Wheel size question

Hi, currently in the very pleasant process of sorting my 1972 Roadster.
The bike was restored once, a very long time ago, and put away. I am now gradually re introducing it to service.

The wheels are 19" front and 18" rear, and the tyres, 90/90H19 front and 110/90H18 rear, both Avon Roadrunners.
The technical manual of my machine states both wheels as 19".
Am I missing something here? Is this normal and OK?

Thanks in advance, the collective wisdom of this forum is highly appreciated.
Aris

I think they would have both been 19" originally, (410H19 tyres)

It's not "normal" , just the previous owner's idea of an upgrade as tire choices are greater and easier to obtain on a long trip. Some owners don't like the skinny/large circumference look of the 19 rear and go to 18 to beef things up too.

You have the perfect setup. Don't change a thing.

Its mostly a matter of taste for the looks or the appearance. The factory Commando ballet act is at its best as it came from factory but the rear wear factor definitely suffers regardless of how tame you behave. I've mostly ended up with 18" 110-120 tires the majority of my Commanding but am recovering a 19" rear to fit used to new bargain tires and sense for the differences till I settle on a favorite and keep the other as flat switch out spare. its pretty subtle effects, a tad more or less effort to lean or fling and more or less delay to various amounts of throttle. You can compensate a bit with more or less air pressure per tires fitted. Main noticeable difference is how soon the baldness and shopping starts again. A schizophrenic patient advised me one time that if I ever found an item i really liked, Get Two of Em!. There are a handful of choices - looks to performance to sort though.

Thanks everyone, this is really useful and reassuring.

Now the tires themselves. My Avon Roadrunners are a tad over 10 years old, have on then ~1400 running in Km, and have spent ALL their life in a dark & well ventilated garage. So I guess they are on the way out on age alone, despite looking brand new.

Re new tires. My other 3 bikes (all Hondas: CBX, GL1000, CX 650 Turbo) are on Bridgestone Battlax BT-45s which I like a lot.
I guess my 72 Roadster would also be happy wearing a pair of these?

Cheers, Aris

The old tires are not unsafe to use up but if hardened do screw with the isolastics isolation and chassis handling road texture so can't be racing about on them. Battlax have gotten hi marks by happy users here.

Thanks Hobot

The tires look, and to the touch at least, feel like new.
But as I am 'sorting' the bike, they are one more parameter to worry about.

For example, at anything over ~100 Km/h, even slightly provoked, the handlebars will go into an oscillation that scares the **** out of me.
I recently replaced the original head steady with a Dave Taylor + Mk3 spring.
This has made the bike a bit 'tauter', but has not helped AT ALL with the above issue.

The isolastics are good, of the vernier type and adjusted carefully.

I did read somewhere of a similar issue (bike weaving at high speed), which was fixed by changing the rear tyre ...
May be a different problem to mine but not sure I have many other options. And they ARE over 10 years old.

Cheers, Aris

Try a Bridgestone BT45 100-90/19 up front and a BT45 120-90/18 in the back.

Sorry, but you must sort out your bank account and purchase new rubber, bite the bullett as they say.

Torontonian said:

Sorry, but you must sort out your bank account and purchase new rubber, bite the bullett as they say.

Click to expand...

Only too true as they say ... and I will follow Snorton74 advice and go with the Battlax.
Will be very interesting to see if, and what sort of a difference they will make.
Cheers, Aris

Avon Venoms are also a great option if available in your area .
Regards Mike

Roadrunners are fine tires, as good or better, in my opinion, than anything else available in 19" and 18" and leaving aside outright racing rubber that is available in those two diameters.

Their age though may well be an issue. Very experienced riders can ride on hard worn out tires and get away with it. Less experienced or less risk tolerant riders cannot, and should not.

If you scuff the tires with a rasp, what do you get? Is there a hard outer surface? If so, then they are marginal but you could try to save them with a belt sander. While the wheel is in the air and free to spin while applying the belt sander at an angle of say 30* or 45* such that the wheel/tire spins and gets sanded at an even and consistent rate. The idea, of course, is to get down to softer rubber but to avoid making high and low spots.

I've done this but then upon test riding decided that they still were not good enough and that I liked new sticky tires more than I did the money that they cost . . . .

