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Subframe brace for your NA/NB Spec Miata in SCCA & NASA

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#41
Steve Scheifler

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Dredging up an old thread.

At Road America we had at least 3 subframes break, that I know of. If you have not put these on, please do so for your own good.

On the one subframe that I saw with my eyes, the upper control arm mount was ready to pull out of the subframe, as well as the lower mount which already had broken. Read the older posts and you will see that I recommended a 4 piece kit be allowed. But nobody else had seen the upper mount break. Well ,know many have. I hope the SMAC will look into allowing an upper brace also.

dave


Dave, is it possible that the uppers failed primarily because the lowers were already compromised? Have you seen an upper fail without a lower also broken?
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#42
davew

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I have seen 2 cases of uppers failing with no problem with the lower. Note that 1 of these was a fairly new Mazda subframe (2-3 weekends) while the other was an oem unit with a lot of street and race miles.

 

The one this summer at Road America, where the lower failed, had a cracked upper mount that had not yet fully torn apart. My opinion is that the upper had no cause or effect from or to the lower.


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#43
Steve Scheifler

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Kobe steel strikes again! :)

We may have to stop blaming only the Chinese for crappy steel.
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#44
davew

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I blasted a subframe and used a dye-chem crack checker on it. Found hairline cracks all over. Lower mount, upper mount, steering rack and motor mount perch. I am usually not one for "slippery slope" changes. But, I would be in favor of allowing the subframe be reinforced by fully welding any seam that is only partially welded from the factory. The factory used a lot of spot and stitch welds. As well as an upper mount reinforcement. Not as a performance enhancement, as a safety item.

 

Can not blame the tires, although they may be a contributory factor. I have seen this on Toyo's also.


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Dave Wheeler
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#45
ChrisA

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Could this be attributed to the non-compliant nature of the harder offset bushing used in the upper a-arms?


Chris

 

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#46
davew

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Could this be attributed to the non-compliant nature of the harder offset bushing used in the upper a-arms?

Not in my opinion as I saw cracks prior to the offset bushings


Dave Wheeler
Advanced Autosports, the nations most complete Spec Miata shop
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Building Championship winning cars since 1995

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2007 June Srints winner, (GT1, Mohrhauser)

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#47
Steve Scheifler

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There are a lot of Miatas in classes which allow more modifications than SM. Has anyone talked to guys running them in those classes about whether they have similar issues and routinely strengthen the subframes? Their total numbers may not match SM but I would expect that they have seen this as well.
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#48
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I just happen to know a guy who has owned three 1990 Miata race cars for maybe 9 years (his original Miata was a Spec Miata from the southeast that had the hell beat out of it by the looks of the unibody frame rails, it was converted to ITA and today is STL) running Hoosier slicks on the two F prod cars and Hoosier A7 on the ITA/STL car. No sub-frame issues. Of course the bump drafting is minimal to none. Hmmm...............


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#49
38bfast

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I think it has more to do with we are bottomed out on the bump stops all the time.
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#50
FTodaro

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Dave I would be interested to know what year Miata's you are discussing. I know in the transmission arena we have seen different quality parts and steel used in different model years and also in the replacement part arena. Likewise, again my personal opinion, front hubs from older cars are better quality than the new replacement hubs of today. My point, there may be a year or two where they had a quality problem.


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#51
Steve Scheifler

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I think it has more to do with we are bottomed out on the bump stops all the time.


Maybe, but it seems to me that has little or no impact, literally or figuratively, on the upper mount points. Interesting thought on the lowers but visualizing where the force goes I think maybe not, at least from what I’ve experienced. We were much harder into much harder stops in the old days.

I think the gators and rumble strips while laterally loaded exiting corners may be a likely source of the forces causing trouble, though perhaps that’s made worse by being deep in the stops? How much of the force is transmitted in which directions?
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#52
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Frank, all 1990's.


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#53
davew

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We need to take things into perspective. Because Dewey's friend has not broken a sub-frame does not mean they do not break. He runs 6-8 races a year in a class that is not known for the bumping, banging, curb hoping, general bad driving that we see on a regular basis. Your typical self-prepped driver who runs 5 races a year will probably never see a broken sub-frame. I am taking 12 cars to Blackhawk this weekend, most will run double classes. So I will get 20 events worth of track time in just one weekend. That is 4 years worth to the "typical" SM racer. The burden of proof that these things break, has to be put on the shops that see 100's of races a year. And all the shops have seen this happen. And I believe all are in favor of allowing additional reinforcements.

 

Yes, installing reinforcements of whatever is allowed, will be a revenue stream for guys like me. But so will replacing sub-frames, fenders, allignments, etc. from broken sub-frames. And none of us want to see someone get hurt.

