Anyone reckon they can ride 69kph on a fix? Might be able to break the world record for 200mts…

# TOPSPEED

man, it would suck pulling up to a set of lights at 69kmh, brakeless.

I’ve managed about 63. Going downhill

I’ll get back to you after I descend from the tidbinbilla deep space tracking station in the hills to the west on friday. My first fixed (metric) century! I’ll take a camera and install a computer for the ocassion.

- Joel

I have no idea.

Does anyone have a computer on their fixie?

My legs would be doing about 225 rpm at 69 kmph on my 42/16!!!

Ouch.

Blakey runs one - he tells me we’ve hit 62K coming down Dornoch Tce - 42 X 16 - that feels about enough to me. Don’t remember just how I did it but my calc was cadence of 183??

calc.

Hmmmmmmm

I used this time trial spreadsheet i got from somewhere on the net.

I might email it to Nick so he can put it up.

Not sure if I got it right or not. Seems like a lot of revs anyway, but when you read that Bayley can spin his cranks at 210 and pound out 2100 Watts makes you think anythings possible!!!

I have always wondered how quick I’m going.

Hmmmmm

The highest I’ve gone is 62kph, running 50t up front and 14t in the back. This was on the way to Williamstown going down a mild incline. I don’t think there’d be much problem hitting 69kph with the right setup.

Doing 69kph on a track and holding it for 200m is a different story.

Yeah but have you seen that guy off the bike? He’s got a but that just won’t quit!

http://www.sheldonbrown.com/gears/

for speed and cadence stuff. Unfortunately he doesn’t let you pick a cadence but you can use the meters (sic) development function for your gearing, multiply by your cadence, then by 60 (to get metres per hour) then divide by 1000 to get kilometres per hour:

(Mdev * Cad * 60) / 1000 = kph in a given cadence.

To approximate cadence just count seconds (one one thousand two one thousand three one thousand etc) without looking at your feet, then decide if you’re doing one revolution per second (60rpm) or two (120rpm) or three (180rpm, see a doctor) or somewhere in between.

I can spin along at 120 on the flat in 48 * 15, which according to sheldon (and my checking) equals 48 kph. Coming down a hill I can maintain approximately 150 (2 and a half rps) for prolonged periods - which equals 60.3 kph - enough to break the speed limit in built up areas!

I’ll get a bike computer tomorrow for my long (solo) ride on friday (I’ll take a camera) which can get max speed (for a ride) and I’ll back-calculate my cadence when I get home. I need to get a cadence computer!

- Joel

when you were mentioning the tidbinbilla deep space tracking station and installing computers, i had this vision in my head of you carrying a big computer to the tracking station and hooking it up with jumper cables. then i realised you meant bike computer-speedo… had i not just realised the first vision was only my twisted imagination, i was going to suggest using your newly installed deep space tracking computer to do the cadence calculations for us.

okie dokie… well, back to doing whatever it was i was doing (not a lot).

n!

It’s much easier than that, just use ‘speed at 100rpm’, then divide that speed by 100 and multiply by your speed.

that does sound easier - but you would have to multiply by your cadence, not your speed.

Blakey=clever

- Joel

It’s much easier than that, just use ‘speed at 100rpm’, then divide that speed by 100 and multiply by your speed.[/quote]

Why do you have to divide and multiply, I just selected the KMPH @ 100rpm. Told me that a 42 / 16 does 33kmph at that cadance or 39.6 @ 120

Very simple!

i like it

Nuh-uh, multiplying by your cadence defeats the purpose of trying to calculate your cadence. There was an error in my post, I meant divide your top speed by speed at 1rpm. It’s obvious when you do it, but I didn’t do it as I was posting.

You find your speed at 100rpm for a given gear ratio, divide by 100 and it’s your speed at 1rpm. Then divide your top speed by the 1rpm speed and there’s your cadence.

Eg 100 rpm on 42/16 with 700x28 = 33.6km/hr.

1rpm = .336km/hr

Then say your top speed is 62 as recorded by the speedo or a cop with a radar gun, 62/.336 = 184.5rpm

But that doesn’t give you a cadence at 55 or 72 or 13 km/hr, so you need a way to calculate it from a given speed.

yeah but when riding with no computer, cadence is easiest to know. So you want to get speed from your cadence. So you get your speed at 1rpm and then multiply that by your ACTUAL rpm to get your speed.

- Joel

get a cyclocomputer!

See, here’s the thing. When I’m bombing down a hill at 60+, I’m not looking at my watch and counting my pedal strokes. Plus I doubt you could count your rpm with accuracy greater than +/- 10-20 at high speed.

Buy a Sigma BC1600. They’re cheap, and if you get it from Bikepro.com.au they might still be bundling it with a… !!Cadence sensor!! (I have one, but haven’t hooked up the cadence.)

Or just estimate. And round up. I reckon I was doing at least 75 and 230rpm this morning. At least.

If you use a computer for a while you’ll get to know what different cadences feel like.

I’ve found that when I used computers and HRMs, after a while you pretty much know what speed/cadence/HR you’re at anyway.

Here’s a spreadsheet that calculates cadence based on gear ratio, wheel diameter and speed. You can use it to make a complete table of cadence vs. speed for given input values.

You beat me too it.

I was going to send in a spreadsheet this arvo!!!

Bugger

I found this cool one for working out speed from gearing and cadence and time per distance. Mainly used for track cycling pusuiting, but useful none the less

Can send it to someone to upload if they want.