Speedo accuracy

[bladerunner 0]

Sat bored at work and just got to thinking how accurate a bike speedo is when the bikes going round a corner. Obviously the speedos something like when your riding in a straight line on the Center of the tyre but when you lean over your effectively running on a smaller diameter as your running nearer to the edge of the tyre. Way too mich time on my hands.

[Stue11 0]

You must be bored

[Robbie 0]

Interesting thought but it won't effected some bikes as they have electronic speedo's that pick up from the output shaft and not the front wheel.

[BanditMike 0]

Definitely bored. I'd be more concerned if he'd worked out how much faster the speedo would be

[fr499y 0]

Not much if anything at all. I actually tried it before although i tried it with a magnetic speedo, the same theory should apply. the time it takes for the magnet to pass the sensor is the same no matter what angle the wheel is at, no matter how flat the tyre is. With mechanical speedo its (if i remember) a magnet and a aluminium disc. Faster the magnet spins, the more the alu disc is 'dragged' its pretty technical for such a simple thing

[bladerunner 0]

what I'm getting at is even if the speeds taken from a gearbox shaft,when the bike leans over its effectively running on a smaller diameter part of the tyre so the wheel will turn faster for any given speed,therefore (big word) if the wheel is spinning faster then the engine and gearbox must be spinning faster for the same speed.If you go into a corner and hold the throttle steady you can sometimes hear the engine revs rise a little as you lean over then slow down as you straighten up.If you look at a rear tyre theres probably between 1-2 inches differance from the crown of the tyre to the edge,that makes a 2-4 inch reduction in the rolling diameter when leant over on the edge of the tyre so effectively,a 17 inch rim with a tyre on it has an outside diameter of say 22 inches and the edge of the tyre is going to be somewhere around 18-20 inches diameter,thats a big differance.

Ill shut up now I'm starting to bore myself a little.

[madsod 0]

A few good points , in that lot ,

[ptolemyx 0]

My 190/55 rear tyre has a rolling radius at the centre tread of 320.4mm and the rolling radius at the edge of the tread (which I don't use cause I'm a chicken) is 288.4mm. If in a straight line my speed is such that my wheel turns 100 times in a given period of time then at the same speed when at full lean the wheel will turn 100 X 320.4 / 288.4 times, that is 111 revolutions so the speedo will read 11% faster and the rev's required to maintain that speed need to also rise by 11%. This is purely academic because when I'm leant over any more than 10 degrees from vertical I'm looking where I'm going, not at the speedo.

Now if I really want to be silly, given a nice big roundabout and a big balls transplant, with my speedo corrected with a Speedohealer to agree with Satnav in a straight line will the Satnav keep up with my position with enough accuracy to verify the amount the speedo theoretically over reads at large angles of lean

Old and Disgraceful

[fr499y 0]

@bladerunner wrote:

what I'm getting at is even if the speeds taken from a gearbox shaft,when the bike leans over its effectively running on a smaller diameter part of the tyre so the wheel will turn faster for any given speed,therefore (big word) if the wheel is spinning faster then the engine and gearbox must be spinning faster for the same speed.If you go into a corner and hold the throttle steady you can sometimes hear the engine revs rise a little as you lean over then slow down as you straighten up.If you look at a rear tyre theres probably between 1-2 inches differance from the crown of the tyre to the edge,that makes a 2-4 inch reduction in the rolling diameter when leant over on the edge of the tyre so effectively,a 17 inch rim with a tyre on it has an outside diameter of say 22 inches and the edge of the tyre is going to be somewhere around 18-20 inches diameter,thats a big differance.

Ill shut up now I'm starting to bore myself a little.

Dont forget the tyre will squash down as well which would in theory make it smaller again. which is why the speedo will show roughly the same speed.

[BanditMike 0]

Interesting read, and it sounds like it needs some independent verification through the use of actual "in situ" testing. Any volunteers?

And when did this become an engineering forum If we're not careful we'll have Dave drilling the middle out of his exhaust to test a theory

[fr499y 0]

@BanditMike wrote:

Interesting read, and it sounds like it needs some independent verification through the use of actual "in situ" testing. Any volunteers?

And when did this become an engineering forum If we're not careful we'll have Dave drilling the middle out of his exhaust to test a theory

Isn't that exactly what his doing

[fr499y 0]

It could also be down to the fact that you automatically accelerate whilst mid/out of a corner?

[ptolemyx 0]

The fact of the matter is when leant over the wheel radius is smaller so the wheel has to turn faster for the same speed and the revs need to be higher so the speedo will read more, whether it's reading from either wheel or the gearbox output shaft. BUT IT DOESN'T MATTER

Old and Disgraceful

......And by the time Dave's got round to buggering up his stock silencer he could have saved for some nice Yoshis to go inside the rocket launchers for the stock look with guaranteed better sounds IMHO Or I could make him a REALLY nice sounding B-King exhaust