Reducing front wheel weight

[nickyboy]

To further expand on my pedaling pedantry, by way of explanation, if the front wheel changes direction then its velocity must also have changed, which in turn requires the application of a force. Given that the only force propelling the bike on the flat is the rider then I'm guessing that this force, or at least the corrective element of it, must come via the pedals, robbing the rider of a tiny element of forward velocity. Or maybe that's claptrap.

By way of an analogy, a rider going around a velodrome must apply extra force to maintain velocity when going round the bends as opposed to the straights since round the bends the velocity is constantly changing. Or may that's gibberish too.

Interesting point. I think that the problem with changing direction is not a change in velocity. The problem is the force being applied to encourage the change in direction. When you steer, what happens is the wheel starts to experience some lateral force. This lateral force is ultimately reflected in an increase in the temperature of the tyre (hence why F1 drivers weave around a lot to warm up their tyres). This energy not being converted into forward movement is the reason for loss of speed when changing direction.

I'm trying to think whether cambering the track reduces the amount of steer (and thus energy loss) but my head hurts when I try. I guess it must. If you imagine a "wall of death" and a cyclist going so fast they are horizontal, they wouldn't need to steer at all as they would feel they were going in a straight line......hmmmm

 

[Yellow Saddle]

Interesting point. I think that the problem with changing direction is not a change in velocity. The problem is the force being applied to encourage the change in direction. When you steer, what happens is the wheel starts to experience some lateral force. This lateral force is ultimately reflected in an increase in the temperature of the tyre (hence why F1 drivers weave around a lot to warm up their tyres). This energy not being converted into forward movement is the reason for loss of speed when changing direction.

I'm trying to think whether cambering the track reduces the amount of steer (and thus energy loss) but my head hurts when I try. I guess it must. If you imagine a "wall of death" and a cyclist going so fast they are horizontal, they wouldn't need to steer at all as they would feel they were going in a straight line......hmmmm

Velocity is a vector (the components being speed and direction) and thus changing any one of the two changes the velocity. Velocity in physics is something very specific whist in street parlance velocity is sometimes used as a fancy word for speed. It isn't the same.

 

[winjim]

I use http://www.lmgtfy.com when people ask me for stuff that can be googled. Though it appears sending to to customers (accidentally) isn't appropriate

I'm not going to do that since it involves personal details of a forum member. I'll just say that there are a lot of snidey comments calling into question the experience of that member, however he is not exactly hiding his identity and his experience is well documented on the web.

 

[nickyboy]

Velocity is a vector (the components being speed and direction) and thus changing any one of the two changes the velocity. Velocity in physics is something very specific whist in street parlance velocity is sometimes used as a fancy word for speed. It isn't the same.

I know that. I was replying to a post where velocity was used in its vernacular as "speed"

 

[Yellow Saddle]

I know that. I was replying to a post where velocity was used in its vernacular as "speed"

OK, sorry. Back to your question then. Heat generated in the tyre is from internal friction as the rubber molecules are "massaged" and energy released when rubber bonds are stretched and even broken.

So, it is not just the lateral force (in this case centripetal force) that increases tyre pressure but any force that makes the tyre squirm. It could even be downforce. On a banked wall, downforce is increased and thus tyre deformation and thus more heat generated. I think by cambering the track you are reducing the heat developed from steer but increasing the heat developed from downforce. I just sucked my thumb and it appears the ratio remains equal and therefore a banked track that describes a certain circumference will generate exactly the same amount of heat as a non-banked track.

 

[Profpointy]

The issue I have with upgrades and light weight wheels. Is that I honestly do not see the point. I don't understand the logic in spending hundreds or even thousands on wheels, to save less weight than cutting out beer and pies for 2 weeks for free.

This of course doesn't mean people shouldn't buy them, I buy plenty of stuff I really don't need. Their money, their enjoyment, but I will still voice my opinion that lightweight components isn't the most cost effective performance increase. The gains are small compared to the money, and the gains that can be made by improving yourself.

Of course, cycling is for enjoyment. If you will enjoy it more by having new wheels, then buy new wheels.

On the whole "upgrade" thing, I've always tended to upgrade only when the old one is broken or worn out. I would then tend to go for lighter, better, shinier - perhaps diminishing returns even then but I might well pay a hundred quid (more) to save a pound or two off the weight. But I'd not pay for a marginal upgrade entailing a complete replacement. I now regret not paying an extra £100 for a significantly lighter (Thorn) frame, but I'm certainly not paying £600 or £700 for a whole new frame to the same end

 

[swee'pea99]

5) Heavy wheels take longer to spin up but the energy is not wasted. When you coast, they return the favour. There is no energy lost.

