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Old 06-03-2011, 06:43 PM   #1 (permalink)
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Rolling Resistance Crr / RRC for specific Tires

Based on the following sources I put together a small collection of specific tire Rolling resistance Crr / RRC values.

~165 so far in attached zipped excel sheet.

Does anyone know of additional good sources of more Crr / RRC to add to the listings?

178 page pdf


6 Page pdf

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File Type: zip SpecificTireCrr.zip (9.1 KB, 53 views)
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Old 06-03-2011, 06:48 PM   #2 (permalink)
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...we need similar information on the "new" crop of LRR tires now being marketed and sold!

...time for an "updated/revised" version of that 2006 document.
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Old 06-03-2011, 09:01 PM   #3 (permalink)
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I bought tires based on the original green seal report, and i think it steered me right. new tires got equal mileage to the old, worn oem tires,which i think is pretty good. i am having trouble making sense of any of the new stuff.
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Old 06-03-2011, 11:13 PM   #4 (permalink)
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Quote:
Originally Posted by IamIan View Post
Based on the following sources I put together a small collection of specific tire Rolling resistance Crr / RRC values.

~165 so far in attached zipped excel sheet.

Does anyone know of additional good sources of more Crr / RRC to add to the listings?
Perhaps:
Tire (tyre) surveys from the EU

Bob Wilson
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Old 06-04-2011, 06:55 AM   #5 (permalink)
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Quote:
Originally Posted by bwilson4web View Post
Thanks ... although I wish they all used Crr , most of those seem to use their own in house rating system ... I updated them into the spreadsheet for what information is there... what is missing I left blank.

Another two I found from the CEC unfortunately do the same kind of thing and don't list the tire load they used to determine the RRF [ Rolling Resistance Force ] ( Rolling Resistance Coefficient = RRF / Tire Load ) ... without knowing what the test load was ... it can be used to rank those tires but as it isn't a general standard like Crr it doesn't track to compare against other Rolling Resistance test results. ... but I also updated those into the spreadsheet as well.

New list now has over 300 test results listed.

CEC 2 page .doc 265

CEC 3 page .doc 195
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Old 06-05-2011, 03:22 AM   #6 (permalink)
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How do you convert to rolling resistance?

Hello
The basic formula for the force required to travel at a particular speed is dragCoefficient*frontalArea*airDensityConstant*spe ed^2 + rollingResistance(CRR)*mass*speed. This rolling resistance (CRR) is different to the tire rolling resistance. It includes calculations relating to both the tire resistance and the road surface resistance.
A polished concrete road (at 0.012) has much less resistance than a dirt road (at 0.1) and sand at (0.15 to 0.35) is much higher again.
Can anyone advise how is CRR calculated from the tire rolling resistance and the surface rolling resistance?
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Old 06-05-2011, 10:57 AM   #7 (permalink)
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Quote:
Originally Posted by thorpie View Post
Can anyone advise how is CRR calculated from the tire rolling resistance and the surface rolling resistance?
The Crr = RRC given from the SAE J1269 tests already includes the road surface contribution.

The RRF given from those tests already includes the road surface contribution... RRC = RRF / Load.

The tests measure the total counter force , thus they already include all sources of counter force.

I do not know of a simple conversion to accurately convert the given numbers to other road surfaces that are different from the road surface used in the testing ... you could assume it will just be the same ratio as some other test using the same tire on different surfaces ... but , I am not sure how accurate that assumption will be.
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Old 06-05-2011, 01:58 PM   #8 (permalink)
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Now here is a problem I'm facing:
  • How to separate transaxle losses from tire losses?
All power from the engine passes through the transaxle before reaching the tires. A Prius transaxle has two active elements, MG1 and MG2, which have (I**2)R losses. But we also know there is stirring and friction losses. Unfortunately, I can't use temperature change to quantify the stirring and friction losses because of MG1 and MG2. I do have an indirect measurement of friction losses from the oil test results. But the real challenge is how to separate tire rolling resistance from the transaxle effects.

Now I could replicate the work of Battelle Labs in their transaxle testing but that is involved. In particular, I have to 'lock up' the PSD (power split device) to get power to flow through the transaxle but then I'm not measuring PSD losses. This is not a trivial problem.

We can get a usable rolling friction metric by using a roll-down test. The tire and friction losses should be fairly independent of speed. But viscosity losses are exponential with speed and these are the ones that have tickled my curiosity.

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Old 06-05-2011, 10:12 PM   #9 (permalink)
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Quote:
Originally Posted by bwilson4web View Post
How to separate transaxle losses from tire losses?
hmm, what about, and i know this is a lot of work, what about removing the halfshafts and then measuring rolling resistance?
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Old 06-06-2011, 08:55 PM   #10 (permalink)
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Quote:
Originally Posted by bwilson4web View Post
Unfortunately, I can't use temperature change to quantify the stirring and friction losses because of MG1 and MG2.
Why not?

Say you're in EV-Mode.
You have
Power flow MG1
Power flow MG2
Trans-axle losses
Combined those are your heat sources to deviate from ambient.

The source of MG1+MG2 heat contribution is their power flow and their efficiency map... which as I recall that motor efficiency map has been done.

If you quantify the contribution from MG1 + MG2 what dT is left is from the trans-axle itself.

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