Wet road, lower pressure?

Andrew Price said:

Watching the club criterium last weekend; rain had stopped but road
was still wet but they held it anyway (probably Not A Good Idea) -
in 10 laps there were about 6 flats and someone remarked that if you
dropped tyre pressure say 10/20 lbs the chance of a flat was reduced
on a road which was clearly giving up its glass fragments in the
wet.

Quoted message said:

True or false, and does it compromise the handling/stability to
reduce tyre pressures in the wet?

If you are aware how easily a wet sharp object can penetrate a tire,
you would have no doubt. I was made aware of this in HS chemistry
class where we made (Florence flask) wash bottles with a two hole
stopper and a glass siphon and blow tube that had a latex rubber
supported aiming nozzle. Cutting the 1/4 inch latex tube with a dry
razor blade was impossible but when wet it sliced like "warm butter."

The same is true for shards of glass upended by the front tire or the
rear tire of the rider ahead. However, glass that has been in a
traveled lane is usually no hazard because car tires break off all the
sharp edges. To the bicyclist there is no visual difference but just
knowing that it has been run over is important.

Jobst Brandt

Quoted message said:

Andrew Price said:

Watching the club criterium last weekend; rain had stopped but road
was still wet but they held it anyway (probably Not A Good Idea) -
in 10 laps there were about 6 flats and someone remarked that if you
dropped tyre pressure say 10/20 lbs the chance of a flat was reduced
on a road which was clearly giving up its glass fragments in the
wet.

Quoted message said:

True or false, and does it compromise the handling/stability to
reduce tyre pressures in the wet?

If you are aware how easily a wet sharp object can penetrate a tire,
you would have no doubt. I was made aware of this in HS chemistry
class where we made (Florence flask) wash bottles with a two hole
stopper and a glass siphon and blow tube that had a latex rubber
supported aiming nozzle. Cutting the 1/4 inch latex tube with a dry
razor blade was impossible but when wet it sliced like "warm butter."

The same is true for shards of glass upended by the front tire or the
rear tire of the rider ahead. However, glass that has been in a
traveled lane is usually no hazard because car tires break off all the
sharp edges. To the bicyclist there is no visual difference but just
knowing that it has been run over is important.

Jobst Brandt

I couldn't really tell if you answered the question or not. Could you
clarify your position?
--
Phil, Squid-in-Training

In the dry I use 7 bar front 8.5 bar in the rear. When the road is wet the front tyre struggles for grip so I lower it to 6 bar and then it is more balanced. I also lower the rear as the brakes work better when it has 8 bar in the rear in the wet.

If the introductory paragraph, 'Watching the club...', is the premise to the
question, 'True or false,...', then I think he was pointing out the falsity
of the premise. Water is the preferred lubricant for cutting rubber. Cut
rubber has little to do with the purported effect of pressure on traction.

(Top and bottom posted)

"Phil, Squid-in-Training" <[email hidden]> wrote in
message news:Kijcf.1637$Xj5.1018@dukeread02...

Quoted message said:

Quoted message said:

Andrew Price said:

Watching the club criterium last weekend; rain had stopped but road
was still wet but they held it anyway (probably Not A Good Idea) -
in 10 laps there were about 6 flats and someone remarked that if you
dropped tyre pressure say 10/20 lbs the chance of a flat was reduced
on a road which was clearly giving up its glass fragments in the
wet.

Quoted message said:

True or false, and does it compromise the handling/stability to
reduce tyre pressures in the wet?

If you are aware how easily a wet sharp object can penetrate a tire,
you would have no doubt. I was made aware of this in HS chemistry
class where we made (Florence flask) wash bottles with a two hole
stopper and a glass siphon and blow tube that had a latex rubber
supported aiming nozzle. Cutting the 1/4 inch latex tube with a dry
razor blade was impossible but when wet it sliced like "warm butter."

The same is true for shards of glass upended by the front tire or the
rear tire of the rider ahead. However, glass that has been in a
traveled lane is usually no hazard because car tires break off all the
sharp edges. To the bicyclist there is no visual difference but just
knowing that it has been run over is important.

