Track racing bike-build

Just to add another little bit of maths. If you are 1½ inches outside the black line, you also end up 25cm behind where you should be over a lap, just to illustrate the scale of the matter.

750W is the average power needed to accelerate 100kg of bike+rider to 15m/s (33.5mph) in 15s.

Kinetic energy = 0.5 x 100 x 15^2 = 22500J
Power = 22500/15 = 750W

25cm as you cross the line at 15m/s is 0.25/15 = 0.016s. Bear in mind that that only applies to acceleration, any steady speed effort is almost completely unaffected by the mass of your bike, apart from a tiny change in rolling resistance. Because most of the acceleration happens early in the lap (when you have a bigger surplus of output power over combined drag + rolling resistance), you spend most of the time doing a speed where more than half your power is consumed by drag, so that is always where your resources should be spent, ahead of trying to lighten the bike.

As a track sprinter with a recorded on track power of 1863W, and the front man of the London Track champs Team Sprint winning team.....

You talk a lot of shit!

As a track sprinter with a recorded on track power of 1863W

That would be the max output recorded for possibly a few seconds

750W is the average

I actually did calculations, assuming acceleration from a standing start to 33mph in 15s, the extra 200g robs you of 1.5W, out of 750W required for accelerating you and the rest of your bike and about 600W of aerodynamic drag at the maximum speed. Working back to distance covered in the time with the acceleration reduced to account for the extra mass puts you about 25cm behind after one lap.

But he said this which is misleading

and this:

25cm as you cross the line at 15m/s is 0.25/15 = 0.016s. Bear in mind that that only applies to acceleration, any steady speed effort is almost completely unaffected by the mass of your bike, apart from a tiny change in rolling resistance

So his calulation based on a steady speed effort (the average) is not relevant to his claim (which apparently only affects acceleration, which you need far more than 750w for, especially seeing as nobody has ever done a 15s opening lap)

Let's recap the original claim:

it might amount to 0.2% of your total bike+rider weight, which could hold you back by 25cm on the first (250m) lap of a standing start event.

For those of you still struggling with the maths, I'll try to restate my claim.

750W is the average power you must exert to accelerate 100kg to 15m/s in 15s. That much is simple, a certain amount of kinetic energy must be gained, and dividing by time gives power. This power is in addition to any power needed to overcome rolling resistance and aerodynamic drag, both of which rise with speed. That's why, if you exert constant power from a standstill, you accelerate quickly at first, then more and more slowly as your speed becomes asymptotic to the equilibrium point where your output is precisely matched by the steady state losses.

Clearly nobody does 15s opening laps, and fast people need to be doing more than 15m/s at the end of lap one to get into the 18s, I was simply taking an illustrative example using simple numbers. My claim holds if you accelerate to 15m/s in 15s and then hold that steady speed for the remainder of the lap, which you'll complete in 20-something seconds. You can do your own super-precise calculations if you want to, I was simply gaining an idea of the magnitude of the problem of having an extra 200g on your bike for the worst case scenario, that being a maximal acceleration from a standing start.

If you disagree with my calculation, show your working. If you just think my illustration is wholly unrealistic, show a better illustration with what you consider to be realistic numbers.

I'm not arguing with the maths, but the science is whack.

A better illustration would be real world terms, for example:

A rider+ bike weighing 100kg in total can complete a standing start lap of an indoor velodrome in 20 seconds.

Can you tell us how much time he will save by dropping 200grams of weight from the bike?

I could if I could be arsed to do detail calculations, but since we're in the same area as my original calculation, I'll say it's as stated, between 0.01s and 0.02s.

25cm as you cross the line at 15m/s is 0.25/15 = 0.016s.

That's assuming all other things remain equal. Per my earlier comments, if your 200g comes at the cost of slightly worse aerodynamics, or a little less stiffness which means you can't hold the line so well and drift out as little as 1½ inches, your weight weenie mod starts costing time, not saving it.

