MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - Fact or Fiction?

After a host of summer mods, next has to be the wheels (when i save up). I think 16 inch ones will look the biz as my standard 15s look a tad small next to similar type cars.My question is will 16 inch wheels rob me of any performance? With a larger diameter wheel more torque is going to be required to turn it, which in theory will result in slightly less power.fact or fiction? Davey.
Davey

Basically fiction. The rolling diameter of the wheel will be the same in either case. Whereas one will have less tyre and more metal wheel the other will have more tyre and less wheel. So in theory it will depend upon the relative weights of the tyre material and the wheel material. Not a lot in it IMHO.

Bruce
Bruce Caldwell

I'm with Bruce, I have 17's and notice no difference.

Can't even feel a difference in weight picking up an original 16" wheel (mine came with) and one of the 17's.

Don't worry about it, IMHO.
Chris

Yes, I think Bruce is right.
You will have performance alteration, because of what Bruce stated. It will alter the inertia momentum of the combination Tyre + Wheel. But I doubt it will be noticeable. In a public road drive, at least...


Cheers, Valter.
Valter

The wheels may weigh the same, but there is more weight distributed further out, so the torque required will be higher, but as to weather you will notice it - anybodys guess (mine is not)

Will
Will Munns

Will???? Not sure what you mean there mate?

Basically any change there'll be will be practically unnoticible - but yes, there may be a small reduction of performance, depending on the tyres used (need to consider the energy losses associated with your current tyres and those on the ones you're replacing them with).

Good chance that the tyre diameter is increasing - so the contact area is increasing. Also a good chance you'll take the opportunity to fit better tyres - more grip also means more rolling resistance = more power lost due to frictional losses.

Bare in mind, that although the 16" alloy wheel sans tyre does not weight that much more than a 15" wheel (and in some instances, it actually weighs less) the tyres available with the necessary profile will be heavier than the optimal tyre for the 15" wheel - so a greater unsprung mass.

BUT as stated before, there really ain't much chance of you noticing the difference.

Have fun! :o)
Rob Bell

Rob,

I think what Will is saying is that (correct me if I'm wrong) the 16" wheel, despite weighing more or less the same as the 15", has more mass distanced from the wheel center. That is: metal is heavier than rubber and the bigger the wheel diameter the farer from the center you have the "metal". Thus You'll need greater torque to move and to stop the wheel, because of a greater inertia. 16" wheels will get you less agility, but you cares and notice? People generaly buy different wheels for beauty porpuses.

Hope I've been explicit...

Valter.
Valter

Rob, Valter is spot on, you can think of it like this
Assuming that the mass of rubber and the mass of alloy is the same to support the same weight (i _know_ but bear with me) a 15' wheel is effectivly a plate welded onto a cylinder, the distance of the surface of the cylinder is 7.5' from the centre of the wheel, the rubber tyre is effectivly a rubber cylinder welded to two rubber discs and the tread is what 10' from the centre of the wheel.
When you increese the size of the wheel, you get a larger cylynder (as it is further away) of metal and the effect is that the wheel acts as a bigger flywheel. The rubber tread is still at the same distance from the centre of the wheel, so there is little diffrence in the tyre. The only diffrences that there are left is that the alloy disc that joins the cylinder to the hub is now larger, but this 'extra' weight is offset by the loss of rubber between the tread and the cylinder.
So the tyre/wheel combo weighs about the same (possibly a bit more) but the weight is distrubited further out.
Will Munns

I see your point guys but I think as you say, the difference is just so negligible.

Maybe on a par with cleaning the mud out of your tread.

Maybe we should use Helium to fill the tyres8-)

or clean the dead flies of the front bumper, to save weight....
Chris

You mean polish the bumper to decresse wind resistance
Will Munns

Thanks Valter and Will - sorry Will, I didn't quite understand that you meant the radial distance from the axis line rather than the difference in wheel track caused by having wider wheels (which for some reason, I thought you meant!).

All explained :o)

BTW, I found that the tyres we fit often weigh more than the alloys they are fitted to - especially the low-profile performance rubber. Unfortunately, tyres such as the Bridgestone S-02 is only available with a 'Z' rating and therefore oever-engineered and over-weight for the F. But given that they perform so well, the disadvanges are massively outweighed by the advantages in terms of grip, slip behaviour and therefore feel and confidence.
Rob Bell

>>Unfortunately, tyres such as the Bridgestone S-02 is only available with a 'Z' rating and therefore oever-engineered and over-weight for the F.<<
That's why I think the RE720 is better (for the F)

I see the point about the mass being distributed towards the tyre tread (with bigger diameter wheels) - but don't the gyroscopic effects of this outweigh all considerations regarding torque when driving / braking the wheel ?

Steve
Steve

Er, a few things, maybe both worth thinking about, Davey. (others will correct me if I'm talking rubbish)

1. One advantage of larger alloys/low profile tyres is that, although they may increase the moment of inertia of the wheel, the 'narrowness' of the side walls makes cornering much more effective.

2. You will have to become paranoid about kerbing them.

3. If you're really worried about increasing the MoI of the wheels, I think extra lightweight ones are available as an (expensive!) option on the TF. Cheaper elsewhere?

4. You may at this point wish to buy Trophy160 or TF160 alloys, as you can fit bigger brake disks/calipers in these. The TF160 brakes are by far the best improvement on the TF over the F, in my opinion. I'd love to have 'em, but they won't fit in my 16" VVC F alloys!
David Bainbridge

This thread was discussed between 23/08/2002 and 27/08/2002

MG MGF Technical index

This thread is from the archives. Join the live MG MGF Technical BBS now