Air pressure

orfeo said:

I was just reading through that pump post, and i saw most ppl talking
about having tyre pressures of 100+ psi (i assume). On my tyres it has a
psi rating of 45-60, which seems a bit low as i can still indent them
with my thumb. What pressures do most ppl pump their tyres up too? I'm
riding a trek 970 with slicks with grooves for the water to run off (not
sure on the brand obviously). Do different tyres have different pressure
ratings?

Yes. Fat tyres require lower pressures than skinny tyres. Yours is an
mtb with fat tyres, so don't pump them up to 100psi, they might blow
them off the rim if you did.

hope this helps
GK

Quoted message said:

and is it better to have a higher pressure (assuming you not
subjecting your tyres to large impact forces).

orfeo

orfeo said:

I was just reading through that pump post, and i saw most ppl talking
about having tyre pressures of 100+ psi (i assume). On my tyres it has a
psi rating of 45-60, which seems a bit low as i can still indent them
with my thumb. What pressures do most ppl pump their tyres up too? I'm
riding a trek 970 with slicks with grooves for the water to run off (not
sure on the brand obviously). Do different tyres have different pressure
ratings? and is it better to have a higher pressure (assuming you not
subjecting your tyres to large impact forces).

orfeo

AFAIK you shouldn't exceed the rating printed on the tyre (every tyre
has this, I guess the narrower the tyre, the higher the pressure). I'd
say road tyres are typically inflated at 100-120 psi. Track bikes might
be even higher (given these bikes are in theory only ever ridden on
perfect surfaces and don't need the shock absorption qualities of a road
tyre).

If you're a bigger guy like me (over 90kg) on a road bike, it's
important to keep the tyres at their upper limit, otherwise you puncture
more easily and if the pressure's low enough, you can damage your rims
when you hit a pothole.

HTH,

&roo

All tires have different pressure ratings. These are set by the maker
and are the safe range. Too low and you risk pinch flats, too high and
risk the tire blowing off the rim.

Having said that, the makers generally are conservative in their
ratings, but the safer answer if you want to run higher or lower
pressures is to get another tire.

I have a set of wheels with 40psi MAX tire pressures, and another set
with 135psi MAX - different tires, different pressures for different
uses.

(Also, at bicycle speeds the grooves for the water to run off is all
marketing.)

Megan

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

Quoted message said:

I was just reading through that pump post, and i saw most ppl talking
about having tyre pressures of 100+ psi (i assume). On my tyres it has a
psi rating of 45-60, which seems a bit low as i can still indent them
with my thumb. What pressures do most ppl pump their tyres up too? I'm
riding a trek 970 with slicks with grooves for the water to run off (not
sure on the brand obviously). Do different tyres have different pressure
ratings? and is it better to have a higher pressure (assuming you not
subjecting your tyres to large impact forces).

orfeo

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

Quoted message said:

ohhh...really, interesting, can anyone recommend some mtb slicks which
are weight friendly? and not too expensive.

Vredestein S-Licks are a bit on the expensive side but they
are damn light and damn fast on the road! $50-$60 each.
They also come in RED!! :-D
There was another thread on mtb slicks recently. When I
ever get spare time I'm going to create an online list of mtb
slicks for us aussies. If you want the info I've got I can email
it to you.

hip

: ohhh...really, interesting, can anyone recommend some mtb slicks which
: are weight friendly? and not too expensive.
:
: orfeo
:
:
I have specialized fatboys. 1.25" ~3.1cm. They are slicks with no grooves.
They are pretty good. There are reviews over the web of these tyres. I
think Cycling Australia reviewed them sometime over the last year. Cost
about $40 a tyre.

Peter

Megan Webb said:

On this, there check out the thread on hydroplaning. The link below
also explains

http://www.sheldonbrown.com/tyres.html#hydroplaning

You know something...I'm not convinced by this (doesn't mean it ain't
true...I just smell a rat).

For bike tyres it says:

"Bicycles can NOT hydroplane because..."

This is a big statement to make. That is, under all circumstances, no
bike can hydroplane.

"A bicycle tyre has a curved road contact. Since a bicycle leans in
corners, it needs a tyre with a rounded contact area, which tends to
push the water away to either side."

The same would apply to Motorbikes. They too have rounded contact
areas, and lean into corners. But no motorbike rider in their right
mind uses a slick, unless its on a track on a dry day.

"A bicycle tyre is narrower, so not as much water is in contact with the
leading edge at once."

Sounds fair to me, but I'm not sure if this totally rules out aqua-planing.

"The high pressure of bicycle tyres is more efficient at squeezing the
water out from under."

Not quite true. Mountain bike tyre pressures are often the same as that
off a car.

"Cars go much faster than bicycles, again leaving less time for water
to escape. At high bicycle speeds, hydroplaning is just possible for car
tyres, but is absolutely impossible for bicycle tyres."

Note sure about this. Bikes go quite fast, and cars can aquaplane at
fairly low speed.

Does anyone have comments? Has the web site conclusively proved its
point, or is it somewhat lacking?

Mike

Slicks for MTB's are also high pressure - 70 to 110psi, which makes them
still 3 times car tyre pressure. A big difference.
Offroad tyres are lower, but still almost double that of cars, but they
have tread anyway.

I'll start conjecturing now:

Considering a bike tyre's contact patch is the size of a single tread
block on a car, you would need triple the speed on a bike to aquaplane
than a car. (Based on the fact bikes are pushing down on the road 3
times the force than a car per sq.inch)

How much speed do you need to drive a car (with treaded tyres) through a
puddle to aquaplane? 80, 90km? That means 240 or 270kmh on a bicycle..

Hope this helps
GK

Mike Doyle said:

Megan Webb said:

On this, there check out the thread on hydroplaning. The link below
also explains

http://www.sheldonbrown.com/tyres.html#hydroplaning

You know something...I'm not convinced by this (doesn't mean it ain't
true...I just smell a rat).

For bike tyres it says:

"Bicycles can NOT hydroplane because..."

This is a big statement to make. That is, under all circumstances, no
bike can hydroplane.

"A bicycle tyre has a curved road contact. Since a bicycle leans in
corners, it needs a tyre with a rounded contact area, which tends to
push the water away to either side."

The same would apply to Motorbikes. They too have rounded contact
areas, and lean into corners. But no motorbike rider in their right
mind uses a slick, unless its on a track on a dry day.

"A bicycle tyre is narrower, so not as much water is in contact with the
leading edge at once."

Sounds fair to me, but I'm not sure if this totally rules out aqua-planing.

"The high pressure of bicycle tyres is more efficient at squeezing the
water out from under."

Not quite true. Mountain bike tyre pressures are often the same as that
off a car.

"Cars go much faster than bicycles, again leaving less time for water
to escape. At high bicycle speeds, hydroplaning is just possible for car
tyres, but is absolutely impossible for bicycle tyres."

Note sure about this. Bikes go quite fast, and cars can aquaplane at
fairly low speed.

Does anyone have comments? Has the web site conclusively proved its
point, or is it somewhat lacking?

Mike

Specialized Fat Boys are the slick to get. Thin as you can get them.

I have used them for years. They are fast and don't puncture often.

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