Are my torsion bars too big?

[luckydynes]

Hi all,

I have a '73 911S track car that I want to make more enjoyable for the street and autoX. The thing is really fast on big smooth tracks but it is just a handful on the street with uneven pavement. I've had this car for almost 4 years and have really not had to touch it ... now it's time.

It looks like the PO put a new rear torsion bar in right before I bought it ... she's got 33mm in the rear and 22mm in front. She's also got re-valved Bilstein "greens".

She rides pretty hard but that really is not my major complaint ... what I absolutely hate is the "darting" all over on uneven pavement. I've played with the alignment a bit. She's still got a bunch of negative camber but I didn't think this would cause such extreme darting???

I don't mind going to softer bars for street/autoX ... but I do not want to loose any autoX lap time ... in fact I'm hoping I'll pick up a second or two going to a more compliant suspension setup.

Thanks for any advice,

Sean

[luckydynes]

Browsing some other threads looks like the massive amounts of negative camber combined with the fact that this car has not had the bump steer set could be contributing?

Should I set the bump or do I just have too much bar?

Thanks,

Sean

[KTL]

What's your toe at the front? Zero toe or a little toe-out can make the car darty.

The bars themselves shouldn't be a cause of the instability. They must make a light car like a '73 ride quite stiff. The low weight reduces amount of travel by suspension because there's less weight in the car to twist the springs. Since there's less suspension travel/compression, you're less likely to see bump steering. But in the event you do see significant suspension travel at the front, you will experience bump steer if the angle of your tie rods is severe enough. Remember, bump steer is caused by the change in angle of the tie rods as the suspension travels. The change in angle that occurs as the suspension compressed effectively causes the tie rod to shorten, which causes a momentary toe out condition.

[Zeke]

Tires? On Victoracers my '71 was all over the place on grooved roads. I mean a handful, just like you say. My Dunlops were very tame. No changes to the car.

BTW, 33 on a light, early car sounds like nothing BUT high speed, smooth tracks. NOt much versatility there.

[luckydynes]

Originally Posted by KTL

What's your toe at the front? Zero toe or a little toe-out can make the car darty.

The bars themselves shouldn't be a cause of the instability. They must make a light car like a '73 ride quite stiff. The low weight reduces amount of travel by suspension because there's less weight in the car to twist the springs. Since there's less suspension travel/compression, you're less likely to see bump steering. But in the event you do see significant suspension travel at the front, you will experience bump steer if the angle of your tie rods is severe enough. Remember, bump steer is caused by the change in angle of the tie rods as the suspension travels. The change in angle that occurs as the suspension compressed effectively causes the tie rod to shorten, which causes a momentary toe out condition.

thanks for the input ... I tried a little more toe in trying to make 'er more stable but no help.

[luckydynes]

Originally Posted by milt

Tires? On Victoracers my '71 was all over the place on grooved roads. I mean a handful, just like you say. My Dunlops were very tame. No changes to the car.

BTW, 33 on a light, early car sounds like nothing BUT high speed, smooth tracks. NOt much versatility there.

Hoosier A6's .

I have scales .. this car weighs 2200 lbs.

2.5 degrees negative front camber also.

Should I try:

1. less negative camber
2. dial in bump steer? .. car is as low as it can be so maybe the geometry is all whacked out there?
3. softer torsion bars

Guys keep in mind I don't want to slow the car down when it comes to autoX which is why I don't like number 1 as a solution. I've heard guys talk about their cars not hooking up in the parking lots with too much spring and it sure seems like that's where I'm at.

Thanks,

Sean

[Steve@Rennsport]

Sean,

You have some decisions to make,...

The "dartiness" is due to your camber settings. All things being equal, those numbers are optimized for grip & DOT race tires, but will make ANY 911 wander around. Toe settings and bump steer can add to the "misery",..

Hoosiers need camber (2 deg min) so if you reduce static camber settings to improve its manners, you will sacrifice some grip. Its all about compromises.

You didn't mention anything about your toe settings or caster so one needs a lot more information to offer anything constructive.

Do you have a bump-steer kit of some kind? Has the car been bump-steered to see what it is?

JHMO, but 22/33mm T-bars on an early narrow-bodied car is an aggressive setup for street driving and this is an area where more compromises must be considered given that you are using Hoosiers. Street tires & race tires require totally different alignment settings as well as spring rates so you need to "pick your poison" and decide which qualities of the car are most important to you.

[Jack Olsen]

Are you running Hoosiers on the street?

[brads911sc]

I bought the street perf 2 package from Elephant and that comes with 23/31's. Alittle stiffer than I expected from a street package.. but its all good...

[Plavan]

I do not know anyone who races with Vara with 33mm on the rear. I currently have 30mm but am looking to go 31mm. 33mm rears sounds pretty darn stiff.

