Cotton cord vintage race tires

Emery

Emery

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We've really needed cotton cord tires for the pre-1958 race cars, so I'm going to try making some and invite others to play along, too.

First hump is to figure out how big the cotton plies are. Written records seem incredibly thin in this regard, so I've resorted to examining this pic of the shredded rear tire from Stirling Moss' Mercedes 300 SLR at 1955 Dundrod TT.

[not sure why pic isn't appearing, but you can click on the attachment below]

We know the tire size was a 7.00-16, so tread width should be approximately 5.5 inches. I counted about 12 cords per inch. That equates to 21+ cords per centimeter. This suggests the cotton cords are no more than 0.083 inches in diameter (2.10 mm) and probably no less than 0.076" in diameter (1.93 mm). [*** see post #8 for updated values]

The cord angle appears to be 38 degrees, up in the passenger tire range and not all that racy. The tires are likely Continental, so maybe this shouldn't be a surprise.

Anybody come up with different numbers? Anybody have pics of other shredded vintage tires?
 

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Interesting idea, been thinking for a while to make an attempt with ttool. I agree they looks about 2mm, and do look to be in about 45-40degs angles.
 
Here's an Englebert tire from Luigi Musso's Lancia/Ferrari D50 at the 1956 Italian GP (Monza). I come up with a cord angle of 30 degrees, much racier than the Continental [had mistakenly typed Englebert, thus late edit] tire. Bad viewing angle to try and count cord density; seems similar, possibly thicker cords.
 

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Corti said:
https://www.longstonetyres.co.uk/vintage-tyres.html
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It's helpful for dimensions (section width, tread width, and overall diameter), but sadly has holes in the offerings. For instance, the smaller Dunlop sizes in R1 and all the R3/R4 sizes are missing, which is troublesome if you're looking for a pre-58 size that fits a Lotus or Porsche or OSCA. And if you're working on Le Mans cars, there were far more Michelin X sizes than are currently available.

For the missing tire dimensions, I think looking at Home | Coker Tire (section width, tread width, and overall diameter) and, for overall diameter, cross-referencing to period road tests where they give mph/1000 rpm (usually in top gear). If anyone needs the period road tests, I can see if I have them in my collection.
 
Tire Wars of the '50s

Avon tires (Aston Martin) switched to nylon ply earlier than Dunlop [Motorsport Magazine, September 1958]. Lister tested them in late 1957, found them significantly faster than the cotton cord Dunlop and Continental, but Avon turned down the opportunity to supply them to anyone other than Aston Martin [Powered by Jaguar, pg 116]. Then the nylon cord R5 came out in 1958 and it was another notch faster than the Avons, so Lister was satisfied.

Firestone released their nylon cord racing tires in 1957 (Super Sports 170-T) after testing in 1956.

