Narrower wheels/tires for better EV efficiency

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Narrower wheels/tires for better EV efficiency

Rob Trahms
Has anyone tried this?  I currently have a line on some thinner wheels/tires that might improve my EV efficiency (and range), and I'd like to check with people who have also made the switch.  What were your experiences, and what was the delta increase in efficency/range?

FYI, I am already familiar with LRR-type tires & increased PSI, I just wanted to investigate this variable as another option.

Thanks,
Rob
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Re: Narrower wheels/tires for better EV efficiency

Phil Marino-2
Rob - we had a discussion about tire widths a year ago ( or maybe more)
In summary - there is no science or data to support the idea that narrower
tires have lower rolling resistance, and  some science and data that shows
that wider tires have lower rolling resistance ( for the same pressure)

Yes, I know most people think that narrower tires roll better, maybe because
bicycles use narrow tires.

Bicyclists use narrow tires because:

They are lighter in weight - VERY important for racers who have to
accelerate quickly, especially since it's rotating weight concentrated at
the outer radius of the wheel.
They have much lower wind resistance ( much more important to a biker than
rolling resistance)
The can take much higher inflation pressures ( for the same tire carcass
thickness and strength) than wider tires, so they may  end  up with less
rolling resistance because of that ( not a relevant for car tires, where
inflation pressure is seldom limited by carcass strength)


What you really want is a tire with a low published rolling resistance
coefficient.  There is quite a bit ( but not as much as there should be)
data available.  Start with this  -  not up to date, but it's a start :

http://www.greenseal.org/resources/reports/CGR_tire_rollingresistance.pdf

Phil Marino
Rochester, NY



On Thu, Apr 23, 2009 at 7:56 PM, Rob Trahms <[hidden email]> wrote:

>
> Has anyone tried this?  I currently have a line on some thinner
> wheels/tires
> that might improve my EV efficiency (and range), and I'd like to check with
> people who have also made the switch.  What were your experiences, and what
> was the delta increase in efficency/range?
>
> FYI, I am already familiar with LRR-type tires & increased PSI, I just
> wanted to investigate this variable as another option.
>
> Thanks,
> Rob
>
> -----
> Rob Trahms
> [hidden email]
> Electro - the Cabby-EV
> http://chaosmgmt.blogspot.com chaosmgmt.blogspot.com
>
> --
> View this message in context:
> http://www.nabble.com/Narrower-wheels-tires-for-better-EV-efficiency-tp23189697p23189697.html
> Sent from the Electric Vehicle Discussion List mailing list archive at
> Nabble.com.
>
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Re: Narrower wheels/tires for better EV efficiency

bruce15236
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Re: Narrower wheels/tires for better EV efficiency

Joseph Ashwood
In reply to this post by Rob Trahms
--------------------------------------------------
From: "Rob Trahms" <[hidden email]>
Sent: Thursday, April 23, 2009 4:56 PM
To: <[hidden email]>
Subject: [EVDL]  Narrower wheels/tires for better EV efficiency

>
> Has anyone tried this?  I currently have a line on some thinner
> wheels/tires
> that might improve my EV efficiency (and range), and I'd like to check
> with
> people who have also made the switch.  What were your experiences, and
> what
> was the delta increase in efficency/range?
>
> FYI, I am already familiar with LRR-type tires & increased PSI, I just
> wanted to investigate this variable as another option.

As Phil noted, you're not likely to see improvement.

This comes down to physics. At a given PSI there is a specific total tire
patch that is necessary to support the weight of the vehicle. For example,
at 70 PSI a 4000 pounds vehicle requires a total tire patch of 57 square
inches. The primary controllable factor of rolling resistence is the amount
of flexing that a tire must do to create that patch.

With a narrow tire significantly more of the tire must be in a flexed stated
to deliver the necessary tire patch. As a result the rolling resistence of
the tire at a given pressure for a given vehicle weight will generally
decrease with tire width.

At high speeds this is overcome by the aerodynamic costs of the wider tire,
but generally you're probably not going to reach those speeds.

Also be sure to account for the decrease in handling in using the narrow
tire, this can be the difference between not having to slow for a corner and
having to spend every bit of saved energy just accelerating back up to speed
after the corner.
                    Joe

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Re: Narrower wheels/tires for better EV efficiency

EVDL Administrator
In reply to this post by bruce15236
On 24 Apr 2009 at 3:52, [hidden email] wrote:

> An HTML attachment was scrubbed...

Note to all -- the EVDL accepts the following types of mail :

multipart/mixed
multipart/alternative
text/plain

The above happens when your email system sends a type which is incompatible
with the list (and most likely with internet standards).  

If this happens, configure your email system to send plain text only.  If
that's not possible, I suggest that you use Yahoo Mail or Google Mail for
your messages to the list.

This message's contents follow.

