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Hossack Motorcycle Front End
bp:
I calculated the braking load by doing a series of timed stops from various speeds, 30kph, 60kph, 100kph etc on a quiet, smooth, well surfaced (grippy) bit of road. The tests were done front brake only, rear brake only, both brakes together. They established that the old wives tale about the front brake doing 75% of the work is about right (mine came out at 81%). The tests also pretty much wore out the front disc and the front tyre, I also learn't how to do "stoppies"!!
I've just had a look at the paper and yes 6.5g is crazy, I measured the maximum deceleration as -6.85m/s2, somehow in my head, the "m/s2" became "g" over the last twenty years!! Sorry about that.
I can second the recommendation for Tony Foales book, really well worth having a hunt around for. I've just had a look at his web site, good stuff there too!!
cheers
bp
sebwiers:
No need to hunt - amazon has it, as does his website. The CD PDF version is about half the cost (for me) and I have a couple tablets, so I'll go that route.
Brake loading calculation sounds pretty basic - I should have considered something so simple. I think I'll just use the "60-0 deceleration" figures from the service manual, rather than burn out my brakes and tire. :) Probably better than I could mange anyhow - they've got pro test pilots for that stuff. I'll assume 100% work by front brakes, for margin of safety and because the bike has MUCH better front than rear brakes (dual disk front w/ anti dive circuit, rear drum w/ shaft drive).
Claim is 60-0 mph in 150 feet when "lightly loaded". Curb weight is ~530 lbs, and most test pilots are smaller dudes, so I think 700lbs is a fair call.
Converting to metric so the math is sane, that's gonna take the same (or less) force needed to haul 320 kg (round up) down from 26.6 m/s (round down) in a distance of 43m (round down).
Looks like it took 3.3s for the test pilot to stop from 60 mph (26.6m/s) - a reasonable figure. That's an acceleration of 8.1m/ss
Given 320kg, how much force would that take? 2600 newtons, or ~585 lbs. I'd been guessing a "typical" brake loading of 500lbs, and shooting for each leg to be able to repeatedly take 1000lbs without issue (at less than half yield strength). I think given the horrors I've seen when cargo bikes with disk brakes fold their forks (and the fact I have no real way of knowing where local stress will shoot above norm) that the safety margin of 8 this would provide is easily justified.
j_e_f_f_williams:
Hello,
Coming a tad late but thought I would pass along. There is an e-mail list that both Chris C (it is a hossack) and Tony belong to as well as many other great resources for motorcycle knowledge (Ian Drysdale, Marty & 2 wheel drive dirt bikes, David Sanchez & his Moto2 bike etc)
MC-Chassis list - details @ http://eurospares.com/maillist.htm
I seem to remember some discussions on loads for suspension and braking a while back and it will be in the archives of the list
Jeff
sebwiers:
Yup - fella on another forum pointed me the same way. It's been moderately useful, probably will be more so once I have photos to post. Which means they can tell me what I've done wrong, but nobody is really saying what to do to get it right (other than buy Tony's software, which is probably a good move, just not in the budget quite yet).
j_e_f_f_williams:
So you are the 7" travel Hossack? (
I used to use SolidWorks and actually found it was just as good as Tony's SW (I also have) if you set things up correctly. I used it to create drawings for my Foale/Parker type front end. I stopped using Solid Works and moved to Alibre as then I was legal :) Alibre I didn't find as good for making dynamic changes to my 3D and seeing the results in the 2D drawing where my % anti-dive etc are. This is when I started to work with Tony's SW as well.
I think you got the answers you got because your general question was "Is that OK?" and the answer generally on MC-Chassis list is "yes, it's OK if that's what you were trying for" :) I assume 7" travel = off-road so I would listen to Marty's comment that large bumps don't like the lengthening wheelbase. Also I don't know enough about off-road to comment on anti-dive. I had on-road have 50% to 75% anti-dive through the range of travel.
The hard part, as Tony pointed out, is to figure out the dive and trail you want. I noodled over it for hours and at the end of the day you really won't know until you try it. I probably noodled too long and should have spent those extra hours welding vs in Solid Works :)
My FFE never got built as my project time quickly disappeared and changed as I had kids :) Keep thinking I should return to it some time soon...
TTYL, Jeff
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