Claudius

Thank you for the insight on the parts that need welding. I imagine the effect of welding the rear bulkhead a little bit like having a rear strut brace (or two ).

Could you explain the following in more detail, please?

If you slow the car coming back up in the rear, then you will get less load on the front and limit turn in ability, wont you? Or are you talking about the fact that the weight comes to the front "less suddenly"? I dont fully understand this part. Thanks again for your help.

johnfelstead

excellent writing Damian. I particularly like your statement about spending time with a quality driving coach such as Don Palmer as imperitive to really get the most out of yourself and the car before you spend money on mods, something i have been trying to get accross to people for a long time.

I have one SERIOUS question. When can i have a drive of the ATD equiped Impreza?

Edcase

OK, I can't believe I've just got out of my nice warm spot next to the missus to type a question on Scoobynet at 1am, (maybe she's right, maybe I AM becoming obsessed ) but I'll either be too busy tomorrow or forget what I was going to ask!

I got to thinking in bed about drivetrains and configurations (as you do) and was thinking how you lose a fair amount through a 4wd system, compared to what is considered the 'optimal' layout of a 'pure' sportscar; RWD.

Obviously RWD also presents its own set of problems when handed buckets of power and torque, namely oversteer.

So obviously with the Scoob you are dictated the AWD setup by FHI, which IIRC is set to roughly 60 / 40 rear to front (with certain models such as the RA / USDM STi8 able to be 'wound forwards' to 50 / 50) but would it not be worth including the option to wind BACK to 100% rear? (Kind of like 'traditional' 4WD off-road vehicles where you can switch 2wd / 4wd)

This would basically allow the driver the full gamut of possibilites, from unrestricted, lightening fast RWD track sportscar through to 50 /50 AWD rain-meister.

Forgive me, things like diffs are my weak point, so I may well be wasting my time with this!

How obtrusive would it then be to fashion an automatic system, whereby on full RWD mode, when traction is lost, the front diff automatically starts feeding power to the front wheels to pull the car back into line? Unlike pure RWD traction control, you could allow a fair delay after traction is lost due to the ability to pull the car back into line with the fronts, and hence less obstruction to the driving experience.

Finally...(phew) if you could develop a chassis / drivetrain from scratch, purely for yourself, rather than from a commercial standpoint, what configuration would you use and why?

Edcase

Ok, having re-read all that, I think maybe I should have stayed in bed!

One last question as I don't want to hog the thread, what are your thoughts on Ford's controversial work with the front LSD as seen on the Focus RS, and where do you think they went wrong, if, indeed they did?

(I appreciate that you may not be able to answer this for a number of reasons, including poss. not having driven one, but I am genuinely interested in an engineers thoughts on the current comments by high profile road testers.)

johnfelstead

Just to add to what edcase has said, the torque split on the viscous centre diff cars (ie normal STi and UK spec) is 50/50. The torque split on a DCCD equipped car is 65R/35F (typeR/RA). The DCCD does not alter the torque split, it alters the % lock of the centre LSD, 2 seperate things. Winding the DCCD lock up isnt altering the torque split ratio as such IMHO.

Also the rear diff's are diferent on various models, being a viscous LSD on a UK car and Plated on a TypeR/RA.

Front diff is open on the UK, normal STi and TypeR car, it's a mechanical LSD on the TypeRA.

The STi7 TypeUK uses an AP Racing Torque biasing front LSD.

All these diferent combinations will alter the handling charicteristics, so if you have time it would be interesting to expand on the effects of each.

AJbaseBloke

I just wanted to express my thanks to both Damian and Simon (and those who asked all the good questions) for this - a treasure trove of information.

Hoppy

Top read! Thanks, Damian

P20SPD

iTrader: (1)

Thank you for your reply Damian and your time in answering other peoples questions. Very interesting.

Thank you once again.

Steven

carl

Another one for you Damian. In a nutshell, are you a good driver?
What I really mean is that do you find that your understanding of vehicle dynamics translates into being a better driver?

My reference point here is that I understand how a perfect golf swing works, what causes slice and hook, etc. and yet I still have a handicap in the mid 20s: the theory does not translate (for me) into practice. Similarly I have a fairly good understanding of oversteer and understeer, and their causes, yet I still don't feel I've come anywhere near mastering them.

ex-webby

I would just like to thank Damian again for his time (which, trust me, is very limited).

