Are New Tires Larger than Originals?

I'm looking at buying new radial tires for my 53 Dodge Coronet Convertible and want something roughly comparable size-wise to the 7.10x15's it came with. The question is - what were the original dimensions of a 7.10x15 tire.

The only decent "original" on the car (which I know to be at least 45 years old because that's when the car was put in storage) is a 7.10x15 Gates retread with over 1/8" tread left. It is 27 1/4" OD, with 7 5/8" section width & 4 3/8" tread width. The tires currently being sold by Coker, Kelsey, etc., are ~29.1" OD, with ~7 3/4" section width & 4 3/4" tread width. That's a significant difference.

The radial tire that matches best to my original (and the recommended replacement for a 7.10x15) is a P215/75R15 with 27.7" OD, 8 3/4" section width & 6 1/8" tread width. The P225/75R15 is closer in size to what's being sold today as a 7.10x15 tire, with 28 3/8" OD, 9" section width & 6.3" tread width. Recommended rim size for the 7.10x15 bias tires is 5", whereas for the two radial sizes it is 5.5-7" and 6-7", respectively. I'd like to use my original 5" wide rims.

So the question is (or are): 1) Are they now making tires larger than they used to, and 2) if you care to venture an opinion, would the larger P225/75R15 tire likely fit on my mid50's Dodge? At $200+ each for whitewalls I'd rather not order the wrong size. The original wheels are freshly painted (I know I got ahead of myself), so I'd rather not have to "test-mount" a tire I won't be able to use.

One of the most common threads is a warning not to use radial tires on rims that weren't designed for them. There is a danger of the rim failing,although you can probably get newer rims to fit.

I know that the tires for my 1915 Buick are over size as they will not fit in the trunk like they are suppose to. Yes, this was a Buick first having the spare in the trunk for the 1915 C-36 Roadster. The original size is 34X4 and fit a 26 inch rim. Dandy Dave!

One of the most common threads is a warning not to use radial tires on rims that weren't designed for them. There is a danger of the rim failing,although you can probably get newer rims to fit.

That was what I was going to say, and is the 1953 originally a tube type also?

I have little experience with pre-1955 (tube type) 15" wheels, but I would think the 225 is too much. Given the Coker size recommendation and your measurements I would probably be comfortable with the 215 BUT would be careful about the rims as noted above. Good luck, Todd C

The original rims have an oversized valve stem hole and riveted construction, so I'll have to use tubes. They are also "safety rims", which have the high step to better hold the tire on the rim. I've read a lot of controversy about putting radial tires on older rims, but have seen nothing conclusive. The rims are pretty heavy duty & although I'm an engineer I can't see where they would be subject to much more stress with a radial tire.

On the topic of radial tires on 50s rims, 15-20 years ago at tire tech sessions at AACA meets Coker advised against mounting radials on older non radial rims because of the much greater cornering force of radials. You need only drive a 50s car with original style 4 ply tires to appreciate the difference in cornering power. 4 plys are kind mushy when you turn the wheel, radials have an instant response.

My advice is to ask Coker if they still advise against radials on 50s rims.

Martin Lum

1955 Desoto and 56 Buick with non radial tires

Radials are definitely wider. Unless you buy the cheapest tires. I used Walmart Marshal 791 radials on my DeSoto, they are a good 2" narrower than name brand tires of the same size, 215R75 15. The 75 is important, this is the height of the tire, lower numbers are low profile. 75s are about the tallest narrowest tires you can find for your car.

The alternative is bias ply antique tires. In other words either the cheapest tires or the most expensive.

You should be okay using with 7.00 x 15 or 7.50 x 15 bias-ply tires.

"Odd" sizes, such as 5.90, 6.25, 7.15 have not been reproduced ( or reproduced in significant quantities) due to limited demand.

It was common for car owners to "go to the next size" way back.

My '41 De Soto is listed as using 6.00 x 16 tires as "standard equipment", but the 7-passenger cars came equipped with 6.50 x 16 tires. Same wheels, same basic car.

I elected to put 6.50s on my car, and they have not caused any problems over the last 13 years / 40,000 miles.

I am less comfortable about putting modern-size radial tires on vitnage stock rims.

The radial tire grips the road better, and transmit more force through the rim to the car than the old bias-plys would... take an exit ramp too fast with skinny bias-ply tires, and you'll see what I mean: the bias-plys start screeching because they are loosing traction on the pavement. This is probably more of an issue with 16" rims than with 15" or 14"...