I wouldn't be surprised to find that two riders which can produce equal amounts of power and have identical bikes could still be a few 100ths of a sec different just from bike handling skill. You watch Obree doing his track persuits - he hardly ever strays from the black line and also relaxes his upper body. A sprinter might need to tense his arms etc to exert max power but it takes skill to relax certain areas and hold the bike bang on line therefore allowing the power exerted to be used efficiently.

So as mentioned losing weight might loose you stiffness which will cost you time.
Having all the stiffness in the world might not always improve your time if you're a messy rider

Assuming all other factors remain constant.

Just to add another little bit of maths. If you are 1½ inches outside the black line, you also end up 25cm behind where you should be over a lap, just to illustrate the scale of the matter.

how much time and distance do you lose looking down to check you only go 1/16 inches outside the black line? and the difference between wearing a pointy helmet that sticks up when you look down and a casco warp?

show you working.

If you have to look down to see that you're on the line
a: you're doing it wrong and
b: you'll ride a worse line than you would if you looked a few metres ahead.

it's a theoretical situation just like most of your spurious arguments.

JESUS FUCKING TITTY CHRIST! just ride yer bike. Assuming your an amateur rider and not right at the top end you'll probably gain more by buying something that looks nice and makes you want to ride your "nice shiny bike" more.

In the olden days, when John Pritchard was 25 champion, he said that he always liked to ride what he believed to be the fastest possible bike because sitting on the line he would always know that nobody could beat him by getting a better bike. Even if the little tweaks don't add up to a winning margin, the comfort which comes from knowing you've done all you can on the equipment side is a worthwhile psychological boost, one which is probably worth more time than some of the very small marginal gains available from equipment once you get past a certain level.

To go back to the original question, the actual performance difference between Campag and SRAM is so marginal that it's all but impossible to test, since nobody can ride repeatably to the precision which would be needed to test the question in the real world. That being so, the correct choice is the one which you believe to be better, since sitting on the starting line with any doubt in your mind is a bigger disadvantage than being wrong about the "correct" answer. I happen to like the stiff feel of UltraTorque cranks, which is why that's what's on my race bike rather than the weight weenie option which is 500g lighter but has been relegated to my lo-pro, a bike which no longer gets raced seriously.

Question for the experts:
I am currently on a Dolan Pre-cursa, an older model with alloy forks, with varno built wheels & Deda pista bars & alloy stem.

I was wondering if it is worth the time and effort to start exchanging parts to reduce weight. Carbon seat post, carbon forks, lighter s inaddle & (if I have the money) carbon clinchers.
Or would I be just polishing a turd?

I am not interested in spending much money as I could train more & lose some body weight to improve performance, I just want to have a faster bike.

I am more interested in races like the devil & points race as I am defo not a sprinter

you could probably save a chunk of weight with carbon forks but overall I'd say it's not worth changing bits to carbon. As for wheels, you aren't going to be doing big bursts of acceleration in the devil and points so it's not really worth changing them for light weight carbon ones infact heavier wheels will keep more momentum.

you aren't going to be doing big bursts of acceleration in the devil and points

How are you going to win them without bursts of acceleration?

I meant not like in a proper sprint, seeing as you have to do it again and again.

Top forum advice.

Do those multiple sprints add up to more or less than one "proper" sprint?

Anyway, buy some smooth, light wheels if you want. Other than that don't worry too much about weight on a track bike. Bling looks nice, but it wont make a noticeable difference (except for in your head).

Harrrong - Are planning to start racing at the track?

Get more aero wheels before thinking about weight, once you're doing 30mph nobody cares what your wheels weigh.

Harrrong - Are planning to start racing at the track?

Yep. Planning on the Back in Black open race day at HH.

Thanks for the info & for making me laugh (JC)

Great. It'll be good to see another Rolla racing.

Can't wait.

If you're thinking of a wheel upgrade, I'll have a pair of mavic elipses spare on the race day that you're welcome to try out. They're not the blingiest wheels out there, but they're good wheels for the money.