Ideal Rake?

[kcdedric]

I just finished installing my new TCK setup today and will be taking it to the shop in a few days for alignment and corner balancing.

I've searched a fair bit on the topic, but I can't seem to find a solid answer. It would make sense that our cars would benefit from having front rake (to reduce understeer), but how much is ideal? If it makes any difference, I'd like to lower the car about 1-1.25" from stock.

[seank]

I don't know of any race car that runs rake (usually squat) and the only reason I can think why the z4 car could benefit from rake is to counter the stock staggered set-up.

Did TC run rake on his cars?

[The HACK]

Rake is for the poseurs in the "stance" crowd. Worry about cross weight and roll center. Don't worry about "rake."

[exdos]

Originally Posted by seank

I don't know of any race car that runs rake (usually squat) and the only reason I can think why the z4 car could benefit from rake is to counter the stock staggered set-up.

Think Red Bull in F1: they run a greater rake angle than all the other teams and it doesn't seem to do them too much harm.

Originally Posted by The HACK

Rake is for the poseurs in the "stance" crowd. Don't worry about "rake."

Rubbish! Rake counteracts the tendency to aerodynamic lift from which the Z4 has a tendency to suffer. According to the information found here: http://www.genmay.com/showthread.php?t=827884 at 200km/h (125mph) the BMW Z4 3.0si Coupe already has 28kgs of front end lift and 43kgs of rear end lift, What happens to all the careful corner weighting then?

Then again, it all depends upon what you're using your car for. If it's relatively slow speed stuff, aerodynamics are less important. But for flying around the Nurburgring, I want all the aerodynamic advantage I can get.

[GuidoK]

Is rake the same thing as caster angle?

[Shipkiller]

[RobertRO]

Originally Posted by GuidoK

Is rake the same thing as caster angle?

By rake or squat of a certain vehicle I understand the inclination when looking from a side.
If the front of the vehicle is lower than the rear of the vehicle, then it sits a little bit inclined to the front. This inclination is called "rake".
If the inclination is the other way around (= the vehicle is higher in the front than in the rear), that is called "squat".

Please correct me if I'm wrong.

[exdos]

Originally Posted by GuidoK

Is rake the same thing as caster angle?

I believe that rake angle is a term that is used in place of caster angle in bikes.

Rake in cars is the angle that the floor of the car makes with the ground.

[GuidoK]

Originally Posted by RobertRO

By rake or squat of a certain vehicle I understand the inclination when looking from a side.
If the front of the vehicle is lower than the rear of the vehicle, then it sits a little bit inclined to the front. This inclination is called "rake".
If the inclination is the other way around (= the vehicle is higher in the front than in the rear), that is called "squat".

Please correct me if I'm wrong.

So rake is an angle of the chassis and not an angle of the suspension geometry?
(caster is the angle of the suspension strut compared to the normal measured in the driving direction)
caster:

(picture from book 'the automotive chassis')

[The HACK]

Originally Posted by exdos

Rubbish! Rake counteracts the tendency to aerodynamic lift from which the Z4 has a tendency to suffer. According to the information found here: http://www.genmay.com/showthread.php?t=827884 at 200km/h (125mph) the BMW Z4 3.0si Coupe already has 28kgs of front end lift and 43kgs of rear end lift, What happens to all the careful corner weighting then?

Then again, it all depends upon what you're using your car for. If it's relatively slow speed stuff, aerodynamics are less important. But for flying around the Nurburgring, I want all the aerodynamic advantage I can get.

Seriously? All that careful corner weighting helps DYNAMIC weight transfer. When the car is either accelerating or decelerating, the "rake" of the vehicle will change accordingly. What happens to your carefully measured "rake" of the chassis when the car is entering a corner or exiting a corner? How often do you drive an entire course while doing exactly 200km/h?

Rake is irrelevant. It is FAR more important that the cross weight is as close to neutral as possible and the car is as low as the roll-center allows while still maintaining a reasonable front/rear weight balance. IF lift or aerodynamic grip is your concern, find ways to add or subtract downforce while minimizing the impact on drag, rather than fix the "rake." If your chassis is set-up right, "rake" will fix itself.

