on my C2 due to tyre wear. Now it sits at RS ride height as the springs have settled (it was +5mm) 5mins of toe in was measured. We then replicated full tanks and luggage with someone sat on the bumper. The ride height lowered 12mm. Toe was measured again and was now 10mins tow out! Funny things happen when they are set too low.
Its the plague of the Porsches. The modern cars have it just as bad if you get them too low. There is very much a threshold where things turn for the worse very quickly. For example we did some tests today on my C2 due to tyre wear. Now it sits at RS ride height as the springs have settled (it was +5mm) 5mins of toe in was measured. We then replicated full tanks and luggage with someone sat on the bumper. The ride height lowered 12mm. Toe was measured again and was now 10mins tow out! Funny things happen when they are set too low.
Edited by ras62 on Tuesday 21st July 22:30
Making sure the lower control arm isn't past horizontal at static ride height is a decent shade tree method but if you have soft springs it could still not be enough to save you.
You can control it to some extent by running mega hard springs to prevent wheel travel if you only track, but its a band aid to the issue and hardly helpful for anyone wanting to drive on the road and keep their fillings in place.
Thanks guys. I am aware that bump steer could well be an issue and am already trying to source some evo uprights. As Neil says, running a stiffer spring rate will make a big difference but there is a pay off with road compliance. This is the main reason that I went for the KW Clubsport package as the spring rate is almost twice that of the Bilstein B10.
I am definitely expecting a degree of bumpsteer. Again as Neil said, it was an issue on the GT3 also. Some very good air cooled drivers couldn't get on with the 996 cup because of the bumpsteer. To a large extent I am used to it. 1000's of laps in GT3's may well prove useful in an air cooled after all! This is one of the reasons that I wanted a little more front brake bias.
Thank you again Gentlemen for taking the time to post. Very good information. I will post up my thoughts in detail once I've tested the car
I am definitely expecting a degree of bumpsteer. Again as Neil said, it was an issue on the GT3 also. Some very good air cooled drivers couldn't get on with the 996 cup because of the bumpsteer. To a large extent I am used to it. 1000's of laps in GT3's may well prove useful in an air cooled after all! This is one of the reasons that I wanted a little more front brake bias.
Thank you again Gentlemen for taking the time to post. Very good information. I will post up my thoughts in detail once I've tested the car
Henry,
The big gain on those uprights pictured is the change to correct the issue of losing camber with lowered cars. IMHO this is the biggest issue with running low ride height. Bumpsteer is ever present of course but easier to work round (and drive round) than camber loss. Ideally one would want neither of course, hence the reason Porsche tend to correct both when the pushed to correct for the camber problem.
Its an issue present in strut setups used on the front of all the 911s. Once the lower control arm reaches the horizontal position, any further movement upwards of the wheel results firstly in reducing rate of camber gain, followed quite quickly by loss of camber itself. The solution, as can be seen in the picture is to use more material to force the control arm downwards.
History repeating? Sadly yes so long as Porsche resisted going to double wishbone on the front. There is a lack of alternative available other than to change the wheel carrier to provide for corrected control arm angles at racing ride heights. As an aside; the 991 RSR finally got double wishbones up front. Nothing else seems to have it yet.
The big gain on those uprights pictured is the change to correct the issue of losing camber with lowered cars. IMHO this is the biggest issue with running low ride height. Bumpsteer is ever present of course but easier to work round (and drive round) than camber loss. Ideally one would want neither of course, hence the reason Porsche tend to correct both when the pushed to correct for the camber problem.
Its an issue present in strut setups used on the front of all the 911s. Once the lower control arm reaches the horizontal position, any further movement upwards of the wheel results firstly in reducing rate of camber gain, followed quite quickly by loss of camber itself. The solution, as can be seen in the picture is to use more material to force the control arm downwards.
History repeating? Sadly yes so long as Porsche resisted going to double wishbone on the front. There is a lack of alternative available other than to change the wheel carrier to provide for corrected control arm angles at racing ride heights. As an aside; the 991 RSR finally got double wishbones up front. Nothing else seems to have it yet.
Edited by fioran0 on Saturday 25th July 03:09
Steve Rance said:
This is one of the reasons that I wanted a little more front brake bias.
