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Discussion Starter #1
Hey All, I've finished building a STREEFIGHTER from my cbr 900RR and added a dual cb400 set of guages, this doesn't give a tru speed reading as the cb400 runs 120x17, cbr runs 130x17.
At 60 k's it's level but by the time I hit 100 it's 10k's out, faster that is, sit on 100 tru speed 90.
Is there an adapter I can add to the speedo cable, or can the guages be clibated to suit.
You blokes know it all, need your help.
REDHORSE.
 

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I'd suggest checking those wheel sizes again. Blades ran a 16" front until they changed to a 120/70 R17...

So if your instrument cluster is cable driven, then you could change out the front wheel and/or cable drive ( bit that fits to the wheel) to the cb400 instrument donor..

If your gauge is electrical (not cable driven) Speedohealer do plug in units that can be programmed to correct the speed reading.

If your gauge is cable and you would prefer an electrical cluster, you could swop the cable drive for a later blade sprocket cover and sensor, which would provide an electrical feed to a speedo unit ( and use a speedohealer to get it calibrated).

One thing though... I can't see how your readings can be level at 60kph but out at 100kph, if the gearing is wrong I would think you will be out all across the range, but it will be more noticeable at higher speeds as the pure value of the "out" will be greater and therefore easier to see...
 

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Discussion Starter #3
Hey Saxon,
Front wheel definitely 130x70x16 Pirelli Tyre, cable drive speedo cable, speed progressively is out between 60 and 100, 60/60, 80/86, 100/110. I'm in the process of mounting phone with speedo app to check gps wise.
 

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Ok. So there is a slight rolling radius difference between the 130/70/16 and the 120/70/17 tyres...

But, if this difference is the cause, it would affect all speeds (unless the tyres are distorting under the increase in speed (as drag racers do))...although in general use I would be surprised.

Are your tyres correctly inflated?

Therefore, I wonder weather the speedo unit is calibrated to the turns of a normally inflated 12/70/17, and by using the slightly different 130/70/17 you would be out - but as this would effectively be a gearing issue, you should be consistently out across the speed range - say 10% (using your 100/110 figure).

But, 10kph is easy to see on 100pkh, 3kph may not be so noticeable on 30kph....

Probably, there are some inefficiencies within the drive, cable or speedo, if you speed is low.

Will be interested to hear what the GPS has to say.

Still, to my mind, the options remain the same... Good luck....
 
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