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/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Tire Size/Spedo /cgi-bin/YaBB.pl?num=1433293168 Message started by MnSpring on 06/02/15 at 17:59:28 |
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Title: Tire Size/Spedo Post by MnSpring on 06/02/15 at 17:59:28 Finally got, arountuit, to mount a GPS unit on the MC (Tanks Dave for the parts, McGivered them) Anyway, running a 130/90 rear tire, and according to the GPS, it is within 10 ths, of what the factory Speedometer Needle says. To some it may be important, some not. Here, a local cop, likes to hide behind a lumber yard building, about 15 feet, from where the S.L, goes from 45 to 30. On Sunday Mornings. And, LOVES, to pass out tickets. The locals call him, ‘Barney”, LOLOLOLO (If you don’t know, 'Barney Fife, from Mayberey') So, it becomes, ‘important’, at that place and time. |
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Title: Re: Tire Size/Spedo Post by Kris01 on 06/02/15 at 18:35:46 So you're saying the 130/90 reads correctly? I'm using a 140/90 and it seems to be waaay more correct than the 130/90. |
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Title: Re: Tire Size/Spedo Post by chzeckmate on 06/03/15 at 00:58:11 0C352E347776470 wrote:
I mentioned this in another thread but I'll mention it again because I didn't really get an answer. I'm running a stock rear (IRC 140/80) and my tank speedo is spot on. We have several "What's your speed?" radar signs here in Houston that I pass regularly at different speeds and when I do I always look at my GPS speedo and the tank speedo and they both read exactly what the radar says. It's my understanding that the stock tire should give a false reading of higher speed but mine doesn't. What could be the explanation for this? |
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Title: Re: Tire Size/Spedo Post by verslagen1 on 06/03/15 at 07:08:07 Do you know how a speedometer works? http://cdn4.explainthatstuff.com/how-speedometer-works.gif The speedo is calibrated by adjusting the strength of the magnet... pret near a black art. 2nd is why they are mostly optimistic... because if they were pessimistic you'd be getting tickets on a daily basis. |
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Title: Re: Tire Size/Spedo Post by Dave on 06/03/15 at 07:22:37 I don't believe mechanical speedometers are calibrated from the factory, and there is some variation in all of them. Newer vehicles with fuel injection are now much better as the speedos are driven by electrical pulses and the needle is also electronically controlled Each Savage is most likely going to be a bit different.....overall however they seem to be a bit optimistic. My Honda ST1100 has a speedo cable and mechanical speedometer, and it reads 60 mph when I am going 55 mph...and is pretty typical of the error to be expected. The |
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Title: Re: Tire Size/Spedo Post by Art Webb on 06/03/15 at 08:21:26 I think Versy got this one right Even when all cars had mechanical speedos, the ones in Police cars were 'certified' meaning they were actually tested to be accurate, while non police cars had non certified speedos that tended toward optimism Newer cars may or may not be more accurate (Although both my Ranger and Lumina, both of which are injected, still have optimistic speedos) but the Police car speedos are still 'certified' |
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Title: Re: Tire Size/Spedo Post by Tocsik on 06/03/15 at 08:31:33 And 2 wheel vehicles HAVE to read optimistic cuz we don't always roll on the maximal diameter of the tires. When we corner, we are rolling around a smaller diameter since we're on the sidewalls. If the speedo is reading from a wheel (and not all do) then the indicated speed will increase in turns over the actual speed. |
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Title: Re: Tire Size/Spedo Post by chzeckmate on 06/03/15 at 09:09:16 42514647585553515A05340 wrote:
Right, I understand now. There are a number for factors that could cause my speedo to read the way it does. The magnetic field generated by any given magnet is specific to that magnet, and the rotation of the speed cup would reflect that. The needle itself may be positioned slightly differently during assembly. Even the the hair spring might have slightly less tension. The position of the dial could also have been positioned slightly clockwise during assembly. Any or all of these things could play a role in the reading of the speedo. Each bike having it's own unique factors would explain why some speedos can be accurate and some can be way off like my Hyosung that would read optimistically as much as 10 mph. Or my Lifan that would read under by as much as 7 mph. Thanks for the good info! |
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Title: Re: Tire Size/Spedo Post by justin_o_guy2 on 06/03/15 at 09:33:13 Whatever it's doing, you can study it and figure out what it's doing. They tend to be off by some%age, and run pretty much There. Prove /test the Speedo at different speeds, 30,60 handy numbers to work with. Of course if it's off 8.238% instead of 5,10, |
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Title: Re: Tire Size/Spedo Post by Serowbot on 06/03/15 at 10:42:55 Just hope it ain't off by pi... that would take forever to figure out... :-?... |
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Title: Re: Tire Size/Spedo Post by Dave on 06/03/15 at 10:48:13 4C5A4D50485D504B3F0 wrote:
My security password is the last 4 digits of pi...... ;D |
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Title: Re: Tire Size/Spedo Post by justin_o_guy2 on 06/03/15 at 10:49:38 I wonder how many of us there are,,,, |
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Title: Re: Tire Size/Spedo Post by Art Webb on 06/03/15 at 11:37:18 7C6A7D60786D607B0F0 wrote:
but if it's cherry pi that'd be awesome ;D |
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