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Tyres

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hello all,

advice is sought regarding tyre sizes on a 72 reg, 750 commando. At the moment both front and rear are 3.50x19. Is this correct? The bike doesn’t handle terribly well and advice would be most welcome regarding tyre size and make. Swinging arm bearings, wheel bearings etc are in good condition! The tyre are Dunlop’s and both the same tread pattern.

regards 

David

 

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Assuming these are TT100's then tyres have moved on a lot since then.

Currently the choices would be

1. 90/90  19 Roadrider MKII front 100/90  19 Roadrider MKII rear

2. 100/90 19 Roadrider both front and rear

Option 1 has slightly faster steering than option 2, all made in UK by Avon and get good reviews including grip in wet. 

Alternatively you can go Continental Classic Attack 100/90 90 19 front and a dedicated rear same size and profile. Again good reviews but not UK made and nearly double the price.

I dropped my TT100's in the bin with loads of tread left as they whitelined so badly, went Avon Roadrunners and been Avon ever since. After Roadrunners I went to Avon Venom's, then Roadrider and now Roadrider MKII.

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My first check was here (I haven't done a second one!) and it shows that the 1972 model changed sizes from the 1969-71 old Dominator sizes of 3.00 x 19 front and 3.50 x 19 rear, to both 4.10 x 19 front and rear for all Commandos thereafter.  It might depend on what your actual rim sizes are. 

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4.10 x 19 has been superseded by width in mm and then profile as a % of height. So 90/90 is 90mm wide and the height is 90% of the width so 81mm, 100/90 is 100mm wide and the height is 90% of width so 90mm.

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With a Commando you will be advised to stick to original fitment ie Dunlop TT100 or Avon Roadrunner as they are still available. Avon only recommend the the Roadrider as 'an alternative fitment' Some use the 90/90 19 on the front, but the weight rating is really only suitable for a Roadster and light weight rider. On an Interstate two up with luggage then the rating could be exceeded.

Frustratingly, there are now 19'' fronts for modern bikes that have a very suitable weight rating but the width and profile are just not quite suitable for a Commando.

The Avon options are ideal, the Conti classic attack is a level above, ideally needs the WM3 rim on the rear, but being a zero belt steel radial approved for road and track use, it does not last long. This seems a common compromise on these new road/track approved tyres no matter the manufacturer. 

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Is Avon's recommendation based upon the fact that they simply don't wish to go through the certification procedures ? Every industrial component that I pick up these days carries a bog standard warning that the 'State of California considers that it may cause birth defects...". If touching a piece of machined steel or synthetic rubber could do that then all of us would have kids with three heads.  I run a 90/90 front (on a Roadster but sometimes two-up)...The Commando is dynamically pretty light on the front unless it has an Interplod fairing and generally the working pressure of any component will be stated as about half of the failure value. Once again though, Avon probably only rated them based upon the largest machines they thought might use them.

Road Riders are great. Cheap, available and as much an improvement over TT100s or Road Runners as they had been over Speedmasters.

 

The Contis in Commando size 100/90 R19 need a 2.50"x19" rim minimum according to their literature. The WM3/2.15" rim is still too narrow although there have been "ifs and buts" about this. 

Changing wheels is expensive and not worthwhile if the bike isn,t used much or an original type tyre is preferred but people have also used the 2.50" x 19" rim on 19" Roadriders to good effect apparently 

On a year round bike doing thousand of miles, a Commando on a set of modern radials with the correct rims have far better grip wet or dry, vice free handling and excellent longevity. They shouldn,t get less mileage than radials on newer bikes with way more horsepower and torque

Look on Norvil website under tech talk/my bike weaves, 72 frames have dirrerent head angle and yokes, making them more liable to feel skittish at rear when motoring, stay below national speed limit should be OK, only long turn solution if tyres don't solve is get later frame and rebuild

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Neil, 

Now smashed through 3 of these Conti's and they are in better condition construction wise than the Roadriders I used before when worn out. Far stiffer, less deformed, no cracking in the remaining tread. A worn out Conti just looks worn out, a worn out Roadrider looks like it is more than just worn out. 

A radial tyre will fit a WM3 - check the EU tyre manufacturers governing body for the approval that was submitted for the Conti. 2.5'' is the recommend rim size, but motorcycle radials are allowed 1 size either side of this, plys are allowed 2 sizes either side, so that is how the Roadrider gets alternative fitment for a Commando on WM2 rims. The same reason you will not readily find Roadrider literature saying it will fit a WM2, they can recommend it due to the guidance of their governing body. A tyre can get approval for rims outside the guidance, but need to pay and submit test data so few manufacturers do. 

If you put a new Roadrider and new Conti side by side, you would be surprised as to what rim you would think would be recommended. One looks more closer to fitting a WM2 and it is not the Roadrider by a large margin. 

The advice from Avon is clear, you must fit a tyre that was original fitment if it is still readily available, I know, as I have asked. 

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Regardless of whether any radial will fit a WM3 or not, truth is the recommended size and correct tyre pressure based on use is always the best option in practice. I noticed your tyres looked very pinched in on the narrow rims which may contribute to the low mileage you get from the Contis.  How do the classic racers get on using these tyres on WM2-3 rims?

Radials need the wider rim  to perform as intended even if you can squeeze it on to a less than optimum size. If I had kept the original 19" Roadrider sizes I would have fitted 2.50" rims like the Fullauto guy did. And he has never stopped raving about them as you may be aware!

I know where Avon are coming from but they cannot speak for every custom fitment used by different riders using other manufacturers tyres. My 18" Conti Road Attack radials are nothing like original size or fitment. They have the recommended rims and work perfectly on all road surfaces including gravel without any of the usual Commando handling problems including those posted here The current set are well on their way to a 13-14k life span despite alot of motorway miles

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Avon’s I have a 72 Commando now with new WM2 Devon rims they have Avon’s front and rear. I love the handling compared to the TT’s. Not doing high mileage on this bike so can’t comment there and tyre life not really a concern to me. Rather have the ride. And agree to whoever commented that the 72 does feel light at the front end and turns in quickly with the Avon’s. 

 

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