If There Are 36 Spokes In A Bicycle

[Alix Stocking]

Yesterdays post about Zipp's new 303 S wheels was a pretty popular topic. The amazing thing is that you can't even find news about them on cycling media sites this morning. The news cycle moves that fast. Campganolo released some very expensive very deep wheels, Specialized released their new Diverge, and Mavic was placed into receivership. We'll no doubt take a look at that in a bit more depth, but first we have to cop to some blame for that; our lukewarm review and subsequent cancellation of their Open Pro rims was clearly the killer there. And then the normal Zwift racing news (which Mike and I just can not get on board with - more on that later, too) and a sporty new tire or two and 303 gets moved to page 2.

So, as the world moves inexorably to disc brakes, offset rims become an easier thing to justify from a production stand point if you want to. Flip an offset front rim around and like magic it's an offset rear rim now. You don't need to make a separate "normal" rim for the front and an offset rim for the rear. Which gets us to the question of "if we can, does that mean we should?" And that answer depends.

To start with, offset rims do one thing: they equalize tension between the spokes on each side of the wheel. This makes it less likely that the lower tension side spokes will go slack, fatigue, and eventually break. That's all. I posit that this is more important in mass produced wheels, as we take great pains to ensure that all spokes are as equally loaded as possible. The extra minutes we spend "cleaning up" the build, transferring tension from tighter spokes to their less tensioned neighbors, really seems to bear fruit, and it's something that wheel building machines are just poor at.

They do not create stiffer wheels. To do that, you would have to increase the overall bracing angle (angle of the spoke between the hub flange and the rim). Using a 590 ERD rim (similar to HED Belgium+ or Boyd Altamont Lite) and a WI CLD front hub, with 28 spokes, the total bracing angle is 11.2 degrees - 4.5 on the disc side and 6.7 on the drive side. Offsetting the rim 3mm, we still get an 11.2 degree total bracing angle, only now it's 5.1 degrees on the disc side and 6.1 degrees on the drive side. Tension ratio goes from 67% with the non-offset rim to 84% on the offset rim.

If we go to a deeper rim with an ERD of 550 (similar to an All Road 38 or RCG) the tension ratio stays about the same (it rounds down to 83% for the offset rim and stays 67% on the non-offset rim), but the total bracing angle moves up to 12.2 degrees. This splits as 4.8/7.3 on the non-offset rim and 5.5/6.5 on the offset rim. A whole degree of bracing angle, or just shy of a 10% increase in bracing angle, makes a bit of a difference. This is part of how ERD influences our spoke count calculus that we talked about the other day.

As we discussed when we talked about rim compression (same link as above - the spoke count post), shallower rims which have higher ERDs are likely to compress more and lose more spoke tension as a result. This makes whatever spoke tension you have on the "off" side more precious. That's simply why offset rims are a bit more attractive on shallower rims. With deep rims, you very often run into funky spoke hole angle things, and it gets tough for the nipples to "seat" properly into the rim bed. The rim has to be nearly perfectly molded to avoid that. And since we keep more of the spoke tension we start with in deeper rims, we're willing to make fewer sacrifices to preserve it.

White Industries chose to go offset with the G25A, RaceFace uses an offset for the ARC25, and Astral has an offset on the Wanderlust. These are all appropriate applications of offset. The Wanderlust has the smallest ERD of all of these, and that's 596. HED chose not to use an offset on the Eroica, which has a 592 ERD. The offset is a fine tool when it's used in the right application, but it's by no means a silver bullet. You can build good wheels with offset and without.

After 8 straight weeks of posting every weekday, we are likely going to a bit more of a normal posting schedule next week. This has been fun and super challenging, and we appreciate all the readership and comments. We're now at a point where quality will likely suffer in the service of quantity, and no one wants that. Also we've used literally every photo we have (most of them 7 or 8 times), so we need to go take some more.

I have a wheelchair with a motor in each wheels and I want to fit fat bike wheels to the motor. I would have to offset the centre so they do not touch the seat as normaly they are just very thin tyres. Do you think this would be posible? I used to rebuild bikes as a teeager and put new spokes on wheels. I would just have to learn it all over again and how to offset them. Thanks if you can give me any advise. The wheelchair makers wont even reply to mails.

