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Compact Space Saver Tire/Wheel Solution

Discussion in 'Model S: Driving Dynamics' started by JST, Dec 15, 2013.

  1. JST

    JST Active Member

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    #1 JST, Dec 15, 2013
    Last edited: Mar 18, 2014
    I had a compact spare that I assembled for my E90 M3 lying around, and when I first started thinking about a Tesla I wondered if it would work on the Model S.

    Short answer--as you can see in the pics which I'll upload shortly--is yes, it does.

    The wheel is an 18" BMW steel wheel from an X5. It's BMW part number 36-11-6-768-861. I'm not sure about the policy w/r/t posting vendor links, but you should be able to order it through any BMW dealer.

    The center bore is 74.1 mm, which is larger than the Model S center bore of 65 mm. That's not really an issue, especially with a temporary spare, since the center bore only provides alignment and the lugs are what holds the wheel on. But a set of 74.1 to 65 mm centering rings can be purchased from Amazon for about $5. You can see in some pictures I have a ring on, and in some I don't.

    The wheel is narrow enough and the offset is sufficient that you don't have to worry about the steering knuckle on the bottom of the suspension. The front brakes clear easily. I haven't tried the rear, but it should fit--and even if it doesn't, I can just swap the other tire front to rear.

    The tire that I have on the wheel now is left over from the M3. It's a Maxxis
    T135/70R18 104M, which is used on prior-generation Cadillac CTSs. It's diameter is 25.4 inches, which is probably too small for the Model S, so I may order a 145/80D18 space saver tire. That would give me a diameter of 27.1 inches, versus 27.7 for the stock 245/45 19. Not ideal, but for purely temporary work I think it should be fine. In all honesty, even with the 135/70 18 the ride height difference is barely noticeable.

    With the 135/70 tire, the wheel fits in the frunk with room to spare. I suspect that a 145/80 18 will also fit.

    I also bought a scissor jack from AutoZone for $30 and a T-handle lug wrench, which both store underneath the tire.

    Edit: I've now gone with a 155 80 18 compact spare, which is very close in outer diameter to the stock tire. That fits fine in the frunk.

    Edit to edit: after a test drive, I can report that the 155 80 18 tire does not produce any issues with ABS, traction control, or regen when you mount it on the car. The outer diameter is clearly close enough that it doesn't cause the car's software to get confused.


    EDIT: Here's everything you need, summarized:



    1 steel temporary spare wheel from a BMW X5, BMW part number 36-11-6-768-861. These are available from any BMW dealer, or online from www.getbmwparts.com. http://www.getbmwparts.com/parts/index.cfm?make=BMW&year=&searchText=36-11-6-768-861&action=oePartSearch&siteid=214672
    Cost: About $75.

    1 155/80 18 compact spare tire. These are available new for about $300, but you can find them used for a lot less. Look for the compact spare tire assembly from a Mercury Marauder or Ford Escape Hybrid. I found a number of them for sale at Automotix.net, a wrecking yard aggregator, for about $150. Note—the automotix search engine makes it seem like all you are getting is a wheel, not a tire. I received both when I ordered, but another forum member called and could not get them to confirm the tire would come, too. YMMV, as they say.

    2007 Ford Escape Wheel (Used VIN H 8th digit, Hybrid 18x4 compact spare aluminum) For Sale - Buy Ford OEM Parts

    1 74.1 mm to 65 mm centering ring adapter (basically just a piece of plastic with those diameters, respectively, outside and inside). I got a set of four from Amazon for about $5.

    1 T-handle lug wrench with a 21 mm socket. Any auto parts store.

    1 jack capable of lifting Model S weight. I bought a scissor jack at Autozone. Some carry bottle or floor jacks, but this seems like too much weight and space.

    1 tire tote from TireRack. I think these are like $30 for 2. I had one lying around.

    Once you get the tire and wheel, you’ll need to have the tire mounted on the BMW wheel. The local NTB did this for me; cost was about $25.

    Of course, this is totally unapproved by Tesla and if you decide to follow this DIY you do so completely at your own risk. I make no warranty, express or implied, about the function or safety of this setup. Etc.
     
  2. JST

    JST Active Member

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  3. ZBB

    ZBB Emperor

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    Great info... Thanks JST!
     
  4. JST

    JST Active Member

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    #4 JST, Dec 15, 2013
    Last edited: Dec 16, 2013
    One other thing--I've come across at least one vendor selling pre-assembled kits for the F25 X3, including the 145/80 18 tire, a jack and tire tote. I haven't confirmed that the wheel they're using is the same as the one that I have, but I suspect that it is. They're asking $400 for the kit, which seems like a LOT; my wheel was about $150, the tire $90, and mounting was like $10. A tire tote is $30 and a jack is $30, too, so all in you should be able to put something like this together for around $300.
     
