Tire sizes

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Model T Ford Forum: Forum 2009: Tire sizes
Top of pagePrevious messageNext messageBottom of page Link to this message  By Thunder on Saturday, October 10, 2009 - 02:32 pm:

I'm at a loss trying to understand the different tire sizes. Would somebody please be so kind as to explain the different sizes?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Layden Butler on Saturday, October 10, 2009 - 02:48 pm:

Early high pressure tires have a different method of size description than later. They use a large number followed by an X and then a small number. The first ( large number) is the outside diameter of the tire, second ( and smaller ) number is the tire height measurement. To find the rim size you deduct from the outside diameter the tire height on one side of the wheel and then dedict the tire size for the other side leaving the rim measurement.
Example: 30 x 3 1/2
30
-3 1/2
-3 1/2
_______
23 rim size

Later with low pressure tires a different measurement system came in. It uses the tire size ( smaller number) followed by a dash- then a larger number which is the rim size.
Example 4.50 -21
This is the method we use today on modern tires.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Hjortnaes, Menomomonee Falls,WI on Saturday, October 10, 2009 - 03:18 pm:

Please explain this for me. My tires are 30 x 3 1/2 oversize. At least that is what is on the side of the tire. If I measure my rims, the diameter of the wheel is 24 inches. The example above states that my rim should be 23 inches. Is the rim measurement the inside surface of the rim, and not the edge to edge distance?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf on Saturday, October 10, 2009 - 04:40 pm:

After reading Dave's question I went out and did some measuring, then made a crude diagram. There are certain terms I've heard and read many times but never had explained to me, so if I'm wording anything wrong here I hope somebody will straighten me out.



I gather this is what they call a clincher rim and tire, because the bead that sticks out from the side of the tire is clinched under the edge of the rim that rolls over to form a sort of hook for it. The proportions aren't right in this quick sketch but I think it gets the idea across. As I understand it, the rim can be demountable, meaning it comes off the wheel so you can bolt on another rim that has a spare tire on it, or it's nondemountable---part of the wheel. I measured a wheel and found it's 24" from outside of rim to outside of rim. Measuring the open space in the center of the tire, it's 22" across. Measuring from the bead to the opposite bead (where it hooks into the curve of the rim), that's where you get the 23".

Now here's my question: what do you call those rims with the snap rings that want to kill you?


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Stroud on Saturday, October 10, 2009 - 05:20 pm:

Steve, you are correct, the rim size is the inner diameter of the tire. The rims with the snap rings that can kill you are flat base rims, the others like the wire wheels are drop center wheels. Dave


Top of pagePrevious messageNext messageBottom of page Link to this message  By Layden Butler on Saturday, October 10, 2009 - 05:31 pm:

Dave, The rim measurement is indeed that flat surface where the inside diameter of the tire ( and tube) go against. The maximum outside diameter of the rim is indeed bigger so the tire does not come off. If you measure your modern car tires you will find for example that a 15" rim measures something like 16 1/2" in maximum outside diameter.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Layden B on Saturday, October 10, 2009 - 05:39 pm:

Steve, This design you drew is indeed a clincher type for the reason you state. The later T's ( like modern tires) are called straight sides although in early days they were called Dunlop after their inventor. There were several other tire to rim designs that were tried and did not stand the test of time. None of the different designs interchange on other rims without modification.
To answer your question: you are refering to lock ring rims. The only Model Ts to use this type was the rear of later TT trucks with 20" tires.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Layden B on Saturday, October 10, 2009 - 05:47 pm:

David, The clincher rim drawing shows a "flat base" from the clincher on one side to the clincher on the other. Technically this too is a " flat base rim". You are correct about 1926-27 wire wheels ( like modern rims as well) being drop centers. The name coming from a smaller diameter than the rims size in the center of the rim to allow tire mounting.


Top of pagePrevious messageNext messageBottom of page Link to this message  By "Hap" (Harold) Tucker on Saturday, October 10, 2009 - 09:49 pm:

Dave,

Yes, for a 30 x 3 1/2 rim -- it measures a little over 24 inches high if it was standing on the floor without a tire. But the curved part of the clincher is approximately 1/2 inch so when you subtract that from both sides the diameter of the rim is 23 inches. Below are some photos that may answer that better.

The metal the rim is made from is approximately 1/16 or so thick (measured in poor light with my eyesight and wooden ruler). So the distance is not impacted that much measuring inside or the outside of the actual metal. The illustration I posted before shows:



I didn’t worry about that 1/16 or so part of the rim. When you place a 30 x 3 1/2 without a tire on the rim next to a 30 x 3 the 30 x 3 is about 1 inch taller. I show the curved sides of the clincher as 1/2 inch. And because there is a 1/2 at the top and 1/2 at the bottom then the rim measured on the inside of the rim is 23 inches for a 30 x 3 1/2 or 24 inches if you include the 1/2 inch distance of the curved section and multiply that by 2 (i.e. two sides) you have 24 inches – again for the 30 x 3 1/2 clincher.