Just stumbled on this thread...I've been hereabouts before, and know better than to stick around, but for my tuppence worth, this is the bit I have problems with. Not that it's not true - I'm sure it is. But to me, it disregards one of the most important issues, which is the kind of riding you do. I can absolutely see how if you go for ten miles on a flattish road with no interruptions, the difference from a light/heavy wheel and/or bike might well be insignificant - what you lose in initial effort (overcoming inertia) you gain over time (in momentum). But I for one don't ride like that. I ride in town, stopping and starting and upping & downing and accelerating and decelerating constantly. So the effort it takes me to start with heaviness is not paid back with coasting; it's just wasted when I have to break hard, then I have to start with heaviness again. Personally I don't go silly with weight saving on wheels, or anything else for that matter. But if I had a 1.8kg front wheel, I'd change it, for sure.

 

[Yellow Saddle]

Just stumbled on this thread...I've been hereabouts before, and know better than to stick around, but for my tuppence worth, this is the bit I have problems with. Not that it's not true - I'm sure it is. But to me, it disregards one of the most important issues, which is the kind of riding you do. I can absolutely see how if you go for ten miles on a flattish road with no interruptions, the difference from a light/heavy wheel and/or bike might well be insignificant - what you lose in initial effort (overcoming inertia) you gain over time (in momentum). But I for one don't ride like that. I ride in town, stopping and starting and upping & downing and accelerating and decelerating constantly. So the effort it takes me to start with heaviness is not paid back with coasting; it's just wasted when I have to break hard, then I have to start with heaviness again. Personally I don't go silly with weight saving on wheels, or anything else for that matter. But if I had a 1.8kg front wheel, I'd change it, for sure.

I think one of the subtle issues in this and other posts of this type is as you say, the type of riding. However, the type of riding that one experiences in motorcar racing cannot be transposed to cycling. In car racing there is lots of energy wastage. You break extremely hard in a corner and then accelerate extremely hard again. This is evident from the way a racer plans the shape of trajectory in a corner. If you study racing driver strategy (even just from Top Gear) they talk about "the line". This is basically an attempt to get the turn as straight as possible. Of course it is a silly way to describe it but that's what they do. They enter at full speed, brake hard up to the apex and then accelerate hard out again. They exit so quickly that they have to allow some drift space on the road, within the turn, to get out. If you study a bicycle line in a corner and ask someone to give it their all, they don't do anything remotely similar. Reason for this is that their acceleration out is so poor that they don't need any drift space out of the corner. They can use it all up in the point up to where they start to brake. This illustrates how energy conscious we are even when we don't think about it.
The reason is because we accelerate extremely slowly. We have a super-low power-to-weight ratio. Further, human athletes don't just waste energy. Our reserves are low. Most people cannot do ten flat-out accellerations within a period of say 20 minutes. Again this is easy to demonstrate. In road racing a common strategy is to first assemble a competitive bunch that can co-operate, have the skill to stay in a bunch and can help the individual arrive at the sprint point for the launch to the finish line. How skilled racers do this is to perform 10 quick accellerations early on in the race. This they usually do just after a corner. These accellerations combined with the corner, string out the stragglers who then have to work hard to catch up. They do catch up, the point is not to lose them in the first corner. However, after 10 catchups they are kaput and only the strongest stay in the first bunch from where they co-operate and compete with a different strategy.
That story demonstrates, especially if you train to race - how small the fuel tank is. You can increase it with interval training but it is an expensive commodity, unlike a large gasoline tank.

I want to drive home the point that we accelerate slowly and expensively and therefore we don't like accelerate. Our riding style is not what we think it is compared to any other type of transport. It is pretty steady. When a red light catches you, you don't hammer until you are on top of it, you coast to the line instead. Pulling off you take your time to reach cruising speed again. It cannot be any other way otherwise your journey will be totally exhausting and unpleasant.

Further, micro-accellerations timed with each pedal strokes are a myth. Your "unit" weighing 80kgs has plenty of inertial and just pulsing fast and slow with each pedal stroke is just not physics. The curve is smooth, not spikey.

We feather our ride nicely by coasting in advance when coming to a stop or bottleneck rather than screeching to a halt only to accelerate off again. Even in a peloton, people won't waste energy by braking, instead they pedal-coast, pedal,coast pedal,coast. Each time the flywheel (and of course body inertia) returns the energy.

So, looking at your description of your riding style, I'll suggest that it is far gentler than you think, hence the burden of spinning up that teensy little flywheel called bicycle wheels is a far smaller drain on your energy than you will give credit. Have a look at the first link in my post above. There's I've described the energy required to speed up to 30kph (IIRC) and separated spinning-up energy from moving forward energy.

