Rake (stink bug mode)

[snowborder714]

I know rake has been mentioned a few times before, both used for combating understeer as well as less of a need for a rear camber kit (less important to me). I am interested in what you guys know about rake and how much is ideal (assuming the only measurements you have are ride height and not roll/moment center).

At some point I'd like to get all the measurements to calculate roll/moment center, but just don't have the time at the moment. So we'll start the thread off basing this only on ride height measurements.

One reason I'm curious about this is I went and looked at my latest ride height measurements and I am actually running the front higher than the rear. Not something that I'd like for my limited reading.


Measured from fender to center of wheel.

RF - 13.75"
LF - 14.0"
RR - 13.5"
LR - 13.375"

Front average - 13.875"
Rear average - 13.4375"

 

[knochgoon24]

Is measuring the fender to wheel center even an accurate method for measuring the rake?

EDIT: Scratch that. I see what you're getting at. You're asking others that may have calculated out their roll centers/moments and what their ride high is. Gotcha.

 

[snowborder714]

No idea

It's just the only measurement I have in regards to ride height at the moment. What's the typically way people measure ride height?

 

[greengoblin]

Of your frame rails or the pinched seam would be better. Some also measure off side skirts like on my kit.

Rake also effects down force.

 

[Pipnorcali]

I'm a 1 1/5 higher the rear, I'll get some measurements later but I take them from the center of the wheel

 

[snowborder714]

Of your frame rails or the pinched seam would be better.

So just measure from frame rail/pinch seam to ground? As far forward and backward as you can get, or somewhere around the wheel well area?

 

[greengoblin]

As far back and as forward as you can get and to the ground. The ground has to be level too to get a good read. They make really cool ride height tapes but I don't own one. I'll be picking one up some time down the road though.

 

[snowborder714]

You can't just say that without posting up a link, Kevin!

 

[jtmcinder]

With regard to "stink-bug mode," the goal is to have the rear roll center be much higher than the front. Thus, the real question is the angle of the lower control arm. I'm assuming that your front LCA is flat or worse. The suggestion is to keep the rear LCA angled down from chassis to knuckle. You want to work over that outside rear tire as soon as possible, snap-spins be damned!

Note: this is for autocrossing. Uncatchable snap-spins on a "real" track might ruin your day.

 

[snowborder714]

I'm well aware of that goal, jtoby. I haven't looked at my car lately, but I'd be willing to be it's around flat at the moment. I know I need to get the front crossmember modified (or replaced with a tubular unit once one is created) to correct this. But as long as I can keep the arm angled down from chassis to knuckle, is there such thing as too much rake? In regards to Kevin's point above and that it affects downforce, I would think there might be a limit where you'd just have the nose too low and it might get pushed into the ground upon braking. Maybe this is just something that you need to play around with and there is no "right" answer other than the control arm check.

I would guess by the "this is for autocrossing" comment that since I'm building the car more for road racing that I would have as extreme rake as I would for autox. But I still think some would be better than none, especially since I still experience understeer push.


Kevin, you should have Paul send me your crossmember after he's done with it so I can have the mod replicated (As much as I'd like to go with Robi since he has the jig, who knows know long it'd take.)

 

[knochgoon24]

I'll try to get measurements from my car tonight or tomorrow night, just to add to the mix. I can confirm that I'm over lowered in the front and rear. I swear my suspension has sagged since I installed it a year ago. I haven't touched it since and it looks visibly lower. I know Hyperco says their springs won't sag, so maybe it's the ES bushings that were installed at the same time?

 

[jtmcinder]

Yes, there could definitely be too much because the CG is between the axles (obviously), so raising the tail raises the CG (as else being equal).

WRT to the "just for autocrossing," maybe the guy who tried tracking Cinder will notice this thread and chime in. He politely once said: "the car was a bit too autocross-oriented when I bought it." A simple translation of this would be: "the car was loose to the point of undriveable."

 

[greengoblin]

Ride Height Gauges- Chassis Height Measurement Tools

 

[snowborder714]

Yes, there could definitely be too much because the CG is between the axles (obviously), so raising the tail raises the CG (as else being equal).

