Wheels, Tyres and Unsprung Weight

[Oversize]

I've yet to weigh them but a bare 6.5 x 14" Bundt seems very light in comparison to later alloy wheels. So I'm now wondering if putting later wheels on a early car may significantly increase unsprung weight which would adversely affecting handling where bumps would become more noticable. Worse still later wheels may prematurely wear bushes and overload other suspension components. I've even heard that the 6.3's earlier suspension can be badly affected to the point that major parts will simply break!

One thing agaist this theory is the fact that the 14" tyre fitted to a Bundt has a higher profile and may weigh more than a tyre with a low profile fitted to a later wheel.

I'll see if I can weigh a few combinations to test part of the theory. Michel, and Styria can you weigh one of your wheels with a tyre fitted??

 

[Styria]

Mark, you raise a very valid point. I have previously referred to the fact that the Taiwanese "Speedy" rims fitted to Gleaming Beauty weigh an absolute ton. Obviously right now I am unable to give you details of weight, but let me assure you that they are much heavier than Bundts. Conversely, the 235.45 (40?).18 Nankangs are probably just as heavy as the 14" tyres, save perhaps for the old, original XWX's, that do weigh a fair bit - probably on a par with the Nankangs. Incidentally, remanufactured XWX tyres are considerably lighter than the originals.

Not so long ago (see GB with Bundts at TK get-together), I was running Bundts with Michelins, and I can say in all honesty that they were no softer or less prone to harshness when compared with the low profile Nankangs. In fact, I would probably go so far as to say that the Nankangs give a better ride. I am sure, Mark, that suspension and steering components could well be affected by the larger and heavier tyres, but the ride, as I said, is probably better. Roadholding as well. When compared with the Italian tyres on Michel's Red Terror, his tyres are certainly somewhat harsher and brick like feeling. Regards Styria

 

[Oversize]

Well here's what I found:

Bundt (14"): 6.3kg,
Steel wheel (14" from W126): 8.6kg,
Tyre (225/50 R16): 9.2kg,
E320 alloy (16"): 9.5kg,
Centra (16"): 9.6kg,
Bundt (14" with 205/70 tyre): 15.9kg,
Penta (16" with 225/55 tyre): 21.3kg.

So an E320 alloy with a 225 tyre is 18.7kg total and 2.8kg heavier than the Bundt with the 205. Disturbingly the 16" Penta with the 225 is 5.4kg heavier than the Bundt with the 205 tyre. That's an extra 21.6kg (4 x 5.4kg) to drag around (not including a Penta spare)! I guess if you remove the spare altogether you're back to roughly the standard total weight, but the suspension still has to deal with the extra unsprung weight.

I'd still like to weigh a 14" Bundt with a 215 tyre (and a 225), so I'll post those when I get them off the cars... It seems the early alloys WERE lighter than the steel wheels, but that's no longer the case....

I wonder if the AMG 6.9 'heavy duty' struts were created to cater for the extra weight of the 16" Pentas and tyres????

Styria are you both running the same pressures??

 

[Styria]

Hi Mark, I usually run about 34-36 lbs./sq.in in both the Bundts and the Speedys. It's a little higher than recommended, but I just seem to feel a bit more assured. 32 is already too low for a big, heavy car like the 6.9. Regards Styria

 

[Oversize]

I think the consensus is higher is far better than lower.... I'd run at least 36. The new Falcs n Commodores run even higher.

 

[Styria]

I can now inform all and sundry that each Taiwanese made Speedie alloy rim and the low profile 235.45.18 Nankang tyre weigh twenty four kilos. I did say that they were heavy, didn't I ? Regards Styria

 

[Oversize]

Styria thow out your spare and that'll help! If GB looks better and still handles and performs well, then who cares about the weight! But I did think this was an interesting subject. Obviously we know our cars as we knew the comparitive weights before the wheels were actually measured! Now I'd like to know the weights of the wider tyres, so I'll keep you posted. Oh and I weighed the Centra without the center cap, so I'll have another go at that too.

 

[Styria]

Mark, this is steering towards Formula 1 technology and research - we mustn't overdo it unless we can raise some sponsorship deals.... Regards Styria

N.B. You know now what I mean about 'heavy' - I think Michel's would probably be round about the same. As I said, however, the ride is just as good when compared with genuine. BTW, I seem to recall that Blue Flame, with its 16" rims and tyres, rode much harsher than Gleaming Beauty's 18ers.

 

[Oversize]

Whilst I can't confirm that one, I think it's possible some of that harshness could be due to tyre age. I know the fronts are stuffed and perished. At the bottom under the weight of the car you can see tiny cracks in the side walls opening up. Anything over 5 years old and this could happen. If they're old they'll be hard and won't flex, or give as much as a newer tyre. I have replacements now and will fit them soon. The back tyres aren't like that but they are an old tread pattern, so I suspect they're hard too and on the way out.

And thinking outside the square, she does appear a little lower than the others. Can anyone tell me how to ID the AMG heavy duty struts? Part number maybe? I seem to recall a thread, so I'll have a search...

Oh and I'm yet to find a set of scales that's calibrated and accurate to three decimal points!!!!!

 

[Styria]

Mark, if you stand on the scales with tyred wheel in one hand, that will give you the three decimal points you're yearning for. That's how I measured mine. Try it - it works.

On a more serious note, surely Blue Flame is no longer sporting the Yokohamas that were on the car about ten years ago ? So, as a matter of some considerable interest to the throng assembled on TK (not BenzBoy - he is standing in a corner and weeping about his thingy), are you making any progress on any of your cars ? I know you have jacked up one of them (and I will comment on that belatedly in due course), but what has happened since ? Questions, questions........Regards Styria

 

[Oversize]

The Penta with tyre is quite heavy and if I hold it with both hands while I'm on the scales I have no digits left!!!!

Refer to the Red Bull thread for an update....

 

[Oversize]

Glad I kept this thread as a reference!! Here I am searching my own posts!!