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Old 10-26-2016, 08:33 PM   #1
RidingOnRailz
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Cool Bias Ply T & F!

True or false:


1. Bias-ply tires in general handle inferior to radials.


2. Bias-ply tires require more toe - specifically toe-in -
to handle more predictably.


3. As opposed to radial tires, bias-ply tires require
negative caster for straight-line stability.


4. Bias-plies give more warning that they are about
to break loose in a high-G turn than do radials.
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Old 10-27-2016, 08:40 AM   #2
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Re: Bias Ply T & F!

Quote:
Originally Posted by RidingOnRailz View Post
True or false:

1. Bias-ply tires in general handle inferior to radials.
True, but if we say "all other things being equal", it's a mixed bag. Please be aware that the definition of "handling" is not the same as traction or grip. Handling means the "feel" - AND - if the tires are otherwise the same, a bias tire has a softer transition at the peak traction point.

Quote:
Originally Posted by RidingOnRailz View Post
2. Bias-ply tires require more toe - specifically toe-in - to handle more predictably.
False. Toe-in is not the thing that determines how predicable the handling is - except to say that toe-out leads to a more unpredictable condition.

Quote:
Originally Posted by RidingOnRailz View Post
3. As opposed to radial tires, bias-ply tires require negative caster for straight-line stability.
I think vehicles need negative caster for straight line stability regardless of the type of tire.

Quote:
Originally Posted by RidingOnRailz View Post
4. Bias-plies give more warning that they are about to break loose in a high-G turn than do radials.
True, but that particular property has been dialed out of modern radial tires, so it isn't as true as it once was.
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Old 10-28-2016, 04:58 AM   #3
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Cool Re: Bias Ply T & F!

Quote:
Originally Posted by CapriRacer View Post
True, but if we say "all other things being equal", it's a mixed bag. Please be aware that the definition of "handling" is not the same as traction or grip. Handling means the "feel" - AND - if the tires are otherwise the same, a bias tire has a softer transition at the peak traction point.



False. Toe-in is not the thing that determines how predicable the handling is - except to say that toe-out leads to a more unpredictable condition.



I think vehicles need negative caster for straight line stability regardless of the type of tire.



True, but that particular property has been dialed out of modern radial tires, so it isn't as true as it once was.

Ok. #2. was based on my readings that,
given the same vehicle, putting bias-ply
tires on a car with alignment specs for
radials resulted in a white-knuckle driving
experience. The writer stated that on his
car at least, radials needed very little toe in,
but the bias plies needed at least 1/6" toe
in to achieve the same feel.


#3. Do you know which caster is which?
Negative = axis leaning forward(toward front
of vehicle), and Positive = axis leaning
backward. For the last 40 years, at least,
the vast majority of vehicles have called for
POSITIVE caster(from half a degree up to
seven degrees depending upon purpose
of vehicle). For reasons I never quite
understood, a lot of cars from 1960s and
earlier speced negative 1-2 deg caster,
and they were from the bias ply era.
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Old 10-28-2016, 08:32 AM   #4
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Re: Bias Ply T & F!

Quote:
Originally Posted by RidingOnRailz View Post
Ok. #2. was based on my readings that,
given the same vehicle, putting bias-ply
tires on a car with alignment specs for
radials resulted in a white-knuckle driving
experience. The writer stated that on his
car at least, radials needed very little toe in,
but the bias plies needed at least 1/6" toe
in to achieve the same feel.
There is quite a bit of variation between tires and what you described sounds like you are dealing with some of the extremes. And while it is true that radials are generally more sensitive to toe-in, this property can be changed with some simple changes in tire construction, so it is highly dependent on what 2 tires are being compared.

Quote:
Originally Posted by RidingOnRailz View Post
#3. Do you know which caster is which?
Negative = axis leaning forward(toward front
of vehicle), and Positive = axis leaning
backward. For the last 40 years, at least,
the vast majority of vehicles have called for
POSITIVE caster(from half a degree up to
seven degrees depending upon purpose
of vehicle). For reasons I never quite
understood, a lot of cars from 1960s and
earlier speced negative 1-2 deg caster,
and they were from the bias ply era.
Oops! I always get that backwards. Yes, it is positive caster that adds stability. I, too, have wondered why some vehicles spec'd negative caster - but I also noticed that they changed to positive caster before they changed to radials. If there was such a fundamental difference between bias and radials (and there are!), why wasn't this a change made EXACTLY when the changeover took place? I suspect it has more to do with how sloppy the suspensions were (maybe I should use the term imprecise here!) I know it was somewhere in the 1960's when Calspan started measuring the forces on tires and maybe that influenced the car makers and their suspension settings - instead of going by the feel of a test driver.
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Old 10-28-2016, 10:09 AM   #5
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Cool Re: Bias Ply T & F!

Quote:
Originally Posted by CapriRacer View Post
There is quite a bit of variation between tires and what you described sounds like you are dealing with some of the extremes. And while it is true that radials are generally more sensitive to toe-in, this property can be changed with some simple changes in tire construction, so it is highly dependent on what 2 tires are being compared.



Oops! I always get that backwards. Yes, it is positive caster that adds stability. I, too, have wondered why some vehicles spec'd negative caster - but I also noticed that they changed to positive caster before they changed to radials. If there was such a fundamental difference between bias and radials (and there are!), why wasn't this a change made EXACTLY when the changeover took place? I suspect it has more to do with how sloppy the suspensions were (maybe I should use the term imprecise here!) I know it was somewhere in the 1960's when Calspan started measuring the forces on tires and maybe that influenced the car makers and their suspension settings - instead of going by the feel of a test driver.

On Toe-in: It's not that the radials were more
sensitive to toe-in, it's that they probably tracked
straighter and were just as stable with less. The
amount of toe-in required for stability with bias
tires would probably cause premature wear on the
radials.


On Caster: I suspect the way the bias-ply tires
'gave' under dynamic stresses and weight was
different than how radials give, so negative caster
provided directional stability to them, as opposed
to simple trail caster(positive) used with radials.

I don't know the specifics on that, perhaps someone
with more engineering prowess could contribute.


All I'm trying to suggest here is that millions of
everyday people - not race car drivers - drove on bias
ply tires from before one war to well after another,
safely, without having to 'saw' the steering wheel back
and forth - just a movie and TV trope used to indicate
driving and being in motion while in the safety of a
sound stage, with a giant projection of a highway
behind it. And aligning properly for bias-ply tires, I.E.
negative instead of positive caster, and different toe
settings than we might spec today, were part of that.
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