Mazda rx8 r3 front subframe

[Django91]

Hello all,

Would anyone be able to comment on the differences between a series 1 front sub-frame and one from an r3?
I am aware that the r3 version subframe is foam filled for better refinement, can this be retrofitted to a series 1?
Have the A-arms/ suspension geometry been fettled with, to aid fitment of the 19'' wheels?

Thanks
Toby

[warpc0il]

The front subframes are not interchangeable as they're a different shape.

Mazda Marketing got a bit carried away with the "foam filled for increased rigidity" as it makes almost no difference to the strength.
Manufacturers tried foam filling such components to reduce vibration resonance (that's what the Engineers were referring to as "refinement") and thought it might help against internal corrosion, which it didn't.

However, the 19" wheels are directly interchangeable with the 18"s on an S1 as they have the same rolling diameter etc, they just have lower profile tyres, so have no impact on the suspension geometry.

[Django91]

The front subframes are not interchangeable as they're a different shape.

Mazda Marketing got a bit carried away with the "foam filled for increased rigidity" as it makes almost no difference to the strength.
Manufacturers tried foam filling such components to reduce vibration resonance (that's what the Engineers were referring to as "refinement") and thought it might help against internal corrosion, which it didn't.

However, the 19" wheels are directly interchangeable with the 18"s on an S1 as they have the same rolling diameter etc, they just have lower profile tyres, so have no impact on the suspension geometry.

Thanks for this, my car currently has Racing Beat ARB'S coupled with Eibach Pro-Kit Springs and slightly lower profile tyres(235/40r18), all of this coupled with custom fast road geometry.
The car feels very different to a standard 231, a lot sportier, but with a slight decrease in ride comfort. More than this, the suspension 'sounds' like its working more harder(more audible and echo-ey), but seems to be dealing with bumps ok. The audible bit could just be down to tyres which are Goodyear SuperSports which is a performance oriented tyre with very stiff sidewalls. Was just wondering if there is a way to bring back some refinement, without detracting from the current set up.

[Phil Bate]

The observations you make are synonymous with running lower profile tyres with stiffer sidewalls, and I saw exactly the same each time I dipped to 235 40s - even with softer winter tyres. I found using a wider wheel with 245 40 tyres to be a perfect compromise

[BigPete]

Out of interest in this subject, which bits are different. As the rack fits the same the rear holes are all in the same place, so the only thing I’m not sure on are the legs a different length? The front lower arms are different but only on the hub end. I’m 99% sure they will fit an S1

[PaulAV]

Unless my 2007 registered rx8 is an R3 in disguise I can confirm that the R3 front subframe fits perfectly in a series 1 everything bolts up perfectly. I'm also going this route with the rear subframe but with series 1 arms as I believe the R3 arms are different as are the hubs maybe?

[BigPete]

Hi Paul yes rear lower trailing arms are different as are the hubs. The rest is the same

[Milos_Balunovic]

.....
Mazda Marketing got a bit carried away with the "foam filled for increased rigidity" as it makes almost no difference to the strength......

This is a highly false statement Sir, it is going to increase the rigidity and strength of a structure (2 different terms), the thinner the steel it the more impact it will have. The whole technology is called "sandwich construction". it will make substantial difference even if the steel is 3mm thick plate and has spacing of 20mm

The observations you make are synonymous with running lower profile tyres with stiffer sidewalls, and I saw exactly the same each time I dipped to 235 40s - even with softer winter tyres. I found using a wider wheel with 245 40 tyres to be a perfect compromise

Same findings Phil, love the car on them

[warpc0il]

.....
Mazda Marketing got a bit carried away with the "foam filled for increased rigidity" as it makes almost no difference to the strength......

This is a highly false statement Sir, it is going to increase the rigidity and strength of a structure (2 different terms), the thinner the steel it the more impact it will have. The whole technology is called "sandwich construction". it will make substantial difference even if the steel is 3mm thick plate and has spacing of 20mm

It really depends on what "foam" they used.

Ford and Mazda did a lot of experiments with foam-filling structural elements of the body structure, subframes and even suspension components.

The main goals were to reduce NVH by not making these sections sounding boxes, while also reducing the opportunity for trapped moisture causing rust. Some structural benefits could be obtained in some cases, and this development work went on to be used in the Ford Touring Cars and World Rally, where time and cost were of little consequence.

However it was not adopted into road car production as there was no cost-effective way of ensuring complete fill of the voids, thus making any potential benefit expensive and inconsistent. Partial fills also made the corrosion problem worse.

The R3 was launched after Mazda become independent of Ford and it's possible that they, or their supplier, had a breakthrough in this area. However, I still believe that the benefits of the foam-filled subframe may relate more to NVH than structural rigidity, again depending on the material and application method. A simple side-by-side load deflection test would prove or disprove the claim.

[Milos_Balunovic]

... However, I still believe that the benefits of the foam-filled subframe may relate more to NVH than structural rigidity, ....

I agree with that part. i.e. I don't believe there was lack of rigidity or strength in the original. NVH is probably made a noticeable change.

even very soft foams do provide significant increase in strength / rigidity and that is what I tried to correct. not that the car now became more rigid in total .


GTR's were also very popular to be foam filled (for racing) and increase in rigidity was substantial. for manufacturing that's a slow process, and all the holes have to be closed etc. not worth it at all