Steve,Was the bias change introduced by swapping the front brakes or something more? Any idea what it was before and what it went to?
How is the weight transfer forward on the 964 under braking.
Hi Neil
It's pretty crude. I've just put bigger front calipers and discs on it basically. So we have big reds on the front with 964 3.6 discs and 993 C2 rears with 964 RS discs. Pagid yellows all round.
The car that I drove at Silverstone had the same set up and was lovely. I found that driving it in a similar way that I would a GT3 was the most effective for me. A trace of oversteer on exit ( it had standard C2 anti roll bars) but it took full throttle from apex. Absolute joy to drive.. Not like my 993 which is a lot lighter and very easy to drive by comparison. Like the GT3, a well set up diff seems key. A car without one would a bit trickier
It's pretty crude. I've just put bigger front calipers and discs on it basically. So we have big reds on the front with 964 3.6 discs and 993 C2 rears with 964 RS discs. Pagid yellows all round.
The car that I drove at Silverstone had the same set up and was lovely. I found that driving it in a similar way that I would a GT3 was the most effective for me. A trace of oversteer on exit ( it had standard C2 anti roll bars) but it took full throttle from apex. Absolute joy to drive.. Not like my 993 which is a lot lighter and very easy to drive by comparison. Like the GT3, a well set up diff seems key. A car without one would a bit trickier
I'm finally getting round to getting mine upgraded, I have a 91 C4 Coupe;
Its currently in a local Porsche specialist being checked over for my piece of mind, apparently its a fairly solid car, needs the typical small jobs sorting which they're doing.
I'm either going to go the 17" Cup 1 Wheels or the 18" Speedlines, but the roads over here being a little s
te, I might stick to the 17" Cup 1's.
Any thoughts on good steering wheel replacements? I was thinking about either a MOMO wheel or such like, I can delete the drivers airbag without law implications apparently. Any suggestions on the best steering wheels to suit the 964 at all?
Whilst I'm at it, the gear shifter needs replacing, I was thinking of going for silver, but changing into 5th can sometimes be a reach, any good replacements I should be considering?
I'm going to change the sound system, have that upgraded and revert back to the factory plain black mesh speaker covers, then have the Classic Nav installed.
Its currently in a local Porsche specialist being checked over for my piece of mind, apparently its a fairly solid car, needs the typical small jobs sorting which they're doing.
I'm either going to go the 17" Cup 1 Wheels or the 18" Speedlines, but the roads over here being a little s
te, I might stick to the 17" Cup 1's.Any thoughts on good steering wheel replacements? I was thinking about either a MOMO wheel or such like, I can delete the drivers airbag without law implications apparently. Any suggestions on the best steering wheels to suit the 964 at all?
Whilst I'm at it, the gear shifter needs replacing, I was thinking of going for silver, but changing into 5th can sometimes be a reach, any good replacements I should be considering?
I'm going to change the sound system, have that upgraded and revert back to the factory plain black mesh speaker covers, then have the Classic Nav installed.
I'm deciding on steering wheels at the moment, I've heard the replacements make the driving position slightly better, I'd love the suede MOMO 3 spoker, either a Proteo or the OMP Superturismo, it looks like i need to make some phone calls as there seems to be some discrepancy with the hub adpators.
I think that it depends on how you prefer to sit. Most racers like to sit upright with the steering wheel close to the body so a deep dish on the wheel and a deep adapter will help bring the wheel forward. This is exactly how my car is set up (see pic). If you prefer to sit with the wheel further from you, a shallower wheel with a smaller adapter will be better. 
Great thread, love to read about fellow PHs taking a journey through their mods.
Funny isn't it, most of us love mods, but then when we are selling we're told everything should be standard for a sale!
Personally, I'm more than happy to buy a slightly upgraded car, I know to well, how much the mod journey costs, so saves me money in the long run.
Keep posting!
Funny isn't it, most of us love mods, but then when we are selling we're told everything should be standard for a sale!
Personally, I'm more than happy to buy a slightly upgraded car, I know to well, how much the mod journey costs, so saves me money in the long run.
Keep posting!
