Speedo Calibration
Anonymous
Posts: 79,667
Hi
Someone told me that this part of road is exactly 1 mile, so I go along it and find my speedo is telling me I've done 0.94 miles, will this mean my speedo will be slower or faster than I am actually doing?
Also when inputing the number into the speedo do I go by the number thats on the tyre, its in the format of --- x --- if you get me.
Someone told me that this part of road is exactly 1 mile, so I go along it and find my speedo is telling me I've done 0.94 miles, will this mean my speedo will be slower or faster than I am actually doing?
Also when inputing the number into the speedo do I go by the number thats on the tyre, its in the format of --- x --- if you get me.
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Comments
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The number you put into the computer is your tyre circumference in millimetres. Measure it by putting the valve to the bottom of your front wheel and making a mark on the ground, then moving forward one full wheel revolution and making another mark - the distance between the marks is your circumference.
After you've done that, if your computer says the section of road is 0.94 miles it's because it's 0.94 miles!
Ok, ok, if your computer reads the distance short and you're absolutely definitely positive it's really exactly a mile then your speedo would read low (same time but smaller distance = less speed).Even if the voices aren't real, they have some very good ideas.0 -
Willhub
If your speedo is wrongly calibrated and showing a shorter distance then it will also show a lower average speed. (You think you've only done 0.94 of a mile but you've really done 1 mile in the same time)
To set the speedo up you can either use the chart that comes with the speedo and input the data for your tyre size ot you can measure the circumference yourself: put a mark on one tyre and on the ground. Roll the bike one full revolution, until the mark is on the ground and then measure how far you have moved - enter this into the speedo.
Assuming the 1 mile measure you've been told is correct, then your speedo is 6% out (cars get away with 10%)
So, when your speedo shows 20mph, you might be doing 21.2mphBe nice to grumpy old men (or else!)0 -
I have gone so far as to pump the tires to riding pressure, put a mark on the wheel,
and a matching one on the pavement, got on the bike, had my wife push me until the wheel did one revolution and the mark hit the pavement again. Then I put that distance in my computer. A bit on the obsessive side but damn it I needed to know, or at least I
thought I did.
Dennis Noward0 -
Hang on, I'm the one with the sig line about hearing voices!dennisn wrote:I have gone so far as to pump the tires to riding pressure, put a mark on the wheel,
and a matching one on the pavement, got on the bike, had my wife push me until the wheel did one revolution and the mark hit the pavement again. Then I put that distance in my computer. A bit on the obsessive side but damn it I needed to know, or at least I
thought I did.
Dennis Noward
Just out of interest, was the result any different from the normal way?Even if the voices aren't real, they have some very good ideas.0 -
Is 6% bad? I dont really want to do reset it again and loose a further 106 miles, I lost the first 50 mile when I dropped the speedo and it reset.0
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Willhub dont worry if you need to reset your speedo, you will not really loose the 106 miles.. they are in your legs.. where it counts.
Try using www.mycyclinglog.com
It is brilliant records all info about your rides and you can compare from previous years.. I have been using it for 3 years now.. unfortunately I can see my mileage is low compared to last year
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A lot of computers will let you manually enter a figure for your total mileage. Might be worth a look in the manual?willhub wrote:Is 6% bad? I dont really want to do reset it again and loose a further 106 miles, I lost the first 50 mile when I dropped the speedo and it reset.Even if the voices aren't real, they have some very good ideas.0 -
Thanks I'll try that cyclinglog, some of the rides on there people have done is really long!! Tomorrow I was thinking about doing a 20mile ride but the wind is apparently going to be around 23mph so dont think it would be good to do it.
So how do I measure the circumference? I'll try and set it in tomorrow.Shadowduck wrote:
A lot of computers will let you manually enter a figure for your total mileage. Might be worth a look in the manual?willhub wrote:Is 6% bad? I dont really want to do reset it again and loose a further 106 miles, I lost the first 50 mile when I dropped the speedo and it reset.
I dont think my speedo has anything like that from what I can see :?0 -
You're best just sticking your head out the window tomorrow to see what the weather's like!
There's a couple of posts further up (mine and killiekosmos's) that tell you how to measure the circumference.
What kind of computer have you got? Most that I've used will let you change the circumference without resetting and allow manual entry of total mileage. Still, as giantscr2.0 says, it's the miles in your legs that matter not what your 'puter says!Even if the voices aren't real, they have some very good ideas.0 -
Oh thanks, I did not udnerstand it before but I get it now
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The value I had put in was 2154 I think.
Got a question, when its like 23+ mph wind what sort of speeds do you get into the wind? I'm down to like 10-12mph sometimes and it really makes me want to stop.0 -
Shadowduck wrote:
Hang on, I'm the one with the sig line about hearing voices!dennisn wrote:I have gone so far as to pump the tires to riding pressure, put a mark on the wheel,
and a matching one on the pavement, got on the bike, had my wife push me until the wheel did one revolution and the mark hit the pavement again. Then I put that distance in my computer. A bit on the obsessive side but damn it I needed to know, or at least I
thought I did.
