93.0KMH on a road bike, but is it true?

[aserota]

Hi all,

I have recently got a new odometer (speedo) for my bike. Its a Cateye Enduro 8 and have had very positive thoughts so far, anyway....

I am a keen cyclist, with a very good road bike, but am unsure on the speed just achieve.

Going down a big hill my speedo has register a speed of 93kmh on Mx setting. The wheelsize set on the cateye is set at 273, but i have no idea if this is correct.

Can anyone help?

 

[RedBike]

60mph ?
Probably not.

Yes it's possible. No it's not very likely.

273, Whats the significance of that?
Most computers need the circumfrence of your wheel/tyre.

 

[aserota]

Thats what i need to work out.

Wheels are xed look 50, not sure on exact specs....ill go on google

 

[bonj2]

no, you've probably got it set for a penny farthing wheel.

 

[domtyler]

I can generally get to forty down a long, straight, steep hill with a good run on the other side, sometimes even a little more. That involves changing into the highest gear available and pedalling like crazy, head down low, on the drops.

You may be 33% faster than me I guess!

 

[longers]

Measure it yourself for the correct circumference.

Different tyres on the same wheels will alter the circumference.

With your valve at the bottom of the wheel make a mark on the ground and after a complete revolution make another mark when the valve is in exactly the same place. Distance between these is your circumference.



I don't know how your computer works and what you need to to with the data but at least you will have the right figure .

 

[RedBike]

I've no idea on the wheels. Besides, it's the tyres that matter.

Have a look at this table.
http://www.sheldonbrown.com/cyclecomputer-calibration.html

I've no idea which value you need but 273 does sound a bit odd. Isn't there a table or explanation in the manual?

 

[aserota]

Would it not be easier to take the radius and times x2 and pye?

 

[aserota]

72.9kmh is the answer

Wheels are 214 in circumferance

 

[RedBike]

Perhaps, but it wouldn't be as accurate.

Any mistakes / errors you make in measuring the radius will be squared; and how would you compensate for the deformation of the tyre.

You're looking for about 2100mm / 82.677 Inches

 

[punkypossum]

That's a 700x28 then?

 

[domtyler]

72.9kmh is the answer

Wheels are 214 in circumferance

Never mind, maybe turn pro next year eh?

 

[RedBike]

Wheels are 214 in circumferance

214cm? Perhaps,
We're talking about a touring bike then?

 

[RedBike]

What does it say on the side of the tyres?

 

[punkypossum]

Red bike, it's the cateye figures quoted in the conversion chart in their manual - if you have 700x28 tyres, you have to program the computer as 214, my 26x1.75 would be a 202 etc....