Rupunzell
Bernice Loui
Similar but related.
The 96' NA miata got put up on the chassis set up rig. Learned much about the Miata's chassis and suspension.
This project began with making and installing anti-roll bar links.
To replace the wore out stock links.
The anti-roll bar links installed:
One discovery, the stock Miata anti-roll bar mounts are prone to failure due to insufficient rigidity and cyclic metal fatigue over load cycles and time. So, this bar and support blocks were made to aid in this design problem.
Bar and block installed;
How does the NA Miata chassis compare to the exxe chassis ?
They are different with a different set of problems and design goals.
The Miata is a front engine chassis with double A-arms front and rear, the exxe is mid-engine, lower A-arms with struts. One might believe double A-arms all around would be superior to the struts.. This is just not true. They are a different set of trade offs.
The weight is higher in the Miata by a few hundred pounds. It does have a more modern motor giving it more power than the exxe.
The front engine layout results in the CG near or at the steering wheel (which does not agree with me at all as to the feel of this chassis). The exxe with it's mid-engine layout has it's CG at or very near the driver's lower back. Why does this matter, human beings center of balance is located at the lower back. This is how human beings sense balance to stand and do stuff while moving. If the CG is placed at that location in a chassis, the driver can sense the balance of the chassis much better than having the CG at the driver's hands.
Being a front engine chassis, nose heavy, it will have inherently understeer or the front end loosing grip before the rear end, opposite of the exxe.
After much tweaking and adjusting of the threaded spring collars. The Miata ended up with these corner weight values;
Overly lowered Miata's are very common. This fashion fad puts the suspension's roll center below ground causing the tires to dig and reduce grip. The most one can lower a Miata is about 2" or so.. even that is pushing it with significantly reduced suspension travel. Also, the Miata's suspension has just under 2" of good, controlled suspension range. More reasons to limit's it suspension travel to keep the tires happy and grippy. Not too different than the exxe in this regard.
Knowing this, the rest of the chassis alignment values became apparent. To achieve a more neutral steering chassis, the grip at the rear needs to be reduced slightly to balance out the higher grip at the front. This means reducing the camber at the rear by 1/2 degree or so at the rear relative to the front. On the exxe, the rear is often set up with more camber at the rear and less camber at the front.
Before adjusting camber, basic toe front and rear is set to near zero. This is important as every chassis alignment adjustment with the A-arm eccentrics interacts with the others, camber affects toe, toe affects camber.. affects castor and ride height and... All this makes setting up a Miata chassis time consuming and not for the un-informed.
Image of the front corner.
Image of the rear corner.
Accuracy of chassis alignment settings needs to be less than 1mm, 0.2 degree on a level surface. This means no tires on the chassis as the alignment is adjusted as tires will not allow the chassis components to move with ease as chassis adjusters are adjusted and changed. This is why hub stands are used. Added to this, the hub stands should be equal in height to the loaded wheel and tire with the point of force equal to the load center of the wheel. This set up is low friction, push the car on this set up too hard and it will roll off the pads with ease.
After much futzing and tweaking, the desired values were achieved.
Front:
* Zero toe.
* 2.2 degrees negative camber.
* About 4.5 degrees positive caster (as much as the adjuster will allow).
Rear:
* 2mm toe in.
*1.7 degrees negative camber.
Cross weights ended up at 49.9% or as good as possible given the as delivered weight distribution.
These alignment values are the opposite of how one would set up a exxe chassis with exception of the cross weight needing to be at or very near 50%.
The results were a much more responsive Miata and much closer to having neutral cornering behavior. More will be learned after it's track day with these settings.
At some point, removing the anti-roll bars and replacing them with higher rate springs front and rear needs to be tried.
At the end of this day, my preference remains the exxe for a host of reasons.
Bernice
The 96' NA miata got put up on the chassis set up rig. Learned much about the Miata's chassis and suspension.
This project began with making and installing anti-roll bar links.
To replace the wore out stock links.
The anti-roll bar links installed:
One discovery, the stock Miata anti-roll bar mounts are prone to failure due to insufficient rigidity and cyclic metal fatigue over load cycles and time. So, this bar and support blocks were made to aid in this design problem.
Bar and block installed;
How does the NA Miata chassis compare to the exxe chassis ?
They are different with a different set of problems and design goals.
The Miata is a front engine chassis with double A-arms front and rear, the exxe is mid-engine, lower A-arms with struts. One might believe double A-arms all around would be superior to the struts.. This is just not true. They are a different set of trade offs.
The weight is higher in the Miata by a few hundred pounds. It does have a more modern motor giving it more power than the exxe.
The front engine layout results in the CG near or at the steering wheel (which does not agree with me at all as to the feel of this chassis). The exxe with it's mid-engine layout has it's CG at or very near the driver's lower back. Why does this matter, human beings center of balance is located at the lower back. This is how human beings sense balance to stand and do stuff while moving. If the CG is placed at that location in a chassis, the driver can sense the balance of the chassis much better than having the CG at the driver's hands.
Being a front engine chassis, nose heavy, it will have inherently understeer or the front end loosing grip before the rear end, opposite of the exxe.
After much tweaking and adjusting of the threaded spring collars. The Miata ended up with these corner weight values;
Overly lowered Miata's are very common. This fashion fad puts the suspension's roll center below ground causing the tires to dig and reduce grip. The most one can lower a Miata is about 2" or so.. even that is pushing it with significantly reduced suspension travel. Also, the Miata's suspension has just under 2" of good, controlled suspension range. More reasons to limit's it suspension travel to keep the tires happy and grippy. Not too different than the exxe in this regard.
Knowing this, the rest of the chassis alignment values became apparent. To achieve a more neutral steering chassis, the grip at the rear needs to be reduced slightly to balance out the higher grip at the front. This means reducing the camber at the rear by 1/2 degree or so at the rear relative to the front. On the exxe, the rear is often set up with more camber at the rear and less camber at the front.
Before adjusting camber, basic toe front and rear is set to near zero. This is important as every chassis alignment adjustment with the A-arm eccentrics interacts with the others, camber affects toe, toe affects camber.. affects castor and ride height and... All this makes setting up a Miata chassis time consuming and not for the un-informed.
Image of the front corner.
Image of the rear corner.
Accuracy of chassis alignment settings needs to be less than 1mm, 0.2 degree on a level surface. This means no tires on the chassis as the alignment is adjusted as tires will not allow the chassis components to move with ease as chassis adjusters are adjusted and changed. This is why hub stands are used. Added to this, the hub stands should be equal in height to the loaded wheel and tire with the point of force equal to the load center of the wheel. This set up is low friction, push the car on this set up too hard and it will roll off the pads with ease.
After much futzing and tweaking, the desired values were achieved.
Front:
* Zero toe.
* 2.2 degrees negative camber.
* About 4.5 degrees positive caster (as much as the adjuster will allow).
Rear:
* 2mm toe in.
*1.7 degrees negative camber.
Cross weights ended up at 49.9% or as good as possible given the as delivered weight distribution.
These alignment values are the opposite of how one would set up a exxe chassis with exception of the cross weight needing to be at or very near 50%.
The results were a much more responsive Miata and much closer to having neutral cornering behavior. More will be learned after it's track day with these settings.
At some point, removing the anti-roll bars and replacing them with higher rate springs front and rear needs to be tried.
At the end of this day, my preference remains the exxe for a host of reasons.
Bernice
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