Jobst Brandt

I couldn't really tell if you answered the question or not. Could you
clarify your position?
--
Phil, Squid-in-Training

If the introductory paragraph, 'Watching the club...', is the premise to the
question, 'True or false,...', then I think he was pointing out the falsity
of the premise. Water is the preferred lubricant for cutting rubber. Cut
rubber has little to do with the purported effect of pressure on traction.

MichaelB said:

In the dry I use 7 bar front 8.5 bar in the rear. When the road is wet
the front tyre struggles for grip so I lower it to 6 bar and then it is
more balanced. I also lower the rear as the brakes work better when it
has 8 bar in the rear in the wet.

At the risk of inciting a religious debate :-) wouldn't this increase
the tendency of the tire to hydroplane in wet conditions?

I know that given the size of the contact patch and the loading of the
wheel, it's almost impossible for a bike tire to hydroplane, but if you
lower the tire pressure and thus increase the size of the contact patch,
wouldn't hydroplaning be more likely to occur?

Don said:

MichaelB said:

In the dry I use 7 bar front 8.5 bar in the rear. When the road is wet
the front tyre struggles for grip so I lower it to 6 bar and then it is
more balanced. I also lower the rear as the brakes work better when it
has 8 bar in the rear in the wet.

At the risk of inciting a religious debate :-) wouldn't this increase
the tendency of the tire to hydroplane in wet conditions?

I know that given the size of the contact patch and the loading of the
wheel, it's almost impossible for a bike tire to hydroplane, but if you
lower the tire pressure and thus increase the size of the contact patch,
wouldn't hydroplaning be more likely to occur?

Not starting a religious debate at all, hydroplaning doesn't happen on
a bike (see http://sheldonbrown.com/gloss_ho-z.html#hydroplaning)

Bryan

Phil Lee said:

Quoted message said:

Quoted message said:

Watching the club criterium last weekend; rain had stopped but
road was still wet but they held it anyway (probably Not A Good
Idea) - in 10 laps there were about 6 flats and someone remarked
that if you dropped tyre pressure say 10/20 lbs the chance of a
flat was reduced on a road which was clearly giving up its glass
fragments in the wet.

Quoted message said:

Quoted message said:

Quoted message said:

True or false, and does it compromise the handling/stability to
reduce tyre pressures in the wet?

Quoted message said:

Quoted message said:

If you are aware how easily a wet sharp object can penetrate a
tire, you would have no doubt. I was made aware of this in HS
chemistry class where we made (Florence flask) wash bottles with a
two hole stopper and a glass siphon and blow tube that had a latex
rubber supported aiming nozzle. Cutting the 1/4 inch latex tube
with a dry razor blade was impossible but when wet it sliced like
"warm butter."

Quoted message said:

Quoted message said:

The same is true for shards of glass upended by the front tire or
the rear tire of the rider ahead. However, glass that has been in
a traveled lane is usually no hazard because car tires break off
all the sharp edges. To the bicyclist there is no visual
difference but just knowing that it has been run over is important.

Quoted message said:

I couldn't really tell if you answered the question or not. Could you
clarify your position?

Even at slightly lowered inflation pressure a water lubricated piece
of glass will penetrate without perceptible difference. Contact
pressure with the road is not moved out of the range of force that
causes a sharp object to penetrate. Consider what 50psi means to a
sharp piece of glass pressed into a wet tire and then what difference
that makes to doing it with 100psi. Both are far above the force
required to cut until the object is flush with the tire surface.

Jobst Brandt

Don who? said:

Quoted message said:

In the dry I use 7 bar front 8.5 bar in the rear. When the road is
wet the front tyre struggles for grip so I lower it to 6 bar and
then it is more balanced. I also lower the rear as the brakes work
better when it has 8 bar in the rear in the wet.

Quoted message said:

At the risk of inciting a religious debate :-) wouldn't this
increase the tendency of the tire to hydroplane in wet conditions?

That is definitely risky considering how often this has been brought up.

