Corner Weight/Suspension setup

[foobar12345]

All,

    What are the standard corner weights for the Atom2 Brammo Ecotec with 200#ish driver?  I am going to have the FR/RL and FL/RR balanced but i wanted to know what percentage of weight is in the front versus the rear.  Any data would be appreciated even if its without driver or with driver/passenger figured in.

    Also, for suspension setup, what are some aggresive/tested track setups for toe/camber/caster which are still driveable on the street.  Based on my time, I need to have one setup for both, but I'm thinking i can get more aggressive than what is in the stock manual.

Thank you,

-Brad

[1965Cobra427]

Brad,

We have run quite a few different setups on my car, going for the best track performance and drawn the following conclusions:

Once the ride heights are set, there's not much you can do to alter the front/rear weight balance.

[img width=800 height=600]http://i66.photobucket.com/albums/h269/ ... 010028.jpg[/img]

Setting the front rh/lh balance is of course easy and we have done it with a driver and without. There is a small but perceptable improvement in grip from setting the front to match the way you will run on the track (IE: set with driver if you will not have a passenger). Our goal is usually to get the front within a pound or so from right to left. We work to improve the R/L balance at the rear, but can't get them terribly close, especially with a driver in place.

This was with an empty car - (with roll bar and individual seating)

[img width=800 height=533]http://i66.photobucket.com/albums/h269/ ... GP1724.jpg[/img]

We would typically dial the fronts to within a pound or so before calling it "good"

Here's another thread on the subject including some numbers -

http://forum.atomclub.com/index.php/topic,4873.0.html

[foobar12345]

Randy,

Thanks for your input.  It was helpful to relay to the folks at the tech shop.    Attached below is the corner weight with driver.  It is 50.0% balanced FR+LR/FL+RR but for L/R is not balanced.  Also, the weight with full fuel and no driver is 1516 which seems high?  They adjusted camber more aggressive than in the manual, front toe a bit less aggressive.  The guys @ the shop primarily do spec miata work, so this was their first experience with an Atom.  I expect a little test and tune from here. 

-Brad

[1965Cobra427]

[quote="Brad Reynolds"]
Randy,

Thanks for your input.  It was helpful to relay to the folks at the tech shop.    Attached below is the corner weight with driver.   It is 50.0% balanced FR+LR/FL+RR but for L/R is not balanced.  Also, the weight with full fuel and no driver is 1516 which seems high?  They adjusted camber more aggressive than in the manual, front toe a bit less aggressive.  The guys @ the shop primarily do spec miata work, so this was their first experience with an Atom.  I expect a little test and tune from here. 

-Brad

[/quote]

If the driver is 200# ish as suggested in your first post, that would work out to 1,316 for the car including fuel. Thats just about right. I agree on the agressive front camber. We have run as much as -2.5 degrees, usually -2.0. The factory guys have suggested more rear camber than we have run (we run -1.5 max) but reviewing the videos and lots of photos shows the outboard rear tire being very straight up in the hardest corners. Our rear tire temps also suggest we're in pretty good territory with the inboard temps still being a little higher than outboard.

Tom from the factory was impressed with the handling of my "older" car after driving it at AtomFest. He did express a concern for the low ride height I had dialed in (3.125" at the rear), due to a possible interference on the upper rod ends at high loading.

I'm eager to hear how your test and tune works out.

[foobar12345]

If the driver is 200# ish as suggested in your first post, that would work out to 1,316 for the car including fuel. Thats just about right. I agree on the agressive front camber. We have run as much as -2.5 degrees, usually -2.0. The factory guys have suggested more rear camber than we have run (we run -1.5 max) but reviewing the videos and lots of photos shows the outboard rear tire being very straight up in the hardest corners. Tom from the factory was impressed with the handling of my "older" car after driving it at AtomFest. He did express a concern for the low ride height I had dialed in (3.125" at the rear), due to a possible interference on the upper rod ends at high loading.

I'm eager to hear how your test and tune works out.

Randy,

It was 1516 with no driver, 1706 with driver as indicated on the readout.  That seems very heavy.

-Brad

[1965Cobra427]

[quote="Brad Reynolds"]
Randy,
It was 1516 with no driver, 1706 with driver as indicated on the readout.  That seems very heavy.
-Brad
[/quote]

Oh, that does seem a little porky. I'm guessing you have individual seating and the rollbar? My car has the one piece seat + rollbar.

