Do I need to get new wheels and tires for my 1940 56S?

[Daves1940Buick56S]

All:

OK, while I am waiting for my back to heal so I can get back to the heavy work on my car, I thought I would try to clean up a few loose ends.

As you can tell from the title: my car does not have the proper wheel or tire sizes. The wheels are 15" and the size is G78 tubeless. From what I could find out and what I remembered about old tire sizes, this is about equivalent to 8.00 x 15, correct? At 78% aspect ratio, this works out to a 27.5" total diameter and appx 8" sidewall width, but please correct me if I am wrong.

The original spec is 6.50 x 16. So, is this at 78%, 80%, or 90% aspect ratio? If 78%, the total diameter is 26.2", if 80% then it is 26.4", if 90% then it is 27.7", with a width of 6.5".

So I think I may have a wheel/tire combo the gives me up to 1.3" more diameter and a 1.5" wider tread.

So, do I have a problem? Any others in this situation? Will the front end align properly? Will this adversely affect handling, or tire clearance on bumps or turning?

Cheers, Dave

[1937-44]

Hi Dave,

Here is a website that has a number of charts to help answer your questions; Tire Size Helper My 1937 Buick originally had 6.50x16 tires on it and for a year or two I had 225-75rx15 tires on it with no issues other than the speedometer was a little off. I personally prefer the look of the 16 inch tires so when the money became available I did switch back, but I must admit it did ride a little better with the radials.

Carl

[egor]

A 6.50x16 tire diameter would be roughly the diameter of the rim plus twice the tire size, 16+6.5+6.5 inches, or about 29". I guess that would be a 100% aspect ratio? Your speedo will read a little fast with your current tires at the diameter you stated. I don't think the other issues you mentioned would be a problem, with the possible exception of tire clearance on sharp turns, but if you haven't noticed this problem yet, then you're good to go.

[Daves1940Buick56S]

Suchan:

I think the 6.5 is the width, I am assuming what they call section width. The sidewall height would be that number times some aspect ratio. I have seen that older tires were wither 90% or 80%. I do not know when the 78% aspect ratio started, maybe the early 60s? Anyhow, I had calculated it to roughly 27.5" assuming "G" == 8.00, but some other charts say G is 8.15 or even 8.25, which would increase this to appx 27.9". I will try to get an accurate measurement when my back gets better.

I cannot say anything much on speed calculation, I have not been able to reliably drive it that much as yet. Have not noticed any rubbing but will look more closely now. It seems a *lot* of physical effort to steer at slow speeds for these old arms, but that may be normal. I dunno, maybe narrower tires would make the car easier to drive but it's a lot of money to pump in and I don't know how much more work I have to put into the engine. I used to drive manuals all of the time when I was much younger, maybe I have forgotten how much effort it was!

Cheers, Dave

[Mark Shaw]

Dave,

Upper body workouts are important as we age... I say keep them until they wear out....

[Guest Grant Magrath]

Yeah! Armstrong steering! Radials have softer sidewalls that can affect handling and make steering a bit harder, and as you mentioned, the width as well. Some folk swear by radials. I don't mind the original crossplys myself. But the coupe has quite light steering for a car of it's age, and dad has no issues, and he's 75 this year!

Cheers

Grant

[Guest]

You could try greasing front spindles thoroughly with a tube of synthetic grease, these lubes have much better "lubricity" engineer speak for more slipperyer(force old grease out to get effect) Front end alignment especially kingpin inclination angle can cause hard steering especially low speed(parking)

All:

OK, while I am waiting for my back to heal so I can get back to the heavy work on my car, I thought I would try to clean up a few loose ends.

As you can tell from the title: my car does not have the proper wheel or tire sizes. The wheels are 15" and the size is G78 tubeless. From what I could find out and what I remembered about old tire sizes, this is about equivalent to 8.00 x 15, correct? At 78% aspect ratio, this works out to a 27.5" total diameter and appx 8" sidewall width, but please correct me if I am wrong.

The original spec is 6.50 x 16. So, is this at 78%, 80%, or 90% aspect ratio? If 78%, the total diameter is 26.2", if 80% then it is 26.4", if 90% then it is 27.7", with a width of 6.5".

So I think I may have a wheel/tire combo the gives me up to 1.3" more diameter and a 1.5" wider tread.

So, do I have a problem? Any others in this situation? Will the front end align properly? Will this adversely affect handling, or tire clearance on bumps or turning?

Cheers, Dave

[1939_Buick]

A little off topic

http://en.wikipedia.org/wiki/Tire_size

http://tire-size-conversion.com/speedometer-calibration/

or

Type 6.50x16 here Tire size calculator Click "compute"

[TABLE]

<tbody>[TR]

[TH]Specification[/TH]

[TH]Sidewall[/TH]

[TH]Radius[/TH]

[TH]Diameter[/TH]

[TH]Circumference[/TH]

[TH]Revolutions[/TH]

[TH]Speedometer[/TH]

[TH]Odometer[/TH]

[TH]Difference[/TH]

[/TR]

[TR]

[TD]6/50-16[/TD]

[TD]0.1"[/TD]

[TD]8.1"[/TD]

[TD]16.2"[/TD]

[TD]51.0"[/TD]

[TD]1242/mi[/TD]

[TD]60MPH[/TD]

[TD]10000mi[/TD]

[TD]N/A[/TD]

[/TR]

</tbody>[/TABLE]

[TABLE]

<tbody>[TR]

[TH]Specification[/TH]

[TH]Sidewall[/TH]

[TH]Radius[/TH]

[TH]Diameter[/TH]

[TH]Circumference[/TH]

[TH]Revolutions[/TH]

[TH]Speedometer[/TH]

[TH]Odometer[/TH]

[TH]Difference[/TH]

[/TR]

[TR]

[TD]225/75-15[/TD]

[TD]6.6"[/TD]

[TD]14.1"[/TD]

[TD]28.3"[/TD]

[TD]88.9"[/TD]

[TD]713/mi[/TD]

[TD]60MPH[/TD]

[TD]10000mi[/TD]

[TD]N/A[/TD]

[/TR]

</tbody>[/TABLE]

Edited July 11, 2013 by 1939_buick (see edit history)

[1937-44]

I think there is something wrong with the tire size calculator you used. The radius of my 6.50x16 tires is a lot closer to 14 inches than 8. The sidewalls are definitely larger than a tenth of an inch.

Carl

[Daves1940Buick56S]

And for the old tire you have to know the aspect ratio, which brings me back to one of my original questions - for the stock, original tires as in 1940, what was it? 78%, 80%, 0r 90%? Anybody know?

Cheers, Dave

[egor]

Those tires weren't described with aspect ratio. All you can do is go back, check the specs, and do your own calcs. Many antique tire websites give you the info to do so. Here's an example: 650-16 Garfield 2 1/2 Inch WW

And for the old tire you have to know the aspect ratio, which brings me back to one of my original questions - for the stock, original tires as in 1940, what was it? 78%, 80%, 0r 90%? Anybody know?

Cheers, Dave

[Daves1940Buick56S]

Very interesting. So in this case the section width is actually wider than the size, and shows about a 95% aspect ratio. If this tire is typical of a 6.5x16 with a 29.2" diameter then I might be about an inch less with my G78-15s. Would mean the car is riding a bit lower. I will have to do some measurements on the car height, etc when I can get back out there again.

Cheers, Dave

[Thriller]

If I only had a brain....

My '41 has the same 6.5x16 and I was out by it today, but never thought to give it a measure to help you out. Sigh.