Speedometer

Wayne Broderick /

I had the wife follow me home from work in the car today. She said my top speed was around 35, with an average speed of 30ish. She was pretty sure I never hit 40.

My tomos targa indicated it was doing 40-45, with an average speed of about 35 mph.(according to the targa speedo).

My friend on a harley was riding down the main strip with me the other day. His speedo said 35 when mine also said 35. When we hit the hill, he took off, cause I slowed to 30 and less...

Just observation... Thought it was weird that in a car it suggests I'm doing 30, but a bike pacing me says 35.

I kept asking my wife "Are you SURE I didn't hit 40??"

Re: Speedometer

Hi,Wayne! Here's the best way to tell your true speed.Find a flat stretch of road with mile marker postings.Go by the marker at exactly 30 mph and click your stopwatch or mark the seconds on your watch at exactly the point you passed the marker.If you hold the bike at a steady 30 mph(it takes concentration but it's worth it)you'll pass the next mile marker in two minutes.If you feel like going on,go to the next marker keeping it at a steady 30 mph and of course that will total 4 minutes.When you do this you can also on the return trip check your odometer because they're not always off the same percentage as the speedometer.Now say it takes you 126 secs. to run the mile.Then your speedo is off(registering too fast)by 5% I think.You just have to figure the percentages.BYE!

Re: Speedometer

Wayne,

I'm thinking that if your 30mph/40mph ratio is taken out to highway speeds, you get 55mph/73mph. Your wife would be zipping by everyone thinking she was only going 55mph, but in fact going 73mph. Unless she chronically gets speeding tickets, or knocks people out of her way wondering why people are "so dang slow", my guess is the problem is with your speedometer. Is your's in kilometers, has anyone changed rim dimensions on the bikes or car? Knowing how wildly my speedometer spins around, i'd throw in a few percentage points for error, and maybe a slightly underinflated tire could count for something. Good luck.

Re: Speedometer

That's an interesting suggestion that would be true - if your tire is low you would read a higher speed than actual.

My experience is that there is a fundamental problem with the speedometer design. It's basically a magnet that spins inside a little "cap", that is attached to the speedometer needle. As the magnet spins it creates edy currents in the cap, that pull it in the direction of rotation. The problem with this is that the pull force doesn't increase the same as the spring force that pulls the needle to zero (there are losses in the edy currents at high rpm and the spring force is not the same the more you unwind it). I've noticed that up to about 25-30mph it's correct, but when you start doing 55-65mph my speedo reads 65-80 mph. I'm assuming that my moped behaves the same way (although I haven't tested it) because they use the same speedometers, just different drive gears and face plates.

LISTEN TO ME!!!

ok now that i have everyones attention....get a bicycle speedo. take the magnet and j.b weld it to the rim or if you have a wire rim install it nomally. these are so acurate! they are even more acurate than car speedos. YOUR WELCOME!

-mike

Re: LISTEN TO ME!!!

Hi,Mike! I appreciate your suggestion,but most of us don't want 2 speedos on our bikes and a lot of us want the original equipment look about our bikes,like the motobecane Huret,which is a good looking speedo.Also the Tomos and Motomarinas have nice ones.The thing I don't like about the digitals I have for my bicycles is mine are hard to read at a glance because the read-out is small.But I'd say if a person can't make his speedo read correctly,it's possible the speedo is worn out.There's a spring which can get weak that the needle is hooked to and it will vary with temperature and fail with age sometimes.BYE!

Digital Speedos

Chris Robertson /

I'm a big advocate of the digital spedometers. I'm always leery about taking a top-speed claim at face value unless it has been verified either with a car (as Wayne has done) or with a digital spedometer.

I also find that the spedometers don't vary by a constant percentage.

Ex: One of my Peugeots stock spedometer is accurate up to about 40km/h (0% error). When it says 55km/h I'm really going about 50km/h (10% error). When it says 70km/h I'm really going about 60km/h (15% error).

If you don't want to add a digital spedometer, you might want to consider <i>temporarily</i> putting one on until you learn what speeds your moped is really going. As an alternative you can verify with a car at different speeds. You can also do the one mile time trials as Don suggested. Once you know how your spedometer behaves you can reliably translate the speed into "real" units.

As a point of interest: Does anyone out there have a stock spedometer that actually gives you a <b>conservative</b> (as opposed to inflated) reading? Broken spedometers that always say "0" don't count, of course!

Chris.

Re: Digital Speedos

I have a tomos targa and i also feel that my speedometer isint reading accurately. I was thinking about getting a derbi's dash installed into my Targa's but I dont fare enough. I think that my Targa may read in km/h (its a 2001 targa fyi). But i KNOW that it can go faster than 33 kmh with a 110 lb. guy on it. So it must be MPH. Ahh, who knows really what the new targas read?

Wisky

Re: Digital Speedos

Chris Robertson /

Tomos mopeds sold in the US read spead in miles per hour, and distance (on the odometer) in kilometers.

Chris.

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