Rake is for "stance" crowd poseurs. You might as well lower the car PAST its roll center with massive negative camber in order to tuck your 10.5" F, 12" rear wheels shod with 205f/225r tires into your fenders.

[exdos]

Originally Posted by The HACK

Seriously? All that careful corner weighting helps DYNAMIC weight transfer. When the car is either accelerating or decelerating, the "rake" of the vehicle will change accordingly. What happens to your carefully measured "rake" of the chassis when the car is entering a corner or exiting a corner? How often do you drive an entire course while doing exactly 200km/h?

Rake is irrelevant. It is FAR more important that the cross weight is as close to neutral as possible and the car is as low as the roll-center allows while still maintaining a reasonable front/rear weight balance. IF lift or aerodynamic grip is your concern, find ways to add or subtract downforce while minimizing the impact on drag, rather than fix the "rake." If your chassis is set-up right, "rake" will fix itself.

Rake is for "stance" crowd poseurs. You might as well lower the car PAST its roll center with massive negative camber in order to tuck your 10.5" F, 12" rear wheels shod with 205f/225r tires into your fenders.

Yes, I agree that the DYNAMIC load shifting that occurs with acceleration and braking also simultaneously affects the rake angle. IMO the Z4MC's OEM suspension is totally unbalanced and far from neutral.

I've recently written in another thread on the forum: "The Z4MC's suspension is too soft at the front which allows pitching on braking and lifting on acceleration, which makes the steering floaty and imprecise, and at the rear it's too stiff, which makes the ride very uncomfortable. The 3 centre coils of the rear springs are 19mm thick whereas the front springs are just 11mm thick: obviously there's a huge mismatch between front and rear spring rates, yet BMW cars supposedly have a weigh balance F:R of 50:50.

I've fitted AC Schnitzer Racing suspension (basically Bilstein PSS9 made to ACS's specification), which has rear springs of 16mm and front springs of 14mm, which redresses the mismatch of F:R spring rates. Instantly, this helps to overcome the inherent ride and handling problems of the Z4MC with OEM suspension."

With my ACS Racing suspension the car is considerably more balanced with considerably reduced tendency to pitching and lifting, which, of course, will simultaneously reduce the dynamic rake change that previously occurred.

You ask: "How often do you drive an entire course while doing exactly 200km/h?" As you know, aerodynamic effects are working at ALL speeds and not just 125mph (200km/hr), and have greater effect at higher speeds. At The Nurburgring I will be doing a lap time averaging in the order of 90mph and reach speeds above 125mph several times and touch above 140mph. As the figures for lift of the Z4 3.0CSi show, the lift is unequal F:R so again any corner weighting done at 0mph goes completely out of the window in the dynamic situation, especially at higher speeds.

As always, it's "horses for courses"; maybe for your purposes you can ignore rake, but for my purpose I consider that it is an important consideration, which I have adressed. I couldn't give a toss about "stance", and I'm not interested in lowering for the sake of it, it's only the performance and handling that concerns me.

This is a photo of me in my M Coupe (S54) at the Nurburgring. It looks to me like my car is very well balanced with minimal lateral bodyroll and a preserved rake angle due to the lack of pitching/squatting. I have also heavily modified that car and it's handling is now superb.

[johanness]

ideal rake:

[seank]

Originally Posted by The HACK

Seriously? All that careful corner weighting helps DYNAMIC weight transfer. When the car is either accelerating or decelerating, the "rake" of the vehicle will change accordingly. What happens to your carefully measured "rake" of the chassis when the car is entering a corner or exiting a corner? How often do you drive an entire course while doing exactly 200km/h?

Rake is irrelevant. It is FAR more important that the cross weight is as close to neutral as possible and the car is as low as the roll-center allows while still maintaining a reasonable front/rear weight balance. IF lift or aerodynamic grip is your concern, find ways to add or subtract downforce while minimizing the impact on drag, rather than fix the "rake." If your chassis is set-up right, "rake" will fix itself.

Rake is for "stance" crowd poseurs. You might as well lower the car PAST its roll center with massive negative camber in order to tuck your 10.5" F, 12" rear wheels shod with 205f/225r tires into your fenders.

I stand with The Hack on this one (and most of them that I recall). But what do we know?

[Ontrack]

Originally Posted by kcdedric

I just finished installing my new TCK setup today and will be taking it to the shop in a few days for alignment and corner balancing.

