Critique Specs for the Alignment Shop

[goldgunner]

Within a few weeks I expect to have the chassis up rebuild complete and assuming that the also totally rebuilt engine runs, the first thing will be to trailor the car over to the top end Porsche shop for a complete alignment, including corner balancing.

Wading thru dozens of alignment threads, here's what I've come up with for a Spirited Street driving set up.

I'd like critique, advice, confirmation - whatever.
And, have I left any specs out that I should detail and require?

Thanks~!
Jim

[ZOA NOM]

Looks good. The caster is +/- .5 degrees, not 5, correct? Everything else looks spot on. What I'd like to do one day is to find a happy medium that I can adjust between quickly with only a couple of settings, like height and camber. It seems like you could have a street setup that could be changed pretty quickly for the track if you had everything marked so you could put it back again.

[goldgunner]

Yes, thanks for pointing out that error: I'll change to .5

anyone else?

[Wil Ferch]

Instead of sums of diagonals method for corner balance, aim for getting front two tires as equal as you can, and let the back two tires be what they end up being ....

I was fairly convinced of a "pure" corner balance target...until I engaged in a lengthy dialogue with Randy Blaylock and others like RacePro. Equal fronts "defines" a degree of weight jacking but is a desirable compromise...as it promotes equal threshhold braking and that is more important than having right turn characteristics * absolutely match * left turn characteristics....see link embedded within--> Corner balance after weight reduction

Also, with fat rear rims and tires that approach Turbo specs.... it is more desirable to not go too crazy on neg camber...to get reasonable tire life by planting the rears a bit more "square" to the ground. Of course, you can keep what you have but be prepared for a bit more rear tire wear.

Common convention says that equal camber front vs rear promotes a more neutral high speed cornering characteristic, while dialing in about 30 minutes *more* neg camber ( rear relative to front) promotes some stabilizing understeer in fast sweepers. Your call.

Front caster max is OK as shown, but it is more desriable to get both sides equal as opposed to "max" as a target.

- Wil

[goldgunner]

Thanks Will –

Corner Balancing: I read several times all of those learned discussions on corner balancing, and almost came close to understanding them – I think. Other than Blaylock’s diagonal specification (“within 2%”), I don’t recall seeing an objective criteria for the Front Right – Front Left balancing. ‘Absolute match’ isn’t going to happen, so what is reasonable and achievable? I’m going to the best shop in my area for this, and might as well give them a target. Is FR-FL balanced within 2% not tight enough? How about .5%? I think it’s worth giving the ace aligners both the diagonal and front criteria and seeing if they can do it. Why not?

Camber: I understand what you’re describing about negative camber. My reading indicated that my range of camber was not excessive, but would produce more tire wear than zero camber. My ongoing budget allows for a ‘bit more rear tire wear’. Of course, a ‘bit more’ is quite subjective…
Further, from my novice’s perspective, considering the ‘neutral high speed cornering characteristic’ of front to rear equal camber versus 30 minutes more negative camber rear to front towards providing ‘some stabilizing understeer in fast sweepers’, has me choosing the latter. However, would you suggest that rather than the range I show (-1.5 to -1.8), that a specific ‘target’ is preferable and achievable? And, if it is, then do I understand correctly that you think -1.5 would be ‘best’?

Front Caster: Similarly, is a fully capable alignment shop working on a capable suspension, able to execute and achieve a smaller tolerance than the specification standard of +/- .5 degrees? If yes – what? And, to achieve – as you say – the ‘more desirable’ equality of both sides – should that be specified objectively with a percentage tolerance? If yes – what tolerance would be appropriate and achievable? Something like: “Both sides must indicate equal caster within +/- 1%? Or what %?

Thanks for helping my understanding not only of alignment specifications and their driving impact, but of the practical application of objective and achievable criteria.

Regards,
Jim

[Wil Ferch]

There is a range of "acceptable" values...we should all understand we're dealing with small numbers on rubber-bushed cars, so that we shouldn't get excessively anal about this.

point#1 -- what I'm saying is that instead of "targeting" proper corner balance...where each corner ends up getting its proper "assigned" weight ( based on the various locations of heavy masses)....try instead to get the front two wheels as equal as you can. This would be "less optimal" than perfect CB target..it actually induces a small amount of weight jacking...but equal fronts as a target is a "better" compromise for most of us in that thresshold braking is more important than At-the-limit cornering equality. Try to get fronts within 20 lbs of one another. If you're 40 lbs off instead I wouldn't sweat it either if it means a lot of extra work.

point#2-- if you focus on -1.0 degree front camber....would suggest up to neg 1.5 degree for rear....especially for novice...to gain some high speed sweeper stability. You don't want neutral on high speed sweepers because you're so close to having it become oversteering tendency there..unless you're REALLY good or experienced.

point #3 - - try for max ( around 6 degrees ) caster...but dont' get 6 on one side and 5 on the other. If 5 is all you can get....go for 5 on both sides. Ask "as close as equal" as possible...don't say within 0.5 or within 0.1....

- Wil