Speedometer buying advice

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ColinJ

ColinJ

Puzzle game procrastinator!
Location
Todmorden - Yorks/Lancs border
fairyhedgehog said:
I can see how that would work. On the other hand, a wireless bike computer is being to sound like an easier option!
Click to expand...
I discovered the other day that my speed in km/hr at my comfortable cadence on a 13 tooth sprocket is equal to the number of teeth on the chainring, which I thought was rather nice! I do 48 km/hr on the big ring (48 teeth) and 38 km/hr on the middle ring (38 teeth). I tried it on the little ring for a short distance, and sure enough - my speed was 28 km/hr, though I didn't stay in that gear for long because the chain was at too extreme an angle and was making horrid noises!

These days, I think money spent on ordinary bike computers is money wasted when you could put that money towards a cheap GPS. I have an old Garmin which acts as a very good bike computer, but is also excellent for navigation. You can pick them up really cheap on eBay now (some for well under £40).
 
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vickster

vickster

Squire
If you ever want a slowish potter, let me know...

Also, the local CTC group do a beginners ride on Saturdays starting at nonsuch

http://www.cyclingswlondon.org.uk

Pop to fudges on upper high street, theylol sort you out with a simple wireless computer :smile:
 
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Piemaster

Piemaster

Guru
Location
UK City of Culture
@fairyhedgehog I've got a Holux GPSPort260 a GPS based unit. It does do some route tracking and allow for a breadcrumb trail style route plotting. Unfortunately since the laptop the software was installed in died I've not been able to use it for either function as I can't find the receipt to register it again on new laptop so have switched to using the phone.It does work as speedometer though. I'm now thinking about a Garmin unit.
Yours if you want it for a donation to charity. PM me.
 
Globalti

Globalti

Legendary Member
ColinJ said:
You can calculate your speed for nothing if you know what your gear ratio and your cadence (revs/min of your pedal action) are!

Count your pedal revs in one minute - that is your cadence. Call that 'Cad'.

Count the number of teeth on the chainring (front 'cog') that you are using. Call that 'Front'.

Count the number of teeth on the sprocket (rear 'cog') that you are using. Call that 'Rear'.

Get somebody to hold you upright on your bike with a clear straight run of at least 8 feet ahead of you. Line the valve on the front wheel up with the ground. Mark that position on the road. Roll forwards slowly until the valve is back in that position again. Mark the road again. Measure the distance between the 2 points in mm. That is the circumference of your tyre. Call that 'Circ'. (It is more accurate to measure the circumference that way than just wheeling your bike forward yourself because your weight will compress your tyres slightly and reduce their effective circumference.)

Your speed in km/hour is (60 * Cad * Circ * Front) / (1,000 * 1,000 * Rear) ~= (Cad * Circ * Front) / (16,667 * Rear)

The '60' converts rev/min to rev/hour. The first '1,000' converts mm to metres, the second, metres to kms.

If you prefer miles/hr then introduce a conversion factor of 1.609, so speed in miles/hr = (60 * Cad * Circ * Front) / (1,000 * 1,000 * 1.609 * Rear) or ~= (Cad * Circ * Front) / (26817 * Rear).

This is not quite as complicated as it sounds. Alternatively, if you think it IS - buy a computer or GPS, or use your smartphone! :thumbsup::laugh:
Click to expand...


Strewth Colin, that's REALLY simple for a novice!

Cateye Velo is the standard for simple, rugged bike computers: http://www.wiggle.co.uk/cateye-velo-9-wired-cycle-computer/
 
snorri

snorri

Legendary Member
Location
East coast, up a bit.
fairyhedgehog said:
I can see how that would work. On the other hand, a wireless bike computer is being to sound like an easier option!
Click to expand...
Don't worry about ColinJ, he's a wee bit old fashioned and never goes cycling without his book of Logarithm Tables, slide rule and calculator with spare batteries.:biggrin:
 
OP
OP
fairyhedgehog

fairyhedgehog

Active Member
Location
Epsom, Surrey, UK
ColinJ said:
These days, I think money spent on ordinary bike computers is money wasted when you could put that money towards a cheap GPS. I have an old Garmin which acts as a very good bike computer, but is also excellent for navigation. You can pick them up really cheap on eBay now (some for well under £40).
Click to expand...
I'll have to have a look at ebay and see what I come up with! Although if I get a badly needed new phone, that might be an alternative for GPS.
 
OP
OP
fairyhedgehog

fairyhedgehog

Active Member
Location
Epsom, Surrey, UK
vickster said:
If you ever want a slowish potter, let me know...

Also, the local CTC group do a beginners ride on Saturdays starting at nonsuch

http://www.cyclingswlondon.org.uk

Pop to fudges on upper high street, theylol sort you out with a simple wireless computer :smile:
Click to expand...

They don't quite know me by name in Fudges, yet ;) Do you rate them better or worse than Pearson's in Sutton?

I've been thinking about the Nonsuch ride for a while and not quite managed to get along to it. It feels rather scary - much scarier than joining a writing or book group!

I cycle as far as Sutton when I'm pottering, but I'm never sure where to go from there unless I go to the wool shop in Carshalton Beeches. It might be fun to meet up for a slowish potter some time.
 
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