VagBremTechnic Big Brake Kit for E85/E86 Z4 'M' models

[MrPT]

What’s involved to mod the front ?

Appreciate the info

Just drive around very fast until the horrendous scraping noise stops.

Seriously, it’s not worth it - you need to heat and push out the arch liner around the front brake vent and shorten the vent itself, roll out the upper, outer arch lip and a small patch directly to the rear of the tyre. 245/35 is a better choice if you want a higher profile front tyre with slightly larger contact patch. Most of the improvement in ride quality comes from changing the rears.

 

[Bodyboarder]

Last question.... ( probably not :lol: )

To run 5mm spacers are longer bolts required ?

Thanks

 

[BMWZ4MC]

I run a set of appropriately longer bolts with each set of spacers (I have lots of spacers - 5mm, 12mm, 15mm and 20mm - and so I have 80 bolts not in use at any one time ).

If there are at least seven complete turns of the OEM bolts engaged when running the 5mm spacers, strictly speaking you don’t need longer bolts.

 

[TomK]

Personally I would never run a 5mm (or anything less than a hubcentric 10 for that matter), it's an unnecessary safety risk imo.
With a 5mm you are almost halving the size of the ledge on the hub that the wheel sits on and placing more load on the wheel bolts. Since many wheels have the center bore chamfered the 7mm you have left can be an issue.
There's also the potential problem if they have not been machined properly of causing vibrarions.
Either get a hubcentric spacer (minimum possible is 10mm) or don't use a spacer at all imo.

 

[craig3.2]

Personally I would never run a 5mm (or anything less than a hubcentric 10 for that matter), it's an unnecessary safety risk imo.
With a 5mm you are almost halving the size of the ledge on the hub that the wheel sits on and placing more load on the wheel bolts. Since many wheels have the center bore chamfered the 7mm you have left can be an issue.
There's also the potential problem if they have not been machined properly of causing vibrarions.
Either get a hubcentric spacer (minimum possible is 10mm) or don't use a spacer at all imo.

I would second that,spacers should be hubcentric,and as said,need to be 10 or 12mm.(depends on make,some 10mm makes are hubcentric,some aren't stated as being by the said manufacturers until 12mm), tWhich is what I found out.
10/12mm on the front with the 245/35 profile shouldn't rub,from what others have had fitted over the years

 

[craig3.2]

Bodyboarder wrote
What's involved to mod the front?

MrPT wrote
Just drive around very fast until the horrendous scraping noise stops.

[/quote/


That made me laugh

 

[Bodyboarder]

My front wheels specs are 19” 8.5 et40 , running a 245/35 tyre .... with a 10mm spacers I’d be at et30 . I’m on eibach springs ... do you think I’ll rub? I do plan to go to a 235/35 265/30 tyre combo also

 

[bmwaddict]

My front wheels specs are 19” 8.5 et40 , running a 245/35 tyre .... with a 10mm spacers I’d be at et30 . I’m on eibach springs ... do you think I’ll rub? I do plan to go to a 235/35 265/30 tyre combo also

I'm running 19x9 et38 with a 245/35 tyre fitted, lowered 25mm it does rub a bit on full lock. I plan to fit this brake kit too, so I will have similar issues to contend with.
For your 19x8.5 the ideal tyre size would be 235 width, and you shouldn't have any rubbing issues, bear in mind that different makes of tyre have slightly different shape sidewalls eg. MPSS are very straight and slender, where as GY F1s have a chunky rim protector, and a much more bulbous sidewall shape.

 

[Bodyboarder]

I guess the sensible thing to do would be buy the Tyres , then the 10mm spacers and see how she goes before purchasing the lovely Brembo’s !

 

[RedUn]

Personally I would never run a 5mm (or anything less than a hubcentric 10 for that matter), it's an unnecessary safety risk imo.
With a 5mm you are almost halving the size of the ledge on the hub that the wheel sits on and placing more load on the wheel bolts. Since many wheels have the center bore chamfered the 7mm you have left can be an issue.
There's also the potential problem if they have not been machined properly of causing vibrarions.
Either get a hubcentric spacer (minimum possible is 10mm) or don't use a spacer at all imo.

