Negative camber with adjustable arms

[gattia86]

For a '74 GTV street/trackday car, with 185/70-14 tires...

I'm installing adjustable upper arms in the front, and am wondering what kind of negative camber settings people are running on trackday cars.

I realize there are a bunch of variables, but I'm just looking for a ballpark starting point.

The car is lowered about 2.5" in the front, with the stock A-arm geometry, so there is not much camber gain in bump. So, I imagine I'd want to start with a significant amount of static negative camber to get optimal grip while cornering.

And what about steering tie-rod length?

Just for fun, I shortened the arms all the way, and got over 5 degrees negative camber. I then measured bump steer, and the curve got all goofy, going toe-IN in bump and droop, probably because the steering tie rods need to be shortened a significant amount with this much camber. With stock camber, the car would toe OUT in bump (after it was lowered). Hmm...

Has anyone else had to change the steering tie-rod length significantly (from the standard specifications) to sort out bump steer on a 105/115 car with significant negative camber?

What kind of bump steer curves are people getting on their track cars?

Thanks,

George

[gtv27]

between 2 and 3 degrees, depending on what sort of tyre, spring, antiroll bars, track type, driver preference, time of day, phase of the moon, etc...

did have to reset toe and caster after camber change, but didn't do anything about bump steer...

putting a knuckle riser between the upright and the ball joint will give you some more camber gain and reduce the initial static setting necessary, but is supposed to do bad things to bump steer - I have it on my racer and haven't done anything about the steering arms and it seems to be OK - could be different away from the track on a bumpy road (eg for tarmac rally - but then you shouldn't really need the big camber anyhow)

[genericwood]

Just my opinion, but I wouldn't put in more than -1 degrees of camber. Sure, more might give you better grip. But with 185/70's I'm guessing that isn't your primary concern. It will look better, stop better and wear better on the street without going overboard on the camber. Also, putting knuckle risers on the top ball joint will just screw up the top to equal the screwed up bottom arm! The right way to do it would be to get your ride height reduction without changing the lower a-arm inclination. Drop spindles or the Alfaholics lower ball joint kit are the way to go.

As for bump steer, I don't think changing tie rod lengths will get you very far. If you want to dial it out, you will need an adjustable pivot at the hub. The cheap and easy way is to buy 2 14mm rod ends, one LH and one RH thread. Then drill out the steering arms to remove the taper. That's all there is to it other than figuring out what you need for spacers.

Erik

[gattia86]

Erik,

Thanks for the input. I finally got some adjustable upper arms, so I'm looking for a starting point. I've got some shorter, lower steering arms to try, which should correct the bump steer issues for my given ride height, while keeping the stock tie-rod ends.

But my car's all apart again.
After my last post, I took a closer look at the front end, and discovered the lower A-arm bushes were disintegrated, causing the left-side camber and toe to go all funny. I also discovered that the front subframe welds were all cracked and separating from the chassis rails. And the chassis rail is cracked around the steering box mount! Arrrgh!

All this probably explains the funny handling I was having and the fact that my camber settings were all out of range.

I've spent the past weekend welding everything back together and ordering new bushings and balljoints. I've also added adjustable 2 1/2" spring perches front and rear, so I can fiddle with ride heights and spring rates. Hopefully I'll be able to put it back together soon and try some new settings. My goal is to have a worthy occasional track-day car.

More input welcome,

George

'74 GTV

[Zunige]

I used to run negative camber on one of my street Spiders... It was a lot of fun... Eventually, however, I decided that it was better to invest in the carbon unit behind the steering wheel, rather than in the tires. That investment produced better handling in all my cars. Below is a picture of my street Pirellis, with 3 degrees negative camber. Both tires where installed new (part of a set of 4, of course), had the same mileage, and came off the same Spider, when the picture was taken. The tires from the other side looked exactly the same as these.



Best regards,

[velocedoc]

I used to auto cross our '69 spider with 1 deg. negative. The tire wear was like what is pictured. The car was a daily driver as well as the weekend warrior. The wear was so hard on tires, I had the camber adjusted to 1/2 deg neg. and the car was still stuck to the corners like it was on rails. Try a 1/2 deg neg and see how you like it before going for more camber.