  5. Panacea

    Panacea TSLA Shareholder/Believer

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    Could I use this for emergency purposes only on my car with 21s on?
     
  6. CalDreamin

    CalDreamin Member

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    Are the tire and wheel rated to handle the weight of the Model S? An E90 M3 is a lighter car.
     
  7. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Have you taken this for a test drive? What did the Traction Control think of this? I know that the Roadster Traction Control will complain with tires that are as little as a half inch off, and refuse to use regen. That is probably fine, but important to know ahead of time.


    The 21's use lower profile tires on the larger rims to get about the same final wheel diameter. If this spare will work for 19's then it should work for 21's. As one of my early mentors taught me, "If it hasn't been tested, it doesn't work." Conservative, but setups like this should be tested before needed.
     
  8. logan

    logan Member

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    Great info! Thanks JST. :)
     
  9. JST

    JST Active Member

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    Yes, I looked at that. The tire that is on my spare wheel now is load/speed rated at 104M, v the 98W rating on the OEM Michelins.


    http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35

    That means the space saver is rated to carry 900kg up to 81 mph, v 750 kg at 168 mph for the stock tire (note that you should multiply these numbers by four when comparing to the weight of the overall car).

    Not sure what the F25 tire is rated at, but I assume it's similar.

    The wheel I have no concerns about, since it was originally intended for an X5.

    I didn't have a chance to road test it, and it may well freak the hell out of the stability control system.
     
  10. CalDreamin

    CalDreamin Member

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    Thanks JST!
     
  11. JST

    JST Active Member

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    Actually, a 155/80 18 tire would be almost exactly the same diameter as the stock Michelin (27.8 v. 27.7). A quick google shows that this size tire may be available from Bridgestone, and apparently were offered as a space saver on the Mercury Marauder. Someone on a Camaro board appears to have found a Uniroyal space saver tire in that size for $40 (!!).

    I'm going to call around tomorrow and see if I can source one for a reasonable cost.
     
  12. montgom626

    montgom626 Active Member

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    Look forward to your post!
     
  13. AmpedUP

    AmpedUP EV Nut

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    @JST , awesome...and thanks for pictures. If you can road test this on the rear, many of us will be "all ears" on your results.
     
  14. JST

    JST Active Member

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    I know I owe everyone a follow-up; things got busy and I haven't had a chance to do anything other than confirm that the local NTB doesn't sell space saver spares. The weather is supposed to be nice tomorrow, so maybe I'll have a chance to mount my existing spare back up and do a brief road test.
     
  15. gene

    gene Active Member

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    Thanks. Many of us are waiting for your follow up road test.
     
  16. JST

    JST Active Member

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    Ok, so I drove around a bit on the compact wheel and existing, smaller diameter tire.

    As expected, it freaked the car out, and the car disabled a whole list of features, including ABS, traction control, stability control, and regen. Power assistance to the steering seemed gone, as well, or at least greatly reduced.

    The good news is a) the car was still driveable, though you obviously had to be careful, and b) when I put the stock 19" wheel back on, it cleared all those errors within a few feet.

    So, I would definitely suggest a bigger tire. The 155/80 I mentioned above is probably the right choice, assuming I can find one with sufficient load rating. Will work on that after the holiday.

    It remains to be seen whether using that size (which is still not exactly the same as the others) will cause the same problems.
     
  17. ZBB

    ZBB Emperor

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    Could the errors be due to no tire pressure and/or ABS sensors on the spare?
     
  18. JST

    JST Active Member

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    Oddly, I didn't see a TPMS warning light, which is consistent with what others have said--it takes several minutes for the TPMS absence to register. I don't know why that would be.

    I am fairly certain it's a wheel speed issue. The only question is how much deviation will the system tolerate before it shuts down.
     
  19. JST

    JST Active Member

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    Still working on this. The only place I've found so far that will order me a 155 80 18 tire (0.3 percent bigger than stock) is Pep Boys, and they want $314 for it.

    Tire Rack has the 145 80 18 tire (2 percent smaller than stock) for $203 prior to shipping.
     
  20. gene

    gene Active Member

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    You might mention to Tire Rack what you are attempting here. It would be to their benefit for you to find a tire/wheel that works out. They then could put together a suggested package for Model S owners. With this in mind, maybe they would loan you or sell you one discount.
     

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