I used to think that but some OEMs (Porsche) run a 5mm spacer from the factory... So I tried it (not on the zed) and many track days and ring trips later, it was fine

I did go for longer studs (bolts on the zed) though just to make sure.

I'd happily run them again if need be

 

[BMWZ4MC]

The spigot is to centre the wheel when fitting it. Compressive forces between wheel and hub are generated by the bolts and it’s friction at that interface that transmits drive to the road. The spigot doesn’t keep the wheel on the car.
As for 5mm spaces being poorly machined leading to imbalance, that risk is true of any spacer or wheel.

 

[TomK]

The spigot is to centre the wheel when fitting it. Compressive forces between wheel and hub are generated by the bolts and it’s friction at that interface that transmits drive to the road. The spigot doesn’t keep the wheel on the car.

I might be wrong (actually probably am) but I thought the idea of hubcentric (which these cars are, like most) is that they are not lugcentric, i.e must be centrally supported by the spigot. The wheel bolts are not designed to take the shear loads unless centrally located?
Either way, with a 5mm you will still be located on the spigot, but if your bolts decide to back out a touch say (has happened to me once upon a time), there's not a lot of meat left on the bone.

As for 5mm spaces being poorly machined leading to imbalance, that risk is true of any spacer or wheel.

true, but I'd say the risk is higher with one that is not hubcentric. Say for instance the 5mm spacer hasn't been machined perfectly to ensure it is centered with equal distance around the hub and then slides over when tightening the bolts.

I used to think that but some OEMs (Porsche) run a 5mm spacer from the factory

Do you know the depth of those spigots? Perhaps they are larger, I see talk of 7mm (not hubcentric) which would be pretty on the limit with these hubs.

 

[BMWZ4MC]

If you were to loosen all the wheel bolts on a wheel without a spacer, a stationary car might be able to stand on the hub spigot. However, as soon as you introduced torque from accelerating or braking, the wheel would rotate on the hub until the bolt holes met the bolts. The bolts would either then shear or transmit the torque between hub and wheel. I would expect any lateral forces from cornering with loose bolts to be carried through the bolts unless the wheel was a virtual press fit on the spigot.

I do take your point about the potential for a spigot not being long enough to centre a wheel if a 5mm spacer is used with a wheel with a chamfered centre bore. However, I’m not sure if I’ve encountered wheels with chamfered centres. Also, the chamfered heads on the bolts will tend to centre the wheel on the hub just so long as you progressively tighten each bolt sequentially, not one at a time.

Anecdotal evidence I know, but I’ve used soft compound track tyres with 5mm spacers over hundreds of miles high G corners as well as full throttle starts and heavy braking without incident.

Edit - Did you replace your wheel bolts after running with them not torqued up? The bolts are intended to see tension loads only and they might have looked ok macroscopically but still have been exposed to huge uncontrolled stresses.

 

[RedUn]

The spigot is to centre the wheel when fitting it. Compressive forces between wheel and hub are generated by the bolts and it’s friction at that interface that transmits drive to the road. The spigot doesn’t keep the wheel on the car.

I might be wrong (actually probably am) but I thought the idea of hubcentric (which these cars are, like most) is that they are not lugcentric, i.e must be centrally supported by the spigot. The wheel bolts are not designed to take the shear loads unless centrally located?
Either way, with a 5mm you will still be located on the spigot, but if your bolts decide to back out a touch say (has happened to me once upon a time), there's not a lot of meat left on the bone.

As for 5mm spaces being poorly machined leading to imbalance, that risk is true of any spacer or wheel.

true, but I'd say the risk is higher with one that is not hubcentric. Say for instance the 5mm spacer hasn't been machined perfectly to ensure it is centered with equal distance around the hub and then slides over when tightening the bolts.

I used to think that but some OEMs (Porsche) run a 5mm spacer from the factory

Do you know the depth of those spigots? Perhaps they are larger, I see talk of 7mm (not hubcentric) which would be pretty on the limit with these hubs.