At Goodwood recently I watched some cadet drivers training on DB3S Aston Martin and it was interesting to watch the rubber disappear off the rear Avon tyres. Goodwood is a notorious tyre killer, so it was no discredit to the Avons especially remembering that they won a nine-hour race there for Astons, mind also the TT in the Ulster. However. this tyre wear, together with tyre troubles experienced during the Grand Prix at Monza and those experienced during the Tour de France, have brought the tyre manufacturers into the limelight once more. When a tyre throws a tread people raise their hands in horror, say "but this must not happen," and get hot under the collar at the tyre experts. During the Grand Prix monster-age of 1934-37 tyre changes during a race were frequent. Mercedes-Benz and Auto-Union often making as many as three stops apiece for tyres during a full Grand Prix race. Then no one complained about the Continental tyre firm, it was more a source of wonderment that tyres would stand up to the enormous strains of transmitting 600 bhp. During the 1947-51 era the Alfa-Romeo team made regular pit stops to change their Pirelli tyres when they wore out, and occasionally one would throw a tread and the driver would have to stop at the pits unexpectedly, with rubber and canvas flailing around the wheel. After that, racing settled into something of a doldrum, with the comparatively meek Formula II cars of 2 litres unblown capacity which were quite incapable of even wearing out tyres, let alone bursting them or throwing treads. Full-length Grand Prix events could be run on one set of tyres and at the end the treads still looked like new. and lots of people went around patting each other on the back for the remarkable progress that had been made in tyre construction. Agreed, progress had been made, in fact it was continuous, but the main reason the tyres lasted full-length races was that the cars of that period were easier on them. Then came the present Formula I in 1954 and tyres still gave no trouble, for the beginnings of the Formula were not far removed from the old Formula II but after three years of Grand Prix development and increased power output tyres are beginning to play an important part once more and the rubber experts are being made to cudgel their brains again.
While a tyre failure may be risky for the driver, as with Castellotti's Monza trash, or infuriating for a manufacturer, such as Ferrari, it all makes for good competition among the tyre firms, and competition is sure to produce better tyres. Not long ago Pirelli had an almost complete monopoly on tyres for Grand Prix racing, but now there is much more activity for Continental are back in the racing game. Dunlop and Englebert are in it more than ever, and Avon are joining in while, as I mentioned earlier, Ferrari has been trying Firestone racing tyres. All this competition among the tyre manufacturers is a very good thing and will certainly result in better tyres for everyone, though perhaps not many people realise just what a vast difference tyres and treads can make to the handling of fast cars. Changing from one make of tyre to another can often transform an uncontrollable car into a reasonable one and make a good one even better, while concerns such as Connaught and BRM can design their suspension and handling characteristics around a given tyre. Connaught believe in Pirelli and find their car does not handle so well on Dunlops, while BRM have concentrated on Dunlops and their car is slower on Pirellis.— DSJ [Motorsport Magazine, December 1956, pg 13]
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Emery said:
This suggests the cotton cords are no more than 0.083 inches in diameter (2.10 mm) and probably no less than 0.076" in diameter (1.93 mm).
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Referring to the Physics blog:
Nylon tyre cords (thread, strings, rope, or whatever you want to call them) are among the most common in racing tyres. They are commonly available in anything from about 0.4mm to 0.8mm diameter for tyre cords. That doesn't mean they can't be thicker, or thinner, though. I chose to go with 0.69mm diameter cords for now. Given they are bias-ply tyres, the construction has to be strong enough to resist the tyre folding in. The spacing values should be roughly 30-150% greater than the diameters of the fibers. In reality, this is necessary to prevent fatigue resulting from cords rubbing. Steel cords will normally have a greater spacing than fabric cords. In the case of nylon cords, typical spacing are around the 0.8-1.5mm range.
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So I've possibly estimated the cotton cord size too large. If we choose the space as 30%, then the cords would be 1.48mm diameter.

All the information I can find suggest the cotton cord tires are 6-ply. That means the vertical allowance below the tread is at least 8.88 mm plus maybe another 0.22 mm to seal the plies in rubber. Sidewalls would also be this thick. Assuming 8/64 inch for tread depth, there'll be 3.175 mm of rubber in the tread face [edit: should be 8/32 inch and 6.35mm].

I think, since these are all estimates, it is safe to round off the thickness to 1.5mm and the allowance below the tread to 9.0mm. Another test of the reasonableness of the estimates is to see how much the tire mass changes due to less rubber volume when the cords are nylon and compare that to known values of, say, the Dunlop R5 vs. the R3.
 
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I wonder how different cars would handle with textile used in in their construction. One thing for sure is that tire robustness and way of failure would be very different. Textile using tires would require higher pressures, and that perhaps would be main difference ?
 
mantasisg said:
Textile using tires would require higher pressures, and that perhaps would be main difference ?
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Higher air pressure (I recall reading 50 psi vs. 35 psi for the cars with bigger tires) and more inertia due to higher mass (both spin inertia and unsprung suspension inertia). One could possibly presume less grip due to the higher pressure.
 
