Wednesday, 17 July 2013


Back in January 2012 (Post 21) I moaned about the problems I've always encountered getting wire wheels balanced and on that occasion it was my Frogeye Sprite causing me the usual grief.  I have copied the relevant part of the post below:

Throughout my ownership it has always suffered to some extent from wheel balance problems and try as I may, I have never found a tyre depot that filled me with confidence; with endless attempts to get the wheels balance correctly.  I am pretty well barred from a couple of my local depots due to my insistence that they do a second check after achieving the usual 0-0 on the balancing machine first time round. Always, and I mean ALWAYS it no longer reads 0-0 when they very reluctantly put the wheel back on the machine. The reason, I'm sure, is that the cones are not designed specifically for wire wheels and the wheels fit on the machine slightly differently each time. That's why, when you take them back to the tyre depot you always hear the guy say "don't know who balanced these mate but they're a ******* mile out" Actually, it was you, last week, and you charged me twenty quid, is a not much appreciated response.

So here I am again with the problem of sorting the XK120’s brand new 16”x5” 60 spoke wires and Michelin Pilotes.  But this time things should be different – I saw a set of wheel balancing cones, made to precisely resolve the problem of fitting the wheels to the machines, advertised in JDC magazine.  The kit sold under the Cutteridge brand name comes with a 50 degree cone to fit both large and small spline wheels e.g.  Jag and Frogeye, plus outer 20 degree cones which effectively replicate the spinners for each of the two sizes.  Additionally there are 3 sets of inner spacers which will allow the kit to be fitted to most types of balancing machine.  Cost £180. With a total of 14 wire wheel, If it works it will be a worthwhile investment.  If it doesn't it'll still makes a great Chinese puzzle figuring out how to get all the bits back in the box.

Cutteridge cone kit for wires
First stop is a local depot with an excellent reputation, (and they don’t know me).  Problem is, its a brand spanking new machine and has some fancy pneumatic locking device so it’s one of the few machines the kit won’t fit.  Second stop is a garage that's had a fair bit of work from me so might be prepared to go the extra mile – Brand new machine with same Pneumatic gadget. 
Third stop is part of a National Chain doing mostly commercials but they have the right sort of machine.  Hoping to motivate the fitter I explain that if he can achieve a satisfactory outcome with my cone kit he’ll be inundated with wire wheel business. I could see by his expression that what I should have said of course was – If he can achieve a satisfactory outcome I promise not to tell anyone.
 The cone kit needed a spacer on the spindle to stop the wheel hitting the machines flange before it bedded onto the 50 degree cone. 

50 degree cone ready to accept wire wheel

The wheel and outer cone went on and it was all tightened up in the usual way.  It all looked good and away we went.  Alas, the by now familiar routine followed, once I had persuaded the guy to take the wheel off and put it on again.  A typical variation from the initial 0-0 would be say 15-30.  All four wheels produced similar results. Weights were moved around, different types tried, the machine switched off and on, re-calibrated and all manner of buttons pushed but to no avail. 

And outer 20 degree cone fitted which replicates the spinner
Eventually the gaffer appeared to see what was going on and proclaimed "it’s bound to be different if you put it on in a differently!” (experience will out!) After 2 hours of head scratching and a good deal of cussing we all agreed the exercise was a failure.  No charge, sorry about ******** up ye powder coating, now **** *** and don’t come back. Great thing about North East England – no ambiguity.

Discussing the problem with an acquaintance, he suggests I try a mate of his who owns a tyre fitting business and is possibly a little more analytical than the average employee.  He has a very new but non pneumatic locking type machine and I feel a little more confident that I might get to the bottom of this. 

