Just for fun: (Or not!) 105 R7000 goes fantastic plastic!

In 1962 Simplex introduced the Simplex Prestige, state-of-the-art and one of the most technologically advanced derailers of the time with dual sprung pivots, one of the most prolific derailers of the bike-boom era, and remarkably light at only 152g.

[pictures coming soon, I need to find a Simplex Prestige]

Five years later, Shimano introduced the Sky Lark, their first dual-sprung derailer, what Shimano would dub their “servo-pantograph” technology, but in fact a copy of the Simplex design. Unlike the Simplex Prestige however, the Shimano Sky Lark was a chromed steel affair that weighed more than twice as much. A close relative of this design is actually still in production and is the design the SunRace M2T is based on.

Fast forward half a century, and we have the Shimano R7000 group replacing Shimano 5800 with a radically different design dubbed “Shadow” and an all new lighter weight. Shimano had shed the “servo-pantograph” design taken from Simplex in favor of the single-sprung “Shadow” design. It used to be that Ultegra had an alloy rear linkage. Prior to R7000, every 105 rear derailer had a stamped steel rear linkage, linking 105 to Shimano’s earliest derailers. But both the dual-sprung-pivots and that last piece of stamped steel which hark back to the Sky Lark are now gone. In its place is a newer, lighter and radically redesigned cast linkage.

But where Shimano once copied their design from the Simplex design of old, but deviated in material from the Simplex derailers of old, we now see the opposite trend. Shimano now copies the materials of the Simplex derailers of old, even though it deviates from the Simplex dual-sprung design of old. In other words, 105 is now being made from plastic.

Many attribute the poor reputation, poor durability, poor performance or worn specimens, and the tendency to break and get tangled in the spokes of the Simplex Prestige to the fact that it was made of plastic. That’s the direction 105 is heading with R7000. 105 has long held a reputation of being the durable no-nonsense Shimano groupset, considered by some to be the minimum acceptable groupset where Shimano wouldn’t cut corners or use inferior materials. Plastic in the rear derailers was relegated to low end garbage like Sora and Toruney, or found in off-brands like SRAM or Microshift.

At first glance, it looks like the lower A-knuckle is made from aluminum since R7000 has a bright aluminum finish. On closer inspection, the unpainted black version resembles the plastic knuckles of a tourney derailer with clear and distinct mold seams and flash and has a slightly different sheen from the front linkage. It wouldn’t be the first time plastic has been used for an A-knucle. SRAM does it, so does Microshift. Shimano does it on Sora and lower too. It wouldn’t be the first time Shimano painted a plastic A-knucle silver. I have in my parts bin a Sora RD-3400 for which Shimano has done exactly that.

At first the new rear linkage might be assumed to be a cast aluminum piece to replace the heavy and pedestrian stamped steel linkage in prior 105 derailers. However, it is telling that it is black on both the black and silver versions. It’s also very different from the stamped steel rear linkage on a SLX (105 MTB equivalent) “Shadow” derailer I also have. But what truly betrays the usage of plastic here, where even my Tiagra, Sora and Toruney derailers have steel, is the pivot pins. On their high end models, Shimano press-fits the pivot pins into aluminum, often with a tell-tale cross mark at the holes. When it comes to plastic or steel knuckles, they use a different kind of pivot, one with a head that flares like a rivet.

The Sora RD-3400 is an excellent example of this. So is the Tourney RD-TX75 which has an alloy front linkage. It becomes immediately obvious about the design philosophy of where the two different kinds of pivots are used. For any given pivot, if the outer lugs are alloy, it gets the press-fit pin. If the outer lugs are plastic, they get the rivet-style pin. This makes is obvious that the cast rear link of R7000 isn’t aluminum, it’s plastic. The rear link has the outer lugs where it mates to the A-knuckle. It also uses the flared rivet used for plastic.

This isn’t something likely to be reported by cycling journalists paid to republish press releases. I haven’t touched R7000 or even seen it in person, but from what I’ve seen so far, I’m not impressed. Plastic in a 105 rear derailer? Combine that with the new R7000 bonded cranksets that glue a sheet-metal stamping to a non-hollow forging. This design has seen many failures at the Ultegra and Dura-Ace level. The only thing remotely good about R7000 is the new hydraulic STIs which replace the monstrous non-series ones. I’m sad I sold my 5800 equipped bike in anticipation of the new 105. Two thumbs down, one for the derailer and one for the crank.

On the off chance I’m totally wrong and there’s some other explanation for the rivet and why everything else seems to fit a plastic rear linkage and A-knuckle, great, I’ll be thrilled that Shimano isn’t trying to cheapen the quality of 105.



A Theory on Gearing: Part 2

Part 2: Rolling Resistance

Some astute readers might note there’s another factor besides drag to consider, and that’s rolling resistance from the tires.