 

[paraffinlamps]

Just wondering , does wheel stiffness ( more rear wheel than front ) play a part ? . Is this perhaps what people feel when they say wheels are faster. I'm assuming a stiffer wheel has less losses when it's being driven and so maybe accelerates marginally quicker ? And perhaps feels more direct , similar to how a single speed feels coming from a geared bike .
I have some Campag Zondas that are renowned for being a " stiff " wheel and certainly in crit/ track races I find them much better to help carry speed through corners and accelerate out of them .
However on a standard rolling club ride I find it hard to tell a difference between my Zondas and some Farsports 50mm deep section carbon wheels

 

[samsbike]

this is worth a read

http://www.wheelfanatyk.com/blog/light-right/

 

[Yellow Saddle]

Just wondering , does wheel stiffness ( more rear wheel than front ) play a part ? . Is this perhaps what people feel when they say wheels are faster. I'm assuming a stiffer wheel has less losses when it's being driven and so maybe accelerates marginally quicker ? And perhaps feels more direct , similar to how a single speed feels coming from a geared bike .
I have some Campag Zondas that are renowned for being a " stiff " wheel and certainly in crit/ track races I find them much better to help carry speed through corners and accelerate out of them .
However on a standard rolling club ride I find it hard to tell a difference between my Zondas and some Farsports 50mm deep section carbon wheels

You've just made the perfect example of how people imagine "feeling" acceleration, responsiveness and all that. Carrying speed through corners implies lots of momentum. Acceleration implies very little momentum.

The two cannot co-exist other than in the imagination.

 

[swee'pea99]

The two cannot co-exist other than in the imagination.

The imagination - or perception - play a crucial role in what actually matters: the experience, as lived. I was thinking about this while walking the dog, and about the hill I climb pretty much every day on my way back from swimming. It's quite a toughie, and I'm always relieved when I reach the top. But on the days I drop by Sainsbury's to pick up some stuff on the way back, it's a whole different experience. Scientifically speaking, I've added maybe 5kg to a 90Kg +/- total package, so the difference should be relatively minor, you would have thought. Maybe my wattage goes up 6% or something, I have no idea, scientifically. But in terms of the actual experience of riding up that hill, it turns a bit of a toughie into a Really Hard Climb. In short, scientifically it may be relatively minor, but in terms of the experience, which is what actually matters to me, the difference is massive.

 

[paraffinlamps]

You've just made the perfect example of how people imagine "feeling" acceleration, responsiveness and all that. Carrying speed through corners implies lots of momentum. Acceleration implies very little momentum.

The two cannot co-exist other than in the imagination.

They are not co- existing though are they ?
Surely you can carry speed into a corner and still accelerate out of it as the road straightens . you have to slow down to go round the corner , however the quicker you can get round the corner the better , but you have still slowed down to go round it and therefore accelerate when you are out of it to regain speed ?
As I enter the corner I ease off the power to roll around the corner( this is the through part ) eventually I will start to come out of the corner as the road straightens and now start to pedal ( this being the accelerating part )
Perhaps my terminology didn't convey what I meant , apologies . As I start to pedal out of the corner and gain speed the Zondas seem much better than other wheel sets I have used . They also seem much better going round corners.

 

[Yellow Saddle]

They are not co- existing though are they ?
Surely you can carry speed into a corner and still accelerate out of it as the road straightens . you have to slow down to go round the corner , however the quicker you can get round the corner the better , but you have still slowed down to go round it and therefore accelerate when you are out of it to regain speed ?
As I enter the corner I ease off the power to roll around the corner( this is the through part ) eventually I will start to come out of the corner as the road straightens and now start to pedal ( this being the accelerating part )
Perhaps my terminology didn't convey what I meant , apologies . As I start to pedal out of the corner and gain speed the Zondas seem much better than other wheel sets I have used . They also seem much better going round corners.

Well, to say that you accelerate out of a corner implies that you have lost speed going into the corner and need to make up for it.
To carry speed through corners (thanks to your Zondas) suggests that your wheels have momentum and prevent loss of speed.
Acceleration requires less mass, momentum requires more mass. Which is it?
You are digging yourself deeper into that hole by now adding that Zondas are better at going around corners too. How do you explain that? Either they follow the line you dictate or they don't. There is no middle ground there. But if you really want to explain "going better around corners" I suggest you try and express it in units of measurements of sorts. No need to give me the quantities, just state what units you envisage for this action.

I have no beef with you but this debate has been muddled by some very fuzzy statements which all detract from the facts.

 

[Profpointy]

just a thought - I am (or used to be) overwhelmingly a commuting cyclist. Thus, I'd frequenlty be accelerating quit hard from rest, eg on busy roundabouts and the like. I would think that acceleraring from rest would be a good bit more important to me than to, say, a time trialist where aeroness is likely the most important thing.

I'm therefore more inclined to believe the 100g off the wheel is worth 200g off the bike for my kind of cycling.

Mind you, my kind of cycling requires mudguards and panniers and adequaltely strong wheels for city riding, but any weight saved is still very welcome.

To be candid, I've never swapped wheels, but can certainly feel an extra kilo (a PC say) in my panniers. It's not necessarily the case I can feel 50g or 100g , but add up 100g here and a 100g there - and pretty soon it's the weight of a PC or a pair of (office) shoes which I can feel