New Member

Hello, Long time Lurker, Now joined. I've had his '72 Roadster, (Fairly complete, matching numbers) for about 12 years. Ridden only occasionally. Want to get serious now and ride it and have some questions for you folks. Tires are 10 years old now and time to make a decision: Alloy front 19" to replace the original steelie, or replace he 18" alloy rear with a 19" steel original type? Tires will be Avons and I'm familiar with sizes and availability. The intent is to to get quite sporty with her, with some light touring. Rearsets on order. Isolastics will be replaced, with a plan to go to a 21 tooth counter sprocket, (from 19). Let the advice begin!
Thanks

A Commando with the same size wheels front and back should be neutral handling. But some of the comments on this forum have mentioned the necessity of counter-steering to get the bike to tip into corners. Half an inch lower at the back increases the rake on the steering head, which increases the trail - the bike should tip into corners more easily, and should have less tendency to run wide as you accelerate out. More trail usually causes oversteer.

Most bikes are designed to become stable when you brake. A dragging front brake will usually make the bike more difficult to steer around corners, because the front stays down. When the back is down or the front is up, life becomes easier. The forces involved are found by addition of vectors.

Welcome lookfar.

Actually the topics you mention are really down to personal choice.

Which Avons are you planning to run?

Avon have a great web site that explains rim sizes etc for their tyres.

If using Roadriders, are you aware of the tread depth difference between 18 and 19 inch rears?

It might be worth waiting to see if Avon fully resume production of your desired sizes before committing to rim sizes etc.

From reading a lot of replies over the years, I would say 21T is vg idea.

Rear wheel: some don’t like the look with an 18 ( a little small visually) , but a lot more choice of tyres, particularly dedicated rear tyres( more mileage). Also look into the rolling radius of the tyre, not just rim size, for visuals. Rim width: again, look into tyre width/ swing arm side clearance.. plenty of previous posts on this, and most would say don’t go extra wide anyway, as there is no advantage, and possibly some disadvantage. Vernier isolastics a big yes, and improved headsteady.

Welcome.

The questions you mentioned have been beaten to death repeatedly. Lots of lively debate.
You can read the pros & cons for hours.
"Get quite sporty"
That's refeshing to hear!
Parade dawdling is so often the case.

Welcome Lookfar,
The questions you have asked are basically a personal choice. You will get opinions from all over the map regarding tires,rims, etc.
Myself I use a 21T sprocket that works well for me and your choice of upgrading the isolastics is a good way to go.
Enjoy your motorcycle and keep us posted
Mike

acotrel said:

A Commando with the same size wheels front and back should be neutral handling. But some of the comments on this forum have mentioned the necessity of counter-steering to get the bike to tip into corners. Half an inch lower at the back increases the rake on the steering head, which increases the trail - the bike should tip into corners more easily, and should have less tendency to run wide as you accelerate out. More trail usually causes oversteer.

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Al - please don't preach shit (again) to a new member!
In Avon Roadrider Mk2 the 19 (100/90) has the identical rolling diameter (671) as the 18 (4.00 - 18) so the 1/2" lower plus the "neutral handling" stuff is just not right.
Sorry @Lookfar , you'll get used to members whose advice is best to be ignored.
I run Avons mentioned above (18 & 19) and the bike handles beautifully.
@Fast Eddie 's advice on the resumption of Avon manufacturing is worth noting though.
Cheers

...here is a spreadsheet I made a couple of years ago comparing suitable tyres (front & rear) The light grey is what I had and the darker grey is what I moved to.
It is worth noting that some makers sizing is misleading so charts should be looked at, particularly WRT rear swingarm clearance.
Cheers (again)

robs ss said:

Al - please don't preach shit (again) to a new member!
In Avon Roadrider Mk2 the 19 (100/90) has the identical rolling diameter (671) as the 18 (4.00 - 18) so the 1/2" lower plus the "neutral handling" stuff is just not right.
Sorry @Lookfar , you'll get used to members whose advice is best to be ignored.
I run Avons mentioned above (18 & 19) and the bike handles beautifully.
@Fast Eddie 's advice on the resumption of Avon manufacturing is worth noting though.
Cheers

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+1

concours said:

+1

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Thanks folks, I know that tires/wheels can become an “oil thread”, and I’ve read a bit about it all. The Avon RR were the tire of choice, and wanted to stay narrower with similar diameters, for the handling, ( the handling comments above didn’t make sense to me also). I guess the real question should should be steel vs aluminum in 19”. Aware of the benefits of alu, just hoping to hear about any sporty experience with the narrow steel setup. Has Avon paused production? I hadn’t heard about that.

Lookfar said:

Thanks folks, I know that tires/wheels can become an “oil thread”, and I’ve read a bit about it all. The Avon RR were the tire of choice, and wanted to stay narrower with similar diameters, for the handling, ( the handling comments above didn’t make sense to me also). I guess the real question should should be steel vs aluminum in 19”. Aware of the benefits of alu, just hoping to hear about any sporty experience with the narrow steel setup. Has Avon paused production? I hadn’t heard about that.

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The handling comments above are WRONG. That guy gets confused and forgets how it works and most of the time posts the opposite of the effects of changing trail distances. It's an ongoing thing here.