The formula for rolling resistance is:

F = Crr*N

Coefficient of rolling resistance (Crr) and normal force (N) are both essentially constant for the point of this exercise, unless you plan on riding to the moon or losing quite a bit of weight during your ride or getting a new wheel with a new tire from the team car. If you recall from earlier:

p = F*V

Let us again, be lazy, and assign arbitrary values of 1 mystery units to Crr and N, so that simply:

p = V

Note that power here is denoted by p, because I don’t know where subscripts are. P from the previous post and p here are both power, but in different arbitrary units. In order to convert p to P, I’ll introduce a new conversion factor, constant a.

P = ap

Adding in the aerodynamic drag component, substitute V for p, we get:

P = aV + V^3

Where a is our conversion factor, V is speed in whatever units, and P is our arbitrary power units that are definitely not watts.

Now we need to determine the value of a to establish the relative relationship between the rolling resistance component (aV) and aerodynamic drag (V^3). We can do so by determining they they intersect and solving for a.

aV = V^3

a = V^2

Now we just need to know V where rolling resistance is equal to aerodynamic drag, and we can skip all the other math and estimating we would have had to do. There’s a few numbers thrown out for when tire rolling resistance and aerodynamic drag are even, oft repeated seems to be 15mph. I can only assume this is because someone misread a graph without unit labels that actually said 15km/h. Schwalbe puts it at around 18km/h (11.2mph). BikeCalculator seems to put it at around 15.1km/h (9.4mph) using default values. Both of these may be right, as the relationship between drag and rolling resistance depends on the bike, rider and tires. But they give a good ballpark figure.

Neither of these models includes drive train losses, but calculating them doesn’t really change the conclusion so I’ll skip it.

The equation for arbitrary power units for Schwalbe is:

a = (11.2)^2 = 125.44

P = 125.44V + V^3

The equation for arbitrary power units for default values for BikeCalculator is:

a = (9.4)^2 = 88.36

P = 88.36V + V^3

And since bike calculator gives us a speed of approximately 15mph for 100w, we can actually come up with a conversion factor to turn our arbitrary power units P into watts.

W ~= (V*9.4^2 + V^3)/47

Which should come within a watt of BikeCalculator with default values.

On flat land with no wind, at a speed of 7.5mph, which is equivalent to 34×32 at 90rpm, about the lowest gear you will find on a road bike, if you increase the gear ratio at a given cadence by 10% you require an additional 19.0% power. At 33.9mph, equivalent to 53×11 at 90rpm, if you increase the gear ratio by 10% you require 31.9% more power. This might be closer to the result you were expecting from the previous post on drag. That seems like quite the difference at first glance, until you realize these speeds are much slower and faster than most people will go on windless flats.

If we narrow it down to normal cruising speeds of amateur recreational riders to 15-20mph and run the same calculations with 15mph and 20mph, we get 26.6% and 28.9% respectively. Much much closer together.

Consider again, that our cog choices must be in integers and often times a limited selection of integers, and we can not arbitrarily increase gear ratio by 10% in real life unless you have a NuVinci.

A Theory on Gearing: Part 1

Part 1: Drag

You’ve probably heard that drag increases exponentially with speed, which is why aerodynamics only matter at fast speeds. Fast speeds variably starting anywhere from 15mph to 25mph. Some people treat it as a magical barrier that only kicks in once you’ve passed a certain speed threshold, then suddenly it takes exponentially more power to increase your speed because of aerodynamic drag. Indeed, anyone who has tried to go as fast as they can can attest to the effects of drag. Some people will say this applies to gearing, and this exponential drag increase is why cogs need to be clustered closely together at the high/small end of the cassette.

NASA provides us with the equation to calculate drag:

One way to deal with complex dependencies is to characterize the dependence by a single variable. For drag, this variable is called the drag coefficient, designated “Cd.” This allows us to collect all the effects, simple and complex, into a single equation. The drag equation states that drag D is equal to the drag coefficient Cd times the density r times half of the velocity V squared times the reference area A.

D = Cd * A * .5 * r * V^2

Cd is called a variable, and it is indeed variable and influenced by a host of variables, but your Cd but for a given rider, for given equipment, in a given position, for the purpose of calculating drag here it’s constant. You will see people doing aerodynamics tests calculating the Cd of a certain part and so on. r is also essentially a constant, given that you cycle at reasonable altitudes in reasonable temperatures, and so on, we can also treat r as a constant for the purpose of this exercise. A will also be constant for this exercise, as the hypothetical bicycle and rider in this example won’t change in area.

Don’t worry, I’ll skip the calculus and present this in simple algebra.

So we will represent the product of these factors as the constant c.

c = Cd * A * .5 * r

Now we simplify to:

D = c * V^2

Now I’m going to just assign arbitrary values to the factors so that

c = 1


D = V^2

because they really don’t matter for this exercise. If it really bothers you, you can multiple our arbitrary drag units (D) by c. We’re just focusing on the relation of an increase in velocity on the increase in drag.

So we begin by calculating our arbitrary drag units (D) for an arbitrary velocity (V) of 15 arbitrary velocity units that are not miles per hour.

D = (15)^2 = 225

We can do this again for 16 and so on.

