How Stiff is Your Stem? Truthful Wheel Updates Impartial Street & Gravel Bike Stem Checks

It’s been over 10 years since Truthful Wheel Bikes in Tucson, AZ first shared with us their unbiased bar & stem testing, however they’re again at it, measuring actual stiffness in a brand new crop of 15 fashionable highway & gravel bike stems. What do you like: absolute lightest weight, most stiffness, the best stiffness:weight ratio, or perhaps some comfortable medium that may not break the financial institution. Truthful Wheel does the testing so we will all make extra knowledgeable shopping for choices.

Truthful Wheel Bikes exams actual highway & gravel bike stem stiffness

So why did Truthful Wheel mud off their check rig? We spoke to long-time head of the store Jason Woznick, and he mentioned merely that, “it has been a few decade since we did testing…. [and] we needed to re-test, bars, stems and cranks and see how issues have modified.”

Sounds good to us.

I’ve personally identified Truthful Wheel since round 2001 or so. That’s once I was first launched to the store and their weight-weenie methods by a good friend who’d labored in there earlier than transferring to the East Coast. After which, quickly after I headed to fulfill them in Tucson in particular person when touring out to race the 24 Hours within the Previous Pueblo. Truthful Wheel bikes has catered to each native in search of trusted service, and bike nerds from far & large looking probably the most unique parts and among the world’s lightest bike builds.

Though we didn’t get to it then, Truthful Wheel not too long ago celebrated their Fiftieth-anniversary final yr by updating their highway crankarm and handlebar stiffness exams with some extra of the most recent & biggest fashionable fashions. You’ll be able to try that Might 2023 highway crank check right here or their up to date November 2023 highway bar check right here.

However now let’s get again to stems.

Why will we belief Truthful Wheel Bike’s unbiased part testing?

The great thing about Truthful Wheel Bikes testing parts is three-fold. First, they’ve been round for greater than half a century, they usually stored the identical check rig at the back of the store simply ready. Secondly, they’re tremendous analytical however sensible, so that they maintain their exams easy and use the very same check protocol at present as once they began testing parts.

And lastly, they’re form of a bunch of nerds. OK, positively fellow bike nerds… our favourite sort.

Try their authentic 2014 stem exams, right here.

Stem deflection testing methodology

Their stem stiffness testing is simply measuring stem deflection – how far a stem bends beneath a repeatable load. Once more, Truthful Wheel introduced again their “favourite engineer” Jason Krantz to run the exams. He’s now a mechanical engineer at a worldwide firm creating testing & measurement tools. However he additionally labored within the biking business over his profession, for instance designing bikes at Titus and sharing our journalistic focus at Bicycle Retailer and Business Information again within the 90s.

The stem deflection testing protocol he developed fixes the stem in a inflexible body, then applies a uniform 100lb (~45kg) load 10″ (~25cm) away from the centerline of the stem. The check simulates an inexpensive approximation of the drive when a rider is sprinting, pulling towards the bar – up on one aspect, down on the opposite – as they attempt to pedal as exhausting as doable. However the precise drive/load/weight doesn’t actually matter, as deflection is linear, and they’re evaluating all stems with the identical forces.

Truthful Wheel has tried to reduce variables as a lot as doable. Their methodology says all stems must be 110mm lengthy and -6° of rise, with a 1.125″ steerer clamp and 31.8mm bar clamp. However some stems examined weren’t obtainable in that precise measurement, so there’s +1° variability in angle and -5mm variability for simply two stems (105mm Professional Vibe Dash Carbon & Syntace F119). However they clarify why which will or could not matter.

What’s stiffness?

One thing of a disclaimer… neither Truthful Wheel nor us at Bikerumor are essentially saying that higher stiffness truly means a greater stem.

Perhaps some lighter and even all-road & gravel riders would possibly like a little bit of compliance of their stem?

And the Truthful Wheel check doesn’t even contact on the potential vibration damping that some supplies can present, independently of stiffness.

