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Rims and Tyres

A review of correspondence from NOC-L

Replacing original 19" rims with 18" ones gives a wider choice of modern tyre types
Should rim locks be fitted or not?     Modern tyre equivalents

 

Spoke Replacement 

Spoke wrenches

"It just occurred to me: there's one single bit of advice for any prospective wheel-truers in NOC-Land .... buy a proper spoke wrench"

I couldn't agree more. I also have one of the Rowe wrenches; it works well, but I found a wrench that I like a lot better. Buchanans in Azusa, California (they also make stainless steel spokes) makes the best spoke wrenches that I have ever used. The wrench is about 8 inches in length and has an angled wrench on each end.

Call them up and give them the nipple measurements, in thousandths of an inch, and they will custom make the wrench for you. I think I paid $15.50 US. They used to be located in Monterey Park, but moved to Azusa in September. Their phone number is 818-969-4655.

Flip Banando (fjbanando@worldnet.att.net) on NOC-L 27th. Mar 1997


Fitting new spokes individually

"Can I replace each of the old spokes, one by one with new ones while all the others are still in place? Or do I have to break the wheel down completely, then try to reconstruct the original spoke pattern?"

You have two choices: do it yourself or pay someone to do it for you. I highly recommend Buchanan's stainless spokes as quality replacements. The normal procedure is to dismantle the wheel, clean up or polish the hub and relace.

You will need a quality spoke wrench, again available from Buchanan's, and will have to develop the skill to lace and true the wheel(s). Many people lace their wheels and then pay someone else to true them up, it all depends on your skill level and how much time you are willing to spend on the project. I charge US$30 to lace and true a wheel, which is about average for this area. The objective of course is to make the rim run true, in the proper relationship to the hub, with adequate tension on the spokes. Nothing will cause spoke failure faster than loose spokes. Be sure to lubricate the threads and the dimple in the rim where the nipple seats. Check the trueness of the rim from where the tyre bead seats rather than from the outer side.

Vernon Fueston (fueston@snowcrest.net) on NOC-L 1st. Dec 1997


Procedure for respoking a wheel

The wheel should be relaced completely. I would remove all the old nipples with vice-grips, clean up the old spokes and re-use them with new nipples, but if you have US$80 to spare, I will say that I just built a wheel with a set of Buchanan's stainless spokes, and it was nice.

Then once it is together, does it take a special touch to get it all straight? Yes, but it is straightforward in principle and easy if patience is one of your virtues. Truing a rim with 130,000 miles on it may be tricky though! It will be surprising if it is not too bent up to be usable.

Luckily the drum brake Commando wheel is a very simple lacing pattern, although on the Brit-Iron list, Vernon Fueston just established for us that the rim should be pulled 1/8" to the right... or was that left?

  • It is always good practice to check truth of a wheel before mounting a new tyre, as it is much easier to true a rim with the tyre off, and of course if the rim needs replacing, you want to know before putting a new tyre on.
  • When a brake drum is part of the hub, over tightening of spokes in an attempt to pull straight a bent rim can distort the drum. Certain designs are particularly susceptible to this, such as 60s and 70s Suzuki front drums.
  • I like to reuse spokes and nipples, but if they don't loosen freely, the wrenching square on the nipples may distort or even collapse, so some nipples may need replacing. Some brands sell nipples separately, some as spoke and nipple only.
       

