Gear ratios

Dellortoman

Dellortoman

Hero member
Location
Tasmania, Australia
For those of a pedantic disposition ...

I've been peering at the innards of my Jota's gearbox. More out of OCD behaviour than anything else. I counted the teeth on each gear and worked out the ratios, but my 1st gear ratio didn't tally with Ian Falloon's Laverda bible. So I went and counted the teeth again. It turns out that Falloon is wrong (shock horror!).

If you have a copy of Falloon's book, you may want to amend the Laverda 1000 specs on page 152. The correct gear ratio is 1:2.857

Actually Falloon is more than just wrong, he's very wrong. He actually says 1:2618 (although I assume he means 1:2.618) which would be very low geared indeed. At 5000 rpm it would take a bit over two minutes to get one revolution of the back wheel!  :D

I thought there may have been an earlier or later version, or a close ratio box that had 2.618 as a first gear, but there is no possible combination of tooth numbers that would give that ratio with a 21/30 sleeve gear. So I dunno where he got it from.

Cape, you might want to amend your gear ratio calculation spreadsheet on your website as you have used Falloon's number. http://www.laverdafinland.org/gear_ratios.htm

If you don't believe me, JLO has it correct on his website http://www.laverdamania.net/chart.htm

For anyone who is interested in tooth numbers for a series 1 1000, here they are:

1st  34/17*30/21 = 2.857
2nd 29/22*30/21 = 1.883
3rd 25/26*30/21 = 1.374
4th 23/28*30/21 = 1.173
5th (direct drive) = 1

Note that the first four gears drive via the layshaft and the sleeve gear. So the sleeve gear ratio of 30/21 is common to all of them.
5th gear is direct drive via dogs straight through from the clutch to the output shaft.

In neutral, drive to the layshaft is disengaged.

Cam
 
I had a copy of this a while back but it gone now.From memory the early triples had a lower first with the rest the same,bit later 1st became higher.And there was a factory close ratio box as well.Thats real fuzzy and from the web,so don't go betting your house on it.
 
The "bible" with faults in it!! Sounds familiar. Good work, Cam. Probably all of these reference works will have faults, the authors have put out what they could find out, second hand info at best. That is one of the best things about this forum, people can confirm details like this.
Your ratio list shows clearly the big gap from 2nd to 3rd, same as on twins. Too slow for 3rd, too fast for 2nd. Hate that, especially on the track. I cannot understand why the factory did it. The close ratio box simply raises 1st and 2nd to even up that gap from what I have heard, not really close ratio in the true sense.
 
strange thing about laverdas the gearing and gearbox, in the press back in the 70s all you heard was the tall gearing and the heavy clutch etc, but take them to the foothills of northern Italy and you find out that they are not that far out and I would suggests spot on.
cheers for the info.
best regards andy
 
The info is in the Green Book (along with a typo for 1st gear on 750s and early triples - corrected here!!):

All 650 and first 100 or so 750 (all SFC & close ratio triples in brackets)

2.406    (2.214)
1.739    (1.607)
1.486    (1.269)
1.173    (1.083)
1.000

All 750 and 1000 up to #3707 (later triples and all 1200 in brackets)

2.618    (2.857)
1.883
1.373
1.173
1.000

Thanks for prompting me to check, Cam - I always wondered about the mysterious close ratio box on the triples...now I know what a beating the clutch would get for ordinary road use after riding my SFC.  Kevlar plates recommended!  :D
 
tom3c75 said:
The numbers for the 3C, mine anyway, differ from the later 180?s.
There are 18 teeth on the main shaft and the matching gear has 33.
Click to expand...

I was wondering whether that was the case. Doing the sums, those tooth numbers give a 1st gear ratio of 1:2.619, which is close to Falloon's 2.618 figure and the same as the 750. But he doesn't make any mention in his "Bible" of a lower ratio for later models. 

In fact, I can't find any mention of the 1:2.857 ratio anywhere in his book. However, he does hint at a lower first gear in the chapter about the RGS when he says "First was now the higher 1:2.619 of the first 1000". So presumably he knew that there was a lower 1st gear somewhere along the evolutionary line.

He also contradicts himself in his spec table in the back of the book, in which he lists the RGS/RGA as having a 1st gear of 1:3.036 which would mean 16/34 teeth. That seems unlikely because it's quite a low 1st gear and would mean even wider spacing between gears (also gives different ratios for 2nd and 3rd).

What we need is a whole bunch of stripped-down gearboxes from various models to count the teeth!

Only definite conclusion I've come to is that the "bible" shouldn't be taken as gospel  :D

Cam
 
Dellortoman said:
Cape, you might want to amend your gear ratio calculation spreadsheet on your website as you have used Falloon's number.
Click to expand...

Done.

www.laverdafinland.org/gear.php
www.laverdafinland.org/gear_ratios.php

Thanks Cam.
 
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