norm007
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| posted on 3/8/09 at 02:54 PM |
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Diff/speedo ratios
I have swapped my 3.62 ratio diff to a 3.92.
Could anybody tell me how to work out how much faster my speedo will be reading than the actual speed?
Cheers
Something about this, so very wrong.....I have to laugh out loud, I wish I didn`t like this!!!!!!!!!!!!!!
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mcerd1
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| posted on 3/8/09 at 03:13 PM |
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3.92 / 3.62 = 1.08
=> you speedo is showing +8% faster than your really going
e.g. your speedo says 60, but your really only doing 55.5
or try this http://locost7.info/gearcalc.php
[Edited on 3/8/09 by mcerd1]
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asl
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| posted on 3/8/09 at 03:21 PM |
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Ok, I am going to make myself look like a complete t#*t but I have to ask this......... I changed my diff from a 3.92 to a 3.38. Has this affected my
speedo?
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mcerd1
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| posted on 3/8/09 at 03:26 PM |
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yes
3.92 / 3.38 = 1.16
=> you are going +16% faster than your speedo says (assuming it was right before the swap)
so if your speedo says 60, your really doing 69.6
try the gear calc program above ^^^
[Edited on 3/8/09 by mcerd1]
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aka Keith
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| posted on 3/8/09 at 03:27 PM |
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Nat, great post. in a word yes, your actual speed will be more than your indicated speed.
cheers
Craig
You will need to recalibrate your speedo, so as not to pick up any speeding tickets. 
[Edited on 3/8/09 by aka Keith]
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asl
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| posted on 3/8/09 at 03:34 PM |
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Bloody hell, you learn something everyday! That will explain why when I took my dad out he was commenting and how it feels like we were goin much
faster than we actually were!! From numpty of Guildford!
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James
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| posted on 3/8/09 at 04:08 PM |
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quote:
Originally posted by asl
Bloody hell, you learn something everyday! That will explain why when I took my dad out he was commenting and how it feels like we were goin much
faster than we actually were!! From numpty of Guildford!
Especially worrying with the new mobile speed camera in Guildford!!!
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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mad-butcher
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| posted on 3/8/09 at 06:52 PM |
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well I'll throw a spanner in the works, I can change my diff without having to recalibrate my speedo.
why you might ask, cos I take my pulses from the driveshaft which only requires rolling distance on the acewell,
tony
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matt_claydon
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| posted on 3/8/09 at 06:54 PM |
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Depending on where your speedo pickup is of course. If it's on the axle or wheel then diff changes will make no difference. If it's on the
prop or transmission then it will make a difference.
Edit: ^ beaten to it
[Edited on 3/8/09 by matt_claydon]
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mcerd1
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| posted on 3/8/09 at 07:56 PM |
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quote:
Originally posted by mad-butcher
well I'll throw a spanner in the works, I can change my diff without having to recalibrate my speedo.
why you might ask, cos I take my pulses from the driveshaft which only requires rolling distance on the acewell,
tony
well remembered, I knew I'd forgotten something 
[Edited on 3/8/09 by mcerd1]
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norm007
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| posted on 4/8/09 at 11:19 AM |
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quote:
Originally posted by mcerd1
3.92 / 3.62 = 1.08
=> you speedo is showing +8% faster than your really going
e.g. your speedo says 60, but your really only doing 55.5
or try this http://locost7.info/gearcalc.php
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Thank you very much for the reply.
Forgot to say that I am running cable driven speedo on Type 9, that I know was deadly accurate from rolling road session.
Could I just swap the drive gear in gearbox? If so, could you tell me which gear I would need?
Something about this, so very wrong.....I have to laugh out loud, I wish I didn`t like this!!!!!!!!!!!!!!
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