The basic procedure for a wheel rebuild is as follows:-

  1. Removing the old spokes by hand gives the amateur a chance to get familiar with the lacing pattern. Take some pictures of it before you disassemble to refer to later anyway.
  2. Determine from part numbers and physical evidence how many sizes and shapes of spokes there are. All 40 (or 36 for Japanese wheels, except Kawasaki) may be identical, or there could be 20 of one type and 10 of two others, or four separate types of 10 each. Conical hubs will obviously have at least two different lengths. Some manufacturers put the same 90o bend on all hooked spoke heads; some make half with a 110o angle and half with 80o. Keep the types separate as you remove them and use anti-seize compound on all spoke threads.
  3. Use anti-seize compound on all spoke threads.
  4. Assemble the spokes and nipples very loosely - ridiculously, absurdly loosely. If you do any sequence too tight, the later sequences won't fit in easily.
  5. Inside spokes go in first. If you have bent head spokes (rather than straight pull, found on BMWs, Matchlesses and some BSAs), those are the ones where the head is outside the spoke hole flange, and in all cases (bent head or straight pull), the outer spoke passes over the inside spoke on the outside of the wheel. I do one side inners and then the other, which will usually spiral or lean in the opposite direction. Then one side outers, then the other. So, left inners, right inners, right outers, left outers.
  6. Very gently take up the slack in the nipples (finger tight). Any incorrect assembly will show up now. Refer to those Polaroid snaps to see where you went wrong.
  7. Mount the axle so that you can spin the wheel freely in a vertical plane with some sort of solid surface or reference point near the rim. A wheel trueing stand is ideal, but clamping the axle in a vice or mounting the wheel in forks or swinging arm can work. Spin and observe the wheel wobbling severely.
  8. Get a good spoke wrench that fits the nipples correctly. Common sense clearly tells us that tightening of spokes will pull the rim in their direction. Loosening a spoke lets the opposite one pull it in its direction. Ponder this well.
  9. Take a deep breath, relax, and get patient.
  10. Work on the eccentric runout first. Side to side wobble comes last!
  11. Once the wheel is more or less round to within 3/16", start paying attention to side to side runout. At this point I like to have a grease pencil to hold steady near the rim as I spin it. I hold the pencil so wobbles to one side will cause marks at the wide spots, and then spin and hold again so high spots (farther from the hub) will also be marked.
  12. If a spot is high and left, tighten the right hand spokes at that spot. If low and left, loosen the left hand spokes.
  13. Radically reduce the tension adjustments you are making as you get the wheel closer to round. When you are working out a 1/16" wobble, a 1/4 turn on two or three adjacent spokes is plenty. Often 1/8 turn gets just the right result.
  14. Watch the overall tension. Spokes will normally end up all equally tight, with a nice 'ting!' when you tap them. If not, go round with an extra 1/8 turn for all nipples and retrue.
  15. Most wheels are centered on the hub, and the usual process will bring them naturally to that point. But some wheels are offset. Manuals will usually specify this. Note this before disassembly if not mentioned in your manual. If need be, loosen all the spokes on one side, then tighten on the other, to pull the rim over. As before, 1/4 turn does a lot!

Ben English (ben.english@dmvms.mailnet.state.ny.us) on NOC-L 1st. Dec 1997


Offsets and wheel building

Having followed the recent threads on wheel offsets discussed lately, I would like to add the following:-

  • In the case of original and basically true old rims (mostly Dunlop in our case), do take the necessary measurements of the rim offset before any attempt to disassemble is made. Make a clear sketch, indicating the brake drum side of hub. Ensure that a proper reference plane (level) at one side of the hub is used. Remember that widths of old and new rims may vary. Offsets should thus be measured between reference plane and centre plane of rims. The centre plane is found by measuring the distance up to the outer rim edge and adding half the width of the particular rim. Repeat the sequence 3-4 times to verify the measure. Use of a fixture is highly recommended.
  • If you don't want to spend the time undoing the old nipples, I use a cutting wheel instead of a torch to divide the spokes. It's fast and safe (use goggles). For future referencing, it's suggested to keep one each of the different (original) spokes used on that particular wheel, so pull these out before going ahead with cutting work.
  • Upon assembly, ensure spokes are fitted in such a way that in the vicinity of the valve hole, spokes run away from it to give access to the tube valve. One spoke on each of the wheel sides will give you the start to the spoke cross pattern (follow your previously taken notes and / or adhere to a picture taken of the original pattern).

Knut Soensteby (kso@lhg.hib.no) on NOC-L 2nd. Dec 1997


Problems with breakage of stainless spokes

"A few folks have had problems with stainless spokes breaking on the Mk.lll Commando rear. It's always the left outside ones that break, probably due to the extreme bend (>90°) at the hub. It's maybe not as much of a problem with 19" rims but definitely is with 18" rims."

I haven't found the fix yet. Maybe somebody can help out here. Mine have been breaking at a rate of one/2500 miles or so for the past 13 years. Buchanan's suggested they were too loose but I can assure you they are quite taut. I have adapted a bodge - I can install the spoke without breaking the wheel down by bending it in an arc and then straightening it after the threads are engaged, although this wouldn't work with an inside spoke. And it's always the left outside ones that break.

Pete Serrino (serrinop@ehsct7.envmed.rochester.edu) on NOC-L 24th. Nov 1998


Stainless spokes - tapered or straight?