I'll answer the "is damian a good driver" question.. Yes he is. Is he world class? No he's not. The difference is, he is good enough to appreciate how bad he is .

Taking the golf swing thing. If you or I were to analyse the swing of a national standard golfer, we would say "wow! perfect".. where as he would look at the likes of Tiger Woods and say "god I'm SO crap".

Thought I would answer the question as Damian will simply say he's crap.. which he is not.

All the best

Simon

carl

Yes, but what I'm interested in is whether he thinks a thorough understanding of the theory helps him in practice.

In a minute I'm going to fall for Adam M's mistake of trying to get in a mention of the racing driver who knew nothing about cars, then realizing it was Tom Cruise in Days of Thunder

ex-webby

hehe

ok, understood.

This is agony for me as I'm desperate to answer some of the questions, but feel it would be better coming from an expert such as Damian.

All the best

Simon

Tone Loc

iTrader: (1)

Brilliant.... thanks Damian . Definately the best thread for a long time (just when i was getting really sick of the impreza v...., how much power if i fit.... look at my flamer kit.... type threads).

These types of thread could well put my interest back in the BBS which over the past 3 years certainly has got less and less.

Tony.

nigelward

Blimey Simon this is quite a queue of people you have to come and talk to us, cheers .

Hi Damian

OK, hopefully this will make some sense...

When a car is cornering, is the amount of body roll indicative of the amount of weight being transfered to the outside tyres, or is this just an indicator of the 'stiffness' of the suspension setup.

For example, given the same car but with different suspension settings (in simple terms), would the soft car that rolled the most be transfering more of its weight onto the outside tyres than the stiffly sprung car, or would the amount of weight acting on the tyres be the same.

Would a car with hypothetically no body roll be able to generate more lateral grip in a corner than one that rolls a little, ie is some body roll good for a vehicles cornering ability, and why would this be the case?

Thanks for your time .

Nigel

carl

For Damian's info:

The Powerstation Bump Steer modification involves shimming the steering rack in order to change its height in relation to the steering joints.

The WhiteLine Anti Lift kit is a set of bushes and mounts which change the pick up points of the rear end of the lower front suspension arms. The ALK K increases the castor which will in turn increase the "steer to center" thus the weight of the steering, and will "resist lift" of the suspension.


[Apologies to original authors -- I hacked these explanations out of other Scoobynet posts using 'search'. Couldn't find any info on the Powerstation or Whiteline sites Pictures stolen shamelessly from the Scooby Mania site]

Do either/both of these sound like sensible solutions to you, Damian?

[Edited by carl - 2/14/2003 2:20:33 PM]

Mungo

Great thread - it has really revived my interest in the technical aspect of the board.
A big thanks to Simon and Damian.

MorayMackenzie

IIRC, I read some rather convincing explanation of how the "Anti-lift" aspect of the Whiteline kit actually also worked as an anti-anti-dive kit... removing some of the resistance to dive on braking that was engineered into the car.

ex-webby

that's right moray.. i remember something along those line also.

great replies and questions chaps. Keep them coming

Edcase

Here's another one. I'm a videogame developer. Have you seen the major advances in this field in terms of driving games (gran turismo 3, Colin McRae rally) and have you been involved in any other their development?

Bearing in mind the difference between simulation and 'playability' what do you consider the key forces that need to be modelled in order to create an accurate but not uncompromising physics model?

MorayMackenzie

Edcase,

Is it just me, or does Colin McRae Rally 3 (xbox) have a deadzone the size of texas in the steering (wheel or thumbstick) that completely ruins the cars "handling"? WRC II Extreme on the PS2 certainly seems to be very much more "realistic", especially with force feedback support. Odd that CMR3 was a big let down after CMR2, and WRCII is a marked improvement over the dumbed down driving model that WRC 1 release version was crippled with.

Damian,

Hi there. Bringing this back onto topic...

I remember reading an article about the original WRC game (in Edge magazine) that stated the original handling model had been so accurate that Prodrive had found some use for it in diff control development... I wonder if this had any bearing in reality?

