ATE Improvised Armor: Rubber Tires

[TheOneRonin]

I'm working on an After The End campaign and need some advice/help from the community.

The campaign will be a North American setting that reached late TL 8 (like today), and the first session will be between 30 and 50 years after the fall.

I'm looking for details on common vehicle steel-belted radial tires...or more specifically, their use as components on improvised body armor.

What DR/inch would a newish tire have? What about a moderately worn one? A well worn one? Would the DR have any particular strengths or weaknesses (like maybe +2 DR vs crushing)?

How much weight per square inch are we talking about? What about for full torso protection?

And if any of the above data exists in any current GURPS publications, I would appreciate someone pointing me in the right directions. I've already read through my copies of ATE1 and 2, ACTION1 and 2, High Tech, Tactical Shooting, and a few homebrew web resources, but have come up dry.

Any help from the community would be much appreciated.

[Varyon]

"Cutting Edge Armor Design" (Pyramid #3/85) includes rubber as one of the materials, as well as several types of steel. A bit of online research should be enough to get a decent approximation of the ratio of steel to rubber, as well as what grade steel is appropriate, which should be (when combined with the article) enough to get a decent approximation of the performance of such armor. If I have time (and remember), I may see what I can figure out for it after work today.

[Varyon]

Alright, at home with access to my books. First off, it should be noted that the articles' values for Scale and Segmented Plate are a bit off - Scale should have a CW of 1.6 (rather than the 1.1 of the articles) and CC of 0.9 (instead of 0.8), while Segmented Plate should have a CW of 1.2 (instead of 1.45) and a CC of 2 (instead of 1.5). This is important, because those are the types of construction you'd use for armor made out of cut-up tires. A good enough armorer could probably create something akin to brigandine, which should have a CW of 1 and a CC of 3.6.

The steel used for radial tires appears to be fairly high carbon, so we'll go with Hard Steel. The rubber is, of course, Rubber. Unfortunately, I can't really find information on typical thicknesses, so I'm just going to assume armor armor that's as thick as it can get, with roughly half the bulk being from steel and half from rubber - 0.1" of Hard Steel and 0.25" of Rubber*. Hard Steel has DR 82 per inch, so we get DR 8.2 from the steel liner. Rubber has DR 14 per inch, so we have DR 3.5 from the steel liner; let's just round these to DR 8 and DR 4, respectively. However, on a new tire, quite a bit of the thickness is only present on half the tire, thanks to the treads. However, having worked it out, this is a complication not really worth bothering with**. Of course, against anything other than crushing damage, we need to halve Rubber's DR - it only provides 1 or 2 DR against most threats.

Making Chest (front only) armor out of this, with the above thickness, means 2.625 square feet of coverage. DR 4/2* rubber would have a base weight of 0.45*2*2.625 = 4.725 lb and base cost of $5*4.725 = $23.625; DR 8 of Hard Steel would have a base weight of 0.5*8*2.625 = 10.5 lb and base cost of $3.5*10.5 = $36.75, for a total base weight of 15.225 lb and total base cost of $60.375. Both materials are TL 6, so for ATE you need to multiply by 4, for $241.50. Making it into scale armor would increase weight to 24.36 lb and reduce cost to $217.35. Making it instead into segmented plate armor would increase weight to 18.27 lb and increase cost to $483. Making it into brigandine would leave weight at 15.225 lb and increase cost to $869.40.

The overall armor would have DR 12 against crushing and DR 10 against everything else, and cover only the Chest from the Front. Personally, I don't think it would be worth the weight and cost...

*Rigid materials can get up to 0.2" thick, flexible ones up to 0.5" thick.
**If we assume half of the DR is in the treads, this makes the above armor be only DR 10 against cr with a 5/6 chance of enjoying a +2 to DR from the treads being hit, being only DR 9 against cut with a 5/6 chance of a +1 to DR, and being only DR 9 against pi/imp with a 3/6 chance of a +1 to DR. It also cuts the weight and cost of the rubber portion to 75% of the current. Honestly, not a complication worth worrying about.

[dcarson]

I'd expect the steel belt is most of the protection compared to the rubber.

[Pursuivant]

I think that Varyon's on the right track.

As a guess, assume that the sidewall of a car tire is 3/8" to 1/2", while the tread portions are 1/2" to 1".

Edit: Estimates of thickness and composition are based on diagrams of tire cross sections and personal experience.

Sidewalls will be a mixture of mostly rubber and nylon thread, while the tread will be mostly rubber with a mesh of thin metal wire. There won't be a whole lot of structural integrity to the wire, so DR from metal is likely to be low. In any case, it will be less than 0.1".