The type of spoke used, tapered or straight, could make a big difference in breaking. It may be that if you are using tapered the greater diameter at the end that fits to the hub will prevent breaking. But if that greater diameter spoke is interfering with the hub itself, then there is a bend where it touches the hub. This condition will put stress at that point and the metal will fatigue and break. If you are having problems with tapered (swaged) stainless spokes try straight ones-- that may solve your problem. If not, then you might have to break the wheel down and take a look at the angle of the hub at that side where the spokes are breaking. Check to see if the spoke is rubbing against the metal-- if so that is not good.

Steven R. Schoner (dm550@cleveland.freenet.edu) on NOC-L 24th. Nov 1998


Some considerations when respoking a wheel

Before you re-spoke, did you know that not all spokes are the same gauge and that not all nipples are the same diameter. Some stainless spoke sets come with plated steel nipples as in later rusted nipples and rims come with the wrong size holes. The holes may not be in the right place on the dimple so the angle to the hub is off. It is easier to get a round wheel if the rim is round to start with.

Some things to consider:-

  • Make certain the hub spoke holes are free of corrosion and burrs and be sure the rim holes are the correct size. It is a good time to polish the hub and replace/re-lube the bearings using new seals.
  • The rim holes must be free of any burrs around where the spoke holes were drilled. Take a ½ inch drill bit and hand turn it to remove any burrs or ridges on the inside of the rim.
  • Before tightening, lube the spoke threads, nipple, and rim dimple/spoke hole with some silicone liquid (not grease).
  • The spokes must go into the nipples straight, no angle of any kind. If any angle exists check the rim hole/dimple positions.
  • The spoke mushroom heads must be up against the hub. Use a brass drift and tap them in place once they have some tension on them.
  • The usual trueing stuff comes next. A big screwdriver works well in the early stages to turn the nipples.
  • Once the trueing is done the spokes must be progressively tensioned while keeping the rim true. The spokes must be tight. You can not get them tight with a screwdriver or an adjustable wrench. Use a spoke wrench and work up the spoke tightness progressively and evenly once the wheel is true. It is pretty hard to over tighten the spokes with a spoke wrench unless you have biceps the size of tree trunks.
  • The usual stuff about spokes going through the nipples to the inside of the inner tube and flat tyres apply next.
  • Clean the lube off of the inside of the rim before putting the tyre back on. Get it all of where the bead/rim face is.
  • The rear wheel spokes need to be checked once the bike has been ridden a while after rebuilding. They do stretch and the wheel does flex. There is a cush drive but the whole thing still flexes.

 

Think of spoke tension checking as routine maintenance. I have not had any stainless spoke problems on my Mk.lll. I do ride it harder than any bike I have, it just begs to be ridden aggressively. The stainless rim/spoke combination is easy to keep clean and shiny and is trouble free.

Dave Schneider (daveatsl@aol.com) on NOC-L 24th. Nov 1998


Wheel lacing

A few years ago I sent my disc brake front hub to a dealer to install stainless spokes and a new Akront rim. It came back nice and centered, but the witness marks on the hub were all backwards. So I disassembled the thing and put it back together the old way and trued it on the forks themselves, worked just fine to make sure the offset is right. A few bits of info were garnered along the way:-

First being that the nipples and spokes need to lubricated, especially if they are stainless, and it's a good idea to use one specifically made for that purpose. Secondly, the wrenches that most people use to tighten spokes make it almost impossible to feel the amount of torque you are applying. Buchanans sells the lube and spoke wrenches that are a delight to use. The wrench is about 8" long and ¼" thick, hardened and ground to the exact size of the nipple. The reason they take such care is that the nipple is a very thin walled nut and very easy to round over which makes them oval. When this happens the torque you apply and the tension you are trying to get aren't related anymore. With a long wrench you can use one or two fingers to get the exact feel for what you are doing. They say it's the loose spoke that breaks.

I know I read someplace that when they were building the wheels at the factory, after they laced them, they would smack the heavily angled outside spokes in the center with a soft mallet to get them to go over the lip of the hub, but I can't find it, so maybe you shouldn't do that.

Bob Patton (bpatton@humboldt1.com) on NOC-L 12th. Mar 1999


More on wheel lacing

The wrench is a very important part of the job. There are a number of Cheap & Crappy™ ones on the market, and they are simply not worth the trouble. It is vital to get a proper fitting wrench, and the ones from Buchanans or from Rowe Products are the only ones to bother with. (besides which, the imitation ones are not that much cheaper).

