MTFCA Forum

Will 30 X 3-1/2" tubes fit 30 X 3" tires? I ordered those two tire sizes for my 1915 T, but all four tubes they sent are marked "30 X 3-1/2."

In recent years, generally speaking, innertubes have been the same for both tire sizes. It does matter a little bit, if an innertube has been used in a 30 X 3 1/2 tire and been stretched just a bit. It is possible that a somewhat stretched (or otherwise ill-fitting tube) may be more prone to folding over inside the smaller X 3 tire and may result in a pinch leak. Most new innertubes will usually fit either tire size okay.

For many years, manufacturers did make two different sized innertubes for the two tire sizes. However, so many users crossed them over both directions and in most recent years the cheapskate manufacturers simply decided to make a single size tube for both tire sizes.

I'm seeing new tubes with 2 or 3 sizes marked on them. In my opinion, using these tubes in a casing of the smallest size listed on the tube would be best. Less stretch, and perhaps better pressure retention. Bean counters dream of one number to fit all applications.

I’ve wondered why Ford didn’t use just I size wheels to begin with and use 30 x3 1/2.

Maybe Fords engineers thought using the smaller size was some sort of advantage for the Model T car. When the smaller size was made that meant the spokes, rims, tires, and tubes had to be made differently too.
That meant maybe a little different tooling and time to make the smaller size.
Anyway after a few years a one size fits all approach began to be used. And if owners who had older T’s had the smaller 30x3 size on their car I’ll bet the owners eventually went to a wrecking yard to get the 30X3 1/2” on their car. But I wasn’t Ford or a Ford engineer to design the Model T Ford.
So I have a question. Are the hubs, brake drums, and differential backing plates the same for all T’s? If they are all the same switching wouldn’t have been hard to do.

John kuehn wrote: ↑

Sat Dec 06, 2025 8:42 pm

So I have a question. Are the hubs, brake drums, and differential backing plates the same for all T’s? If they are all the same switching wouldn’t have been hard to do.

For All T's the answer is No.
There are early smaller hubs, and later larger hubs that are interchangeable, sorta as in both inner and outer parts and with redrilling holes.
There are ball bearing hubs and tapered roller bearing hubs that I believe you could call interchangeable.
There are straight axle and tapered axle rear hubs that are not interchangeable.
There are wire wheel and wood wheel hubs that are not interchangeable
There are small drum brakes and rear drum brakes that are not interchangeable drums.

The majority of T's built they are generally interchangeable but you have to pay attention and pick and choose your parts and maybe change other parts also.
If you pay attention and pick and choose swapping wheels, hubs, they can easily be swapped around like was done since Henry was offering to "upgrade" customer cars to modernize them.
Dealers, Junk yards and customers have been swapping things around since day one giving us so many mixed up cars today.
Mostly interchangeable, but not completely universal ALL interchangeable.

I suspect Ford used 2 different sized wheels in the beginning since it was normal to do so back in the day.
The carriages preceding automobiles and even a lot of bicycles back then had 2 different sized wheels.
And if it is felt to not need spend the extra money on larger wheels and tires then don't spend it.
Economies of scale and simplification were just coming into consideration when the Model T started.
Efficient production was just starting to become a bigger deal than just making a good design that works, lasts, serviceable, and all that stuff.

Philip,
Some manufacturers make tubes that fit several size tires and mark the tube as such. Other manufacturers make one tube for a given size tire. Changing clincher tires is not something I want to do more than I need to, so I am not going to use the wrong tube and have to change it again anytime soon. They sent you the wrong tube, send it back.

Straight answer, yes, you can put 30x3.5 inch tubes into your 30x3 tires. The size difference is minimal.

IMO, don't think that can work to stuff a 23" dia flap and the smaller 23” tube in the 30x3 tire casing that is made to fit 24" clincher rim.

30 x 3 1/2 clincher tires and tubes and flaps go on the 23” rim.




Got these from Coker, right size 24” dia. 30x3 brass stem tube, and proper 24" flap to go into the 30x3 tire clincher 24" front rim.

Somewhere in the period Ford literature there is a dissertation by Ford on why Ford used the two different size tires. Economy in weight and first cost were the plusses, as I recall. A narrower, lighter front tire will steer more easily and the reduced unsprung weight, and rotating weight, will enhance performance and ride. Ford emphatically stated that the tires specified for the T were fully adequate and that the T had more tire for the load carried than most other cars. I would think that having all 4 tires and rims the same would have saved Ford money.

Dan, did you have any problems cutting off the rubber stem on those Hartfords? I haven't tried it yet. I see you have an incorrect bridge washer. I wonder why that company can't make them as original?

The last set of Blockley tyres I fitted came with Michelin tubes. These were metric equivalents. They were much thicker than any others i have ever fitted, with the exception of two old red rubber Goodyears. They were also smaller in cross section, so should fit 3" tyres well. I have had no experience with "skinnies" on the front wheels though, but have fitted quite a few "fat" 4.40 x 23"' tyres. The tubes that fit those will certainly not fit well in a 30 x 3.5" tyre.

Allan from down under.

"Wrong" bridge washers cost $12 each, new

Who here would pay $30 each for "Correct" washers?

I seriously doubt that there is a market for correct new washers given that authentic parts can be had for a couple bucks, but I would not consider tooling up and making dies for less than that, and it would have to be for a market that displayed a healthy demand. I don't make parts on speculation any more - got enough of those on the shelf already...

I'll just sit back and wait for pre-production orders to roll in and see if it leads to anything.

"Wrong" bridge washers cost $12 each, new
Who here would pay $30 each for "Correct" washers?

$30 for a bridge washer is pretty scary. I'm glad I got into this game when you could still pick up tire hardware cheap at swap meets.

What are the correct bridge washers?

BillM wrote: ↑

Sun Dec 07, 2025 6:01 pm

What are the correct bridge washers?

See above Jelf pix.

Of course the correct is the original type of combination ring and bridge washer. The ring preforms the pressure around the base of the stem to prevent leakage.

With modern new metal stem tubes, the stem is already vulcanized to the tube, so the ring is insignificant, the repro flat bridge washer does it's duty of keeping the stem from shifting, as the rim nut exerts the pressure.


Now if the owner wants to cut off a new rubber stem tube to place a metal stem, the combo ring and bridge washer is needed, and the correct "777" small size ring and bridge washer and associate hardware has to be located, as this size isn't made new.

The advantage of the new metal stem tubes is the "725" size dust caps and rim nuts will fit with ease.


The "777" is the smaller stem, but most later cars used the "725".

Well, now...

$1.85 in 1920 is equal to $31.13 in todays gelt, so it looks like my estimated price is just a little bit LOW and a bargain, too boot - compared to the original!

Such a deal!

Thanks for that, Dan

Note in Dan's first printed page....the tube is sandwiched between the flange on the valve stem and the bridge washer with its pressed in sealing ring. That drawing that keeps on being posted showing the FLAP also sandwiched between the flange and bridge washer is just that, somebody's inaccurate drawing.

With rubber stemmed tubes, there is no bridge washer and no stem nut to take a dust cap, because there is no need for them, just as there is no need for them on brass stems, some of which were thinner and never had thread anyway. If any stem is canted in use it indicates that the tyre is running under-inflated. Anchoring it with a stem nut to keep them upright Is not the amswer. Noticing a canted stem may well be a wake-up call that the tyre needs to be re-inflated.

Allan from down under.

My supplier (Blockley) tells me their 30x3 and 30x3.5 tubes are identical. I asked why the 30x3 tubes cost $5 more, and they replied that they will correct the pricing error on their site.