Emery said:
Another test of the reasonableness of the estimates is to see how much the tire mass changes due to less rubber volume when the cords are nylon and compare that to known values of, say, the Dunlop R5 vs. the R3.
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A quick estimate suggests the numbers are in the ballpark. Probably need more bulk rubber up in the tread face to support the tread depth.

Oh, wait, I see my mistake on the tread! I said 8/64 inch and really meant 8/32 inch, so double the thickness I originally wrote. And then there's the buildup under the shoulder since these old tires are nowhere near as flat and low profile as modern tires.
 
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Corti said:
https://www.fondazionepirelli.org/e...ote-borrani-where-tradition-meets-innovation/

https://velaqui.gal/link/T0RnMU1UVXlORFkzOjpoYXNoOjowLjI2ODM2MzAwIDE2OTg5Njc2MDE-
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Thanks, Corti!

Pirelli's technical items are pre-Hitler war (darn it). Their advertising drawings helped clear up when their product lines were available. Couldn't really find anything specifically on the full race Stelvio tires, just the general use Stelvio.

Already have the book; others will find it useful, particularly for the nylon cord R5 years and development of compounds.
 
Working on tire shape via the spreadsheet. I've got a shape that resembles a tire, but it doesn't look correct. What's bothering me most right now is now the nodes have crammed themselves into the tread rather than spacing evenly from the bead. I'd also like to reduce the total number of nodes... the few attempts I've tried weren't successful.

Here's the current tire (generic '50s uninflated F1 front tire) compared to the sample inflated Brabham rear tire that ships with the spreadsheet. See how my tread face has tight node spacing while the sidewall nodes aren't tight?
View attachment upload_2023-11-8_15-17-35.png

Here's the shape I'm aiming towards.
View attachment upload_2023-11-8_15-22-8.png
 
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Emery said:
Working on tire shape via the spreadsheet. I've got a shape that resembles a tire, but it doesn't look correct. What's bothering me most right now is now the nodes have crammed themselves into the tread rather than spacing evenly from the bead. I'd also like to reduce the total number of nodes... the few attempts I've tried weren't successful.

Here's the current tire (generic '50s uninflated F1 front tire) compared to the sample inflated Brabham rear tire that ships with the spreadsheet. See how my tread face has tight node spacing while the sidewall nodes aren't tight?
View attachment 54506

Here's the shape I'm aiming towards.
View attachment 54507
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I didn't work with the Tire Spreadsheet yet, but you can import the Picture from the Tire into the Spreadsheet and then you can create a semi-transparent "Chart Overlay" above of it, that shows the Nodes, that you can exactly position them along of the wanted Line from the Picture.
That at least should give you the wanted Tire Shape with the Amount of Nodes that you want to use.
 
Trying to get the nodes to do what I want with just the officially intended spreadsheet cells, I managed to make the spreadsheet blow up a few times, so I'm taking a few days away from it. Glad I'm experienced enough to always be working on a copy, LOL!
 
Emery said:
Trying to get the nodes to do what I want with just the officially intended spreadsheet cells, I managed to make the spreadsheet blow up a few times, so I'm taking a few days away from it. Glad I'm experienced enough to always be working on a copy, LOL!
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Do you mean that the Spreadsheet crashed?
Now i get curious.
How many Nodes do you want to use for your Tire and do you have the Sizes?
 
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redapg said:
Do you mean that the Spreadsheet crashed?
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Yes, I crashed the spreadsheet, LOL! I was poking around though, trying different things on the General tab to influence the shape on the Geometry tab.

Looking at 55 nodes since, generally speaking, the tires are smaller than the Gasoline Alley tires and 55 nodes is what they have. The Gasoline Alley front tire is a good model and I've successfully got that showing as my comparison tire.

So far, creating the shape is the only tough part of the spreadsheet and that's really only difficult because I'm trying to manipulate it with the spreadsheet numbers rather than plotting points via a drawing. Have to keep giving myself permission to make mistakes in that regard.

Working with the cord layers, cord materials, and bulk rubber seems to go well. At least the spreadsheet macros are happy to make a TGM file, so I consider that a success.
 
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