Date: Fri, 24 Apr 2009 03:52:08 -0500 (CDT)
From: [hidden email]
To: [hidden email]

This one's primarily for Phil (by the way, I tried to post on this group
without success so I had given up...hopefully this goes through).  

My '97 Ford Ranger has been in steady service for approx. 2 months (don't
drive it in Pittsburgh winters because of the temps. and the salt). When I
bought the vehicle it had (and still does have) nearly new, very aggressive
snow tires (225x70x14). I can't help but wonder if these may have a negative
effect on my charge distance (approx. 20 miles per charge).  

Actually, I have a feeling that what affects my low charge mileage most is
vehicle weight (approx. 4200 lb), lots of stop & go driving, and serious
hills. Of course since this is my first attempt at building an EV from a pre-
existing ICE-powered unit, everything is assembled properly for optimum
efficiency...NOT.  

Bruce Webster
'97 Ford Ranger EV

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: Narrower wheels/tires for better EV efficiency

Roland Wiench
The best tires I ever had on my EV, was back in 76 which was A GoodYear
H-78-15 Subernite x G Polyglass 8 Ply face with a 6 Ply side wall with a
load rating of 2010 lbs @ 40 psi.

The tire was 28.35 inch in diameter and 89.1 inches in circumference with a
6 inch wide smooth highway thread. At 40 psi, it only had a 3/8 inch side
wall deflection which was measure from grade to wheel rim unloaded and
loaded.

The EV at that time had 90 each 300 AH lead acid cells.  The EV weigh in at
7850 lbs. Drove up and down a very steep 7 to 8 percent grade 2 mile long
hill every day at speeds of 60 mph up hill and would get up to 85 mph down
hill and have another 3 mile roll out with no additional power.

Drove this route for 10 years with these tires and replace them with a
Radial Dunlap all weather steel nylon tire that had load rating of 2350 lbs
@ 65 PSI. It had a 8 ply face and a 4 ply side.  This tire was the worst
tire I every had.

The side wall deflection rate was terrible.  Rolling down this hill, the EV
would actual slow down.  Could not do a roll out at all.  It felt like I was
dragging a huge weight. Airing up to 65 PSI, the side walls still had a huge
bulge in it like a radials did at that time.

Back at the dealer, said that's what radials are suppose to do, the side
wall deflects so the face of the tire stay flat on the pavement.  Well, that
did not work, and went back to the Polyglass type tires.

I also found out latter that the steel nylon tires had more rolling
resistance at lower temperatures which cause a flat spot when the vehicle is
setting.

Today, I am using a Polyglass radial tire with a 6 ply very stiff face with
a 2 ply side way by Pirelli which is rated at 2640 lbs @ 65 psi.  This type
of tire with a very stiff face, keeps the tire more rounded and the 2 ply
side wall picks up the deflection, but does not transfer the deflection
rated to the face like the other tires I had.

Choose a tire for the proper load rating and air it up with psi proportional
to the load rating that is on the side of the tire. Use a all Polyglass tire
that has a stiff face with a soft side wall.  This is how the new Low
Resistance tires are built.

A narrow tire will have a longer foot print then a wider tire will at the
same psi at the same load.  The shorter foot print will reduce the face
deflection rate. The square inch contact area may be the same, except the
wider tire may have a 2 inch wide foot across the width of the tire, where a
narrow foot print may be up to 6 inches long.

Roland




> On 24 Apr 2009 at 3:52, [hidden email] wrote:

> This message's contents follow.
>
> Date: Fri, 24 Apr 2009 03:52:08 -0500 (CDT)
> From: [hidden email]
> To: [hidden email]

> My '97 Ford Ranger has been in steady service for approx. 2 months (don't
> drive it in Pittsburgh winters because of the temps. and the salt). When I
> bought the vehicle it had (and still does have) nearly new, very
> aggressive
> snow tires (225x70x14). I can't help but wonder if these may have a
> negative
> effect on my charge distance (approx. 20 miles per charge).
>
> Actually, I have a feeling that what affects my low charge mileage most is
> vehicle weight (approx. 4200 lb), lots of stop & go driving, and serious
> hills. Of course since this is my first attempt at building an EV from a
> pre-
> existing ICE-powered unit, everything is assembled properly for optimum
> efficiency...NOT.
>
> Bruce Webster
> '97 Ford Ranger EV
>
> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
 

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Re: Narrower wheels/tires for better EV efficiency

Go@GoWheel.com
In reply to this post by Rob Trahms

Hi all,

The "surface patch" (footprint) can be measured by lifting and printing a mounted wet tire on a piece of cardboard while parked.  

Most skinny tires will have an oval or round footprint.

Some wide tires will have a round, oval, (or even a sideways-figure-eight footprint).

This of course could be tested a few times at different tire pressures for various measurements.  But, some brands would show a dramatic difference at different pressures, while others almost no difference.

This footprint is a small part of the story.  The distortion is a huge consideration during speed with load.

