[Healeys] Speed to RPM ratio?

[banjojohn]

Thanks.I am actually just comparing the tach with the speedometer indicated speed, which, I believe reads a little high due to tire size.  But the relationship between the indicated speed and the tach should be consistant since they are both driven by actual engine or output shaft speed.JohnSent from my T-Mobile 4G LTE Device
-------- Original message --------From: Bob Spidell via Healeys <healeys at autox.team.net> Date: 6/12/21  12:25 PM  (GMT-06:00) To: Bob Haskell <rchaskell at earthlink.net>, healeys at autox.team.net Subject: Re: [Healeys] Speed to RPM ratio? That's it!On 6/11/2021 4:31 PM, Bob Haskell wrote:> http://longstonetyres.co.uk>> Cheers,>> Bob Haskell> Austin Healey 3000 BN7/BT7 registrar>> On 6/11/21 7:01 PM, Bob Spidell wrote:>> Note there is a not insignificant difference in diameters of tires >> with the same nominal size (e.g. '165/80-15'). The English tire >> site--can't think of the name offhand--has (had?) a table comparing >> the diameters of different brands/models of the same size tires, and >> IIRC they could differ by as much as half an inch. I'd say to measure >> the actual diameter of your tires, but it's kinda hard when moving; >> the 'flat spot' goes away--partially, at least--and the tires 'grow' >> some from centrifugal force (anyone seen film of top fuel dragsters >> launching; the rear tires must expand a few inches or more?).>>>>>> On 6/11/2021 3:36 PM, John OBrien wrote:>>> Thanks to all who replied.  These will give me something to work with.>>>>>> John>>>>>> On 6/11/2021 4:26 PM, John OBrien wrote:>>>> Hi Guys and Gals>>>>>>>> I am trying to calibrate my tach.  I installed a Spiyda RVI - RVC >>>> conversion board, because my tach was acting wierd. Anyway, I am >>>> still trying to get this setup to read correctly.  My question is, >>>> on my BJ8 with standard 3.9:1 diff. what should my RPMs be in >>>> fourth gear going 50 MPH , without overdrive engaged.  I'm running >>>> 165/80R15 tires. I'm just looking for a reference point to compare >>>> what should be, and what I am reading.>>>>>>>> Any help is appreciated.>>>>>>>> Thanks>>>>>>>> John>>>>>>_______________________________________________Support Team.Net http://www.team.net/donate.htmlSuggested annual donation  $12.75Archive: http://www.team.net/pipermail/healeys http://autox.team.net/archiveHealeys@autox.team.nethttp://autox.team.net/mailman/listinfo/healeysUnsubscribe/Manage: http://autox.team.net/mailman/options/healeys/banjojohn@cox.net
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/healeys/attachments/20210613/5e067665/attachment.htm>