Dennis Noward
Just out of interest, was the result any different from the normal way?
That was some years back before I got old and lazy. It made a bit of a difference but
nothing worth worrying about. However, for those obsessed with acuracy, I guess
it's the way to go. I have a friend who always tells me his exact mileage(49.56 or
whatever), now he's really obsessed.
Dennis Noward0 -
12mph into a 23mph headwind would be pretty good going I think, though it'd be unusual to get a steady headwind that strong. Usually the wind is gusting and coming from all directions* so it's anybody's guess how strong it actually is at any given moment... Just deal with the conditions as you find them and make what headway you can, if it gets too much stop or head home - nobody's going to mind (assuming you're not on your way to work, of course!). Treat headwinds as horizontal hills and remember what good training you're getting!willhub wrote:Got a question, when its like 23+ mph wind what sort of speeds do you get into the wind? I'm down to like 10-12mph sometimes and it really makes me want to stop.
*Except behind, of course.Even if the voices aren't real, they have some very good ideas.0 -
Doing a rollout with wheel/tyre which the computer uses to measure speed from would be sufficient. Yes the most accurate method is to be on the bike and ensure tyres are pumped up and doing multiple revolutions in a dead straight line - measure that distance and divide by the number of revolutions.
Even with the simple method at most you'd be 5mm out which for a rollout of ~2100mm is only 0.24% out. Most can live with that.
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I think I will try the putting lines on a pavement way.
I need a good pump but that combined with getting some cycling clothes comes to 50+ quid which I dont have at the moment, I am currently having to use a friend of my dads big bump for cars, like its got a big tank on it but I need to use an adaptor.
Shadowduck, thanks I think I'll give a 6 mile ride a try today, nothing too long and see how I go into the wind, but I always thought the wind was coming from one direction even though no matter which way I am going it still seems to be slowing me down apart from when its right behind me and I hit 24mph easilly then, the other day it was a 36mph wind, well gusts I think and wind was pushing me and I managed to hit 35mph for first time.0 -
I,ve done mine and on 2 rev's I got 4210mm so 2105. Thats on 700cc wheels and 23mm tyres @ 100psi.0
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In Gosport we have two sets of large markers on the shore.... align the fiorst two and travel until you align the second two. The distance is actually one nautical mile.
Bad news is that you have to be out on the Solent to use it!
More realistically......
The accuracy of a speedometer is not going to matter greatly beyond the calibration you will get by the "rolling method".
If you travel an exact "mile" and take the cut the corners, then repeat taking the corners wide, then it is easy to get a 5 or 6% difference in the route... Set the Speedo up and accept it as accurate then use the figures in a comparative way. i.e. if you do 5 of "your" miles with decreasing times then you are improving<b><i>He that buys land buys many stones.
He that buys flesh buys many bones.
He that buys eggs buys many shells,
But he that buys good beer buys nothing else.</b></i>
(Unattributed Trad.)0 -
Well I do want it to be fairly accurate.
I did a route today, and my speedo recorded it as 10.98 miles, but I've drawn in on bikely using the google maps thing and its showing 10.7-10.8 miles, so how much slower will I be going than what it is showing on the speedo? Surely nothing too big?
http://www.bikely.com/maps/bike-path/10-mile-TT0 -
willhub wrote:Well I do want it to be fairly accurate.
I did a route today, and my speedo recorded it as 10.98 miles, but I've drawn in on bikely using the google maps thing and its showing 10.7-10.8 miles, so how much slower will I be going than what it is showing on the speedo? Surely nothing too big?
http://www.bikely.com/maps/bike-path/10-mile-TT
That is 0.1 miles in 10 - about 1% or less than 200 yards, as I said before - the difference between cutting the corners and taking them wide.
It is best to get away from an empirical measurement - comparison is more accurate for training purposes. Your "distance" will always be the same if you measure it with the same speedo and the same settings. You can then guage your improvement more accurately than the same route.<b><i>He that buys land buys many stones.
He that buys flesh buys many bones.
He that buys eggs buys many shells,
But he that buys good beer buys nothing else.</b></i>
(Unattributed Trad.)0 -
Ok I wont worry about it anymore, just I never realised these distances I did were actually like 10+ miles, the 10 mile distance I did before I got a speedo I thought it was more like 5-6 miles and I was like noo way can I bet doing 10 mile.0
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Just a rough enquiry here, does it matter where on the wheel you mount the magnet/transponder that'll ultimately receive the signal for your wheel revolution?
I've always mounted mine about 2/3rd's of the way towards the rim but I've seen some pics with people with their wheel magnet way out towards the rim and others with their's a few cm from the hub.
With fairly high extremes like this is this not more important than tyre size? I've recently switched from a matching 23C Vredestein Fortezza Tricomp to a 25C Conti GP3000.
I didn't bother recalibrating my Cateye Micro Wireless. Doesn't seem to have made a huge difference to me avg. speed wise. Still, averaging 15.7-17.1 mph, fair enough considering the naff winds we've experienced recently.0 -
It doesn't matter where you mount the magnet on the wheel, one revolution is one revolution no matter where you put it.0
