Are these tires too old?

Like steele mentioned there really is no such thing as a "tube" tire still available. Pretty much every tire is "tubeless, if using a tube type wheel fit a tube". There may be tube type tires still out there, but would be way lowline tires. I think the main thing is to buy decent tires when you do buy. I've never had a problem with dry rot in my life on a motorcycle tire but always used top line tires so I don't care if they are 20 yrs old, nothing in the world wrong with the way they work. The 78 and 80 models I have still running factory tires, they work just fine too and I doubt they were all that great of a tire. Like the other guy said, if you're worried replace them. I'm not worried because I've been around to say the least, and have never had a hint of problem except on those Dunlop D404s.

ghunt81 wrote:

So is there a performance difference between tubed and tubeless tires?

Yes and no

First off most, if not all modern tires are marked as tubeless, but can also be used with tubes.

There "is" a difference between tubeless and tube type rims, you can use a tube in a tubeless rim, but you "really" shouldn't install a tire without a tube on a tube type rim, the rim construction is different (I've posted pics of both here to illustrate the difference).

A wheel with a tube may weigh more than a wheel without a tube, thus increasing gyroscopic affect, braking, and acceleration, but not by a whole lot, and that's assuming the rims weigh the same. KZ spoke wheels are lighter than KZ mag wheels (both tube and tubeless type) of the same size (I have weighed them), so the weight ends up being fairly equal.

I believe the first KZ's with tubeless mags were some 1980 models, the earlier ones all used tube type mags stock from the factory.

Since you have spoke wheels you are limited to using tubes anyway.

There was a Dealer installed optional Morris Mag wheel kit (tubeless wheels) available for the 750 twin (at least in 79), I've seen one NOS kit on eBay in three years of searching, and I bought it.

They can sometimes be found used, just make sure you get the wheels hub adapters with them.

No big deal...been browsing tires on Denniskirk.com, found some good priced Pirellis I really like, and tubes are $20 each.

Another question- when I go on Denniskirk.com and search for "tires by make & model" it gives me metric size tires anyway, not 3.25's and 4.00's. There's definitely a way bigger selection of metrics. Is it really so bad to use a 120/90 and 100/90 instead of a 4.00 and 3.25, respectively?

Don't search by model, search by size. Search on 4.00-18 and 3.25-19

RonKZ650 wrote:

Like I said though, there is no metric equiv. Sure 110/90 or 120/90 *works*, but it's not equivalent. 120/90 beats 110 though if you need *equivalent* NOT, otherwise I'd recommend 4.00-18

There may not be a metric equal, but there is a metric equivalent. That's why they call it an equivalent.

Dictionary.com Unabridged
e·quiv·a·lent

corresponding in position, function, etc.: In some ways their prime minister is equivalent to our president.

I might be able to help with a couple of these topics. Sorry for the jumble, I'll just toss some stuff out.

Starting with the simplest, the key difference between a tube and tubeless tire is the presence or absence of an innerliner.

Rubber is quite permeable to air (and moisture, more on that in a moment). The innerliner is a special compound of halogenated butyl rubber which is much more resistant to loss of air. It makes little sense these days to produce a series of tires with and without innerliners, so for tube-type rims (which do not hold air), you use a normal tubeless tire with a tube in it. There may well be some old designs still in production, but if so they will be dwindling to be sure.

Another side note, the mobility of oxygen through rubber is the primary benefit of nitrogen inflation. Larger molecule, less loss over time.

Aging is a wide open question depending on storage and use. I have a 7 day old gallon of milk, is it good? Well, was it refrigerated or on the counter or in the yard?

You have two concerns, weather checking (degradation of the sulfur cross-linking or to butcher the language, anti-vulcanization) and moisture. Location and use make a huge difference in both.

Our great debt to Charles Goodyear (whose discovery was too basic to control through patent and died broke. The tire company is named in his honor.. [/digression]) is the discovery of vulcanization. Sulfur added to rubber with heat will create a cross linked matrix of incredible durability. With weather checking, also known as dry rot or ozone damage, oxygen breaks down the sulfur cross linking and weakens the rubber. Anti-ozonants are added to protect the rubber. These work at the surface and are replaced by exercising the tire (lucky for us this translates as "riding"). Add in direct sunlight and active sources of ozone (as mentioned, electric motors and transformers) and you can have relatively rapid destruction of stationary tires.

A tire which sits still has two problems, nothing to work fresh anti-ozonants to the surface, and nothing to force out the demons of penetrating moisture. As mentioned way back at the start of this ramble, rubber is permeable to air and moisture, except the liner. So let's save time and jump to the extreme example, a tire sitting in the yard while the temperature jumps up and down, summer and winter, with moisture seeping in and pooling against the liner. On the outside of the liner are those nice body plies, soaking in a pool of stagnant water. A tire against concrete in a dry, somewhat temperature controlled, normal attached garage which is ridden even on an occasional basis will heat up and drive the moisture out.

Our lonely bike-by-the-fence, well, have you ever found an old t-shirt stuck to the ground and tried to pick it up?

I have an affinity for derelict bikes, and I err on the side of caution. If I ain't sure, I replace. On a worn tire you're only hoping to save about $30 on the margin before replacing anyway.

If you bought your tires new 6 years ago and know how you've used and stored them, that's another story. Car clubs actively hunt and run original bias tires that are decades old.

As for sizes, they are not exact. 100/90, MM90 and 3.25 are nominal sizes. The Tire and Rim Association and the European Tire and Rim Technical Organization promulgate books of accepted standards for design, which include the acceptable ranges for these categories. Going too wide for the rim (like a 130/90 on a 2.15" rim)will give you crappy handling, but moving between metric and standard sizing won't have any effect.

Last thing (anyone still reading this?), the semi tire died from heat and inflation/overload. Commercial tires have steel sidewall cords. Most likely one of the duals was low on air, forcing the weight onto it's mate and causing both to flex too far in the sidewall on each rotation (about 450 times per mile). Imaging bending a wire clothes hanger back and forth at a rate of 450 times per minute. The wire cords heat and stretch and as they weaken, they force the cords beside them to work harder. Now add 120 psi of pressure and guess why the sidewall plies would eventually break on that line. It's a circumferential fatigue rupture, or zipper failure as the common term.

Ok, I've got to get back to my coffee now.

Thank you, Guder, for the interesting and informative post. It was thoroughly enjoyed!

Guder, best first post ever!!!