OZ Alleggerita and spacers question

[Peopleandcars]

I'm starting to think these might be way cheaper option to the Fuchs and yet achieve unsprung mass reduction and look great... in Silver

 

Front 8.5j 5x130 53

Rear 10j 5x130 40

 

Now my question -- currently not 100 percent happy with wheels not being flush with body and thinking spacers

 

What should I fit spacers wise? All around?

 

 

 

 

[Beanoir™]

I like these wheels on the Cayman, and many any cars too.  Good choice.  

 

Spacers for cosmetic reasons then 7mm all round, if you want to reduce understeer then less at the rear. 

[Craiglm68]

Interesting string (and the usual suspects on it!). I'll hijack and ask (off the back of the post I just made in response to Peopleandcars), re the Fuch style items I'm looking at, fronts are 8.5 front, 10 read (18" wheels)..some of the companies I'm in touch with think spacers are required, others don't.....opinions?

[Peopleandcars]

3 hours ago, Craiglm68 said:

Interesting string (and the usual suspects on it!). I'll hijack and ask (off the back of the post I just made in response to Peopleandcars), re the Fuch style items I'm looking at, fronts are 8.5 front, 10 read (18" wheels)..some of the companies I'm in touch with think spacers are required, others don't.....opinions?

 

When I spoke to RPM they said spacers are indeed required - I trust them with anything technical on the car

 

Another EU shop (Twinspark Racing) I spoke too that race cars and sells the original Fuchs said spacers required, so one more for the spacers.

 

RPM stated 42mm rear while twinspark 20mm rear...have not investigated further because the cost of it all would be north of 2900GBP and just don't have the budget right now...aside from questioning if is really worth it..hence the Allegerita idea, but I digress

 

As far as I understand spacers are needed as the offset is quite different from the OEM setup/spec...

 

The OEM specs for Cayman are

Front  8Jx18 ET57 
Rear  9Jx18 ET43

PCD 5x130

 

The original Fuchs are

Front 8J x 18 ET52
Rear 10J x 18 ET65

 

The Allegerita are

Front 8.5j 5x130 ET53

Rear 10j 5x130 ET40

 

 

This is a good guide about it all https://www.superforma.co.uk/wheel-spacers-explained

and here https://www.performancealloys.com/alloy-wheels-offset and here https://www.moderntiredealer.com/article/312133/an-installer-s-guide-to-wheel-offset

 

If a wheel has an offset of 'ET45' it means it has a positive 45mm distance from the centerline of the wheel. The ET is short for Einpresstiefe which is a German word that translates as 'press depth'.

 

The particular offset {...} determines how the wheel will sit in the car’s wheel well, and how much of the barrel will extend toward the suspension. While most aftermarket wheels are made in multiple offsets, most OEM wheels only come in the offset that is correct for the specific car for which they are made.

 

This is why that ideally, you don’t want the new offset to be more than 5 millimeters away from the old offset in either direction. However, this isn’t always possible. What you do need to keep in mind is that more negative offset, i.e., an offset that is less than the original, will push the wheel out farther from the wheel well. Usually, this will not cause a problem, although it might result in a pretty funky look.

 

In contrast, too much positive offset is a danger, as it will push the wheel farther in toward the suspension. Here’s an extreme example: If you have to go from a 45 mm offset to a 20 mm, the wheels will protrude from the sides of the car. But going from a 20 mm to a 45 mm offset not only may destroy the tires, but also has the potential of affecting vehicle control and injuring the customer — not an optimal customer service outcome!

 

Offset spacers are metal shims drilled with a bolt pattern designed to compensate for too much positive offset by fitting between the wheel and the rotor to push the wheel farther away from the suspension (it’s impossible to compensate for too much negative offset). It is better to install the correct size and offset wheel in the first place, but if you must use spacers, ensure that they are hub-centric, meaning that they fit precisely over the car’s axle hub and precisely inside the wheel hub, as it is this connection that actually holds the weight of the car. It’s also usually necessary to use longer lug bolts or lug studs to install the wheels.

 

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So if I read the above correctly, I might not need the spacers with the Alleggerita since with the ET being lower than OEM stock, the wheels should protrude out already...now getting it proper flush might be a different question...but would probably be better than now where they sit inward after the change in suspensions @Beanoir

 

 

 

Edited September 30, 2018 by Peopleandcars

[Craiglm68]

Great response, very informative, thanks @Peopleandcars

Edited September 30, 2018 by Craiglm68

[Beanoir™]

4 hours ago, Peopleandcars said:

 

RPM stated 42mm rear

 

 

Can you even get spacers that wide...? Sounds dangerous to me anyway.  

