Calculating Tire Pressure question?

Werehatrack said:

Tom Nakashima said:

Got into another discussion with my friend about tire pressure on a

road

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bike. I've been putting in 100-105psi equal amounts in both the

front and

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rear tire just from trial and error and what feels good over the

years. My

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friend rides the same tires as I, but puts more in the rear

110-115psi and

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100psi in the front, unequal amounts. Says I should do the same

because

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there is more weight loaded in the rear than in the front, and he

also

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claims my bike would handle better. He's a bit heavier than I am

by about

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10 lbs. Is there a way to calculate correct tire pressure for each

front

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and rear tire due to riders weight and load distribution?

IMO, "correct" tire pressures are a matter of experience, not
calculation. Like many other facets of bike tuning, math can provide
the starting point for finding the right setup, but the *rider's own
judgment* is the best final arbiter. You know what works for you; I
would not advise letting someone else's slavish devotion to

numerology

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override your own collected observations.

- Why? I see no reason not to trust the math, assuming that one has
correctly identified one's goals and the math was performed
correctly.
Better still to use measurement where possible (difficult off the
track).
- Motorsports have shown that setup is all-important, and that a
stopwatch
is a better indication of correct tire pressure that seat-of-pants.
- Folks' abilities vary widely. The OP apparently does not have as
much
faith in his ability to detect small changes as you.

But first, the question must be asked, what is the goal, no? Is the
goal
neutral handling? Race cars, for example, are set up to understeer, so
they'll handle closer to neutral when braking hard while turning.

If neutral handling is desired, then equal size contact patches are
not,
eh, since there is more weight on the rear?

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If neutral handling is desired, then equal size contact patches are
not,
eh, since there is more weight on the rear?

When? In braking or downhill, there's more on the front. Sometimes
it's equal. Sometimes it's rear-biased. The distribution of load is
dynamic; the tire pressure is *not*. Anything that tries to determine
the "correct" pressure is an approximation, and I seriously doubt that
it's as critical for a non-racer as the OP's "adviser" had implied. I
smell a tweak-snob; one more interested in his own definition of
"correct" than in just getting on the bike and down the road.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Werehatrack said:

Quoted message said:

If neutral handling is desired, then equal size contact patches are
not,
eh, since there is more weight on the rear?

When? In braking or downhill, there's more on the front. Sometimes
it's equal. Sometimes it's rear-biased. The distribution of load is
dynamic; the tire pressure is *not*.

This proves my point - you must first ask yourself what you are
trying to achieve. During what conditions is part of that.

Anything that tries to determine

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the "correct" pressure is an approximation, and I seriously doubt

that

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it's as critical for a non-racer as the OP's "adviser" had implied.

I

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smell a tweak-snob; one more interested in his own definition of
"correct" than in just getting on the bike and down the road.

I don't see any reason not to ponder interesting questions here
even if the answers are more acedemic than practical.

Now, pointing your seat one degree to the right because your left
nut hangs lower, that's the sign of a tweak snob.

dkl

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Werehatrack said:

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If neutral handling is desired, then equal size contact patches are
not,
eh, since there is more weight on the rear?

When? In braking or downhill, there's more on the front. Sometimes
it's equal. Sometimes it's rear-biased. The distribution of load is
dynamic; the tire pressure is *not*.

This proves my point - you must first ask yourself what you are
trying to achieve. During what conditions is part of that.

Anything that tries to determine

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the "correct" pressure is an approximation, and I seriously doubt

that

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it's as critical for a non-racer as the OP's "adviser" had implied.

I

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smell a tweak-snob; one more interested in his own definition of
"correct" than in just getting on the bike and down the road.

I don't see any reason not to ponder interesting questions here
even if the answers are more acedemic than practical.

Now, pointing your seat one degree to the right because your left
nut hangs lower, that's the sign of a tweak snob.

Or a Scotsman who rides Regimental, since riding shorts tend to
preclude dangle.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Werehatrack said:

Quoted message said:

Now, pointing your seat one degree to the right because
your left nut hangs lower, that's the sign of a tweak snob.

Or a Scotsman who rides Regimental, since riding shorts
tend to preclude dangle.

Sounds like there's a limerick in the making there, Laddie.

--
"There once was a Scotsman who rode Regimental
..."