Below are two wheels for comparison – first the 30 x 3 then the more common 30 x 3 1/2.



Above is a 30 x 3 front wheel with a 30 x 3 1/2 wheel without a hub in the background. Note the hub prevents me from measuring directly across the center of the wheel – but it is fairly close.



Above is a close up of the same picture of the 30 x 3 clincher rim. The rim from outside to outside is just a little more (larger diameter) than 25 inches – but I could not measure directly across the wheel because of the hub.



Above is a 30 x 3 1/2 clincher with a 30 x 3 clincher shown behind it. Note the 30 x 3 is easily seen as it is about 1 inch taller.



Note this is the same photo – just zoomed in on the 30 x 3 1/2 clincher wheel showing it is just over 24 inches in diameter from the outside of the rim to the outside of the other rim. This wheel did NOT have a hub in it so it was easy to measure directly across.



Above the 30 x 3 1/2 rim is on the left and is approximately 3 inches wide (the last time I did a sample of several 2 7/8 inches is what I decided was a reasonable number for the 30 x 3 1/2 clincher rim outside to outside. Note – this rim is rust some –so the distance between the inside edges of the rim are a little wider than if all the metal was still there.



For those of us that don’t like to do math --- now the 30 x 3 rim is on the left an it measures about 2 5/8 inches outside to outside of the rim. You can zoom in and see that easily.

Note depending on which company made the rim and when – there were a lot of minor variations. The key point is the 30 x 3 is about an inch taller than the 30 x 3 1/2 when they are both on even ground. The 30 x 3 is noticeably thinner than the 30 x 3 1/2..

This is another example of how difficult it sometimes is to explain something that is obvious if you can just see the two wheels next to each other. I hope the pictures help.

Respectfully submitted,

Hap Tucker 19l5 Model T Ford touring cut off and made into a pickup truck and l907 Model S Runabout. Sumter SC.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Hjortnaes, Menomomonee Falls,WI on Saturday, October 10, 2009 - 10:18 pm:

Hap:
You outdid yourself on this one. The diagram did not explain things as well as the pictures. The pictures prove that a picture is worth a thousand words & clearly shows the differences between the 2 sizes. I am sure that Thunder and I now understand this quite clearly.

This explanation brings up 2 more questions.
1. Why is one rim 2 5/8 and the other 2 7/8, since both rims appear to be 1/2 inch in depth? What is the benefit?
2. In an earlier post, someone said that my front tires should be one size and back tires the other size. Why would Ford build a car this way so the spare would only match front or rear, and if the spare was not matched with the opposite tire it would affect the car's balance?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Ouellette on Saturday, October 10, 2009 - 11:01 pm:

Hello, my name is Mike and I am new to the Model T world. I to am having issues with tires but I now know that I have 23" wheels, thank you! But here is my question, I have the cincher style wheels what is the best way to remove and install the tires? or if there is a past thread pertaining to this could someone assist me with the info

Thanks

Mike/Sparks nevada


Top of pagePrevious messageNext messageBottom of page Link to this message  By Thunder on Saturday, October 10, 2009 - 11:30 pm:

Dave, I have a better comment about Hap.... Is there any way that we can just bottle all of his knowledge?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Hjortnaes, Menomomonee Falls,WI on Saturday, October 10, 2009 - 11:58 pm:

Let's see. Hap is in South Carolina. How about you and I share a bottle of Southern Comfort with Hap, and when he is not looking we will stuff him into the bottle and cap it. We will only let him out if he gives us 3 wishes. The 3rd wish will always be that he goes back into the bottle. Then we pass the bottle around and everyone gets 2 wishes before he goes back in the bottle.

In that picture of his, he looks like he thinks he is pretty tough stuff.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Thunder on Sunday, October 11, 2009 - 12:22 am:

So Co is one of my favorites.... But do you think Hap will buy into this?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Hjortnaes, Menomomonee Falls,WI on Sunday, October 11, 2009 - 01:17 am:

Just watch and see. Probably taking a nap right now.


Top of pagePrevious messageNext messageBottom of page Link to this message  By "Hap" (Harold) Tucker on Sunday, October 11, 2009 - 09:38 pm:

Yes – napping – about 8 hours worth and then a few of the “Honey Do items.” I’m glad the pictures helped. And thanks for the warning to be extra careful if anyone offers me some Southern Comfort. Of course there are plenty of other beverages to choose from so I guess I’m still safe.

For the question: Why is one rim 2 5/8 and the other 2 7/8, since both rims appear to be 1/2 inch in depth? What is the benefit? The front tire is 3 inches wide while the rear tire is 3 1/2 inches wide – so the rim is wider for the wider tire.

