Unsprung mass - how much difference?

[mjennings23]

Dropping sprung weight is far better for improving performance and handling.

You've got that the wrong way round.

From any on the number of things that pop up on google if you don't believe me...
"Racing teams thus reduce unsprung weight by, for example, using lightweight but delicate magnesium wheels, and engineers try to design suspensions with as little unsprung weight as possible. That’s why a few cars such as the 1961–75 Jaguar E type have employed brakes mounted not to the wheel hub, but to the inboard end of the half shaft: it’s all an effort to reduce unsprung weight.

Note that unsprung weight or mass is sometimes confused with rotating mass because some parts (tires, wheels, most brake discs) fall into both categories and because racers want to reduce them both. But they’re not the same thing. Rotating mass is what it sounds like, anything that has to rotate when the car goes forward, so for example the steering knuckle is unsprung but doesn’t rotate, while the half shaft is rotating but only partly unsprung. Lower unsprung weight improves handling and sometimes traction, while lowering rotating weight improves acceleration."

Be realistic and relative to the question.

What difference is a minor difference in weight going to have a 10+ year old Z4? f**k all is the answer.

Want a realistic option of improving handling, wrap wheels in some T888s. Stick to the road like a limpet.

Increase in acceleration? If it makes ANY gains over several runs £/s gained will be through the roof in a negative way.

There isn't much you can actually drop off this motor to make any substantial saving or gains. If you strip the seats for light buckets, change the dmf for a single mass lightweight job, lop the cat and back box off, you may then notice something.

Dropping a set of wheels on what is a relatively tanky and flimsy roadster isn't doing anything.

And all of these expected gains the internet raves about is assuming that all bushes, clutches, diffs and boxes etc etc are all mint.

Not trying to be rude or start an internet war but some of the stuff in this thread is offering some serious disappointment to the OP.

Appreciate your input. Trust me, I'm expecting nothing other than having nicer looking wheels in a lovely colour. I'm also happy in the knowledge they're going to be both stronger and lighter than the current MV3 wheels I have on.

Any gains I may or may not notice, well let's just call them a nice bonus. As I said this was more a curiousity than anything!

 

[mjennings23]

I love the Raijin!!!!

I wonder if they do offset compatible with the Z4M...

Think you'd need spacers, assuming you want 18s it's 8j ET32 or 42, 8.5j ET38 or 9.5j ET35, none ideal for the M I believe. 19s are also the same offsets.

 

[mr wilks]

I love the Raijin!!!!

I wonder if they do offset compatible with the Z4M...

Think you'd need spacers, assuming you want 18s it's 8j ET32 or 42, 8.5j ET38 or 9.5j ET35, none ideal for the M I believe. 19s are also the same offsets.

For front either 8j et 32 8.5j et38 / rear 9.5j et 35 would work sweet on a Z4M

 

[Monkeydonkeyratmagic]

You've got that the wrong way round.

From any on the number of things that pop up on google if you don't believe me...
"Racing teams thus reduce unsprung weight by, for example, using lightweight but delicate magnesium wheels, and engineers try to design suspensions with as little unsprung weight as possible. That’s why a few cars such as the 1961–75 Jaguar E type have employed brakes mounted not to the wheel hub, but to the inboard end of the half shaft: it’s all an effort to reduce unsprung weight.

Note that unsprung weight or mass is sometimes confused with rotating mass because some parts (tires, wheels, most brake discs) fall into both categories and because racers want to reduce them both. But they’re not the same thing. Rotating mass is what it sounds like, anything that has to rotate when the car goes forward, so for example the steering knuckle is unsprung but doesn’t rotate, while the half shaft is rotating but only partly unsprung. Lower unsprung weight improves handling and sometimes traction, while lowering rotating weight improves acceleration."

Be realistic and relative to the question.

What difference is a minor difference in weight going to have a 10+ year old Z4? f**k all is the answer.

Want a realistic option of improving handling, wrap wheels in some T888s. Stick to the road like a limpet.

Increase in acceleration? If it makes ANY gains over several runs £/s gained will be through the roof in a negative way.

There isn't much you can actually drop off this motor to make any substantial saving or gains. If you strip the seats for light buckets, change the dmf for a single mass lightweight job, lop the cat and back box off, you may then notice something.

Dropping a set of wheels on what is a relatively tanky and flimsy roadster isn't doing anything.

And all of these expected gains the internet raves about is assuming that all bushes, clutches, diffs and boxes etc etc are all mint.

Not trying to be rude or start an internet war but some of the stuff in this thread is offering some serious disappointment to the OP.

Appreciate your input. Trust me, I'm expecting nothing other than having nicer looking wheels in a lovely colour. I'm also happy in the knowledge they're going to be both stronger and lighter than the current MV3 wheels I have on.

Any gains I may or may not notice, well let's just call them a nice bonus. As I said this was more a curiousity than anything!

Another thing OP....

Those 1st wheels will just look awesome. I get they are pretty much csl reps but they are cool rims.

Even if no gains are had... who cares right? It'll still look the bollocks.

The performance thing is always negligible on streets. Mine now flies in a straight line. So long as I can take the m11/m25 South slip road at xxxMPH what's the need to achieve any better.

The z handles it's own pretty well as it is.