If you do something to give your bike more trail, it turns in slower and with more effort, while increasing the bike's straight line stability.... For most sport bikes, the trail is designed to give quick, light steering without making the bike potentially unstable by reducing the trail number. A commando handles pretty well as designed

WTBS, I run 19 front and 18 rear, and have no steering or handling issues. I also have rear sets and prefer them. I use the dunstal rearset reproductions that Don Pender (madass140) now makes. I like them because they fold up out of the way which is helpful when moving the bike around and they work well.

I run a 21 sprocket, and feel that's best for average american roads. Maybe if you were riding in some mountainous region, a 19 or 20 tooth sprocket would be a better choice, but opinions vary on this. I live near a highway so occasionally I have to go 80mph just to stay with traffic. Even with the 21 tooth, I think the engine has plenty of power, and can still pull in a wide range of rpm's, but if I was doing 80mph on the hiway more often, I would like either another taller gear in the gearbox or a bigger than 21 sprocket up front,.... but then I would think my gearing would suffer on the "B" roads... Not many people set their commando up as a highway cruiser....

As far as Alu rims go, the lighter your unsprung weight, the better your suspension will function, so IMO lighter is better.

Regarding tire width,.... Modern tires have compound radius shapes that help increase the surface area contact patch when you are leaned over. Wider tires, generally have more surface area and a better "grip", but narrow tires tend to steer more quickly. So you don't get both advantages with either choice. If you get fatter tires and mount them on wider rims, you get less sidewall flexing if they are inflated correctly which leads to more precise handling due to the lateral rigidity of the tire. If you go with a wider tire on a narrower rim, I found that I had to run higher tire pressures to help counteract sidewall flexing which contributed to a sloppy feel that I initially thought was an isolastic issue.... I like the avon road rider tires a lot...

I had same bike as yours except mine was ‘72 Combat , I went with single Mikuni 34 & 21T ,used cNw front brake upgrade , Landsdowne Fork mod , got 19” alum. rims built onto my hubs by Don Pender , upgraded all ISO’s , rebuilt GB, and on and on etc. …. I had that bike for many yrs , so long my Wife cried while shipper loading it up for new owner … Damn I still miss it , but time changes things , Only the best of luck for you , get new tires

Are you replacing the tires because they are worn, or because they are 10 years old?
Depending how the bike was stored, the tires might be perfectly serviceable.
Lots of different opinions on this.
I just watched Allen Millyard's video on his Velocette twin where he casually mentions (at 4:25) that the rear tire was bought second hand in 1979 and is still perfect because of how it was stored.

If the engine is a Combat, I would not use a 21T sprocket unless you'll be riding mostly at highway speeds. I recommend staying with 19T for Combats and general riding. If not riding around town much, then I would say 20T.

19 vs 18 debate goes on forever. I'm 'Old' school and prefer the 19's.
I have alloy's front and rear. The issue is, a dedicated 19" rear is not made.
They are univeral, just rotated different directions front and rear.
As a result the rear wears very quickly. I assume from the softer compund to be compatible with the front.
The 18" rear gives far more tire choices.
Very little talk about a 20" sprocket. Combat's like to rev.
Vernier Iso's. Only if necessary, as in old ones wore out. If measurements and ride are still in spec, leave them.
If they are bad replace with verniers.
Check all engine mount connections, 5 total on the cradle, 3 on rear, 2 on front.

My check list would be,
1. Leave 18" rear, replace front with matching alloy
2. 20" sprocket.
3. Adjust Iso's, double check all engine and Iso mounts.
4. Check swing arm for slop, proceed accordingly.
5. Replace rear engine breather with reed breather. CNW has one. Access may be an issue with Gear box in place.
6. Be aware of Layshaft bearing issue in Trans. A sign is kickstart rotates back while accelerating.

Lookfar said:

Thanks folks, I know that tires/wheels can become an “oil thread”, and I’ve read a bit about it all. The Avon RR were the tire of choice, and wanted to stay narrower with similar diameters, for the handling, ( the handling comments above didn’t make sense to me also). I guess the real question should should be steel vs aluminum in 19”. Aware of the benefits of alu, just hoping to hear about any sporty experience with the narrow steel setup. Has Avon paused production? I hadn’t heard about that.

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How much money you got?

Most Commandos probably have a seat for a pillion passenger. If you do not wind up the suspension, do they handle better when you carry a passenger ? - Or do they oversteer ?

I am also old school, if the rims are not rusty and in good condition why replace them your bike looks very original, re tyres if you stay with 19" originally your bike came out with 410x19 front and rear but my experience a slightly narrower tyre on the front is an advantage 2 options that work for me [if available in your country] are- 100/90x19 Dunlop TT100GP front with a 410x19 TT100 rear or 325x19 Avon roadrider front with a 100/90x19 Roadrider rear, I have measured the width of the 100/90x19 Roadrider which is very close to the same width as the 410x19 TT100.

Welcome Lookfar.

I can’t tell from your pics, but if your bike doesn’t already have a rear brake pedal return spring, you should definitely add it to your shopping list. Without it, if the cable happens to snap the pedal will drop to the ground ( not good)