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Thank you for your replies.
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For the OP, all of my post below is way beyond what you need to think about - just fit the wheels, and you'll probably be fine. You only need to consider special matching balancing if you're having a problem.
>>check the balance of both & place the heaveist parts of each oppossing each other to counter act the weight. this reduces the weights required & make sfor much more accurate balancing & less issues with wheel balance problems.
I'm not doubting that this is what the machine makers say, or that you're reporting accurately what you've been told, but, I don't think the statement as is stands is actually true.
The accuracy of the balancing machine is the accuracy of the balancing machine, full stop. Whether it is balancing with 20g or 40g really doesn't matter on an wheel/tyre assembly that is probably over 20kg, the residual error in balance (expressed as gram metres for static imbalance, or gram metres squared for dynamic imbalance) will be within the same limits.
If, however, the balancing machine scans the rim and tyre tread for geometrical errors, and then prompts the operator to re-assemble the wheel so there is the minimum radial run-out, and then balances, you'll get a wheel that will run truer, and produce lower vibration forces.**
Of course, it's good practice to reduce the total number and mass of balancing weights if the facility to match assemble is available, but, given the choice, I would optimise geometry first, and then correct for errors in mass distribution.
** I say vibration forces, because there is true out of balance force - static, where the centre of gravity does not lie on the axle, dynamic, where one of the three principal axes of inertia of the wheel doesn't align with the axis of the axle, and simple geometry errors which mean that the wheel isn't round, or isn't centred on the axle. i.e., geometry errors *as well* as mass distribution errors produce vibration forces which can be felt inside the car.
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Number cruncher, I don't go by what the machine makers say or do . I go by 40 years experience & having been on the vehicle manufacturing side, sales & the spanner end I go by experience. I have also experienced dynamic balancing for my self where my own cars have suffered incurable wheel balance & I can assure this works & some times is a neccsasity. There is a specialsit near the 303 Andover who has customers travelling far & wide for this service
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>>dynamic balancing
Are you sure that's what you mean?
p.s. Although I try to avoid trading experience in a tit for tat way during internet discussions, I'm not without significant practical experience either!
;-)
Edited by Number_Cruncher on 11/10/2008 at 22:56
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Well its 3 years since I last had it done & the grey matter is getting older but as with new cars they actually remove the tyre & find the heavy spot. they then check the wheel & clean it & reduce the imbalance & then oppose the two heaviest parts reducing the need for weights to a minimum & its always been very good. That why when you buy a new car with more accuratley made tyres & wheels first assembled it reduces the balance issue on a car when new.
It may be called something more fancey but I can't remember. Its not common to find a tyre specialist who carry's out this service & it is more expensive but its so much better to drive a car balanced this way & easier on the suspension. I think it used to be about £ 20 a wheel but O'boy what a difference
I will churn the grey matter over to see if I can remember if it wa called anything else!
I Doc
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Yes, the reason I'm not sure about the name is that I would say that dynamic balancing is correcting the type of imbalance that makes the wheel want to alternately steer and camber as it rotates, as opposed to static imbalance, which makes the wheel want to try to hop up and down.
I do agree that match assembly works, but the distinction which I'm not sure about is, does the machine match assemble based on a mass distribution error (i.e. a trial balance), or becasue of a geometry error (probably via a laser scan of the profile).
As the wheel and tyre (from a rotating unbalance point of view) is short and rigid, matching the mass imbalance of wheel and tyre will make no real difference - the machine still balances the assembly as one.
If, however, the matched assembly reduces run-out first, and then does a mass balance on the assembled wheel, then that will make a very real difference to how the wheel runs. I think that the top of the range Hoffmann machine does this.
I can also see that a road load balance - where a roller presses onto the rotating wheel, and measures the changes in the tyre's stiffness can produce an even better estimate of the geometry error.
Geometry error manifests itself like static imbalance, becasue the actual centre of rotation doesn't lie on the axis of the axle.
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Here's more info on the machine/method I was describing;
www.optima-balancer.com/en/whyoptima.asp
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Thanks guys for the replies.
Don't beat yourselves up over this one. I put the lighter weighted wheels on the fronts and it has no vibration that I can detct at the tell tail 56 and 90mph so I'm sure SWMBO will be delighted as the steering is now unbelievably light.
Compared with the summer 225/45x17's, winter 205/55x16's feel like piloting a boat but I'm sure my wife will appreciate the extra comfort.
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Further question in relation to this.
Still have some light vibration, had the wheels back and rebalanced but still have the vibration, usually at higher speeds.
Is there a preferable material for spigot rings on aftermarket wheels ?
The only thing I can put the vibration down to is the rings. The ones that came with the wheels are a hard plastic.
Would I be better off with alu or would tighter fitting rings on the stub axle be a better solution (I can't feel any play in the wheel when fitting with the current spigot rings) ?
Or, is it a feature of aftermarket wheels which will never be as good as the correct size OEM wheels ?
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I wouldn't be happy if the wheel has more than about 0.1 or 0.2mm radial *and* lateral run out - either when mounted on the wheel balancer, or, when mounted on the hub.
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Thanks. I'll get the wheels off and measure them again.
Maybe need some better fitting rings.
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