Lab test: the stiffness of the stems

By: kiritozhang　　Translator: alanyu

OK here we come again. Since our first lab test on the stiffness of the integrated bars in 2019, we have then conducted the tests on the braking performance of the carbon wheels in the early 2020 and the stiffness of the drop bars in the mid 2020. Now it’s the time of the stems. What do you want to see next? Cranksets? Wind tunnels? Or others? Hahaha, it’s not a voting.

Back to the topic, we chose eight different stems including seven alloy ones which are easy to get and one super light carbon stem for reference, to study the stiffness on the different weight group. You may be disappointed if you’re aiming at some “rigid” stuff such as Pro Vibe Sprint and Zipp Sprint SL whose weight is around 200g, as they are designed to be as stiff as possible, which is not on our list.

Test list:

1, Extralite Hyperstem

One of the top brands who aim at the weight. Compared to those Germany brands insisting on carbon fiber, Extralite ticks all their skill points on the alloy. Their products are usually seen on various super-light-built bikes. However, its remark is not that high. “Nothing else good but only light” is one of those remark.

Extralite has several different kinds of stems and our tested product is Hyperstem road, which offers normal size and OD2 size, with 0°, 6°, 12° and 18° choices and 40~120 mm length.

The production rate and the import to China is extremely suppressed since Covid-19 pandemic. I couldn’t get any 110 mm one, so I used my own 120 mm one to test instead. Note that the weight is a bit heavier and the stiffness is a bit lower than the 110 mm one.

You need a Torx 20 tool to mount the stem instead of the normal T25 and follow the manual strictly, or you can easily break the stem. That’s $$$.

2, Deda Superleggera

Another brand from Italy. The high-end products of Deda are not common in China, but there are a lot of Zero 100, since there are too many OEM products. Superleggera is one of their high-end production lines, including bar, stem and seatpost.

Superleggera is actually very light weight if you don’t take those super light and super expensive products in consideration. The 110 mm one is only 109 g on my scale. The angle labelled on the stem is a bit special, 82°, which is effective to 8°, and it offers 80~140 mm.

3, UNO 7

The cheapest stem on our list, whose price is only a fraction of those big brands’ high-end products. I used an UNO stem on my S-works Tarmac SL4 when I was a student due to its price. However, I ditched it since its low stiffness. There are UNO 6 and 7, and the later one is better.

UNO 7 offers 7° and 17°, 60~130 mm length. The 110 mm one is only 111 g on my scale, only 2 g heavier than Deda Superleggera. OK it’s 1.7 g to be honest. I have to mention that these are steel bolts. You can spend one or two dozen of dollars to shave down another 8~12 grams with 6 (hollow) Ti bolts, which nearly double the price.

4, FSA OS99 (Energy)

The next one comes from the old big brand FSA, Full Speed Ahead. I have been a fan since my student time due to the performance of FSA K-force and OS99 stem. The top-end OS99 is updated to OS99-CSI now, which has a carbon reinforcement layer. The tested stem is OS99 alloy version, which is now the Energy series.

OS99 has a simple design and only offers 6°, 80~130mm. The reason for its name OS99 is due to the weight. I forgot whether it was the 80 mm one or the 90 mm one to be 99 g. Its weight is on the average level, as it aims at the balance of both stiffness and the weight, and there are still quite a few Pros using this stem in the big tour, indicating that they are satisfied with the performance of it. This Energy series OS99 is 133 g on my scale.

5, 3T ARX2 Team

Another big brand from Italy, 3T. OK nearly half of the tested stems come from Italia. Similar to FSA, you can see quite a lot 3T products in the big tour and they sponsor several teams. I have to say that 3T Ergonova drop bar is still being copied by the Chinese factory, and its shape is used for reference by some other brands: the “unique” bending and 77 mm reach.

ARX stems are also very classic and the carbon version, ARX LTD, has been copied to be an open mould. ARX2 is the second generation, which has a different set of bolts, and have two different production lines: white logo Pro level and red logo Team level. ARX2 team is one of the most used stems of Pros.

One of its issue is the T30 M6 bolt, which is used to locking itself on the steerer. Some mini torque tool sets don’t include this T30 bit.

ARX2 Team offers 6° and 17°, 80~140 mm length. The weight is also on the average level. The 110 mm is 140 g on my scale.

6, Pro Vibe Alloy

Pro is a brand in Netherland under Shimano Group and some people still call it Shimano. Another popular product in the big tour. Pro has Vibe Track and Vibe Sprint for those who need an extremely stiff stem. The carbon version is released in 2019, but most riders is still using the alloy version.

