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OT: Can someone explain "Jacking Compensation Method" for wheel alignment?

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  • OT: Can someone explain "Jacking Compensation Method" for wheel alignment?

    I've seen it mentioned in lots of info on wheel alignment, but nothing I can find explains the procedure.

    Some equipment uses "rolling compensation" instead of jacking compensation, and the idea I get is that it's a way to cancel out errors from the rims not being perfectly true to the rotation axis of the wheel. Some carmakers specify that jacking compensation be used to align their vehicles, so it sounds like it's better, but involves raising the vehicle and takes longer.
    Last edited by winchman; 06-16-2011, 04:47 AM.
    Any products mentioned in my posts have been endorsed by their manufacturer.

  • #2
    Is it something to do with torsion bar front suspension?
    I know with my 4wd and my old ute the torsion bars are used to get the wheel alignment. When I raised it up I had to use blocks on the top arms to get the suspension back over.

    Dave

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    • #3
      I was looking at alignment procedures for several vehicles, but none of them have torsion bar suspension, so I doubt it's something just for that type.

      The term was mentioned in the sales literature for some alignment equipment, so I get the impression it's common to all vehicles and has something to do with the equipment itself.
      Any products mentioned in my posts have been endorsed by their manufacturer.

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      • #4
        Don't know for certain but i could take a guess based on recent observations...

        About a month ago i had to get my car's alignment reset (swmbo decided to drive over a pot-hole instead of actually using the steering-wheel!!)

        Went to my local Audi garage and they bung it on the ramp and raise it up. Next the mechanic puts blocks under each corner and jack up even further; not lifting clear of the ramp but obviously taking a lot of the weight off the wheels. He then carried on and did the complete alignment.

        When finished i asked if i could have a quick chat with the mechanic and asked about why he lifted each corner. His comment was that for my car (Audi RS4) some parts of the alignment was easier and more accurate if the car was given a specific amount of lift at each corner.

        I don't pretend to know/understand how suspension works/is designed but it sounded odd to me. However i can't argue with the results - car drives perfectly again...

        Batt

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        • #5
          I will take a stab at this, although I have never heard the terms I can imagine what they might be.


          Rolling compensation, car wheels do not roll straight down the road, think of the front tires on RWD vehicle. If the wheels rolled straight they would shimmy, there is always some amount of compliance in the system and if the wheels were rolling straight they would tend to shimmy between the extremes of allowable toe in and toe out, so they are designed to always be against one limit or the other, usually toe in. They might be stable if adjusted for toe out but applying the brake may make it dive to one side or the other. Perhaps if the wheels are being set for rolling compensation they might be held in the limit of toe in compliance while being adjusted.

          Jacking compensation, there are few if any suspension systems where the wheels move truly up and down, there is always some degree of splaying in or splaying out depending on suspension travel. Maybe jacking compensation is relating to adjusting the alignment at a defined point of the suspension travel.

          Just what comes to mind, I may be way off track...

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          • #6
            Originally posted by winchman
            I've seen it mentioned in lots of info on wheel alignment, but nothing I can find explains the procedure.

            Some equipment uses "rolling compensation" instead of jacking compensation, and the idea I get is that it's a way to cancel out errors from the rims not being perfectly true to the rotation axis of the wheel. Some carmakers specify that jacking compensation be used to align their vehicles, so it sounds like it's better, but involves raising the vehicle and takes longer.
            You got it.

            The alignment heads need to be "compensated" to adjust for errors in the wheel run out to find the spindle axis. Jacking compensation involves raising the wheels and spinning them a full 360° (or 180 depending on the machine) to adjust the alignment head spindle to match the vehicle spindle angle.

            Rolling compensation is done by simply rolling the vehicle backwards to allow the alignment head spindle to turn approx 45° and then rolling it forwards. This reading is then used to "calculate" the vehicle spindle position via the machine software.
            Saves time, so more profit for those collecting the cash...

            Example of the rolling compensation method:
            http://www.youtube.com/watch?v=I3wiokcmysM
            Last edited by Highpower; 06-16-2011, 09:43 AM.

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            • #7
              It seems mad to jack the car during tracking!
              If you measure the track, then lift the vehicle the wheels will invariably drop inwards due to the camber change permitted by the track control arms.
              You then lower the vehicle the tires engage the ground at a narrower track position but due to the friction of the rubber do not slip back out to where they started from.

              Measuring the track at front and back of the wheels followed by rolling forward half a turn and rechecking front and back is the safest way. It should also make you aware if a rim is buckled.

              Safer still to roll forward 4 quarters checking at each.