However if you’re in search of cockpit rigidity for some discount of vitality loss or improved dealing with efficiency advantages, stem stiffness is actually an excellent place to start out in comparisons. And so, we’re fairly psyched that Truthful Wheel is there out crunching these numbers for everybody to see.

Scroll all the way down to the underside of this text if you wish to learn Truthful Wheel’s personal detailed description.

2024 Truthful Wheel stem stiffness exams’ outcomes

High 5 Stiffest

1. FSA SL-Okay at simply 3.7mm deflection, made from 2014 aluminum with metal bolts
2. FWB machined Ti prototype at simply 3.7mm deflection, made from titanium with ti bolts
3. Ritchey Superlogic C260 at simply 3.7mm deflection, made from 2024 aluminum with metal bolts
4. ENVE Carbon at simply 4.2mm deflection, made from carbon with ti bolts
5. Uno Stealth at simply 4.5mm deflection, made from 2024 aluminum with chrome steel bolts

High 5 Lightest

1. Extralite Hyperstem at 82.5g from 7075 aluminum with titanium bolts
2. THM Tibia at 91g from carbon with titanium bolts
3. MCFK Carbon at 92.3g from carbon with titanium bolts
4. Schmolke TLO (ICR) at 94.5g from carbon with titanium bolts
5. Uno Stealth at 104.7g from aluminum with chrome steel bolts

High 5 Stiffness:Weight Ratio

1. Extralite Hyperstem with 5.6mm deflection at 82.5g for a 2.16 S/W ratio
2. Uno Stealth with 4.5mm deflection at 104.7g for a 2.12 S/W ratio
3. Ritchey WCS C260 with 4.7mm deflection at 108.1g for a 1.97 S/W ratio
4. Ritchey Superlogic C260 with 4.1mm deflection at 128g for a 1.91S/W ratio
5. FSA SL-Okay with 3.7mm deflection at 144g for a 1.88 S/W ratio

Full 2024 Check Knowledge

Mixed 2014 & 2024 Check Knowledge

Bonus stem stiffness content material

Quoting Woznick once more, “In the event you’ve made it this far, you’re in all probability fairly within the subject typically. For some bonus content material we determined to run a check of the identical stem in 8 completely different lengths. You might be shocked how predictable the variations within the outcomes actually are.“

My Bikerumor Takeaways from Truthful Wheel’s stem exams

My first impression when trying on the new knowledge and evaluating it to the outdated was that on common the brand new stems are 7.1% lighter however 8.9% much less stiff, giving them a mean 2.7% lower in stiffness:weight. Truthful Wheel clarified a bit that we in all probability can’t so simply evaluate the figures total, as the person stems principally fell in comparable ranges. However they did be aware that new to the 2024 testing had been some prototype titanium stems, that are stiffer, but additionally heavier, skewing the averages a bit.

It’s exhausting although for me to miss that there have been already 8 stems in 2014 (out of 25) with ~4mm or much less deflection, whereas solely 2 had been so stiff within the new 2024 batch (of 15). I take that to counsel that the business as a complete would possibly probably not be making an attempt exhausting to make stems stiffer, as a lot as they’re making an attempt to enhance aerodynamics & integration.

However, trying carefully although at like stems (Ritchey & FSA, for instance the place there are primarily the identical fashions in 2014 & 2024), it appears the newer iterations are both a bit lighter or a bit stiffer. That matches with the concept that part engineers try to incrementally enhance efficiency, even on primary parts like stems.

Truthful Wheel’s Takeaways

Jason Woznick of Truthful Wheel Bikes did say that he sees, “that as an business development, stems have gotten disproportionally heavier than they’ve stiffer. That is doubtless because of extra fashionable stems accommodating inner cabling. We plan on doing extra testing with extra internally routed stems to bear this out a bit extra.“

Of be aware outdoors of simply trying on the numbers, Truthful Wheel additionally provides that their testing exhibits for highway parts “the extra aero a bar or stem is the extra compliant it is going to be since flat surfaces deflect greater than a spherical one“. In order that’s additionally a bit extra context on decoding their knowledge.

