Rear subframe spacers

#1

So there is a lot of talk about rear alignment here. Obviously most people here like the weld in cabmber/toe adjusters. I just dropped my rear subframe and am looking into what to buy. I came across AKG selling poly rear subframe bushings with either a 9mm spacer or 12mm spacer for “cars with extreme negative camber”. I have not heard anyone here talk about that kit or that idea. Has anyone used this set up? I’m curious how this will change your camber and by how much? Any input?

#2

Those are intended to reduce the camber gain the results from lowering a car, which will reduce rear tire wear. On a race car, the weld in camber/toe adjusters would be the better choice as they allow independent adjustment of each side.

#3

Yeah so how is it changing the camber angle? Does it change ride height at the same time? Has anyone tried this kit?

As far as the weld in adjusters, I have heard bad things such as loosening up on the track. Also it cocks the bushing at an angle which it is not intended for, which doesn’t seem good. I have a friend with many E30 m3 racecars and he will not use them.

#4

The geometry of the trailing arms is such that as the wheel rises relative to the subframe camber increases. I don’t remember what happens to toe. So if you lower the car with shorter springs camber increases. The spacers push the subframe back down and reduce camber. since the springs are between the trailing arms and body the ride height doesn’t change.

#5

Toe doesn’t change, or at least not enough that I was able to detect it. Last year when I was playing around trying to understand how best to do my own alignments, I found that I could measure rear toe with the car up in the air and when I put the car down the toe measurement wouldn’t change. This was a great big help when adjusting eccentric rtabs because it allowed you to make changes and then check how those changes affected camber and toe without putting the car down.

Toe wouldn’t change and for camber it worked pretty well too. If I knew that I wanted -0.2deg more camber for example, I would lift the car, check the camber, play with the eccentric rtab, and then see what affect it had on alignment without putting the car down. This technique worked perfect for toe and “pretty good” for camber.

Re. rear camber/toe weld on kit bad because it causes off-axis rotation. Well, this is and issue, but lets look at it more closely.

In terms of off-axis rotation an eccentric rtab set up is the same as a weld on kit. The only difference is how you got the rotation points off-axis. I think that most eccentric rtab kits use relative soft bushings, so if you put soft bushings on your weld on kit you’d have no more stress on anything. The only difference is that your eccentric bushings wouldn’t rotate on you. Assuming you got the weld on kit’s bolts to stay put.

If, on the other hand, you put harder bushings on the weld on kit, like I’m doing, now you create off-axis forces on the connection points. If these are severe enough, it’s going to cause problems.

Consider tho what happens to those off-axis connection points with soft bushings. You’ve got the alignment that you want because your pivot points are off axis. If, when subjected to loading, the rubber bushings tend to allow the pivot points to go back on axis, then you just lost your desired alignment. So what you’ve just created is a suspension that works fine except when it’s loaded. Which is to say, when it’s needed. So that’s not ideal either.

There’s no perfect answer, I’m not a suspension guru, and different cars are likely to exhibit different behavior. But maybe the best approach is to put in relatively hard bushings and see if the connection points can handle the stress. And if your rear end explodes at the apex of RA’s turn 1 at 100mph, put softer bushings on your next car.

#6

the motor’s more likely to explode first :slight_smile:

#7

The rulebook says:
9.3.8.5. Unless otherwise stated in these regulations, any suspension toe setting, front and rear
and not requiring machining or modification to factory parts, is allowed.

9.3.8.8. Suspension bushing material replacement is permitted.

So, the question is; are the offset subframe bushings Legal?

Raise 12mm Aluminum

Raise 12mm Poly

Also, what is the general consensus for a SE30;
Aluminum, Delrin, or Poly for the subframe and diff bushings.

and while we are at it, are these legal?
GC

Thanks for helping with my first SE30 build!

#8

Would it be worth it simply for the roll center?

#9

[quote=“SoloJoe” post=55365]The rulebook says:
9.3.8.5. Unless otherwise stated in these regulations, any suspension toe setting, front and rear
and not requiring machining or modification to factory parts, is allowed.

