How many watts a crr difference of 0,0025 would mean?

[xptxc]

Hi all!

The reason of my question is because In order to improve my CDA measurements accuraçy, I would like to manually set crr to 0,0055 - as "advised" on FW400 owners manual.

But has 0,0055 wouldn`t be exactly my Victtoria Diamante Pro (clincher) drag - I would like to know if the 0,0025 of positive or negative error ( from the 0,003 to 0,008 possible "minimum" and "maximum" crr values) will mean a lot in terms of wattage error.

I race and wouldn`t like to use estimated values if they would give me a considerable amount of error on my files - but if being a negligible value, I would prefer to sacrifice it in order to get more reliable cda.

Thanks in advance!

[racerfern]

0.0025 is a tremendous change from 0.0055. You can take any of your existing rides and click on Tools > Tweak... and change the Crr to see the resultant power numbers change.

However if you KNOW the Crr of your setup then just punch it in. Keep in mind that it's not just tires. Rolling resistance of bearings can be significant and even tubes affect Crr. So, just because your tire has a lower rolling resistance doesn't mean thats the end of the calculations.

BTW, did you mean 0.00025? If so, that's just essentially insignificant.

[mds]

Power attributed to Crr at a particular speed can be easily estimated as 9.8 * weight(kilograms) * speed(meter/second) * Crr.

Examples:

Weight 90kg (198lbs), speed 8.8m/s (20mph), Crr = 0.0025: Power = 19watts
Weight 90kg (198lbs), speed 8.8m/s (20mph), Crr = 0.0055: Power = 43watts

[rruff]

But has 0,0055 wouldn`t be exactly my Victtoria Diamante Pro (clincher) drag - I would like to know if the 0,0025 of positive or negative error ( from the 0,003 to 0,008 possible "minimum" and "maximum" crr values) will mean a lot in terms of wattage error.

The real error you might expect is +-.001 and this will be due more to road roughness than anything else. Note that your *power* will not be in error this much, since if you set your Crr higher than reality, the calibration will create a CdA that is slightly lower than reality to compensate.

BTW... those are pretty good tires. A Crr of ~.005 would be a good guess, and even less if you use light tubes and your roads are smooth.

[xptxc]

Hi all,

thanks a lot for the replyes !

I´m going to still use the crr got from the coast downs till I have a value that I considerer reliable - after that value found, onwards I will set it manually.

Cheers!