[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?
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?
[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.
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.
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.
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.
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.
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.
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.
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.
[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.
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.
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.
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.
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.
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.
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.
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.
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.
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...
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.
