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Negative Camber in the Rear and Expensive Tires

Discussion in 'Model S: Driving Dynamics' started by lolachampcar, Feb 13, 2013.

  1. lolachampcar

    lolachampcar Active Member

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    I have had several cars that run better than 1.5 degrees of negative camber in the rear. Looking at my MS and comparing the front to the rear I'd guess the rears are over -1.5. Camber gain is built into suspensions so the negative value will only increase as the car lowers going down the road.

    Running this much camber reduces contact patch which decreases rolling resistance. It also helps save you on throttle off over steer. Most people's normal reaction when they feel like they have entered a corner too fast is to lift off the accelerator. This causes forward weight transfer, unloads the rear and the car can swap ends. Negative camber in the rear gives more safety margin.

    The down side is it wears the inside of the tire, sometimes very quickly. I've had cars that would destroy rears in 4,000 miles. I have addressed the problem by going to the lower limit of the factory recommended values for rear camber (and sometimes less) and have even had to adjust ride height to get to an acceptable number. That acceptable number is no more than -1.0 degree for me but this is a personal preference.

    Has anyone looked at this? Have you measured tread wear across the rear contact patch? I'll do mine shortly and share the results. At $500 a piece, I would prefer to not be buying Pilot's on a regular basis.
     
  2. Zextraterrestrial

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    I was going to get a tread depth gauge but haven't done so yet. I had my tires rotated at ~ 3500 miles, the rears were a little worn and at 4700 it seems like I may be almost 1/2 done with my tires.
    I have the Continentals though and not the Pilots- which I think they switched to on the later deliveries
     
  3. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    Is the rear setup likely to be any different with the non-Perf and/or 19" all-seasons?
     
  4. lolachampcar

    lolachampcar Active Member

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    I measured mine at 500 miles and they were 0.280/0.270/0.210" with the 0.210" number being the inside. That is 70th of wear out of 280th of total in 500 miles or 25%. Huston, we have a problem.

    It is time for me to visit the alignment shop and see how much adjustment there is.

    With respect to performance versus non, I would think the suspension is the exact same from a geometry standpoint. Tesla's published alignment specifications will tell.
     
  5. childressmd

    childressmd Member

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    #5 childressmd, Feb 13, 2013
    Last edited: Feb 13, 2013
  6. lolachampcar

    lolachampcar Active Member

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    Nice! I was waiting on that from Tesla. It is a little sad to see that the minimum is -1.4 as this will still eat the inside of the tire, just not as fast.

    I also asked about inflation for the Pilots. It is 42 psi, same as the Conts.

    The camber explains the wear I am seeing. I'll post when have information about the adjustment range for rear camber. I will also confirm which suspension setting achieves the reference heights and the camber gain when lowered further.
     
  7. rogbmw

    rogbmw Member

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    I wonder if you could decrease the camber setting on the rears. Note the front is 0.75, and the rear 1.75. I wonder if it a typo??? By decreasing the camber, you may not be able to drive as agressively, but really wonder if you would notice. That rear wear does seem to be pretty excessive.

    Remember the Acura NSX? It would eat up rear tires with many people replacing the rears at around 7K miles, and some owners decreased the rear camber setting to lengthen rear tire life.
     
  8. childressmd

    childressmd Member

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  9. lolachampcar

    lolachampcar Active Member

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    I have a Maranello that I ended up taking down to -1. This extended the life of the rears by a factor of two. I also move the unidirectional tires across the rear to further extend the life of the tires. Neither practice has hurt the tires and only marginally decreased the margin of safety on throttle off over steer. I am very comfortable with a neutral car on throttle but would encourage anyone not comfortable with this to find a safe place to upset the car and verify any rear camber changes. Manufacturers put the camber in for a very good reason as things happen quickly at speed when you lift.

    Removing camber will increase static contact patch and thus rolling resistance. I would not be surprised to see a slight reduction in range. Daytona was always a balancing act between high negative camber to get straight line speed and the ability of the tires to shed heat and not come undone. I suspect a secondary reason for Tesla's rear camber choice is increased range.