Steve Rance said:
I think that it depends on how you prefer to sit. Most racers like to sit upright with the steering wheel close to the body so a deep dish on the wheel and a deep adapter will help bring the wheel forward. This is exactly how my car is set up (see pic). If you prefer to sit with the wheel further from you, a shallower wheel with a smaller adapter will be better.
Steve, that works for me, I wanted the wheel a little closer, and the gear lever actually, but can't seem to find a shifter that suits, the old 5th gear is a slight reach with my current driving position. I'm torn between the Momo that you have, which i'm assuming is the Momo Mod.07? did that come with the horn mods as well? I'm thinking either this one or the OMP Superturismo wheel.
A quick update.
Have now driven the car on the road on both bumpy suffolk lanes and smoother tarmac. No scuttle shake at all, it feels good and the chassis has no problems at all dealing with the much stiffer spring and damping combo - although i'm expecting flex some flex when it's loaded up on circuit. I was worried that the spring rates would result in an uncomfortable ride but absolutely no probelm at all. The damping is well judged with decent control. Damping has come a long way over the past 10 years. The very low ride height is fine to live with no major issues with front axle bump steer that I was fearing. I think the gamble of running KW Clubsports with the Higher spiring rates has paid off.
The brakes are very strong. On road biased tyres - currently running crappy old carlos fandango rubber - i'd say it's over braked. Very easy to snatch the fronts unless the nose is loaded first. The level of dry grip in the chassis is so great - even on low grip rubber - that there is no need at all to trail on the road. With a set of cups fitted, the car should come to life and allow much later braking points and then the brakes will come into thier own. On saying that, I tend to mince about on the road and leave driving quickly exculsively to the circuit.
All in all, I am absolutely delighted with this little car. I wanted to create something that would be comfortable to drive on the road, be an interactive event at low as well as high speeds and quick enough to be fun on the circuit. Some of the the modifications were a bit of a gamble but in the event are soft enough to be comfortable on the road yet offer serious potetial for track performance.
The only downside so far have been the fuchs - which when fitted with 265 cup 2's refused to fit under the rear arches. The car is just too low. Paul told me to fit 255's and he was right. Luckily they will it on the speedline reps that the car came with. I am really looking forward to driving the car on the cups. If it can be this good on crappy rubber, it will be lovely on cups. I am sure that the set up will need fettling a little to optimise track performance but alreadly I can tell that this will be a very fast little car.
Looks good Steve. Sounds like it will be a bunch of fun too.
No problem ref the bias. Crude is as good as anything else. All that matters ultimately is that it works tbh.
I was purely being nosey incase you had any numbers knocking around from the process. I had quite literally just got finished doing weight shift plots and brake bias adjustment plots for my own car (to inform in car setting versus driving condition/tyre type/etc) so it was literally on my mind as I was reading along. I was curious how the weight was shifting forwards in comparison between the newer and older cars. I expect its pretty similar but don't know for sure.
Would be interested to hear more feedback on the spring rates as you get it. If you feel you want something extra, you can stick in a soft spring to give you a few mm of compliance before moving you to the main rate. Can be useful for wheel control and also for slow speed stuff.
No problem ref the bias. Crude is as good as anything else. All that matters ultimately is that it works tbh.
I was purely being nosey incase you had any numbers knocking around from the process. I had quite literally just got finished doing weight shift plots and brake bias adjustment plots for my own car (to inform in car setting versus driving condition/tyre type/etc) so it was literally on my mind as I was reading along. I was curious how the weight was shifting forwards in comparison between the newer and older cars. I expect its pretty similar but don't know for sure.
Would be interested to hear more feedback on the spring rates as you get it. If you feel you want something extra, you can stick in a soft spring to give you a few mm of compliance before moving you to the main rate. Can be useful for wheel control and also for slow speed stuff.
Can't believe I have only just discovered this thread. A return to form for the forum.
Jamie Summers said:
Some light exhaust mods and a trip to see Wayne will have you at 300bhp or thereabouts and will keep a 996 GT3 honest
To be fair, I suspect Steve Rance in a Yaris would keep most of us numpties in a 6GT3 honest.
