[ausev] EV tires

[Brian Lasseter]

On Thu, Dec 11, 2008 at 10:17 AM, The Mullins <ckmullins at earthlink.net> wrote:
> I hear a lot about the LRR ability of tires for EVs but not much on tires
> that can handle the additional weight after conversion. I read that the
> GAWF/GAWR ratings are mostly about the ability of the tires provided by the
> factory to handle the weight. Supposedly the springs, shocks, etc can handle
> more, I hope so because I'm having a hard time coming up with a plan that
> won't result in 600 or so lbs over GVW.

Your brakes will wear much faster if you are over the GVWR, and if you
can not get under the GVWR then I might question whether you are using
the correct donor vehicle... The weight of people in the car is
supposed to be taken into account with the GVWR too.

In my Saturn for instance, the curb weight (how much the car weighs
unloaded) was 2326lbs and my GVWR is 3338lbs (how much the car is
rated to hold).  That gives me 1000 lbs of play room... however this
means that with my EV Saturn being 500lbs heavier than the original,
my car is not really rated to carry 4 adults any more.  (Which is fine
by me.)


--

As for low rolling resistance tires (LRR)... I have done a lot of
thought in this area because my donor car came with crappy tires, and
my EV is not evenly weighted (for a number of very good reasons).  In
fact it was front passenger side heavy enough to effect steering until
I had the alignment over corrected in the other direction.

So... This puts me in the position of wanting tires that have a low
rolling resistance AND can carry a lot more weight.

In my research, I have found that almost all tires in a given size can
handle the same amount of weight.   Therefore, to hold something
heavier, you need a wider tire and/or a bigger tire (and possibly a
bigger rim too).

To use myself as an example again, I have the following tires on my
electric Saturn SL (the same tires the donor car came with):
  Tiger Paw AS6000 - P185/65R14 - 85S - 1124lbs @ 35psi (max 45psi) -
23.5" diameter

After much looking around... this is the tire I have settled on, but
have not bought yet:
  Sumitomo HTR 200 - P195/65R15 - 91H - 1356lbs @ 36psi (max 51psi) -
25.0" diameter

The Sumitomo HTR 200 is mentioned as having a low rolling resistance
by Green Seal: http://www.greenseal.org/resources/reports/CGR_tire_rollingresistance.pdf
 and the tire can carry over 200 lbs more per tire.  That is a win-win
in my book.

These new tires will be 1.5" larger in diameter and 0.4" wider though.
 However I know the electric Saturn SL can take 195mm tires as my
older Saturn SC2 has some high performance 195mm tires on it.  I also
know that losing 0.75" in the wheel well of my electric Saturn SL is
not a problem as the springs Aaron bought me to hold the weight of my
EV ended up raising my car about an inch higher than stock.  So I have
room for both larger and wider tires.  (The only down side is that
this will make my speedometer read 6.4% slower than my actual speed.
http://www.discounttire.com/dtcs/infoTireMath.dos )

The moral of this EV story?  Make sure your new springs raise you up
high enough to fit beefier tires on your EV to hold all of that
battery weight.  Maybe this is all more than you wanted to know... but
as I said, EV tires is a subject that has been on my mind.


-- 
TTFN,
Brian "Lasso" Lasseter

"No Sane man will dance."   -Cicero (106-43 B.C.)