Alloy rims worth it?

ashman · Apr 24, 2018

I was lucky when I first built my Commado/Featherbed back in 1980 my new Akront alloy wheels cost $90 each and cost $80 for both to be laced up to my hubs, they been on the bike for 37 years now and they still look as good as the day they went on, so $260 all up for wheels that will be on the Norton for life of the bike and they have clocked up a lot of miles in that time.

Ashley

Stephen Hill · Apr 24, 2018

Fast Eddy wrote: "Regarding 18 or 19 inch, as I’ve said many times before, if you choose the right combo of Roadriders you get a 19 front and an 18 rear with exactly the same rolling radius. But you get a rear that has slightly more cushioning, a bigger contact patch, and importantly, a proper rear tyre tread depth."
I agree with all of the above. And add that the correct 18 inch rear tire will last much longer than a 19 inch rear. With 19 inch tires front and rear, the rear wears twice as fast as the front.

Stephen Hill

NortonMKIIA850 · Apr 25, 2018

Stephen Hill said:
[snip] ... the correct 18 inch rear tire will last much longer than a 19 inch rear. With 19 inch tires front and rear, the rear wears twice as fast as the front.

I know nothing about this at all, except that Norman White told me many years ago that the final thing needed to bring my bike to its best was to fit 18" rims – I still haven't done it, for various reasons, not because I doubt his word. But would you explain to this ignoramus how a tyre with a smaller circumference can last longer than one with a larger circumference? Are you talking about a wider tyre, where wear would be spread across a greater surface area? Even though most wear is to the centre of the tread? TIA

Bernhard · Apr 25, 2018

kommando said:
If you research the tyres of the time the only tyres capable of the high speeds and loading of the Commando and the Trident were 19 inch, 18 inch could not handle it. This is the reason for the 19 rims front and rear, the tyre technology has now moved on and the restriction forgotten.

Absolute B/S IMO- the Avon G.P. tyres were originally racing tyres that they started fitting to road going bikes- yes of course they wore out quicker than say, other road tyres- they were made of a 1960's race rubber compound after all.
If I had the money, go alloy almost every time.

Fast Eddie · Apr 25, 2018

No BS, voodoo or Hokus-pokus...

The comments about 19 inch rear tyre wear were only referring to Avon Roadriders gents...

The 19 inch Roadrider is a universal tyre.

Universal tyres have more tread depth than dedicated front tyres.

But less tread depth than dedicated rear tyres.

I forget the specific (easy to find on Avon’s web site) but I think it’s around a third less.

That means the tread on a universal rear Roadrider will get down to the min depth quicker than a dedicated rear Roadrider.

Hence the tyre wears out faster.

NortonMKIIA850 · Apr 25, 2018

Fast Eddie said:
[snip] ... Universal tyres have more tread depth than dedicated front tyres.

But less tread depth than dedicated rear tyres.

I forget the specific (easy to find on Avon’s web site) but I think it’s around a third less.

That means the tread on a universal rear Roadrider will get down to the min depth quicker than a dedicated rear Roadrider.

Hence the tyre wears out faster.

That makes sense!

kommando · Apr 25, 2018

Bernhard said:
Absolute B/S IMO- the Avon G.P. tyres were originally racing tyres that they started fitting to road going bikes- yes of course they wore out quicker than say, other road tyres- they were made of a 1960's race rubber compound after all.
If I had the money, go alloy almost every time.

Not sure why you are saying my post is BS, Avon GP tyres were racing tyres, the link I posted confirms they were racing tyres and Bob Currie when riding the first Commando production model for a road test in 1968 says they were fitted with Avon Ribbed front 3.00x19 and Avon GP rear 3.50 x 19 which confirms the info in the link I provided is correct ie they were used on Commandos. If you believe that UK 18 inch rear tyres of the day were capable of coping with the power of the Commando and Trident then you need to explain why both Norton and Triumph independently fitted 19 rims to both models at the same time with both claiming 60 BHP, all other lower HP 650's and 750's were using 18" rears. I also have a very fuzzy Earls Court info sheet for the show bikes showing in 67 they were using 18 WM3 rim, so something caused the change changed between 67 and 68 to make them go 19 on the rear.

JimC · Apr 25, 2018

Actually, the 1969 Honda CB750 weighed 481 lbs and was rated at 68hp. It was shod with a 18” rear.
The 1969 Commando weighed 429 lbs. and was rated at 58hp. Also, the Honda has a claimed top speed of 125 mph vs. 115 mph for the Norton.

