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Re: Hard to believe that a 7.4 vs. 7.2 diff in caster is that significant...

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Alignment question
dallas01s - Tuesday, 21 February, 2012, at 11:46:19 am
Just had an alignment after my drive axle replacement and now have a slight pull to the right. Tech set all toe F/R to middle of range (.05 front, .09 rear) but camber was set to minus 1.8 deg rear L/R and minus 0.4 deg front L/R. (seems to be right at edge of range) Tech claims that the pull is due to the (unadjustable) caster which is currently 7.4 deg L and 7.2 deg R. Michelin Pilot Super Sports are virtually new with ~1K miles.

The pre-alignment setup had +0.4 deg LF camber and -0.4 RF camber. (not a typo) I'm guessing that this somehow compensated for the unadjustable caster offset to eliminate the pull. (car used to be dead straight, and tire wear was fine) Tech suggests keeping the alignment "square" (as is after the new alignment) for better handling. They will be glad to reset to the previous camber if I desire....we agreed to drive it a few days and see. For me the slight pull is too annoying....not just due to the road crown. I was fine with the factory alignment setup.

Has anyone else had similar issue, and if so what did you do? Is it conceivable to eliminate the pull just by tweaking the front camber?

FYI, shop was Autoscope Park Cities in Dallas, a well outfitted 3-yr old facility that has served me well in the past.

Thanks...
Quote
dallas01s
Just had an alignment after my drive axle replacement and now have a slight pull to the right. Tech set all toe F/R to middle of range (.05 front, .09 rear) but camber was set to minus 1.8 deg rear L/R and minus 0.4 deg front L/R. (seems to be right at edge of range) Tech claims that the pull is due to the (unadjustable) caster which is currently 7.4 deg L and 7.2 deg R. Michelin Pilot Super Sports are virtually new with ~1K miles.

The pre-alignment setup had +0.4 deg LF camber and -0.4 RF camber. (not a typo) I'm guessing that this somehow compensated for the unadjustable caster offset to eliminate the pull. (car used to be dead straight, and tire wear was fine) Tech suggests keeping the alignment "square" (as is after the new alignment) for better handling. They will be glad to reset to the previous camber if I desire....we agreed to drive it a few days and see. For me the slight pull is too annoying....not just due to the road crown. I was fine with the factory alignment setup.

Has anyone else had similar issue, and if so what did you do? Is it conceivable to eliminate the pull just by tweaking the front camber?

FYI, shop was Autoscope Park Cities in Dallas, a well outfitted 3-yr old facility that has served me well in the past.

Thanks...

but I've never had any reason to look into this. (My Turbo's has zero caster difference and the tech at Rector said the car was one of the squarest cars he's come across. I do not recall how much caster difference (if any) my Boxster has. But neither car when aligned properly has any tendency to pull. I couldn't stand it and would have it addressed quickly.)

Once my Turbo came away with while not a bad alignment (it had one of those too but the car felt 'fine' just the rear tires wore out in a hurry) an alignment that left the car feeling out of sorts. After a short drive I took it back and the tech told me he gave the car a bit of an aggressive alignment to make the car's handling sharper. Sharp I don't recall but I was unhappy with the car's feel and the tech (with the ok of the service manager) put the alignment back to a more neutral setting and the car felt fine and tire life was up to its usual 20K or more miles.

Camber can be used to some extent to compensate for a car that has enough caster difference to result in pull. It could be the camber difference from the earlier alignment did just that. This time the alignment's by the numbers so to speak and the result in the car feels like it does because of this.

You'll have to speak to your alignment tech and get his input. If he can throw a bit more camber at the car and compensate for that caster pull... that's the way to go.

But before you do that ask him what amount of caster difference starts to cause the car to pull.

Oh, assume the tires are all properly mounted with the tires mounted to turn in the right direction and are inflated properly and the tires are all the same in terms of not only size, but in hardness, tread wear and so on?

Oh, and when you had the car aligned it had a full tank of gas? And the spare/toolkit/etc were all present and properly secured?

I have had cars aligned with and without ballast on the driver's seat and I never could tell the difference. In each case the car felt just fine and tire life and such was acceptable.

Lastly, I have Michelin tires -- I do not recall the style (they're N-rated though) -- and they are directional but have asymmetrical tread pattern. Even though each outside sidewall has an "Outside" on it showing the tires because they have an asymmetrical tread pattern the tires look like they are mounted incorrectly that is mounted so the tires are turning in the wrong direction. Just thinking out loud: I wonder if this might exacerbate the caster difference and result in more pull when there wouldn't be any otherwise?

Sincerely,

MarcW.
That's what I thought as well. After some more research, what I'm seeing now and the previous setup makes sense - a difference in caster will generate a pull in the direction of the smaller positive caster (in my case the right), and a difference in camber will, all else being equal, pull in the direction of the more positive camber. (my left on original setup) So it does appear that there was some compensation in the camber to offset the non-adjustable caster imbalance. (which was removed in the recent alignment.)

I'm with you - the slight pull will drive me nuts and the compensation described above never made a difference to me in the handling as a street car. So I'm going to have the shop dial back in the camber compensation and hopefully that will take care of the pull...
By the way....
dallas01s - Tuesday, 21 February, 2012, at 1:45:33 pm
the shop claims that he's never seen a boxster have a pull with the alignment setup that he dialed in, so if true, my vehicle is an outlier. Also FYI, my 7.4 and 7.2deg caster readings are both slightly beyond the factory 8deg +/- .5deg. (I had a dealer shoot me the factory settings list...)
Quote
dallas01s
the shop claims that he's never seen a boxster have a pull with the alignment setup that he dialed in, so if true, my vehicle is an outlier. Also FYI, my 7.4 and 7.2deg caster readings are both slightly beyond the factory 8deg +/- .5deg. (I had a dealer shoot me the factory settings list...)

If the alignment numbers are correct -- I like to see a before and after printout of the numbers -- and if the pull is real (not just some transient road surface anomaly) -- then your car is pulling and the shop should be more supportive than to claim to have never seen that before.

Even if true, so what? They're seeing it now.

Sincerely,

MarcW.
Like MW said, no better than, "They all do that." *NM*
Laz - Tuesday, 21 February, 2012, at 4:25:55 pm

Edited 1 time(s). Last edit at 02/21/2012 04:46PM by Laz. (view changes)
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