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| xj750 Seca Hossack Front (and mono rear, bodywork, etc) |
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| bp:
Good project!! I've always been interested in motorcycle suspension, in fact my final project at college was titled "Motorcycle Suspension". So I'll be really interested to see how you get on....best of luck! cheers Bill |
| sebwiers:
So, things have been rolling along pretty well. Just don't get many hours in the shop, and was out all November with bronchitis, so its a slow burn of few hours over many weeks. As tends to happen with these projects, some of the work was premature. The pivot mountings I ended up building were not really compatible with the arm's I made. So now I have the fork bolted on with some new mock-up arms made from wood. :) |
| steampunkpete:
I haven't seen a set up like this before, and don't really understand the how it works. Weight transference is unavoidable, so how does the Hossack arrangement prevent or reduce dive under braking? How does the un-sprung weight compare with that of a telescopic fork? Answers on the back of a post-card please .... The hub centre steering (HCS) concept seemed to have a lot going for it, with the possible exception of the difficulty of achieving the same lock-to-lock angle as telescopic forks. The Earles forks as used by BMW also appealed as in both increased rigidity and reduced un-sprung weight. A particular problem with teles is their tendency to twist when braking (except when twin discs are fitted - I think this is why twin-disc conversion kits for Bonnevilles were so popular). |
| sebwiers:
--- Quote from: steampunkpete on January 06, 2015, 02:30:47 AM ---I haven't seen a set up like this before, and don't really understand the how it works. --- End quote --- It works pretty much like trailing parallel arms on a car would, only with the arms located above the wheel. Or, as Hossack describes it, like a pair of conventional A arms rotated 90 degrees. --- Quote from: steampunkpete ---Weight transference is unavoidable, so how does the Hossack arrangement prevent or reduce dive under braking? --- End quote --- The dive that it cancels it is the portion of brake force that normally goes into compressing front suspension. If you do a vector diagram overlayed on a conventional fork, its obvious that if you push back on the wheel (braking force), you also push it up (suspension compression). Because the Hossack (and other linkage designs) allow the wheel path to be nearly vertical (and the wheelbase constant), the resulting upwards vector component from braking force can be reduced to nearly 0. If the wheel path is such that the wheelbase actually gets longer, the resulting vector component actually opposes weight transfer. Hence, dive (even from weight transfer) is minimized. --- Quote from: steampunkpete ---How does the un-sprung weight compare with that of a telescopic fork? --- End quote --- For equal design & fabrication skill and cost, the Hossack is claimed to weight less. Mine probably has more unsprung mass than the fork the bike came with, but if I built a telescopic fork, it wouldn't be very light! Norman Hossack has built a Ducati that he claims has less upsprung mass less than stock, but I think the larger weight saving was in sprung mass; the design places less stress on the frame, because the lever arm is shorter. Another advantage is the it doesn't have issues with the sliders binding, so there isn't that variable force resisting the wheel motion. --- Quote from: steampunkpete ---The Earles forks as used by BMW also appealed as in both increased rigidity and reduced un-sprung weight. --- End quote --- Earles also offers the same potential for anti-dive. The early BMW's that ran sidecars had the fork set up so that you could move the pivot between two locations. One provided stronger anti-dive for when stopping the greater weight of a sidecar. Pivot based front suspensions are pretty much standard for sidehack rigs; tele's just dive way to much with all that weight. BMW also currently sells a Hossack design very much like the one I'm building, as the Duolever on thier K series bikes. Apparently the upright is on the heavy side, but they also use the same parts on all K models, including the behemoth 6 cylinders. |
| micktoon:
Hi sebwiers, I am not really into bikes that much but interesting projectcwell explained and nice fab plus welding. I look forward to seeing it develop. In response to the question you had of why .................... I think as lots of modders look at it ..............I have the gear to give it a go so its more a case of Why Not lol. Good luck with the build. Cheers Mick |
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