I never said that. Total rubbish is correct.
This statement from you... "The most accurate measurement is comparisons of radius from axle centre to the ground at pressure and rider weight
Yes that statement above totally implies... the Static radius of a tyre measured to the ground of a stationary bike, is exactly the same radius to the ground, as a bike at speed... which is total rubbish
How can it be the most accurate measurement with the radius constantly changing as the tyre deforms. Yes total Rubbish...
According to what empirical data?
Your above quote was quoting my statement "The radius of a tyre will change from deformation to the road during use a fair amount, but the change in overall circumference length of a tyre would be totally negligible in comparison...
With the tyre deformed to the road, the overall circumference length will be the same
The more a tyre deforms (there is more tyre in contact with the road) and the less a tyre deforms (there is less tyre in contact with the road). The measured circumference is the most accurate measurement, the measured radius would be all over the place as the tyre deforms, plus it's impossible to measure with the bike in motion...
Obviously you wouldn't be riding on a tyre which is way under inflated.
Eg... (190/55) circumference of 2013.13mm with a radius of 320.4mm
If the tyre deforms 20mm into the road surface, it would reduce the radius to 300.4mm.
The new circumference is now 1887.46mm, a full 125.66mm shorter... That's massive!!!...
The 125.66mm doesn't just disappear from the circumference of the tyre into thin air, it's still there...
Not if the tire compresses at the contact patch or if the tire actually expands at a certain speed.
Your above quote was quoting my statement "With the tyre deformed to the road, the overall circumference length will be the same. This is the reason why gearing calculations use the overall circumference of a tyre... For each wheel revolution, the tyre will travel the overall circumference length across the ground.
You can't measure tyre deformation/expansion from the radius to the ground with the bike in motion, it's constantly changing and is useless for gearing calculations as shown calculated above...
2 rims, maybe? Or how about removing one and measuring the next once mounted, then start crunching gearing numbers, then make adjustments?
Your above quote was quoting my statement "The 2 tyre sizes in question from the OP was a (190/50) and his (190/55) which he currently has fitted.
How is he meant to measure a tyre he doesn't have fitted!!! ??? (190/50)...... to compare the difference in gearing with his larger circumference (190/55)... He can't...
You said previously "but OP wanted to pick flyshit out of pepper. .
You implied above comparing the two different sizes using "that number
" ie (the aspect ration on the side of the tyre) to calculate the circumference is a waste of time...
You also said "The most accurate measurement is comparisons of radius from axle centre to the ground at pressure and rider weight.
You also siad "The only thing that number tells you is that the tire is taller or shorter than another within the tire line
". No the aspect ratio tells you the exact tyre height, as a direct percentage from the tyre width.
You can't measure a tyre you don't have, using the calculated norminal circumference of the two different sizes tyres, is a quick/easy and accurate way, while excluding tyre deformation / expansion out of the equation, which is totally impossible to measure anyway.
Your above quote was quoting my statement"The whole Crux of the OP's question was comparing the effect to the gearing from the two sizes (190/50) and (190/55)...
Just measuring his currently fitted (190/55) won't tell him Squat about the comparison effect of the (190/50)!!!......
To quote you again"The most accurate measurement is comparisons of radius from axle centre to the ground at pressure and rider weight.
, how does he measure a tyre he hasn't got fitted......
It's so easy and accurate to just calculate the difference in nominal tyre circumference from the different aspect ratio between the two sizes (190/50) & (190/55), which at the same time excludes all the stuff that is impossible to measure anyway...
My whole goddamned first post highlighted the absurdity of picking flyshit out of pepper without exact data for a street bike. Matching exact gearing of a streetbike going from a worn 50 to a new 55 profile? To which decimal point shall we measure the gear ratio, sir? Don't like your gearing? Change it. Still don't? Change it again. Hauling out the J-blocks to calibrate your caliper for a new tire measurement is silly.
The OP question was spot on IMO... You still say it's "picking flyshit out of pepper without exact data for a street bike
" Believe whatever you like...
It's simple as this... you use the two different tyre sizes (190/50) & (190/55) to accurately calculate the nominal tyre circumference's from their respective aspect ratio's and set them as constants... By doing this, it excludes all the stuff that's impossible to calculate. (ie excluding drive line loses thru gear mesh, tyre slip on the road, and tyre size variation from wear / temperature / tyre deflection etc in the perfect world...")
Then you can work out the direct effect the gearing changes alone... will have on the two different set constant nominal tyre circumference's of the (190/50) and (190/55).
Then you can directly compare the data to your own bike, and your'll be able to make a very well informed decision, instead of just chucking random size sprockets on it, stabbing in the dark...
That's the way I would do it.
You can do it which ever way you please.