I hardly think the 1969 Commando overpowered a top rated 18” tire of the day. I smell a marketing ploy. Oh look, the Norton is so fast it needs a special new rear tire!

JimC · Apr 25, 2018

I had a 1969 Trident in 1969. It had more steam than any stock Norton I’ve ridden. I had a 1969 Commando with a Norris R cam. Don’t recall the countershaft sprocket count. Drag racing a 1969 CB750 I stayed ahead until ~100, then the only thing I saw was a disappearing Honda.

Stephen Hill · Apr 26, 2018

NortonMarkIIa850 wrote: "But would you explain to this ignoramus how a tyre with a smaller circumference can last longer than one with a larger circumference? Are you talking about a wider tyre, where wear would be spread across a greater surface area? Even though most wear is to the centre of the tread? TIA"

The 18 inch tire is wider, which provides a larger contact area. Same horsepower passing through a larger contact area gives you lower wear and longer tire life. Sure, most wear would occur in the centre of the tread, but the centre is larger, and will wear less. Most tires are thrown away because of wear in the centre.

Stephen Hill

NortonMKIIA850 · Apr 26, 2018

Stephen Hill said:
NortonMarkIIa850 wrote: "But would you explain to this ignoramus how a tyre with a smaller circumference can last longer than one with a larger circumference? Are you talking about a wider tyre, where wear would be spread across a greater surface area? Even though most wear is to the centre of the tread? TIA"

The 18 inch tire is wider, which provides a larger contact area. Same horsepower passing through a larger contact area gives you lower wear and longer tire life. Sure, most wear would occur in the centre of the tread, but the centre is larger, and will wear less. Most tires are thrown away because of wear in the centre.

Stephen Hill

Thank you!

Fullauto · Apr 26, 2018

Stephen Hill said:
NortonMarkIIa850 wrote: "But would you explain to this ignoramus how a tyre with a smaller circumference can last longer than one with a larger circumference? Are you talking about a wider tyre, where wear would be spread across a greater surface area? Even though most wear is to the centre of the tread? TIA"

The 18 inch tire is wider, which provides a larger contact area. Same horsepower passing through a larger contact area gives you lower wear and longer tire life. Sure, most wear would occur in the centre of the tread, but the centre is larger, and will wear less. Most tires are thrown away because of wear in the centre.

Stephen Hill

Really? How can a tyre of the same size, ie 100/90, suddenly become wider? I think you'll find the difference is in the compound, otherwise, being much, much wider, modern sports tyres would last forever, which they don't.

lcrken · Apr 26, 2018

Fullauto said:
Really? How can a tyre of the same size, ie 100/90, suddenly become wider

Because the front and rear are not the same size, i.e. 100/90. I'm pretty sure Stephen is talking about the usual combination of tire sizes used on a Commando when an 18" rear is used with a 19" front. Most of the Commandos I've seen with 18" rear and 19" front use a wider tire at the rear. For example, the 100/90x19 Roadrunner universal (on the front), mounted on the recommended 2.5" rim, is 109 mm wide. To get close to the same diameter on the rear, you would use the 120/90 rear, which, when mounted on the recommended 2.75" rim, is 129 mm in width, significantly wider than the front tire.

Not saying it's better or worse than your 19" combo. Personally, I really like the feel of the 19" roadriders on my MK3 for street riding, and they'd probably be even better on wider rims, but for serious work like road racing, 18" tires are what most of the Commando racers use, and for good reason.

Ken

NortonMKIIA850 · Apr 26, 2018

Fullauto said:
Really? How can a tyre of the same size, ie 100/90, suddenly become wider? I think you'll find the difference is in the compound, otherwise, being much, much wider, modern sports tyres would last forever, which they don't.

Well, yes, but much can be lost in transmission – face-to-face is always better – what I understood was that a tyre with wider tread ought naturally to offer a segment of a larger lateral circumference, which logically should offer a larger contact area to the road surface. But, like I said, I have no technical knowledge about this topic; although now I'm minded to add that I have many, many thousands of miles under my belt as a professional road rider, FWIW – I've found tyres that I liked best, and tyres that I would avoid like the plague. I've been a fan of TT100s since we used to junk Japanese tyres as death-traps 3o-odd and more years ago [disclaimer: that no longer applies]. Compound has, I've thought, always been paramount for getting around that corner safely; tread pattern is important but, it seems, secondary to compound, on tarmac, when wet. But as I say I have very limited (close to zero?) technical knowledge here. And I can vouch for the fact that modern sports tyres can last only a few short weeks, let alone forever!

