Rolling Resistance (RR) - Understanding Tires

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Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 27, 2013 8:25 am

While at high speeds, Rolling Resistance (RR) is a minimal factor, at speeds below 20mph, it is a major factor and well worthy of consideration!

Image
At 50mph the rolling resistance is approximately 3.5% of the energy required from "Mountain Bike".

An alternate source (Schwalbe) demonstrates the transition between rolling resistance and air resistance as the major energy robbing factor as speed increases.
RR vs AS.jpg
RR vs AS.jpg (37.99 KiB) Viewed 3620 times
"Speed" is in KPH.
I removed "Gradient" factor-lines.

As demonstrated, 18km/h looks to be the transition point of RR being surpassed by AR (Air Resistance) as the primary resistance creating force.


Please note that RR increases at a linear rate ... 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 etc.
While AR increases at a geometric rate ... 1 - 2 - 4 - 8 - 16 - 32 - 64 - 128 etc.

As speed increases, RR becomes an increasingly minimal factor-consideration.
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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 27, 2013 8:40 am

"What exactly is rolling resistance?

Rolling resistance is the energy that is lost when the tire is rolling and the main reason for loss of energy is the constant deformation of the tire. In addition to rolling resistance, there are also other resistances that have to be overcome when riding a bicycle.

Other resistance factors.

Air resistance rises squared with increased speed. At a straight-line speed of 20 km/h on the flat, air resistance is the main resistance force.

Energy is also required to accelerate. For instance, the weight of the wheels is of great importance when this mass has to be brought up to rotation.

When riding uphill, the main resisting force to overcome is the gradient resistance (descending force).

In addition to these, there are other friction resistances in the chain and all of the other moving parts. Yet in a well-serviced bicycle, these represent a very minor part of the total resistance.

Which factors affect rolling resistance?

Tire pressure, tire diameter, tire construction, tire tread and other factors all have an effect on rolling resistance. The higher the tire pressure, the less is tire deformation and thus the rolling resistance.

Small diameter tires have a higher rolling resistance at the same tire pressure, because tire deformation is proportionally more important, in other words the tire is "less round". Wider tires roll better than narrow ones. This assertion generally generates skepticism, nevertheless at the same tire pressure a narrow tire deflects more and so deforms more.

Obviously, tire construction also has an effect on rolling resistance. The less material is used, the less material there is to deform. And the more flexible the material is, such as the rubber compound, the less energy is lost through deformation.

Generally, smooth treads roll better than coarse treads. Tall lugs and wide gaps usually have a detrimental effect on rolling resistance.

Why do wide tires roll better than narrow ones?

The answer to this question lies in tire deflection. Each tire is flattened a little under load. This creates a flat contact area.

At the same tire pressure, a wide and a narrow tire have the same contact area. A wide tire is flattened over its width whereas a narrow tire has a slimmer but longer contact area.

The flattened area can be considered as a counterweight to tire rotation. Because of the longer flattened area of the narrow tire, the wheel loses more of its "roundness" and produces more deformation during rotation. However, in the wide tire, the radial length of the flattened area is shorter, making the tire "rounder" and so it rolls better.

Image

Why do Pros ride narrow tires if wide tires roll better?

Wide tires only roll better at the same inflation pressure, but narrow tires can be inflated to higher pressures than wide tires. However, they then obviously give a less comfortable ride. In addition to this, narrow tires have an advantage over wide ones at higher speeds, as they provide less air resistance.

Above all, a bicycle with narrow tires is much easier to accelerate because the rotating mass of the wheels is lower and the bicycle is much more agile. At constant speeds of around 20 km/h, the ride is better with wider tires. In practice, the energy saving is even greater than in theory as the elasticity of the tires absorbs road shocks, which would otherwise be transferred to the rider and so saves energy."

