Refer to Bob Hokanson's XL gear ratio calculator on TigersUnited.com to
make this easy. XL reader download is free.
http://www.TigersUnited.com/tech_tips/HokansonGearSpeedXL/pt-HokansonGearSpeedXL.asp
Steve
Tom Witt wrote:
>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
>>
>>---
>>Outgoing mail is certified Virus Free.
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>>
>
>
>
--
Steve Laifman
Editor
http://www.TigersUnited.com
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