Real world difference between 8,9,8.5 and 9.5” wheels

[djstan]

Following on from my thread about which new alloys to get, I want to make sure I get the right things...

So, in the real world, what actually is the difference between a combination of 8 & 9” widths and 8.5 & 9.5” widths? The tyre sizes appear to remain the same, so is there a difference in handling or is it purely cosmetic? I assume that the extra .5” will push the wheels out further so they may sit flush with the edge of the wheel arches?

Have I got complete the wrong end of the stick?! oke:

 

[Anonymous]

Following on from my thread about which new alloys to get, I want to make sure I get the right things...

So, in the real world, what actually is the difference between a combination of 8 & 9” widths and 8.5 & 9.5” widths? The tyre sizes appear to remain the same, so is there a difference in handling or is it purely cosmetic? I assume that the extra .5” will push the wheels out further so they may sit flush with the edge of the wheel arches?

Have I got complete the wrong end of the stick?! oke:

The wheel width is a second order issue driven by the primary issue of how wide a tyre do you want?

On a Z4 there is a further variable of whether you go with symmetrical or asymmetrical set up ie wider tyres on rear.

Then the 3 order variable as far as widths of rims are is what rim widths are available in the 17/18/19 sized that a Z4 can use..

To come back to you point for any size of rim eg 8j there are probably 3 or 4 tyre widths that can be used:

The minimum width tyre eg 215

The maximum 245

And the 'most appropriate /best' 225 or 235

In a simple world you should have a rim width that matches the most appropriate /best

Tyre manufacturers in their designs may optimise the tyre for the 'perfect' fit..or they may not..that data is not published..

So you need to decide:

What size wheels? 19 18 17..most reviews suggest that for road use 18" is the best trade off between 'comfort' and 'handling' which are highly subjective unless you have a warehouse of wheels / tyres to try back to back.

Then you need to decide if you want staggered or not, there are pros and cons but a simplification suggests that staggered are better as the front end understeers before the back end oversteers

Then you need to decide how much contact patch you want..the simplified logic is that steering and ability to counteract ripples and faults in the road is inversely proportional to width, ie wider tyres tend to 'handle' not as well as narrower tyres..On the flip side (pun intended), the wider the tyre the more grip for cornering and handling engine power..

There are some great videos on Youtube where they have done back to backs on the wheel diameter effects and the non staggered /staggered using Goodyear Asymmetric on similar power /weight cars..

My comments are in part a synopsis of those videos..

You can see on the G29 M40i that the 19" 10J wheels /tyres are 'over tyred' and cause poorer handling than the 18" 9J wheels!!

This should induce a flame war oke: /some abuse! :fuelfire:

 

[djstan]

This should induce a flame war oke: /some abuse! :fuelfire:

... or not, so it would seem!

My requirement comes from having some OEM wheels which have now cracked, all with practically brand new (non-RFT) tyres so I want to transfer them to the new wheels.

My understanding is that, given the sizes that they are, this will be fine, but I was curious to know whether .5” will actually make any difference at all to the car - the handling, the looks etc.

 

[Anonymous]

This should induce a flame war oke: /some abuse! :fuelfire:

... or not, so it would seem!

My requirement comes from having some OEM wheels which have now cracked, all with practically brand new (non-RFT) tyres so I want to transfer them to the new wheels.

My understanding is that, given the sizes that they are, this will be fine, but I was curious to know whether .5” will actually make any difference at all to the car - the handling, the looks etc.

Well grasshopper...

You go here..

https://www.wheel-size.com/ find BMW Z4

then plug your numbers in here..

https://www.wheel-size.com/calc/

and all your answers will be furnished!

 

[Mister T]

Following on from my thread about which new alloys to get, I want to make sure I get the right things...

So, in the real world, what actually is the difference between a combination of 8 & 9” widths and 8.5 & 9.5” widths?

Not really, it mostly comes down to looks. If you're looking for a wheel with dished/concave spokes then this is usually more pronounced on the wider versions. Real world driving you really wouldn't notice.

The tyre sizes appear to remain the same, so is there a difference in handling or is it purely cosmetic? I assume that the extra .5” will push the wheels out further so they may sit flush with the edge of the wheel arches?

Personally I'd not run the same size tyres on an 8/9 setup vs a 8.5/9.5 setup. I'd want a 225/40/18 and 255/35/18 on the 8/9 setup and 235/40/18 and 265/35/18 on the 8.5/9.5 setup.

Offset makes more difference to how far out the wheel sits rather than width.

Have I got complete the wrong end of the stick?! oke:

 

[Anonymous]

Following on from my thread about which new alloys to get, I want to make sure I get the right things...

So, in the real world, what actually is the difference between a combination of 8 & 9” widths and 8.5 & 9.5” widths? The tyre sizes appear to remain the same, so is there a difference in handling or is it purely cosmetic? I assume that the extra .5” will push the wheels out further so they may sit flush with the edge of the wheel arches?

Have I got complete the wrong end of the stick?! oke:

To simplify my previous post if you are simply looking at transferring your existing tyres then you want 8/8.5j
with offset as close to oem as possible..the front offset is more relevant since the offset also effects the scrub radius which is a much more sensitive variable as it dramatically affects steering ‘feel’

 

[Zedtastic]

One thing to note. If you use a wheel that is 0.5" wider, and has the same off-set, it will not mean that get an extra 0.5" closer to the wheel arch. You will get 0.25" extra width on the outside of the wheel and 0.25" extra width on the inside.

I've always liked the look of matching a tyre width to the rim width. If the wheel is too wide for the tyre you not only get the stretched look (which some people like), but you also have the risk of curbing the rim easier. A matched size or slightly under sized wheel width means the tyre side wall scrubs the curb before the rim.