Car Setup: Back to the drawing board ..., hey JP, you were right ;-) Options

[SirAndy]

well, today was a good day. 200 mile roundtrip and 13 timed runs and nothing broke.

the motor was running great.
the only small hiccup, that little oil-overfill that decided to fill up my puke-can and spill all over the engine and headers.
quote from a bystander: "dude, your car is smoking!"
oops ... (IMG:style_emoticons/default/rolleyes.gif) i guess the top mark really means full! (IMG:style_emoticons/default/biggrin.gif)


now back to the topic at hand.
i need to get back to the drawing board in regards to the car setup.

i had *massive* understeer all day. backed off the front swaybar to full soft with almost no change.
people on course later told me that every time i hit the fast pedal, the front of the car would come up.
i guess you could call this "torque understeer". (IMG:style_emoticons/default/biggrin.gif)

of course, like any good wannabe racecar-mechanic, i changed a whole bunch of stuff since the car was last running and not just one at a time ...

a few things:

- i have too much negative camber front/rear. tiretemps were from mildly warm to cold (inside to outside) and the wear on the tires shows that the outside 3rd of the tire didn't do any work at all.

- i need more rear spring. a lot more. i'm guessing that now that i run the rollerbearings, i lost ~50 lbs of sticky rubber bushing springrate in the rear.

- traction. i simply could not get all that power to the asphalt. i ran the whole course in 2nd gear (including the start) and i was at 1/2 throttle at the most.
i tried a few times to go full throttle and it would just spin the wheels.
same goes for coming out of a corner trying to accelerate. the unloaded wheel would just spin.
i'm thinking in need a limited slip ... (IMG:style_emoticons/default/idea.gif)


and lastly, forget about trying to run a good line through the course.
whenever i came out of a corner and touched the gas pedal, i was instantly at the next corner.
no time to think or even try to set the car correctly.

my guess is this is just me needing to get used to drive a car with power, but man, what a damm workout that was ...
(IMG:style_emoticons/default/huh.gif) Andy

[ConeDodger]

well, today was a good day. 200 mile roundtrip and 13 timed runs and nothing broke.

the motor was running great.
the only small hiccup, that little oil-overfill that decided to fill up my puke-can and spill all over the engine and headers.
quote from a bystander: "dude, your car is smoking!"
oops ... (IMG:style_emoticons/default/rolleyes.gif) i guess the top mark really means full! (IMG:style_emoticons/default/biggrin.gif)


now back to the topic at hand.
i need to get back to the drawing board in regards to the car setup.

i had *massive* understeer all day. backed off the front swaybar to full soft with almost no change.
people on course later told me that every time i hit the fast pedal, the front of the car would come up.
i guess you could call this "torque understeer". (IMG:style_emoticons/default/biggrin.gif)

of course, like any good wannabe racecar-mechanic, i changed a whole bunch of stuff since the car was last running and not just one at a time ...

a few things:

- i have too much negative camber front/rear. tiretemps were from mildly warm to cold (inside to outside) and the wear on the tires shows that the outside 3rd of the tire didn't do any work at all.

- i need more rear spring. a lot more. i'm guessing that now that i run the rollerbearings, i lost ~50 lbs of sticky rubber bushing springrate in the rear.

- traction. i simply could not get all that power to the asphalt. i ran the whole course in 2nd gear (including the start) and i was at 1/2 throttle at the most.
i tried a few times to go full throttle and it would just spin the wheels.
same goes for coming out of a corner trying to accelerate. the unloaded wheel would just spin.
i'm thinking in need a limited slip ... (IMG:style_emoticons/default/idea.gif)


and lastly, forget about trying to run a good line through the course.
whenever i came out of a corner and touched the gas pedal, i was instantly at the next corner.
no time to think or even try to set the car correctly.

my guess is this is just me needing to get used to drive a car with power, but man, what a damm workout that was ...
(IMG:style_emoticons/default/huh.gif) Andy

I wondered if you were going to have enough tire...

What was the ambient down there today? It is tough to get temperature into the tires on that track. Particularly race tires. I checked Grant's tires there last year I think? Maybe the year before and he didn't break 100 degrees F.

I bet it was fun to watch (IMG:style_emoticons/default/biggrin.gif) Sorry I missed it. I was buying new tires for the 4Runner after running over construction debris on the freeway this afternoon. I caught enough nails to build a doghouse!!!

[J P Stein]

Andy:

Driving a hi powered 914 does take some learnin'. (IMG:style_emoticons/default/biggrin.gif)
No more foot to the floor & steer deals like a stocker 2.0 4.