Moray

[Edited by MorayMackenzie - 2/14/2003 4:03:16 PM]

markd

is it me being stupid...as answerd in a earlier question i am right in saying that its ok to change to the solid drop links but do the arb bushes as well ....thanks mark

Catalunya Pete

Thanks for the reply Damian, I think i should have been more specific in my first post so here goes again. I am going to buy the Prodrive Suspension pack My97/98 secondhand, which I think was intended to use a 17in Speedline Superturismo wheel. I currently have 17in Speedline ST2 wheels on my car which I 'think' are a bit heavier than the Superturismos though I haven't weighed them yet. If they do turn out to be heavier will stiffening the dampers up( which I can get done) compensate for loss of of control/ ride quality that the heavier wheels may cause.

Thanks again
Pete

Damian Harty

Thanks for all your encouragement, it's much appreciated.

Wheelspin after ECU Upgrade Q: The underlying problem is associated with torque rise rates - i.e. how fast the engine responds to a 'step-in' on the throttle. As a general principle, torque rise rates really dominate perceptions of performance (we call it 'performance feel'). One of the reasons the manufacturers slug torque rise rates is because of the other problems they generate. Chief among them is that if the torque builds up too quickly the tyre is prone to spinning, as you've discovered. Kinda dumb really that we do loads of work on fuel injection to make it respond fast and then notice we have to turn it down again to make the car work properly... The engine mounts, some flexibility in the driveshafts, the rear diff mounts, the suspension bushing stiffness and the detail of the front suspension geometry all work together to limit how fast what the engine does gets to the wheels - it's torque rise rate at the wheels that really counts. I'm betting some detail changes in these areas will sort you out.

Anti-Lift Downsides Q: If the anti-lift kit is what I think it is, then anti-lift is very similar to "pro-dive" - in other words you may get less lift under acceleration but more dive under braking.

NSR Rattle Q: I'm sorry, I have no idea about this - maybe one of the other Prodrive guys can contribute? However, one possible reason it's always NSR and changing the strut doesn't cure it is that maybe it's the toolkit rattling? Just trying to think laterally... but seriously, if changing the struts doesn't cure the problem it sounds awfully like the problem isn't actually in the strut?

Rear Rebound Damping Q: If you imagine the body rolling out of a turn, the inside rear damper is trying to lift the inside wheel to make it follow the body. If there is enough rebound damping, the inside wheel will lift on the damper. This means all the weight is on the outside wheel and is like having a really big anti-roll bar, but only for a moment or so - it helps suppress understeer during the roll-in part of the turn. You don't need to lift the wheel clear of the ground, just make it "more nearly" lifted.

ATD Impreza Drive Q: As soon as you come up with a question better than the earlier winning question...

Edcase's Automatic Diff Setup Q: It's not at all difficult - it's called ATD! You have just described the essence of the ATD system - RWD when that would be good, 4WD when that would be good, FWD when that would be good. And you are exactly right about less obstruction to the drive experience. A journalist from Evo magazine today said "so it's like an empowering traction control?" - he has it exactly right, and so do you. I've always said that once you understand the problem, the solution suggests itself and so I'd say you therefore understand the problem well.

Ideal Chassis / Drivetrain Q: A nice question. Since I'm an old fart now, I think I wouldn't waste time developing one, I'd go to AMG and buy a Mercedes AMG C32. Quite the most exquisite and subtle piece of kit I have ever driven - normally I struggle to be graceful in a RWD automatic but this was just heaven. Not necessarily the concept I would have chosen but an absolute triumph of development. Close behind it would be a P1 but with ATD added to it - that would be a great toy. However, that wasn't really your question, so... I'd want something light, short wheelbase, with quite quick steering but not exceptionally so. I'd like a non-linear steering rack that gets quicker the more lock you put on and I'd like a smart 4WD system - maybe like ATD but with a few more bits and pieces. It would have ABS but no traction control and no ESP. Did you know that stands for "Enjoyment Spoiled Persistently"? I'd like double wishbone suspension (or a variant thereof) but more for ride quality than for handling - strut handling isn't all bad, as the Impreza proves. The engine would have to be supercharged and not turbocharged as I hate delays in engine response. I'd like an engine with a nice noise - a boxer or a vee - because inline engines are a little bland, by the by. So all in all it would probably end up being Impreza-based, I reckon.

