Converting OLD Biasply to modern measurements

Hello all,
I am new to the forum and have a question.


My dad has been asking me what equivalent tire sizes are for his old Bias plys on his 55 F1, and I have no idea.


Is there a formula I can use, I am savvy with math and excel.


His original tires are 6.50R16LT, I assume that is 6.5 inches wide (165mm), but what is the aspect ratio? On a Bias, is the sidewall height a percentage of the tread width, or its own static height?


Can anybody help me out?


Thanks all!

Coker tire has a chart online.

Scroll half way down for chart:

https://www.cokertire.com/blog/tire-size-cross-reference

I had found that chart and it has some of the info on it but not all.


When I look at a 6.50R16, how do I get sidewall height, so I can calculate overall tire height?
And for the width, the 6.5, I assumed that was wheel width, or is that tread width, if it is tread that is easy to add out. If it is wheel, then there is a variable as tires can go a little wide or narrow.

I had found that chart and it has some of the info on it but not all.


When I look at a 6.50R16, how do I get sidewall height, so I can calculate overall tire height?
And for the width, the 6.5, I assumed that was wheel width, or is that tread width, if it is tread that is easy to add out. If it is wheel, then there is a variable as tires can go a little wide or narrow.

6.5" works out to 165mm - which is horrendously narrow for an inflated tire, at least by today's standards. So that 6.5" is probably the rim width.

For tire sidewall height, I would inflate the tire to, maybe, 3-4psi below the max pressure listed on the tire, remember, it doesn't even have to be on a car, just on a rim.

Next, measure from the rim up to the highest point on the tread. That's your sidewall height.

http://barrystiretech.com/vintagetireexchange.html

Unfortunately, there is no modern equivalent for a 6.50-16. That's a "Low Section Height" tire (Yeah! The name seems funny to those of us in the 21st Century!)- meaning it has an 88 Aspect ratio. Few modern tires go that high.

So you have to make a compromise of some sort.

According to my chart (http://barrystiretech.com/vintagetireexchange.html):

The best fit is a .......uh .....Mmmmm...... Well, my chart doesn't list one! That means you'll have to do some more figuring.

Since you are trying to replace a tire on a 1955 F1 (????), maybe we need to start there. Did you mean a Ford F100?

What's the vehicle going to be used for?

Are you trying to just get tires on it, but don't care if it has enough load carrying capacity? (tire failure possibility!)

Or are you try to use it as a work truck?

Do you care about authenticity?

http://barrystiretech.com/vintagetireexchange.html

Unfortunately, there is no modern equivalent for a 6.50-16. That's a "Low Section Height"
tire (Yeah! The name seems funny to those of us in the 21st Century!)- meaning it has an
88 Aspect ratio. Few modern tires go that high.

So you have to make a compromise of some sort.

According to my chart (http://barrystiretech.com/vintagetireexchange.html):

The best fit is a .......uh .....Mmmmm...... Well, my chart doesn't list one! That means
you'll have to do some more figuring.

Since you are trying to replace a tire on a 1955 F1 (????), maybe we need to start there.
Did you mean a Ford F100?

What's the vehicle going to be used for?

Are you trying to just get tires on it, but don't care if it has enough load carrying
capacity? (tire failure possibility!)

Or are you try to use it as a work truck?

Do you care about authenticity?

I'd love to drive something with 80-series tires on it. Probably tracked so straight you could finish this sentence on a 60mph quarter mile before having to touch the steering wheel again :D

The F1 was a 50s designation, and dad had always said it was an F1, which probably means Lloyd (his step dad who gave it to him in the early 70s) said that's what it was. I looked and the F1 stopped in 52, so yes it is a F100.



Yeah I had worked out 165mm as well which is basically a bicycle tire, I had suggested he go to the Schwinn shop for new tires, he wasn't amused \shrug.


It is interesting that from what I am seeing across these links that there doesn't seem to be enough info on the tire to get all i was looking for, almost seems like some up front info was assumed, or you had a reference book. Am I wrong, or am I missing something?


As for usage, it is going to be an around town cruiser, its days of being a legit farm truck, which is how it started it's life are behind it. Wanting to bring parts of it into this millennium but still keeping more or less the retro look, so sure we can go with something more modern, but not going to hugely wide tires and 20s like so many others now.


Now I cannot confirm but I assume, dad tends to not be forthcoming with details, but I think he was wanting to know so he could find something close to the same over all height so the speedo\odometer are correct or at least close.


Also, thanks guys for the help so far. I have gotten used to forums being angry places with lots of trolling, you all have been nice and helpful so far, THANKS!

OK, thanks for filling in some of the gaps.

So I am going to recommend a 215/70R16. It has more load carrying capacity and about the same overall diameter.

Just for reference: A 6.50-16 is about 28" in diameter and a 215/70R16 is about 27.9".

But there are some other issues: The wheels on that F-100 are probably 4.50" wide - and maybe even tubetype. The 215/70R16 requires a 5.50" minimum wheel width - and it is tubeless. If it is tubetype, that is a whole new kettle of fish to stink things up. Reply back if you find out it is, because there are options, but there aren't cheap!

