*KITS HAVE SHIPPED* 5 Lug and BBK Group Buy Round 3

[tally159]

Sign me up for mine being made for z4 hubs as well!

[LowR3V'in]

make mine for the z4 hub pls.

[elcoy]

I guess unless anyone says otherwise, Ill run them all to Z4 hubs?

[LowR3V'in]

unless that 4% strength reduction will make them flex, ya, sounds good.
if anyone needs that extra 2mm, spacers are $10. vs $494 for the rear m3 hubs.

[BBDirtbiking]

If anyone is interested in looking in to the E30M3 vs Z4 hub changes, Djmack talks about it in the previous group buy (https://www.r3vlimited.com/board/sho...d.php?t=383082) around post #110-#118. Here is #118 quoted, showing his setup:

If you look closely, the blue anodized surface is gone from the bracket (shaved). And this is also a decent example of what i did to extend my brake line.

(Use https://chrome.google.com/webstore/d...giikdkpmcpkaon to see photobucket image.)

With all that said, I have heard that there can be differences in the 530i and 540i carriers/calipers, so go z4 hubs with shaved brackets at your own risk.

[itsonlygeorge]

In for a set for the e30 m3 hubs! I think I sourced a set.

This should retain e-brake and ABS functionality without any modification?

Will I need a 14mm spacer for the back?

Is there a way to not have to run spacers or roll fenders?

What's the approximate delivery date?

[-J-]

Sorry for the delayed response with the calcs. Life and other excuses, etc... Here's my half-assed explanation of the calculations, paint images and all.

*DISCLAIMER*
I MAKE NO GUARANTEES FOR THE STRENGTH OF THIS BRACKET. USE THIS PRODUCT AT YOUR OWN RISK.

Like any engineering problem, it's simply a matter of solving a series of little problems that ultimately solve the big problem. So we want to know the stress (engineer for strength) at the bracket during maximum braking. What creates stress? Forces. What creates the force at the bracket? The brakes. How do the brakes create forces? Friction at the pad/rotor reacting against the tire force at the road. How do the tires generate forces? Normal force and slip. We'll start here and work our way back.

When you hit the brakes, the car pitches forward. This is known as weight transfer, and it directly effects the normal (downward) forces at the tire. Here's the visual:



The bottom calculation is for the change in normal force during a 1g deceleration event (I have data of my E30 pulling 1g on shitty no-seasons). For the rear I subtracted that value from the static rear weight distribution to end up at 3634N. The numbers I'm using are based on the corner weights from my stock Touring. This is actually a worse case than a coupe or sedan because of the extra normal force over the rear.

To find the longitudinal tire force, you need the tire normal force and tire data. The latter is extremely expensive to find accurately, so this is the biggest assumption in this whole process.



Based on research, most tires put out a 1:1 ratio of normal force to longitudinal force at optimal slip (at least in the E30 range of normal forces), i.e. 3000N of normal force is capable of producing 3000N of longitudinal force. Higher performance tires can do higher so I assumed a 1.1:1 ratio, which I ballparked to 4000N of longitudinal force.

Plugging in the tire force into a free body diagram of the tire-brake assembly, we get this:


Converting to torques, we can solve for the force at the caliper:



The caliper bolts to the bracket with two bolts, so the load is shared equally.



Now that we know the force at the bolt we can analyze the stresses in the bracket. The bracket and caliper combo function as a single-shear pin joint. In all cases of my analysis, bearing strength was always the limiting factor, so that's what I'll highlight here. Using 6061-T6 for the bracket, I ran the numbers through an online calculator:



I don't have the actual bracket dimensions, so I eyeballed it and guessed 15mm for the full version and 13mm for the shaved version. As you can see, the bracket is plenty strong under sustained braking, even assuming a heavy ass and higher performance tires. The actual strength reduction in this case was 7% because I used normal tires in the previous calculations. Also note that these calculations do not take into account shock loading or thermal effects (which are significant), however even with a safety factor of three it is nowhere near maximum allowable stress.

Feel free to pick apart my calculations; all criticisms welcomed.

[elcoy]

Sorry for the delayed response with the calcs. Life and other excuses, etc... Here's my half-assed explanation of the calculations, paint images and all.

*DISCLAIMER*
I MAKE NO GUARANTEES FOR THE STRENGTH OF THIS BRACKET. USE THIS PRODUCT AT YOUR OWN RISK.