Focus RS Q: One thing that all the ATD work has taught us is that if you think of the driveline as a device to optimise traction then the vehicle as a whole suffers. This applies to FWD and RWD as well as 4WD. I can't be seen to agree with the road testers you cite, so it's best if I just don't mention that I do. I can't really go into any more details but a smarter LSD would transform the car...don't ask me how I know.

Diff Type Q: In general, the centre diff matters when the car is sideways, the rear diff matters on high grip and the front diff more or less always matters. These are empirical observations made over some time testing on different surfaces and although I think I have explanations, they might not be right so I won't go into too much detail. Under these different conditions, the
smoother the operation of the diff the more fluid the car will feel - so viscous types invariably feel nice. However, they usually end up being set quite soft to be compatible with ABS systems and so on road vehicles they often feel less powerful than other types of diff. Mechanical types usually use some mechanism that transfers a small speed difference to a big clamping torque and in general anything with mechanical amplification ends up being a bit lumpy - it's all to do with the nature of frictional effects. Mechanical diffs can also be built to effectively "freewheel" to ensure they don't lock under braking. This means they can be set stronger than viscous units but their lumpy nature can give a slightly unnerving and erratic feeling to the drive experience. The "suretrak" diff on the front axle that I've driven uses a so-called "shuffling block" technology that I absolutely cannot understand but gives a very good, smooth operation and has impressed me greatly and is the exception to the "mechanical is lumpy" rule. A final word on the open-diff torque split...there is a lot of discussion about how important it is but the truth is if you're not using much power then it doesn't influence the vehicle handling much and if you are using a lot of power then the limited slip function of the diffs is working and as you say, this is not the same as the torque distribution at all. Basically, a fully locked diff transmits torque according to weight split whereas an open diff transmits what the designer had in mind. This is a really non-intuitive area and might need a bit more space than I have here to go into more depth on, but I will have a go if anyone's interested.

Am I a Good Driver Q: As Simon predicted, I believe I'm crap. He's right that I'm good enough to realise how bad I am... My personality is such that I can't do something well unless at some level I understand it. So for me, my vehicle dynamics understanding improves my driving, yes - but this may well not be true for everyone. However, the thing that really changed my driving was Don Palmer's coaching technique - he got me to do a series of "drills", then talked to me about the psychological side of what I was doing, then had a manic session pointing where the wheel should be and shouting "gas! gas! gas!" until it all gelled together. Something about his coaching style and my learning style fitted together very very well.

Body Roll Q: Another excellent question. Body roll is really an indication of suspension stiffness. However, it's usually true that cars with not much body roll have quite good tyres and quite good suspension, so they generate more grip than cars with bad tyres and bad suspension and probably lots of body roll - but there is no real cause-and-effect relationship with roll and grip. There is a tiny amount of extra weight transfer because the body rolls out of the corner but it really is small, and there are suspension geometry benefits if the car doesn't roll - but these are really secondary effects. If a car had no roll - like an active suspension car or a kart - it still has some weight transfer because the CG isn't at the ground.

Powerstation Bump Steer Q: Moving the rack by astonishingly small distances makes a big difference to the car. Which way does what depends on too many things to make a generalisation, sadly - I'll keep looking for the detailed information about this one. If you fit it, make sure you re-track the car afterwards!

Whiteline Anti-Lift Q: The anti-lift kit looks like it stiffens and lowers the rear mount. This changes that part of the suspension geometry we call "anti-dive" and reduces it. Less anti-dive is more anti-lift - they are connected as simply as that - so the anti-lift kit will indeed reduce the amount the nose lifts. Whether or not it solves the wheelspin problem is difficult to say but the anti-lift geometry will help - it's just difficult for me to know whether it's "enough". Stiffening the bush could go either way - personally I'd like to try the revised geometry with the original bush as a start point, and maybe try to stiffen that "a bit" with my drilling holes/poking in steel rod trick. Note that to help with the wheelspin problem you need to be working on the outside edge of the front suspension rear mount bush - the arm moves out at the back under traction. Don't work on the inside or else you'll find the ride gets harsh over poor surfaces, particularly on the brakes.

