Commuting on a mountain bike - a few questions

As an alternative to mounting a rack on my roadie (something I'm still
trying to do anyway, but I want to try it both ways) I've just cleaned
the crud off a rather crappy (probably ex-Kmart) mountain bike which I
was given.

A few questions...

For commuting on roads and cycle paths, with no off-road use likely,
what is the correct tire pressure? (Additional info: I weigh 100kg and
will be carrying maybe another 7-15kg of gear... plus this is a rather
clunky steel tubed bike!)

The tires at the moment are the usual knobbly ones people have on
these bikes, but I'm wondering if it's worth chucking these
immediately or waiting until they've worn out before buying ashpalt-
oriented slicks. Is the rolling resistance improvement significant
enough to warrant an immediate switch? (if it'll cut 10mins off my
20km journey each day, the answer is yes!)

I rode it around the block and found it a fair bit more tiring to ride
than the roadie. I felt soreness in parts of my legs which I don't
normally feel when riding the roadie. Presumably the sitting position
is different enough that I'm working out different muscles. For anyone
who has had to switch bikes and had this before, did it take you long
to get over that?

Travis

Travis wrote:

The tires at the moment are the usual knobbly ones people have on
these bikes, but I'm wondering if it's worth chucking these
immediately or waiting until they've worn out before buying ashpalt-
oriented slicks.

Chunky equals noisy.
Slicks equals accidents ad injury. Great in theory, but the theory
doesn't cover dirt, gravel, etc.
The compromise is something with a centre ridge and moderate bumps on
the sides.
What size tyres will the rim accept? You certainly wouldn't need the
2.25" stuff or maybe even the 1.75"(yes, it is a while since I've
purchased new stuff).
As to pressure, pump em up to what feels nice. Almost the same as on
your roadie, unless you really are using the 2.25"(lot f air going out a
large sudden puncture).

On May 7, 2:50*pm, terryc wrote:
Travis wrote:
The tires at the moment are the usual knobbly ones people have on
these bikes, but I'm wondering if it's worth chucking these
immediately or waiting until they've worn out before buying ashpalt-
oriented slicks.

Chunky equals noisy.
Slicks equals accidents ad injury. Great in theory, but the theory
doesn't cover dirt, gravel, etc.
The compromise is something with a centre ridge and moderate bumps on
the sides.
What size tyres will the rim accept? You certainly wouldn't need the
2.25" stuff or maybe even the 1.75"(yes, it is a while since I've
purchased new stuff).

I haven't encountered anything which has been an issue for my roadie
to date, I would have thought that anything a roadie can handle on
slick roadie tires should be just as easily handled by a mountain bike
on slicks... no?

The current tires are 1.75". Never having ridden a mountain bike
before I couldn't tell you what range of thicknesses would work, in
fact that was something I was hoping aus.bicycles could tell me. I
just measured the rims with a ruler and they seem to be about 25mm.

That got me looking at http://www.torpedo7.com.au/products/...puncture-proof

Which indicates that a 1.25" tire with a maximum inflation pressure of
100PSI would work.

That's very roadie like, which I favour. I want something as similar
to my roadie as possible, but with the ability to haul all my gear to
uni!

As to pressure, pump em up to what feels nice. Almost the same as on
your roadie, unless you really are using the 2.25"(lot f air going out a
large sudden puncture).

1.75", I'm seeing 65-70PSI with Google. Does that sound about right?

Travis

Travis wrote:
On May 7, 2:50 pm, terryc wrote:
Travis wrote:
The tires at the moment are the usual knobbly ones people have on
these bikes, but I'm wondering if it's worth chucking these
immediately or waiting until they've worn out before buying ashpalt-
oriented slicks.

Chunky equals noisy.

Agree. Unpleasant on the road.

Slicks equals accidents ad injury. Great in theory, but the theory
doesn't cover dirt, gravel, etc.
The compromise is something with a centre ridge and moderate bumps on
the sides.

Probably better to get the type with centre ridge and cut-in off centre, rather
than something with bumps off centre. If you're hardly ever off road, the
cut-in types means far less likely to slip and fall on corners.

Shirley Nott.

What size tyres will the rim accept? You certainly wouldn't need the
2.25" stuff or maybe even the 1.75"(yes, it is a while since I've
purchased new stuff).

They are still called 1.75" and 2.25". Go 1.75"

I haven't encountered anything which has been an issue for my roadie
to date, I would have thought that anything a roadie can handle on
slick roadie tires should be just as easily handled by a mountain bike
on slicks... no?

The current tires are 1.75". Never having ridden a mountain bike
before I couldn't tell you what range of thicknesses would work, in
fact that was something I was hoping aus.bicycles could tell me. I
just measured the rims with a ruler and they seem to be about 25mm.

That got me looking at
http://www.torpedo7.com.au/products/...puncture-proof

Which indicates that a 1.25" tire with a maximum inflation pressure of
100PSI would work.

That's very roadie like, which I favour. I want something as similar
to my roadie as possible, but with the ability to haul all my gear to
uni!

As to pressure, pump em up to what feels nice. Almost the same as on
your roadie, unless you really are using the 2.25"(lot f air going out a
large sudden puncture).