AND, your Dad is going to have trouble going to the local tire shop to replace the tires. They are not going to know what to do. Worth a try to go down and see what they say. There is always the option to buy on-line and take them somewhere to mount.

Thanks for the help, it is appreciated. I am thinking I will use this info to try to get him to go to a modern wheel, even a plain steel so it keeps the aesthetic. Not really sure about the wheel width, I know it is in storage right now, but I will see what I can find out.


As per one question I had asked, ti does seem that there is info that it is assumed we know or that there is a tire reference book, as the sidewall measurement is missing. Is this just how it was, and it was all supposed to be looked up from reference material? Or am I missing something?

Thanks for the help, it is appreciated. I am thinking I will use this info to try to get him to go to a modern wheel, even a plain steel so it keeps the aesthetic. Not really sure about the wheel width, I know it is in storage right now, but I will see what I can find out.


As per one question I had asked, ti does seem that there is info that it is assumed we know or that there is a tire reference book, as the sidewall measurement is missing. Is this just how it was, and it was all supposed to be looked up from reference material? Or am I missing something?


http://barrystiretech.com/tiresizing.html

In this specific case, a 6.50-16 is a "Low Section Height" tire (88% Aspect Ratio). The key is the ".50" in the size. That's just the way they did things back then. Things are different now.

So as background, there are reference books. They are published by tire standardizing organizations. In the US, it's The Tire and Rim Association (TRA).

TRA publishes a yearbook every year that contains the latest information and some useful recent information, but deletes information that is too old to be much value - and that includes old sizing, like we are dealing with here. For that, you have to go back to those yearbooks that have that information - which means someone has to have an archive. When I was working, the company I worked for had such an archive - back to 1929. I hope they keep it going.

OOOOOHHH, ok. I thought that meant 6 1/2 as a width, I didnt know that the .5 was referencing something else entirely.
So I assume that there are other designations, and anything after the decimal is referencing the section height. That is quite enlightening, I knew I was missing something.


I will go over the link later when I have some more time.


THANKS!

http://barrystiretech.com/tiresizing.html

In this specific case, a 6.50-16 is a "Low Section Height" tire (88% Aspect Ratio). The key is the ".50" in the size. That's just the way they did things back then. Things are different now.

So as background, there are reference books. They are published by tire standardizing organizations. In the US, it's The Tire and Rim Association (TRA).

TRA publishes a yearbook every year that contains the latest information and some useful recent information, but deletes information that is too old to be much value - and that includes old sizing, like we are dealing with here. For that, you have to go back to those yearbooks that have that information - which means someone has to have an archive. When I was working, the company I worked for had such an archive - back to 1929. I hope they keep it going.

So ".50" refers to 88% aspect ratio? And that was considered "low" profile back then??

So ".50" refers to 88% aspect ratio? And that was considered "low" profile back then??

So you may ask, why can we have such low aspect ratios now? And the answer is radial tires.

Ya' see, a radial ply tries to make a circular cross section - very high aspect ratio - but the belts restrict the diameter, so any aspect ratio is possible.

In bias ply tires (no belt!) as you increase the ply angle from zero, the natural aspect ratio goes down - away from a circle. There is a limitation on the angle of the plies and still be able to build it. The lower limit seems to be about 78%.

So you may ask, why can we have such low
aspect ratios now? And the answer is radial tires.

Ya' see, a radial ply tries to make a circular cross section -
very high aspect ratio - but the belts restrict the diameter,
so any aspect ratio is possible.

In bias ply tires (no belt!) as you increase the ply angle
from zero, the natural aspect ratio goes down - away from
a circle. There is a limitation on the angle of the plies and
still be able to build it. The lower limit seems to be about
78%.

So Bias-ply tires with aspect under 70 are not common?

So Bias-ply tires with aspect under 70 are not common?

It is likely they are non-existent. From what I can reconstruct, anything lower than 78 aspect ratio was either a radial (belted) or bias belted. (Note: I've seen bias belted tires incorrectly labeled as bias!)

It is likely they are non-existent. From what I
can reconstruct, anything lower than 78 aspect ratio
was either a radial (belted) or bias belted. (Note:
I've seen bias belted tires incorrectly labeled as bias!)

The street calls them 'bias ply', as do I.

@ CapriRacer


Thanks a lot for all this. In general I am rarely looking for only an answer, usually I want this extra info you provided so I understand WHY and HOW as applicable to thew question so I can answer my own future questions now that I have an understanding.


Thanks again, this was very helpful!


Also, Happy 4th to all!

@ CapriRacer


Thanks a lot for all this. In general I am rarely looking for only an answer, usually I want this extra info you provided so I understand WHY and HOW as applicable to thew question so I can answer my own future questions now that I have an understanding.


Thanks again, this was very helpful!


Also, Happy 4th to all!

More than welcome! It's why I started posting on the interwebs. And why I made that website.