this post was submitted on 10 Jun 2024
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bike wrench

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A place to ask bicycle repair questions, and for bike shop monkeys to share advanced non commercial wrenching resources (no YouTube self promotion). This is only for repair related topics.

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submitted 3 weeks ago* (last edited 3 weeks ago) by evasync to c/bikewrench
 

Any brands that sell a rack like the one in the picture? (Edit: what i like from this rack is the mounting points on the frame that will result in a more comfortable ride than carrying the weight on the handlebars or fork))

If not do you recommend someone that can make this without breaking the bank? (I grew up in an agricultural area and there were a lot of folks that could weld something like that for a small fee - but some people online are charging 300+ for this, which is insane)

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[–] j4k3 4 points 3 weeks ago (1 children)

I think that is something someone made themselves. The mounting holes for the basket are most telling. I've never seen anything like that.

I'm very skeptical of this as well. If that basket is loaded heavily. it is likely going to cause problems with steering due to trail and rake dynamics against leverage forces altering the center of gravity overall.

[–] [email protected] 3 points 3 weeks ago* (last edited 3 weeks ago) (1 children)

One of the things I really like about bicycles is that they really push one's understanding of dynamics. For an automobile, putting a heavy load ahead of the front axle, or behind the rear axle, tends to reduce stability. The cure for that would be to distribute the load evenly, front to back. So a heavy load (eg an engine) in the front can be countered with a load in the back, acting like a seesaw.

But that same trick doesn't guarantee success for loading a bicycle, because bikes need front-to-back stability in addition to roll stability. This arises because when turning, bikes have to bank to one side while also turning. To use aircraft terminology, there is a coupling between the roll and yaw axis.

Ships use a keel to independently stabilize the roll axis, but bikes can't just stick a keel into the ground, so must rely on tire resistance, which is coupled to the steering direction. What this means is that for some ways of loading a bicycle, it may genuinely end up being unrideable at any speed, in any direction.

The simplistic rules for land vehicle stability are to keep loads within the wheelbase, and preferring closeness to the axle's height, with the peak height at the exact middle of the wheelbase. For a standard bicycle, the rider is the biggest load and is positioned optimally per these rules; history shows that some really tall bikes work just fine.

A man on a tall bicycle in rural New Zealand, 1949

[–] j4k3 4 points 3 weeks ago (1 children)

The one I like to mention to really twist someone's mind on this subject is that, when leaning, you're actually counter steering the opposite direction. Then, in a controlled safe place I tell them to try and turn at speed while consciously weighting the outside pedal in the down position while intentionally pressing down with force to weight the inside drop. This is how you turn as fast and tight as possible. Anyone that does not know this will have a major lightbulb moment when they suddenly learn such a pronounced fundamental handling principal that is not part of the intuitive natural learning process.

[–] [email protected] 2 points 3 weeks ago (1 children)

Why does the outside petal need to be down?

...pressing down with force to weight the inside drop.

To make sure I understand you, you're saying apply your weight on the inside of the turn,

[–] j4k3 2 points 3 weeks ago (1 children)

It is the logical pedal configuration for clearance. So inside (of turn) pedal high; outside pedal low. Putting your weight on the outside, means just add a little bit of conscious effort and force into the foot on the outside. Likewise, just think about your hand on the inside of the turn and press down consciously, it doesn't take much.

Practice this in an area where you will not hit the inside of the turn and crash; somewhere open, like a parking lot. It may surprise you at how much faster you can turn at speed. Please don't let yourself get hurt learning this. I've seen it happen before.

This is a CAT 4 level amateur racing skill for being in tight quarters racing at full race speed. It is the key to not losing all of your speed in much tighter turns.

[–] [email protected] 2 points 2 weeks ago

Thanks I'll try this with a helmet and gloves