Lastly, let’s all thank Truthful Wheel for doing the work to assist us decide what parts we would like on our bikes!

FairWheelBikes.com

Full Truthful Wheel Bikes description of their stem testing course of, in their very own phrases…

Stem Deflection Testing:

We’ve as soon as once more introduced again our favourite engineer, Jason Krantz. Jason’s a mechanical engineer whose graduate work targeted on the intersection of composite supplies and finite ingredient evaluation. Jason has labored for a number of firms within the bicycle business and by no means fails to amaze us with the depth of his biking associated information.

Disclaimer: Numerous typing and numbers have gone into this text and we apologize upfront for any typos ought to they occur, however would warn that the potential of errors is current.

Some Preliminary Notes on Testing

Testing Methodology:

Every stem was mounted within the fixture and the testing carried out 3 occasions after which averaged. All stems examined had been 11cm apart from a number of which aren’t obtainable in these lengths. Every stem was mounted with its beneficial torque specs and preloaded with 20 kilos of drive utilized 10 inches from the stem (about half manner between a highway bar and mtb bar) As soon as preloaded the tools was zeroed and one other 100 kilos of drive was added and a measurement recorded. The measurement was taken on the level of load, once more 10 inches from the stem centerline.

Masses Examined:

Whereas the precise load doesn’t matter as a result of the response of the construction is linear. [That is, a stem with a stiffness of 150-foot pounds per degree will deflect one degree with a torque of 150 foot-pounds and two degrees with a torque of 300 foot-pounds.] Jason chosen a load of 100 kilos as a result of it’s a pleasant spherical quantity, and fairly practical to what some riders could expertise.

For a sprinting rider, let’s say he’s pushing on the left pedal with 300lbf (in different phrases, he can squat 600lbs). The pedal is about half as removed from the body centerline because the handlebar is, so it might take a response drive of 150lbs on the right-hand bar to counteract the pedaling drive. This is similar as making use of 75lbf up on the one aspect of the bar and 75lbf down on the opposite; the second on the stem is similar.

Normalizing for Stem Size:

In principle, it’s doable to measure a selected stem of 1 size and extrapolate its outcomes to longer or shorter variations of the identical stem mannequin. In technical phrases, that is “normalizing for stem size.” We are able to do that as a result of torsional displacement is instantly proportional to size for a tube of a given cross part. It’s true {that a} good engineer will use thinner partitions on shorter stems (which see decrease stresses) and thicker partitions on longer stems (which see larger stresses). Nonetheless, normalizing to size inside a single stem make and mannequin is legitimate to a primary approximation, no less than with steel stems. A composite stem is a special beast, as a result of layups (AKA laminate schedules) can differ considerably with size.

Whereas torsional displacement is instantly proportional to stem size, bending displacement is proportional to the dice of the size. Our first cross at a stem check setup measures mixed bending and torsional displacement, so it might not be legitimate to extrapolate to longer or shorter stems, even inside the similar mannequin, no less than for those who’re in search of absolute values.

In the event you’re focused on relative values–for instance, if you wish to know whether or not stem A is stiffer than stem B–then these outcomes must be fairly helpful whatever the precise size you propose to make use of.

For this check we used 11cm stems in each case besides 2 (Professional Vibe Dash Carbon and Syntace F119) that are each 10.5cm. The stems had been comparable sufficient in size that we didn’t normalize any stems on this check, however sooner or later we could check some stems that must be normalized for a good comparability.

Stiffness to Weight Ratio:

This was calculated utilizing =((1/avg. defl) / weight) * 1000

Bolt Materials:

One query we needed to reply was if there was a noticeable distinction between stems with titanium and metal bolts. We chosen a number of random stems and examined them each with titanium and metal bolts and located no significant distinction in deflection in stems with one materials over the opposite.