I've searched a fair bit on the topic, but I can't seem to find a solid answer. It would make sense that our cars would benefit from having front rake (to reduce understeer), but how much is ideal? If it makes any difference, I'd like to lower the car about 1-1.25" from stock.

I just worked with James Clay from Bimmerworld in setting up my Z4 MC and he suggested running 1/4" - 3/8" rake. I have mine at 1/4" right now and I am running a Motion Control Systems 2 way suspension. With staggered setup running rake helps and a lot of race car run rake from the research I have seen. Especially GT type cars.

[Kgolf31]

I'll talk to my friend who works at TCK and get a definite answer.

As in terms of caster, you want to max out caster to increase turn-in.

[tikamak]

Originally Posted by exdos

I believe that rake angle is a term that is used in place of caster angle in bikes.

Rake in cars is the angle that the floor of the car makes with the ground.

You may need to buy another car. if you like this raked stance and you want your car to perform and handle well at the same time, you may need another car because the Z4 will always have the ass lower than the nose due to most of the weight of the car centered in the front and when corner balancing you will need to lower the rear more than the front.

Check how a Z4 is setup by BMW and listen to what Hack has to say.
I'd say corner balance that sweet ride and forget about its stance.

If you really want to impress someone, go do the following:
1- Euro headers
2- Decat Spipe leaving the chamber to pseudo- resonate.
3- Buy a straight-through muffler like RE diablo or RPI or SS or eisenmann.
4- Get evolve NA software
5- Shift @ redline

Pure DTM aural sex. I can post a video if you're interested.

[Beedub]

Tika ,exdos, is soooooo far from a stance idiot, he other end of the scale he's a proper engineer. He added rake angle to his car for nothing other than performance I can assure you :-)

[GuidoK]

Originally Posted by Kgolf31

I'll talk to my friend who works at TCK and get a definite answer.

As in terms of caster, you want to max out caster to increase turn-in.

Minimalise caster.

less caster means stronger steering effect when turning into a corner and more caster means more steering effect when leaving the corner (and increases straight line stability)

[exdos]

Originally Posted by tikamak

You may need to buy another car. if you like this raked stance and you want your car to perform and handle well at the same time, you may need another car because the Z4 will always have the ass lower than the nose due to most of the weight of the car centered in the front and when corner balancing you will need to lower the rear more than the front.

Check how a Z4 is setup by BMW and listen to what Hack has to say.
I'd say corner balance that sweet ride and forget about its stance.

If you really want to impress someone, go do the following:
1- Euro headers
2- Decat Spipe leaving the chamber to pseudo- resonate.
3- Buy a straight-through muffler like RE diablo or RPI or SS or eisenmann.
4- Get evolve NA software
5- Shift @ redline

Pure DTM aural sex. I can post a video if you're interested.

Tikamak,

You're talking drivel!

This is a photo of how I've set up my Z4MC on ACS Racing suspension (adjustable), with H&R E46 M3 ARBs F&R and with 10mm spacers F&R and RTAB limiters. I have also reconfigured the geometry. It has been set up by the way it feels and performs to my handling taste and requirements. The appearance of the final result has been of no interest to me, all the mods and set up have been refined by performance, only.

Go on, tell me I'm a poseur who's just gone for stance.

[exdos]

Originally Posted by GuidoK

Minimalise caster.

less caster means stronger steering effect when turning into a corner and more caster means more steering effect when leaving the corner (and increases straight line stability)

More caster produces an increased dynamic negative camber. Which means that you need less static negative camber. You should play around with some camber/caster plates on your car and measure the camber changes when you turn the steering wheel and you'll soon see that an increase in caster produces a greater increase in dynamic negative camber on the outside front wheel, as in cornering.


By increasing the caster and running less static negative camber, you'll get less tyre wear, have better self-centring and great turn in, due to the increase in dynamic negative camber.

[tikamak]

What's this? "my handling taste and requirements"

[GuidoK]

Originally Posted by exdos

More caster produces ...

That's a very clear explanation, thx
So the dynamic camber created is sufficient to produce the grip for turning in.

Originally Posted by exdos

on ACS Racing suspension (adjustable),

What's ACS? A brand or so?