Any rider with a few years riding should be able to ride a flat down from high way speed barring any 60mph gusts or drainage ditch crossings so same with the most crappy tires you can imagine that still hold air w/o spitting before leaving, just take it easy in the turns and wet and braking till used up is all plus a good sense of self and bike control as crappy tires do screw with the Cdo hinging onset much soorner but a non issue just to cruise about legally. After the crap tires you will be so pleased with any new ones, till they get to feeling a bit like the old ones so know time to show again. If you don't have the road smarts and self control to use up any tire then better think twice moving up the speed scale of false security new tires give. I don't hardly ever hear any complaints about THE Hingle so always makes me wonder what the big deal is on tires as if Ya ain't regularly having to damper down THE Hinge then you don't know what you are in for when you do hit the hinge but already too fast to riding it out while leaning to make the committed turn. Its not traction that limits Cdo's but better traction does help extend the speeds before danger zone hits. Ride on low aire tires to find out how your bike will behave just before it goes nutzo and a reflex sense how to react.

Thanks for all replies and words of wisdom.

My Avons ARE over 10 years old and although practically unused (~1400 running in Km) they are bound to be less than optimum.
Rubber does age with time, and I guess not only on the outside ...
Of course I can ride the Avons for ever and a day, but really, why not take advantage of a fresh set.

In any case, I have already ordered my Battlax's and planning to fit sometime tomorrow.

I will test over the weekend and, allowing for running them in, hope to report back soon.
I will be looking out, especially with regard to that nasty oscillation / weave I was getting with the Avons, as reported above. Wish me luck.

Best and thanks, Aris

Snorton74 said:

Try a Bridgestone BT45 100-90/19 up front and a BT45 120-90/18 in the back.

Click to expand...

this is the combination i run on my 850 and i'm very happy with them - i like them more that the road rider combination (which are good, but the lack of rear wheel options made me switch)

mikegray660 said:

Snorton74 said:

Try a Bridgestone BT45 100-90/19 up front and a BT45 120-90/18 in the back.

Click to expand...

this is the combination i run on my 850 and i'm very happy with them - i like them more that the road rider combination (which are good, but the lack of rear wheel options made me switch)

Click to expand...

This is exactly what I am getting tomorrow.
Thanks!

Changing the front wheel size alters the steering geometry, and that is a dangerous exercise. If you reduce the wheel size in a featherbed norton to fit better 18 inch tyres, without adjusting the rake, it will handle like a bag of shit ever after. When Peter Williams as working for Norton, they produced one model of commando with decent geometry, and a few inexperienced riders got chucked up the road after riding over 'cats eyes' lane markers. They reduced the severity on later models. I would never reduce the front wheel size on a bike designed for 19 inch wheels. These days you can buy decent 19 inch tyres, so there is no reason to go there and risk necking yourse lf. If you insist on going there , you should at least measure the rake and trail of the front end, and make sure it is sensible. There is nothing worse than having the handle bars disappear in a blur, and the bike turning itself into a ball of screeching metal sliding down the bitumen in front of a lot of speeding cars.

acotrel said:

Changing the front wheel size alters the steering geometry, and that is a dangerous exercise. If you reduce the wheel size in a featherbed norton to fit better 18 inch tyres, without adjusting the rake, it will handle like a bag of shit ever after. When Peter Williams as working for Norton, they produced one model of commando with decent geometry, and a few inexperienced riders got chucked up the road after riding over 'cats eyes' lane markers. They reduced the severity on later models. I would never reduce the front wheel size on a bike designed for 19 inch wheels. These days you can buy decent 19 inch tyres, so there is no reason to go there and risk necking yourse lf. If you insist on going there , you should at least measure the rake and trail of the front end, and make sure it is sensible. There is nothing worse than having the handle bars disappear in a blur, and the bike turning itself into a ball of screeching metal sliding down the bitumen in front of a lot of speeding cars.

Click to expand...

This tire and wheel combination works perfectly! When sat side by side, they are the same height.

I've been through all combo's of sizes on Cdo's and they all work fine from 90 to 110 front. Only thing I note is a tad easier forks on smaller tires and some lack of brake grip on narrower front than wider. I now like 110 front and back best for ease and balance and tire mileage and sure'r whoa's. For max out road work I'd go 120 rr 100 front. For nicest real life ease on a Cdo I like 90 90 but costs ya in tire wear.