Fullauto · Apr 26, 2018

lcrken said:
Because the front and rear are not the same size, i.e. 100/90. I'm pretty sure Stephen is talking about the usual combination of tire sizes used on a Commando when an 18" rear is used with a 19" front. Most of the Commandos I've seen with 18" rear and 19" front use a wider tire at the rear. For example, the 100/90x19 Roadrunner universal (on the front), mounted on the recommended 2.5" rim, is 109 mm wide. To get close to the same diameter on the rear, you would use the 120/90 rear, which, when mounted on the recommended 2.75" rim, is 129 mm in width, significantly wider than the front tire.

Not saying it's better or worse than your 19" combo. Personally, I really like the feel of the 19" roadriders on my MK3 for street riding, and they'd probably be even better on wider rims, but for serious work like road racing, 18" tires are what most of the Commando racers use, and for good reason.

Ken

Ah, but that's the thing. Almost nobody uses the correct size rims for the tyres of today which suit the Commando. They almost always use a rim which is too narrow, causing "mushrooming" of the tyre, thereby reducing the amount of usable tread as well as putting less tread on the road at ANY lean angle. Like I've said before (ad nauseum), I would put money on the fact that my 100/90 x 19 Roadriders on my WM4 (2.5 inch) rim, would put more tread on the road at any lean angle than a 120 section 18" tyre on a WM3 (2.15) inch rim.
A simple test. Have a look at your 100/90 Roadriders from the rear and work out how much of the crankcase would need to be ground away on the road before you get to the edge of the tread. Having said that, the 100/90 Roadriders do work very well on the standard WM2 rims, just not in the same league as when mounted on a 2.5 inch rim. And I've been through over 20 of these tyres on both size rims to know. Try it. You'll like it.

Stephen Hill · Apr 26, 2018

As lcrken said, typically the tire on the 18" rear is a 120/90/18, compared with the 100/90/19 on the front. I did the math at the time and the rolling diameter is almost bang on. And you get a bigger contact area, and less wear.
I installed the 18 inch rear tire three years ago and 6 thousand miles later the tire is still in great shape.
BTW, I am not recommending this tire/rim combination. I just like the look, and the tire life is a bonus.
There are other reasons to stick with 19" tires.

Stephen

Fast Eddie · Apr 26, 2018

Fullauto said:
Ah, but that's the thing. Almost nobody uses the correct size rims for the tyres of today which suit the Commando. They almost always use a rim which is too narrow, causing "mushrooming" of the tyre, thereby reducing the amount of usable tread as well as putting less tread on the road at ANY lean angle.

That is very true indeed. Even some wheel builders (big ones who ought to know better) are guilty of this.

Avon have a great web site where they show the ideal, as well as min and max rim sizes for their Roadriders. I had to insist on the size I wanted when having a Central Wheels build mine as they were adamant I needed thinner rims!

Fullauto · Apr 27, 2018

Fast Eddie said:
That is very true indeed. Even some wheel builders (big ones who ought to know better) are guilty of this.

Avon have a great web site where they show the ideal, as well as min and max rim sizes for their Roadriders. I had to insist on the size I wanted when having a Central Wheels build mine as they were adamant I needed thinner rims!

Me too.

Fullauto · Apr 27, 2018

Stephen Hill said:
As lcrken said, typically the tire on the 18" rear is a 120/90/18, compared with the 100/90/19 on the front. I did the math at the time and the rolling diameter is almost bang on. And you get a bigger contact area, and less wear.
I installed the 18 inch rear tire three years ago and 6 thousand miles later the tire is still in great shape.
BTW, I am not recommending this tire/rim combination. I just like the look, and the tire life is a bonus.
There are other reasons to stick with 19" tires.

Stephen

Diameter is one thing, profile is another. What widtg rim are you using for your 120?

mdt-son · Apr 27, 2018

850commando said:
consider that rust never sleeps, if you go chrome steel rims, They will rust....

That's why I have fitted stainless steel rims to my bike. Living in a coastal area, it's the only way to preserve the rims and maintain the bike in a manageable time.

-Knut

Alloy rims worth it?

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