Like any engineering problem, it's simply a matter of solving a series of little problems that ultimately solve the big problem. So we want to know the stress (engineer for strength) at the bracket during maximum braking. What creates stress? Forces. What creates the force at the bracket? The brakes. How do the brakes create forces? Friction at the pad/rotor reacting against the tire force at the road. How do the tires generate forces? Normal force and slip. We'll start here and work our way back.

When you hit the brakes, the car pitches forward. This is known as weight transfer, and it directly effects the normal (downward) forces at the tire. Here's the visual:



The bottom calculation is for the change in normal force during a 1g deceleration event (I have data of my E30 pulling 1g on shitty no-seasons). For the rear I subtracted that value from the static rear weight distribution to end up at 3634N. The numbers I'm using are based on the corner weights from my stock Touring. This is actually a worse case than a coupe or sedan because of the extra normal force over the rear.

To find the longitudinal tire force, you need the tire normal force and tire data. The latter is extremely expensive to find accurately, so this is the biggest assumption in this whole process.



Based on research, most tires put out a 1:1 ratio of normal force to longitudinal force at optimal slip (at least in the E30 range of normal forces), i.e. 3000N of normal force is capable of producing 3000N of longitudinal force. Higher performance tires can do higher so I assumed a 1.1:1 ratio, which I ballparked to 4000N of longitudinal force.

Plugging in the tire force into a free body diagram of the tire-brake assembly, we get this:


Converting to torques, we can solve for the force at the caliper:



The caliper bolts to the bracket with two bolts, so the load is shared equally.



Now that we know the force at the bolt we can analyze the stresses in the bracket. The bracket and caliper combo function as a single-shear pin joint. In all cases of my analysis, bearing strength was always the limiting factor, so that's what I'll highlight here. Using 6061-T6 for the bracket, I ran the numbers through an online calculator:



I don't have the actual bracket dimensions, so I eyeballed it and guessed 15mm for the full version and 13mm for the shaved version. As you can see, the bracket is plenty strong under sustained braking, even assuming a heavy ass and higher performance tires. The actual strength reduction in this case was 7% because I used normal tires in the previous calculations. Also note that these calculations do not take into account shock loading or thermal effects (which are significant), however even with a safety factor of three it is nowhere near maximum allowable stress.

Feel free to pick apart my calculations; all criticisms welcomed.

Wow this is amazing! Great work.


I sent out an email to everyone that paid so I can get an accurate count of kit configuration. They are being machined these next two weeks and I should have them to customers mid-april!

[BBDirtbiking]

even with a safety factor of three it is nowhere near maximum allowable stress.

Such is design, haha.

Thanks for sharing the calculations you did, very thorough.

I sent out an email to everyone that paid so I can get an accurate count of kit configuration. They are being machined these next two weeks and I should have them to customers mid-april!

Thanks for the timeline update. I just saw your email now - gmail put it as "Promotions" so glad I checked.

[LowR3V'in]

so it says m3 hubs & 540i calipers
or z4 hubs & 530i calipers.

What's the difference?

[elcoy]

so it says m3 hubs & 540i calipers
or z4 hubs & 530i calipers.

What's the difference?

I have heard that 530i and 540i calipers are different? But also have heard they are the same. I have confirmed 530i calipers work with Z4 parts so that's what I recommend with that setup.

[elcoy]

In for a set for the e30 m3 hubs! I think I sourced a set.

This should retain e-brake and ABS functionality without any modification?

Will I need a 14mm spacer for the back?

Is there a way to not have to run spacers or roll fenders?

What's the approximate delivery date?

Sent you a PM but I believe your inbox is full.

[LowR3V'in]

I have heard that 530i and 540i calipers are different? But also have heard they are the same. I have confirmed 530i calipers work with Z4 parts so that's what I recommend with that setup.

i see. but they also work with the m3 hubs or no?

i'm asking on bimmerforums see of those guys know if there's a difference.

[elcoy]

i see. but they also work with the m3 hubs or no?

i'm asking on bimmerforums see of those guys know if there's a difference.

I know the 540 calipers work with E30M3 hubs, because thats what I used.


The Z4 hub is thinner, so the thinner brackets shift the entire assembly over to match.

If the calipers are really the same, either would work. The bracket decides which hub is needed.

[LowR3V'in]

ok but the same rotor is used on both m3 and z4 hubs
and the only difference in the adapter on the z4 is shaved down 2mm
if it's just the caliper then it doesn't matter.
i'm guessing you're talking about the the brackets being different?

To me it looks like calipers are the same
The 99+ brackets looks like they get pushed out 3mm. is that what you have?

https://www.bimmerforums.com/forum/showthread.php?2372497-530i-vs-540i-rear-brakes