Been pondering some shiny new wheels, and on scanning the excellent Aftermarket Wheel Gallery (thanks Miniac) I also started to wonder about weight.
I've read a few threads about the value of lightweight wheels, unsprungweight, etc. BUT my question is this:
Will a normal bloke, like me, who doesn't autocross, go on track days, or carry a GPS performance meter in the car REALLY notice the difference by fitting lightweight wheels & tyres?
As a point of reference, I've considered replacing the S-spokes - 11.4kg / 25lbs - with OZ Superleggera - 6.8kg / 15.4lbs... and also changing from runflats to normal rubber with the associated weight saving.
But surely a lightweight 18" will still be significantly lighter than the S-spoke?
And I would guess that a standard 18" tyre will still be cheaper than a 17" runflat?
Will a 20kg reduction in UNSPRUNGweight (ie wheels & tyres) be more noticeable than a 20kg reduction in SPRUNG weight (ie stripped interior or whatever)?
The 18" Superleggeras only weigh 7.5kg, thats still 3.9kg (15.6kg total saving) lighter than the S Spokes!
So you can see they aint heavy as lead. I found a set of 2piece wheels that are 18x7.5 and they still lighter than the S spokes by 2kg.
Yes 18" tyres are slightly more expensive, IIRC about £400-£500 for a set of Toyo Proxies but probably around the same as runflats.
Yes it will, but less weight anywhere eg sprung or unsprung will make a difference.
Simple rule, you notice what you car is like when you say have one passenger, you notice its abit slower, whne its only you in the car its much nicer, same thing really, but you won't notice 20kg too much.
Unsprung wise you will notice your car is easier to steer and will handle better due to the loss in weight, which can help to lessen damaging effects on the suspension apparatus.
Another simple analogy,( in know its not car related but it will give you a jist of what I mean) Imagine putting on really heavy boots on your feet, you notice you cannot run as fast as you can't raise you legs quickly enough for each step you make. whne you have lightwieght traniers on you notice you can run much more easily.
Same thing kinda applies to wheels the less weight the easier it is for your car to accelerate and brake.
Maybe wrong but the answer would have to be yes ... reduction in weight for wheels / tyres also reduces rotational inertia of the wheel, thereby reducing work required to turn the wheels and improving responsiveness ... not to say that any reduction in weight wouldn't be of some benefit (as long as the reduction did not significant alter weight distribution ratios)
Larger wheels inherently have a greater rotational inertia than smaller wheels (mass of rim is further from the centre of rotation) and therefore will always be harder to spin up ... this has to be balanced with the fact that larger wheels typically accept wider tyres that provide increased contact patch and hence traction ...
Bit of a juggling act ... personally I think light weight 17" are a good comprise between looks, handling and performance but I suspect that opinions will vary
I totally agree with you there, but would like to add a point. The overall diameter of a wheel tyre combination can be kept the same, this relates to tyre thickness. 17" wheels on the MINI have a tyre thickness 45, whereas 18s have 35mm of thickness to compensate for the overal diamter of the wheel. I may be wrong but an 18" tyre say 215\35 is similar in weight to a 17" 215\45.
Isn't the diameter that is the killer its the weight distribution
Rotational inertia is very dependent on how mass is distributed ... a wheel with most of its weight close to the centre of rotation will have considerably less rotational inertia than a wheel with a lot of it's weight at the rim ... I can't remember the equations anymore but the difference can be quite dramatic
Larger wheels therefore tend to have greater rotational inertia than smaller wheels even though they may weigh the same ... a lot can depend on the tyre though, as being the farthest point from the centre of rotation, they can affect the weight distribution a lot ... needless to say this is one of the reasons that the runflats don't exactly cover themselves in glory
Hence the F1 wheel: relatively small diameter wheel with large profile rubber = light, low rotational inertia.
So its the usual compromise situation. Do you want the looks or the performance? Best performance would be to actually down-size alloys, but best looks are probably from up-sizing & lowering ride height.
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Lightweight wheels 
