Ron,
A math major? I recently pestered Jim Boynton to measure his original spare
for me. With a cloth tape measure he got a real world measurement (but not
factoring for weight) of his free standing tire of a 74-7/8" circumference.
Just thought I would throw this out and see if it stuck to anyone's wall.
And, while we are on the subject, and the reason I was interested in the
size of Jim's spare is that I was looking for a baseline on the Tiger. Often
people will change tire size for looks without regard to the fact that they
are effectively changing the trans or the rearend ratio (depending on how
you look at it). IF in fact it could be said that Rootes got it right (I'm
sure a point of debate depending on application) then changing tire size
would need to be "corrected" be either trans ratio changes or rearend ratio
changes.
Someday I want to take the most popular trans and rearend ratios used in
Tigers and factor them with different tire sizes using the 74-7/8"
circumference as the baseline of comparision (i.e. distance traveled
dependent on tire size -vs- engine revolutions). This would tell the "true"
story as opposed to the "I use use this trans..., I use these rear
ratios..., I use these tires...," but where none of the three elements are
considered together. Of course I was always bad at math so if anyone wants
to jump out and........ .
Tom Witt B9470101
----- Original Message -----
From: ron fraser <rfraser@bluefrog.biz>
To: <tigers@autox.team.net>
Sent: Wednesday, April 23, 2003 12:10 PM
Subject: RE: Speedo Gear...for 2.88 gear set
> Good Question about the original tires. I don't know the real answer; I
> can only reverse engineer the size of the tire from the printed facts in
the
> manual and on hand.
>
> Original Tire = 5.90 x 13 - not much help here.
>
> 1-From the Tiger Manual - 23.92mph @ 1000 rpm
> Calculate tire size using 2.88 gears
>
> Tire circumference = 72.75" - Diam. = 23.15"
>
> 2-Let's calculate again using the speedometer gear ratios.
> Speedo cal# = 980 rev/mi, speedo cable gear = 15 teeth,
> trans drive gear # B7C-17285-A = 6 teeth, 2.88 gears
> This gives you 24.49mph @ 1000rpm
>
> Tire circumference = 74.48" - Diam = 23.71"
>
> Now what this means to me is that you want a tire with a circumference
> larger than 74.48" so that as it wears down the speedometer would read
> nearly correct all of the time. This only applies to the stock gear set.
>
> 3-Using the speedometer gear set but changing to a 16 tooth gear
>
> Tire C = 69.83" - Diam = 22.23"
>
> The biggest problem here is what information is absolutely correct.
> The speedo cal #
> The speedo cable gear set
> The differential gear ratio
>
> This information can only help you get close to the correct gear set and
> tire size you want to run.
>
> I hope this helps and doesn't confuse people too much.
>
> Ron Fraser
>
>
> -----Original Message-----
> From: DrMayf [mailto:drmayf@teknett.com]
> Sent: Wednesday, April 23, 2003 7:33 PM
> To: rfraser@bluefrog.biz
> Subject: Re: Speedo Gear...for 2.88 gear set
>
> Hey, thanks, Ron. So the original gear with the original rear gear set was
> off that much? Original tires were tall? Nah, they were really dinky
> small, like 22 inches in diameter or some such, weren't they? Anyhoo, many
> thanks for the part number. And reminding me of the Mustang Restoration
> folks for source.
>
> mayf
> ----- Original Message -----
> From: "ron fraser" <rfraser@bluefrog.biz>
> To: "'DrMayf'" <drmayf@teknett.com>; <tigers@autox.team.net>
> Sent: Tuesday, April 22, 2003 5:43 PM
> Subject: RE: Speedo Gear...for 2.88 gear set
>
>
> The original gear had 15 teeth part #C3OA-17271-A. You would need
> rather tall tires like the originals for this gear to give you the correct
> mph.
> I believe 16 teeth is closer to accurate with 175/70x13 tire. You
> can get them at Sunbeam Specialties, a Ford dealer, or any vintage Mustang
> shop like Mustangs Unlimited.
>
> Ron Fraser
>
> ---
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