Rick Onanian writes:
>>> Your paved-drum/leaned-bike experiment sounds like a reasonable,
>>> if imperfect, test method for fictional roads made of perfectly
>>> clean and perfectly flat pavement. I rarely find roads like that,
>>> and when I do, the new-pavement fumes make riding somewhat
>>> unpleasant.
>> Maybe you can explain what is "imperfect about this test.
> The shape of the contact patch is different; the tire must conform
> to the drum's convex shape. Further, it sure sounds like a perfect
> surface, unlike a road surface, which is rarely so.
I think you'll find that a six foot diameter is adequate to
approximate a road for test purposes, considering the contact patch
length of a normally inflated tire. Besides, this is a comparative
test and the values it produced are repeatable and close enough from
road values for side slip that one cannot readily see a difference.
What is it that the drum diameter obscures?
>>>> I have experienced such slips often and even done so crossing
>>>> smooth paint stripes in the rain, but I don't attribute those
>>>> incidents to the tire but rather to sand on the road or a slick
>>>> wet spot. We ARE talking about handling ability of one tire over
>>>> another.
>>> Yes, but what good is it to know the handling ability on perfect
>>> pavement when we don't ride on such surfaces? We ride on roads
>>> with a bit of sand or a slick wet spot. Knowing the handling
>>> ability of a tire for such conditions is immensely more useful.
>> Let's not get into philosophy.
> What philosophy? I ride on real roads, with imperfect pavement,
> sometimes with sand or a slick wet spot. If a tire can't give a
> little and let me know before I suddenly find it airborne (and my
> body grounded), I want the BEST handling tire I can get.
Perfection is philosophical. Besides, if you cannot control the test
conditions you cannot perform the test. What you are suggesting is
that such tests cannot be performed because roads vary too much. Such
tests are performed on standardized conditions that give typical best
values. The user must estimate what degraded conditions he is
encountering that will give poorer results, such as loose gravel, oil,
slick spots and the like.
>> You claim to have slid tires on clean dry pavement and I said that
>> is not a recoverable condition so it
> I claim to have slid tires on real pavement. I doubt it was
> perfectly clean, and I doubt it was perfectly flat, although I
> didn't feel bumps.
Lets get away for your definition of "real pavement" and use pavement
like that in the picture I attached:
http://tinyurl.com/2gbsj
I think that is real enough and Pescadero Road has a few of these
curves with "real" pavement at about 40mph.
I'm sure you didn't slip in a curve when banked over at near 45
degrees because that is unrecoverable. What were the circumstances
and what was the speed.
>> cannot be the criterion for handling among different tires. We
>> generally don't ride beyond the limit of traction so the criterion
>> must be something else. I'm trying to get to the bottom of how you can
>> give comparative ratings to tires of similar size, inflation and
>> essentially smooth tread.
> I don't know how it can be done. IANAE. Something more realistic
> than a paved drum may be in order.
Again, what is it about a drum that you find deficient? It is the
common way tires are laboratory tested.
>>> Well, then we're not talking about a lot of precision here. Wheel
>>> imbalance can bounce a bike up and down in my hand at >20mph; that
>>> lifting/weighting force must affect the tire's load (and therefore,
>>> contact patch) each revolution.
>> I doubt that.
> Which part do you doubt? That the wheel can bounce the hand-held
> bike at >20mph, or that such a force must affect the tire's
> connection to the road?
Both. As I have explained at length.
> The first part can be tested by holding the rear of the bike a foot
> off the ground, and using the other hand to pedal it up as fast as
> you can. Mine provides a definite up-and-down motion, which I
> experimentally corrected by balancing the wheel.
THAT is an unrealistic test.
>> Having descended at more than 50mph often without having balanced
>> wheels, I have not felt so much as a hint of imbalance from my
>> conventional wheels that are not balanced. Besides that, as I
> I've never passed 45mph, but even at that speed, I either did not
> feel imbalance or wouldn't know it from road vibration.
>>> A rider can tell if he got through his favorite curve (which has
>>> real-world pavement) at a higher speed without any traction
>>> reduction.
>> Yes? How do you determine "traction reduction". This is what is
>> at the root of this subject and I propose that you cannot sense
>> this without exceeding the limit and crashing. Therefore, claiming
>> that one tire handles better than another is an undefined
>> subjective claim.
> I don't know how you determine it. I agree that such a claim would
> be subjective.
I know what it is and have crashed as well as having measured it the
test equipment I have described. I don't think you have the
information to make the suppositions you do.
>> I repeat, you didn't slip on clean dry pavement. I don't claim that
>> you didn't slip but it was for some reason other than traction
>> limitation of the tire. It was more likely some foreign object on the
>> road or a spot of some lubricant.
> Like I said, real world road. Not a testing machine in a lab. I
> can't imagine how it could be tested.
Are you implying that the scene in the attached URL is not real world.
I ride around that curve in that manner often as I do with many other
curves. I also have piles of tires I have worn to the cords as well
as rims on which they served. There are a lot of test miles
accumulated.
I think you need to get out of your "real world" pavement and get to
reality.
Jobst Brandt
[email protected]
