Like a dog with a bone

[Petrus]

I just could nót let it go. The Sportivo kit ´dog bones´ kept bugging me.

The problem is that the ´Rear Suspension Member Spacer t=3.2 Material: Steel Changing roll-centre position´
lówers the rear roll centre.
As such it does nót ´correct´ the 20 mm. lowering of the suspension.

Appearantly TRD thought it important so Í thought it important to try understand WHÝ??!!

I think I have unraveled the enigma: It is about balance.
1. Roll centre tuning is much more about the front and rear roll centers in correlation with eachother than their absolute positions.
2. The effect is instantanuous and irrespective of roll.

I will explain the latter. Anti roll bars and springs are action= - reaction: the more they are distorted the more they push against this distortion.
The roll centre is ALL about geometry: The effect is from zero.

Ok, now back to the kit.
The Sportivo kit firms up the front more than the rear. The front gets more responsive, gets more traction.

Now a step back again, sorry.
As with understeer/oversteer, more traction fron/rear does NOT mean the inverse at the other end. It is relative to the rear.
This is more easily understood with a tyre example: Going from 185 to 195 at the front gives a bit more traction. a bit less understeer. It does nót give less traction at the rear although the efféct is ´more´ oversteer. The brackets are essential: It is relative.

We all know that our Spyder is very sensitive to changes in balance.
We have seen that roll centre tuning is ALL about balance.

Now, with the Sportivo kit, TRD lowers the front and rear the same.
It adds a relatively stiffer front arb though. This is connecting left and rear wheels with a stiffer torsion spring. Compressing one wheel will see the spring pushing the other wheel down with the same force.
Although not without down side, it overal keeps more front rubber on the tarmac; increases front traction thus responsiveness. It relatively! gives  relatively more oversteer etc.
By slightly changing the roll centre balance towards more decline at the rear, the traction at the rear increases. It does in effect the same as a stiffer arb at the rear, without the down side and waht´s more from zero.

What the spacers do is;




lower the chassis attachement of the lower suspension side = lower the roll centre. It is easy to see that it is geometry. That it works at any position at any speed.

So, there we have it. The spacers in the Sportivo kit make the rear relatively more stable, will improve throttle control.


Now bear with me a bit more.
This álso applies to other stiffening of the front like by mounting a front strut brace!!
A  front brace adds a support between the two McPherson struts. Forces on the one are supported on the other.
Not the same as an arb but it does give more traction at the front. More responsiveness, less understeer = réatively more oversteer.
And now we get to the fire cracker: Imo the spacers are also beneficial when ónly a front strut brace is mounted. It restores the balance without the down side of stiffening springs/arb.

[Petrus]

Me digging this up was triggered by stateside questioning TRD´s wisdom.

Boris (Snelbaard) has sold very few.
Now, it does work.
If you have a front strut brace then PÍNG!

I say get them while they are availeble; they are easy to fit, cheap, work and roll centre tuning is quite trick. They are the dog´s ... bones 

[Ardent]

Fascinating stuff.

Can follow it and understand it. Could not explain it back.

[Petrus]

Fascinating stuff.

Can follow it and understand it. Could not explain it back.

Simples: Have a front strut brace? Do the spacer too.
Why: To maintain traction balance.

Says I and you know how I am about bolt óns....

[Ardent]

Thats my take away.

As i do not have any additional bracing.
Nothing for me to do.

[Petrus]

Thats my take away.

As i do not have any additional bracing.
Nothing for me to do.

Spot on.

[shnazzle]

Interesting. Wonder how that applies to my setup. 
TRD being based on a stock MR2 with stock wheel/tyre sizes and stock struts, camber etc. 
If all of that is different, do they still make a difference? Or has the balance been counteracted already somewhere else..

[Petrus]

Interesting. Wonder how that applies to my setup.
TRD being based on a stock MR2 with stock wheel/tyre sizes and stock struts, camber etc.
If all of that is different, do they still make a difference? Or has the balance been counteracted already somewhere else..

Go back to the TRD Sportivo kit.

The kit consists of several elements which do different things ánd TRD also had most availeble as a seprate set too:

Coil overs with lowering springs, balanced front rear as set.
ARBs front rear, balanced as set.
Imo you can thus take them out of the equasion concering front strut brace and/or subframe spacers.

So, the front strut brace and the subframe spacers. Imo balanced as set.

Now if you would firm up only the rear arb a whiff, that would also match the front strut brace but with the down sides of a stiffer arb.

The odd thing is that they only provided the spacers with the complete kit, not when the brace was sold seprately.
I thínk that is because the Sportivo set was to be non plus ultra and beefing up the rear arb even more has downsides. Thus they came up with this.

