cycle computer vs gps accuracy

Smokin Joe

Legendary Member
More accurate.

The computer depends on correct setup which is hard to get exactly right, and will be affected by your tyre pressures.
 

Garz

Squat Member
Location
Down
Depends on the update/refresh rate tbh. I tend to believe my computer but your right it has to be setup correctly.
 

ColinJ

Puzzle game developer
I stopped using a bike computer when I realised that it was spoiling my enjoyment of rides. I'd spend the whole time trying to go faster, beat my time up climbs and so on. I'd get back from a ride hardly remembering anything other than a load of numbers.

I now ride with a GPS unit on my bike. I usually have it set to the navigation screen so I don't see any numbers but it is busy logging all the ride data I could ever want. I could examine the data out when I get home but I don't usually bother.

A gps ride tracklog will give you very detailed information if you want it and it is very accurate. I don't know about the accuracy of instanteous speed readings because as Garz mentioned above, it depends on sample rates but distance covered and average speed are very accurate.
 
I used to have a gps and a separate computer fitted to the bike but I found there was only 0.1mph of a difference on average. Usually the computer recorded more but nothing to worry about IMO. I decided that occasionally I wouldn't go in a straight line :laugh: (too many :wacko: I think) and the computer recorded that whereas the gps records the straight line between two points and as said by other posters will depend upon the refresh rate and signal coverage.

Wrt 44 & 46kph, the latter is more impressive so it must be accurate :biggrin:
 

GrasB

Veteran
Location
Nr Cambridge
It's touch & go between gps & a trip comp as when you lean the bike your tyres rolling radius changes, gets smaller, this makes the trip comp over read distance as the wheel is turning faster for the same speed.

With GPS you get the opposite, under reading as it's assuming a straight line between 2 points. You'll also get GPS jitter & wandering, both shown below on a slow ride into town, the faster you go the less jitter effects the reading but you'll get wandering, however that's more systematic. The effects cancel each other out to for the most part.

So over distance I'd say that GPS is probably the more accurate, but for instant measurement, eg your peek speed, a wheel based method is more likely to be accurate.
 

jimboalee

New Member
Location
Solihull
My ride today.

Computer said :-

Distance 69.32 miles.
Time 4.27.44
Avg 15.5
Max 36.0

Garmin said :-

Distance 69.02 miles.
Time 4:27:57 Garmin was in back pocket and I stopped it a few seconds after the Cateye.
Avg 15.5
Max 35.7


No grumbles.
 

HJ

Cycling in Scotland
Location
Auld Reekie
A well set up computer is more actuate than a GPS. Unless you have a differential GPS system with a correctly set up base station, your ordinary GPS is, at best, only accurate to +or- 5m.
 

Smokin Joe

Legendary Member
It doesn't really matter if your computer is a few percent off accurate. As long as you keep the same setting all the time you have a comparison to work on, whether it is 1% over or 1% under true reading is irrelevant.
 

Garz

Squat Member
Location
Down
Agreed so judging by how much a gps may cost I think the value comes from the computer! :rofl:

(I use my smartphone as gps and stopped doing this as it hammered the battery life and was as discussed slightly less accurate with more of a faff around)
 

ColinJ

Puzzle game developer
Garz said:
Agreed so judging by how much a gps may cost I think the value comes from the computer! ;)
Yeahbut you can't navigate by bike computer!

I've got a cheapo Garmin Etrex GPS. You can get the newer version (the Etrex H) for under £60 now. You'd probably need to spend another £20 on NIMH batteries, PC interface cable and a bar mount so call it £75. Knock off the cost of the computer that you'd no longer need, so only about £60 extra. (Or buy an old one on eBay for about £20)

The batteries last 24 hours+ between charges/changes.
 
OP
alecstilleyedye

alecstilleyedye

nothing in moderation
Moderator
ColinJ said:
Yeahbut you can't navigate by bike computer!
indeed, and i can use my smartphone as a sat nav should the unthinkable* happen and i get lost on the club run having been dropped by the fast group while the steadier group turns off behind me.

* actually happened a few times and involved phoning the wife to look at a map…
 

Garz

Squat Member
Location
Down
The thread title states 'accuracy' and not navigating.. :tongue:

I wouldnt be happy strapping my phone to the handlebars and it wouldnt be weatherproof or probably readable in the sunshine.

Factor in the handlebar mount (otherwise you cant really use it to nav) big C and it jumps say to around £100 with added risk. :biggrin:
 
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