Hardtop or Soft-top for track days?

[murph]

Hey guys,

Just wondering what people's thoughts are on using hard vs soft tops for track days, particularly at a track such as Phillip Island with lots of high speed areas.
I have an NA6, and the hard top adds quite a bit of weight for a track day because in order to stay in my class, and also enjoy the car for other purposes, I keep the soft top in the car aswell.

I've heard that running with soft top up creates more wind drag - I know with the top down is a LOT slower, but would have thought the soft top and hard top were fairly comparable in terms of aerodynamics.
I also get a lot of wind noise through my hard top, where the soft top seals a lot better, plus it gives me the bonus of being able to drive home from the track with the roof down

Anybody got experience running both - whats your thoughts? Did you notice much of a difference?

[Lokiel]

Based on weight alone, I'd recommend using the hard top only if you remove the soft top.

[Guran]

A while ago I compared my times and maximum speeds for soft-top vs hardtop, and the hardtop seemed to be a little quicker. However, that was comparing different days and I'm not convinced of the result. In the interests of good science, next time I visit the track, I'll lug along my hardtop and try running in both configurations: hardtop vs soft-top. To be honest, I don't think there's much in it. But like you, I like to drive down & back with the roof dropped, so my hardtop is gathering dust in the garage!

[SIB]

I know Guran has done some science on this and I have been tossing this up too. In theory, less weight and lower centre of gravity will favour softtop, which on a circuit like Wakefield may outweigh slightly higher vmax on the straight. I have been running hardtop for added stiffness and dubious rollover protection, but am thinking about softtop only next trackday. Given Guran has done both and chooses softtop in standard class, I suspect there is your answer.

[greenMachine]

Softtop, for weight/cg reasons. I doubt that the slightly different profiles would have any material impact on laptimes, but perhaps Guran will prove me wrong!

[murph]

I think I'll give the soft top a run this weekend at phillip island and see how it goes.....if nothing else it will make the trip there and back much more enjoyable!

[Jeo]

I have been running hardtop for added stiffness and dubious rollover protection, but am thinking about softtop only next trackday.

If you think the hardtop is dubious for rollover protection, I'd be looking very closely at the suppsoed benefits of any additional stiffness.

[16bit]

only stiffness you will get will be if you have bolted plates instead of the latches.

[Lokiel]

only stiffness you will get will be if you have bolted plates instead of the latches.

I disagree. Prior to fitting my roll bar, the chassis felt firmer with the hartop+latches.

[Guran]

I know Guran has done some science on this and I have been tossing this up too. In theory, less weight and lower centre of gravity will favour softtop, which on a circuit like Wakefield may outweigh slightly higher vmax on the straight. I have been running hardtop for added stiffness and dubious rollover protection, but am thinking about softtop only next trackday. Given Guran has done both and chooses softtop in standard class, I suspect there is your answer.

I think this is the bit you might be thinking of ...

viewtopic.php?p=514755#p514755

I also discovered that my Vmax on the main straight is typically about 3km/hr quicker with the hardtop fitted compared to the roof down. FYI here's the breakdown:

soft-top down - 142.4km/hr
soft-top up - 143.9km/hr
hardtop (with soft-top fitted) - 145.3km/hr

That was a couple years ago and my PB has improved by a whole second since then. I'm now much closer to the limits of the car, and more consistently able to find the best laptime for the conditions. Additionally, that Vmax with the hardtop was from a different day and may well have been affected by different conditions. Ideally, I would prefer to try all three variations on the same day. I just need to take my hardtop down to the next club trackday. All in the name of good science! However, I don't think there's any question that driving with a roof (soft or hard) is quicker than with the hood dropped.

[Guran]

only stiffness you will get will be if you have bolted plates instead of the latches.

I disagree. Prior to fitting my roll bar, the chassis felt firmer with the hartop+latches.

http://forum.miata.net/vb/showpost.php? ... stcount=14

Like the soft top, the hardtop is an unstressed component. If the hardtop were carrying structural loads, the rear window would pop out of its mountings as the bodystructure flexed by any degree.

The top is able to dampen (slightly) some of the lateral movement of the windscreen header, but the primary reason behind this is that with the top up the visual contrast between header and sky is diminished. With the convertible top raised, the multi-component aspects of the top induce rattles which the single-piece hardtop doesn't have, thereby creating the impression that the hardtop has stiffened the car vis-a-vis the erected convertible top or with the top down.

The car's torsional rigidity was measured in all three planes (as a body-in-white as well as a completed car) with the top down, top up and the hardtop on and there were no appreciable differences in the figures.

I don't question that it may feel stiffer, but this is much more an example of the placebo effect than one actually reducing the bending moment of the car, I'm afraid.

bwob

[lightyear]

At phillip island the car is 2 seconds slower with the roof down (I have data to prove it). The hardtop adds too much weight to be able to make up any aero advantage. To get the fastest laptimes - remove the softtop and add a lightweight hardtop. You get a lighter car and all the aero advantage of the hardtop. So the cheapest - vs - fastest option is just to leave the softtop up. And the ultimate fastest is also the most expensive as usual. I will get some data at phillip island next year with the softtop up - vs - with it removed and a carbon fibre hardtop installed. It will be interesting to see how much difference it will make.

[murph]

so from the sounds of it, there is concensus I'm no worse of running a soft top than a hard top with the soft top still on the car. ie any wind drag created by soft top would be minimal, and probably offset by the weight saving of not having a hardtop & soft top combo....

Lightyear - agree a CF hardtop with soft top removed would be ideal, but then I loose the daily functionality of roof up or down, which I like.....and also more money which I dont like

Guran - I think the only truely scientific way to test as you say is 2 runs one after the other same day same conditions, and see how it reacts.... straight line speed would really be the only difference I could think off given I've got a BD rollbar which does a pretty good job of bracing....

[oztrackdays]

Very practical on a race car at least.

Maximum weight advantage I have ditched the clips as well literally dozens of grams saved there.

I can't see there is all that much drag I suppose the roll cage and no roof is a little more disruptive to the air.

[zossy1]

I think basically all the Spec Miata racers in the States run hardtops - and it's not because they have to.

That's OEM hard tops mind you. But they do remove their soft tops to save weight.

The aero advantage is significant. At a track like Wakefield it won't make as much difference, but at a track with a longer straight...