Wheel Spacers ？

[emyxu]

What size would you all recommend that goes great with the BONOSS wheel spacers? I’m a newbie so all the information I can get will be appreciated!

[mmm-five]

Your only other post mentions 10-15mm BONOSS spacers - so you must have done at least a little research to find them, but didn't realise they don't make them specifically for a Z4...but as you provided no detail as to what Z4 you have (E85, E89, G29) or wheels you were using/fitting (offsets are important as the spacer will have an impact on the effective offset you end up with) or what the use case is (cosmetic, track work, bigger brakes, etc.)...so recommendations are very difficult.

BONOSS aka Bloxsport seem to claim lots of 'benefits' of their wheel spacers, but don't actually show you much technical detail about them (just claim to have lots of patents)...but the 'active air cooling technology' seems to be a PASSIVE machined knurling effect on the outside edge to increase the surface area to reduce temps 'a little bit'.



However, their prices don't seem particularly expensive to me ($100-$200), but I'm not sure what you consider expensive...unless you're trying to compare them to cheap stamped steel ones from ebay/AliExpress.

All their TÜV certifications are for their wheel bolts, nothing for their spacers.

Depending where you are - you've not completed a welcome post, or location in your profile - I'd buy some from a reputable brand like H&R or Eibach.

They also don't seem to offer spacers for any generation of BMW Z4...in fact their website doesn't seem to list spacers for most European marques....just for Asian/American marques.

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[emyxu]

Hi, I would like to add 12mm BONOSS forged lightweight plus wheel spacers to the front, and 15mm to the rear.

May I know what are sizes of extended bolts should I use?

Thanks!!!

[Pbondar]

Which version of Z4 are you referring too?

[Nictrix]

12mm longer than you have now

[sars]

12mm longer than you have now

Seriously though if they’re more than 10mm you usually bolt the spacer to the hub and then the wheel to the spacer

[BMWZ4MC]

12mm longer than you have now

Seriously though if they’re more than 10mm you usually bolt the spacer to the hub and then the wheel to the spacer

10mm? I’ve not seen spacers smaller than 20mm that bolt to the hub.
I’m concerned that you say that because I routinely use 12mm and 15mm spacers with some of my sets of wheels, especially given your engineering background (IIRC).

[Mr Tidy]

10mm? I’ve not seen spacers smaller than 20mm that bolt to the hub.
I’m concerned that you say that because I routinely use 12mm and 15mm spacers with some of my sets of wheels, especially given your engineering background (IIRC).

I'm surprised too as my current Z4 had hub-centric 15mm spacers on the front and 12mm on the rear with longer bolts when I got it.

I'd only expect to see spacers "bolted" to the hub with wheels attached to the spacers on cars that have wheel nuts, rather than BMWs that use bolts you struggle to line up!

[BMWZ4MC]

10mm? I’ve not seen spacers smaller than 20mm that bolt to the hub.
I’m concerned that you say that because I routinely use 12mm and 15mm spacers with some of my sets of wheels, especially given your engineering background (IIRC).

I'm surprised too as my current Z4 had hub-centric 15mm spacers on the front and 12mm on the rear with longer bolts when I got it.

I'd only expect to see spacers "bolted" to the hub with wheels attached to the spacers on cars that have wheel nuts, rather than BMWs that use bolts you struggle to line up!

Lining up the bolt holes in the hub, a spacer and the wheel is much easier with a couple of these:

CAB05EB5-7E73-472D-9F84-2BFD143EB3BA.jpeg (26.32 KiB) Viewed 1248 times

504BA916-76D3-41E2-B310-31929C34AF50.jpeg (38.53 KiB) Viewed 1248 times

[mmm-five]

Or you could do a long stud conversion and then put whatever size spacers/wheels you wanted on, with the added benefits of the studs holding the spacer/wheel in place whilst you secure them, and being able to swap out different sized spacers on a whim.

[TheDan]

May I know what are sizes of extended bolts should I use?

To answer the original question, the standard bolts have a 26mm thread. So for 12mm spacers you will need ~38mm thread length and for 15mm spacers you will need ~41mm thread length.

Do bear in mind that if you can't find bolts the exact lengths a general rule of thumb I follow is a max of -1mm and +2mm on thread length. If you go less than -1mm you run the risk of the bolt not having enough thread in the hub. If you go greater than +2mm you run the risk of the bolts catching on the brake dust shield.

If I were to do it again (and I may do this in the future), I would go with what mmm-five said and do a long stud conversion alongside a set of open wheel nuts.

[Zedebee]

Lining up the bolt holes in the hub, a spacer and the wheel is much easier with a couple of these:

CAB05EB5-7E73-472D-9F84-2BFD143EB3BA.jpeg

504BA916-76D3-41E2-B310-31929C34AF50.jpeg

Certainly, a pair of locating pins is very handy. If you are intending to use them as a “handle” to turn the hub, be careful not to screw them in too far or they will foul the brake dust shield resulting in much head scratching until you realise the problem is not your brakes!

[sars]

10mm? I’ve not seen spacers smaller than 20mm that bolt to the hub.
I’m concerned that you say that because I routinely use 12mm and 15mm spacers with some of my sets of wheels, especially given your engineering background (IIRC).

I'm surprised too as my current Z4 had hub-centric 15mm spacers on the front and 12mm on the rear with longer bolts when I got it.

I'd only expect to see spacers "bolted" to the hub with wheels attached to the spacers on cars that have wheel nuts, rather than BMWs that use bolts you struggle to line up!

10.0 mm is about the smallest size for bolt to hub wheel spacers, these are available from ST Suspension, at 15.0 mm there’s plenty of choice and at 20.0 most are bolt to hub.

[BMWZ4MC]

But would you recommend bolting spacers to the hub at 10, 12 or 15mm?

[sars]

Definitely, because the primary forces acting on the bolt are radial not axial, thus the longer the bolt the lower the radial force the bolt can withstand. Think of the wheel bolt as a lever, the bolt is gripped at one end and a force applied uniformly and perpendicular to it along the length, the longer the bolt the greater the torque. Bolt stress calculations are fairly complex with many variables, so it's not linear, if you double the bolt length you will more than halve the maximum permissible radial load.

A hub bolted spacer is more expensive to manufacture as there are more operations to perform so they only do it when they have to, there is a DIN standard and a TÜV approval thereto that governs the design of wheel spacers so I don't imagine that fitting bolts through a 12.0mm spacer is dangerous if done correctly.

I would always go with bolt to hub if I really had to use spacers. I know that wheel design is a personal choice and we all have different tastes, but I would rather choose an alloy that had the correct offset than one that was more aesthetically pleasing and have to add spacers as there will always be concentricity issues due to tolerances.