Body Roll

[tacker]

A question for the suspension gurus.

how do you tune body roll out of your car. It seems like my gtr is suffering form this after looking at some pictures taken when car was last on the track.

Do i need to look at sway bar or coilovers or both to combat this.

[sh@un]

how track biased is it? do you use it on the street on a regular basis?

you can certainly tune the pretty much all roll/dive/squat out of the car by substantially uprating the sway bars and damper/spring combo, but it'll turn it into a disgusting thing on a public road- not to mention skittish in the dry and somewhat more dangerous in the wet.

[tacker]

LOL

with a paint job like that it aint going on any road:-)

It is purely a track car and is not registered at all.

and disgusting is my middle name :-)

[djr81]

You have some options:

1. Increase the sway bar stiffness.

2. Increase the spring rate.

3. Move the cars centre of gravity.

4. Move the cars roll centre.

Unfortunately these all have downsides.

1. Increased sway bar stiffness will hurt traction because it will pick up your inside rear.

2. Increased spring rates will make the car less forgiving but are worth a look. From the photos it looks like your car is falling over the front wheel, so could easilly live with a higher rate.

3. Lowering the c of g is basically impossible relative to the roll centre other than by changing the ride heights.

4. Moving the roll centres is an option. Check moon face racing for their adjusters. Having tried some of the stuff I can tell you that this is a difficult path.

From the photos I would recommend you throw some -ve camber at the front end before you do anything.

Edited October 22, 2007 by djr81

[tacker]

You have some options:

1. Increase the sway bar stiffness.

2. Increase the spring rate.

3. Move the cars centre of gravity.

4. Move the cars roll centre.

Unfortunately these all have downsides.

1. Increased sway bar stiffness will hurt traction because it will pick up your inside rear.

2. Increased spring rates will make the car less forgiving but are worth a look.

3. Lowering the c of g is basically impossible relative to the roll centre other than by changing the ride heights.

4. Moving the roll centres is an option. Check moon face racing for their adjusters. Having tried some of the stuff I can tell you that this is a difficult path.

1. have 30mm rear and 24mm front cusco items

2. ok but should both spring and damper be done together

3. you mean lower the car with adjustable coilovers?

4. How?

1. as by the pics i am picking up the inside rear now

2. i can live with a less forgiving car , at this point its far to forgiving to be honest

3. need to get some adjustable coilovers then any suggestion as i am shit scared of chossing the wrong type size color etc etc

4. ok last option then

[djr81]

1. have 30mm rear and 24mm front cusco items

2. ok but should both spring and damper be done together

3. you mean lower the car with adjustable coilovers?

4. How?

1. as by the pics i am picking up the inside rear now

2. i can live with a less forgiving car , at this point its far to forgiving to be honest

3. need to get some adjustable coilovers then any suggestion as i am shit scared of chossing the wrong type size color etc etc

4. ok last option then

First lot of questions:

1. How heavy are they (just out of interest)

2. Ideally, but not necessarilly (See below)

3. Yes or with the circlip type height adjusttment.

4. Roll centre adjusters alter the suspension geomtery hence migrate the roll centre.

Answering the second lot of questions:

1. So you need more spring stiffness relative to sway bar stiffness.

2. Then big up the spring rates. Dampers will work within a range of springs - but you need to check.

3. I understand where you are coming from. I got the wrong colour springs & I needed to go buy some new handbags, damn it all. I would recommend a combination of Eibach springs & Bilstein shocks. Springs can be chucked at little cost if they are wrong & the shockers re-valved if necessary.

4. Yes. I have some spares somewhere + some drawings if you can get stuff fabbed.

5. Get some more -ve camber! Particularly at the front.

Edited October 22, 2007 by djr81

[tacker]

First lot of questions:

1. How heavy are they (just out of interest) I am not sure of the rating but they are the solid jobbies

2. Ideally, but not necessarilly (See below)

3. Yes or with the circlip type height adjusttment. NOPE

4. Roll centre adjusters alter the suspension geomtery hence migrate the roll centre.

Answering the second lot of questions:

1. So you need more spring stiffness relative to sway bar stiffness. OK I HAVE 7.1 KG/MM FRONT 6.6 KG/MM REAR

2. Then big up the spring rates. Dampers will work within a range of springs - but you need to check.

3. I understand where you are coming from. I got the wrong colour springs & I needed to go buy some new handbags, damn it all. I would recommend a combination of Eibach springs & Bilstein shocks. Springs can be chucked at little cost if they are wrong & the shockers re-valved if necessary.

