TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Unsprung Weight and Range

Discussion in 'Model S: Driving Dynamics' started by lloyds, Sep 18, 2013.

  1. lloyds

    lloyds Member

    Joined:
    Apr 3, 2013
    Messages:
    890
    Location:
    Bay Area
    So I've been thinking about changing out the 21s to accomplish both a new look and also to improve the range with lighter weight wheels. I know that the factory 19"s would provide an improvement of 3% in range. Wondering if there is any formula to use to calculate weight savings for range improvement?
     
  2. mnx

    mnx 2013 P85

    Joined:
    May 6, 2009
    Messages:
    2,281
    Location:
    Ancaster, Canada
    #2 mnx, Sep 18, 2013
    Last edited: Sep 18, 2013
    If you're hoping to get more range for road tripping (high speed / steady speed type of driving) the mass of your wheels doesn't make a difference, aero is far more important. When you're in city/stop and go driving range doesn't matter at all. (IMHO)

    That said I have 19" wheels which are 19.8lbs. :) I got them primarily for better performance however.

    FWIW that 3% you mention is mostly differences in tires/tire compounds based on what I've read on here (I read all of Jery33's posts). :)

    If you're really serious about efficiency/range. Make some wheel skirts, and try out some narrower LRR tires. (as long as everything has the necessary load ratings). You might be able to get away with a 225 width tire (it won't look very good between the 225 tires and wheel skirts/aero rims though)...
     
  3. lloyds

    lloyds Member

    Joined:
    Apr 3, 2013
    Messages:
    890
    Location:
    Bay Area
    Well I guess I was trying to give myself a reason to upgrade to new wheels. You know how that goes especially when I have to convince the other half.
     
  4. mnx

    mnx 2013 P85

    Joined:
    May 6, 2009
    Messages:
    2,281
    Location:
    Ancaster, Canada
    Well it was easy for me, lower unsprung weight = better handling, acceleration and braking. And I sold my brand new 21's for more than I paid for lightweight wheels + tires + TMPS.
     
  5. nrcooled

    nrcooled P#8946 VIN 03225

    Joined:
    May 22, 2012
    Messages:
    565
    Location:
    NoVA
    I changed out my wheels also to lighter aftermarket 19s and they, from my observations, didn't make much of a difference in energy efficiency. BUT...it's a big but...I was going from the factory 19s. When driving a loaner P85 with 21s I couldn't keep the energy usage anywhere near where my S85 w/ aftermarket wheels.

    I do think that going from 21s to lightweight aftermarket 19s will gain you better efficiencies (my unscientific opinion based upon 3 days with a P85 w/ 21s)
     
  6. jerry33

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

    Joined:
    Mar 8, 2012
    Messages:
    12,766
    Location:
    Texas
    The wheel is closer to the centre of rotation than the tire so the wheel has less effect on energy used. The reduction in energy used will be most noticeable at lower speeds, where aerodynamic drag is minimal, and stop and go driving, where you have to accelerate the mass of the tire and wheel assembly. However, it may not show on the standard displays (at a casual glance) because the wheel's portion is not large. Note that this assumes smooth pavement; for rough surfaces there is potential for a much larger gain because of the energy used for up and down movement.

    One big thing less unsprung weight will do is reduce damage from potholes because the tire and wheel assembly will lift more easily.
     
  7. TylerCA

    TylerCA Member

    Joined:
    Sep 1, 2013
    Messages:
    300
    Location:
    portola valley, ca
    I went with the 21" Turbines, but will probably change them out for aftermarket to get a more distinct look. Since this is our first EV, I'm concerned about range or at least not having add-ons affect the range.
     

Share This Page