Everything You Ever Wanted to Know About Rake

[cij911]

Originally Posted by GTWORX.com

Sort of. In practice that's what I look at with cars that I know and measure from stock as a baseline. So yes I would say the Swifts have 15mm more rake than stock for example (from the 35mm front 20mm rear drop).

But really it's the roll axis. That's just a bit tougher to measure.


- Andrew

OK so what I was saying is correct then...Which is why I was a bit concerned with the swifts in the first place, the other reason being the reduced suspension travel (in the front)....

I really enjoy the feel of the stock setup on the street and am just hesitant to do anything that will make the ride quality worse, not to mention decrease performance. I would like the setup to be a tad closer to the GT3 ...

[EVOlutionary]

Don't "RAKE" me over the coals for bringing this back!

I kid, I kid!

So is there anyone else out there who runs the rear lower than the front??

[GTWORX.com]

^ that was terrible! haha.

on subarus we used to run the rear slightly lower....but we've been experimenting. For EVO's we generally do not, but don't take that to mean too much.

- andrew

[NWM_Tech]

""So is there anyone else out there who runs the rear lower than the front?? ""

""on subarus we used to run the rear slightly lower""

For aerodynamics you don't want the rear lower than the front, you want some rake. Maybe not on autocross but any track with a high top speed. Especially if you have a full pan.

[GTWORX.com]

Well...used to. The rear slightly lower was a very popular thing for Subarus (and still is).

And yes for aerodynamics it's not the best thing.

- andrew

[EVOlutionary]

Not always this low - accel in while hitting a g-out. . .

[madmax199]

Great thread (thanks Andrew for pointing it out),

Most evo owners talk about rake judging from the fender gap difference front and rear, but the rake should really be a difference from the front roll center height when compared to the rear's. Also, in the evo platform a somewhat level roll axis would result in the rear fender gap being significantly less than the front.

For high speed stuff it is always recommended to run some rake to help airflow around the car's mass, but for solo I found a level car(roll axis parallel to the ground plane) to be faster. like in evolutionary's picture my car's static rear fender gap is lower than the front but my roll axis is not negatively raked.

I think the real reason people ask about rake is because they want to know how low they should drop the car front vs rear without hurting the handling. In theory, regardless of what rake you end up with, you want the lowest center of gravity, and roll centers as close as possible to that CG height. However, in real life that is practically impossible in the evo because of the car's design(unless somone alters suspension pick up points etc). Once you start droping the car for a better CG(effectively reducing weight transfer wich is btw different from body roll) you also lower the roll center at a much higher rate, increasing the roll couple and making the car more prone to roll.

I believe it's far more important to properly lower the evo(lowest possible CG while still maintening the smallest roll couple) than having a rake or not. I'd take a car at any rake angle if that meant a low CG with and virtually zero roll couple.

In this pic I'm lowered as much as I think possible without negatively affecting the roll couple and the LCA are slightly angled down at the outer mounting points.
(I should mention that I run a RC correction kit and the fenders are cut or they'd be sitting on the tires)

[RaNGVR-4]

Also, Rake can increase downforce, even without an undertray. As viewed from the front, any extra "square footage" the car has increases downforce. Our Motorsports Engineering director preeches that, compared to a larger wing or other aero aid, extra rake increases DF/decreases lift more than anything else.

[Bryan at JRZUSA]

There is no front Cg and rear CG unless you have a extremely soft chassis or a tractor-trailer. Either way the analysis doesnt apply here. In a decent racing car, there is only one CG.


Read it, love it:
http://www.neohio-scca.org/comp_clin...Center2007.pdf


Pick up the recent issues of racecar engineering and listen to what Danny Nowlan has to say. He's math heavy, the way it should be. There is too much conjecture in racecar "engineering". If we don't have the data, go and test it.

Good to see everyone having a good tech discussion. A good thing to mind with rake, roll centers, pitch centers, springs, bars and the rest of the "static" adjustments: the "static" balance is the sum of its parts. People may run a high rake with soft rear springs to affect their balance through the corner. Mathematically and otherwise, its useful to view the mechanical balance "map" as various combinations of accelerations are applied to the car.This includes vertical, since the whoop-de-doos have their own considerations. Tire sensitivities aside of course.

[GTWORX.com]

I had read that before and i was still guilty of a couple of those myths.

thanks for the link....i need to keep up with this stuff more.

- andrew

[Tahoe55]

After reading this great thread, I wonder why no one has mentioned corner balancing as part of the adjustment/measurment/compromise "zen" that is EVO

If you add rake to a car, you are shifting weight forward and can measure it with racing scales. Has anyone measured their car weight at each wheel when adjusting rake?

When sitting in the car I have LF=1020; RF=1052, LR=752, RR =604
total = 3420, cross = 1813 52.8%

With my current setup, adjusting the weight back, lowers the rear springs and reduces rake. This is where the compromise part comes in.
What is a good corner balance for an EVO and what is the resulting rake? I'm interested to hear what choice people have made from experience.

This is probably a complex equation that factors in speed and aerodynamics. Loosely you can say lower speed favors optimal balance where aerodynamics are not a big factor versus higher average speed which must factor in changes in aerodynamics

I haven't found much info on rake vs cornerbalance and this thread seems like a decent place to have "coffee talk"

Here's a thread on corner balancing:
corner balance - yeah but what numbers

[Tahoe55]

After giving this more thought, I believe the best approach is to set desired ride height (correcting for steering geometry if going much lower). Adjust for desired rake, then fix any wedge by balancing. Sorry to bring the CBword into the rake thread...

[GTWORX.com]

Originally Posted by Bryan at JRZUSA

There is no front Cg and rear CG unless you have a extremely soft chassis or a tractor-trailer. Either way the analysis doesnt apply here. In a decent racing car, there is only one CG.


Read it, love it:
http://www.neohio-scca.org/comp_clin...Center2007.pdf


Pick up the recent issues of racecar engineering and listen to what Danny Nowlan has to say. He's math heavy, the way it should be. There is too much conjecture in racecar "engineering". If we don't have the data, go and test it.

Good to see everyone having a good tech discussion. A good thing to mind with rake, roll centers, pitch centers, springs, bars and the rest of the "static" adjustments: the "static" balance is the sum of its parts. People may run a high rake with soft rear springs to affect their balance through the corner. Mathematically and otherwise, its useful to view the mechanical balance "map" as various combinations of accelerations are applied to the car.This includes vertical, since the whoop-de-doos have their own considerations. Tire sensitivities aside of course.

i read this again. it's really good.

- drew

[Ludikraut]

Just as an FYI,

I just measured the ground clearance on my sideskirts (I know, I know there's probably a better way to measure this but...) after installing a set of Swift Spec-R springs:

Ground clearance @ front of sideskirt = 6.125"
Ground clearance @ rear of sideskirt = 7.125"

I also measured the front crossbar mounting points, which were:

Ground clearance @ front crossbar mount, driver's side = 5.25"
Ground clearance @ rear crossbar mount, driver's side = 5.3125" (5/16)

Figure the accuracy to be about +/- 1/16th of an inch; a.k.a. me lying on my back in my garage with a tape measure.

l8r)