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]