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Good afternoon All, hope your all staying cool in the heat wave.

The bike is a 78 750 5 speed and i am curious if my speedometer vs tach is correct. In 5 the gear at 2500 i am seeing about 50mph, at 3000 about 60 and 3500 about 70. Sound about right to ya'll?

mark
 

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Great to have you on board. Aren't the classic Meriden bikes great? But what heat wave? :) It's always hot here in South Africa....
 

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'79 T140E, gearing / sprockets are 'standard', i.e 47tooth rear sprocket.

3000revs, 3rd gear ~ 30mph
3000revs, 4th gear ~ 40mph
3000revs, 5th gear ~ 50mph
4000revs, 5th gear ~ 70mph

This figures have helped me out over several thousand miles of riding with a non working speedo when the p.o.s. Veglia speedo drive has failed.

manual states that in 5th gear 10mph = 627revs, but I guess the rev counter wont be particularly accurate.

Does your bike have a 45tooth rear sprocket?
 

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Discussion Starter #6
Thanks teologie, I have no doubt that South Africa is very warm.

Pointing at the same clock position seems about right- till my tach rotates 90° to the left. Of course i expect that in the southern hemisphere they rotate right....


I should go count my rear sprocket.. manual states 47 tooth. It also states 1 to 1. I guess you can multiply up using 627. 6*627=3762rpm=60mph. Sound logical?

mark
 

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10 mph @ 627rpm sounds about right.That's 6270rpm @ 100mph , 8778 rpm @ 140 mph.
4000 @ 70 mph would give 8000 @ 140 mph,so something's not right.

With 20/44 sprockets,you'd be spinning 4100 rpm @70 mph;not with 20/47.
 

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On a 78 with stock gearing and wheel size in fifth gear every 500 rpm equals 8 mph.
2000 = 32 mph, 2500 = 40, 3000 = 48, 3500 = 56, 4000 = 64, 4500 = 72. I have had both of my gauges rebuilt by Nisonger and they check out within a couple of mph of what they should be. I was surprised that it was the tach that was really off.
 
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