Motorcycle Tires, A Primer
By David Tong
Many motorcycles, particularly classic models, heavyweights and those with laced wheels, ride on bias-ply tires. However, radial ply tires are supplied on the majority of new motorcycles. The thing to keep in mind is that both designs use belts to ensure that the tire maintains its designed shape and accounts for thermal (heat) expansion during use.
Whether of bias-ply or radial design, a tubeless tire is less likely to suffer a blow-out than a tire with an inner tube and is therefore safer. A tubeless tire is also easier to repair at the side of the road in case of a small puncture (typically less than 1/8 inch).
Motorcycle specific tubeless tire repair kits are preferred over those intended for automobile tires. A kit that resembles the ones I have used in the past is made by a company named DynaPlug. It is a very simple, bullet shaped rubber plug inserted with vulcanizing cement that can get you going again quickly.
Like their automotive counterparts, a bias-ply motorcycle tire has layers of fabric. These are usually rayon, polyester or kevlar and these cord reinforcements crisscross diagonally across the tire carcass. Due to its construction, a bias-ply tire has a nearly equal amount of sidewall height and tire width.
The upside to bias ply tires on a motorcycle is that they can withstand heavy loads, so they may be more suitable for heavyweight motorcycles. Bias-ply tires are supplied on many cruisers, touring bikes and some standards.
A bias-ply tire will almost always be found on any bike with traditional laced (wire spoked) wheels that require an inner tube, as all radial tires are tubeless. Bias-ply tires are versatile, in that they can be tubeless or used with an inner tube.
Radial tires have a base layer crossing at a 90-degree angle across the tire carcass (from bead-to-bead) and generally the cords are thin steel wires. The radial will also have crisscross layers, or belts, to provide under-tread reinforcement, but will not add material to the tire sidewall, as would a bias-ply tire. Typically, a radial tire will have a low-profile sidewall. All radials are tubeless tires.
The upside of a radial tire is its increased carcass flex, due to its non-belted sidewall, which offers a larger footprint for better traction, especially under heavy side loads. This is why radials are better on bikes made for cornering (sport bikes and sport tourers, mostly).
Because the sidewall flexes more it allows for a smoother ride. A radial's lighter construction aids gas mileage, due to less rotating mass. The less rotating mass, the quicker the bike responds to steering inputs. In addition, the lighter construction of radials means they dissipate heat better than a bias-ply tire, which translates to a higher mileage and generally longer wearing tire.
I can speak from experience on this last point. I can remember riding on older Continental, Dunlop and Metzeler bias-ply tires. Typically, even with my comparatively light throttle hand, I would get 4,500 to perhaps 6,500 miles out of a rear tire. There are exceptions, such as the Metzeler ME-88 Marathon, which was specifically designed for long-distance touring, and these might last over 10,000 miles. However, they have pretty stout sidewalls, so some loss of ride quality was normal.
When I transitioned to more modern motorcycles in the mid-1990s, I found that radials simply felt better. They were more supple riding and provided a more precise steering feel. In addition, it appeared that I had more tire to use while cornering, as I found it harder to use the whole tread width of a radial-ply tire than I did with bias-ply tires, given the speeds and lean angles I was willing to ride.
Another advantage of radials I have noticed is they tend to wear in pairs more evenly than bias-ply tires. I would sometimes wear out a rear bias-ply tire about 30% faster than a front tire, having to replace both before the front was worn out.
If you choose your compound carefully and ride accordingly, radials are able to run at least 8,000 miles before replacement and several times I achieved 12,000-14,000 miles before relegating them to the recycle pile at the local tire monger. This may not sound all that great compared to a premium automobile tire that can last 50,000+ miles, but car tires do not have motorcycle lean angles and camber thrust with which to contend.
Radial tires generally require wider rims than bias-ply tires and that can sometimes be a problem for traditional style motorcycles. Motorcycles with suspensions not designed for radial tires may feel squirmy if equipped with radial tires.
Since the majority of motorcycles these days use radials, this is where the major manufacturers are going to concentrate most of their engineering and development time and money. Of course, this does not mean that bias-ply tires are not also being improved in similar ways, including life, ride quality and handling.
It is usually the type of motorcycle that dictates the type of tire fitted. Older bikes, cruisers, many touring bikes and some standards are the most likely candidates for bias-ply tires. Most sport, sport touring, standard and some touring motorcycles are designed for radial tires.
None of this should indicate that a bias ply tire cannot be a good choice. However, for the foreseeable future, the radial tire will continue to dominate the bike market, just as it does with cars.
Copyright 2015 by David Tong and/or chuckhawks.com. All rights reserved.