You may cure your push with proper front camber. Rather than make a bunch of other changes, go for that first. IIRC, Mr. Rogers runs 0 camber with Goodyear cantis.....he'd be the guy to talk at....run bias ply Hoosier cantis up front @-.5 and that seems to be just a bit too much... looking at the wear patterns. My front bites good ...which doesn't change with loud pedal application, but the back will come around with too much input. Too much camber out back will cause wheel spin and an unloaded tire don't help (IMG:style_emoticons/default/blink.gif)

Stiffer rear springs sounds like what it will come to. I found that 250s were not enuff, but 275s worked fine....as did 300s. An LSD does not help keep the wheels loaded. Get the unload fixed first then an LSD.....I need one of them too.

You also need suspension travel.......at least 2 inches. Riding the bump stops up front is guaranteed push.

Welcome to the jungle...... (IMG:style_emoticons/default/aktion035.gif)

[Joe Ricard]

OMG this sounds so familiar.
Now I don't have a big honkin motor but then again you were not using all your power either.
You have more ballast (bigger engine) so it would stand to reason that you need more spring.

BIAS PLY SLICKS NEED VERY LITTLE CAMBER!!!!!!!!!!!!!!!!!!
I am running -.7 out back and -.5 up front. I went all the way down to 23 PSI front and 24 PSI rear and got my tires up to 120 degrees inside and 115 outside.

You know as the rear squats you gain lots of camber so stiffer springs are definately in order. 300's are where I went. PLUS I have shocks that will control the high spring rate, lighter wheels, lighter car,

[grantsfo]

Andy:

Driving a hi powered 914 does take some learnin'. (IMG:style_emoticons/default/biggrin.gif)
No more foot to the floor & steer deals like a stocker 2.0 4.

You may cure your push with proper front camber. Rather than make a bunch of other changes, go for that first. IIRC, Mr. Rogers runs 0 camber with Goodyear cantis.....he'd be the guy to talk at....run bias ply Hoosier cantis up front @-.5 and that seems to be just a bit too much... looking at the wear patterns. My front bites good ...which doesn't change with loud pedal application, but the back will come around with too much input. Too much camber out back will cause wheel spin and an unloaded tire don't help (IMG:style_emoticons/default/blink.gif)

Stiffer rear springs sounds like what it will come to. I found that 250s were not enuff, but 275s worked fine....as did 300s. An LSD does not help keep the wheels loaded. Get the unload fixed first then an LSD.....I need one of them too.

You also need suspension travel.......at least 2 inches. Riding the bump stops up front is guaranteed push.

Welcome to the jungle...... (IMG:style_emoticons/default/aktion035.gif)

From what I see Andy has plenty of suspension travel. I think stiffer rear springs and LSD will clear up most of the problems he has. I put a little more weight on value of LSD for AX - especially in a street going car like Andy's. He is never going to get rid of all the unloading with a street setup.

The course at Marina did bring out understeer charateristics for all the mid engined cars. Every 914 out there was pushing at some point. I had to adjust my driving style to get the car to turn. Also if one didnt late apex some of the corners with some trail braking you were garunteed to push, regardless of setup. Funny thing - my car was understeering as I was fighting to get it out to correct postion to go into turns.

It was a nice day at Marina and cement had some warmth to it. Much better than those cold foggy days. Cars were hooking up better than usual. I think thats part of why Andy was having understeer problems, rear end was getting traction and making front of car light

[SirAndy]

thanks for all the comments guys! (IMG:style_emoticons/default/beerchug.gif)


one of the problems, this is always going to be a street car.
right now, it's my daily driver ... (IMG:style_emoticons/default/driving.gif)

heavier rear springs are not a problem, the roller bearings and the koni's on full soft make for a nice ride.


here's the current setup:

Front:
- stock 911 ('84) torsion bars
- koni adjustable shocks
- tarett swaybar, 22mm, now on full soft
- 9" GoodYear R250 slicks on 7" wheels with 1" spacer
- Camber: left = -0.4 | right = -0.4
- Caster: left = 5.5 | right = 5.5
- Toe: left = 1/16th | right = 1/16th
- Steer Ahead: 0

Rear:
- koni adjustable shocks
- 250 lbs eibach springs on adjustable collar
- stock sway bar
- 9" GoodYear R250 slicks on 7" wheels with 1/2" spacer
- Camber: left = -0.7 | right = -0.7
- Toe: left = -2/16th | right = -2/16th
- Thrust Angle: 0


so, i'm thinking i'll try the following:

- set camber to 0 front/rear
- try a set of 350 lbs springs in the rear


hoepfully, that'll give me the full thread width contact patch on the slicks and keep the front planted.
that should also put me back into a position where i can actually use the front bar for some fine-adjustment ...


(IMG:style_emoticons/default/idea.gif) Andy

[J P Stein]

I don't have much of a push problem except when our shitty asphalt
starts chunking. First end end into the gravel goes straight (IMG:style_emoticons/default/blink.gif)

When your running big stickey tiars chassis flex becomes a serious issue.
Handling can become ....like a box of choclates. All the suspension alignments
in the world aren't worth spit if you can't hold them within a fairly small range.