 

[mjennings23]

Another thing OP....

Those 1st wheels will just look awesome. I get they are pretty much csl reps but they are cool rims.

Even if no gains are had... who cares right? It'll still look the bollocks.

The performance thing is always negligible on streets. Mine now flies in a straight line. So long as I can take the m11/m25 South slip road at xxxMPH what's the need to achieve any better.

The z handles it's own pretty well as it is.

I wouldn't classify them as CSL reps, personally. I'd say they're based on the 7 spoke wheels that used to be used a lot in racing, of which the CSL was BMWs interpretation.

I actually massively prefer them over CSLs, from the neater and more concave centre face to the lesser number of spokes, even to the spoke design. They don't seem to have the bit of a kink at the end like CSLs.

That being said, I expect they will regularly be confused as CSLs as the Y spoke design on BMWs seems synonymous with that one wheel!

Just want to get them already, impatient now unfortunately they have to come from the factory in Japan, seems retailers rarely hold stock of Enkei wheels

 

[Attilio]

I love the Raijin!!!!

I wonder if they do offset compatible with the Z4M...

Think you'd need spacers, assuming you want 18s it's 8j ET32 or 42, 8.5j ET38 or 9.5j ET35, none ideal for the M I believe. 19s are also the same offsets.

For front either 8j et 32 8.5j et38 / rear 9.5j et 35 would work sweet on a Z4M

Thank you mr wilks!

 

[mjennings23]

I love the Raijin!!!!

I wonder if they do offset compatible with the Z4M...

Think you'd need spacers, assuming you want 18s it's 8j ET32 or 42, 8.5j ET38 or 9.5j ET35, none ideal for the M I believe. 19s are also the same offsets.

For front either 8j et 32 8.5j et38 / rear 9.5j et 35 would work sweet on a Z4M

The expert speaks

I wasn't sure on rears for the M, but if Mr Wilks says it works I'd be inclined to believe!

Going for 8J ET32 and 8.5J ET38 myself, I don't know if a 9.5j would fit properly on rears, and my current tyres are nearly new 245 wide, so a stretch to fit on a 9.5j rim

 

[NickDE]

Style 32 staggered 18s are about as light a OE Bmw wheel you can find .

Very true. Plus they look great. Plus can be picked up cheap on ebay if you are patient.

 

[Ewazix]

Grab a coffee for a read on some test, not truly scientific but interesting 8)

https://www.tirerack.com/wheels/tech/techpage.jsp?techid=108


And apparently using Helium in tyres instead of air can significantly reduce unsprung weight, anybody tried it?

 

[mjennings23]

Well, difference or no, a new set of wheels is making its way from the factory now. With luck, they'll be on for the weekend.

On a side note my tyre picked up some extra weight in the form of a screw. Lovely when you have to replace a nearly new UHP tyre :thumbsdown:

 

[Rich8]

And apparently using Helium in tyres instead of air can significantly reduce unsprung weight, anybody tried it?

I do hope you typed that with a massive smirk on your face and it’s not a serious question

 

[Ewazix]

And apparently using Helium in tyres instead of air can significantly reduce unsprung weight, anybody tried it?

I do hope you typed that with a massive smirk on your face and it’s not a serious question

Busted :wink:

The thing is, on PH someone would have bitten

 

[cj10jeeper]

As a real rough rule of thumb reducing unsprung weigh is the equivalent of 4x sprung weight so take you 3kg per wheel. 3x4x4=48

Dropping sprung weight is far better for improving performance and handling.

You've got that the wrong way round.

From any on the number of things that pop up on google if you don't believe me...
"Racing teams thus reduce unsprung weight by, for example, using lightweight but delicate magnesium wheels, and engineers try to design suspensions with as little unsprung weight as possible. That’s why a few cars such as the 1961–75 Jaguar E type have employed brakes mounted not to the wheel hub, but to the inboard end of the half shaft: it’s all an effort to reduce unsprung weight.

Note that unsprung weight or mass is sometimes confused with rotating mass because some parts (tires, wheels, most brake discs) fall into both categories and because racers want to reduce them both. But they’re not the same thing. Rotating mass is what it sounds like, anything that has to rotate when the car goes forward, so for example the steering knuckle is unsprung but doesn’t rotate, while the half shaft is rotating but only partly unsprung. Lower unsprung weight improves handling and sometimes traction, while lowering rotating weight improves acceleration."

+1 on thi of rotational vs unsprung, but it's a hugely complicated subject to calculate and sort out.

One interesting factor though is that unsprung weigt is worth at least 4x of sprung weight in performance. So, taking your 3kg x4 wheels x4 =48. So your wheel change is like dropping 50kg from the car.
Also remember that the lower the unsprung weight the easier the wheel can move to remain in contact with the ground so better all sosts of cornering and braking becomes, assuming suspension is correct.
Will the average driver notice this on the average spirited drive? Probably not..

 

[mjennings23]

On a note as to the mass, certainly no real difference in acceleration and braking that I'd notice, the main thing is it seems a bit more compliant over bumps, in an odd way.
You can feel more bumps, even painted lines on the road when driving over are very noticeable, but it's less harsh over them too if that makes sense.

Basically the feedback seems amplified, without making the car feel crashy over bumps.

Plus Hyper Silver is lush!