For the question: In an earlier post, someone said that my front tires should be one size and back tires the other size. Why would Ford build a car this way so the spare would only match front or rear, and if the spare was not matched with the opposite tire it would affect the car's balance?

Below is a advertisement for tires from 1916.



Those are the retail prices but the 30 x 3 is about $2.45 less than the 30 x 3 1/2. Ford had already produced over a million Model Ts by then. If we guess the wholesale difference was 50 cents a tire then each car had two tires so $1 per car was saved. By the end of 1918 (demountables with 30 x 3 1/2 all around were introduced during 1918 for the 1919 model year) it was 2,831,426 Model Ts. Note all those number include approximately 22,057 to 37,714 Canadian produced cars that used USA engines and serial numbers up through at least May 1913 as well as used 30 x 3 1/2 on all four tires. It also includes the UK cars (I’m not sure of that number) which all used the USA engine numbers but were assembled in the UK after 1911. There were also USA produced ambulanced for WWI that used 30 x 3 1/2 on all four wheels. But it is clear that a little money saved with that sort of volume results in a lot of money saved. Based on the 1907 & 1908 Model N, R, S, & SR Retail Price List of Parts – Ford charge the customer the same for a front or a back wheel (complete wheel including the hub cap and the bearings for the front wheel or the brake drum for the rear wheel). Ford also charge the same for the 28 x 3 or the 30 x 3 which were the two sizes used on most of the N, R, S, & SR production (ref page 30 of the 1907 N, R, & S Price List of Parts (the Roadster (SR) was not made yet – that came in 1908).

Note the wise owner would not have mounted a 30 x 3 1/2 on the front 30 x 3 wheel or vise versa. It is almost impossible to mount the 30 x 3 1/2 on the larger diameter 30 x 3 rim. It would take a lot of strength and a hot tire. However, it is very easy to mount a 30 x 3 tire on the 30 x 3 1/2 smaller diameter rim – but if it runs low on air it will come off very easily all by itself. So neither way is recommended.

Note Ford USA did switch to all 30 x 3 1/2 when they introduced the demountable rims. That way the spare tire already on the rim would fit any wheel. But notice Ford USA continued with the 30 x 3 front wheels in the non-demountable style until the 1926 “improved models” were introduced and then before the end of Dec 1926 Ford USA discontinued the non-demountable wheels (ref: http://mtfca.com/encyclo/1926.htm ). [I don’t know if that also applied to the TT trucks or not.]

For Mike – welcome aboard! From your profile it looks like this is your second posting and your first posting at: http://www.mtfca.com/discus/messages/80257/109964.html?1255280357 had a similar question. You asked

I have the cincher style wheels what is the best way to remove and install the tires? or if there is a past thread pertaining to this could someone assist me with the info

I would recommend take a look at Dan Treace’s excellent article “15 Minute Clincher Tire Mounting in 9 Pictures” located at: http://www.mode l-t-ford.org/pr ojects/clincher _tire_mounting. htm

See also: http://www.mtfca.com/discus/messages/80257/82443.html


Note he shows how to change the clincher tire on a non-demountable wheel. But it works very similar on a demountable wheel that the rim can be taken off of. Some folks prefer to block the car and leave the wheel attached to the car and take the tire and tube off. That is the way it was normally done back in the day.

You are very fortunate – you live in Sparks Nevada and the Silver State Model T Ford Club is located around there.

• Silver State Model T Ford Club
c/o Wendell Newman
5 Lewers Creek Road
Carson City, NV 89704
The link on the web page to e-mail Wendell did not work – but I will e-mail you what I think is his telephone number after I finish with this posting.

I think the folks with the Silver State Club will be able to help answer a lot of your questions and also help you decide if you need another rear wheel or if the one you have is repairable etc. Note if you have rims that are removable – usually called Demountable Rims and if they are the clinchers they came in several different styles. In General you would want to make sure that the wheels (especially the felloes on the wheels) were all the same and that the demountable rims were the correct ones for your felloes. If you have demountable / removable rims see the links below. If your rims are nondemountable – don’t worry about looking at the links – there are a lot of different versions used and if you don’t have any of them – it doesn’t impact you. Although long term for a driver – demountable wheels are a nice thing to have.

http://www.mtfca.com/discus/messages/80257/92314.html

http://www.mtfca.com/discus/messages/80257/105383.html accessory demountable wheels

http://www.mtfca.com/discus/messages/29/39491.html Ford of Canada

http://www.mtfca.com/discus/messages/50893/73786.html accessory demountable

http://www.mtfca.com/discus/messages/50893/77434.html 2846C removable clamps

http://www.mtfca.com/discus/messages/29/33266.html nice info on Kelsey 88 rims and felloes

Again welcome aboard. And let us know if you are able to contact the folks at the Silver State Model T Ford Club or not.

Respectfully submitted,

Hap Tucker 19l5 Model T Ford touring cut off and made into a pickup truck and l907 Model S Runabout. Sumter SC.


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