1957 Wheel sizes . . How to measure

[knuckle47]

I know that the 1957 has 14” wheels. But, to be absolutely sure, I am trying to measure them accurately. So far, few locations to measure from actually measure 14”. Does anyone know the place for an accurate measurement to the other side of the wheel.

Additionally, would a 15” wheel fit on these “assumed” 1957 hubs or is there a marking I should be looking for that clearly identifies which size they may be rather than assume only by what year the car is/

 

[jack-in-sac]

The width of the wheel should be 5.5". Thunderbirds used the wider 14" wheel. If your wheels are original they will be welded and be 5.5" inner lip to inner lip. Assuming my memory is correct.
Yes 15" wheels will fit a 1957 Thunderbird again assuming that you use the ford 4.5" lug spacing as original.

 

[My1966T-Bird]

If you switch to a 15" wheels, you will need to switch to a lower profile tire where the diameter of the 14" tires matches the diameter of the 15" low profile tires because you will throw off you MPH on your speedometer. Ford may have a new speedometer gear to match your new needs or you find an electronic speed-healer to solve your problem. (Motorcycles have a speed-healer to solve MPH speedometer when gearing changes occur)

 

[knuckle47]

This entire quest developed since I stuck my phone on the seat and the gps started reading 36 when the speedo was at 30. Followed similar differences at high speeds..that’s when I started to think about the tires and wheels.

 

[55blacktie]

I've been communicating with the owner of a 1957 Thunderbird, who says his 14-inch rims are riveted, like earlier 55-56 rims. Rivets were an industry standard, but later rims have the center section welded to the rim.

 

[55blacktie]

1957 Thunderbird original tire size 7.50/14. The tire diameter is 27.8. 1955-56 Thunderbird original tire size 6.70/15. The tire diameter is 27.5. More than likely, your speedometer is off, even with the correct tires.

 

[Ward 57]

This entire quest developed since I stuck my phone on the seat and the gps started reading 36 when the speedo was at 30. Followed similar differences at high speeds..that’s when I started to think about the tires and wheels.

Where does the needle set when not moving? It should be directly on the 0. If it sits lower than that ,the needle may have slipped on the spindle.

 

[paul5456]

If your speedo is off, you can usually fix it with a new driven gear (the one at the end of the cable. 55 and 56 owners only have a limited number of gears (tooth count) but 57 has a wide varity of gears. Lots of the 57 and up type can be found on ebay, not expensive.

 

[knuckle47]

What shows the accuracy of the gps is one of those signs they sneak in the shoulder that flashes your speed. This one happens to be 35mph. In both of our modern Chevy trucks the digital speedometers, gps and that flashing sign are always spot-on in sync with each other, no matter what the speed. When I drove by it with the t-bird…it was off at the speedo. I will measure the overall diameter , hopefully tomorrow..

Speedometer needle is at zero when parked. @55blacktie , good information.

Besides the Ford shop manual and I have all of the official ford re-prints……is there another guide that has better images and exploded views of the many assemblies someone might recommend?

 

[Ward 57]

If your speedo is off, you can usually fix it with a new driven gear (the one at the end of the cable. 55 and 56 owners only have a limited number of gears (tooth count) but 57 has a wide varity of gears. Lots of the 57 and up type can be found on ebay, not expensive.

Not only Ebay but CASCO has a huge range of gear tooth numbers. I think the original is 19 but they can explain how many teeth per mph reading is involved. But trust me I walked away from replacing mine a few times as re-installing the retaining clip bolt is a challenge on jack stands but with your available lift so much easier to wriggle the bolt in position to secure.

 

[doug7740]

What shows the accuracy of the gps is one of those signs they sneak in the shoulder that flashes your speed. This one happens to be 35mph. In both of our modern Chevy trucks the digital speedometers, gps and that flashing sign are always spot-on in sync with each other, no matter what the speed. When I drove by it with the t-bird…it was off at the speedo. I will measure the overall diameter , hopefully tomorrow..

Besides the Ford shop manual and I have all of the official ford re-prints……is there another guide that has better images and exploded views of the many assemblies someone might recommend?

I have the original 6.70/15 tires on my 1955 Thunderbird, but my speedometer read 5 mph faster than I was actually traveling. I calibrated my speedometer by adjusting the return spring on the speedometer needle. It is easier to do this on a 1957 Thunderbird, because the speedometer can be removed from the back of the instrument cluster. On a 1955 and 56 Thunderbird the entire instrument cluster has to be removed first.

Here is an article from the March/April 1994 Early Bird magazine that will tell you on how to improve the accuracy of your speedometer. I also attached a picture of the speedometer return spring adjustment on my speedometer.

doug7740
1955 Thunderbird Blue

 

[knuckle47]

Geez…that is interesting.. so if my tire diameter is correct or not, this spring adjustment can help to increase it’s accuracy..is it due to the 65 years of use or was it never really tuned in to begin with. I am anxious to get this resolved.

 

[doug7740]

If you have larger than stock tires on your car it will lower your speedometer reading. To correct his you will have to change speedometer drive gear. Changing the tooth count on the drive gear will change the speedometer reading by 6%. If you have the original 7.50/14 tires on your car and your speedometer in inaccurate than adjusting the speedometer needle return spring should correct your problem. I want to warn you that you have to make very small adjustments until you finally get it right. It will take patience and many attempts until you get it right.


doug7740
1955 Thunderbird Blue

 

[Ward 57]

If my memory serves me correctly ( questionable ) I think the T-Birds used a different off set than the sedan wheels to tuck them under the skirts. 1/4"-or more. A big difference on rub issues. That's why you can't find them. Bazillions of sedan wheels but T-Birds not so much.

 

[wineaviator]

So this is an older thread but I was wondering if anyone has tried an 18” rim on the 57. Using a tire calculator online I see that a 205/50/R18 or 205/50/R18 computes to the same “size” but with a reduction in the sidewall height. Anyone tried this on a little bird?