Mounting Course:

We additionally needed to see if mounting a stem with an increase vs a drop made a distinction within the deflection. Whereas we had been in a position to measure a distinction, lower than 0.1 mm at 100 kilos, it was not sufficient to say that there’s a significant distinction, and was doubtless inside the margin of error of the testing.

Notes about Stem Angles:

One different merchandise we needed to check was the distinction in like stems with completely different angles. We examined a few stems which might be obtainable in each 7 and 17 diploma angles and located that 17 diploma stems deflected a mean of seven% much less. The examined stems differ from 5 to 10 levels which ought to end in deflection variations of as much as about 3%, so maintain that in thoughts when evaluating two stems of various angles.

Carbon Fiber vs. Aluminum:

Carbon fiber stems don’t provide the load financial savings that, say, carbon fiber rims do. There’s a motive for this: stems are frequently burdened in 3 ways: bending, torsion and shear. In different phrases, the stresses in a stem are practically isotropic (uniform in all instructions). Carbon fiber is very anisotropic (stiffer/stronger in a single course than within the others). While you attempt to lay up anisotropic carbon to take care of isotropic stresses, you find yourself with what engineers check with as “black aluminum,” or pseudo isotropic carbon–and a weight that’s very near an aluminum stem.

There could also be different benefits to a carbon stem; vibration damping is one that’s typically put to the forefront of the controversy. It’s true that composite constructions typically damp vibration higher than metallic ones, and there could also be real-world damping advantages to a carbon stem. One method to check stem damping could be to wire an accelerometer to the stem after which strike it gently with a hammer, studying the accelerometer knowledge to see how rapidly the vibrations dissipated. This ring-down check could also be on the Truthful Wheel menu for a future article, however is outdoors the scope of this check.

Combined supplies:

Hybrid stems, a carbon overlay on an alloy stem. We examined solely a few these however neither did properly, we’ll do extra testing on others sooner or later to develop our ideas on this medium additional.

We examined two comparable stems one in full alloy (7s) and one in hybrid (vibe carbon) to see if there was a bonus to the hybrid stems. Each are the identical weight and similar dimensions with the identical puzzle lock clamp. The distinction being that the Carbon has thinner alloy, bolstered with carbon. Deflection was noticeably completely different, the total alloy was considerably stiffer than alloy/carbon.

To take a position on why exams put carbon/aluminum stems on the versatile finish of the spectrum, one would possibly contemplate two competing design constraints. First is galvanic corrosion. When aluminum and carbon contact one another, they’ve made a weak battery. The electron-swapping that goes on will trigger an aluminum/carbon half to fail in brief order. To keep away from this, producers use a layer of insulating materials. This layer is commonly a fiberglass/epoxy composite however might be plain epoxy. Neither materials is as stiff as aluminum, so that you’re taking a stiffness loss instantly.

Secondly, the market gained’t tolerate a carbon-wrapped aluminum stem that’s each costlier and heavier than its plain-aluminum counterpart. So producers are compelled to make use of thinner-walled aluminum forgings for his or her carbon-wrapped stems than they do for his or her straight-up aluminum stems. Successfully, they’re changing comparatively stiff aluminum with comparatively compliant fiberglass and/or epoxy.

Making issues worse, some carbon-wrapped aluminum stems use a 0°/90° weave for aesthetic causes. This weave’s stiffness displays the dreaded pseudo isotropy referred to earlier, and is especially compliant in shear–which, in a stem, determines torsional stiffness.

The web result’s a carbon-look stem that has enough energy however extra compliance (and probably higher vibration damping) than a “pure” aluminum stem.

To be clear, the above is what engineers name a SWAG: a Scientific Wild-Ass Guess. It’s an inexpensive first cross, however there could also be different elements at play that we haven’t thought of and which might be additional explored in future exams.