Commuting wheels

Darth. said:

[Also posted on the forum at BikeRadar - need to get replacements this
weekend!]

After nearly 5,000 miles of London potholes, sudden braking at traffic
lights and near misses with transit vans the wheels on my Specialised
Sirrus have finally given up the ghost. The braking surface on the
rear one is completely worn and the front wheel isn't far behind. I'm
looking for advice on replacements.

Ideally I'd like to get some wheels where I'll notice the difference.
I'm a fairly fast commuter (20-24 mph) so a nice light set of wheels
would be great fun. However, I'd also like something quite sturdy so
that I don't have to replace them again for a while. Are these
mutually exclusive?

The brake tracks will always wear out. I don't think it makes much
difference what rim you've got, although it may be that some brake pads
scrape away the rims more rapidly than others.

Ideally you would just change the rims since after only 5k miles the
hubs should still have plenty of life in them. But it means rebuilding
the wheels and I don't know if you're up for that.

If the only thing wrong is the brake tracks and you've not had any
buckles or anything in spite of the pot-holes then you're doing well. Go
for something similar next time.

Lighter wheels won't really make much noticeable difference to
performance I don't think, because the difference in weight won't be all
that much. Tyres and tyre pressures make more difference.

Darth. said:

After nearly 5,000 miles of London potholes, sudden braking at traffic
lights and near misses with transit vans the wheels on my Specialised
Sirrus have finally given up the ghost. The braking surface on the
rear one is completely worn and the front wheel isn't far behind. I'm
looking for advice on replacements.

That's about how long the original wheels on my Sirrus lasted too, not
including the spokes which all got replaced under warranty as they
were a dodgy batch.
I was getting concerned about the amount of wear on the braking
surfaces, but then the hub bearings got crunchy as well, and after
keeping them going for another few weeks with a strip down, grease and
adjust I decided it was time for new wheels. Shame because I'd hoped
to make them survive last winter and replace in the spring.

Quoted message said:

Or does the frame mean that a wheel upgrade is not worth it? Should I
stick to something sensible and boring and save the money for the new
bike, planned for Spring 2008?

I got some sensible Shimano Tiagra R500s and they're just fine. I say
go for reliability through the winter and have fun with something less
practical in the spring.

Ben C said:

Lighter wheels won't really make much noticeable difference to
performance I don't think, because the difference in weight won't be all
that much. Tyres and tyre pressures make more difference.

Lighter rims really do make a big difference. Being nearly the
furthest point out from the hub, they have a great impact on radial
inertia. The mass of anything that rotates has a disproportionate
impact on energy input required. This is why, when considering
upgrading a bike, wheels should be the first thing to be swapped out.

So if Darth finds that the hubs are OK, I'd advise him to save the
cash he would spend on whole wheels and splash out on higher quality,
lighter rims and a rebuild.

David Lloyd.

David Lloyd said:

The mass of anything that rotates has a disproportionate
impact on energy input required.

Only on acceleration. This could result in a bike feeling more
responsive, this is subjective, but it may have a psychological benefit.

During normal sustained travel the mass acts as a flywheel, the energy
it stores in minor accelerations should be fully returned.

On slowing down or stopping via use of the brakes energy is transformed
into heat, and a higher mass will require more effort to get back up to
speed, but this is not something I would value to highly (with the
possible exception of the aforementioned psychological aspect),
certainly not on a commuter bike.

--
Membrane

Darth. said:

Ideally I'd like to get some wheels where I'll notice the difference.
I'm a fairly fast commuter (20-24 mph) so a nice light set of wheels
would be great fun. However, I'd also like something quite sturdy so
that I don't have to replace them again for a while. Are these
mutually exclusive?

To some extend, yes. I'd look into switching to less abrasive brake
pads, 5000 miles out of a set of rims isn't great.

For a commuter you need fairly strong wheels first and foremost. I'd put
your desire for something noticeably lighter than what you had on a low
priority. If I were you I'd opt for a set of Mavic Aksiums, good
commuter wheels, strong, good quality, affordable (~£100 for a set), and
a good weight for their category.

--
Membrane

Membrane said:

Darth. said:

Ideally I'd like to get some wheels where I'll notice the difference.
I'm a fairly fast commuter (20-24 mph) so a nice light set of wheels
would be great fun. However, I'd also like something quite sturdy so
that I don't have to replace them again for a while. Are these
mutually exclusive?

To some extend, yes. I'd look into switching to less abrasive brake
pads, 5000 miles out of a set of rims isn't great.