[JP911]

Originally Posted by luckydynes

car is as low as it can be so maybe the geometry is all whacked out there?

If it's REALLY low you may be riding on the bump stops (no shock travel), which would produce some whacky handling as well.

[berettafan]

yowsa that's some big bars!

should be driving my '70 w/ newly installed 22/28's in a week or two so i'll comment then. the stock bars were very comfortable and i will not have an issue switching back if i don't like the 22/28 combo.

[Tim L]

Get some street tires on 16" rims it will make huge difference.

[sjf911]

I had 28/21's on an un-lightened SC with Bilstein HD's and that was unacceptable on our roads.

[luckydynes]

Originally Posted by Steve@Rennsport

Sean,

You have some decisions to make,...

The "dartiness" is due to your camber settings. All things being equal, those numbers are optimized for grip & DOT race tires, but will make ANY 911 wander around. Toe settings and bump steer can add to the "misery",..

Hoosiers need camber (2 deg min) so if you reduce static camber settings to improve its manners, you will sacrifice some grip. Its all about compromises.

You didn't mention anything about your toe settings or caster so one needs a lot more information to offer anything constructive.

Do you have a bump-steer kit of some kind? Has the car been bump-steered to see what it is?

JHMO, but 22/33mm T-bars on an early narrow-bodied car is an aggressive setup for street driving and this is an area where more compromises must be considered given that you are using Hoosiers. Street tires & race tires require totally different alignment settings as well as spring rates so you need to "pick your poison" and decide which qualities of the car are most important to you.

I toe'd in the front and rear just a tad which helped. No bump steer kit so who knows what's going on there .. especially since she's so low.

Not sure what the caster is but from memory seems like the adjusters are slid all the way back for max caster.

She's got the later trailing arms and "wide body" flares also.

Another poster mentioned it ... what about just going to good street tires when I'm playing on the street? I'd really hate to loose any grip for autoX but I do think this setup is way too hard for even the most hard core autoX'r so I was hoping that going to softer torsion bars would help for autoX and make the car more streetable.

Thanks for mentioning the bump stop thing ... that could be contributing to the problem.

Thanks everyone for the input.

So now I'm debating between street tires and softer rear torsion bar. I would have brought some good street tires already but couldn't find anything in the size that the Hoosier's are so needed rims too . I'll report back the size ... maybe I was missing something.

Thanks again everyone,

Sean

[luckydynes]

A thought about the bump stop ... it's not just bumps but uneven pavement which make the car go all over ... even when the suspension hardly has to move. That's what led me to unhooking the sway bar which didn't seem to help. When I bought the car I remember seeing how the front wheel would come off the ground on just the slightest uneven surface even standing still which made me think the swaybar was too stiff.

[luckydynes]

And I put new bushings inside the Bilstein's ... but they're not as tight as I'd like them to be ... was expecting .002" clearance but brand new there's still .005"-.007".

[Jack Olsen]

Hoosiers on the street is a crazy waste of your money, in my opinion. They age by heat cycle more than wear, and every time you get them warm you tick off another cycle. At the same time, you're not going to be able to keep them consistently hot enough in street driving for them to stick all that well. On top of that, they slap loudly on the pavement, which is going to make the ride seem rougher just because of the weird feedback.

In your shoes, I'd definitely get a set of rims with more-quiet and more-compliant street tires.

The stiffest torsion bars are still pretty mild, as far as contemporary spring rates go. Tires weren't as good when the 911 was engineered, and there's only so much room in there for torsion bars to fit.

[luckydynes]

Originally Posted by Jack Olsen

Hoosiers on the street is a crazy waste of your money, in my opinion. They age by heat cycle more than wear, and every time you get them warm you tick off another cycle. At the same time, you're not going to be able to keep them consistently hot enough in street driving for them to stick all that well. On top of that, they slap loudly on the pavement, which is going to make the ride seem rougher just because of the weird feedback.

In your shoes, I'd definitely get a set of rims with more-quiet and more-compliant street tires.

The stiffest torsion bars are still pretty mild, as far as contemporary spring rates go. Tires weren't as good when the 911 was engineered, and there's only so much room in there for torsion bars to fit.

Okay thanks for the advice. I've been putting such few street miles on this car that the cost didn't seem that significant vs. shelling out for a new set of rims "just to put more street miles on the car" ... guess I've grown older LOL . I have 2 sets of lightweight 16" rims for the race tires so I was only running the older set on the street ... probably contributing to the problem also.

Is there a quick answer to "optimum wheel size for tire choices" or is there volumes on the subject?

Do you know what kind of wheel spring rate the 33 mm rear torsion bar equates too and likewise for the 22 mm in front?

Thanks,

Sean

[Jack Olsen]

22mm front = 210#
33mm rear = 427#