[gtv27]

If you run hard on the track, with less than 2 deg negative, you'll get tyres just like that, except they will be bald on the outside, not the inside...life is a compromise and optimising for road or track is one of those areas where you have to choose what is more important to you.

However, picking up on what Erik said, if you plan to use 185/70 tyres, there's prob not a lot of point in getting carried away with camber (or anything else particularly racy) as I doubt that you can buy any sort of rubber other than very basic shopping car variety in that size these days...

[gattia86]

About the tire size choice, 185/70-14...

From reading other posts and from the way the car feels on the street, I'm hoping the relatively narrow (and gripless) tires will provide a bit of give and prevent the need for really heavy spring rates and race-spec dampers, as might be the case with wider, stickier tires.

Plus, I've heard horror stories of steering boxes cracking under high cornering loads. My frame's already cracked around the steering box, leading me to believe these cars can't really handle high tire/suspension loads without some serious re-working.

I've kind of been talked into sticking with the narrow 14" tires by others.

But... I'll try a set of wider, stickier tiers at some point to see how it feels.

George

[gtv27]

I believe the car is more enjoyable to drive on a narrower and taller tyre than those commonly used for racing eg 185/70 or 195/65 compared to 195/60. I'd love to try a set of 165/75 15 (is that the right OEM size?) for a few laps on my GTV, just for the big long slides that I'm sure it would do They probably be toast after a short time thou.

Also, you are correct in that using narrower and harder rubber will allow you to run softer spring rates.

So if the times don't matter, go for the narrow rubber and a supple set up and have fun four wheel drifting! In this case, around 1 deg negative camber, 3 castor and 0 toe should get the job done nicely.

Re breaking steering boxes, my understanding is that it is largely a maintenance issue with excessive play developing and or blunt impact trauma. You should know from your own experience that it is when parking that the steering is the heaviest (and therefore subject to the most load) that it ever will be (check the flex then :O ). Even when racing on slicks, I've never had the steering load up as much as it does when parallel parking with standard road tyres.

[conedriver]

Hi George,

You're correct regarding the amount of variables for suspension settings; let me add one more: Caster. By increasing caster, the outside tire assumes more negative camber when turned. This allows you to run less negative camber, reduces inside tire wear, and provides a better tire footprint for braking. It's kinda a crapshoot, especially by changing more than one thing at a time, but definitely worth a try. Also, a cheap ($100) tire pyrometer can be very valuable as you experiment with settings.

Quote:

Originally Posted by gattia86 For a '74 GTV street/trackday car, with 185/70-14 tires...I realize there are a bunch of variables, but I'm just looking for a ballpark starting point....

[genericwood]

Quote:

Originally Posted by gattia86 Plus, I've heard horror stories of steering boxes cracking under high cornering loads. My frame's already cracked around the steering box, leading me to believe these cars can't really handle high tire/suspension loads without some serious re-working.

[Tifosi]

Regarding the sheet metal around the box, any reason not to put a backer plate in there like what's found on a spider chassis stiffener front mount?

Big steel sandwhich is gotta be more stronger than a steel box hanging on foil don't it?

[genericwood]

Sounds like a reasonable plan to me. Should spread the loads out.

Erik

[Andrew]

A fair number of race 105/115 Alfas have reinforcing plates around the steering box area. I just wonder if a purely local sheetmetal fix moves the cracking point somewhere else on that chassis rail? I have seen many many street cars with cracks in this area, and of course they all flex an alarming amount even when not cracked.

Andrew

[gattia86]

Andrew,

I think your suspicion might be right on this: the crack occurred just ahead of the triangle formed by the steering box bolts, not around the bolt holes, suggesting the whole triangulated area (not just a small part of it) is flexing relative to the chassis rail. In other words, the steering box itself is a pretty rigid backing plate already. A triangular "backing plate" in this same shape and area would flex in the same way as the steering box, relative to the chassis rail. New cracks would occur just outboard of the triangular backing plate.

I think for a brace to limit the flexing, it would have to extend all the way to the front crossmember, and have some tubular or 3-dimensional shape to limit flexing along the whole chassis rail.

Either that, or the steering box would have to be braced to something on the engine compartment side... again, mabye a tubular brace running down to the corssmember/motor mount area.

Hmmm...

George