For a commuter you need fairly strong wheels first and foremost. I'd put
your desire for something noticeably lighter than what you had on a low
priority. If I were you I'd opt for a set of Mavic Aksiums, good
commuter wheels, strong, good quality, affordable (~£100 for a set), and
a good weight for their category.

--
Membrane

Another keen cyclist (commuting and tri) in the office has recommended
the Aksiums as lovely all-round commuting wheels. Several comments
above recommend replacing the rims but to be honest I'm a little
concerned about the hubs as well. It's a shame to get new wheels just
at the start of winter but I'm planning to buy a fun bike in spring
anyway.

Simon

Membrane said:

Only on acceleration. This could result in a bike feeling more
responsive, this is subjective, but it may have a psychological benefit.

During normal sustained travel the mass acts as a flywheel, the energy
it stores in minor accelerations should be fully returned.

On slowing down or stopping via use of the brakes energy is transformed
into heat, and a higher mass will require more effort to get back up to
speed, but this is not something I would value to highly (with the
possible exception of the aforementioned psychological aspect),
certainly not on a commuter bike.

I value responsiveness very highly on a commuter bike as sustained
travel while commuting is anything but normal. Most of the time is
spent accelerating, braking and/or weaving through traffic. In London
anyway.

David Lloyd said:

Ben C said:

Lighter wheels won't really make much noticeable difference to
performance I don't think, because the difference in weight won't be
all that much. Tyres and tyre pressures make more difference.

Lighter rims really do make a big difference.

How many grams and how much difference?

Quoted message said:

Being nearly the
furthest point out from the hub, they have a great impact on radial
inertia. The mass of anything that rotates has a disproportionate
impact on energy input required.

Only when accelerating.

Quoted message said:

This is why, when considering
upgrading a bike, wheels should be the first thing to be swapped out.

Even if it means spending big money to save 50 grams per rim? I don't
think so.

Anyway you might actually want heavier rims if they are stronger or more
aerodynamic.

~PB

In article <53a961e1-5a4c-4829-a595-5cbab0888dc8
@i37g2000hsd.googlegroups.com>, Darth.
[email hidden] says...

Quoted message said:

[Also posted on the forum at BikeRadar - need to get replacements this
weekend!]

After nearly 5,000 miles of London potholes, sudden braking at traffic
lights and near misses with transit vans the wheels on my Specialised
Sirrus have finally given up the ghost. The braking surface on the
rear one is completely worn and the front wheel isn't far behind. I'm
looking for advice on replacements.

If the hubs and spokes are fine just swap them onto new rims of the same
effective diameter - you can do it without unlacing by putting the new
rim next to the old one and swapping one spoke at a time. Then try some
different brake blocks, because it sounds to me that the ones you have
might be a bit too aggressive. :-)
As for weight, you can probably make as much difference to the feel of
the bike by changing tyres - if the main durability problem is potholes
this is probably a better approach, but if road debris is a significant
problem then lighter tyres might cut more easily.

POHB said:

I value responsiveness very highly on a commuter bike as sustained
travel while commuting is anything but normal. Most of the time is
spent accelerating, braking and/or weaving through traffic. In London
anyway.

But would you prioritise weight over for example robustness on a
commuter bike (used on relatively flat terrain)?

A significantly lower weight is not a penalty free option, it comes at a
price, both literally and in terms of robustness.

--
Membrane

Membrane said:

But would you prioritise weight over for example robustness on a
commuter bike (used on relatively flat terrain)?

Indeed not. A broken lightweight wheel is much slower than a working
heavy one. Same with tyres, I put up with the weight of Marathon
plusses because the extra pedalling effort is far outweighed by not
having to sit by the road in the dark and rain fixing punctures.

Membrane said:

Darth. said:

Ideally I'd like to get some wheels where I'll notice the difference.
I'm a fairly fast commuter (20-24 mph) so a nice light set of wheels
would be great fun. However, I'd also like something quite sturdy so
that I don't have to replace them again for a while. Are these
mutually exclusive?

To some extend, yes. I'd look into switching to less abrasive brake
pads, 5000 miles out of a set of rims isn't great.

Not to most of us. But a commute speed in london of 20-24 mph is very
fast to phenomenal.

Nick said:

a commute speed in london of 20-24 mph is very
fast to phenomenal.

I'm assuming that he referred to the speed he can achieve when
unimpeded, if he achieves that as an average speed on his commute
through London then you're absolutely correct, that would be excellent.

