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Re: [Healeys] Speed to RPM ratio?

To: Harold Manifold <manifold@telus.net>
Subject: Re: [Healeys] Speed to RPM ratio?
From: Roger Grace via Healeys <healeys@autox.team.net>
Date: Sun, 13 Jun 2021 18:17:06 -0700
Cc: Ahealey help <healeys@autox.team.net>, i erbs <eyera3000@gmail.com>
Delivered-to: mharc@autox.team.net
Delivered-to: healeys@autox.team.net
References: <20210613225132.02B21A0BC7@autox.team.net> <4C449F50-2ECE-4AC1-B4AF-DFDB38B15169@hxcore.ol>
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Content-Transfer-Encoding: quoted-printable

I usually check by ensuring rear tires are at correct pressure, then making
a mark on pavement at valve and counting say 8-10 turns then measuring
distance carefully with a tape measure. Gives good results when doing the
usual calculations. This takes the mystery out of data that the tire people
publish.
rg

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On Sun, Jun 13, 2021 at 5:29 PM Harold Manifold via Healeys <
healeys@autox.team.net> wrote:

> The Tach is an accurate way to determine vehicle speed and can be more
> accurate than the speedometer but you need to know these variables:
>
>
>
> Tires =E2=80=93 either Revs per Mile or loaded radius (this is different =
than the
> nominal diameter and usually available on the tire manufacturers website)
>
> Rear End Ratio =E2=80=93 for a Healey there are limited options usually 4=
3/11 =3D
> 3.91, 41/10 =3D 4.10 or 39/11 =3D 3.55
>
>
>
> If you do the check while driving in 4th without the overdrive engaged
> the math is easier. One complication is the tire manufactures do not repo=
rt
> Revs per Mile consistently and sometimes a conversion is required. Assumi=
ng
>  Vredestein Sprint Classic      165HR15 and 4.10 rear end ratio this tabl=
e
> will work:
>
>
>
> MPH
>
>  RPM
>
>                 30
>
>                   1,670
>
>                 40
>
>                   2,230
>
>                 50
>
>                   2,790
>
>                 60
>
>                   3,350
>
>                 70
>
>                   3,910
>
>
>
> if it would help anyone send me your tire make and size and rear end rati=
o
> and I will sent a chart like the above.
>
>
>
> Harold
>
>
>
> *From: *banjojohn <banjojohn@cox.net>
> *Sent: *Sunday, June 13, 2021 3:51 PM
> *To: *Jim Ryan <ryan@jimryan.com>; i erbs <eyera3000@gmail.com>
> *Cc: *Ahealey help <healeys@autox.team.net>
> *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 direc=
t
> relationship in any given gear.
>
> Thanks again for all the opinions and various charts and facts provided b=
y
> the list members.
>
>
>
> John
>
>
>
>
>
> Sent from my T-Mobile 4G LTE Device
>
>
>
>
>
> -------- Original message --------
>
> From: Jim Ryan <ryan@jimryan.com>
>
> Date: 6/13/21 4:17 PM (GMT-06:00)
>
> To: i erbs <eyera3000@gmail.com>
>
> Cc: banjojohn <banjojohn@cox.net>, Ahealey help <healeys@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@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@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 consistan=
t
> 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@autox.team.net>
>
> Date: 6/12/21 12:25 PM (GMT-06:00)
>
> To: Bob Haskell <rchaskell@earthlink.net>, healeys@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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<div dir=3D"ltr"><div>I usually check by ensuring rear tires are at correct=
 pressure, then making a mark on pavement at valve and counting say 8-10 tu=
rns then measuring distance carefully with a tape measure. Gives good resul=
ts when doing the usual calculations. This takes the mystery out of data th=
at the tire people publish.<br></div><div>rg<br></div></div><div id=3D"DAB4=
FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2"><br>
<table style=3D"border-top:1px solid #d3d4de">
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style=3D"width:470px;padding-top:12px;color:#41424e;font-size:13px;fo=
nt-family:Arial,Helvetica,sans-serif;line-height:18px">Virus-free. <a href=
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</table><a href=3D"#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2" width=3D"1" heigh=
t=3D"1"></a></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"=
gmail_attr">On Sun, Jun 13, 2021 at 5:29 PM Harold Manifold via Healeys &lt=
;<a href=3D"mailto:healeys@autox.team.net";>healeys@autox.team.net</a>&gt; w=
rote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0p=
x 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style=
=3D"overflow-wrap: break-word;" lang=3D"EN-US"><div class=3D"gmail-m_-40227=
33508395426119WordSection1"><p class=3D"MsoNormal">The Tach is an accurate =
way to determine vehicle speed and can be more accurate than the speedomete=
r but you need to know these variables:</p><p class=3D"MsoNormal"><u></u>=
=C2=A0<u></u></p><p class=3D"MsoNormal">Tires =E2=80=93 either Revs per Mil=
e or loaded radius (this is different than the nominal diameter and usually=
 available on the tire manufacturers website)</p><p class=3D"MsoNormal">Rea=
r End Ratio =E2=80=93 for a Healey there are limited options usually 43/11 =
=3D 3.91, 41/10 =3D 4.10 or 39/11 =3D 3.55</p><p class=3D"MsoNormal"><u></u=
>=C2=A0<u></u></p><p class=3D"MsoNormal">If you do the check while driving =
in 4<sup>th</sup> without the overdrive engaged the math is easier. One com=
plication is the tire manufactures do not report Revs per Mile consistently=
 and sometimes a conversion is required. Assuming =C2=A0Vredestein Sprint C=
lassic=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 165HR15 and 4.10 rear end ratio this t=
able will work:</p><p class=3D"MsoNormal"><u></u>=C2=A0<u></u></p><div><tab=
le style=3D"width:153pt;border-collapse:collapse" width=3D"204" cellspacing=
=3D"0" cellpadding=3D"0" border=3D"0"><tbody><tr style=3D"height:12.75pt"><=
td style=3D"width:68pt;padding:0.75pt 0.75pt 0in;height:12.75pt" width=3D"9=
1" valign=3D"bottom" nowrap><p class=3D"MsoNormal" style=3D"text-align:cent=
er" align=3D"center"><span style=3D"font-size:10pt;font-family:&quot;Arial&=
quot;,sans-serif">MPH <u></u><u></u></span></p></td><td style=3D"width:85pt=
;padding:0.75pt 0.75pt 0in;height:12.75pt" width=3D"113" valign=3D"bottom" =
nowrap><p class=3D"MsoNormal" style=3D"text-align:center" align=3D"center">=
<span style=3D"font-size:10pt;font-family:&quot;Arial&quot;,sans-serif">=C2=
=A0RPM <u></u><u></u></span></p></td></tr><tr style=3D"height:12.75pt"><td =
style=3D"padding:0.75pt 0.75pt 0in;height:12.75pt" valign=3D"bottom" nowrap=
><p class=3D"MsoNormal" style=3D"text-align:center" align=3D"center"><span =
style=3D"font-size:10pt;font-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A030 <u></u><u></u></span></p></td><td style=3D"padding:0.75pt 0.=
75pt 0in;height:12.75pt" valign=3D"bottom" nowrap><p class=3D"MsoNormal" st=
yle=3D"text-align:center" align=3D"center"><span style=3D"font-size:10pt;fo=
nt-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
1,670 <u></u><u></u></span></p></td></tr><tr style=3D"height:12.75pt"><td s=
tyle=3D"padding:0.75pt 0.75pt 0in;height:12.75pt" valign=3D"bottom" nowrap>=
<p class=3D"MsoNormal" style=3D"text-align:center" align=3D"center"><span s=
tyle=3D"font-size:10pt;font-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A040 <u></u><u></u></span></p></td><td style=3D"padding:0.75pt 0.=
75pt 0in;height:12.75pt" valign=3D"bottom" nowrap><p class=3D"MsoNormal" st=