BTW, do you mind if we move this to the US Atom tech section?

[foobar12345]

move it, and there is a sway bar post too we can move

[dp]

i just corner weighted my v8 atom - yep, the 400 hp v8 is indeed quite a bit lighter than the 4 cyl ecotec!

empty car (about 6gal fuel) and before setting corner weights:




car with me in it, corner weights set:

[CalScot]

Nice one, but my Honda 4 cyl 400HP is still lighter than your V8
Fancy a race at Reno?
Just what do we have to do to get you to bring that beast of yours?
Ive tried to be nice, now Im offering a duel. The loser buys dinner! Just like your last offer, but in RENO.

C'mon DP, you can do it! 

[twebb]

Wow,

The cross looks pretty good, but I'm suprised that you could not get better than a 40 pounds spread differential on fronts and the rears.  

The biggest problem I've found in messing with Cobra's car is sticktion.  It's really is amazing how much exists in these cars.  Perhaps it's the geometry...maybe someone with more knowledge can chime in.

If I were going to set up the car, here is the method I would use.  

I would first pull the shocks off of the car and reset the spring perches such that length from the bottom perch to the top perch is absolutely equal between the left and right shock.  On my formula car, I measure them with a micrometer.  Then set the push rods to the exact same length (a trammell rod comes in handy at this point).  Assuming that your car is straight and with the spring perches and push rods set correctly, front corner weights should be very close.  If they are not very close, then you have to deal with the sticktion issue, the springs are not of equal rate or something bent.

I would go through the same process with the rear of the car.

Now, to adjust for the addition of a driver or to get the corners absolutely equal (up front) you adjust the rear push rod length.  Make all of your changes with the rear push rods.

It's a bit more envolved than the aobve, but it will get you started.

Tim

[dp]

[quote="CalScot"]
Nice one, but my Honda 4 cyl 400HP is still lighter than your V8
Fancy a race at Reno?
Just what do we have to do to get you to bring that beast of yours?
Ive tried to be nice, now Im offering a duel. The loser buys dinner! Just like your last offer, but in RENO.

C'mon DP, you can do it! 
[/quote]


we'll see.  i'd like to do it but have to juggle a lot of things and reno is not exactly a one hour drive for me...

[dp]

[quote="twebb"]

The cross looks pretty good, but I'm suprised that you could not get better than a 40 pounds spread differential on fronts and the rears.  

The biggest problem I've found in messing with Cobra's car is sticktion.  It's really is amazing how much exists in these cars.  Perhaps it's the geometry...maybe someone with more knowledge can chime in.
[/quote]

there are different schools of thought in setting up corners.  basically overall left/right balance, like the overall front/rear balance, can only be changed by moving things in the car.  what one has control over is crossweights and left/right balance at one end (at the expense of the other end).  i prefer to set it up so that corner weights are equal and instead of equalizing front weights i try for a similar front/rear balance PER SIDE. 

sticktion seems to come at least in part from the bellcranks.  even though the brammo ones have needle bearings any off-axis forces are taken up by just a thrust washer so there's a bit of sticktioin in that.  i use tapered roller bearings in the dp1 for example, other designs have used nadella (?) combo needle/thrust bearings.

but ultimately unless setup is grossly off the differences are pretty subtle on a road-going car.  it would need bearings instead of bushings in arm pivots and a good deal more chassis stiffness before the last little bit of setup makes a real difference - in my opinion anyway.  for what the car is i think i've got it close enough.

what my atom does need is a lot more rear tire - it's very easy to powerslide it around even with partial throttle.  fun, but not the fastest way around a corner

[twebb]

I couldn't agree with you more.  When I was racing a left hand drive car I worried about getting the fronts very close.  I never could get the rears close until I started moving weight.  That was done by stripping the car so that it was under weight for the class and then adding back weight in the right spots to bring it into spec.

Now that I run a single seater, the side to side weight is pretty darn close and getting the corners spot on is much easier.

Tim

[nickpoore]

[quote="dp"]


[/quote]

I just like the magic paint that you have on the rollbar that makes it visible from one side, but not from the other.

[dp]

[quote="Nicholas"]

I just like the magic paint that you have on the rollbar that makes it visible from one side, but not from the other.
[/quote]

bar just got fabricated so it's not on in the first picture (stock configuration wouldn't clear the engine).  in the second picture it's on but photoshopped black.  i'll get it back from powdercoaters this week, then i'll have fully 'real' pics with the bar on