State of things: 21" radials
 

I'm in the process of switching to radials on my '29 coupe and I wanted to post a few updates here based on what I'm learning.

The first issue when switching to radials is what to buy. Currently there are two radials for the 21x3 Model A wheel (I'm not counting whitewalls as a separate tire):

• American Classic
• Excelsior Stahl Sport

Both of these are manufactured by Coker. The Excelsiors are the "premium" tire here. They're an inch wider than the Classics (4" vs 3"), which makes them look more like later radial tires that were designed to balloon out a bit from the rim. They're rated for a higher weight than the Classics (1500 vs 800 lbs per tire), so if you have an AA truck then that could be a factor in your decision. They also cost twice as much as the Classics. From all my research, it doesn't seem like we're looking at a "bad" tire and a "good" tire here, more like a "good" tire and an "extra good" tire.

Remember that you'll need to buy 5 or 6 tires to cover your spares, so factor that into your budget.

Along with your tires, you will need tubes and rim strips. The rim strips are rubber bands that protect the tube from getting abraded by the ends of the spokes. Coker is currently out of stock on 21" rim strips and could not provide an ETA on the next shipment. I sourced some rim strips from Lucas. Their strips are 1.5" wide and 1/32" thick.

For tubes, I spoke to Coker technical assistance and was directed to the following tubes:

• 440/450-20/21 Tube | TR135 Center Rubber Stem for the American Classic
• 600/700-20/21 Tube | TR13 Offset Rubber Stem for the Excelsior

Note that both of these tubes say "not for radial tires." Coker was clear that these were nevertheless their recommended tubes for the 21" radials. Their explanation – which I'm not sure I believe – is that the "not for radials" warning isn't literal, but rather is a warning to people trying to use a tube with a tubeless radial. Whether you believe them or not, I was unable to find any 21" tubes for sale anywhere that explicitly claimed to work with radial tires.

Note also that the tube for the Excelsior has an offset stem. I'm not sure about this discrepancy; if you're planning to go that route, you might should ask Coker about it.

Update: This tube is not the one Coker recommended but it does look like a better match for the Excelsiors.

Coker also notes that they are out of stock of the American Classic tubes through the end of July. Lucas carries a tube with similar specs that is in stock. I've attached a photo of the Lucas 440/550 tube. The Lucas tube is manufactured by Custom Classic, I believe they're based in India. I don't know who manufactures the Coker tubes. It's Hartford brand, but all these brands have been bought and sold a dozen times by now.

Right now I'm at the stage where I have all the parts stacked in the garage. Will post updates when things get mounted.

Re: State of things: 21" radials
 

Hello,thank you for all the information,although my car is a 31 it’s nice to a “consumer report “ to help base decision on something like tires , so many choices and prices it’s nice to have information what might the the best for your needs.

Re: State of things: 21" radials
 

The landscape for the 19" wheels is similar, except there are more tube options and you might be able to find tubes that claim to be for radials. Same choices on the tires though.

Re: State of things: 21" radials
 

Re: State of things: 21" radials
 

I do not know, that's why I said anyone going that route should take it up with Coker. That was the SKU the Coker rep pointed to. Looking at their tube inventory more broadly, I think this may have been the correct tube:
https://www.cokertire.com/accessorie...stem-tube.html

It's center stem, the ratio matches the Excelsiors, and it's actually designated for radials. I'll update my original post.

Re: State of things: 21" radials
 

Re: State of things: 21" radials
 

The expensive 19 inch tubes recommended for radials are very thick and heavy.

The 21 inch Excelsior's have a large diameter 32.1 inches and need a rim width greater than 3 inches.
Actually, the American Classic is a large diameter tyre as well, at 31.7 inches.

This is a bias Firestone which I think is the largest 21 inch Model A tyre:

Brand Firestone Product Size 440/450-21
Tire Construction Bias Ply Sidewall Style Blackwall Width Bias Ply 4.40/4.50
Rim Diameter 21
Overall Diameter (in) 30.79
Section Width (in) 4.69 Tread Width 3.75
Rim Width (in)2.50 - 3.00

A more normal size Brand BF Goodrich:
Product Size 440/450-21
Tire Construction Bias Ply Sidewall Style Blackwall
Width Bias Ply 4.40/4.50 Rim Diameter 21
Overall Diameter (in)29.75

That's a two and a third inch jump from a BF Goodrich to an Excelsior. Hope you've got good brakes!

