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Question about speedo drive ratios. Since doing all the mods to my Manta A, I now have a speedo that is reading about 20% low, ie Speedo reads 50 mph when actual road speed 58 mph
The gear box (Carlton R25) has a Yellow (19 teeth) drive fitted at the moment, but a Red (18 tooth) or Blue (20 tooth) drives are available. Am I correct in thinking that by fitting a red drive, the drive will turn faster and therefore increase the speedo speed reading.
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You're correct, less teeth would make the speedo read higher, but only by 5% so you're still a good way off. You'd need a gear with 20% less teeth. Assuming you could get one, the pitch would be too far different to stock that they'd be unlikely to mesh properly.
You can get inline "converters" with gears which run in the middle of your speedo cable, or it might be possible to tweak the calibration of your speedo - "Speedy cables" do it for something like £80, or you could have a go yourself (I presume you adjust the clearance between the magnet and the "cup" to adjust for scale, or you could probably tweak the spring. It'd be easy to get yourself into a mess without an accurate RPM signal to drive the thing and calibrate it though.
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Last Edit: Mar 6, 2017 19:59:50 GMT by cobblers
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Can you get a new dial printed for yours (change the position of the numbers on the dial, rather than recalibrate the mechanicals) Not an ideal solution but it used to be legal (might still be) to put stickers on a KMH import bike speedo, so a "30 dot" at 30mph, 50mph, 70mph etc. I have used a kmh/mph adaptor before but don't think the ratio would suit your setup. I think the Manta speedo will be mechanical, so "adjusting" it would need a thicker/thinner speedo spring, possibly retension the existing spring.
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bortaf
Posted a lot
Posts: 4,549
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Are they not like Fords where you change/match the worm and pinion to get the ratio right ?
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R.I.P photobucket
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