4. Yes. I have some spares somewhere + some drawings if you can get stuff fabbed.

5. Get some more -ve camber! Particularly at the front. GOT 5 AT THE MOMENT

[djr81]

Hmm, what ride heights you running (front & rear?)

[blind_elk]

No way known is that -5 deg camber. (It looks nothing like a V8 supertaxi, which run -6)

[tacker]

350 mm rear wheel centre to guard front 340mm

[tacker]

ok then Mr cusco owes me my money back for the neg 5 upper control arms i purchased

[salad]

From what I've seen, the Cusco arms state that they're X amount longer or shorter, my guess is you bought arms that say -5mm shorter?

Just a guess anyway.

Lowering the CoG should be done in conjunction with raising the roll centre as lowering the car changes the geometry and your roll centre actually falls faster than your CoG, leaving you with more roll.

What are your spring rates at the moment? If you do get the shocks revalved too, try a bit more low speed bump in them too

[tacker]

Would appear that 7.1kg/mm front and 6.6 kg/mm in rear is not enough.

Now need to look at a spring / damper package to help correct this. I am sure that the upper arm was neg 5 as we did discuss the merit of the 2.5 verus the 5 with the supplier and yep i have just check the emails on it and they are neg 5 upper arms. May be the pics that are not showing this as that corner is a 16 degree banking.

[Duncan]

Is it possible you are already going around corners quick on tyres with good grip....and there isn't much quicker you can corner with a 1500kg car?

You can stiffen up the rear bar but it will just start to lift a wheel instead. I guess you can get away with heavier springs on a nice smooth track maybe

mine

dont forget the car behind you is a good 300kg lighter and has a lower CoG.....

[tacker]

forget him LOL i dont think so thats all i could see out back and side of the car for most of the race. But i can go faster and have done with the slick tyres. But come to the point where the slicks were covering up the problem i now face. I have found out today the ohlin shocks on the car are not much more than OME and quite a soft spring rate for such a smooth track.

I am not under any kind of false impressions that i can make it hugely better, but i dont need much of an improvement to really give him a run for his money let me find 5 to 7 tenth a lap and i will make him honest at least.

I have spent bugger all on the car in the grand scheme of car racing and i would like to see if i can improve the roll and hope that it equates into a reduced lap time.

I can get a set of older tein HR for next to nothing and play with the springs until i can find some improvement, then invest in some better shocks with a more suitable spring rate.

then again i might be all wrong as i have a habit of being so LOL

[djr81]

350 mm rear wheel centre to guard front 340mm

Interesting. You may like to try raising the front up. I use 355 front, 345 rear. The more nose down it goes the more it understeers.

Secondly, with regard to camber there are two sorts. Static camber, ie measured at rest & dynamic camber, measured when the thing is loaded up through the corners. However much static camber you car may be running you seem to have insifficient dynamic camber. This is shown in the photos as the front wheel "tucking under" during cornering. Anyway, form what I understand, this is a suspension geometry issue tiedlinked to too low a ride height.

So it would be worth (IMHO) trying the car with an extra 15mm in the front ride height.

Anyway here is mine cornering - note the soft springs (Half your rate) but the front tyre -ve camber is still ok, even though the static is only - 2 degrees. I awill be chucking some harder springs at it today/tomorrow.

[Abo Bob]

I've definitely seen and heard Sydneykid say that GTR's should be slightly higher at the front than the back for best performance. You might be on to something there djr.

[Beer Baron]

I reckon harder springs are the winner here and tune a bit with sway bars if you have the stock ones still. maybe try the stock front bar again to dial out a bit of the understeer.

I think salad may be right that cusco sell their arms with a mm shorter number, not a degree number. I'll check tonight I have the full cusco catalogue.

and whatever you do don't buy some Tein HR, they are very ordinary, and being used will be even more so. buy my Tein RA instead!

[tacker]

Nice punt there BB

And i would try to lift the front but the coilovers i have are not adjustable hence was i thought a pair of height adjustable HR for 150$ would be a good test of raising the height of the car.

Car is going back in to get another alinement so i will check.

Was going to try the following settings

FRONT

1mm toe out

neg 5 Deg camber

8 Deg positive castor

Ride height 355mm

REAR

0 toe

3 deg neg camber

ride height

345mm

[Beer Baron]

sounds good. personally I prefer a little more toe out on the front. maybe another half mil each side. give a little toe in on the rear as that will help it stop moving around under brakes. also how have you set the rear traction rods?

I'm also keen to try a little less castor as even though it makes the car feel brilliant on turn in it can make the thing a little nervous in longer fast corners.

you may be able to machine up a spacer to go between your lower spring platform and your spring to adjust the height, just need to figure out a way to make sure it stays in place, maybe just 1 or two tack welds would do it.