1.75", I'm seeing 65-70PSI with Google. Does that sound about right?

Travis

In aus.bicycle on Sat, 7 May 2011 00:07:33 -0700 (PDT)
Travis wrote:
Which indicates that a 1.25" tire with a maximum inflation pressure of
100PSI would work.

that's what I used to use on the rear of the 'bent which has 26"
wheels. I now use slightly narrower Marathons.

The original tyres ran at 80psi, these run a 100 and I prefer them.

1.75", I'm seeing 65-70PSI with Google. Does that sound about right?


Probably. Get smaller high pressure ones, the difference is good.

Zebee

Travis wrote:

Which indicates that a 1.25" tire with a maximum inflation pressure of
100PSI would work.

Give it a try. So long as it sits safely on the rims, there is no reason
why you shouldn't


1.75", I'm seeing 65-70PSI with Google. Does that sound about right?

Try it. The low MTB pressure is only to spread the load for soft
surfaces. Firm surfaces should be firmer, especially if you have speed.
My 2c. I've run them higher.

Travis wrote:

For commuting on roads and cycle paths, with no off-road use likely,
what is the correct tire pressure? (Additional info: I weigh 100kg and
will be carrying maybe another 7-15kg of gear... plus this is a rather
clunky steel tubed bike!)

The maximum pressure the tyre is rated for will be on the
sidewall. For most 26 x 1.75 tyres, that's 65 PSI. But some
quality brands allow higher pressure.

I'll mention that my wife once experienced a front tyre blowout
(sidewall failure) with a new cheap tyre pumped up to its rated
pressure.

I like to ride with my front tyre a little softer than the
maximum for the sake of comfort. The front carries much less
weight than the rear.

Unless a narrower tyre permits running a higher pressure (most
do), be aware that a wider tyre will have less rolling resistance
than a narrow one (at the same pressure). That's because the
contact patch (the area touching the road) will be exactly the
same size, giving the wide tyre a more efficient (shorter and
wider) contact patch. This results in less flexing losses
overall.

John

"John Henderson" wrote

Unless a narrower tyre permits running a higher pressure (most
do), be aware that a wider tyre will have less rolling resistance
than a narrow one (at the same pressure). That's because the
contact patch (the area touching the road) will be exactly the
same size, giving the wide tyre a more efficient (shorter and
wider) contact patch. This results in less flexing losses
overall.

Hmm. Sheldon Brown says at http://www.sheldonbrown.com/tires.html

"A common debate among cyclists centers on the issue of whether a
wider tire has more or less rolling resistance at the same pressure.
The constant pressure is proposed because it appears more scientific
to eliminate this as a variable, but this is not realistic in
practice. The short answer to this question is that, yes, a wider tire
of similar construction will have lower rolling resistance than a
narrower one at the same pressure. This fact is, however, of no
practical value. If you are comparing two tires of similar
construction, with the same load, and the same pressure, either the
wider tire is overinflated, or the narrower tire is underinflated!"

He goes on to say
A 37mm (1.5") tyre with a 50kg wheel load should be inflated to 60lbs,
a 23mm tyre with the same load to 120lbs.

I can assure you, as does Sheldon, that the smaller tyre at 120lbs
will have far less rolling resistance.

Theo

Theo Bekkers wrote:


Hmm. Sheldon Brown says at http://www.sheldonbrown.com/tires.html

"A common debate among cyclists centers on the issue of whether a
wider tire has more or less rolling resistance at the same pressure.
The constant pressure is proposed because it appears more scientific
to eliminate this as a variable, but this is not realistic in
practice. The short answer to this question is that, yes, a wider tire
of similar construction will have lower rolling resistance than a
narrower one at the same pressure. This fact is, however, of no
practical value. If you are comparing two tires of similar
construction, with the same load, and the same pressure, either the
wider tire is overinflated, or the narrower tire is underinflated!"

He goes on to say
A 37mm (1.5") tyre with a 50kg wheel load should be inflated to 60lbs,
a 23mm tyre with the same load to 120lbs.

I can assure you, as does Sheldon, that the smaller tyre at 120lbs
will have far less rolling resistance.

I agree that a tyre at 120 PSI will roll easier than a wider one
at 65 PSI. However, 65 PSI is a common maximum pressure for
tyres in the width range around 1.75 to 2.25". In that case, and
assuming inflation to the same pressure, the wider tyre will have
the lower rolling resistance.

While I find it hard to disagree with Sheldon about most things,
his statement "either the wider tire is overinflated, or the
narrower tire is underinflated" is not strictly true as a
generalization

John

John Henderson wrote:

While I find it hard to disagree with Sheldon about most things,
his statement "either the wider tire is overinflated, or the
narrower tire is underinflated" is not strictly true as a
generalization

On what basis?
I think it is true. My 2c.
1. Lower pressures are generally used to cover softer ground, which
means the surface sinks more, so you are effectively riding steeper
grade and thus more resistance.
2. On the same surface,there is more tyre rubber to be deformed to meet
the surface, hence more resistance.
3. There is more centrepetal/centrifugal/centipedal(no idea which one)
resistance in bigger tyres from the greater air mass(plus bigger rim and
rubber).