The most likely method of making armor from tires is to cut them into pieces. Cross sections could possibly be used as arm or leg armor - particularly to cover the knees or elbows. Torso armor would have to be made from "scales" made from overlapping flat tire sections, which might mean an effectively +50% to 100% increase in thickness.

As data points, GURPS 3E Vehicles 2E gives DR 2 for standard car tires, which might be a bit low. GURPS 4E Basic assumes DR 4-5, which might be a bit generous.

Edit: FWIW, a freely-swinging tire makes a decent target when practicing with "live steel" melee weapons, and is capable of taking repeated strikes without suffering serious damage. That suggests DR 4-5, per GURPS 4E Basic.

[Rupert]

Originally Posted by Pursuivant

As data points, GURPS 3E Vehicles 2E gives DR 2 for standard car tires, which might be a bit low. GURPS 4E Basic assumes DR 4-5, which might be a bit generous.

VE2 is probably assuming shots hitting the sidewalls, as that's by far the most likely by exposed area on most wheeled vehicles.

Campaigns just assumes the same DR as the rest of the vehicle, so far as I can see.

If considering the Pyramid articles:

I would not call the wire in a steel-belted tyre 'Hard Steel' - it's not face-hardened or a special high-strength (in armour terms) steel. At best if might be 'High-Strength Steel' (i.e. RHA equivalent).

Given the way the mesh is made, not interlinking, etc., it would count as badly-made mail - arguably it'd be 'Layered Fabric'.

However, I wouldn't bother with that sort of detail. Use the sidewalls, get DR4/2*. Use the tread, get DR6/3*, +1/+1 DR for steel-belted, -1/-1 DR if the tread is bald. Unless very well-crafted, assume that armour chinks have no DR at all, because it's not going to be easy to reshape tyre rubber to cover a body well.

[tshiggins]

Originally Posted by TheOneRonin

I'm working on an After The End campaign and need some advice/help from the community.

The campaign will be a North American setting that reached late TL 8 (like today), and the first session will be between 30 and 50 years after the fall.

(SNIP)

Soooo, now that others have adequately answered the question about tire armor, I have to ask about your setting.

Within 5-10 years, muzzle-loading muskets and rifles should be at least reasonably available, in most settlements.

The primer problem is huge, but even that would be solved to such an extent that brass cartridge rounds should be routinely available (if variably expensive), in 15-20 years (at most).

As soon as muzzle-loading firearms become available, even a steel cuirass becomes only marginally useful. Once cartridge ammo exists, body armor becomes completely pointless unless it consists of Kevlar with ceramic inserts.

What's going on, in your setting, that keeps progress so retarded?

[mlangsdorf]

Steel cuirasses were actual armor for heavy cavalry through the Crimean War, so the mere appearance of muzzle loading firearms wouldn't make armor useless.

But I do agree (and have stated previously) that the minimal firearm for established villagers, post-Apocalypse, is a rifled blackpowder muzzle loader firing Minie balls. Someone is going to figure out how to salvage a lathe and use it for rifling, and someone is going to read up on Minie balls, and getting musket loading times while getting rifle accuracy for almost no additional complexity in the gun design is just too valuable for anyone to bother making unrifled muskets.

A DR 10ish, tire tread breastplate looks like it would weigh around 20 lbs and turn direct hits from .69 caliber Minie balls from "say goodbye to your spine" to "serious but survivable trauma" which seems reasonably worthwhile for settlements that have maintained antiseptic practice. It might not be daily wear, but certainly something to have in the armory for when raiders come raiding.

That said, cartridge ammo didn't sweep non-Kevlar armor from the battlefield. The first Spencer repeating rifles used cartridges. It's smokeless powder that makes the bullets too powerful for armor, and that's a lot more complicated to make.

[(E)]

Speaking as someone who has used pieces of old tires as shock absorbers on machinery, the steel belt will fragment and work its way out as small chunks of rusty wire.

Outdoor and earth moving conveyor belt material is a better material choice. Rather than wire, the laminated rubber has Kevlar based reinforcing. Its also in large easy to work with sheets and when it is found it is found in lengths that may be up to multiple kilometers long.
Enough for a semi unified force maybe...

[DanHoward]

Originally Posted by tshiggins

As soon as muzzle-loading firearms become available, even a steel cuirass becomes only marginally useful.

Depends on the cuirass. I know of three different eye witness accounts of Polish cuirasses stopping cannon balls. Hussar breastplates were very thick, though, around 8-9mm across the chest. But there are plenty of lighter cuirasses that were proofed against muskets.