9.3.8.8. Suspension bushing material replacement is permitted.

So, the question is; are the offset subframe bushings Legal?

Raise 12mm Aluminum

Raise 12mm Poly

Also, what is the general consensus for a SE30;
Aluminum, Delrin, or Poly for the subframe and diff bushings.

and while we are at it, are these legal?
GC

Thanks for helping with my first SE30 build![/quote]

The definition of “replaced” means “meets or exceeds OEM specs”. I would interpret that as meaning that both raised bushings and those trick CABs are legal. Some might not agree that a bushing that raises the car is the same as a “replacement” bushing, but IMO the word “exceeds” allows the use of a bushing that dimensionally “exceeds” OEM. If the authors meant to say “exceed in hardness” they would have.

Re. bushing type. There’s a few of us that have aluminum subframe and diff bushings but we’re in a minority. Most folks are mix of original bushings and harder non-aluminum replacements. Today TC Motorsports posted a vid of rear suspension in action that showed a lot of diff movement. I would interpret that as a case for aluminum rear subframe and diff bushings.

There was a thread at bf.c a while back re. modifying E30 suspension characteristics by using these kinds of bushings to raise the subframe. A person would really have to know what they were doing to dabble in this sort of thing. Otherwise every time the guy behind you came out of a turn with 0.5mph on you, you’d be wondering about whether your raised bushings were such a good idea after all.

#10

It’s hard to say, but I think it would be beneficial. I’ve been thinking about this for some time… Lowering our cars with the H&R springs clearly lowers the roll center in the front and rear. Raising the rear roll center will decrease the rear roll couple and stiffen up the rear a little bit. This will allow you to run the bar on full loose and transfer less weight to the outside wheel coming out of a corner. This sounds like a great thing for Turn 7 at RA and the Turn 6 at CMS…

#11

[quote=“Ranger” post=58259][quote=“SoloJoe” post=55365]The rulebook says:
9.3.8.5. Unless otherwise stated in these regulations, any suspension toe setting, front and rear
and not requiring machining or modification to factory parts, is allowed.

9.3.8.8. Suspension bushing material replacement is permitted.

So, the question is; are the offset subframe bushings Legal?

Raise 12mm Aluminum

Raise 12mm Poly

Also, what is the general consensus for a SE30;
Aluminum, Delrin, or Poly for the subframe and diff bushings.

and while we are at it, are these legal?
GC

Thanks for helping with my first SE30 build![/quote]

The definition of “replaced” means “meets or exceeds OEM specs”. I would interpret that as meaning that both raised bushings and those trick CABs are legal. Some might not agree that a bushing that raises the car is the same as a “replacement” bushing, but IMO the word “exceeds” allows the use of a bushing that dimensionally “exceeds” OEM. If the authors meant to say “exceed in hardness” they would have.

Re. bushing type. There’s a few of us that have aluminum subframe and diff bushings but we’re in a minority. Most folks are mix of original bushings and harder non-aluminum replacements. Today TC Motorsports posted a vid of rear suspension in action that showed a lot of diff movement. I would interpret that as a case for aluminum rear subframe and diff bushings.

There was a thread at bf.c a while back re. modifying E30 suspension characteristics by using these kinds of bushings to raise the subframe. A person would really have to know what they were doing to dabble in this sort of thing. Otherwise every time the guy behind you came out of a turn with 0.5mph on you, you’d be wondering about whether your raised bushings were such a good idea after all.[/quote]

Note - non-poly diff bushings are illegal :slight_smile:

#12

[quote=“dgorman” post=58324]
Note - non-poly diff bushings are illegal :)[/quote]
I disagree. Engine and tranny bushings need to be non-metal but the diff bushing is a suspension bushing. It’s one of 3 bushings that locate the rear subframe.

