73T: front end suspension geo issue

[911hillclimber]

Noticed a bit of unusual NS Front tyre wear on my old Goodyears, LHS is OK.

Car steers straight etc.

Put some fishing lines down the side of the levelled car this morning (garage floor has quite a slope) and the front toe is 0.5mm toe in each side and the camber is 2 deg negative both sides. Camber measured with a good Dunlop camber gauge referenced to the wheel rim, not the tyre.

I don't remember setting the camber to 2 deg, more like 1 deg but those are the results.

No time to do the caster today, but doubt caster angle would do this (I think I set to 6 degrees).

I'm thinking of having the car checked/aligned at the front for camber/tracking by a good local tyre place (laser equipment), but not sure what settings to tell the technician who I doubt has touched an early 911 before.

Any thoughts please.
Car is a simple road car.

[PeterK]

My notes suggest

Camber (nut torque 47Nm on 3 allen bolts
- Spec - 0 degrees negative ±10” (max. diff L to R - 10”)
- increasing by 1 - 1.5’ is a good street / track compromise
- Target max camber
 
Caster
- spec 6’ 5” ±15” (max. diff L to R - 30”)
- target max caster
 
Toe in - +15” ±5”

[911hillclimber]

Thanks Peter,
I'm sure Bob Watson called for 2 deg neg camber way back when I was hillclimbing it, but it seems excessive (today).

I can only measure the toe by mm not angles, but I think 0.5mm is a good deal more than 15 mins. over the 15" dia wheel.

Best take it to a specialist, but not a Quik Fit Fitter type!

Have sent a pm to you about another subject.
Graham.

[Gary71]

What’s ’unusual’ tyre wear?

[Lightweight_911]

.

On my last 911 (uprated '73 2.4 E/S) I ran the following settings:

front toe = 1/16in
caster = 6.5 deg
front camber = 1.5 deg negative

rear toe = 1/8in
rear camber = 2 deg negative

.

[911hillclimber]

I'll take a pic of the two front tyres tomorrow pm so you can see it.
It is the fact they are different that irritates me, and soon I'll be fitting new Conti tyres following Gary's and others advice, so I want the car to be reasonably straight before the new tyres obviously.

Andy's front toe is more than mine (0.5mm v 1/16").

Bruce Anderson's tuning book says Zero to -10 mins for the front camber too as Peter says, quite a difference to 1.5 to 2 deg negative.

Always thought radials needed a good dose of negative?

Rear tyres are bang on, in fact, just like the OSF tyre. Just that NSF tyre that is a bother, but the angles are the same both sides.

[Nine One One]

Weak shock absorber on that side????

[Gary71]

Weak shock absorber on that side????

That’s where my mind was going.
Or just turning right a lot

[911hillclimber]

The front dampers are custom Bilstein's commissioned by Bob Watson in about 1994 when the 3.5" struts were fitted for the A callipers, and about 60K miles old.

There are no patter-patter feelings, corners well and all that.

The wheels have given me grief for several years with balance issues and the fronts were the rears and back and forth until the wobbles disappeared about 3 years ago. I am very sure to put the wheels back on the right corner and the right hub position using the valve as the marker to 2 of the hub studs.

No wobbles at all now. Tyres are old, about 10 years but pass the MoT and no rubber cracking etc, but a few are looking a bit tired, hence one of my other recent threads about tyre choice for replacements next spring.

In recent years I have spent very little on the 911, but I think things are changing! The forthcoming event at Shelsley Walsh has focused my attention...

The wear on the NSF is on the inside blocks ( about 40mm x 40mm) and the wear is as smooth as the surface of the rest of the tyre, no feather edges etc, more the look of excessive neg camber, hence doing a quick geo measure yesterday on the front.

I'm back to 28 /32 pressures as used for decades.

Thank you for those details Andy.

[PMNorris]

I took mine to Centre Gravity. I was there from 8:00-19:00. They completely transformed my car. Far more than wheel alignment.

[911hillclimber]

I am absolutely sure you are right, the best you can get I think.
However, I am resistive to specialists unless it for a gearbox of the 915 variety.

Suspension has to be DIY for me as it is interesting and quite simple though tricky to get the accuracy but ok for a 'good-enough' result.
This 911 just bumbles around, rarely over any speed limit and certainly no over steer moments round roundabouts etc.

Back from coffee and rock cakes so will post the pics of the tyres soon.

My LOLA has been set-up using fishing line and a Dunlop camber gauge but the man knows very well what he is doing!

Pics do not make it look like there is a problem/difference, but there is!

Awkward to photograph on the car, but:

NSF (prob tyre)



and NSF (the rears are much the same)

[Dougal Cawley]

It does of course raise the suggestion that some proper period tyres would better suit the car with the correct size and carcass structure.

I 'm assuming you guys are all aware that Pirelli are making the original equipment tyres in all the right sizes, tread designs, but most importantly the correct carcass strctures.

so if you have the early stuff. (pre 1968) then this is what Porsche fitted.

https://www.longstonetyres.co.uk/165-r1 ... -ca67.html

165HR15 Cinturato CA67 FULL 700x700.jpg

then in 1968 pirelli developed the CN36, some cars like the 912 stuck with the 165 section tyres, because cars are nicer to drive on a thinner tyre. But on the mopre race cars like the 911 they used the new low profile tyre technology to fit 185/70VR15 Cinturato CN36 and then in the early 1970s Pirelli went a little further and invented 60% profile tyres and the back of the RS ended up with a 215/60R15 Cinturato CN36 on the back.

https://www.longstonetyres.co.uk/pirell ... -cn36.html

as time moved on Porsche developed more of their models to be suited to these new wide tyres.

Pirelli Cinturato 18570R15 FULL 600x600.jpg

But don't just assume a wider tyre makes your car better, often the opposite is true.

Your car wouldn't have had a tyre wider than 185 section and at that it was an early 185/70 tyre. so very different to what you are fitting.

[Dougal Cawley]

what size tyre is it and what width rim?

[911hillclimber]

7” rim width and 65 ratio.
With 185 section The tyres are clear, just, of the 4 wings.

[Dougal Cawley]

7” rim width and 65 ratio.
With 185 section The tyres are clear, just, of the 4 wings.

Oo right there you go then, wrong size rim, that isn't helping.

these are the best tyres for your car.

https://www.longstonetyres.co.uk/185-70 ... 36-n5.html

Really you want a 70% profile tyre, not 65% it is the wrong shape and structure for your car. it will never handle or ride very nicely like that. but your weird wear is down to stretching a 185 tyre onto a 7" rim.