WRT to the "just for autocrossing," maybe the guy who tried tracking Cinder will notice this thread and chime in. He politely once said: "the car was a bit too autocross-oriented when I bought it." A simple translation of this would be: "the car was loose to the point of undriveable."

Makes sense in relation to CG. Obviously we don't want this very high.

Do you remember how much rake you had when you sold it?



Thanks Kevin!

 

[ACM]

A solid AWD autocross DSM will have 3-4 fingers between a 24.5-24.8" tyre in the rear and just enough room in the front to slide one's hands in to clean the tyres, up to the base of one's thumb.

 

[ileagleracing]

A solid AWD autocross DSM will have 3-4 fingers between a 24.5-24.8" tyre in the rear and just enough room in the front to slide one's hands in to clean the tyres, up to the base of one's thumb.

Charles, you should clarify that the front clearance includes "massaging" the fenders a bit

Samuel Krauss
08 Expedition (TSP)
04 S4 (STU)
98 Talon (SM?)
95 Talon (STX)

 

[romeen]

One reason I'm curious about this is I went and looked at my latest ride height measurements and I am actually running the front higher than the rear. Not something that I'd like for my limited reading.


Measured from fender to center of wheel.

RF - 13.75"
LF - 14.0"
RR - 13.5"
LR - 13.375"

Front average - 13.875"
Rear average - 13.4375"

I've practically obsessed over this the last few weeks. I've spent a lot of time looking at pics of stock ride height GS-T's. From what I've seen, the front wheel well gap is always larger than the rear (stock). But the car as a whole appears fairly level (to the naked eye).

Paul measured a '97 GS-T on stock suspension a few years back. I know this doesn't answer your specific question about how much rake is ideal, but it confirms that front height measured at the wheels is indeed higher.

http://www.dsmtuners.com/forums/handling-tech/86981-stock-ride-height-2g-gst.html#post151554936

I'm hoping to finally get my alignment done and new Star Specs mounted next week. I'm going to have the rear higher than the front but haven't decided by how much yet. I'll update this thread then.

Just curious though, since you corner weighted the car wouldn't it be more advantageous to just maintain that? Or is it better to try to compensate for the profound understeer that our cars naturally have? Racers please chime in.

 

[snowborder714]

I was thinking of trying to fix for the understeer issue. We just installed Eric's suspension stuff and got his car to have ~3/4" rake (measured at the pinch weld as far forward and backward as possible) plus be corner balanced. It's possible to have both and isn't very hard to do.

 

[romeen]

Brian, do you recall what the measured height ended up being front and rear?

 

[snowborder714]

In regards to wheel to fender or pinch weld? I remember wheel to fender, but don't think I remember the exact heights on the pinch weld. Plus we were using a measurement not from the pinch weld to the ground, but to where the tape measure disappears into the housing.

 

[black_gst]

I have a slight rake on my Talon and I noticed a difference in handling, though it could have been going from a 225/35/18 to my 245/40/17's but i also like the look.

im in for more info on this

 

[snowborder714]

The tires would definitely have done that. I notice I can't drive my car hard with my 225's. My brother almost ran my car into a tree on the 225's since he was so used to driving it hard with the 245's


Next time I'm home and can get the car on fairly level ground, I'm going to measure at the pinch weld and see what measurements I have.

 

[romeen]

In regards to wheel to fender or pinch weld? I remember wheel to fender, but don't think I remember the exact heights on the pinch weld. Plus we were using a measurement not from the pinch weld to the ground, but to where the tape measure disappears into the housing.

The wheel to fender numbers would be great. That's what I've been using.

I have a slight rake on my Talon and I noticed a difference in handling, though it could have been going from a 225/35/18 to my 245/40/17's but i also like the look.

Same here.

 

[snowborder714]

This is for Eric's car:

Front wheel to fender: 14"
Rear wheel to fender: 14.5-14.75"

 

[black_gst]

Yeah I'm trying to go 255s next, maybe that will stop 4th gear wheel spin on the freeway