Quoted message said:

I know that given the size of the contact patch and the loading of
the wheel, it's almost impossible for a bike tire to hydroplane, but
if you lower the tire pressure and thus increase the size of the
contact patch, wouldn't hydroplaning be more likely to occur?

http://www.sheldonbrown.com/brandt/slicks.html

Jobst Brandt

"Andrew Price" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Watching the club criterium last weekend; rain had stopped but road was
still wet but they held it anyway (probably Not A Good Idea) - in 10 laps
there were about 6 flats and someone remarked that if you dropped tyre
pressure say 10/20 lbs the chance of a flat was reduced on a road which

was

Quoted message said:

clearly giving up its glass fragments in the wet.

True or false, and does it compromise the handling/stability to reduce

tyre

Quoted message said:

pressures in the wet?

regards, Andrew

I used to do a lot of wet riding- lower pressures are very important to help
maintain stability in the wet. A harder wheel will more likely slip out
under you in a slippery corner. My experience is that there are much more
flats in the wet, part of this is that it is harder to see bits of glass
that you might otherwise avoid, but also those bits will stick to your wet
tire increasing the chance of eventual puncture.

Laz

quote='yorky'Don said:

MichaelB said:

In the dry I use 7 bar front 8.5 bar in the rear. When the road is wet
the front tyre struggles for grip so I lower it to 6 bar and then it is
more balanced. I also lower the rear as the brakes work better when it
has 8 bar in the rear in the wet.

At the risk of inciting a religious debate :-) wouldn't this increase
the tendency of the tire to hydroplane in wet conditions?

I know that given the size of the contact patch and the loading of the
wheel, it's almost impossible for a bike tire to hydroplane, but if you
lower the tire pressure and thus increase the size of the contact patch,
wouldn't hydroplaning be more likely to occur?

Not starting a religious debate at all, hydroplaning doesn't happen on
a bike (see http://sheldonbrown.com/gloss_ho-z.html#hydroplaning)

Bryan[/QUOTE]

I'm just quoting what I have experienced. If my front wheel is too hard the bike doesn't turn in to a corner very well. Similarly it is much easier to feel when the rear is going to lock with a bit less air in it.

'quoting an experience', i'zat like citing an anecdote? Pretty useless

"MichaelB" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Quoted message said:

I'm just quoting what I have experienced. If my front wheel is too
hard the bike doesn't turn in to a corner very well. Similarly it is
much easier to feel when the rear is going to lock with a bit less air
in it.

[quote="Doug Huffman"]'quoting an experience', i'zat like citing an anecdote? Pretty useless

/[QUOTE]

The handbag is out! Making such a statement is also pretty useless so why dont you say something more usefull yourself!

Take it from me lower tyres pressures in the front may not ultimately give you much more grip but for all intents and purposes you will get a bike that turns in to a corner much better in the wet. We soften the suspension on our race cars when it rains because it makes the car less sensitive to steering input and small changes in grip and effectively cures understeer. With a bike you only have the tyre so softening this has a similar effect.

Quoting an experience like this is quite usefull actually because when it rains I test my bike and I always find more confidence with a softer front tyre. How else are you going to learn without using past experience Mr Smarty Pants 😉 ?

Andrew Price said:

Watching the club criterium last weekend; rain had stopped but road was
still wet but they held it anyway (probably Not A Good Idea) - in 10 laps
there were about 6 flats and someone remarked that if you dropped tyre
pressure say 10/20 lbs the chance of a flat was reduced on a road which was
clearly giving up its glass fragments in the wet.

True or false, and does it compromise the handling/stability to reduce tyre
pressures in the wet?

Wet sharp things will puncture the tire more easily than dry sharp
things, as noted elsewhere. Lowering the tire pressure will increase
the chances of a snakebite flat, but will not make much (if any)
difference in tire punctures relative to running at a higher pressure.

As for traction in the wet, while there's no danger of aquaplaning
with a bike tire anyway, reducing the pressure will increase the
contact patch size and reduce the ground pressure per square inch.
That latter effect may reduce the side force required to break
traction, so reducing the tire pressure in the wet is a bad idea all
around.
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