#13

[quote=“Ranger” post=58326][quote=“dgorman” post=58324]
Note - non-poly diff bushings are illegal :)[/quote]
I disagree. Engine and tranny bushings need to be non-metal but the diff bushing is a suspension bushing. It’s one of 3 bushings that locate the rear subframe.[/quote]

I agree it should be solid, I’m stating what the RULES state.

#14

[quote=“dgorman” post=58327][quote=“Ranger” post=58326][quote=“dgorman” post=58324]
Note - non-poly diff bushings are illegal :)[/quote]
I disagree. Engine and tranny bushings need to be non-metal but the diff bushing is a suspension bushing. It’s one of 3 bushings that locate the rear subframe.[/quote]

I agree it should be solid, I’m stating what the RULES state.[/quote]
This is what the rules state.

9.3.8.8. Suspension bushing material replacement is permitted.

Therefore aluminum diff bushings are legal.

#15

[quote=“Ranger” post=58328][quote=“dgorman” post=58327][quote=“Ranger” post=58326][quote=“dgorman” post=58324]
Note - non-poly diff bushings are illegal :)[/quote]
I disagree. Engine and tranny bushings need to be non-metal but the diff bushing is a suspension bushing. It’s one of 3 bushings that locate the rear subframe.[/quote]

I agree it should be solid, I’m stating what the RULES state.[/quote]
This is what the rules state.

9.3.8.8. Suspension bushing material replacement is permitted.

Therefore aluminum diff bushings are legal.[/quote]

I just looked it up again - I apologize, I was wrong - I could have swore I saw that you could only use poly bushings in the diff… :slight_smile:

I was thinking this was transmission … :slight_smile:

9.3.12.5. Alternate, non-metal, transmission mounts, providing the same height as original, are permitted.

#16

[quote=“dgorman” post=58329][quote=“Ranger” post=58328][quote=“dgorman” post=58327][quote=“Ranger” post=58326][quote=“dgorman” post=58324]
Note - non-poly diff bushings are illegal :)[/quote]
I disagree. Engine and tranny bushings need to be non-metal but the diff bushing is a suspension bushing. It’s one of 3 bushings that locate the rear subframe.[/quote]

I agree it should be solid, I’m stating what the RULES state.[/quote]
This is what the rules state.

9.3.8.8. Suspension bushing material replacement is permitted.

Therefore aluminum diff bushings are legal.[/quote]

I just looked it up again - I apologize, I was wrong - I could have swore I saw that you could only use poly bushings in the diff… :slight_smile:

I was thinking this was transmission … :slight_smile:

9.3.12.5. Alternate, non-metal, transmission mounts, providing the same height as original, are permitted.[/quote]
When you first wrote that they were illegal, me and my wafer thin facade of self-assurance reacted by thinking “HOLY F**K, DID I SCREW THAT UP? OH NO!” But then I went and looked it up and my heart rate slowed significantly.

#17

[quote=“Ranger” post=58330][quote=“dgorman” post=58329][quote=“Ranger” post=58328][quote=“dgorman” post=58327][quote=“Ranger” post=58326][quote=“dgorman” post=58324]
Note - non-poly diff bushings are illegal :)[/quote]
I disagree. Engine and tranny bushings need to be non-metal but the diff bushing is a suspension bushing. It’s one of 3 bushings that locate the rear subframe.[/quote]

I agree it should be solid, I’m stating what the RULES state.[/quote]
This is what the rules state.

9.3.8.8. Suspension bushing material replacement is permitted.

Therefore aluminum diff bushings are legal.[/quote]

I just looked it up again - I apologize, I was wrong - I could have swore I saw that you could only use poly bushings in the diff… :slight_smile:

I was thinking this was transmission … :slight_smile:

9.3.12.5. Alternate, non-metal, transmission mounts, providing the same height as original, are permitted.[/quote]
When you first wrote that they were illegal, me and my wafer thin facade of self-assurance reacted by thinking “HOLY F**K, DID I SCREW THAT UP? OH NO!” But then I went and looked it up and my heart rate slowed significantly. [/quote]

Same here - gunna throw out the poly now.