Re: State of things: 21" radials
 

Here’s what the radials are replacing - probably should have done this earlier.

https://uploads.tapatalk-cdn.com/202...cf07506e03.jpg

Re: State of things: 21" radials
 

I checked the tire diameter, my old bias-ply tires are 30.5" diameter and the new American Classic radials are 31.0." So I don't think it'll be too big a shift. Although I am glad I haven't rebuilt the speedometer yet so I don't have to calibrate it twice.

Re: State of things: 21" radials
 

The problem with wider and larger sizes is hitting the brake rods on full lock.

Re: State of things: 21" radials
 

Update: I finally got my wheels powder-coated and the tires mounted. I put the wheels on the car tonight to test for leaks. When I inflated them, one tube immediately started leaking around the stem, so that one is set aside for the moment. The other four held air. I left it overnight with jack stands under the frame, in case one of the other tubes decides not to hold air.

Here are some close-up pictures of the 21" American Classic radials.

Per the other thread comparing the ACs and the Excelsiors, the plan is to deflate them tomorrow, assuming the remaining four tubes are good, and put a bit of bead sealer on the rims.

Re: State of things: 21" radials
 

A good thread. I am thinking about replacing the old Garfields on my 28 with radials.

I have the Excelsior radials on my 30 and have been happy with them. I used the special radial tubes from Coker and had metal stems installed. I ordered my tires from Summit Racing, which did offer free shipping. Looking at their site now, it appears they charge 9.99 for shipping. They only stock the 19's, not the 21's unfortunately. Quite a difference in price between the American Classic and the Excelsiors. I like my Excelsiors, but at the difference in price, it's hard to justify the additional cost!

I am puzzled by the "not for radial" tubes for 21" tires. Why would they have radial tubes for the 19" and not for the 21"?

Re: State of things: 21" radials
 

I have no idea. I did later find radial tubes in the 550R21 size for the Excelsiors, but, just checking now, Coker's website lists no radial tubes in the 440/450R21 size.

Re: State of things: 21" radials
 

Excellent information, many thanks for sharing!!

Re: State of things: 21" radials
 

Alexiskai, any update on how these tires are performing?

Re: State of things: 21" radials
 

I've only had them out on the road a few times, but it was really nice. A huge improvement over my decades-old dry-rotted bias-ply tires.

The main downside is that some of the tubes seem to have a very slow leak, like 1 psi a week. This may be due to my buying tubes not explicitly rated for radials for reasons described in detail above, or maybe they're just low quality tubes and the radial thing has no bearing on it. We're still in the midst of the tube supply chain crisis, so for now I'm just putting up with it.

Re: State of things: 21" radials
 

I recently went through the same process but with 19 inch American Classic. I pinched one tube which put a hole in it but the tire did not go flat for a couple weeks. I think the tube closed off the hole in the rim and the tire acted like a tubeless, or it started leaking after it was flexed for a while. I just used the old tubes and the other tires are holding air OK. I had one heavy duty tube approved for radials that I put in the one flat tire.

I think tires are going to leak a little air naturally. Your air pressure loss could be a change in the ambient temperature as we get more into winter.

I love the radials. Smoother ride and better traction. The sidewalls flex quite a bit. I am running 40 psi instead of 35 psi.

Re: State of things: 21" radials
 

Motocross bikes use 90/100 21” tubes. That might be a possibility.

Re: State of things: 21" radials
 

My understanding is that they do work, but the valve stems need washers to work with the Model A wheels and the stem is threaded.

Re: State of things: 21" radials
 

I have been running 19” Stahl Sport Radials for two years now and am very happy with them. I mounted them with Hartford tubes. The Hartford tubes are the thickest, heaviest tubes I have ever used. I cut the rubber stems off and installed metal stems in them. They hold air great. I think I’ve only had to add air a couple of times in two years. They are smooth and quiet. They are expensive, but worth the cost in my opinion.