If you're dead-set on radials for your '53 Dodge, and want to keep the tire size & aspect-ratio as close to the original tires as possible, you should look into Coker's "vintage radials" - their line of modern radials that are designed and built to closely resemble the bias-ply tires they are being substituted for.

Good luck !

Ordered a set of Goodyear Custom Super Cushion Classic Radials yesterday through a local Goodyear dealer, who will obtain them from Kelsey cheaper than I could. They're P215/75R15's with 3" whitewall and are closest in size to the original 7.10x15's that came on the car. I compared the P215's against P225's and decided the larger tire would be too big, primarily in width.

Also contacted Coker who finally gave me a reason new tires are larger than original tires of the same size designation were back in the days. It seems new tires are required to be inflated right out of the mold when still hot, resulting in the tire growing. Anyway, that's their explanation. I hope they're not too large to fit in my trunk as I also ordered one 7.10x15" bias tire for a spare.

Thanks for everyone's input.

Just remember to not mix a bias and radial tire on the same axle. You would be better off purchasing a 5th tire as mixing them is not a good idea.

I have the same exact problem. Please email me and tell me all you have found out. Mine is a 1949 Dodge Coronet Coupe with 7.10 x 15 with a 5" rim. I have been planning to put radials on the original wheels that I have already put a lot of work into refinishing. I have also purchased a disc brake kit and 3" lowering kit front and back. Hope you can help. jimibedsoul@gmail.com Thanks.

Did you end up using your original wheels?

I have been running radial tires on all of my cars for the last 30 years with the stock wheels and have had no problems. And I don't baby my cars either.

Ordered a set of Goodyear Custom Super Cushion Classic Radials yesterday through a local Goodyear dealer, who will obtain them from Kelsey cheaper than I could. They're P215/75R15's with 3" whitewall and are closest in size to the original 7.10x15's that came on the car. I compared the P215's against P225's and decided the larger tire would be too big, primarily in width.

Also contacted Coker who finally gave me a reason new tires are larger than original tires of the same size designation were back in the days. It seems new tires are required to be inflated right out of the mold when still hot, resulting in the tire growing. Anyway, that's their explanation. I hope they're not too large to fit in my trunk as I also ordered one 7.10x15" bias tire for a spare.

Thanks for everyone's input.

Tires grow? Don't believe it. I grew up in Dad's recapping shop. It was common practice to cap several size tires in the same molds due to the high cost of size specific molds. For instance Dad capped 6.70-15s and 7.10-15s in the same molds resulting in both sizes ending up the same. It's the same today. the cost of molds to produce repro tires is very high so several "different" sizes are made in the same molds by simply changing the slug that identifies the size. When tires come out of the mold the rubber is already vulcanized and won't "grow". I can't think of a reason tires would need to be inflated right out of the molds, makes no sense.

I have mid 1930's Auburns. Many of these cars have sidemount tires. The typical eight cylinder Auburn came from the factory with 6:50x16 tires. Metal tire covers were supplied. It has been my experience that new tires are larger.

- The tire spacers in the fender pocket have to be removed or altered to fit the new tire.

- The metal tread cover does not fit the circumference of the tire properly hence not covering the complete edge of the metal face cover.

It is my opinion that the factory did provide such ill fitting sidemount tire covers. Two options are available, run 6:00x16 tires in the side-mounts OR do not inflate the 6:50's.

Been running radials on my cars last 20 years 1966 Plymouth fury run it it highway speeds all over the country don't buy cheap ! when I bought the car it had cheap radials on it , first trip I had a blow out on 81 . put good tires on , haven't had trouble since . We have put about 50,000 on this car touring. Have 50 Chrysler put radials on it handles better haven't had any trouble with it . I don't drive it like a hot rod it's a old car use some %%%%%%% kings32

I don't know exactly what tire, (I think they were Firestone 500's,) I had on my 55 Chrysler back in 1960 but I went into a corner and the front tire completely deflated. The rims were stock 55 Chrysler New Yorker's.