Source - Largely Quoted - http://www.schwalbetires.com/tech_info/ ... resistance
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Re: Rolling Resistance (RR) - Understanding Tires

Post by cwah » Oct 27, 2013 9:06 am

Interesting! I need flat tyre then
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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 27, 2013 9:43 am

Hypothetically ...
Since "tire deformation" is the primary RR factor ...
At some speed, centrifugal force should offset a goodly percentage of the tire deformation!
This affect should be most apparent in heavier tires, especially those with a substantial protective belting.

Many were surprised by this back in the 70's.
As a result of the introduction of steel belts in automobile tires ...
Most felt the extra weight might be a detriment to gas mileage.
Quite to the contrary, uses reported a noticeable mileage increase, especially at highway speeds!
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Re: Rolling Resistance (RR) - Understanding Tires

Post by Samd » Oct 27, 2013 6:54 pm

Great summary - and a good rule of thumb for when tyre choice really matters.

Some tyre manufacturers make the same tread pattern with different wall inclusions (such as Kevlar and Twaron) for a few dollars more.
Cheers.
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Re: Rolling Resistance (RR) - Understanding Tires

Post by davec » Oct 27, 2013 7:40 pm

someone should test these claims
i find it hard to believe- thin diameter are lighter and are def have lighter resistance than wider tires
this can be tested by putting different tires on a e-bike and seeing if theres a difference on the CA

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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 27, 2013 9:45 pm

Demonstration of different tire deformation.

ImageImage
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Re: Rolling Resistance (RR) - Understanding Tires

Post by dogman dan » Oct 28, 2013 8:47 am

I agree about the deformation.

If you have to push a truck across the yard, it's always much easier to push a truck with 90 psi tires that stay round, vs 32 psi tires that have a large flat spot at the contact patch. Even when the 90 psi truck is heavier, it's easier to push across the yard.

Why would it not be the same for a bike tire?

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Re: Rolling Resistance (RR) - Understanding Tires

Post by davec » Oct 28, 2013 8:49 am

interesting
so the wider tire is rounder - the skinnier is less round thus more rubber touching the pavement creating higher RR

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Re: Rolling Resistance (RR) - Understanding Tires

Post by gogo » Oct 28, 2013 9:25 am

davec wrote:interesting
so the wider tire is rounder - the skinnier is less round thus more rubber touching the pavement creating higher RR
Roughly, the area of the contact patch is proportional to the weight (normal force) it bears. There are upper and lower limits to this and there are designs that affect the shape of the patch and rolling resistance significantly. Computer aided design and testing has yielded advancement in every facet of human existence, and tires are no exception.
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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 28, 2013 9:48 am

davec wrote:interesting
so the wider tire is rounder - the skinnier is less round thus more rubber touching the pavement creating higher RR
Re-read the #2 post more carefully, more-less "round" refers to tire flat spot.

The "skinnier" tire, at the same tire pressure as the "fatter" tire, deforms (squashes) more, creating much more resistance.
It might be analogous to the extra energy required to climb a gradient.
All tires deform at road contact.
The greater the deformation = the steeper the gradient the bike must climb.
A 700c x 48 @ 85 psi might deform 2mm.
A 700c x 24 @ 85 psi might deform 4mm.
Or, fat tire bike climbing a 2 degree gradient vs a thin tire climbing a 4 degree gradient.

Not precise by any measure, but I'm hoping the idea come across.
Last edited by DrkAngel on Aug 17, 2015 5:43 am, edited 4 times in total.
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Re: Rolling Resistance (RR) - Understanding Tires

Post by davec » Oct 28, 2013 11:28 am

of course
however we put more PSI in skinnier tires to make up for this no?

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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 28, 2013 12:03 pm

davec wrote:of course
however we put more PSI in skinnier tires to make up for this no?
Yes ...
Try re-reading post #2. Why do Pros ride narrow tires if wide tires roll better?