I did not believe the internal and hidden design of a tire could have so much to do with so many things until I went through the engineering classes at Michelin.

It was proven to me that the best way to get low rolling resistance was to reduce (or try to eliminate) the distortion of flexing tread as it is "forced" over the road. The more the tread flexes, the more resistance.  That affects rolling resistance, gas milage, treadwear, vibrations, heat, traction, noise, cornering, etc.

Bias ply (criss-crossed layers) tires make improvements to stiffen  tread by making the tread thicker, or harder, or wider or more plys (layers) or harder layers.  But, that also made the whole tire heavier, stored more heat, took more energy to roll (offsetting the lesser rolling friction), cost more in materials, and allowed the heavy portion to be at the outer part of the moving mass, and many tires would throw the tread at high speed.  Even worse in hot climates.

Michelin solved the problem by inventing the steel radial.  It gave them a very stiff tread with lots of steel criss-crossed in the tread.  That almost eliminated the friction from flexing and scrubbing and reduced the heat.  It also allowed them to get great puncture resistance, treadwear, and yet reduce thickness and weight (offsetting the added weight of the steel).

Creating non-flexing tread made the tire ride very rough, regardless of the method to stiffen it up.  So Michelin made the sidewall soft by NOT criss-crossing the sidewall plys.  They have angled (radial) (radius) plys.  

The "radial" part is what reduces (most types of) the stiff ride, by allowing the sidewalls to flex easily.  Even if the sidewalls are really strong and thick, radial plys still flex pretty easily.

Bias ply tires get stiffer all over when you make them with more layers or with stronger layers, because the plys are everywhere.  

Almost all other companies had trouble creating quality steel radials, because they had trouble bonding steel to rubber.  So most tried to use alternate materials like Kevlar, fiberglass, nylon, or a just a very tiny amount of steel.  There was trouble with that method, because other materials might be stronger than steel, but be more brittle, or less heat tolerant, or less firm, and certainly less effective with less steel.

If you want to see the difference, take a few junkyard tires and cut a one inch wide strip of cross section of tire (looks like a "U"), and twist it vigorously with all of your strength to distort it.

A cross section of Pirelli, Bridgestone, or Michelin will not allow you to distort the tread very much, while most other brands will distort the tread and sidewall in equal distortion.  The lesser performing tires will distort easily in the tread area.  Also note the amount of steel in various brands.  Wildly different amounts.

They say the rubber compounds, the amount of carbon, the style of grooves, the tread depth, are significant, but I believe far less than achieving "stiff tread & soft sidewall".

At the Goodyear, Firestone, BFG, and Michelin factories, I saw the loaded high speed distortion of cheaper (tires that were lighter, or weaker plys), compared against their expensive tires.  In the old days, the U.S. tire makers could not get steel radials perfected.  Today, there is a much narrower difference between brands and quality products are available from almost all brands.

Still, they can predetermine the treadwear, rolling resistance, traction, or selectively any aspect to guarantee that the tires don't last too many miles, and artificially make differences between priced models to determine product life.

Soon, they will finally be comparing and competing for Low Rolling Resistance (LRR) as an advertised factor.  Gov regs will require LRR ratings too.  

They will still be able to manipulate treadwear, traction, ride, and appearance, while having high or low LRR.  They already have this tested and analyzed.  

Another way to test the LRR is to take two identical vehicles (with brake pads not dragging) and (in neutral) push them apart on a level surface while pushing from bumper-to-bumper.  Repeat the test after swapping the tires car-to-car for verifications of backwards testing.

UPS has used Michelins since 1967.  So has Yellow Cab and their competition in Las Vegas.  I was there for the tests (as above), yet they paid twice as much purchase price for the tires.  They determined, as did many cross country fleet rigs, that there was about a 8% reduction in fuel used with the Michelins.  Thet still lowered their operating costs by huge amounts.  Now, Bridgestones, Toyos, and many other brands are about equal, often undercutting the acquisition prices per tire.

By the way, aluminum rims save lots of energy over heavy steel rims, and pay for themselves on many vehicles.  That explains why ugly trucks often have aluminum rims and quality tires.  Their meticulous records prove the savings over time.  Ask any fleet manager or fleet sales force.

At any rate, wide tires, "might" roll easier (or not), might be heavier (or not), might grip better (or not), etc.

The aerodynamics are another issue, but the body shielding the wind exposure might limit differences somewhat.

Another consideration is overall tire weight (and the wheel), and secondly the amount of weight that is distributed farthest from center (taking more energy), especially to start and stop.

To optimize this consideration, try for less weight, less weight to the outside of the circle, less wheel weight, while maintaining strength and other benefits.

In the end, the only true test is field testing for absolute proof.

Good luck and happy testing.
Jay Lashlee
[hidden email]
---------------------------------------------------
<snip> > This comes down to physics. <end snip>



     

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