 

My my advice was assuming standard offset wheels, apologies didn’t read the original post properly. 

[Beanoir™]

P.S. If you were not already aware of this website, then it's very useful calculating different dimensions of wheels.  ?

 

https://www.willtheyfit.com

 

 

[Peopleandcars]

3 hours ago, Beanoir said:

P.S. If you were not already aware of this website, then it's very useful calculating different dimensions of wheels.  ?

 

https://www.willtheyfit.com

 

 

Amazing, thanks

 

So according to this and keeping my 18 wheels, changing to the Allegerita will make the fronts 0.2cm closer to the suspension strut and poke out 1cm more, while the rears will be 0.9cm closer to suspensions and poke 1.5cm more

 

Am I right to assume I should measure the longitudinal distance from the tyre wall to the arch and try to match the gap with the extra poke?

 

So for example if the gap is currently 2.2cm at the rear, if I get 0.7cm spacers (7mm) + extra poke from the bigger wheel, tyres will sit flush...

 

 

[Peopleandcars]

@Beanoir sorry to nag wonder if you read my above? Ta

[Beanoir™]

3 hours ago, Peopleandcars said:

@Beanoir sorry to nag wonder if you read my above? Ta

 

I haven’t input your wheel dimensions into the calculator but your logic is correct yes.  

 

My advice however would be to see how the wheels look without spacers first, because an extra 15mm at the rear is quite a lot more than your current wheels.  Fronts not so much.  

 

Bear in mind that aside from aesthetics, even without any spacers you will be extending the rears more than the fronts and so the car will undetsteer more than it does from stock.  

[Peopleandcars]

@Beanoir thank you !

 

What's the relation between extension of wheel from suspension and under/oversteer? 

 

 

[Peopleandcars]

So i kind of answered myself via PH

 

Do bear in mind that if a car has wider tyres at the back, and the measurement across the outside faces of the wheels is the same front and back (which is often the case purely for packaging reasons), then the track will be narrower at the back, since it's measured from centreline of wheel to centreline of wheel.

Having said which, to answer you question... and sorry, but this is a bit complicated (I'll keep it in layman's terms, though, so apologies to Scuffers and other experts for the generalisations):

* Track affects weight transfer when cornering. Basically the wider the track the less weight will be transferred across the car from one side to another.

* TOTAL weight transfer is a function of the height of centre of gravity, cornering force and average track.

* The wider end of the car transfers a smaller share of this total, though, so in effect, the car 'leans' diagonally onto the end with the narrower track. 

* More load on a tyre generates a higher slip angle, therefore, all other things being equal, wider track at the rear will make a car lean on its outside front tyre and cause understeer, whereas wider track at the front will make it lean on its outside rear tyre, which will cause oversteer.

...so track width is one tool that the chassis engineer can use to manage understeer/oversteer balance.

But there are lots of other tools/factors than can be used (tyre width, weight distribution, different front and rear spring/anti-roll bar stiffnesses to give different roll resistances, etc.), and it's a matter of juggling all these factors (many of which have other side-effects) to give the overall compromise you want.

Most designers strive for slight understeer, therefore if all other factors were equal and perfectly balanced you'd want slightly wider track at the rear. But other factors never are equal and perfactly balanced, so the short answer to whether front or rear track should be wider is 'it depends'!

(edited for crap typing last night after a bottle of wine...)

[footnote]Edited by Sam_68 on Saturday 14th March 08:53[/footnote]

 

 

 

Quote

that's not the best/simplest solution - it's going to cause other issues too..

I would suggest running a stiffer ARB would have the desired effect..

 

SO probably after a stiffer / adjutable ABR too with the wheels....

https://www.hrsuspension.direct/pages/products/product_info.mhtml?product=1825114521;car=porschecayman

 

 

Edited October 4, 2018 by Peopleandcars

[Beanoir™]

9 hours ago, Peopleandcars said:

@Beanoir thank you !

 

What's the relation between extension of wheel from suspension and under/oversteer? 

 

 

 

Yes, so that explanation is perfectly correct and is basically a longer hand explanation of the relationship between wheel track and over/understeer.   Nicely explained actually.