Radial Tyres?

Radial car tyres are defined by the pattern of the reinforcing wires in the tyre...

As far as I'm aware there are two main types in use the old cross-ply and the new radial tyres...

As to their exact differences I will have to leave that up to someone else to explain...

John.

Radial tires are defined by the apparent direction the sidewall cords take as they radiate out from the rim toward the tread. These cords (which are generally polyester fabric) run from bead to bead, at 90 degrees to the tread. The tread, in turn, has wire fabric reinforcement that is laid at a high bias angle, and there are a minimum of two such layers, one balancing the other.

The other wire in a tire is around the bead area (where it attaches to the rim, in a force fit). The wires, unlike the many fine wires that make up the fabric reinforcement of the tread, are larger and very stiff (each wire is roughly .5 mm in dia) and are wound (on a wire winder machine) into a hoop of slightly more than nominal rim dia, then wrapped with thin fabric, and finally covered with Bead rubber. A finished "bead," before being assembled into the tire, has a roughly triangular cross section with the long sides being about 50mm.

The radial ply fabric is simply a lot of parallel fabric cords, held together by a rubber coating applied in a calendering machine. (The steel tread plies are made in the same way, but when cut to the correct width, the fabric sheet (more than a meter wide) is cut on the bias into strips of roughly tread width). The radial ply cloth, on the other hand, is cut right at the tire assembly machine (still usually by hand with a hot knife slid along between cords) to a length corresponding to the bead diameter, and with the cord running straight from bead to bead (and once assembled, actually wrapping around the beads).

You end up with "carcass" which is a tub of bead diameter and about .6M wide -- something that looks nothing like a tire. In fact when you look at it, you winder how it could become a tire. Turns out, this cylinder gets inflated at the tire assembly machine, into a donut shape. and for that to happen the beads must move inward to about the intended wheel width, which allows the thing to balloon out, so that the centerline is about tread size. Because the circumference at the tread is about twice that at the rim, the cords at the tread are twice as far apart as they are at the rim -- the rubber (calendered on previously) stretches between cords.

At another part of the tire assemble machine, the tread package (tread rubber ans two steel plies) is put together. The tread and carcass are then brought together, and "stitched" -- meaning firmly pressed together. What leaves the tires assembly machine is a "green tire" which is only vaguely tire shaped. The final shaping and pressing in of the tread is done in the curing presses. Some trimming and final inspection and sorting, and you have a tire.

A high quality tire typically has 22 - 28 pieces making it up, and still requires a lot of hand labor.

SO.... that doesn't really answer your question yet.

Radial: the sidewall cords radiate straight out from center.

Different: Bias ply tires have cords crossing in the sidewalls at a steep angle. There must be at least two sidewall plies, and the tread is usually not reinforced by any additional plies. The crossing of plies makes both the sidewall and tread stiff. In radial construction the tread is much stiffer, and the sidewall is much less stiff. Therefore, a radial tire can keep its tread on the road with much less squirming, and the tread tends to stay flat on the road under cornering loads (with the sidewalls flexing in parallelogram fashion). In bias ply tires, when the sidewalls flex the tread flexes too, so the tread tends to twist off the road, under cornering loads.

In use: radials get much better fuel mileage because of less tread squirm and less energy consumed in flexing the sidewalls. The last much longer -- so much longer, that creating radial tires dramatically reduced production in tire plants. They handle better, generating higher cornering forces, because the tread stays on the road better. Bias ply tires should cost less, because they have far fewer assembly operations and lower parts count, but now, they are made in lower numbers, somewhat cancelling that advantage. Thus when you buy a tire for your boat trailer, which should cost about $3.00, given what's in it, it costs as much as a cheap radial car tire ($20 - $30)

Bias ply tires are used in trailers, and preferred by some, because their sidewalls flex less, and the trailer may wander a little less. These "problems" don't show up in cars because the chassis is designed differently.

