365BB Alignment setup

Well not that the BB is back on the road, I'd like to get the alignment set.

In the past, I've set the car to the following settings with the OE 15" wheels and tires:

Front:
2mm total toe-in
10min +camber
4.5 degrees castor

Rear:
3mm total toe-in
1.5 degrees neg. camber

Now, I have new BBS 17" wheels with 225/45/17" on 8" rims and 265/40/17" on 10" rims...(Offset the same as stock)

Prior to the wheel/tire switch the car always felt a bit numb to me when the steering was on-center....and the tail felt a bit twitchy, particulary on a long 70-80 mph sweeper.

I'm using a starting point of 34psi front and 38psi rear...

I'm a bit confused as to the postive camber specified in the front per the WSM...

Input/thoughts appreciated.


Regards,
David

Haven't been ignoring this David. Just trying to think of the best way to proceed that gets you in the ball park of experimental settings.

I can see the why of the stock setup, build in understeer to keep the tail behind the front end and prevent swapping ends by less than stellar drivers.

The tail was twitchy becuse of the front understeer built in...I never have been a fan of nuetral or positive camber front or rear, to vague for my taste and style .

I'd start with 1/2 - 3/4 degree neg. front w/1/4 in. tow and leave the back at 1.5 degrees neg. with 1/4 in. tow per side not overall...

I'm thinking that if you don't align to the vehicle centerline the handling will be very squirely in striagt lines at high speeds and on turn ins, since you're not lowering or adding to sway bar diameter even though grip is increased about 4-5 fold.. You might eventually end up finding it necc. to go with bigger sway bars at some point, but getting the car dead nuts in a striaght line at high speeds should be first imo.

Feel free to question & critasize my ramblings.

JR,
No critcism from me...open dialog works just fine.
There's alot of factors to consider when dialing these cars in, and I never was particulary fond of the positive camber specifed. I'm well versed in the dynamics of doing a proper alignment, having had, at the time, a state of the art alignment machine in my shop...

Agree completely with the negative setting in the front. I was thinking initially -.75 deg.

As for the toe settings...
You're saying .25"(6mm) total front toe?
That's about twice what's suggested....
Seems a bit excessive, but not unrealistic...OK

As for the rear:
Agree 1.5 deg camber (minimum of OE spec...)-OK
But the toe-in...Are you nuts???
.5" (13mm) total toe-in?
With that kind of toe-in, the back tires will be bald before I get out of my driveway? I don't really care about tire life...but I've never heard of such an extreme setting.

Am I misunderstanding your figures, for the rear?


Regards,
David

What the hell was I thinking {}...now you're going to force me to check thru about 6 books to see what I'm remembering wrong {}

I'm think going to check the alignment on my lawn tractor today...LOL. Thanks JRV.

David

Any luck coming up with the specs. you'd use?

Thanks,
David

David, sorry to report that I've been running like a chicken with it's head cut off and haven't had time to follow up yet.

{}

Ok...I went to the Bible of Aligning = "How to make Your Car Handle" by Fred Puhn

The reason I'm referencing this guide rather than other sources is because there is no Factory numbers to address your tire & wheel size changes.

BBi specs would be in the ball park but truly I don't think the TRX's are very close in size and especially grip to be valid for your setup.

according to Puhns recs front static toe should be just enough to bring underspeed toe to zero, based on the amount of deflection the suspension will suffer under load. The caveat is that, toe should remain slightly towards 'in' as default to prevent high speed wandering induced by toe out.

By using those basic rules of thumb with wider stickier tires in front Toe In of the 1/4" sounds like a close place to start imo. Of course if you feel it's unlikely the front can deflect that much at 100mph then of course the number would be reduced, keeping in mind that at no speed should there be deflection induced toe out.

Rear: Puhn's reccs = toe out on cars with independent suspension on rear causes instability & oversteer. Also, driving forces on RWD cars tend to force toe in and thus many have rear toe settings to zero. With high powered cars having the most need for a toe in setting.

Based on those rules of thumb, a rear toe setting of a somewhere around 1/32 per side looks in the ballpark possibly slightly more with the size of your rear tires..

Camber: In Puhn's words - Start with the Manu. settings, if not availible start with settings of Zero for Road use and 1/2-degree negative for a racing car.

Using that as a basis for creating new specs for your setup it would appear that a starting point of .25 degrees front and .5 degrees rear is the rough baseline. Seems contrary to my thinking, but I'm not well enough versed to question Puhn..{}

Sorry it's not more in line with what you may have wanted, but with your tire sizes being such a departure from stock, I really don't think definative numbers exist.

Regards, JRV

Follow-up:

As the driving season here in the Northeast comes to an end for a while...It's time for a bit more suspension work on the BB. After much experimentation, it seems that 35 psi for the front and rear tire pressures feels about right, in terms of overall feel. Tire wear looks good, though a bit less negative camber in the rear may be in order. (Currently -1.8 deg)

Although the car exhibits good grip and excellent straight line stability, the car still exhibits an odd feeling in a sweeping, moderate speed corner. The other observation is that while hitting an expansion joint on the highway, the front end "slams" over the bump, whilst the rear just "wallows" over it. So, my next plan of action is to remove the shocks and have them checked. They were replaced with new Koni units in 1988, although there are very few miles on them.

So friends...Do I,

Have them rebuilt?
Replace them with new Koni units?
Or, install Ohlins or Penskes, instead?

No track use, just a "daily" driver....Thoughts?

Regards,
David

David - I replaced 6 shocks on my Boxer, and the car handles significantly better. (Must admit, the rubber was changed at the same time). There is a gentlemen in Arizona, Jeff LeBlond, that rebuilds Konis, but as the Boxer shocks are available new, I went that route. I was able to negotiate the price to the same as the rebuild (approximately $130 per shock).

The bushings were changed as well. These can be acquired from multiple sources, including U.K.

Jeff LeBlond was invaluable when rebuilding the load levelers on my C4 - these were simply not available new.

Jim S.