I can confirm Bob's recollection of the practice of 'smacking' the outer spokes with a mallet to get them to seat against the spoke flange. This is required so as to minimize the loss of spoke tension when the wheel is put into service. There is a section on wheel building in every Royal Enfield factory workshop manual that specifies this procedure. Further, the Enfield factory specified that each rim must be measured for circumference after building, as follows: -

"tolerances on the circumference on the shoulders of the rim where the tyre fits are 59.925" - 59.865" for the 19" rim, and 56.783" - 56.723" for the 18" rim."

"the standard steel measuring tape for checking rims is ¼" wide and 0.011" thick, and its length is 59.985" - 59.925" for the 19" rim and 56.843" - 56.783" for the 18" rim."

"rim diameters after building are 19.06" and 18.06" respectively."

Greg Kricorissian (gregg-k@spyder-it.com) on NOC-L 12th. Mar 1999

Rim Locks

Rim locks - a discussion

I don't use rim locks anymore but use a tyre mounting lube that sets up tacky. You still need to check the valve for 'cocking' and deflate/adjust for a few hundred miles until the tyre sets up and finds its bead. For home use you can't beat belt dressing spray available at your auto parts place. It is generically the same as the spray 'tyre mounting lube' and is slick while you stretch the tyre on then sets up real tacky.

A tip given by me and the Euro tyre guys is to leave the valve lock nut against the cap and not the rim to allow a visual check of valve cocking to indicate a tyre slip. New rims do that even with the ribs that are in the rims. As anyone who changes their own knows there is tyre goo left on the bead and it's good to leave a bit on because it helps in the sticky dept. And as always, you should allow run in time to scuff the mould release agent off your new tyres or you will slip! If I was really worried about a racing slip I'd use rim screws. The extra weight via rim locks isn't the way, in my opinion. Just check the valve for cocking and you'll be way ahead of most riders in the maintenance department.

Tim Bond (wirewheels@aol.com) on NOC-L 7th. Jul 1997

 

I also run high-flanged Akront without rim locks and have seen no movement whatsoever in over a year of spirited riding with SuperVenom rubber. My tyre guy didn't put them in when he mounted the new rubber; he said they were superfluous and it appears that he was right. I would feel better to have them in there, if for no other reason than to fill the holes in the rim.

Joe Michaud (triumph@fia.net) on NOC-L 8th. Jul 1997

 

In my opinion, rim locks don't do anything as long as the tyre pressure is up. If you run low pressure in sand or whatever, the lock keeps the tyre from spinning on the rim. If you get a flat on the road the rim lock does the same thing and you can repair the puncture and go on. Without the lock you are likely to rip the valve stem out of the tube and have to replace the tube to continue. As most folks don't seem to carry tyre irons and most bikes are not equipped with pumps anymore, rim locks are not needed.

Vernon Fueston (fueston@snowcrest.net) on NOC-L 8th. Jul 1997

 

An ex-Norton dealer once told me the rim locks were a marketing gimmick. "Yup, these Commandos are so powerful they need rim locks to keep the tyre from spinning off the rim from the incredible torque of that stupendous motor"..... or something like. In others words he thought they were useless. In case I didn't mention it before, I have the rim lock installed to fill the hole in the rim.

John S. Morris (jsm@mediaone.net) on NOC-L 8th. Jul 1997

 

I am on my second set of K81s on Akront high flange rims with no rim lock, no tyre movement and no problems.

Joe Michaud mentions the hole(s) in the rim being ugly: my rims where not drilled for locks although they came drilled for spokes. My wheel builder (Jock Graham, a master) says that there is no need for the lock.

David Ritchie (photog@kanservu.ca) on NOC-L 9th. Jul 1997

 

My view on rim clamps ('security bolts' in England) are that they are a good idea. They are usually only fitted to the rear wheel. They are one of those items that you think are unnecessary until you need them. With wheels and tyre in good condition you will probably see no effect but if your tyre pressure falls or you get a puncture, they are invaluable.

They prevent the tyre coming off the rim. If you get a puncture of any kind, it is not usually practicable to repair it or get assistance on the spot. Rim clamps have enabled me to ride at a slow speed (very slow) so that I could reach home or get assistance. My 16H unfortunately has not got rim clamps in the rear wheel (overlooked when the wheel was rebuilt). When I got a rear puncture a year ago, I rode the ¼ mile to work very slowly (have you tried pushing a bike with a puncture?) so that I could mend it. When I got there the tyre was half off the rim and the inner tube was wrapped around the wheel spindle and shredded. That would not have happened if rim clamps had been fitted. Rim clamps were fitted as standard by many English factories from before WWII up until the 1970s.

