What's the final answer on negative camber?

Zeke · 06-21-2003, 05:09 PM

Here's the specs: Khumo V700s on 15 x 7 wheels, narrow body (for now), no spacers. I'm looking a neg 2 degress at the rear and about neg 1.5 in front as set up in the driveway (level pad). I've got a 1/16 tow in both front and rear. Before I go to the alignment shop, should I run it that way or is there a better setup to put on the car for long track racing? No ax at this time.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Depends on a whole lot of things... Sounds like a good start if you aren't a novice and don't have mega-super-stiff roll resistance.

I say give it a try and use a pyrometer (and lap times) to tell you if and how to modify.

--DD

J P Stein · 06-22-2003, 06:50 AM

I'm finding (at AX) that -2 is about right in the front, but too much in the rear.....but.

The Welt 180lb springs are progressive and the first 2(or so) inches of compression are WAY too soft. When I'm on the gas, the rear end squats, turning causes compression.....both increase the rear negative camber. I'm 20 deg hotter on the inside than outside of the tread. I have some 200lb springs (non-progressive) OTW from
Renegade....the only place I could find em'.....short of going to a different spring set-up in back(threaded collars & smaller dia spring). It may come to that, but not this year. Here's a pic of OTG.
.........

Zeke · 06-23-2003, 07:23 AM

Thanks to JP & DD, but that's it? All the racers have left for another BBS?

John Rogers · 06-23-2003, 07:38 AM

Well Milt I can't help you as I run Goodyear slicks and they use nearly 0 camber. On our stock 914 with V700s we use about the same specs as you do but a bit more toe in (0.25 inch) on the rear as it moves more under breaking. I'd try it some place like the Streets of Willow and check the handling, temps, etc and make adjustments then. I'd recommend having an experienced 914 driver check it too if you don't mind someone else driving it. Good luck

campbellcj · 06-23-2003, 10:56 PM

Milt, I've been running very close to that setup on my previous and current cars (kind of embarrased to say I don't have the precise specs for the latest alignment) and it works well. I can get a bit more camber in the front, at least on this car w/ the aftermarket camber plate thingies, but from what I've always heard, the usual desirable range with radials on stock-ish cars is -1.5 to -1.9 or so up front. Many cars with stock strut towers can't go beyond 1.6 or so no matter what you do anyway. (IIRC, JP had to tweak his car to even get anywhere near that.) My tire temps looked pretty good at the last Streets event. I plan to continue testing and tweaking thru the next few months and will hopefully have some better real-world data later. It has been tough to pin anything down so far, because there have been multiple changes to the car between events...brakes, tires, wheels, spring rates, etc. Now that it is getting more dialed-in (dare I say "finished"?) the real fine-tuning can proceed.

J P Stein · 06-24-2003, 12:37 AM

Ayup, tweaking with some Tarret offset strut mounts to get -2 deg.

Betty Church · 06-24-2003, 04:49 AM

"Well Milt I can't help you as I run Goodyear slicks and they use nearly 0 camber."

John, what size springs/sway bars are you using? I'm running GY slicks on my 914/6 project and know I have way too much negaive camber. I'm trying to sort out the suspension at the moment so haven't messed with the camber settings yet. Any help would be appreciated.

Betty
1971 914/6 3.2

John Rogers · 06-24-2003, 05:44 AM

Well Betty, let me see??? I have Koni Sport adjustable shocks set minimum, 300# springs in the rear with the rear sway bar connected. In front there is 23mm torsion bars and an adjustable sway bar set a little stiff. The front settings are 1/16 toe in, 0 deg camber and the rear is 1/8 toe in and 15 minutes of neg camber. These were at the start of the year and seem to have not changed much. The car is very flat and the only place I have had any troubles is at PIR on turns 3 & 4 which have very little banking and I could not go flat out but on corners it works well. The car weighs 2278 with a full tank of gas and I run 25# cold pressure (soft compound) front and rear and tire temps are within 1 deg across all tires. Good luck.

Betty Church · 06-24-2003, 09:39 AM

Okay now the stupid question. How would a 23mm torsion bar equate to spring rate?

After 10 years of autox, de and racing I've learned more about setup with this 914 in the past 6 months than I ever wanted to know!

I've never tracked a car that was older than a 92 until now so please...have pity.

BTW this 914 is sooo much fun to drive. I giggle every time I get into it whether it's on the track or just driving 15minutes to the shop (where it seems to live).

J P Stein · 06-24-2003, 10:03 AM

The short answer is ....pretty damn stout.

911 Torsion bar to coil conversion chart
This chart was developed using actual geometric measurements.
Note that Kw/Ks is NOT constant, since we used neumerical analysis over a range from
Kw is calculated using the actual load at the wheel center calculated with +- 1" travel from center.
Note nonconstant Kw/Ks
Front Rates
Torsion Kw (lb/in) Ks (lb/in)
Dia (mm) (Wheel) (Spring)
16 77 90
17 97 112
18 122 138
18.5 137 154
19 152 170
20 187 207
21 227 249
22 273 298
23 327 355

I stole this from somewhere(that BBS that Zeke aluded to)....they'll never miss it

I seen other WAGs but this one looks mo betta.

Front 914 T bars are the same length as 9eleben T bars so this should work.

John Rogers · 06-24-2003, 10:13 AM

As JP noted the springs are pretty stiff but I drive on pretty smooth tracks such as PIR, CA Speedway and Willow Springs. I stopped doing events at the stadium in SD since it is so rough it bends suspensions! If the surface is bumpy, rough or uneven then I'd say go with lighter t-bars and springs. Note that mine get close to being the same rates front and rear and the weight is pretty close to even since I moved the gas tank forwards some when I went to a fuel cell. Good luck. What you should not have happening is lifting of a front wheel on hard turns since this reduces the contact area (obviously) and that was happening to mine when I had 220# springs in the rear. Going to 300# rear springs pushed the corner down. Good luck

J P Stein · 06-24-2003, 10:38 AM

Quote:

Originally posted by john rogers
What you should not have happening is lifting of a front wheel on hard turns since this reduces the contact area (obviously) and that was happening to mine when I had 220# springs in the rear. Going to 300# rear springs pushed the corner down. Good luck

Swell.......I just got some 200lb springs to keep from doing this. .....

I'm kinda between the rock & the hard spot as all our AX venues are rough as a cob. The cubic money approach would be an LSD & rear anti roll bar.....that won't happen any time soon. It gets worse. ...

John Rogers · 06-24-2003, 11:07 AM

The LSD makes the roll even worse since there is much more bite. I have seen some videos of the previous owner of my car with it on TWO wheels at the stadium but so far I haven't done that!!!!

Bleyseng · Bleyseng's Garage

Shoot mine does that too, just gotta keep throwing money at it JP. You can be the test case to see if 200# work. If not I'll order some 220#'s.

Geoff

J P Stein · 06-24-2003, 12:45 PM

Whall, shoot.......

The other reason for the 200 lb jobbies is to get a better balance in the car without softening the front AR bar. At the moment, it's pushing in the tight stuff.

There are a couple of ways to get around this (driving techniques) but they involve getting out of the throttle, bliping the clutch, hitting the brakes or a combination of all the above ....then back on the gas to make the car rotate....my feets ain't that quick....tho my attempts at left foot braking have have gotten 2 out of 3..

I really don't mind waving at the crowd IF the car rotates.

Sorry about your thread, Milt.