yle=3D"text-align:center" align=3D"center"><span style=3D"font-size:10pt;fo=
nt-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
2,230 <u></u><u></u></span></p></td></tr><tr style=3D"height:12.75pt"><td s=
tyle=3D"padding:0.75pt 0.75pt 0in;height:12.75pt" valign=3D"bottom" nowrap>=
<p class=3D"MsoNormal" style=3D"text-align:center" align=3D"center"><span s=
tyle=3D"font-size:10pt;font-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A050 <u></u><u></u></span></p></td><td style=3D"padding:0.75pt 0.=
75pt 0in;height:12.75pt" valign=3D"bottom" nowrap><p class=3D"MsoNormal" st=
yle=3D"text-align:center" align=3D"center"><span style=3D"font-size:10pt;fo=
nt-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
2,790 <u></u><u></u></span></p></td></tr><tr style=3D"height:12.75pt"><td s=
tyle=3D"padding:0.75pt 0.75pt 0in;height:12.75pt" valign=3D"bottom" nowrap>=
<p class=3D"MsoNormal" style=3D"text-align:center" align=3D"center"><span s=
tyle=3D"font-size:10pt;font-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A060 <u></u><u></u></span></p></td><td style=3D"padding:0.75pt 0.=
75pt 0in;height:12.75pt" valign=3D"bottom" nowrap><p class=3D"MsoNormal" st=
yle=3D"text-align:center" align=3D"center"><span style=3D"font-size:10pt;fo=
nt-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
3,350 <u></u><u></u></span></p></td></tr><tr style=3D"height:12.75pt"><td s=
tyle=3D"padding:0.75pt 0.75pt 0in;height:12.75pt" valign=3D"bottom" nowrap>=
<p class=3D"MsoNormal" style=3D"text-align:center" align=3D"center"><span s=
tyle=3D"font-size:10pt;font-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A070 <u></u><u></u></span></p></td><td style=3D"padding:0.75pt 0.=
75pt 0in;height:12.75pt" valign=3D"bottom" nowrap><p class=3D"MsoNormal" st=
yle=3D"text-align:center" align=3D"center"><span style=3D"font-size:10pt;fo=
nt-family:&quot;Arial&quot;,sans-serif">=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
3,910 <u></u><u></u></span></p></td></tr></tbody></table></div><p class=3D"=
MsoNormal"><u></u>=C2=A0<u></u></p><p class=3D"MsoNormal">if it would help =
anyone send me your tire make and size and rear end ratio and I will sent a=
 chart like the above.</p><p class=3D"MsoNormal"><u></u>=C2=A0<u></u></p><p=
 class=3D"MsoNormal">Harold<u></u><u></u></p><p class=3D"MsoNormal"><u></u>=
=C2=A0<u></u></p><div style=3D"border-color:rgb(225,225,225) currentcolor c=
urrentcolor;border-style:solid none none;border-width:1pt medium medium;pad=
ding:3pt 0in 0in"><p class=3D"MsoNormal" style=3D"border:medium none;paddin=
g:0in"><b>From: </b><a href=3D"mailto:banjojohn@cox.net"; target=3D"_blank">=
banjojohn</a><br><b>Sent: </b>Sunday, June 13, 2021 3:51 PM<br><b>To: </b><=
a href=3D"mailto:ryan@jimryan.com"; target=3D"_blank">Jim Ryan</a>; <a href=
=3D"mailto:eyera3000@gmail.com"; target=3D"_blank">i erbs</a><br><b>Cc: </b>=
<a href=3D"mailto:healeys@autox.team.net"; target=3D"_blank">Ahealey help</a=
><br><b>Subject: </b>Re: [Healeys] Speed to RPM ratio?</p></div><p class=3D=
"MsoNormal"><u></u>=C2=A0<u></u></p><div><p class=3D"MsoNormal">Jim, you ar=
e right.=C2=A0 I have used GPS and my speedo is not accurate, but close eno=
ugh for me.=C2=A0 My point was that the speedo is mechanically linked, from=
 the tranny, to the engine, and my tach gets its signal from the coil, whic=
h also is directly linked to engine speed through the distributor.=C2=A0=C2=
=A0<u></u><u></u></p></div><div><p class=3D"MsoNormal">Regardless of my act=
ual speed, my speedo and tach should maintain a direct relationship in any =
given gear.<u></u><u></u></p></div><div><p class=3D"MsoNormal">Thanks again=
 for all the opinions and various charts and facts provided by the list mem=
bers.<u></u><u></u></p></div><div><p class=3D"MsoNormal"><u></u>=C2=A0<u></=
