27 replies to this topic

[exitspeed]

Hi Everybody,

 

New to this forum and the SM community. I just purchased a 1990 donor car that I'll be building into a SM over the winter.

 

I have a question re the required hardtop. I found a manufacturer of light weight hardtops and for a race car this makes a lot of sense, but it appears that the hardtop is no longer required. The SCCA spec 9.1.7.6e indicates that it is now optional and I can find no mention of it in the NASA spec (probably me).

 

So, if you choose to run a hardtop does it have to be a Mazda Factory unit? Now that the hardtop is optional, are a lot of guys going topless? It must be nice to lose the weight from up top, but a hardtop should improve aerodynamics and increase safety.

 

Thanks in advance!

 

 

 

[Neil O]

Pretty sure it needs to be the factory hardtop & you will want one.  Aero (speed) you get is WAY more important than the weight saved.

[LarryKing]

Hardtop always was optional. Yes, it needs to be an OEM top for SCCA. I think NASA permits aftermarket tops as long as they are equivalent (not certain of this).

 

Maybe we should let the 1.6 cars use the lightweight top. (Sorry, couldn't stop myself)

[Ron Alan]

I seem to remember the Snug top brand being ok'd a little while back?

[DCP]

NASA spec rule is 8.1.2. "Aftermarket hard tops are allowed provided they meet the exact original equipment specifications for both design and weight"

[James York]

I seem to remember the Snug top brand being ok'd a little while back?

Not in SCCA.  This has been asked before.  Mazda top only, no provisions for substitutes.

[RussMcB]

A hard top is optional.  I ran topless at Barber (with arm restraints).

 

I'm totally convinced that running a hard top is faster.  Not because I've done back to back testing, or because I was noticeably slower than others, but because I have NEVER seen anyone race topless at an SCCA event in decades, even though they could.

 

I'll have mine installed for the ARRC next week.  Might consider running without it for the ARRC Fun Race on Sunday.

[steveracer]

RTFR...

 

Read the F'n rules!

 

There was a guy racing here in SoWDiv without a top several years ago.

 

He was slow, though I can't say it was only from running topless.

[Jaime Florence]

I think the aero effect (if it hurts or not) will depend on the track configuration.  I tested a car with/without the top back to back at Thunderhill and saw zero difference in lap time.  It sure felt a lot faster!  However, even though it's just a little bit of flimsy fiber glass, I felt much more vulnerable without the top.

 

Given that I couldn't prove any gain or loss in laptime...I'm not sure the weight or the aero effect is signiificant enought to matter much...at Thunderhill.

 

Just my thought.

[FTodaro]

I like the added safety of running with a top, you ever see the size of the rocks at the exit of 5 at Atlanta, [ARRC]

[Sean - MiataCage]

Keep in mind that the cage rules change slightly for an "Open Top" car versus a "Closed Car".  From the GCR:

 

"On open cars retaining the windshield frame the main hoop must be full height for the entire width of the hoop. The top of the main hoop must be at least 2 inches above the driver’s helmet as illustrated in figure 11."

 

From the SMCS:

 

"Convertible tops and attaching hardware shall be completely removed. Cars may compete with the Mazda factory detach- able hard top in place (latches shall be replaced with positive fasteners), but it is not mandatory. When no top is used, driver shall wear arm restraints, and the cage will meet the helmet clearance rule. It is allowed to attach the hard top to the upper windshield bar of the roll cage."

 

In these small cars depending on your seating position, seat slider, torso height etc, it could be difficult to have your helmet be 2" beneath the main hoop.

 

I am not arguing for or against that rule or what is right or wrong, just simply pointing out the rule.  

 

Now.... Since it is silly season......  

 

Running with no rear glass is probably the best of both worlds.... Good external aero and a place for the air that does get inside the cockpit to escape with the rear glass removed.  This happened at the NASA Nationals and there was talk of a 100lb penalty for the car with the busted rear glass to run that way.  The glass was not there do to an impact, not trying for a competitive advantage but when I heard about it, I told NASA I would trade 100lbs for no rear glass all day long.  They ultimately decided not to let the car run without the rear glass and the driver borrowed some rear glass from a busted car from earlier in the week.

 

I personally believe the rules to preclude one from doing it, but I'm surprised someone hasn't tried it yet based on some of the other interesting rules interpretations on things like exhaust and radiators in years past.

 

Sean

[James York]

......  However, even though it's just a little bit of flimsy fiber glass, I felt much more vulnerable without the top.

 

 

You would be surprised.  I once saw a SM flop to its lid on the concrete after performing a pirouette off a tire barrier and the top was only scratched.

[James York]

 

Running with no rear glass is probably the best of both worlds....

 

....I personally believe the rules to preclude one from doing it, but I'm surprised someone hasn't tried it yet based on some of the other interesting rules interpretations on things like exhaust and radiators in years past.

 

Sean

That's too obvious.  Instead they try the floating hardtop approach.....

[Keith Novak]

 

 

Running with no rear glass is probably the best of both worlds.... Good external aero and a place for the air that does get inside the cockpit to escape with the rear glass removed. 

It would be interesting to know if it really is more or less aero.  A pickup truck is actually more slippery with the tailgate up as opposed to down.  With the tailgate up, a bubble of pressure buillds up behind the cab and helps the moving air flow over the truck with less turbulence.  The rear glass could do the same thing in a miata and cause more air to flow over the car as opposed to through all the cockpit clutter causing more drag.  After all, it's not windy in the car at 100mph. 

[Sean - MiataCage]

It would be interesting to know if it really is more or less aero.  A pickup truck is actually more slippery with the tailgate up as opposed to down.  With the tailgate up, a bubble of pressure buillds up behind the cab and helps the moving air flow over the truck with less turbulence.  The rear glass could do the same thing in a miata and cause more air to flow over the car as opposed to through all the cockpit clutter causing more drag.  After all, it's not windy in the car at 100mph. 

The data showed it was faster at the end of the Miller front straight.

[Kyle Keenan]

It would be interesting to know if it really is more or less aero.  A pickup truck is actually more slippery with the tailgate up as opposed to down.  With the tailgate up, a bubble of pressure buillds up behind the cab and helps the moving air flow over the truck with less turbulence.  The rear glass could do the same thing in a miata and cause more air to flow over the car as opposed to through all the cockpit clutter causing more drag.  After all, it's not windy in the car at 100mph. 

I know Sean has tested it, but IIRC Bockman did it at Portland with chicane and saw 4mph more (With Top On) straight speed at the end of the straight. I've been wanting to pull my top off for an STL race for a while now.

[LarryKing]

 

That's too obvious.  Instead they try the floating hardtop approach.....

 

Seen that before.

 

I guess wind-tunnel tuning in SM will be the next raise of the bar. What am I thinking - probably already being done.

 

[Caveman-kwebb99]

Seen that before.

 

I guess wind-tunnel tuning  probably already being done.

 

Ya think???

[pat slattery]

If running without a top were faster, there would be many running that way, sort of like how one model of car is picked over the other. 

[Sean - MiataCage]

I know Sean has tested it, but IIRC Bockman did it at Portland with chicane and saw 4mph more straight speed at the end of the straight. I've been wanting to pull my top off for an STL race for a while now.

The 4mph gain was with the top on versus off. Top=faster.