Some useful info for you chaps looking to modify 964s.
I mounted up the Michelin Cup2's on my track wheels and scrubbed them in ready for the first track test. Definately a leap forward from the original Cups. Very easy to get heat into them even at road speeds and the grip levels are noticably higher. The car came alive and the brakes began to make a lot more sense. No longer do they feel overkill and snatchy. Less willing to lock up at the front, now just dropping the nose immediately on even light applications which is exactly what I wanted. The brake pedal is reasonably firm with decent feel which is encouraging. However, the big test will be how they perform under track conditions. I am keen to pass on as much info as I can to other 964 owners looking to modify thier cars so aplogies if this post becomes a little tiresome.
So;
I am very happy with the whole set up on the road which is important to me as the aim is to provide a high level of feel and interaction at lower as well as higher speeds. I have never subscribed to driving like a lunatic on the road but still like to enjoy the feel of a car communicating to me at legal speeds. There is something special about connecting with a vehicle from 1 to 11/10ths. The cups are definately the final peice of the jigsaw as far as the road set up is concerned. The car has a lovely balance and has so much grip that trail braking is just not necessary. No specific driving style is required, such are the reserves of grip that the car just goes where you point it, either on throttle, on trail throttle or on brake ( providing obviously you are smooth if the car isnt straight ). It will take a lot more abuse that say a GT3 before a driver finds himself in trouble. All of the time, the chasis is telling the driver exactly what is going on. The steering is very nice, lots of feedback from straight ahead to full lock. There is kick back which is amplified with the fitting of the cups but it's perfectly acceptable. The cups also add a layer of physicality to the steering which I think will be a welcoming factor to the driver as it adds a layer of security reminding him that the onset of understeer is some way away and there is plenty in the bank for avoidance should it be needed. There is no need to describe the behaviour of the chasis on turn in, apex or exit because at road speeds the car has so much grip and is so far away from it's limits that only a complete idiot would get anywhere near the point at which the chasis even began to start to do it's thing. Instead it just keeps on telegraphing everything that is going on under each wheel with such clarity that it becomes almost intoxicating. The nose still snuffles along reminding the driver that he is driving a 911 but the higher spring rates and sharper geometry combined with the huge grip levels of the tyres make the car feel almost mid engined at road speed levels. Even with the huge grip levels, the engine and greabox do not feel overwhelmed. The single mass flywheel makes a big difference here and is definately a modification that this set up would miss. I have not weighed the car but ditching much of the heavy interior definately unlocks more performance and makes the car feel genuinely fast on the road.
The thing that most comes across when driving the car on the road is that although it provides a level of interaction that is lacking in modern 911's, it chasis has a level of compitence that would fool any driver into thinking that it was indeed a brand new car. It is not an old car that feels like it is punching above its weight, it feels like a new car with new car levels of grip and braking whilst still managing to provide a level of feel and interaction which just isn't there any more. The stiffer spring rates and roll rates combined with decent modern damping have unlocked in this little chasis someting realy special and shows what an amazing car this realy is. If it had benefitted form modern damping technology in 1990 it would have taken the game forward light years.
The next big test is the circuit. The set up will show it's real character and - I suspect - where the flaws in the balance are. Track set ups are rarely bang on straight out of the box and I am expecting some nipping and tucking.
To you guys thinking of building something similar, a few things to note;
The front brake calipers are very big by 1990 standards and will need careful wheel choice to prevent the calipers from binding of the front wheels- see attached pic. Make sure that the design of your wheels will accomodate the front calipers before you source them.
Secondly, tyre choice is a key component in the balance of the build, I found that there was more choice of available tyres in 18" than 17". Again, this may effect your wheel choice.
Finally, the shoulder of the cup 2 tyre is very square and with the low set up of the car can lead to them not fitting unless the correct wheel offsets are chosen since they sit well under the wheel arches. I was very lucky - There is a 2mm gap between my rear arches and the tyres that sit under them. Very close! I will post up the offsets after Ive checked them. You can use these as the max offset possible to use. Another option would be to use 255 section rear tyres. I could not find a 255/18 in the Cup 2 but they may be available.
Thats it.
Will post up next after the track test.
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