slowster wrote:...........
How about...
69deg 51mm offset
68.5 deg 51mm offset?
Thats a lot of trail.....getting into noticeable "wheel flop" territory, I suspect.
https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometryslowster wrote:Those are the figures for Salsa's [url=https://salsacycles.com/bikes/fargo/2020_fargo_apex_1Fargo drop bar MTB[/url]. They use the 69 degree HA throughout the range, except for the extra small frame, which has 68.5 degrees.
The medium size frame has a ~650mm front centre measurement, and using Pythagoras I calculate the front centre measurement for the extra small frame is ~614mm. Moreover the reach on the extra small is only 350mm, although I think that the relatively high stack of 594mm makes that figure somewhat deceptive (i.e. if it instead had a lower 558mm stack like the 50cm Elan, the reach would be longer, but crucially I presume still significantly less than the Elan's 380mm, and likewise for pretty much every other brands' bikes in that category).
Well, yeah. For Elan, I'm stuck with 45mm offset for a carbon fork, and not too far from 72 degrees for sensible steering. If you go longer offset and very much shallower head angle then you are obviously shooting for short top tube and toe clearance.....but I'm all out of fairy dust! ....to sprinkle over it to make the steering work.
slowster wrote: I suspect that the Fargo's steering geometry might be dependent upon very wide tyres (to offset a relatively low trail?), whereas the Elan and similar bikes are often marketed on the basis of being able to take narrower tyres for road use, e.g. 32mm. However, whenever I read owners' comments about that type of bike the focus almost always seems to be a) on how wide a tyre will fit, with 40mm being a minimum and many wanting to fit 47mm or even more, and then b) insufficient clearance for mudguards with the preferred width of tyre.
If suitable 50mm offset forks are starting to become available, I wonder if it would be worthwhile Spa getting a couple of prototype frames made for an Elan style bike, but copying the Fargo geometry for the medium and extra small sizes, and then seeing what you and the other test riders make of them.
Well, Fargo is high trail. You can get used to all sorts of steering feel; but the steering feel is imparted by (1) tyre drag....thats the force which is trying to keep the steering centred; and (2) trail....thats the lever through which tyre drag acts. So I would think that if you fit a big draggy tyre, then you need short trail to counterbalance it and get the steering back to "neutral" ....shades of Jan Heine with short trail and fat tyres.
It would be much cheaper and quicker to just buy a Fargo and see how it rides?
One reason I got a Longitude was to try the steering, before I even think about wishing it on paying customers. Longitude is 68deg 50mm offset. Thats "modern" mountain bike geometry....to get the front wheel way out in front, so you don't take a header over the front end. Designed to be ridden with flat bars and a very short stem, I will be riding it with bullbars because I don't have a choice. I'm fascinated that "modern" mountain bike geometry is all going for high trail/slack angles, but "Gravel" bikes seem to be sticking with "road" steering geometry. I'm assuming that my Longitude (when I finally get it built) will be very stable on stony tracks; as I get older and slower, a major problem I have is the front wheel getting bumped off line and being unable to recover.
Don't get me wrong, I love my Elan; but if I'm brutally honest, I prefer the steering on stuff like Spa's Tourer (and roughstuff) and Wayfarer.
45mm offset is classically paired to 72 deg head angle, to give fairly bright steering on narrow tyres; you can slalom the cats' eyes no hands, but for me its too easily deflected by random inputs like wind or camber, or me not looking where I'm going. Half a degree shallower just makes it a bit more forgiving of the random inputs, but its just fractionally less sweet steering....its impossible to explain; the Tourers just go where I want seamlessly, apparently requiring no input from me at all. My daughter talks about riding her favourite pony (now too old) where she just thinks "canter" and they would canter.....whereas with a different pony she has to remember to actually ask for canter using her hands and feet (or whatever they do).
I suspect I may be a bit on the fussy side regarding steering geometry. I also suspect people are more influenced by fashions in tyre size than by any objective need. I have done most of my roughstuff on nothing bigger than 35mm original Marathons with the kevlar, and plenty on 28mm tyres. I have some 47mm tyres now, but I still can't ride stuff on them which I used to ride on 28s. Ho hum! I mainly use just one size up (40mm) to compensate for deteriorating vision and reflexes.