The #2 post is fairly thorough about tire-rolling resistance, but also mentions all resistance factors.
All factors are considered and, reasonably well, explained.
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Re: Rolling Resistance (RR) - Understanding Tires

Post by MAGICPIE3FOCUSPOWER » Oct 28, 2013 1:11 pm

I like tires with deformation performance :mrgreen:
It gives me more grip :lol:
Nothing is perfect until I touch it...

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Re: Rolling Resistance (RR) - Understanding Tires

Post by gogo » Oct 28, 2013 1:49 pm

Energy is also required to accelerate. For instance, the weight of the wheels is of great importance when this mass has to be brought up to rotation. …
Above all, a bicycle with narrow tires is much easier to accelerate because the rotating mass of the wheels is lower and the bicycle is much more agile. At constant speeds of around 20 km/h, the ride is better with wider tires. In practice, the energy saving is even greater than in theory as the elasticity of the tires absorbs road shocks, which would otherwise be transferred to the rider and so saves energy."

Source - Largely Quoted - http://www.schwalbetires.com/tech_info/ ... resistance
Here's an interesting summation of the energies involved with the rotating mass on bicycles:
http://pardo.net/bike/pic/fail-027/index.html
Two questions:

Is it true that 1 gram of rotating weight is like 2 grams of frame weight?
Is the weight savings what riders feel when they switch to lighter tires or wheels?
No, on both counts. Now let's see why:
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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 28, 2013 2:51 pm

All tires are a compromise.
Low rolling resistance vs traction.
Size, tread pattern, pressure, "rubber" compound formulation etc, etc, etc.

At the one end might be solid smooth titanium tires ...
At the other might be bubble gum tires ...

Start with your most important factor ... ?
traction
low rolling resistance
durability
protection
comfort
cost
then choose the most acceptable, for you-your needs, from the remaining factors.

Remember going high on one factor will degrade other factors.
Last edited by DrkAngel on Nov 01, 2013 10:10 pm, edited 3 times in total.
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Re: Rolling Resistance (RR) - Understanding Tires

Post by arkmundi » Oct 28, 2013 3:16 pm

Hey thanks for the great summary. Interesting graphs. You however forgot the resistance of the peddler on an ebike to peddling, which of course would effect performance more than anything mentioned. :lol:

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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 29, 2013 8:19 am

arkmundi wrote:Hey thanks for the great summary. Interesting graphs. You however forgot the resistance of the peddler on an ebike to peddling, which of course would effect performance more than anything mentioned. :lol:
Now you are talking eaBike vs eBike!
Actually, above 30mph, substantial pedal assist on a mountain bike provides less speed than a race bike on motor alone.
A proper pedaling position and substantial effort might provide less speed than merely lowering your seat and crouching!

Image

See - Output watts for MPH

Also see - eaBike vs eBike vs eMotorcycle
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Re: Rolling Resistance (RR) - Understanding Tires

Post by davec » Oct 29, 2013 8:59 am

http://www.livestrong.com/article/91339 ... e-tires-vs./
http://www.exploratorium.edu/cycling/wheel3.html

these sources above seem to agree that on pavement- the thinner tires run faster and better than wider tire- but than again Schwalbe does not agree with these assesments
i dont believe the information above to be any true- just claims from Schwalbe
fat tire = more weight + more rubber hiting the pavement(higher RR) - there is a real reason pro's use thinner tires for races
again if i'm wrong than i'm wrong- but until there's conclusive unbiased testing done than these are simply claims to me.
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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 29, 2013 9:19 am

With an eBike or eaBike, rolling resistance becomes an increasingly minimal factor as speed increases.

Image

Justifiably, above ~20mph, traction and durability become the overwhelmingly most important factors ... for those more concerned about ... survival.

So, I personally, even though limited to ~30MPH, have opted for larger tires 1.90"x26" with a nice "compromise tread" and Kevlar belting.
I lucked into finding these tires that meet my requirement almost perfectly!
Image
Tread is a a nice compromise between the mountain bike tread and the smooth tires that came with the eZip.