Long answer, but grossly oversimplified re production process. The production process is fascinating, and the tire plants are often .4 km square, so there is a lot to see. When I worked in the tire industry, the plants would open, maybe once a year, to the public, for tours. The tours are interesting, with about 400 different machines to see (and some with multiples of 10, 20 , or 30 of a type) The biggest machines are the rubber mixers (often about 4 per plant) each of which can mix about a million pounds (500,000 kilos) of rubber a day.

In terms of handling...the radial is a better choice. The radial chord allows the sidewalls to flex, therefore, when cornering, the sidewall flexes and allows more of the thread to remain in contact with the road surface. The greater the contact "patch" the more thread in contact, the greater the friction surface, thus the better roadholding capability. It is critical that radials remain inflated to their recommended pressure, as a lower pressure allows the sidewalls to flex too much during normal driving and causes premature failure of the sidewalls.

The load carrying capacity of a radial tyre will be more than of a biyas tyre,

the width of the tyre will be more than the ordinary tyre which will help

better driving pleasure and road grip and for sudden braking system more

effective to minimise damage.

The difference in construction between a radial tyre and a cross-ply gives different handling characteristics. Generally, in increasing harshness of cornering, radial tyres will hang on, and hang on, and hang on, and hang on, and then let go suddenly when the cornering is just too severe for the tyre to cope any more. The same vehicle fitted with cross-plies will produce a proportionate degree of sliding for the same increase in severity. Cross-ply tyres are therefore "poorer performers" than radials, though their lower value may make them a more attractive proposition in some scenarios.

For some vintage vehicles, radial tyres may simply be unavailable.

It is illegal to mix tyre types on the same axle on the road in the UK. It is also illegal to fit cross-ply tyres to the rear axle of a 2-axle vehicle in the UK if radial tyres are fitted to the front axle, though one may fit cross-plies to the front and radials to the rear; mixing tyre types on one vehicle will require the carrying of a second spare wheel for the vehicle to remain legal.

Benefits;- radials will give you road holding and grip, crossply's won't!

I remember when radials first began to be used, there was a lot of discussion as to which were the best...

If I remember correctly radials had the best traction / road holding but when they broke away on a corner they just let go!! Whereas with cross ply tyres they were supposed to give the driver a 'feel' of when they were about to break away by sliding etc...

So some peeps insisted cross ply were safer as you could push them to their limit knowing that you would get a warning before a slide...

Well that's what I remember!! John.

I was driving a restored Anglia 105e the other day, with X ply's, and yes you've got feed back, but the grip levels are no where near a radial. Do you remember the old driving test, when we where told always brake in a straight line, never when turning? That was because of X ply's. These day's you can brake while turning without thinking about it. Even in the wet.

Yes, you remember correctly... if my own failing memory serves. In fact, I remember having participated in such discussions. Racing tires remained cross ply for a few years after radials were common on road cars, but they too were replaced by radials, as it became clear that radials offered more cornering grip. Development of cross ply tires ground to a halt many years ago (about the time of 70% profiles -- which were available in both configurations) and since, radial tires have become progressively lower profile, dramatically reducing slip angle for a given cornering force. If you drive a modern sports car with 35 - 50 series tires, and then drive a similar car shod with bias plies, the difference is phenomenal. Relatively subtle suspension recalibration over the years has retained (and improved) road feel while permitting cornering forces to move from .7 or so to over 1G.

It's interesting to compare a really excellent handling car of today (Lotus Elise) with a really excellent handling car of yesteryear (1965 Lotus Elan). The suspensions are are nearly identical, in the sense that the same basic geometries are used, and in both cases the specific angles employed are optimized for the tires of the day. The Elan would manage maybe .8 G on early radials, and the Elise will manage 1.1. Tires are are the single contributor to the much better handling of todays cars. The Elan is probably every bit as fun to drive, depending upon your perspective. And you may be a little less likely to stuff it -- because when you hit gravel in the middle of a turn, the change in handling will be less dramatic in the Elan, and your entry speed will be lower. Interesting that a road test of the Elan (1250 lbs, 105 hp) showed 25 MPG, while the Elise gets the same at 1950 (and 190 hp) lbs. (The additional hp pays off in top speed, with the Elise at 150, and the Elan at 115.)