Quick question... and whilst I may (albeit probably not) sound as though I know what I'm talking about, I really don't. Please keep that in mind.
I presume you felt full sus would have been better on that one occasion for the usual reasons. My question, however, relates more to geometry.
I imagine your KTM geometry is more XC oriented with a fairly steep head angle (say 70*), whereas your full sus will have a slacker head angle (say 67*). Do you notice the difference? For example, on a steep descent or on a drop off, do you feel the front wheel of the hardtail is 'under' you a little vs. 'in front' of you a little on the full sus leaving you more vulnerable to being exited from your chariot over the handlebars?
There's a drop off that I feel confident flying off on my current 29er full sus that I felt very weary of on my old (non-eMTB) 26" XC hardtail. Never thought about it until recently... is it the geometry (slack vs steep head angle), wheel size (29" vs 26"), something else, that contributes to that increased confidence.
I'm hopefully demoing a plus size hardtail this weekend which is more trail oriented with 67* head angle, so I'll be interested to compare.
This probably isn't going to be the answer that you are looking for, but to be honest, I just get on the bike and ride it, and give no thought to the geometry of either bike. The two things that make a difference to me are tyres that have an aggressive edge pattern to the tread, and the recent addition of the dropper seat post to both bikes. I need to change the tyres on the had tail to something like Hutchinson Toros, that still offer reasonable rolling, but also have a decent side edge, which is something very desirable when riding the very narrow and rutted local terrain.
At the organised mtb bike shop ride a couple of weeks ago, I was out with a group who predominantly ride down hill. A couple of the lads were saying that I should do this, do that, and switch to a short stem.
I didn't say anything at the time, but I thought what utter ******. People, example above with SW, read far too much into what they see on the internet, or in magazines and get sucked in. I even often wonder how many it through their childhood days. Don't know about anyone else, but I just rode whatever we made or found at the dump. None of us are pro riders, and none of us would really know a good from bad set up.
My point being that yes a shorter stem would mean that I am in a potentially better position to ride down hill, but if those lads on that ride had stopped to think about it a bit more, I had never ridden down hill as such before, was riding a bike with considerably less suspension travel, and no short stem, but in the scheme of things I wasn't exactly too far behind them by the end of each run.
Of more importance is something that they and SW are missing the point of, and that is what the purpose of an eMTB actually is. Surely the first and most important point, is that eMTB is designed to make climbing easier, and hopefully if desired, faster as well. By shortening the stem as suggested, you are having the opposite effect of what is desired. The bulk of my riding involves climbing, and more often than not, there is at least one climb per ride that is always very debatable about whether or not you can make it to the top. Sometimes these climbs are just metres long, sometimes they are hundreds of metres long. I realise that SW only rides on canal towpaths and public pavements, so all that I have just said about him is rubbish anyway.
I really can't say that I have yet really noticed any major difference between the two bikes, both do the job, but what I really prefer about the hardtail, is how connected and solid that everything feels. It is seemingly tighter and neater to ride, hopping over things is a doddle, it's lighter, and the rigid back end makes climbing so much better with zero squat, and I love the idea of no maintenance to the rear end. Riding the FS bike last night, didn't give me the same buzz.
Thinking about it again, there were actually two occasions that I would have preferred the FS bike on the recent South Downs ride. Once when going down a long descent across a field that had previously been used to graze cattle in, and the constant dip into the now hardened hoof prints marks, wasn't exactly comfortable. The second time was going down a long chalk track that had loads of small drops/steps.
Sorry that my reply wasn't perhaps what you were looking for, but as said, I just get on and ride.
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