Nick Clark (n.j.clark@amme.salford.ac.uk) on NOC-L 9th. Jul 1997

 

If you delete the rim lock, have a flat tyre while riding and do not stop quickly, the tyre will likely slip on the rim. When it does this the tube will go with it. The stem will then be torn out of the tube, especially if you have used the evil little nut that comes with every tube to screw down over the stem against the rim (these should always be discarded). In this circumstance, you have a ruined inner tube. It is not fun, as I can testify, having once been in exactly this situation.

Now I use my rim lock, and carry a spare tube as well as patch kit and pump. Belt and suspenders both are almost enough when it comes to flat tyres.

Ben English (ben.english@dmvms.mailnet.state.ny.us) on NOC-L 9th. Jul 1997

 

Has anybody tried balancing a wheel with a rim lock? I just took my rear wheel in for a spin balance after replacing the wheel bearings and discovered to my surprise that over 5oz. would be required to counter-balance the rim lock!

The cycle shop was reluctant to use that much weight and recommended removing the rim lock, but being a traditionalist and figuring I surely should have noticed a wheel spinning under me that was that far out of balance, (the bike has run fine for years), I neither removed the rim lock nor finished the balancing exercise. Any comments?

Les Scourse (scourse@adan.kingston.net) on NOC-L 13th. Jul 1997

 

Maybe this is why rear rims are hardly ever balanced. Also, I believe that rear rim balance factors do not affect handling or stability as much as front wheels do. Imagine riding at speed with a 5oz. imbalance on the front wheel! Sometimes we can attempt to fine tune our machines too much.

Joe Michaud (triumph@fia.net) on NOC-L 14th. Jul 1997

 

Tyre sizes

Early Commandos Fastbacks and 'S' models, up to 1970, used a rather small front tyre with more fork trail, a 3.00 x 19 Avon Speedmaster Mk II. Later in the year, the front end geometry was revamped (the triple clamps are notably different) and the front tyre was increased in size to match the rear.

Replacing this with a K81 or early Roadrunner calls for a 3.60H19. In later tyres such as Super Venoms, you will want a 90/90H19 (or V rating if that suits you). All rear tyres and later fronts are 3.50 x 19, or 4.10H19, or 100/90H19 (or V rated) in the three different sizing systems.

Avon confuses things by using the 'Roadrunner' name on a K81-like tyre they have been making for ages, and a Super Venom look-alike. When I tried Super Venoms a couple of years ago, I didn't like the looks of the 100mm wide front SV, thinking it was too wide to clear the forks. Although I later saw that others have successfully fitted them, at the time I decided to use a 90/90 instead. I found that a 90/90 SV is not made, so I used the 90/90 RR that looked like a SV. I liked it; very light and precise steering, although to some degree that may be because it is at least nominally smaller than the 410H19 Roadrunner I was replacing.

I did not like the 100/90V19 SV in the rear. Bopping around town, not exactly dragging my knee, it would occasionally step sideways quite without warning, apparently because, being a tyre of modern roadracing heritage, it needed to be warmed up. It always hooked up again right away, so I never crashed. Even though I do some very high speed riding on occasion, I can't really say it was ever better than the old Roadrunners and so I have gone back to them.

Generally speaking, you will find that the new generation of super high performance tyres based on recent developments in roadracing tires are:-

  • very sexy looking
  • not easily found in 19" sizes
  • wider than their nominal sizes compared to more traditional tyres
  • offering a degree of performance more oriented to race track use than you may want

Ben English (ben.english@DMVMS.mailnet.state.ny.us) on NOC-L 11th. Mar 1997


Avon tyres on 18" rims a success

My 1973 750 Roadster has been using Akront alloy wheel rims for the last 15 years, an 18" WM2 on the front and an 18"WM3 on the back. My tyre choice at the present is an Avon AM20 100/90 H18 on the front and an AM21 120/90 H18 on the rear (which is the largest you can fit).

Both rims are of the flangeless type with stainless steel spokes and there are no problems at all as regards seizing . If you only change the rear wheel, as I did at first, straight line stability over 70 m.p.h. gets a little interesting, but only when solo. As soon as I changed the front as well, the handling returned to normal.