 

My personal experience is that this will become a bigger problem as time goes on. I feel it is a fatige issue. As we get more miles, we get more fatige and more breakage. I can only remember a single NA car with a crack. But I could be wrong. And remember that the vast majority of cars running nationwide are NB's. Tracks with big curbs and bumps on track out, seem to be the most prone to breaking sub-frames. Road America and Sebring are the most often reported. But we have seen them at Blackhawk, Mid Ohio and at Indy (smooth track with BIG curbs). I have only installed a single new subframe in recent years. As mentioned above, it only lasted a couple races.

 

My proposal was a 4 piece kit, 2 upper and 2 lower. I proposed specing the design, rather than the supplier. I offered to put my drawings out on the internet for anyone to copy. In the end the SMAC and Mazda decided to go with only the lower mounts and only from Mazda. A good start, but in my opinion they only solved part of the problem.

 

My 2 cents worth.

Dave


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Dave Wheeler
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#54
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My personal experience is that this will become a bigger problem as time goes on. I feel it is a fatige issue.

Dave

Not to hijack this thread but i totally agree on the point of the fatigue issue. I have been seeing more and more 3rd gear and 5th gear failures. I understand why it happens but I believe that stress builds up over time causing the failures. If your are easy on a trans then it will not be much of an issue if your hard on a trans, i think they have a limit to the number of times they can be rebuilt without certain part replacement.

 

Taking this to a sub frame, there are likely micro cracks that you cannot see till its an obvious failure.

 

A friend of mine is a forensic metallurgist, If someone has a failed sub frame they want to send to me, i would be happy to have an expert look at it.


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#55
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Davey, someone asked other than Spec Miata, I answered. Let's use you 8 weekends per year times 9 years equals 72 weekends on one car. Please don't be so selective with your data. :bigsquaregrin: 


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#56
Erik Hardy

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These cars will continue to show fatigue failures the longer they are raced. 

 

All failures are cumulative in terms of fatigue damage. The material still remembers the big curb impact it took the day after the showroom floor. Depending on the material used a small 10% change in reversed loading can change the durability life expectancy of a component by an order of mangitude.

 

Keep in mind, that your data logger only shows global accelerations of the vehicle. The wheel end, suspension, subframes, etc. have to react the instantaneous accelerations when you chatter over the gators which can easily be over 10g. 

 

Turning down the idea of a properly designed reinforcement would suggest the problem is not understood. It saves everybody headache & Money. Nobody is forced to install these reinforcements if they don't want to. 


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#57
davew

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Davey, someone asked other than Spec Miata, I answered. Let's use you 8 weekends per year times 9 years equals 72 weekends on one car. Please don't be so selective with your data. :bigsquaregrin:

 

I still will do more races this month than KK has in 9 years. 


Dave Wheeler
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#58
Brandon

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Turning down the idea of a properly designed reinforcement would suggest the problem is not understood. It saves everybody headache & Money. Nobody is forced to install these reinforcements if they don't want to. 

 

Not specifically targeting you with my reply but this was a similar justification the SMAC referenced when approving the floor drop.

And every (nearly every) new build now has a dropped floor.

Same goes for the offset bushings - now every new build or replaced UCA gets the offset bushings.

 

About the only allowance in the past 2-3 years (from my recollection) that hasn't appeared to attain some form of critical mass in terms of a "must have" update is the allowance of the 1.6L front sway bar on NA1.8s and the Cusco LDS in the 1.6s. If you are racing a 1.6 competitively, you've got a Mazdacomp and judiciously maintain it and have a spare on the shelf should it fail. For the sway bar, we already have enough roll stiffness up front.

 

The position of "not being forced" to do something has never been a solid foundation to approve an allowance from my experience yet the pursuit of one from a safety perspective (see floor drop) seems to have a higher probability of being approved by the CRB.


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#59
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I still will do more races this month than KK has in 9 years. 

Damn Davey, what does this comment have to do with anything, your a friken race shop. I provided data and you want to argue the data. 


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#60
Erik Hardy

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The position of "not being forced" to do something has never been a solid foundation to approve an allowance from my experience yet the pursuit of one from a safety perspective (see floor drop) seems to have a higher probability of being approved by the CRB.

 

Well if you want the safety justification:

Cracked subframe can easily send the car into an undesirable direction and potentially you could up into a wall or hitting another competitor. At which point, you will wish the rules organizations would allow for improved component durability.

 

There is no performance advantage from installing subframe braces. If you race a lot or run on tracks with harsh curbings, it will save you money in the long run. 

 

Doubling up the material in know failure zones, eliminates the need to worry about a fatigue issue.

Stress = Force / Area

With the same force inputs, doubling up the area reduces the resultant stresses by half.

 

For Example - Lets say these cars see a peak load of 60ksi during a gator curb impact. When you double the material, the stress is now 30ksi. Look at the fully reversed (The -1 "o" curve), now all of a sudden you went from failing in 100k cycles to infinite fatigue life (<<<This is where you save money and headache) The subframes aren't 4130 but all steels have a similar shaped curve.

 

4130_SNcurve.jpg


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