Video Game Q: I have indeed been involved in them. Two certain companies, who I won't name, came to us and asked us to improve their physics model. One gave me a really great programmer to work with and I just scribbled differential equations while he did all the hard stuff. What we came out with was a fantastic real-time driving simulator in a playstation box and I was delighted. However, when it was given to their gameplay testers they discovered to their surprise that it's hard to drive a rally car really really fast down a stage, and they kept crashing. Golly, there's a thing. So the realism was turned down and some "magic skyhook" terms were added into my beautifully elegant 10 degree-of-freedom vehicle dynamics model...the rest is history. I'd never played those video games before and I've never played them since! The forces that matter are tyre forces and roll moment distribution. If you contact me offline (via Simon) I can tell you all you need to know for a 50 Hz real-time vehicle model.

WRC/Edge Magazine Q: It's got a little bit of PR spin in it. One of the companies I mentioned above was Evolution and we used an initial version to demonstrate ATD before we had prototypes. I was so gutted when they fudged the model to make it more playable - it was fantastic for teaching you the rhythm of the car, timing for Scandinavian flicks and all sorts.

Drop Link/Bush Q: Yes, you've understood - do both links and bushes together for good effect.

Heavier Wheels Q: Make sure you weigh them (and all the suspension bits) to really understand the difference and try it first before you do anything to the dampers. Then yes, a bit more damping can help overcome the deficit - but be prepared for a reasonable amount of experimentation. That's why I say not to go into the dampers unless you're really serious - otherwise you're unlikely to get them right first try and depending on how much it costs you to get damper work done, it might just be cheaper to get a set of the right weight wheels.

carl

More excellent answers
Scoobynet just gets better and better, IMHO

Claudius

I have noticed that the more I increase the rebound and the bump, the "jumpier" the car gets. So even if the car has better turn in due to the roll bar effect the rear rebound damping increase has, wouldnt it be a better compromise to leave the rebound damping alone or put less and have a bigger anti roll bars instead? Since that gives less understeer as you explained previously. What would that sort of compromise depend on? I drive mainly on bumpy roads with potholes and the like, not on smooth tarmac.

Phil Harrison

Really readable stuff, Damian, thanks a bundle

(and yes, the jack is under the driver's seat )

Phil

Nigeyboy

Damian

Well done for taking on the challenge of SN. Maybe you could spread the word to your engine tuning colleagues .

I would like to know a little more about Geometry settings. I drive a 60 mile round trip to work each day mostly m/way/A road, but like a good blast at the weekend. Basically, before I get Geometry "done" I want to know a bit more about what effect changing each setting starts to have, both for the handling characteristic and tyre wear.

e.g. I've heard that too much -ve camber is more geared towards serious track/country lanes and increases tyre wear on the inside shoulder

Many Thanks
Nigel.

Subarussian

Sorry, double post...

[Edited by Subarussian - 2/15/2003 12:48:59 AM]

Subarussian

Hi there,

I have had my Scooby for 3 years (MY00) and decided to keep it for another 2-3. I am a bit used to the car by now and would like to "transform" it, so that it feels like I've got a new car. What mods would you recommend? I am considering the Prodrive suspension upgrade. Should I go for the Performance kit or the Professional one? What are the main differences between them? I know the Pro kit has a rear anti-roll bar, and is a little stiffer (?) than the Performance kit. But what does it mean in terms of the end result?

Many thanks for your advice!

I've also been running a separate discussion thread on the Prodrive handling pack here:

http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=162672

... it would be great if you could review the comments and post your thoughts there too. Many thanks in advance!

Best regards,

Andrei

carl

Another Q for Damian -- what's your opinion of adjustable dampers? There are people on here who swear by them, yet others (SDB in particular) who are of the opinion that with any adjustable dampers there's only one setting where it really feels right. Intuitively, I would agree as you're altering the damper settings without altering the spring rate. There are a lot of people on here who have really screwed the handling of their Scoob, failing to appreciate that there's been a lot of research gone into the standard Scoob suspension: something that's difficult to improve upon with some 800 quid adjustable coilovers and a spanner.

In the event that you think adjustable dampers are a good idea, what do you think of the options available? Some are adjustable bump/rebound, some adjustable bump only and some adjustable rebound only.