26" x 1.90"
Pressure @65psi is acceptably "good".
"City/commuter sidewall protection."
"Kevlar reinforced for puncture resistance."
"Reflective sidewall."
The reflective stripe, though a cheap add-on (under close inspection), is a nice bonus.
Best of all ... CST Corporal Tire - 26 x 1.90, Black/Reflective - only $15.72 each.
This is great bicycle parts source w/free shipping on $100 order (USA only).
Sadly, they have not embraced eBikes ... yet.
Last edited by DrkAngel on Aug 03, 2014 9:05 am, edited 2 times in total.
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Re: Rolling Resistance (RR) - Understanding Tires

Post by Sancho's Horse » Oct 31, 2013 9:43 am

So, if that first graph is in kph, that would mean air resistence overtakes rolling resistence around 18kph or a paltry ~ 11 1/2 mph?

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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 31, 2013 10:18 am

Sancho's Horse wrote:So, if that first graph is in kph, that would mean air resistence overtakes rolling resistence around 18kph or a paltry ~ 11 1/2 mph?
DrkAngel wrote: An alternate source (Schwalbe) demonstrates the transition between rolling resistance and air resistance as the major energy robbing factor as speed increases.

Image "Speed" is in KPH.
I removed "Gradient" factor-lines.

As demonstrated, 18km/h looks to be the transition point of RR being surpassed by AR (Air Resistance) as the primary resistance creating force.

Please note that RR increases at a linear rate ... 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 etc.
While AR increases at a geometric rate ... 1 - 2 - 4 - 8 - 16 - 32 - 64 - 128 etc.

As speed increases, RR becomes an increasingly minimal factor-consideration.
Correct!
Schwalbe factors RR & AR transitioning at ~18km/h.
(Also interesting is that they graph Air Resistance below 10km/h as a ~0 factor.)
However, a vast multitude of other sources determine this transition as ~"somewhere below 20mph", or ~"wind resistance becomes a major factor near 20mph".

Although their testing is probably derived from the higher quality models of their tires, higher RR tires would transition closer to 20mph.
I have seen no better-more reliable charting of these 2 factors. ... ?
In fact this is the only graph I have seen that clearly separates these 2 resistance factors.

Any other sources?
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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Oct 31, 2013 11:04 am

Found another graph, specifically from a race bike .
It shows an even lower RR - AR resistance transition.
sheldonbrown_2.gif
sheldonbrown_2.gif (37.42 KiB) Viewed 3326 times
............ 50km\h = ~31mph .................
I like the inclusion of the Drivetrain Resistance line!
Last edited by DrkAngel on Nov 11, 2013 1:28 pm, edited 1 time in total.
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Re: Rolling Resistance (RR) - Understanding Tires

Post by Gregor » Oct 31, 2013 10:13 pm

The graphs are probably showing the RR effects with a 25 lb bike and a 170 lb rider. The total wt. on our rear axles alone may be 170+ lbs if you have a rear hub motor! The choice of a good tire (and the right psi) would make an efficiency difference of at least 10% in the speeds between 16 to 25 mph in my estimation (IMHO). One of my favorite tires is the Kenda Kiniption, it comes in a 26 (or 24)x 2.3" that takes 30 to 80 psi. Of course if you want to spend a little more, Schwalbe makes quite a few nice ones. Thanks for the graphs--makes you think about the range you can get if you get things just right.

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Re: Rolling Resistance (RR) - Understanding Tires

Post by DrkAngel » Nov 07, 2013 6:11 am

Might have just found my new - Best Bargain Tire!

Made by INNOVA for Schwinn
2.125" x 26" heavy! and it doesn't look too impressive ...
But!
Kevlar Belted!
40-65psi!
Price: $15.38 & FREE Shipping on orders over $35. (I bought 2 & $5 gloves to get free shipping)

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Tall ... with flat tread.
Perfect for my eTrike!
Last edited by DrkAngel on Nov 10, 2013 7:12 am, edited 3 times in total.
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