[ausev] thoughts on tires

Thu Jan 22 15:15:41 GMT 2009

Chris,

A wider tire has more rolling resistance than a narrow tire, and a smaller
diameter tire also has more rolling resistance than a taller tire. You
didn't mention the rolling resistance coefficient of the 235s that you have,
and my guess is that you'd have a hard/impossible time finding that data,
anyway. The RRC has as much impact as difference in width that you are
talking about.

That being said, the documentation that I can find says that the original
tire was 255/70R15. Mine were the same as yours: 225/70R15, but I replaced
them with larger tires. Unfortunately I can't recall how much bigger (I'll
check when I get home), but according to my GPS, the speedometer became more
accurate. Like I said, the range did drop a bit, but my batteries were in
serious decline by this time. I also had an alignment at the same time. So
it is hard to say how much impact the wider rubber made or if it was due to
the (presumed) higher rolling resistance coefficient of my new tires.

Like Mark said, your driving habits will probably have more of an impact on
your range than these tires are likely to have. All things held constant,
these will reduce your range no more than 5%. The financial benefits of
using existing tires over new ones would be much greater than any savings
you'd get from increased efficiency of LRR tires - especially relative to
the life of the Pb-acid batteries.

If you want to read some more about LRR tires, I suggest the following links
that I found at the time of my replacement. Michelin has expanded their LRR
tire line since then, as have other tire manufacturers, so you may look into
that.
http://www.energy.ca.gov/transportation/tire_efficiency/documents/2007-12-07_workshop/presentations/Lambilotte_Bruce_Task%204%20Rolling%20Resistance%20Testing.pdf
http://www.energy.ca.gov/transportation/tire_efficiency/documents/2007-12-07_workshop/presentations/Pottinger_Walter_Eagleburger_Synopsis%20of%20the%20National%20Tire%20Efficiency%20Study.pdf

- ian

On Thu, Jan 22, 2009 at 8:52 AM, Marc Kohler <mkohler at austin.rr.com> wrote:

>  Mount the new set and move on down the road.  Your speedometer is
> probably 1/65th off anyway from absolute true so don't let that bother
> you.
>
> As for increased friction or footprint, there are many other aspects that
> effect your efficiency much more (driving habits, terrain, weather) that
> will make the difference unnoticeable.
>
> I say slap them on and get driving to get that EV grin back as soon as
> possible.
>
> You can always change them out later if you really notice a difference when
> you have more change in your pocket.
>
> My two cents.
>
> Marc Kohler
>
>
>
> *From:* ausev-bounces at austinev.org [mailto:ausev-bounces at austinev.org] *On
> Behalf Of *chris clark
> *Sent:* Thursday, January 22, 2009 8:39 AM
> *To:* AustinEV News Announcements and General Discussion
> *Subject:* [ausev] thoughts on tires
>
>
>
> Now that Mark Witt's old Ranger EV is finally finished, I have to replace
> the tires.  Unfortunately, I've spent all my money buying and working on
> this thing and now, money for tires is pretty limited.  If I could afford
> it, I'd just go by a new set of 225/70/15's like the ones it came with.
> That's pushing $500, though, to get a set of good quality tires.  So here's
> my question.  I have a new set of 235/70/15's that would cost me very little
> to have mounted and balanced, but the tires are roughly 1/2" taller and
> almost 1/2" wider, creating a little larger 'footprint' and distorting the
> mileage/range computations slightly.  I've been told by Discount tire that
> with the larger 235's, a speedometer reading of 65mph would actually be 66
> mph.  So the calculations would be effected about 1/65 and there would be a
> small increase in friction because of the larger footprint, at least this
> makes sense to me instinctively.  And this begs the question "would one size
> smaller tire decrease friction by having a smaller footprint?"  If the
> answer is yes, there are many 215/70/15's or even 215/75/15's available at
> salvage yards.  For some reason, though, 235/70/15's are very difficult to
> find used.  Enough of my ramblings.  Any thoughts?
>
>  ----- Original Message -----
>
> *From:* Marc David Kohler <mkohler at austin.rr.com>
>
> *To:* 'AustinEV News Announcements and General Discussion'<ausev at austinev.org>
>
> *Sent:* Wednesday, January 21, 2009 7:24 PM
>
> *Subject:* Re: [ausev] ReinCarNation
>
>
>
> Welcome Gary.
>
> We look forward to meeting you at the next AustinEV.org gathering.
>
> Marc Kohler
>
>
>  ------------------------------
>
> *From:* ausev-bounces at austinev.org [mailto:ausev-bounces at austinev.org] *On
> Behalf Of *Gary Ellis
> *Sent:* Wednesday, January 21, 2009 7:15 PM
> *To:* ausev at austinev.org
> *Subject:* [ausev] ReinCarNation
>
>
>
> Hi,
>
> My name is Gary Ellis and I just subscribed to the AustinEV mailing list as
> I'm starting an EV conversion company, here in Austin, and wanted to
> introduce myself.  Our company is called ReinCarNation -- please check-out
> our web-site, when you have a chance.
> http://www.rcnmotors.com
>
> I'm very interested in meeting many of you at your next meeting, seeing
> your EVs and showing you my electric Miata.  I have heard about Revolt
> Custom Electric, but have yet to contact them to see what their experience
> has been like.
>
> Thanks and any feedback is welcome.
>
> Gary
> ReinCarNation
> RCN Motors, LLC
> http://www.rcnmotors.com
>  ------------------------------
>
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