BritBike Forum logo
BritBike Sponsor BritBike Sponsor BritBike Sponsor
BritBike Sponsor

BritBike Sponsor

BritBike Sponsor
BritBike Sponsor BritBike Sponsor BritBike Sponsor
The Bonneville Shop JRC Engineering dealers
Home | Sponsors, Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons, "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Member Spotlight
Monty777
Monty777
Cambridge UK
Posts: 56
Joined: July 2012
Show All Member Profiles 
Shout Box
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Who's Online Now
14 registered members (Alan_nc), 211 guests, and 372 spiders.
Key: Admin, Global Mod, Mod
Newest Members
Don Verdiani, Rauno Nyblom, mtbackroads, goatroper, Hawaii70BSA
10453 Registered Users
Top Posters(30 Days)
NickL 79
franko 68
Jeff K. 60
Popular Topics(Views)
737,594 mail-order LSR
Forum Statistics
Forums34
Topics68,622
Posts668,314
Members10,453
Most Online3,995
Feb 13th, 2017
Like BritBike.com on Facebook

Previous Thread
Next Thread
Print Thread
Rate Thread
Smiths Speedo Drive Ratios #46275
03/09/06 7:50 pm
03/09/06 7:50 pm
Joined: Aug 2004
Posts: 354
Iowa
Pender Offline OP

BritBike Forum member
Pender  Offline OP

BritBike Forum member

Joined: Aug 2004
Posts: 354
Iowa
Howdy all!
This may seem like a really stupid question, but what's the difference between a Mr. Smiff's 1.25:1 ratio and a 15:12 ratio?
My '72 T120 used to have a 15:12 but it bit the dust and I've replaced it with one with a 1.25:1 ratio which I figured would be the same. But now the bike reads too fast - possibly installed wrong or just wrong box altogether??? Thanks for any insight!


Furies and Apaches and Interceptors, oh my!
Support Your #1 BritBike Forum!

Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Re: Smiths Speedo Drive Ratios #46276
03/10/06 6:10 pm
03/10/06 6:10 pm
Joined: Sep 2005
Posts: 250
Tennessee
T
triumphmike Offline
BritBike Forum member
triumphmike  Offline
BritBike Forum member
T

Joined: Sep 2005
Posts: 250
Tennessee
There have been several speedo drive ratios over the years that must be matched to the speedo itslelf. Personally, I am most familiar with the 2:1 and 1.25:1 (which is the same as 15:12) ratios of the speedo drives. Usually the Smith's speedo will have a number on the face at the bottom in small print. For the 2:1 ratio the number is 1600, I belive, and for the 1.25:1 the number is 1000. The way I remember this is if you divide the Smith's tach number by the speedo ratio you get 800 (i.e., 1600/2=800, 1000/1.25=800). Of course you have to match the proper speedo drive to the proper speedometer.

This is just my 2 cents, I am sure we will hear from many others more knowledgable than I on this subject. Good Luck.

Re: Smiths Speedo Drive Ratios #46277
03/10/06 6:13 pm
03/10/06 6:13 pm
Joined: Sep 2005
Posts: 250
Tennessee
T
triumphmike Offline
BritBike Forum member
triumphmike  Offline
BritBike Forum member
T

Joined: Sep 2005
Posts: 250
Tennessee
sorry, I meant speedo number instead of tach number in the above reply.

Re: Smiths Speedo Drive Ratios #46278
03/11/06 12:55 am
03/11/06 12:55 am
Joined: Aug 2004
Posts: 354
Iowa
Pender Offline OP

BritBike Forum member
Pender  Offline OP

BritBike Forum member

Joined: Aug 2004
Posts: 354
Iowa
Thanks for the info Mike - but I guess my question got a bit muddled. Theoretically, a 1.25:1 and a 15:12 should read the same, correct? But is there a physical or mechanical difference between the two or is it just a different way of saying the same thing?


Furies and Apaches and Interceptors, oh my!
Re: Smiths Speedo Drive Ratios #46279
03/13/06 4:53 pm
03/13/06 4:53 pm
Joined: Sep 2005
Posts: 250
Tennessee
T
triumphmike Offline
BritBike Forum member
triumphmike  Offline
BritBike Forum member
T

Joined: Sep 2005
Posts: 250
Tennessee
From a ratio point of view, the 15:12 should be the same as the 1.25:1 I would think. However you never know with the British motorcycle industry. I have a '72 TR6R and have replaced the speedo drive. It was a 1.25:1 ratio originally and I replaced it with an identical part (part number 60-3213). I did not have any problems with the speedo readings with the replacement.

Re: Smiths Speedo Drive Ratios #46280
03/13/06 8:02 pm
03/13/06 8:02 pm
Joined: Jan 2006
Posts: 57
wellington, New Zealand
H
hunt the Offline
BritBike Forum
hunt the  Offline
BritBike Forum
H

Joined: Jan 2006
Posts: 57
wellington, New Zealand
hi , i could be wrong here but i thought that you used to be,( but not now) able to buy repair kits for these,so is it possible that your 15:12 ratio was actually another ratio,or maybe your new one labelled 1.25:1 is different, is it still possible to count or is it totally destroyed, i've been trying to think about it because as you say the ratio's pan out to be the same,
what percentage increase are you getting on your speedo?


Moderated by  Alan_nc 


Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.6.2