--
Membrane

David Lloyd said:

Ben C said:

Lighter wheels won't really make much noticeable difference to
performance I don't think, because the difference in weight won't be all
that much. Tyres and tyre pressures make more difference.

Lighter rims really do make a big difference. Being nearly the
furthest point out from the hub, they have a great impact on radial
inertia. The mass of anything that rotates has a disproportionate
impact on energy input required.

That is true. In fact, the energy stored in a rotating wheel travelling
at a given speed is exactly twice the energy stored in the same wheel
travelling at that speed and not rotating (treating the wheel as a thin
cylinder with all its mass on the outside).

Lightweight racing rims weigh about 400g each. A much chunkier rim
perhaps 600g. That's 200g per rim, so 400g for both, and you can double
that because of the rotational inertia. So that's like an extra 800g
(from the point of view of power required to accelerate the bike on the
flat).

Less than 1% of the combined weight of rider and bike. All the same,
perhaps you might notice 800g.

Quoting David Lloyd <[email hidden]>:

Quoted message said:

Lighter rims really do make a big difference. Being nearly the
furthest point out from the hub, they have a great impact on radial
inertia. The mass of anything that rotates has a disproportionate
impact on energy input required.

ie, twice if they really were at the very edge (which they're not) for
acceleration only, which a moment's consideration will show makes the
difference between light rims and heavy ones about diddly for normal
purposes. You'd do just as well making sure you pee before setting off.
--
David Damerell <[email hidden]> Kill the tomato!
Today is First Tuesday, November.

Quoting Ben C <[email hidden]>:

Quoted message said:

That is true. In fact, the energy stored in a rotating wheel travelling
at a given speed is exactly twice the energy stored in the same wheel
travelling at that speed and not rotating (treating the wheel as a thin
cylinder with all its mass on the outside).

Ie, treating the wheel as something it's not.
--
David Damerell <[email hidden]> Kill the tomato!
Today is First Tuesday, November.

David Damerell said:

Quoting Ben C <[email hidden]>:

Quoted message said:

That is true. In fact, the energy stored in a rotating wheel travelling
at a given speed is exactly twice the energy stored in the same wheel
travelling at that speed and not rotating (treating the wheel as a thin
cylinder with all its mass on the outside).

Ie, treating the wheel as something it's not.

It doesn't make much difference. We're talking about the rim here.

If the rim weighs 400g, has a diameter of 622mm, and zero thickness,
then at 30kph I make its rotational KE 13.88J (the same as its linear KE
at that speed).

Now if I give it a thickness of 25mm, I get 12.8J rotational KE instead.
A difference of about 1J per wheel.

Membrane said:

Nick said:

a commute speed in london of 20-24 mph is very
fast to phenomenal.

I'm assuming that he referred to the speed he can achieve when
unimpeded, if he achieves that as an average speed on his commute
through London then you're absolutely correct, that would be excellent.

--
Membrane

Average is about 14-15 because I stop at lights. I'm very lucky to
have big empty bus lanes almost all the way to and from the office so
can get up to 20+ mph for quite long stretches. However, this is
clearly hard on the brakes - I go through a set of brake pads every 8
months or so...

Ben C said:

David Lloyd said:

Ben C said:

Lighter wheels won't really make much noticeable difference to
performance I don't think, because the difference in weight won't
be all that much. Tyres and tyre pressures make more difference.

Lighter rims really do make a big difference. Being nearly the
furthest point out from the hub, they have a great impact on radial
inertia. The mass of anything that rotates has a disproportionate
impact on energy input required.

That is true. In fact, the energy stored in a rotating wheel
travelling at a given speed is exactly twice the energy stored in the
same wheel travelling at that speed and not rotating (treating the
wheel as a thin cylinder with all its mass on the outside).

Lightweight racing rims weigh about 400g each. A much chunkier rim
perhaps 600g.

Perhaps not supplied with a road bike.

Quoted message said:

That's 200g per rim,

In your imaginary extreme example.

Quoted message said:

so 400g for both, and you can
double that because of the rotational inertia. So that's like an
extra 800g (from the point of view of power required to accelerate
the bike on the flat).

Less than 1% of the combined weight of rider and bike. All the same,
perhaps you might notice 800g.

Mavic Open Pro, road rim often recommended for good wheels: 425 grams
(officially). Open Sport, bog standard cheap road rim: 490 grams.

That's a difference of 65 grams, and often the difference is less than that
between a "good" rim and a "cheap" rim. Also note that actual weights vary
from example to example due to the manufacturing process. Open Pros can
weigh as much as 450 grams.

~PB