Radial or bias, is there a difference

[rphillips]

I've used Metzler MEZ II & Dunlop 205 radials on my GS 1150's, & a friend has 205's on his "83" CB 1100 F Honda. The bike radials, much unlike the radials for autos, don't seem to be a lot different than the bias ply tires. When radials for autos were introduced, the would get about double the mileage & double the traction than we would get from the bias ply auto tires. I was expecting the same from the bike radials, but was severely disappointed. The radials wore out in about the same mileage as the bias, and crank the throttle in a lower gear & the radial will lose traction just like the bias. I was ready for the front end to be hard to hold down because of the extra traction I was expecting from the radial, but there isn't really a noticible difference. Can't comment on the side, or lean angle traction, cause after I passed 50 years old, I'm don't ride the twisties near as fast as I did a few years ago. Does anyone see a significent difference in the radials & bias for bikes

[Billy Ricks]

It made a huge difference in the way my bike handles, but then I went to GSXR wheels as well. Radials need wider wheels than bias or you end up with a pinched down sidewall and less contact patch that you would with a bias on the same wheel. You would need to go to a race compound to get significantly more grip than with a bias ply tire.

[themess]

Radials improved mileage and traction in car tires because they squirm less. Bias ply tires have an even number of layers of

Body ply fabric that extends from bead to bead. The angle of the cords in these plies determines if the tire is "radial" or "bias" ply. The cords in radial tires go straight from bead to bead, taking the shortest route. They are at 90 degrees from the direction of motion. On radial auto tires, there is usually a single body ply.

The cords in bias tires run "on the bias", or at about a 30 degree angle from the direction of motion. The tire has a slight tendency to walk the direction of the cords. To compensate, there will be a second body ply, cut in exactly the opposite direction. The angle formed by the cords of the two plies forms a "vee". Each ply tends to push the tire in the opposite direction. That makes the rubber in the tire carcass and tread squirm. The rubber builds up heat from squirming, so the body ply rubber has to be compounded to reduce heat build up. The tread also squirms, which also builds up heat. The squirming slightly reduces traction, as the tread doesn't grip the pavement well. Friction against the pavement and squirming increase tire wear.

Since radial plies are at 90 degrees to the direction of motion, radial tires don't squirm as much, grip better, run cooler, and wear slower.

Motorcycle tires are mostly designed for high performance, which means, among other things, very sticky tread. Tread rubber gets sticky in large part by using a lot of oil in it. A typical all season car tire will have about 30% oil in the tread. A racing tire might have more than 70% oil in the tread. That's a big part of why racing tires wear out very quickly. I never worked with motorcycle tire compounds, so I don't know how much oil is in them. But from reading the boards I know that mileage from most motorcycle tires is really low. High performance bikes need sticky tires, which will have low mileage. So I'm guessing that when manufacturers go to radial tires, instead of getting longer life from them, they mostly use sticky treads to get better handling.

I'd like to see motorcycle tires tested for relative traction, heat build up, and mileage, the way that car tires have been for 20 years.

[Hoomgar]

Radials.............

That is the most information I have ever read on the subject. Thank you. I would like to learn more about this subject. If there are any more sources of info on it I would be grateful.

[rphillips]

Thanks, that says a lot. But still wondering if anyone is seeing big increases in traction or milage. I know high performance sport tires, bias or radial, are made from softer rubber that will wear out faster than harder rubber higher milage tires. I know you can't compare a high performance sport radial to a high milage touring bias. I guess what I'm asking is, Has anyone tried a radial and said "shucks" I got twice the the milage with this new radial, or gosh since I put this radial on the bike, I just can't keep the front end on the ground. I'm trying to find a difference, but really not finding much

[Steve]

Probably the biggest problem is one that was mentioned above. To achieve proper mounting and support, a radial requires a rim that is substantially wider than a bias-ply tire.

If a radial is mounted on a (stock) narrow rim, it will be pinched in, decreasing the natural curve of the tread profile, giving you LESS rubber on the road. In my book, that is not really desireable.

If a bias-ply is mounted on a (wider) rim meant for a radial, you will first have a hard time getting it to seat, because the rim is so wide. Now the tire is stretched wider than intended, which flattens out the profile. Might be OK for casual riding, but when you really crank it over in the curves, all you have left is the narrow ridge at the edge, where it turns down to the rim. Not a good time to have LESS rubber on the road.

So...the best way to do this comparison test is to have two wheels with different rim widths that you can swap back and forth.

Is it worth it? Might be to some, but not for me.


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[bwringer]

If you're comparing apples to apples, that is bias and radials in the same sizes on the same bikes, then there's little difference.

Many have tried radials on a GS and been disappointed because they were not the correct size tire to fit the narrower rims. (The exception would be the 1150 -- many owners prefer radials, even if the sizes are slightly different.)

My "other" bike, a 1990 Suzuki VX800 is rather unique in that both bias ply and radial tires are easily available in the correct sizes: 110/80-18 front and 150/70-17 rear. Bridgestone, for example, offers the BT45 bias ply and the BT020 radials in these sizes, and Pirelli offers the Diablo Strada radials and Sport Demon bias ply. Metzeler also offers the opportunity for a similar comparison, but I can't make sense of their jumble of tire designations...

From the scanty info on the VX800 forum (not very many of these beasties in the US), radials seem to have an edge. Maximum mileage, as with all motorcycles, depends far more on the rider and maintenance than on the tires chosen. But radials are significantly lighter and more flexible than bias ply, and most prefer the livelier, more communicative feel of radials.

For example, the shipping weight of the rear radial BT020 is listed at 14 pounds, while the BT45 in the same size is listed at 17 pounds. Same with Pirelli's Diablo Strada vs. the Sport Demon in these sizes -- the radial is a few pounds lighter. The radials are generally regarded as lasting just as long, but the more flexible carcass is lighter, runs cooler, and offers more feel and possibly more grip.

The differences aren't as pronounced as they were with car tires -- I don't think we'll ever see a mileage guarantee on bike tires. And generally, I've noticed that tire makers will readily sacrifice tread wear for grip, and I can't say I totally disagree with that strategy.

The radial BT020 tires on my VX were new when I bought it (lucky me!) and the tread depth was probably half of the original tread depth on the Dunlop 491 tires I just removed from my GS after 12,000 miles. However, there are reliable reports of the BT020 tires lasting 10,000+ miles on VX800s.

I think the tire makers may be seeking to reduce the changes in profile and handling as a tire wears by reducing the tread depth and using a more wear-resistant compound. A more flexible carcass that develops less heat can serve both purposes -- it may help the thinner tread last longer and help ensure that harder compounds can grip the road adequately.

[Jethro]

I've been researching a rim swap just so I can run radial tires. The rumor is that they have a much nicer feel to them, and a more supple sidewall, so the tire performs better when at high lean angles. Rather than skipping across the road, like my 130 bias ply does when I'm leaned over and I open the throttle. Apparently the radials maintain a larger contact patch with the road. I don't know if the rumors are true, just what I have heard.

[Billy Ricks]

I've been researching a rim swap just so I can run radial tires. The rumor is that they have a much nicer feel to them, and a more supple sidewall, so the tire performs better when at high lean angles. Rather than skipping across the road, like my 130 bias ply does when I'm leaned over and I open the throttle. Apparently the radials maintain a larger contact patch with the road. I don't know if the rumors are true, just what I have heard.

Absolutely true. They soak up minor road irregularities so you feel very little of it. Leaned over is where you feel the benefit of running radials. You do have to have the suspension up to snuff or the tires will overpower the chassis. In a straight line you won't feel or benefit much from radials aside from better braking performance.