Upon examination, the rim had split along the outside sealing edge and formed a 12 crack. It was obviously a fatigue crack. They were tubeless, so the crack opened all at once as the tire was not low on air pressure while I was driving it. I have never seen anything like it before or since.

all Chrysler product rims after about 1940 are known as safety rims [ a name Chrysler selected ]. they are a heavier thickness metal than some of the later gm rims and have the lip around the rim. they will work just fine with radial tires. my 54 Windsor has 235/75R/15 tires and they have been fine since 2008. I have driven the car on trips of 700 miles. my question is what is the correct tire pressure.seems like everybody has their own preference. truck tire valves can seal some of the larger valve stem openings to make any rim take a tubeless tire. shops that do tractor trailers will have these, or look on line. capt den

Jim, I went with the tires described in my June 2010 entry. Used the original wheels, along with radial tubes. Have had no problem with them. My car still has its original style brakes, steering & suspension. Regarding the comment on bias tire size, the 7.10 x 15 tire I purchased as a spare was too tall to fit in the trunk wheel well, eventhough the car came originally with that size. I returned that tire and bought another P215/75R15 for the spare. The width was all the well could handle, but at least the trunk lid would close. So, for whatever reason or whatever method, that size bias tire is larger than they were originally.

Don't forget to use radial tubes with radial tires, regular tubes will fail in radial tires, too much movement of tire against tube.

Why use tubes? I wan't planning to use tubes.

I used tubes because the rims are constructed with rivets, so was concerned about leakage. I suppose I could have used a sealant of some type, but tubes (radial-type) seemed more of a fail-safe solution.

^ I think you did the right thing if the rims aren't welded.

I got so sick and tired of the (*$^&*)% aluminum rims on my '02 S10 leaking air, even AFTER my shop tried rim sealer, I had them put in radial tubes all around.

That was the end of THAT.......

Over a year ago they put a new set of radials on the '59 Chev I had just bought.

I checked their air a week ago and they were all nearly dead on since they were inflated.

When you use tubes inside, the new radial tires will "squirm" against the paper tags which are vulcanized inside of each tire. The abrasion of these tags will wear into the tube in short order, and will cause the tube to go flat.

Three of my new radial tires with radial tubes (a few years back from a supplier in the Carolinas) went flat within the first 100 miles. I had carried two spares, and STILL had to be flat-bedded home.

It MAY be possible to remove the tags and to smooth the surfaces to avoid this problem, but we did not know of the problem, nor did the manufacturer admit to knowing, despite selling me both products as a package for use on my car - the tubes were considered necessary due to the wire-spoke elDorado wheels. The answer was for me to buy aftermarket wire rims with a gel inside to stop air-leakage.

It has been answered many times here that radials are larger in general. I can spot them on cars in period piece movies right away not being "skinny" tires. I believe Coker is about the only one out there that makes vintage sizes but they are not the most roadworthy brand. Great for show cars but not daily drivers.

I remember in the 1970s you could still readily buy 4-ply and used them on my 1960s cars. They road better on my luxury cars and had better wear too. I never had luck with tube tires.

As far as wheel squalling on turns... you are driving too fast then... aggressive driving.

My 1930 Dodge has 5.50 x 18 tires. I had one 6.50 x 18 as a spare and it was smaller than the others! Apparently bias ply tires were also availble in different aspect ratios.

When you use tubes inside, the new radial tires will "squirm" against the paper tags which are vulcanized inside of each tire. The abrasion of these tags will wear into the tube in short order, and will cause the tube to go flat.

It MAY be possible to remove the tags and to smooth the surfaces to avoid this problem, but we did not know of the problem.

Yup......tire people need to check the tire interior for any molding tags and grind them out or the tube WILL get a hole in it in fairly short order.........my guys learned something about that little detail too....... :mad:

I also learned that tube protector flaps (for wire wheels) must be continuous, not an overlapping strip. The tube pinches at the overlap. After several pinches, I replaced them all.

I also learned that tube protector flaps (for wire wheels) must be continuous, not an overlapping strip. The tube pinches at the overlap. After several pinches, I replaced them all.

In an emergency, I once made a flap from the to-be-discarded inner tube by slicing off the exterior portion and carefully cutting out the valve stem to allow for the new one.

It worked so well that I used it as-is for several years.

Are you guys using soapstone powder with your inner tubes?

jimbaustin; your stock rims probably won't fit over your disc brake conversion. You don't need disk brakes if your only running a flathead six!

I have used "talcum" powder. But the tire moves and pulls the tube and looks like it will pull the valve stem out. I tried suds once. A couple of years later it was still wet inside the rim and there was rust. The hard thing on narrow locking ring rims is to get the tube valve and rust band in at the start. After that it is much easier. The problem is opening the tire wide enough to get the rubber and one's hand in there to push the valve stem through.