I initially take in two wheels, first thing in the morning when hopefully the day’s pressures are minimal.  The cone kit requires a spacer as before and the previously semi balanced wheel now shows 45-60.  Very quickly this is adjusted with weights to 5-0, by now a more than acceptable result.  Then the acid test – off and back on - 30-20  I ask the operator to check the machine with a normal wheel and surprisingly he agrees.  Its a 14” alloy with brand new low profile tyre.  0-0 with around 70 grams added.  Then the acid test – off and back on – now 15-20.  The guy looked genuinely perturbed. 
So what’s actually going on here?  As far as I can ascertain the machines all work in a similar way.  I've come across all manner of complex explanations but in essence they all seem to boil down to this.  The spindle that the wheel is fixed to extends into the business part the machine.  The shaft is rotating in bearings set into ‘soft’ housings allowing some movement.  Transducers on the bearing housings measure shaft movement and another on the end of the shaft measures lateral movement.  I would guess that some form of rotating disc on the shaft, indexes / informs the programme where the movement caused by imbalance is occurring and the programme then calculates the most likely location of a given additional weight to correct the imbalance.  This is all purely conjecture as I've yet to find a satisfactory and simple explanation of the process.
I would guess that when a wheel is perfectly in balance all transducers register zero (0-0 on the machine) – Why wouldn’t they?  This is interesting (if correct) because it means that the wheel must be in balance at that point in time.  It can then only be down to the precise re-fitting of the wheel on the machine in order to re-create the same result.  Even with the special £180 mounting cones the consistency of attachment may not be sufficient to produce an absolutely consistent result, but I suspect it's a lot better than it might otherwise be.  The only other explanation is that all the machines I’ve tried over the years are randomly inaccurate.  Possible but unlikely.   
Another interesting thing is that all machines appear to have self calibration programmes, I suppose negating the requirement for an independent check.  Try googling 'wheel balance calibration services' – clearly not a popular business.  One of the depots even volunteered the information that their two machines always give different results!
The company that supplied and balanced my 140 tyres (also Michelin Pilotes) on a static balancer assured me they would be fine but they absolutely weren’t.  Again I tried two other companies with dynamic balancers, the second spending some time and getting them almost spot on but there was still some slight vibration around 75MPH I borrowed a static balancer which had been modified to specifically accept the larger hubs on 15 and 16” wire wheels.  It’s a very simple piece of kit and will certainly get you in the ball park but how good can it be when it relies on your perception of when the bubble is in the middle of the circle.  I put one of my newly balanced (dynamically)120 wheels on it and it did look spot on with the bubble almost dead central.   

Fresh from the Dynamic balancing machine - looks spot on

Then I added 3 nuts each weighing 17 grams – 51 grams in total to the rim – I barely saw it move and had a couple of mates verify the result just in case it was the previous night’s gin and tonic making me a bit cockeyed and upsetting the outcome. 

And with 50 grams added (3 x 7/16 nuts to the right)
 The single most frustrating thing in all of this is that I have never been able to establish how far out of balance a wheel needs to be in order to create some vibration.  Problem is, I would think there are a good number of other things involved that might exacerbate even very small vibrations caused by an out of balance wheel.  Worn suspension bushes, resonant frequency of suspension, wheel run out, tyre flat spots etc. etc., but I would have thought someone would have a rough idea.  My guess, is around 30 grams. (1 ounce).  Doesn't sound much but with a 30 gram weight whizzing around on a big XK wheel revolving at 750RPM (around 70MPH) I would guess that centrifugal force will multiply that many times.

The point is, the machines are designed to balance a wheel to within one gram.  Given that the most likely cause of vibration is wheel imbalance; naturally this should be the first thing to be ruled out for certain.  If you’re trying to locate a vibration but it persists even after you've seen 0-0 on the machine and been relieved of some hard earned, it seems you still can’t be absolutely certain that it’s not a wheel balance issue that’s causing the problem. 
So – next time you get your wheels ‘balanced’ stand well back then ask the operator to take the wheel off and put it back on to verify the 0-0 result – best of luck.  And I bet the parting words are “give it a run and see how it feels”.   

To be fair I haven't given my 120 a run since the wheel balancing saga so I might well be crying before I'm hit.  This weekend it's the big classic show at Newby Hall near Ripon which requires a drive up the A19.  A section of this road was re-surfaced a few years back and it must be one of the smoothest ten miles of dual carriageway in the country so ideal for a test run.  I'll let you know the outcome.

If anyone out there can throw any more light on this conundrum, add anything or just generally confirm my findings or otherwise perhaps you could email me at :  

Next post beginning of August