Commuting on a mountain bike - a few questions

terryc wrote:

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.

It's an oversimplification, is what I meant. Maximum rated
pressure usually goes up as width goes down. But not always, as
I pointed out.

I've had 26 x 1.75 tyres rated to 85 PSI (it was some Michelin
model) and seen 1.50 tyres rated to only 65 PSI.

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).

For the same pressure, the contact patch area will be identical
regardless of tyre width. And the wider tyre will roll more
efficiently because its contact area is shorter and wider.

To quote Schwalbe: "The flattened area can be considered as a
counterweight to tire rotation. Because of the longer flattened
area of the narrow tire, the wheel loses more of its roundness
and produces more deformation during rotation. However, in the
wide tire, the radial length of the flattened area is shorter,
making the tire rounder and so it rolls better." -
http://preview.tinyurl.com/3suok2f

And there's another consideration. Many riders have a
comfortable inflation pressure they inflate to regardless of
the tyre width. As long as the pressure rating isn't exceeded,
it's at least as safe and it's more efficient to use a wider tyre
to take advantage of the lower rolling resistance.

In fact it may be safer to use a wider tyre. Hit a patch of
deep loose gravel, a wide tyre can mean the difference between
being able to control a bike and having the front wheel dig in
and being thrown off.

Wide tyres get a worse name for rolling resistance than they
deserve. I just want to set the record straight.

John

John Henderson wrote:


And there's another consideration. Many riders have a
comfortable inflation pressure they inflate to regardless of
the tyre width.

Bing. Yumchas, so who worried about rated pressure.

"John Henderson" wrote
Theo Bekkers wrote:

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.

I agree that there is far less difference between a 1.75 and a 2.25 as
far as recommended pressure for specific loads, and that you can run
both at 65lbs without noticeable performance difference and that the
2.25 will have less rolling resistance.

I still believe that at the same pressure one of the two will be
incorrectly inflated. The narrower tyre should run at higher pressure
for the same load and therefore will have less 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

I believe he is quite correct.

Theo

Travis wrote:

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.

They work OK for commuting. I'm still riding mine, up to around 7,000km
now:

http://www.humbletown.org/budgetbike/index.htm

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!)

I use 1.5" almost-slick (i.e. beach-cruiser grooved) tyres inflated to
65psi. I have a feeling that the wider tyre might be better for heavy
loads, but I've never done any testing to verify that - my main reason for
running relatively low-pressure tyres is that I almost never have
perfectly trued-up wheels.

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!)

Yes, ditch them. The knobby ones on K-Mart bikes are usually only rated
at 45psi, and the constant droning on asphalt will annoy you very quickly.

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?

Not too long, but then drop-bar roadbikes are pretty nasty for my lower
back so it's not as though I have any nostalgia for them!

Look on the bright side - you'll be getting a much more thorough workout
on the heavy bike! :-)


BTH

--
Posted at www.usenet.com.au

On May 10, 11:42*am,
m.au (BT Humble)
wrote:
Travis wrote:

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.

They work OK for commuting. *I'm still riding mine, up to around 7,000km
now:

http://www.humbletown.org/budgetbike/index.htm

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!)

I use 1.5" almost-slick (i.e. beach-cruiser grooved) tyres inflated to
65psi. *I have a feeling that the wider tyre might be better for heavy
loads, but I've never done any testing to verify that - my main reason for
running relatively low-pressure tyres is that I almost never have
perfectly trued-up wheels.

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!)

Yes, ditch them. *The knobby ones on K-Mart bikes are usually only rated
at 45psi, and the constant droning on asphalt will annoy you very quickly..

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?

Not too long, but then drop-bar roadbikes are pretty nasty for my lower
back so it's not as though I have any nostalgia for them!

Look on the bright side - you'll be getting a much more thorough workout
on the heavy bike! :-)

BTH

--
Posted atwww.usenet.com.au

I rode the MTB this morning for the second time (first time was
yesterday) and got a sidewall blowout on the rear tyre, forcing me to
walk/run my bike to the nearest train station, lock it up there and
then take the train to uni.

Rear tyre was only inflated to 65psi, admittedly though it wasn't in
especially good condition.

I ordered those 1.25" semi-slicks from Torpedo7 a few days ago so
they're on their way, but Torpedo7 didn't have any 1.25" tubes in
stock (in any quantity, in any brand!) and I have an aversion to
paying $12 "a pop" (heh) for tubes, so I'm just going to have to ride
the roadie for a bit longer until T7 or PBK or whoever get them in
stock again.

It's a shame, because although it was a little bit slower and I felt a
little tiny bit (but not very) goofy riding a p.o.s. MTB while being
passed by all those hooligans on their shiny road bikes, I did
actually arrive with a less sore lower back and bum. Partly it was the
seating position, mainly it was the fact that there was room to mount
my U-lock's hanger on the upper tube, so it hung off the frame rather
than my lumbar spine!