Why so much focus on these little unobtrusive, when mounted invisible even, spacers? Well, becaúse they are. Why would TRD come up with them, include them in the kit whereas it is the one and ony non-bling part of the kit?
Imo it is glaringly obvious that Toyota thought them important.
I thínk I have worked out why.

Back to your question.
If you have your mods balanced to achieve what you want, including balancing the effect of the strut brace, then it is superfluous.
This takes into account that you may have prefered chánging the balance. I myself p.e. have more air in the front tyres because I prefer a whiff less initial understeer.
Lastly there is a difference in balance between the pre face lift and face lift models.
Bottom line is you may or may not want to match what the strut brace does.

[Petrus]

A neat explanation of what the TRD Sportivo subframe spacers do; as per TRD info ´correct roll centre´:

http://speed.academy/suspension-tuning-how-to/2/

[tets]

got the right size bar - making them for when the subframe goes back on - great read by the way

[Petrus]

got the right size bar - making them for when the subframe goes back on - great read by the way

Boris (Snelbaard) had them on the shelf.  Thanks. 

[1979scotte]

A neat explanation of what the TRD Sportivo subframe spacers do; as per TRD info ´correct roll centre´:

http://speed.academy/suspension-tuning-how-to/2/

I've got roll centre correcting ball joints in storage somewhere.
Will fit one day.

[Petrus]

I've got roll centre correcting ball joints in storage somewhere.
Will fit one day.

Where did you get them from?
Looked around on the web and find them a bit costly.

[1979scotte]

I've got roll centre correcting ball joints in storage somewhere.
Will fit one day.

Where did you get them from?
Looked around on the web and find them a bit costly.

Gt4 play I think had them years.

[1979scotte]

Made by hard race.

[Petrus]

MR2Ben is the only one at the moment. Indeed HardRace. His price is in line internationally. Just think it costly.  Will think about it but probably bite that bullet.

Why have you not fitted them yet?

[1979scotte]

MR2Ben is the only one at the moment. Indeed HardRace. His price is in line internationally. Just think it costly.  Will think about it but probably bite that bullet.

Why have you not fitted them yet?

Because I'm on my 3rd mr2 and still own 2 and always have other mods to do.

Was told it was a great handling mod buy somebody who had them fitted seems to be rare.
Stupink it was I think.

[Petrus]

Was told it was a great handling mod buy somebody who had them fitted seems to be rare.
Stupink it was I think.

I totally get the need; it is simple geometry.

About nobody fitting them I am not that surprised as it is not cheap yet not visible. I do think it a bit odd if dedicated racers did not fit them.

[tets]

got the right size bar - making them for when the subframe goes back on - great read by the way

Boris (Snelbaard) had them on the shelf.  Thanks. 

I know but I have the correct size bar so drilling 2 holes and cutting to length is easier!

[Petrus]

I know but I have the correct size bar so drilling 2 holes and cutting to length is easier!

Ok.

[ralf321]

Hello,

I wonder how thick the bones are and why not just take some washers instead ?
Going to replace my rear subframe over winter and I intend to give it a try.

BR
Ralf

[Snelbaard]

they are 3mm thick. Washers could also be used but I wanted to make as exact a replica of the TRD items as I could, so I did

[Petrus]

MR2Ben is the only one at the moment. Indeed HardRace. His price is in line internationally. Just think it costly.  Will think about it but probably bite that bullet.

Why have you not fitted them yet?

Because I'm on my 3rd mr2 and still own 2 and always have other mods to do.

Was told it was a great handling mod buy somebody who had them fitted seems to be rare.
Stupink it was I think.

Ah, the ball joints are not a replaceble item?! Need to fit a replacement lower arm assy? How does thát work?! You´d still need to fit the after market ball joints! If that is possible on say a Yaris arm, how come the OEM ball joints cannot be swapped?

[Joesson]

MR2Ben is the only one at the moment. Indeed HardRace. His price is in line internationally. Just think it costly.  Will think about it but probably bite that bullet.

Why have you not fitted them yet?

Because I'm on my 3rd mr2 and still own 2 and always have other mods to do.

Was told it was a great handling mod buy somebody who had them fitted seems to be rare.
Stupink it was I think.

Ah, the ball joints are not a replaceble item?! Need to fit a replacement lower arm assy? How does thát work?! You´d still need to fit the after market ball joints! If that is possible on say a Yaris arm, how come the OEM ball joints cannot be swapped?

This was discussed in the thread ending here :
https://www.mr2roc.org/forum/index.php?msg=836158

[Petrus]

This was discussed in the thread ending here :
https://www.mr2roc.org/forum/index.php?msg=836158

I see that in #73 you mention you changed ´just the ball joint´.
Further on I read OEM DIY refurbishing too.
Also read Dev commenting that on some cars they cannot be removed.
Hmmm....
Just ´want´ to swap the ball joints and not get into a complex going for more expensive still project.