Advanced handling concepts

[campbellju]

Thought I'd start a more high brow post on setting up the R's suspension.

To get the topic started I've post a few intersting pieces of information to generate a few ideas.

From a VW forum there's been a huge discussion on the whole lowering looks vs. handling debate here with the occassional nugget of very useful information:

http://forums.vwvortex.com/zerothread?id=621342&page=1

The key point is macpherson struts have an optimum location so the camber changes the least ubder compression/extension.

Next one....

Some great stuff on roll-centres, centres-of-gravity, roll-axis, etc. here (even though it is for RC cars, you can see where the theory becomes unimportant for a road car!):

http://home.tiscali.be/be067749/58/c2/index.htm

Contrary to popular belief, reducing you CofG is not always for the best as the car's roll centre is as important.

Practically where does all this leave us for setting up a car properly?

Discuss....
Jim

 

[Nad]

Lets Discuss Polar Inertia's instead

 

[campbellju]

Wasn't going to leave you out Nad, see chapter 6 in the Radio controlled car's link. Like I said, some of it is only applicable to RC cars but most of it like this chapter is all relevant. If you look at the diagrams for the R/C car and invert them you get a GtiR.

I'm assuming by polar inertia you are talking about rotational inertia before I start discussing the wrong thing?

Jim

 

[campbellju]

Thinking of your comment on a previous post, If you compare a lighter car to one say 20kg heavier but with a more centralised weight distibution, then all other things being equal then I agree with you, the heavier car would have better handling than the lighter car.

 

[turblio]

When I used to Rally we would always cure chassis flex before even thinking about suspension, ride height, or rotational torque etc

 

[Nad]

Its a shame as back in 2002 I posted a load of stickies in tuning along the lines of what you have said, but they got lost in the forum change and I have never had time to compile them all again.

Anyway, sticking to Poles, I know before we have discussed that an ideal would to be have all the weight in the centre of the car, but if we have a large amount of weight at the front, would it not be better to but weight over the rear axle to pull the centre point in the middle of the car and balance poles out?? rather than twice the amount of weight just off the centre off the axles towards the rear??

Nad

 

[Fast Guy]

Its a shame as back in 2002 I posted a load of stickies in tuning along the lines of what you have said,

Nad

I'm looking for em. Found this so far

An LSD works with clutches inside the hub with a spring. Literally the harder the spring the harder it is for the wheels not to turn at the same time.

Look at the spring and clutches

There are a couple of different ways of getting the LSD to work - There are the options of a '1 way, 1.5 way, or 2 way'. What this means is that with a '1 way', you only get the LSD action when under power. A '1.5 way' has a little LSD action when on trailing throttle. (good for controlling the car when cornering) And finally the '2 way', which is the sideways driver's dream, as the car will want to slide everywhere. Not the fastest way to get around a corner, but it looks pretty cool ...

This is how a 1, 1.5 and 2way LSD works: LSD workings

All LSD's will make the initial turn in harder on the front, aka more understeer. On the rear wont be as noticable on turn in, but when u boot it the back is more likely to come out.

What u really want is a better centre diff but I have yet to find one.

Right I have found way too much to cut and paste here for you lot to read so here are the links which i think u will find cover everything. If u cant find what u want tell us and I will search furhter. Right the top link is the best, have a good look round the site, it will explain almost all u want to know.


http://auto.howstuffworks.com/differential.htm

http://www.houseofthud.com/differentials.htm#limited slip

http://www.club4ag.com/faq and tech_pages/limited_slips_differential_101.htm

http://www.phantomgrip.com/

Nismo LSD's for sale

Go to performance parts, then ATS This is a good read, explains turn in etc[/red]

I know they dont do an LSD for our car but the info is good.

Right the top link is the best, have a good look round the site, it will explain almost all u want to know.

UPDATED LINKS AND INFO

Handling differences

Right if u put a 1.5 on the front u will get understeer on acceleration, but only if u r still doing a lot of the turning out of the corner under accelertation. You will not get as much under braking, so as long as u set ur corners up properly u will be ok.

Likewise 1.5 on rear sounds good as u shouldnt get too much drag when braking and turning in but enough kick out of the corner which may induce some oversteer.

Centre diff, well lets try and find one first, apparently on some viscous diffs u cant pass a current thru the fluid to thicken it up.....

....oh and then there is also the fact that u should be able to adjust all the diff as to when they lock up also, just somehting else to think about hey lol[/red]

Right the top link is the best, have a good look round the site, it will explain almost all u want to know.


Nad

 

[campbellju]

When I used to Rally we would always cure chassis flex before even thinking about suspension, ride height, or rotational torque etc

agree totaly. I've got various strut braces already. I had a rollcage in the car when I first goti it too but removed it due to safety and insurance concerns. This did reduce chassis flex a bit but was 6 point bolt in rather than multi point weld in so probably no where near as well as a professional cage. In terms of chassis stability, I didn't miss it that much when it went.

 

[campbellju]

Anyway, sticking to Poles, I know before we have discussed that an ideal would to be have all the weight in the centre of the car, but if we have a large amount of weight at the front, would it not be better to but weight over the rear axle to pull the centre point in the middle of the car and balance poles out?? rather than twice the amount of weight just off the centre off the axles towards the rear??

Thinking out load...

If we take edd's example of a 67/33 split for the R. If we simplfy this and assuming corner weighting has been done so the CoG is down the middle of the car and 1/3 back from.

Thinking about this practically, the only reason you might add weight to a car is because you are below some form of competition entry reg. Now say you have 30 kg to add, then your question is where do you add 30kg to get the best effect??

My question would be what are you trying to achieve? I don't think anyone would argue that the weight should be towards the back rather than the front but should it be inside, in line with or outside the wheels. I don't think either of us are advocating putting the weight behind the rear axel so in simple terms that leaves in the centre or on the rear axel.

If you have it in the centre this will speed up the turning repsonse relativley speaking and make the back more lively. At this point it all gets very subjective though as you are also making the rear less stable, desirable on a gravel circuit with lots of handbrake turns, less good on a high speed tarmac circuit where stability becomes important. However, if you were into gooning around on a circuit then I'd put it back in the middle again as the car would have less momentum and make the back end easier to recovering.

Not saying I'm right, just that personally I'd stick my 30kg between the rear axle, offset just enough so the L an R are balanced without needing their ride height or spring rate adjusting. To me this would give a good base for setting up the car.

Anyone please add or contradict what I'm saying, its good to talk.

 

[Nad]

When I used to Rally we would always cure chassis flex before even thinking about suspension, ride height, or rotational torque etc

Well the cage will sort that out, which is why I skipped chassis flex

I doubt at the going rate of insurance mine will ever get back on the road anyway, not unless its fast enough to out run every type of police vehicle.

Jim, yea rotational as in turning forces etc. You have already gone into it. I posted a while back as to be the 3rd post but for some reason its down quite a few.

Nad

P.S. Will read a bit more later and post again

P.P.S. Thanks Carl for finding that.