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              • #8
                Originally posted by john11668
                It seems mad to jack the car during tracking!
                If you measure the track, then lift the vehicle the wheels will invariably drop inwards due to the camber change permitted by the track control arms.
                You then lower the vehicle the tires engage the ground at a narrower track position but due to the friction of the rubber do not slip back out to where they started from.
                Compensation is done before you take any readings. Even so, modern alignment machines also have a "jack and hold" function which allows you lock in weighted readings then raise the vehicle to take the weight of of the suspension and make adjustments. Slip plates on the alignment rack allow for proper settling of the suspension, but standard procedure is to bounce the vehicle on the slip plates occasionally to ensure the proper ride height and suspension position.

                The engineers have covered all the angles (pun intended) when designing these machines.

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                • #9
                  Thanks, Highpower.

                  Now all I have to do is get the guys at the dealer to follow the service manual when they do the alignment. The service manual specifically says to use the jacking compensation method because the rolling method can result in errors. It also says to disregard the Green/red, plus or minus, Go/No Go indicators, and go by the numbers only when setting the alignment.

                  I watched them do it, and they did EXACTLY what the service manual said NOT to do. The results they got said it's OK, but the car is eating the front tires with VERY conservative driving. They put in a call to the tech reps, and they're going to call me to bring it back in when they get an answer. I'll be a bit more informed, and insistent they follow the manual when I go back.
                  Last edited by winchman; 06-16-2011, 11:23 AM.
                  Any products mentioned in my posts have been endorsed by their manufacturer.

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                  • #10
                    I don't know what kind of compensation they used on my car, but it's got 135,000 miles on it, and it's had one "four-wheel, thrust alignment" since it was new. The tires usually last 60,000 miles with no visible signs of mis-alignment (the tread wears equally all the way across).

                    When I worked fleet, we had similar cars, from the same manufacturer that were driven their entire service life without an alignment, and auctioned off with over 200,000 miles on them, and some of them were police cars.

                    Each manufacturer has their own specifications and proceedures for alignment. Failing to follow them will usually cost the car owner a few tires.
                    No good deed goes unpunished.

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                    • #11
                      I spoke to someone I know who does alignments, yesterday. He said "Jacking compensation method" means you have to align the wheels so you can get the wheel off when you jack it up to change the tire.

                      Please bear in mind that I live in Kingman, Arizona....
                      No good deed goes unpunished.

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                      • #12
                        You should use anti-jacking compensation. By which I mean you should have the alignment done with your normal complement of bodies (you) in the car.

                        Your car is never driven without the driver, yet the moment you sit in the car the suspension geometry alters, and the tracking with it.
                        Richard - SW London, UK, EU.

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                        • #13
                          Originally posted by winchman
                          The results they got said it's OK, but the car is eating the front tires with VERY conservative driving.
                          Did they give you a print-out of the readings before and after the alignment?

                          If not, make sure you get them next time and compare them to the service manual specs. The tolerance specs programed into the alignment machine may be more "generous" than the factory specs. That would be the reason to ignore the "red / green" indicators. Ideally all readings should match the "nominal" specs unless superseded by a service bulletin. That is not always possible, but the closer the better.
                          Last edited by Highpower; 06-19-2011, 09:20 AM.

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                          • #14
                            Originally posted by winchman
                            Thanks, Highpower.

                            Now all I have to do is get the guys at the dealer to follow the service manual when they do the alignment. The service manual specifically says to use the jacking compensation method because the rolling method can result in errors. It also says to disregard the Green/red, plus or minus, Go/No Go indicators, and go by the numbers only when setting the alignment.

                            I watched them do it, and they did EXACTLY what the service manual said NOT to do. The results they got said it's OK, but the car is eating the front tires with VERY conservative driving. They put in a call to the tech reps, and they're going to call me to bring it back in when they get an answer. I'll be a bit more informed, and insistent they follow the manual when I go back.
                            Highpower has it nailed, and I believe you as well knew all along what was going on and what the jacking compensation meant.

                            If I'm not mistaken you own a Nissan 350 Z, although I am unclear as to what year. Nissan has several PDFs available on line stating it's position on it's insistence on using the jacking compensation method for wheel alignment.

                            Below are two of them.
                            http://www.nissantireproblems.com/046TSBNTB04-043.pdf

                            http://www.lyberty.com/car/Maxima_A3.../NTB04-054.pdf

                            Tell your service department they can do as they please as long as they supply the tires and suspension parts.
                            Home, down in the valley behind the Red Angus
                            Bad Decisions Make Good Stories​

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                            • #15
                              Big mistake, Winchman. You NEVER mention that you actually read the service manual....or they'll do it exactly what the manual said not to do.

                              After 45 years in the business, I've seen this many times (yes, I'm guilty of doing it once or twice, too).

                              Another way to get the work performed EXACTLY wrong is to state loudly that the guy doing the job don't know what he's talking about. Mechanics have feelings, ya know. Too bad we don't have any MECHANICS left anymore, just "Technicians". And most "Technicians" have trouble reading the manual (too many big words), let alone performing the work properly.

                              No, I'm not a mechanic or a "technician" any more...I'm retired, and don't care to fix anybody's car any more (even my own.)
                              No good deed goes unpunished.

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