D = (15)^2 = 225

D = (16)^2 = 256

D = (17)^2 = 289

D = (18)^2 = 324

D = (19)^2 = 361

D = (20)^2 = 400

When we increase V from 15 to 16, D is increased by 31, from 16 to 17, and increase of 33. Then 35, 37 and finally 39. Each additional unit of V results an increasing amount of D. This is the common understanding of drag be proportional to velocity squared. From this, some come to the conclusion, you need smaller gaps between gears to compensate for this non-linearity, so each increase in speed is proportional to a certain amount of power.

However, we can rephrase the problem into a question of gearing. Let’s assume out cassette isn’t bound by the fact that the number of teeth have to be integers. Each gear results in a 10% greater gear ratio, and therefore a 10% increase in speed at a given cadence. That is after all, how we look at gearing when examining gear calculators.

Starting again with 15.

D = (15)^2 = 225

For our next gear

V = 15*1.1 = 16.5

D = (16.5)^2 = 272.25

And again

V = 16.5*1.1 = 18.15

D = (18.15)^2 = 329.4225

We’ll stop there. Maybe you noticed a pattern in the way it increments?

272.5/225 = 329.4225/272.25 = 1.21

That is, every time we change gearing and therefore speed by 10%, the amount of drag is increased by 21%. In fact, plugging in our relative change in gearing results in the relative change in drag.

D = (1.1)^2 = 1.21

Let’s not stop there though. The equation to calculate the power needed to counteract a drag is

P = D*V

D = V^2

P = V^2*V = V^3

Now calculating arbitrary power units (P) that definitely aren’t watts if V is measured in mph, which it isn’t.

P = (15)^3 = 3375

P = (16.5)^3 = 4492.125

P = (18.15)^3 = 5979.018375

Do you notice the relationship this time?

P = (1.1)^3 = 1.331


An increase of 10% gearing increases drag by 21% and requires 33.1% more power, or force at a given cadence to counteract that drag, at any speed, fast or slow. Or decreasing the gear by 9.1% (the same gears, the change just measured from a different point of reference, 1-1/1.1) is 24.9% easier, at least the power component to counteract the increased drag.



GUB SI Seatpost

gub si
GUB SI Seatpost (27.2 x 240mm)

This seatpost weighs only 146g when cut down to 240mm, saving up to 128g over a generic 300mm seatpost. In the original form at 350mm, it weighed 188g. It resembles numberous light weight seatposts and some of the lightest seatposts share the cross-pin design. The yokes are flat, making them easier to align with the rails. It has an oval bore to save weight and the cross-pin has a flange to prevent slipping and is also angled to keep the screws straighter. However, it does not have spherical screw-heads although the need is lessened because the cross-pin is angled. The clamp design offers less support to rails, imparts a bending load instead of a clamping load to grip them, and is very wide offering little adjustment, features common to this design. Larger riders and riders with lightweight rail materials should exercise caution when using this post. For each centimeter removed, the weight will be reduced about 3.8g, but remember to leave enough post for safe usage.  In stock form, at $12 and saving 8.8g per dollar, it represents an excellent value, moderate cost upgrade. This increases to an exceptional 10.7g per dollar when cut down. It can be found on eBay.

generic sp
Generic Seatpost (27.2 x 300mm)



Price: $12 [Moderate Cost]

Value: 8.8g/$ ($0.09/g) [Exceptional Value]

✔ Recommended with caveats

These seatposts are zero setback and offer even less adjustment range than the GUB GS Seatpost, so they are not for everyone. These are both cheaper and lighter, but the clamp design is also less friendly to exotic rail materials. There is little to lose by cutting them down for further weight savings.

UNO ASA-105 Stem (31.8)

uno steel
UNO ASA-105 100mm

This 100mm stem weighs only 107g, saving up to 53g over an OEM stem. They are made by Kalloy, a major OEM supplier of components like stems, seatposts and bars. Fit and finish are good, they meet CEN standards. UNO is their own house brand, but you can also find these rebranded for much more money. Comes in a wide variety of lengths 80-130mm, in both 7° and 17° versions. While not the best value if replacing purely for weight reduction, if you need to change stems for fitting purposes, you will most likely end up paying more for a heavier stem buying anything else. They come with different logos depending on year. There is another version of the stem that looks almost identical, but is slightly heavier and made from 6061, the ASA-025. At $21, and saving 2.5g per dollar, it represents a good value, moderate cost upgrade. They can be found on eBay. If you can’t wait for overseas shipping you can pay a premium for a similar OS stem made by Kalloy from Nashbar or Performance Bike.

Stock Stem



Price: $21 [Moderate Cost]

Value: 2.5g/$ ($0.40/g) [Good Value]

✔ Recommended


Example Bike Build Spreadsheet

If you want to build a light weight bike on a budget, you have to keep track of every part to figure out upgrading which parts saves you the most weight for the least money. You should budget $10 for a cheap kitchen gram scale to verify weights as well.

I’ve done most of the hard work for you, and modified and simplified one of my personal spreadsheets for your use. Attached is a spreadsheet with two examples. One is an example build on a $1,500 $1,400 budget that weighs 16 lbs with pedals and cages. The other is is an example of a sub-UCI build for less than $2,000 $1,900.

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