acceleration

bikeguy

I just did a few short sprints yesterday on a flat section of bike path and hit about 37 km/hr within just about 25 meters from a speed as slow as I could go without falling over measured as a max off my cateye speedo. Anybody else tried something like this? I wonder how fast a top track rider could reach 40 km/hr?!

taras0000

I think your speedo is off mate. through physics calculations, the numbers you gave means that you covered those 25 meters in about 2.5 seconds. how fast was "as slow as you could go without falling over"? A top level track sprinter takes about 10 seconds to get to 40 kilometers pre hour

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Taras

bikeguy

A top male 100 m dash sprinter will reach 37 km/hr in about 3 seconds, you must be severely underestimating a track cyclist sprinters speed. 10 seconds?? Yeah right. No the speedo is accurate, I took a rollout accurately and have measured against a known distance of 100 metres (100 meter straightaway on track). As slow as I could go is about 30 cm/sec. I know a really fast time for a 250 m is 18.0 sec so these guys must be ripping through the first 100 meters really fast. By the way I'm using a regular geared racing bike not a fixed gear.

velomanct

i did some big gear starts today. used a 53x13 and started at about 10km/hr. it took me exactly 10 seconds to reach 45km/hr on flat road. looking at my powertap data my peak watts were about 1400, but that was at a very low 75rpms. peak torque was 475 inch lbs, i thought it would be higher.

standing starts are a lot faster in a smaller gear like 39x15. elite track racers can hit 65km/hr 20 seconds off the line(standing start, team sprint) BUT that is in a big gear like 50x14.

what gear were you using? try a 53x13 from 10km/hr, it takes some muscle.

velomanct

i think he is about right. at an average of 5.36m/sec(~20km/hr) he will cover the 25 meters in about 4.5 secs. from 0 to 37km/hr at an acceleration rate of 8.2km/hr per second, that's about what i can do, at these lower speeds(<40km/hr).
the difference is, he is probally using a smaller gear than trackies, which makes the acceleration a lot quicker.

i myself can go from 0 to 40km/hr in about 10 or 11 seconds, in a big gear like 53x14, and i consider myself a sprinter.

velomanct

you can't compare the acceleration of a runner vs a cyclist.

plus, the trackies are using big gears like 50x14, so they are way overgeared at the start.

bikeguy

I think I used 36x17 or something like that so it was easy to accelerate although starting up the first 1/2 sec was slow as heck and I was spinning too fast at 34 km/hr. As to running and cycling if a sprinter can come up to 37 km/hr in 3 sec a top track cyclist should be able to easily beat it with the efficiency of cycling being much better than that of running assuming a suitable gear. As for time to cover the 25 meters I'm estimating about 3.40 sec assuming a similar accel curve to top 100 m sprinters. If I was held in blocks and could press down hard on the pedals while holding the brakes and then release the brakes I would be able to go much faster.

Velomanct, 10 sec 10- 45 km/hr in 53x13 sounds quite good, unfortunately by left upper back and shoulder were injured in a crash and I try and avoid accelerating really hard in big gears 'cause you have to pull up so hard on the handlebars if you actually want to accel quickly. I really shouldn't even be doing these accels.

-bikeguy

velomanct

i would have to say that the most efficient way to accelerate from 0 to 37km/hr would be running, not cycling. cycling is not more efficient than running, when you are accelerating from a dead stop, no matter what the gear. the only way cycling could become more efficient than running in this situation is if a highly advanced automatic transmission was used on the bike to allow the rider the most optimal cadence throughout the whole effort.
give an elite trackie the choice of any gear combo and put him up against an elite 100m sprinter(runner). i still think the runner would reach 37km/hr first.
i just can't imagine there being a faster acceleration from 0 than running.

RyBike

Well said, I completely agree. You need some kind of specail gearing system to beat a runner in initial acceleration.

Now...if we are talking about top-end speed, I think the cyclist has a little bit of an edge.

taras0000

simple reason why a runner will always beat a cyclist is the fact that a runner is not applying his force through a disadvantaged lever. the bigger the gear you use, the less leverage you have. it doesn;t matter how small a gear you use, you will never be able to accelerate as fast as the runner for the simple fact that the runner has not lever to work against.

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Taras

velomanct

i am willing to bet that elite track sprinters can go 0-40km in considerably less than 10 seconds, in those big gears.
i did some more standing starts in the 53x14 today. it took me 8 seconds to go from 0 to 40km/hr, according to my powertap data, during 2 of these efforts.

i will have to ask christian stahl about this, he is racing the team sprint in athens.

taras0000

velomanct, what sort of wattages were you hitting for these efforts. 0-40 in 8 seconds is pretty good.
Haven't tested it in a while, but my best 0-40 time was 9.02s

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Taras

velomanct

after looking at the downloaded data, i started at 4kph and 7(!) seconds later hit 40kph. so i adjusted for that and said 8 seconds for 0-40. (next time i will make sure i am completely stopped)

around 1400 in the last half of the effort. my true peak is 1700, during normal sprints. i don't know how accurate this timing is, i am just looking at the power tap data on my pc.
i should also add i am 80kg

drewjc

Im not too sure about the speeds that i am reaching but if it helps, i am a reasonable sprinter (11.5sec 200m) and state medallist in the team sprint (as starter) and i can do 100m standing starts in around 9.8secs. Sorry i have no way of telling you how fast i am travlleing at this point but i thought that some of you physicists may have a formula that can approximate the speed? I usually ride about a 91.8 (51x15) gear for this type of effort. From my estimates i would be doing over 45km/h by the 100m as a runner doing the same distance would be doing a similar time (ie 10sec) but i would overtake him basically at the 100m mark at a much higher speed.