I also have a 1973 850 and that has the same combination of wheels and tyres and again with no problems at all. I have used Avons for years and I can not fault then both on price and mileage. I did try an 850 with a pair of Pirellis last year, but to me they did not feel any better or worse than the Avons and they were ' V ' rated which seemed a waste of time on a Norton.

Mike Hull (mike.hull@pace.co.uk) on NOC-L 9th. Mar 1998


19" front and 18" rear configuration

As far as the 18" wheel conversion goes, I had a bad experience with a 120/90/18 rear tyre on an 850; it wobbled really badly over about 80 m.p.h. Unfortunately, this bike came to a sad end in an accident without the problem really being solved; however, tinkering with other Commandos it seems that one way out is to keep the tyre width down both at the front and at the rear. One successful combination I have seen in modern tyres is a 90/90/19 at the front and a 110/90/18 at the rear in Dunlop performance tyres. The 18" front & rear combination also sounds OK.

Kelvin (cmnind@topend.com.au) on NOC-L 10th. Mar 1998


Another 19" front and 18" rear configuration

I have very good experiences with a 18" x WM3 rear rim. The widest possible tyre on my 1971 Commando is a 120 x 90 which gives approximately the same o.d. as the standard rear wheel. There are a lot of different brands and types to choose between in this dimension. At the front I still use the standard 19" rim with no stability problems.

Jerry Hurum (jhurum@online.no) on NOC-L 10th. Mar 1998


19" front and 18" rear - but beware oversized rear tyres

I'm currently running a 4.60 x 18 K81 clone rear and a 4.10 x 19 K81 Dunlop front. With properly shimmed Isolastics it handles like it's on rails. The tyre height is the same front and rear with this setup, but you gain a bit more meat on the rear with the larger 460 tyre.

When I first got the bike, it had a 5.10 x 18 on the rear; this seemed to be a more bite in the back than the frame really wanted. Also it barely fitted in the swinging arm, so that whenever the chain was adjusted the rear wheel alignment had to be checked carefully or the tyre would rub.

Ken Dubey (kdubey@exchange1.pria.com) on NOC-L 10th. Mar 1998


19" front and 18" rear configuration on a Featherbed

I have a Featherbed twin with an 18" rear wheel and a 19" front wheel, as per the Atlas and both on Borrani rims although I'm not sure of the size, I use a pair of Metz, a ME11 on the front and a ME77 on the rear. This is a set up used by many BMWs and I figured that if a 120 m.p.h. R100RS ran well on it, then my Dommi should do OK!

The handling is predictable and good, mileage is about twice that of the TT100s that I used to use, and the price less than a TT100. The ME11 is a block type tread and looks well on the 'older' Featherbeds, but might be too 'old' for you Commando riders! I can ground the old girl any time I like and run rings around BSA A10s.

Eddie Stephenson (esteph@globalnet.co.uk) on NOC-L 10th. Mar 1998


19" front and 18" rear again

I have an 18" rear combined with a 19" front on a Mk.lll and have had no stability problems either solo or with pillion, so there are probably many other variables involved such as tyre choice. I've got modern Michelins on both wheels at present, but up till recently I had a well worn Avon Roadrunner on the front, with no ill effects.

Mark Chambers (mark.chambers@)iviquida.demon.co.uk) on NOC-L 10th. Mar 1998


Dunlops

I have had an 850 with 18" rear wheel and running Dunlop sports tyres front and rear 120/90 x 18" rear & 100/90 x 19" front - Arrowmax both. I spent ages setting up the geometry including the Isolastics.

The bike handled extremely well except in a straight line at over 80 m.p.h. The verdict by a few 'experts' was tyre squirm, or in another language that Commando frames are not capable of handling the stresses put on them by modern tyre technology. I have since built a Combat engined Fastback out of bits with the transition period 'bad handling frame' of 1971/1972 that handles and grips nicely with a combination of TT100s - 3.60 x 19 front and 4.10 x 19 rear. They are not that bad; in fact they handle and stick very well due to modern compounds in a period designed tyre.

I still own both bikes and I love the looks of the fat rear tyre, but if you must have an 18" rear wheel just use a 110 profile tyre and you will get good modern tyre choice and not suffer with handling problems.

Kel (cmnind@topend.com.au) on NOC-L 25th. May 1999


Problems with fitting a K70 front tyre

"I bought a K70 (3.25x19) front and K81 (4.10x19) rear as a pair, but when I tried to put the front one on the bike, it seemed to be to big. That is, the radius of the wheel with the tyre on it is smaller than the distance from the axle to the fender (in fact, it seems to be just about the same; I can just get the tyre in and the axle installed but the tyre will not turn)."

