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Discussion Starter #1
I'm thinking of putting 15" tires on my 66 A code coupe.
I want the speedometer to still be accurate though.
Does anyone know if I can change the speedometer gear in the transmission and, if I can go to my local Ford dealership to get this different gear and finally, I know this is a stretch, a possible part number?
 

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A basic answer to your question would be yes you can. However, it depends on what size tire you change to. I can not remember how to calculate tire diameter right now but http://www.4lo.com will do it for you. If you change to a smaller diameter then the speedometer gear that goes into the trany needs more teeth. Part numbers are nice to have, but it would be much easier to take your gear to your local Ford parts guy and tell him you need one like this with "X" amount of teeth.

1967 GT coupe been in my garage since 1974
1993 Ranger ExtCab 4.0L daily driver
1996 Aerostar wifes ride
 

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There is also a tire dimension calculator at http://powerdog.com/tiresize.cgi/ At that site you can input your current size tires and play with the dimensions of the 15s to get a near identical diameter tire to minimize any error in the speedo and save having to swap speedo gears

Tom Kubler, Long-time Mustang Enthusiast & San Antonio Mustang Club Founder
 

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The main reasons for going to 15" as opposed to 14" would be to get a wider footprint, shorter sidewalls and the ever popular "cool" factor. None of these things would necessitate changing your speedo gear. Overall diameter of the tire/wheel combo is what affects what gear you need. The car was set up to use the overall diameter you probably had, changing to 15" should not change that. You gain 1" on the rim size, so you give up 1" on the tire size....thus all will be equal (a 26.5" diameter tire wheel combo can be attained in 14", 15" 16" 17" etc. The difference when going up in size has more to do with width and shorter sidewalls, both of which enhance handling, grip and looks. Sorry to be so longwinded. Short answer, use one of the tire calculators and find a 15" that is the same diameter and drive it like you stole it. In my case it was 215/60R15 T/A radials. No difference in my speedo at all....

When I can't stand, I must lean...
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Russstang got it just right. 215/60R15 is the perfect size... it is the same overall size and will improve handling, especially steering response. Used that combination on '67 and '68 Mustangs and a '64 Falcon.

It is not a big secret, but those are 15" LTD rims on my car. The wire spokes are LTD with Mustang center caps. Only difference is I used 225/60R15's on the rear. I'm not sure how the 225 size would fit in the wheel well on your car.

Russ

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Discussion Starter #8
i hope you plan on putting 15" wheels on your stang, otherise driving with 15" tires on it will be a little hairy...

/forums/images/icons/cool.gif[color:blue]Todd Dietrich
restomod junkie, 19 year old kid who has too many ideas and not enough money to finish any of them..
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I've also found 215/60/15s to be fine. Originally had 195/75/14s on the previous FB before stepping up to 15s for a while. Then I went back to 14" Shelby 10 Spokes and used 205/70/14s. Speedo read fine.

Regards,

Dean T

Shikatta Ga Nai - "It cannot be helped"
 
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