I set out to make a knife using an unusual material, something I hadn't used before. And a quick search on the web yielded few results of anyone forging a knife from bicycle spokes. At the beginning I wasn't sure if the spoke material was suitable for a knife blade so I did a quick spark test (see step 1) and found there should be sufficient carbon content. However, when later testing the hardness of the quenched blade, it didn't harden to my satisfaction. (EDIT: See below) Even though the finished knife isn't going into active kitchen service, I went on to complete the knife as I was intrigued by the pattern in the blade. And I'm hoping you may learn something from reviewing the steps in my process.

In this instructable I'll show you how I forged 90 bicycle spokes into an 8 inch chef knife. This knife features a full tang, integral forged bolster, stabilised New Zealand native timber and stainless steel pins.

The spokes are coated to prevent corrosion. This coating gave off some nasty fumes when heated and also contributed to some gaps in the forge welding which can be seen in the photos. Cleaning the spokes back to shiny steel would probably have resolved these issues.

I cut the spokes into lengths of 110mm then bundled them together using wire. I mig welded one end to hold the spokes in place then attached a length of rebar at the other end to use as a handle when forging.

Note

I wanted to check the presence of hardenable material in the spokes. Performing a spark test on the belt grinder resulted in star-burst sparks, a good indicator of the presence of carbon in the spokes.

From competitive racing to simply the bicycle you use to get to class- materials design applications are all around you. Take a look at the simple two-wheeled mechanism called a bicycle. To a materials engineer this is "design heaven". The wheels, seat, handlebars, and frame are all comprised of different materials that when adjusted just right can make one bicycle more desirable than another. For simplification matters and to prove that even looking at just one part of the bicycle is a complicated process I shall talk about the material design applications behind the bicycle spokes.

Spokes are the connecting rods between the bicycle hub and the rim. Their main purpose is to transfer the loads between the hub and the rim, which are caused by the weight of the rider and the bike. Ever wondered if the bike spokes are laced to the rims in a pattern? The lacing of the spoke is most commonly tangentially attached. This means the spoke on the ground has almost no load because the load is distributed among the other spokes.

The materials engineer asks now, "What material to make the spokes?" The obvious answer is steel, but should it be a stainless steel or high-carbon steel. The choice here depends on corrosion resistance or fatigue failure- whichever one the rider deems more important. The stainless steel would resist corrosion due to the amounts of chromium whereas the carbon containing steel must have a protective layer applied over the steel to prevent rust.

The materials engineer is now faced with the question of how much chromium in the steel spoke is needed for optimum results. This varies from company to company but a rule in materials science is that to be a stainless steel it must have at least 12% chromium. Making of the spokes is another area that the materials engineer would put into practice their knowledge. Drawing the rods through dies until the wire is of the desired diameter makes the spokes. This drawing process creates dislocations (a crystalline defect) in the wire which increases the strength. But the process has to be timed perfectly. Too much drawing and the spoke could break; not enough, and the wire won't carry the load to meet design specifications for the bike.

As one can see even something as simple and everyday as a bicycle spoke is surrounded by materials processes and design concepts leading to an exciting and unrestricted career in Materials Engineering.

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Okay, nothing to see here. The entire wheel is solid so there is no question of pushing/pulling. These were our earliest wheels until somebody realised they could be made a whole lot lighter by cutting a bunch of holes into them.

So, only the bottom spokes are actually supporting the wagon. The ground pushes up into the rim, which pushes up into the spoke, which pushes up into the hub. The hub pushes back down on the spoke. The spoke is said to be in compression, because both ends are being pushed in towards each other (compressed).

Superficially, it appears similar to our wagon wheel. however there is a very big difference. Steel wires are not good at taking compressive loads . A Wagon wheel is simple to explain, all the wooden spokes are rigid solids, so the spokes directly in contact with the ground bear the load of the wheel and of course, keep the hub in place.

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