u></p></div><div><p class=3D"MsoNormal">John<u></u><u></u></p></div><div><p=
 class=3D"MsoNormal"><u></u>=C2=A0<u></u></p></div><div><p class=3D"MsoNorm=
al"><u></u>=C2=A0<u></u></p></div><div id=3D"gmail-m_-4022733508395426119co=
mposer_signature"><div><p class=3D"MsoNormal"><span style=3D"font-size:9.5p=
t;color:rgb(87,87,87)">Sent from my T-Mobile 4G LTE Device<u></u><u></u></s=
pan></p></div></div><div><p class=3D"MsoNormal"><u></u>=C2=A0<u></u></p></d=
iv><div><p class=3D"MsoNormal"><u></u>=C2=A0<u></u></p></div><div><p class=
=3D"MsoNormal"><span style=3D"color:black">-------- Original message ------=
--<u></u><u></u></span></p></div><div><p class=3D"MsoNormal"><span style=3D=
"color:black">From: Jim Ryan &lt;<a href=3D"mailto:ryan@jimryan.com"; target=
=3D"_blank">ryan@jimryan.com</a>&gt; <u></u><u></u></span></p></div><div><p=
 class=3D"MsoNormal"><span style=3D"color:black">Date: 6/13/21 4:17 PM (GMT=
-06:00) <u></u><u></u></span></p></div><div><p class=3D"MsoNormal"><span st=
yle=3D"color:black">To: i erbs &lt;<a href=3D"mailto:eyera3000@gmail.com"; t=
arget=3D"_blank">eyera3000@gmail.com</a>&gt; <u></u><u></u></span></p></div=
><div><p class=3D"MsoNormal"><span style=3D"color:black">Cc: banjojohn &lt;=
<a href=3D"mailto:banjojohn@cox.net"; target=3D"_blank">banjojohn@cox.net</a=
>&gt;, Ahealey help &lt;<a href=3D"mailto:healeys@autox.team.net"; target=3D=
"_blank">healeys@autox.team.net</a>&gt; <u></u><u></u></span></p></div><div=
><p class=3D"MsoNormal"><span style=3D"color:black">Subject: Re: [Healeys] =
Speed to RPM ratio? <u></u><u></u></span></p></div><div><p class=3D"MsoNorm=
al"><span style=3D"color:black"><u></u>=C2=A0<u></u></span></p></div><div><=
p class=3D"MsoNormal">Am I missing something?=C2=A0 I just check accuracy w=
ith the GPS on my phone.<u></u><u></u></p></div><p class=3D"MsoNormal"><u><=
/u>=C2=A0<u></u></p><div><div><p class=3D"MsoNormal">On Sun, Jun 13, 2021, =
3:25 PM i erbs via Healeys &lt;<a href=3D"mailto:healeys@autox.team.net"; ta=
rget=3D"_blank">healeys@autox.team.net</a>&gt; wrote:<u></u><u></u></p></di=
v><blockquote style=3D"border-color:currentcolor currentcolor currentcolor =
rgb(204,204,204);border-style:none none none solid;border-width:medium medi=
um medium 1pt;padding:0in 0in 0in 6pt;margin-left:4.8pt;margin-right:0in"><=
div><p class=3D"MsoNormal">My tach is driven by my distributor gear<u></u><=
u></u></p><div><p class=3D"MsoNormal" style=3D"margin-bottom:12pt">Speedo c=
omes off my transmission.=C2=A0 Not sure about the relationship to accuracy=
.=C2=A0<u></u><u></u></p><div><p class=3D"MsoNormal">Ira Erbs<br>1959 AH 10=
0-6<br>1967 MGB<br>Milwaukie, OR<u></u><u></u></p></div></div></div><p clas=
s=3D"MsoNormal"><u></u>=C2=A0<u></u></p><div><div><p class=3D"MsoNormal">On=
 Sun, Jun 13, 2021, 11:50 AM banjojohn &lt;<a href=3D"mailto:banjojohn@cox.=
net" target=3D"_blank">banjojohn@cox.net</a>&gt; wrote:<u></u><u></u></p></=
div><blockquote style=3D"border-color:currentcolor currentcolor currentcolo=
r rgb(204,204,204);border-style:none none none solid;border-width:medium me=
dium medium 1pt;padding:0in 0in 0in 6pt;margin-left:4.8pt;margin-right:0in"=
><div><div><p class=3D"MsoNormal">Thanks.<u></u><u></u></p></div><div><p cl=
ass=3D"MsoNormal">I am actually just comparing the tach with the speedomete=
r indicated speed, which, I believe reads a little high due to tire size.=
=C2=A0 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.<u></u><u></u></p></div><div><p class=3D"MsoNormal"><u></u>=C2=A0<u><=
/u></p></div><div><p class=3D"MsoNormal">John<u></u><u></u></p></div><div><=
p class=3D"MsoNormal"><u></u>=C2=A0<u></u></p></div><div><p class=3D"MsoNor=
mal"><u></u>=C2=A0<u></u></p></div><div id=3D"gmail-m_-4022733508395426119m=