While a K70 is a reasonably good all around tyre for front or rear use and functionally might be fine, it is aesthetically all wrong for any Commando. K70s belong on 1960s bikes, especially Triumphs. Commandos look right with original equipment tyres or a tyre with performance and sporting pretensions at least in the era in which it was originally designed. K70s lost all such pretension after 1968.

Furthermore, the correct size is really 3.00 x 19, or 3.60H19 in more modern nomenclature. That is why the 3.25 K70 is rubbing, although I will admit to being somewhat surprised at the problem.

The standard 3.00 x 19 Speedmaster Mk.ll is a good tyre, but I believe the size is available in H rating and race compound. Wear will most likely be terrible, but the confidence level should be higher. Best would be a 3.60H19 Dunlop K81, a perfect match for the rear, but hard to find over the counter in North America. Dunlop USA seems not to import it, but I think it is still manufactured - try specialist British bike parts importers. I am pretty sure it is in the Walridge catalogue.

An Avon 3.60H19 Roadrunner Universal would be very nice also, but harder to locate I am sure. Either of these two tyres will be wider and 'meatier' than the 3.00 x 19, but have a low profile so that they will clear the fender.

Ben English (ben & linda@319nline@wizvax.net) on NOC-L 1st. Jun 1999


K70 and K81 do not match

The K70 and K81 are no where near to being a match. Each of them was designed to be used with a like tire. A K70 can also be used with a rib tire front, like the Speedmaster.

Using a K70 on the front will also have a major downside: they have a nasty propensity for forming cups in the tread after very little use. Having said all this, like Ben, I cannot for the world understand why one will not fit into the forks. Could it be that the forks have the narrower triple clamps that came with the early Roadholders?

I'd suggest another K81 4.10 x 19 for the front; it is really not a very large tyre. Many people suggest using the K81 3.60 x 19 on the front to lighten the handling, but man is that a skinny tyre! I have a 3.60, but chose to run 4.10 x 19 on both ends of my Mk.lll, and I found them to be perfectly adequate.

Greg Kricorissian (greg-K@spyder-it.com) on NOC-L 2nd. Jun 1999


Earlier Commandos take a smaller front tyre

Early Commandos with steel chrome guards could not accommodate a 4.10 tyre; the fitment was 3.60 as can clearly be seen by the small section and height front mudguard. The later stainless ones are measurably bigger in width and also the centre stay is longer from the forks to the mudguard.

Kel (cmnind@topend.com.au) on NOC-L 6th. Jun 1999


K81s to Avons change a success

As far as what sort of tyres, on my 1973 750 I have recently changed from K81s to Avons; an AM18 100/90 Super Venom on the back and an AM20 90/90 Roadrunner on the front. I cannot speak highly enough of the positive change in the handling. The difference is something like, it was alright before, now I love it.

The reason why I went to the 90/90 (apart from the fact that I was following good advice from people I respect) was to maintain the same relationship between the front and rear sizes as I had with the K81s. (4.10/3.60); it keeps that quick steering feeling.

The reason for the different sort of tyre front/back is SuperVenoms are not available in 19" in a smaller size for the front, hence the Roadrunner.

Chris Ghent (we@amaze.net.au) on NOC-L 10th. Jun 1999


Tyre sizes

The 100/90 is theoretically equivalent to a 4.10 or 3.50 in new inch and old inch sizing systems respectively. That's why when I decided to modernize and try the AM series Avons I purchased a 100/90V19 Super Venom for the front of my 1972.

When I got the tyre home, I decided it looked like such a tight fit between the fender brace that I did not want to risk the labour of mounting it on my wheel and finding it would not fit. So I returned it to my dealer before it was scarred up from mounting. The next size AM20 down was 90/90, but as Chris said that tread pattern and size is only available as a Roadrunner. So that's what I tried- and I loved it.

It greatly sharpened the steering (as you would expect a smaller tyre to do), but since it is several generations newer in design than the old Roadrunner Universals, it is much wider than those, even though they are nominally larger. Thus it plants the front end far better than an old fashioned (K81 or RR Univ, etc) in the nominally equivalent size (90/90 = 3.60 or 3.25) This highlights the inadequacies of the tyre sizing designations especially when comparisons are made across generations of design. Personally, I think if the AM series 90/90 were designated 100/80, and 100/90 called 110/80, and so on, the comparisons would be much more accurate.