I think a lot of LSDs. I need more budget room tho. Maybe next winter.....

[drew365]

What size are your front torsion bars? I have the opposite problem in that I cant get rid of oversteer since I put the fuel cell in and added the front splitter/winglets. I have:
Front - 23mm torsion bars, 23mm Smart bar set 2/3 stiff, Hoosier 225/40 on 7"
Rear - 400# springs, Welt bar set full soft, Hoosier 245/45 on 8"

I'm thinking of dropping down to 350# springs in the rear so I can keep my front bar near mid point while tipping it to slight understeer. That's my hope.

With that much power and meaty tires, I think if you get the rear hooked up you better keep a close eye on the ears and swing arms for stress cracks.

[jhadler]

Andy,

It's possible that the torsion bars might be the culprit. You can get push from bars that are too soft as well. If they're worn out, or just too soft for the setup, you will bottom out, and then you'll push like crazy. With sticky slicks, you generally need a bit more spring to keep the bumpstops clear...

-Josh2

[Joe Ricard]

That's exactly what was happening to me. Static ride hieght was 4.250 inches in front.
With big sticky race tires I was creating alot of force and completely compressing the front suspension to the bumpstops. This gave me like 2000 pound spring rates and would cause a push.
Never suspected this till looking at video and still pictures of the car in hard cornering.
Once I put zip ties on the shock pistons was I able to verify. I am up over 5" static in the front and it goes to near 3.5 ish when racing.

[ottox914]

That's exactly what was happening to me. Static ride hieght was 4.250 inches in front.
With big sticky race tires I was creating alot of force and completely compressing the front suspension to the bumpstops. This gave me like 2000 pound spring rates and would cause a push.
Never suspected this till looking at video and still pictures of the car in hard cornering.
Once I put zip ties on the shock pistons was I able to verify. I am up over 5" static in the front and it goes to near 3.5 ish when racing.

Sounds like you have done the zip tie test, and have raised your front ride height a little because of that. What is the length of travel of the front strut from the top of the strut to the bottom of the bump stop? I suspect you tossed the dust shields long ago, so getting a few fingers in around the tire to measure this shouldn't be to bad. Just curious, as I've got my 914 slammed down a bit for auto-x, and while on 205-50 710's I don't generate the forces you do on slicks, I've wondered a bit what other guys run for front end travel.

And, from what points are you measuring ride height? I have measured from the top of the wheel rim to the bottom of the fender, although on your car w/flairs the measurements this way would not translate to us narrow body cars.

[J P Stein]

I measure from the doughnuts to the ground.....fairly level concrete.
My doughnuts are in plane +/- 1/8 inch....gud enuff for tape measure work.

A good ride height for me is 4-3/4 inch at both ends. This is just a reference, corner balance sets the heights from there.I have raised spindles
that leave me with 3/4 inch of travel un-used up front.....which just happens to coincide with the amount the spindles were raised. These are Bilsteins with one bump cut off the internal stops. The venues I run are very rough. 21mm Tbars do the trick for me with 275 lb springs in back, 22mm (effective) Tarret bar set 2/3 hard....kinda soft & kinda high, but I need the travel to maintian contact. If you think it don't work, come up & play.(IMG:style_emoticons/default/biggrin.gif)

One also has to watch for the pinch seam below the front fenders contacting the A arms....maybe the ultimate bump stop. (IMG:style_emoticons/default/blink.gif)
Weltmiester downlinks can go into bind at the A Arm...enuff to break them....that don't help. Too low is not gud...too stiff is not gud..unless you run on a billiard table.....my .02.

[john rogers]

- I would recommend leaving the negative camber in the rear and remove it from the front. Also some toe in in the rear.
- What is the caster seting, when I did auto-x we took as much out as possible but for road racing we have the max possible in.
- What tire pressure do you have cold, when I did auto-x I set them at 24# cold front and rear.
- What are the corner weights?
- How does the car sit, we always set the car nose down when static.
- How are the front shocks set, we set mine for the stiffest possible so the nose does not rise under power or dive under braking. The rears are set softest possible
Good luck with it.

[grantsfo]

- How does the car sit, we always set the car nose down when static.

Shhhhhh dont let all the secrets out! (IMG:style_emoticons/default/biggrin.gif)

[Joe Ricard]

in reference to the questions asked of me. JP pretty much sumed it up.

I do not have raised spindles but do have shortened strut tubes to house the Koni 8610 race inserts. About 1.5 inches shorter.

The zip tie gets to about 1/8" from a full Koni foam bump stop.
Yea the flares are not a good place to measure. but lift donuts are pretty consistant for most everybody.