    The alignment specifications listed above also shed some light on my car's tendency to hunt when there is any grooving in the pavement. The other trick for Daytona was removing toe which caused a normally very stable car to follow every groove on the banking.
     
  10. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    I'm not buying that one. It will change the shape of the contact patch a bit, but the size of the contact patch is determined almost entirely by the load and air pressure. If anything it will increase range because the tread will be evenly compressed.
     
  11. lolachampcar

    lolachampcar Active Member

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    jerry33,
    I'm speaking from practical experience with 200 mph cars at Daytona. I am guessing at the exact reason but the results were more negative == improved top speed and a better chance of ripping a rear corner off the car when the tire blew.

    Just got back from the alignment rack. Rear camber was -1.53 and -2.30. Personally, I would have rolled the car out and tried again to see if there was any body roll or side load on the tires from the driver getting out of the car. This may have reduced the spread between the numbers but the average of 1.9 or so negative camber verifies my concerns. What was even more concerning was the apparent lack of camber adjustment on the rear of the car. There were no eccentric adjusters on the bottom arm and it was tough to verify that there were no adjusters on the top. The alignment tech and I both looked and saw none but this needs to be verified with Tesla.
     
  12. lolachampcar

    lolachampcar Active Member

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    I've got the top rear suspension link on the way. When I get it, I'll make up a temporary adjustable link based on the production link's dimensions to be used to dial in about one degree or slightly less negative camber in the rear. Hopefully there will be sufficient clearance in the stock link's isolation mount end to allow for an offset insert to change camber. In addition, there will need to be sufficient toe adjustment to make up for the change in camber geometry.
     
  13. Benjam

    Benjam Member

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    So, from what I'm hearing, the Model S comes with some significantly negative rear camber and there are no adjustments on the car that can correct for this?
     
  14. Kaivball

    Kaivball Member

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    Yes, the car was designed that way.

    Making significant changes to the recommended suspension settings is at the owners peril.
     
  15. lolachampcar

    lolachampcar Active Member

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    Always is :)
    All kidding aside, I would not consider changes if you were not completely comfortable with how they will affect the car.
     
  16. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    For those who can remember the Fiat X/19, there was a similar problem. The front tires were toed-in to improve handling. This caused the tires to wear out in about 8,000 to 9,000 miles and also caused endless complaints to the tire manufacturer. The European office told us that 8,000 miles wasn't a problem--just a small amount low and they really couldn't understand why anyone would complain. To us this was unacceptable as the tires typically lasted for 30,000 miles on other cars. After about six months, Fiat had two alignment recommendations: Handling or tire life. The complaints stopped.

    My hope is that Tesla will do something similar.
     
  17. lolachampcar

    lolachampcar Active Member

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    Tesla has fixed rear camber :( I really do wish it were adjustable as I have no problem determining values that are safe for my driving.

    I'm heading down to the Miami store this AM to shoot some pics of the rear suspension and make measurements of the geometry. My primary concern is opening a can of worms as toe changes with camber. I hope there is enough toe adjustment to allow camber adjustment without redoing toe links as well.
     
  18. rogbmw

    rogbmw Member

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    Are you saying they are delivering cars with a different rear camber? If so, do we know when they started the change in the production sequence? I have had my car for 2 weeks.
     
  19. lolachampcar

    lolachampcar Active Member

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    #19 lolachampcar, Feb 22, 2013
    Last edited: Feb 22, 2013
    My only reference point is my car delivered at the start of the month. I have no information (or indication) that Tesla has evolved the settings in production.


    I see from the comment below where the confusion came in. Yes, by fixed I ment there was no way to adjust the rear camber.
    Thank you childressmd.
     
  20. childressmd

    childressmd Member

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    By 'fixed' he meant that the degree of rear camber is non-adjustable.
     

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