In addition to the conventional (non-cantilever) rack I ordered from
T7 for the MTB, for the roadie I've ordered one of the cantilevered
seat post mounted racks from eBay (for the princely sum of $25
shipped) and a convertible (i.e. unzip the sides and the panniers hang
down, otherwise it's just a rack-top bag) bag for the even more
Brobdingnagian sum of $34.they don't need to take vast volumes or
weight, as long as they'll carry a few of the more weighty and bulky
items (U-lock, lab coat, lunch and soon my more bulky winter change of
clothes too) that'll do. Better than carrying it on my back anyway!

Travis

Theo Bekkers wrote:

"John Henderson" wrote
Theo Bekkers wrote:

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.

I agree that there is far less difference between a 1.75 and a 2.25 as
far as recommended pressure for specific loads, and that you can run
both at 65lbs without noticeable performance difference and that the
2.25 will have less rolling resistance.

I still believe that at the same pressure one of the two will be
incorrectly inflated. The narrower tyre should run at higher pressure
for the same load and therefore will have less 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

I believe he is quite correct.

When I first read Sheldon's article many years ago, it struck me
that he was encouraging people to ignore tyre manufacturers
maximim inflation recommendations.

If that's what he was doing, I still believe he's wrong to do so.

John

On 10/05/2011 3:42 PM, Travis wrote:
On May 10, 11:42 am,
m.au (BT Humble)
wrote:
Travis wrote:

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.

They work OK for commuting. I'm still riding mine, up to around 7,000km
now:

http://www.humbletown.org/budgetbike/index.htm

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!)

I use 1.5" almost-slick (i.e. beach-cruiser grooved) tyres inflated to
65psi. I have a feeling that the wider tyre might be better for heavy
loads, but I've never done any testing to verify that - my main reason for
running relatively low-pressure tyres is that I almost never have
perfectly trued-up wheels.

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!)

Yes, ditch them. The knobby ones on K-Mart bikes are usually only rated
at 45psi, and the constant droning on asphalt will annoy you very quickly.

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?

Not too long, but then drop-bar roadbikes are pretty nasty for my lower
back so it's not as though I have any nostalgia for them!

Look on the bright side - you'll be getting a much more thorough workout
on the heavy bike! :-)

BTH

--
Posted atwww.usenet.com.au

I rode the MTB this morning for the second time (first time was
yesterday) and got a sidewall blowout on the rear tyre, forcing me to
walk/run my bike to the nearest train station, lock it up there and
then take the train to uni.

Rear tyre was only inflated to 65psi, admittedly though it wasn't in
especially good condition.

I ordered those 1.25" semi-slicks from Torpedo7 a few days ago so
they're on their way, but Torpedo7 didn't have any 1.25" tubes in
stock (in any quantity, in any brand!) and I have an aversion to
paying $12 "a pop" (heh) for tubes, so I'm just going to have to ride
the roadie for a bit longer until T7 or PBK or whoever get them in
stock again.

It's a shame, because although it was a little bit slower and I felt a
little tiny bit (but not very) goofy riding a p.o.s. MTB while being
passed by all those hooligans on their shiny road bikes, I did
actually arrive with a less sore lower back and bum. Partly it was the
seating position, mainly it was the fact that there was room to mount
my U-lock's hanger on the upper tube, so it hung off the frame rather
than my lumbar spine!

In addition to the conventional (non-cantilever) rack I ordered from
T7 for the MTB, for the roadie I've ordered one of the cantilevered
seat post mounted racks from eBay (for the princely sum of $25
shipped) and a convertible (i.e. unzip the sides and the panniers hang
down, otherwise it's just a rack-top bag) bag for the even more
Brobdingnagian sum of $34.they don't need to take vast volumes or
weight, as long as they'll carry a few of the more weighty and bulky
items (U-lock, lab coat, lunch and soon my more bulky winter change of
clothes too) that'll do. Better than carrying it on my back anyway!

Travis
Aldi have 26" tubes for not much money this week.

Moike

Travis wrote:
It's a shame, because although it was a little bit slower and I felt a
little tiny bit (but not very) goofy riding a p.o.s. MTB while being
passed by all those hooligans on their shiny road bikes, I did
actually arrive with a less sore lower back and bum. Partly it was the
seating position, mainly it was the fact that there was room to mount
my U-lock's hanger on the upper tube, so it hung off the frame rather
than my lumbar spine!

I think you'll find that moving your luggage onto a pannier rack will
relieve your back pain more than the change in riding position.

I've also found that one of those thick slime-filled tubes fitted to the
rear tyre avoids a lot of broken-glass related punctures (breaking bottles
on the cycle path seems to be a favourite sport in my area).


BTH

--
Posted at www.usenet.com.au

On May 11, 5:53*am, Moike wrote:

Aldi have 26" tubes for not much money this week.

Moike

It would be luverly if they would come to Perth!

I just bought a couple of tubes off eBay. $12, problem solved.

Travis

On 11/05/2011 6:35 PM, Travis wrote:
On May 11, 5:53 am, wrote:

Aldi have 26" tubes for not much money this week.

Moike

It would be luverly if they would come to Perth!

I just bought a couple of tubes off eBay. $12, problem solved.

Travis

Who were that mob in the ACT that were flogging off tubes in packs of 10
at a ridicules price?