I was quite surprised when I first saw a 100/90 AM series on the front of a Commando. Sure enough, they do fit, although clearances are close. But those who use them seem quite satisfied. Nevertheless, I am convinced that if sharp 'flickable' handling is of primary concern, late Commando riders should try the 90/90 AM20 rather than the 100/90. And of course early Commandos, delivered by the factory with 3.00 Avon Speedmasters and fork geometry to match, should avoid 100/90 or 4.10 sizes of any kind and for any purpose.

Since I wrote this up in a comprehensive guide to Commando tyre selection that was published in the Norton News last fall, and keep reiterating the advice here and on Brit-Iron, I will take credit for the trend.

Ben English (ben & linda@319nline@wizvax.net) on NOC-L 18th. Jun 1999

 

Imperial to metric tyre equivalents

Tyre Size Comparison

OLD SIZES NEW SIZES 
Low Profile Imperial  Metric
2.50/2.75 3.10 80/90
3.00/3.25 3.60 90/90
3.50 4.10 100/90
4.00 4.25/85 110/90
4.25 4.70 120/90
4.50/5.00 5.10 130/90

Colin Steer (goscard@aol.com) on NOC-L 11th. Mar 1998


More on Commando tyres

1969 and 1970 Commandos came with 3.00 x 19 Avon Speedmaster Mark II front tyres. The correct replacement size in the neo-inch size nomenclature is 3.60H19, or 90/ 90H19 in the latest metric designation. In 1971, Norton introduced the practice of using identically sized (4.10H19 or 100/90H19) tyres front and rear, with the fork yokes revised to give the appropriate geometry.

My basic summation of Commando tyre choices is as follows:-

The traditional choice comes down to Dunlop K81 (aka TT100) or Avon Roadrunner Universal. The Dunlop originated in 1969, and was used as original equipment on Commandos from the 1971 adoption of 4.10H19 tyres front and rear. Since Sumitomo, Dunlop's former Japanese subsidiary, took over Dunlop worldwide, these are made in Japan. They have good handling but poor wear.

The Avon Roadrunner (now known as 'Roadrunner Universal') came out around 1973 as Avon's answer to the K81. Most people think it is better in all regards than the K81, but not by colossal margins, and some will argue the point anyway. It shows very good handling with fair wear; there is no such thing as good wear on a Commando rear tyre!

For serious high performance, many people these days are using Avon Super Venoms or the new AM series Roadrunners. Super Venoms are the current development of the Venom introduced for the Hesketh. Avon brought out the Roadrunner AM series a few years ago. These are sort of an everyday Super Venom, and share tread patterns and general construction with the SVs, but are H rated (good for sustained 130mph) whereas Super Venoms are V rated (sustained 140 mph). At that time they renamed the original Roadrunner the 'Roadrunner Universal'. It sure would have been easier if they had used a different name for these completely different tyres, but they didn't; so when you go tyre shopping you must keep this clear if you look at Avons.

Then there are Cheng Shins which are made in Taiwan, are cheap but have truly lousy wear (in my observations from years ago), yet actually recommended as giving decent performance and good value for money by some people. They do make a copy of the Dunlop K81.

Ben English (ben.english@DMVMS.mailnet.state.ny.us) on NOC-L 17th. Apr 1998

 

 

Competition Tyres

Here is the current Avon list of tyres available in competition compound:-

Avon Competition Tyres
Speedmaster Mk.ll
  • 3.00 H19
  • 3.25 H19
  • 3.00 H20
  • 3.00 H21


G.P.
  • 3.50 H19


AM22
  • 110/80-18 Front
  • 110/80-18 Rear

 

 

 

   

Roadrunner
  • 80/90 H18 Universal
  • 80/90 H18 F2
  • 90/90 H18 AM20 CR
  • 90/90 H18 R2
  • 100/90 H18 R2
  • 110/90 H18 R2
  • 120/80 V18 AM18 CR (on 2.5" rim 121mm)
  • 90/90 H19 F2
  • 90/90 H19 AM20 CR
  • 100/90 H19 Universal
  • 100/90 V19 AM18 CR

AM23
  • 130/70-18 (on 2.5 rim 140mm)
  • 130/650-18 Cantilever (on 2.5 rim 140mm)
  • 135/70-R18 AV23R Special to P&M

Philip Pick (p.m.pick@triples.demon.co.uk) on NOC-L 25th. Nov 1998

[See also the Avon web site ]

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