I can't remember the depth (it looks about the same!?) but on the Porsche the spigot is not a full spigot, it's machined away to save on weight, it's basically like a castellated nut if that makes sense? I suppose there's even less surface area there though which makes me think they aren't that worried about it?

 

[TomK]

If you were to loosen all the wheel bolts on a wheel without a spacer, a stationary car might be able to stand on the hub spigot. However, as soon as you introduced torque from accelerating or braking, the wheel would rotate on the hub until the bolt holes met the bolts. The bolts would either then shear or transmit the torque between hub and wheel. I would expect any lateral forces from cornering with loose bolts to be carried through the bolts unless the wheel was a virtual press fit on the spigot.
Edit - Did you replace your wheel bolts after running with them not torqued up? The bolts are intended to see tension loads only and they might have looked ok macroscopically but still have been exposed to huge uncontrolled stresses.

Thanks, i'm beginning to understand the concept of a bolted joint, and yes therefore the spigot is really just for locating.

I can't remember the depth (it looks about the same!?) but on the Porsche the spigot is not a full spigot, it's machined away to save on weight, it's basically like a castellated nut if that makes sense? I suppose there's even less surface area there though which makes me think they aren't that worried about it?

Seems BMW chose to run 5mm spacers on the front of the E92 GTS too so I'll get me coat :lol:

 

[TomK]

Interesting explanation of it all from Apex, who I guess know their stuff.

5mm spacers are fine in most cases as they can keep the car 100% hub-centric. It seems there is a LOT of misinformation about what hub centric really means, and how spacers effect a hub centric fitment.

Just because 5mm spacers do not have an extended hub, does not make the wheel assembly non-hub centric. As long as hub material is making contact with the center bore, the assembly will remain hub centric, and in most cases a 5mm spacer works as there is enough of the factory hub sticking through, that everything remains centered.



Hub centric means the hub keeps the wheels centered. The lugs hold the wheels to the car. This is important to understand, because the hub itself holds very little load on it's own. It's simply a guide to keep the assembly centered as there is a lot of slop and play with BMW lugs. Many cars on the other hand are lug centric. Meaning the hub is meaningless and the lugs don't have the same slop. They can center the wheels on their own. Two different designs, both work. BMW chose one.

The important thing to remember about the above is that the hub on a BMW only has to keep things centered, which is not a complex task. To do that, it only needs a few millimeters of contact with the wheel. Most BMW hubs have about 10mm of hub extension. If that sticks into a wheel 10mm, then you can use a flat spacer so long as there is still a few millimeters of material making contact with the wheels center bore.

Some wheels have a chamfered edge on their center bore, while others don't, and that chamfer can very in depth as well. That has an impact on how deep the hub has to reach to make proper contact with the center bore. In most cases a 5mm spacer will still have a few millimeters of center bore contact even on a wheel with a chamfered center bore.

An 8mm spacer on the other hand would not leave enough hub to keep the wheel centered since most wheels have a chamfered edge that is a few millimeters deep, that would make it impossible for the remaining factory hub material to make contact with the wheel. Because an 8mm spacer is flat (no attached hub extention) people tend to pool them all together and make generalizations.

The spacers shown in that thread above are NOT a universal spacer. They are still a bmw specific spacer as they are 5x120. It doesn't need an extended hub, as the factory hub does that work, and it would be impossible to create 5mm spacer with an attached hub.

In Summary:

The chamfer of your wheels are the determining factor of whether or not a 5mm spacer will work.

 

[MrPT]

Cheers for posting that - really good info.

Really does emphasise how important the centre bore contact is, not just for spacers but for anybody looking at non-standard alloys. I wonder how many people are using 5 x 120 aftermarket wheels with no hub contact?! :?

 

[Bodyboarder]

..... so we are now saying a 5mm spacer should be good to go :wink:

Where are people buying said spacers and longer bolts ?

Thank you

 

[Mister T]

I like the H&R Trak+ ones

 

[BMWZ4MC]

I make my own from old baked bean cans....
Otherwise, H&R spacers from eBay are usually a reasonable price.