_-8612040742838000386m_-7997059852725315655composer_signature"><div><p clas=
s=3D"MsoNormal"><span style=3D"font-size:9.5pt;color:rgb(87,87,87)">Sent fr=
om my T-Mobile 4G LTE Device<u></u><u></u></span></p></div></div><div><p cl=
ass=3D"MsoNormal"><u></u>=C2=A0<u></u></p></div><div><p class=3D"MsoNormal"=
><u></u>=C2=A0<u></u></p></div><div><p class=3D"MsoNormal"><span style=3D"c=
olor:black">-------- Original message --------<u></u><u></u></span></p></di=
v><div><p class=3D"MsoNormal"><span style=3D"color:black">From: Bob Spidell=
 via Healeys &lt;<a href=3D"mailto:healeys@autox.team.net"; target=3D"_blank=
">healeys@autox.team.net</a>&gt; <u></u><u></u></span></p></div><div><p cla=
ss=3D"MsoNormal"><span style=3D"color:black">Date: 6/12/21 12:25 PM (GMT-06=
:00) <u></u><u></u></span></p></div><div><p class=3D"MsoNormal"><span style=
=3D"color:black">To: Bob Haskell &lt;<a href=3D"mailto:rchaskell@earthlink.=
net" target=3D"_blank">rchaskell@earthlink.net</a>&gt;, <a href=3D"mailto:h=
ealeys@autox.team.net" target=3D"_blank">healeys@autox.team.net</a> <u></u>=
<u></u></span></p></div><div><p class=3D"MsoNormal"><span style=3D"color:bl=
ack">Subject: Re: [Healeys] Speed to RPM ratio? <u></u><u></u></span></p></=
div><div><p class=3D"MsoNormal"><span style=3D"color:black"><u></u>=C2=A0<u=
></u></span></p></div><p class=3D"MsoNormal" style=3D"margin-bottom:12pt">T=
hat&#39;s it!<br><br>On 6/11/2021 4:31 PM, Bob Haskell wrote:<br>&gt; <a hr=
ef=3D"http://longstonetyres.co.uk"; target=3D"_blank">http://longstonetyres.=
co.uk</a><br>&gt;<br>&gt; Cheers,<br>&gt;<br>&gt; Bob Haskell<br>&gt; Austi=
n Healey 3000 BN7/BT7 registrar<br>&gt;<br>&gt; On 6/11/21 7:01 PM, Bob Spi=
dell wrote:<br>&gt;&gt; Note there is a not insignificant difference in dia=
meters of tires <br>&gt;&gt; with the same nominal size (e.g. &#39;165/80-1=
5&#39;). The English tire <br>&gt;&gt; site--can&#39;t think of the name of=
fhand--has (had?) a table comparing <br>&gt;&gt; the diameters of different=
 brands/models of the same size tires, and <br>&gt;&gt; IIRC they could dif=
fer by as much as half an inch. I&#39;d say to measure <br>&gt;&gt; the act=
ual diameter of your tires, but it&#39;s kinda hard when moving; <br>&gt;&g=
t; the &#39;flat spot&#39; goes away--partially, at least--and the tires &#=
39;grow&#39; <br>&gt;&gt; some from centrifugal force (anyone seen film of =
top fuel dragsters <br>&gt;&gt; launching; the rear tires must expand a few=
 inches or more?).<br>&gt;&gt;<br>&gt;&gt;<br>&gt;&gt; On 6/11/2021 3:36 PM=
, John OBrien wrote:<br>&gt;&gt;&gt; Thanks to all who replied.=C2=A0 These=
 will give me something to work with.<br>&gt;&gt;&gt;<br>&gt;&gt;&gt; John<=
br>&gt;&gt;&gt;<br>&gt;&gt;&gt; On 6/11/2021 4:26 PM, John OBrien wrote:<br=
>&gt;&gt;&gt;&gt; Hi Guys and Gals<br>&gt;&gt;&gt;&gt;<br>&gt;&gt;&gt;&gt; =
I am trying to calibrate my tach.=C2=A0 I installed a Spiyda RVI - RVC <br>=
&gt;&gt;&gt;&gt; conversion board, because my tach was acting wierd. Anyway=
, I am <br>&gt;&gt;&gt;&gt; still trying to get this setup to read correctl=
y.=C2=A0 My question is, <br>&gt;&gt;&gt;&gt; on my BJ8 with standard 3.9:1=
 diff. what should my RPMs be in <br>&gt;&gt;&gt;&gt; fourth gear going 50 =
MPH , without overdrive engaged.=C2=A0 I&#39;m running <br>&gt;&gt;&gt;&gt;=
 165/80R15 tires. I&#39;m just looking for a reference point to compare <br=
>&gt;&gt;&gt;&gt; what should be, and what I am reading.<br>&gt;&gt;&gt;&gt=
;<br>&gt;&gt;&gt;&gt; Any help is appreciated.<br>&gt;&gt;&gt;&gt;<br>&gt;&=
gt;&gt;&gt; Thanks<br>&gt;&gt;&gt;&gt;<br>&gt;&gt;&gt;&gt; John<br>&gt;&gt;=
&gt;&gt;<br>&gt;&gt;<br><br>_______________________________________________=
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