Please, excuse me to post in English. I wouldn't express all that in german.
Classicals are intended for nylon strings. With a regular scale length (mensur) nylon strings tension use to be around 40,5 Kg. Strung with light steel strings .011-.047 this will be around 63 Kg, wich is about a 50% more. This uses to be too much for top's integrity. But there are alternatives to use steel strings in lightly braced acoustics like classicals and most parlors. One typical option is using Silk and Steel strings. They give a nice sweet tone in-between regular broze wound strings and nylons due to the silk or nylon wrap around the steel core and the silverplated copper wound. The tension of these strings (.011-.047) use to be around 55 kg in standard tuning. Depending on particular guitars this could be an aceptable load. Anyway I like to tune parlors two steps down, because the soundbox use to resonate best this way in most cases. So strings tension will be more than adecuate and safe for guitar structural integrity. Specially on old guitars.
There is another really good alternative if you like the sound of Phosphor bronze strings.
Newtone Strings is offering the "Heritage Series" intended for parlors and old guitars needing fairly low tension. And that's not all, they are of great quality and sound superb. One of the best strings I,ve ever tried. Their gauges and cores/wound ratios are selected for even tension from string to string. This is really good, because you get a really even and balanced guitar this way. They're available in .011-.047 @ 51,7 Kg. (They use to be perfect on old parlors) and .010-.043 @ 42,5 Kg. Just perfect for nylon strings guitars under regular standard tuning.
There's an usual belief that acoustics should use heavy gauges to get good volume and punchy lo-end response. Well, this is because most guitars on the market are X-braced and heavily built Dreadnoughts and Jumbos. Ladder and fan braced light built guitars play in other league. They were designed for low tension and don't need heavy gauges to resonate at their maximum. In fact we can destroy them using heavy gauges on them. I've seen too many old parlors over there with symptom of this mistake and show badly bowed necks and stress cracks on the top near the bridge area and parallel to the fretboard extension. String gauges must be chosen conciously for every particular guitar and tuning.
Check the
D'Addario Website. They offer string tension charts showing the tension for a particular gauge tuned to different pitches. This is really helpful to choose the perfect gauges for every guitar and alternative tunings under good and safe margins.
D'addario Strings Tension Chart
Hope this helps.
GruÃ.
