[Healeys] Speed to RPM ratio?

Mon Jun 14 03:02:20 MDT 2021

All

Here in the UK speedos are set to read about 3% high so that any minor
variation such as tyres with a different rolling radius does not cause you
to inadvertently exceed the speed limit.

It has been known for people to be fined for going 31 mph in a 30 mph
restricted area.

On Mon, 14 Jun 2021 at 00:40, Len and/or Marge Hartnett via Healeys <
healeys at autox.team.net> wrote:

>
> John:  On a previous long Healey trip with my son, I commented on the fact
> that my odo was not in agreement with the GPS.  I was confident that my odo
> was correct having compared it to official highway mile markers.  His
> brilliant solution (he is brilliant of course because he is my son ) came
> up with the following:  the automobile is travelling up and down various
> hills and mountains whereas the GPS is calculating the distance on a level
> altitude.  The difference is the added distance created by going up and
> down the fluctuating altitude of the highway.  This may or may not be the
> solution but it sounds logical to me.
>
> (The Other) Len
> Fairfield, CA, USA
> 1967 AH 3000 MkIII, HBJ8L39031
>
>
> ----- Original Message -----
> *From:* banjojohn <banjojohn at cox.net>
> *To:* Jim Ryan <ryan at jimryan.com> ; i erbs <eyera3000 at gmail.com>
> *Cc:* Ahealey help <healeys at autox.team.net>
> *Sent:* Sunday, June 13, 2021 3:50 PM
> *Subject:* Re: [Healeys] Speed to RPM ratio?
>
> Jim, you are right.  I have used GPS and my speedo is not accurate, but
> close enough for me.  My point was that the speedo is mechanically linked,
> from the tranny, to the engine, and my tach gets its signal from the coil,
> which also is directly linked to engine speed through the distributor.
> Regardless of my actual speed, my speedo and tach should maintain a direct
> relationship in any given gear.
> Thanks again for all the opinions and various charts and facts provided by
> the list members.
>
> John
>
>
> Sent from my T-Mobile 4G LTE Device
>
>
> -------- Original message --------
> From: Jim Ryan <ryan at jimryan.com>
> Date: 6/13/21 4:17 PM (GMT-06:00)
> To: i erbs <eyera3000 at gmail.com>
> Cc: banjojohn <banjojohn at cox.net>, Ahealey help <healeys at autox.team.net>
> Subject: Re: [Healeys] Speed to RPM ratio?
>
> Am I missing something?  I just check accuracy with the GPS on my phone.
>
> On Sun, Jun 13, 2021, 3:25 PM i erbs via Healeys <healeys at autox.team.net>
> wrote:
>
>> My tach is driven by my distributor gear
>> Speedo comes off my transmission.  Not sure about the relationship to
>> accuracy.
>>
>> Ira Erbs
>> 1959 AH 100-6
>> 1967 MGB
>> Milwaukie, OR
>>
>> On Sun, Jun 13, 2021, 11:50 AM banjojohn <banjojohn at cox.net> wrote:
>>
>>> 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.
>>>
>>> John
>>>
>>>
>>> Sent 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
>>> >>>>
>>> >>
>>>
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