You can also choose OD2 version of it, and it offers -10° and -17°, 80~130 mm length. However, the 130 mm one seems not to be imported into China and I couldn’t order it in the Shimano system. Maybe it needs a special order.

You can not mount it in a positive angle since it uses a special top cap, and you need a special spacer if your steerer is too long, which is not elegant. The bolts of the stem cover are mounted from the backside. Some torque wrench may be too large to deal with them.

The 110 mm is 150 g on my scale, and you have to use its heavy top cap. The OD2 version is several grams heavier.

7, Zipp Service Course SL

The rival of Shimano on the other side of the Pacific —— SRAM. As the saying goes, Red and blue have always been a couple. Note that Zipp is now under SRAM.

The style of this generation Service Course is different from the last version, sturdier. There are two different lines, SL and normal one.

Service Course SL offers 6° and 17° and also OD2 version. The longest is 150 mm but is hard to get.

The 110 mm one is 159g on my scale. Emm… It’s the heaviest one in this test, though it is called SL. It is really Zipp style —— The weight is always the last to be considered. One Service Course SL is almost twice the weight of the Hyperstem road.

8. Darimo IX2

“Xun Lu is wanted, so why do you catch me Shuren Zhou?” (Translator’s note: Just Google Xun Lu (鲁迅), one of the pseudonym of Shuren Zhou(周树人))

“I’m a carbon stem passby. Please don’t test on me.”

“According to the regulation, you need to be tested just in case during the pandemic.”

Darimo is a small brand from Spain, whose products are famous for its extremely light weight. The most famous product is neither the bar nor the stem, but its seatpost T1 loop. Moreover, they custom make the special seatpost for different bikes such as specialized for those who want a lighter one.

There are two different models of its stem: IX2 and IX4. As the name suggests, IX2 uses two bolts to lock the front cap while IX4 uses four. You can only choose IX4 to pair with an aero drop bar. IX2 also offers OD2 size and the weight is almost the same with the normal one. It offers 6°, 12°, 17° and 25°, 60~130 mm length.

I have two different IX2 stems, one 6° 100 mm and the other one 12° 120 mm. I chose the 100 mm one to test as the shorter the stiffer.

The steerer mounting part (stack), which is 46 mm, is higher than the other stems in this test, maybe because it is glued together. Check your steerer length before ordering this stem. You can not over torque and if your steerer is not long enough, the stem can be loosened under duty. The 100 mm one is 71 g on my scale, and it is not suggested for those who are heavier than 90 kg.

Method

Seems familiar right? Yes, it is still that machine used in our previous test of the bars. We applied 30 kgf force in a fixed distance on one side both upwards and downwards and tested dozens of times to get a weighted average value.

Since the method may be different from other tests, it is not suggested to compare our results with others directly.

Results

Conclusion

Note that stiffness to weight ratio only counts when the stiffness is enough for you.

1, The stiffness of Extralite Hyperstem, Deda Superleggera and UNO 7 is on the same level. I have to respect the ability of Extralite. Its light weight and the stiffness make it worth that price, while Deda Superleggera is the most embarrassing one: it is only 1.7 g lighter than UNO 7, but its stiffness is only a tad higher.

If only take Superleggera and UNO 7 into consideration, UNO 7 has an absolute advantage due to its price, and even you spend some dollars on Ti bolts. However, quite a lot riders feel that the stiffness of these three stems is not enough, and I suggest these for those who are not heavy or just ride for fun. Note that the longer stem has a lower stiffness. These are definitely not for those sprinters.

2, According to the riders’ feed back and our lab test, I think FSA and 3T have redesigned and tested their stems quite a few times before their release. These two stems from FSA and 3T are at the sweet point of the weight and the stiffness, and the performance should be enough for over 90% riders. It is similar to the bar, the frame and the wheel, as one may neither ask for an extremely high stiffness, nor not too low.

3, Pro Vibe alloy and Zipp Service Course SL though have an excellent stiffness, they are a bit too heavy. Maybe only 0.1% rider can feel noodle when they use these one of these two stems. These two stems are for those who want an excellent stiffness but don’t what to pay $$$ for the top-end (heavy) carbon stem such as Zipp Sprint SL. The stiffness to weight ratio is around 3 N/mm/g for the alloy stems in our test, except Extralite.

The torsional stiffness of Darimo IX2 is way to low. I don’t know if it is due to its low-cost glue-together craft instead of one mould. Its stiffness to weight ratio is lower than Extralite Hyperstem road and its stiffness is way lower, but it calls for a higher price. I can only suggest this stem to those “scale-player” without any performance requirement.