Kingfish
100 MW
Greetings –
Thus begins another design-build thread. The goals are:
Tight fit for a 2.50-24 Hookworm; About 5 mm between the tire and the frame.
Let’s discuss the issues in detail:
Discoveries
In the process of doing the layout I came across an artifact of the bikes’ design that I suppose is common though nary a word is spent on it. Ever look at the alignment of the rear tire with the centerline of the bike frame – and notice it’s off by ½ inch or more? I guess if you run skinny tires you wouldn’t see it, but with phatties we have to dish the tire a bit more towards the center of the gap. On MtBs, just after the chainring, the gap opens up more. I just thought that was odd, and I’m thinking this could be an opportunity to slew the crank to port by 5mm or more; in my case I moved it to starboard by 10 mm to accommodate the 53T Campy. Anyways – could be an opportunity to fix another pesky problem.
No drawings to show. Just ruminations as I progress through the layout and plan for the next upgrade to facilitate better trailering… and ultimately a better xCountry experience.
More as the designs advance. KF
Thus begins another design-build thread. The goals are:
- Enhance the convenience of trailering through quicker connect/disconnect without affecting motor alignment. Essentially, create a separate attachment point slightly rearward from the motor axle.
- Expand the frame width to allow wider tires such as DOT-rated 3.0-18.
- Better torque arm integration.
- Horizontal Rear Dropouts with chain tensioning ala BMX and motorcycle design.
- Allow for kickstand attachment using common off-the-shelf components.
Tight fit for a 2.50-24 Hookworm; About 5 mm between the tire and the frame.
Let’s discuss the issues in detail:
- Create a new attachment point for the trailer. On The Road in 2011, the original design of my trailer was for a pusher, and the connection point was on the bike rear axle using a standard freehub. This design didn’t work out and I made some fast changes and put the motor on the bike instead – thus creating the 2WD. Problems followed because I could never tighten down the axle nuts well enough to allow the trailer to pivot and keep the wheel locked in place; every day I had to tighten the nuts. PITA as you could imagine. The new design eliminates the problem altogether by creating a separate attachment point a few fingers back from the axle where it can live in blissful harmony. In doing so we create a slightly longer trailering wheelbase which is fine for high-speed handing, though we also add slightly more handling problems in high-wind where the tail could wage the dog; I think that’s less of an issue than having a wheel wobble out of alignment on a daily basis.
- Expanding the suspension framework to accommodate a wider tire opens up better selection of DOT-rated tires which are tougher and better balanced than bicycle tires. At the speeds I travel with the xCountry loads I’m under it just makes better sense. Presently I’m using 2.50-24 2-Ply Hookworms which aren’t made anymore, and figure I have one season left on them. Not worth expanding the frame for 2.75, so might as well take a stab at something bigger. My suspension is a complex six-part linkage which allows the rear upper/lower to float almost directly up and down as opposed to pivoting on a cantilever like most motorcycles. Costs too much to replace the entire frame; if I did that – might as well do a custom, but I’m not there yet. Material-wise it’s cheaper to replace the lower suspension frame where the pinch-point occurs and move the axle back a bit to allow a wider tire. Advantages are slightly longer wheelbase which enhances higher speed stability, though at the cost of slightly less turning radius. We also have the option of lowering the center of the bike up to an inch (easier to let a picture explain it), but as it is this is one of the tallest medium-sized bikes on the planet and I’m on my toes at a stoplight, so a small win here for short people.
The lower rear suspension framework attaches at the pivot below the reddish link. Notice it drops about an inch here. Only reason I can fathom for it is to give the chainring more clearance.
- I have two torque arms, both are custom adaptations. They work fine, though I can craft a better design based upon the desire to have horizontal dropouts.
- I prefer horizontal dropouts over vertical after my experiences On The Road with wheel wobble and alignment. I like the way BMX and motorcycles apply chain tensioning; it takes the guesswork right out of the equation. There are some disadvantages such as it’s more difficult to de-chain with the added complexity, however we’re locked in place and I think the solution I came up with solves that and the torque arm in one.
- A kickstand for my ride would be more convenient than trying to find a place to lean against. My frame just doesn’t have a way to make that happen. Although if I move the axle back an inch or so to accommodate a wider tire then an area for a traditional mount opens up, and well – pretty cheap to add one more hole; not quite free by design, though pretty close.
Discoveries
In the process of doing the layout I came across an artifact of the bikes’ design that I suppose is common though nary a word is spent on it. Ever look at the alignment of the rear tire with the centerline of the bike frame – and notice it’s off by ½ inch or more? I guess if you run skinny tires you wouldn’t see it, but with phatties we have to dish the tire a bit more towards the center of the gap. On MtBs, just after the chainring, the gap opens up more. I just thought that was odd, and I’m thinking this could be an opportunity to slew the crank to port by 5mm or more; in my case I moved it to starboard by 10 mm to accommodate the 53T Campy. Anyways – could be an opportunity to fix another pesky problem.
No drawings to show. Just ruminations as I progress through the layout and plan for the next upgrade to facilitate better trailering… and ultimately a better xCountry experience.
More as the designs advance. KF
