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 trendy street & gravel bike stems. What do you favor: absolute lightest weight, most stiffness, the very best stiffness:weight ratio, or possibly some joyful medium that may not break the financial institution. Truthful Wheel does the testing so we are able to all make extra knowledgeable shopping for choices.
Truthful Wheel Bikes assessments actual street & gravel bike stem stiffness
So why did Truthful Wheel mud off their take a look at rig? We spoke to long-time head of the store Jason Woznick, and he stated merely that, “it has been a couple of decade since we did testing…. [and] we wished to re-test, bars, stems and cranks and see how issues have modified.”
Sounds good to us.
I’ve personally recognized 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which, quickly after I headed to fulfill them in Tucson in individual when touring out to race the 24 Hours within the Outdated Pueblo. Truthful Wheel bikes has catered to each native in search of trusted service, and bike nerds from far & extensive looking essentially 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 12 months by updating their street crankarm and handlebar stiffness assessments with some extra of the most recent & best trendy fashions. You may try that Could 2023 street crank take a look at right here or their up to date November 2023 street bar take a look at right here.
However now let’s get again to stems.
Why will we belief Truthful Wheel Bike’s unbiased element testing?
The fantastic thing about Truthful Wheel Bikes testing parts is three-fold. First, they’ve been round for greater than half a century, and so they saved the identical take a look at rig behind the store simply ready. Secondly, they’re tremendous analytical however sensible, in order that they maintain their assessments easy and use the very same take a look at protocol in the present day as once they began testing parts.
And lastly, they’re form of a bunch of nerds. OK, positively fellow bike nerds… our favourite kind.
Try their unique 2014 stem assessments, right here.
Stem deflection testing methodology
Their stem stiffness testing is simply measuring stem deflection – how far a stem bends underneath a repeatable load. Once more, Truthful Wheel introduced again their “favourite engineer” Jason Krantz to run the assessments. He’s now a mechanical engineer at a world firm creating testing & measurement gear. However he additionally labored within the biking trade over his profession, for instance designing bikes at Titus and sharing our journalistic focus at Bicycle Retailer and Trade 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 take a look at simulates an affordable approximation of the pressure when a rider is sprinting, pulling towards the bar – up on one facet, down on the opposite – as they attempt to pedal as arduous as potential. However the precise pressure/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 attenuate variables as a lot as potential. 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 out there in that precise dimension, 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 that will or could not matter.
What’s stiffness?
One thing of a disclaimer… neither Truthful Wheel nor us at Bikerumor are essentially saying that larger stiffness really means a greater stem.
Perhaps some lighter and even all-road & gravel riders may like a little bit of compliance of their stem?
And the Truthful Wheel take a look at doesn’t even contact on the potential vibration damping that some supplies can present, independently of stiffness.
However in case you are in search of cockpit rigidity for some discount of vitality loss or improved dealing with efficiency advantages, stem stiffness is definitely a superb place to begin 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 assessments’ outcomes
Prime 5 Stiffest
FSA SL-Okay at simply 3.7mm deflection, made from 2014 aluminum with metal bolts
FWB machined Ti prototype at simply 3.7mm deflection, made from titanium with ti bolts
Ritchey Superlogic C260 at simply 3.7mm deflection, made from 2024 aluminum with metal bolts
ENVE Carbon at simply 4.2mm deflection, made from carbon with ti bolts
Uno Stealth at simply 4.5mm deflection, made from 2024 aluminum with stainless-steel bolts
Prime 5 Lightest
Extralite Hyperstem at 82.5g from 7075 aluminum with titanium bolts
THM Tibia at 91g from carbon with titanium bolts
MCFK Carbon at 92.3g from carbon with titanium bolts
Schmolke TLO (ICR) at 94.5g from carbon with titanium bolts
Uno Stealth at 104.7g from aluminum with stainless-steel bolts
Prime 5 Stiffness:Weight Ratio
Extralite Hyperstem with 5.6mm deflection at 82.5g for a 2.16 S/W ratio
Uno Stealth with 4.5mm deflection at 104.7g for a 2.12 S/W ratio
Ritchey WCS C260 with 4.7mm deflection at 108.1g for a 1.97 S/W ratio
Ritchey Superlogic C260 with 4.1mm deflection at 128g for a 1.91S/W ratio
FSA SL-Okay with 3.7mm deflection at 144g for a 1.88 S/W ratio
Full 2024 Take a look at Knowledge
Mixed 2014 & 2024 Take a look at Knowledge
Bonus stem stiffness content material
Quoting Woznick once more, “When you’ve made it this far, you’re most likely fairly within the subject generally. For some bonus content material we determined to run a take a look at of the identical stem in 8 completely different lengths. It’s possible you’ll be stunned how predictable the variations within the outcomes actually are.“
My Bikerumor Takeaways from Truthful Wheel’s stem assessments
My first impression when wanting on the new information 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 most likely can’t so simply examine the figures general, as the person stems largely fell in related 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 arduous 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 recommend that the trade as an entire may not likely be attempting arduous to make stems stiffer, as a lot as they’re attempting to enhance aerodynamics & integration.
However, wanting 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 element engineers try to incrementally enhance efficiency, even on fundamental parts like stems.
Truthful Wheel’s Takeaways
Jason Woznick of Truthful Wheel Bikes did say that he sees, “that as an trade pattern, stems have gotten disproportionally heavier than they’ve stiffer. That is seemingly attributable to extra trendy 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 wanting on the numbers, Truthful Wheel additionally provides that their testing exhibits for street parts “the extra aero a bar or stem is the extra compliant it will likely be since flat surfaces deflect greater than a spherical one“. In order that’s additionally a bit extra context on deciphering their information.
Lastly, let’s all thank Truthful Wheel for doing the work to assist us decide what parts we wish 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 factor evaluation. Jason has labored for a number of firms within the bicycle trade and by no means fails to amaze us with the depth of his biking associated data.
Disclaimer: Numerous typing and numbers have gone into this text and we apologize prematurely for any typos ought to they occur, however would warn that the opportunity of errors is current.
Some Preliminary Notes on Testing
Testing Technique:
Every stem was mounted within the fixture and the testing carried out 3 instances after which averaged. All stems examined had been 11cm excluding a couple of which aren’t out there in these lengths. Every stem was mounted with its beneficial torque specs and preloaded with 20 kilos of pressure utilized 10 inches from the stem (about half approach between a street bar and mtb bar) As soon as preloaded the gear was zeroed and one other 100 kilos of pressure was added and a measurement recorded. The measurement was taken on the level of load, once more 10 inches from the stem centerline.
Hundreds 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 sensible 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 pressure of 150lbs on the right-hand bar to counteract the pedaling pressure. This is similar as making use of 75lbf up on the one facet of the bar and 75lbf down on the opposite; the second on the stem is similar.
Normalizing for Stem Size:
In idea, it’s potential to measure a specific 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 will do that as a result of torsional displacement is straight 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 increased stresses). Nonetheless, normalizing to size inside a single stem make and mannequin is legitimate to a primary approximation, not less than with metallic stems. A composite stem is a special beast, as a result of layups (AKA laminate schedules) can range considerably with size.
Whereas torsional displacement is straight proportional to stem size, bending displacement is proportional to the dice of the size. Our first move at a stem take a look at 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, not less than should you’re in search of absolute values.
When you’re involved in 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 take a look at 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 related sufficient in size that we didn’t normalize any stems on this take a look at, however sooner or later we could take a look at 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 wished to reply was if there was a noticeable distinction between stems with titanium and metal bolts. We chosen a couple 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 Route:
We additionally wished to see if mounting a stem with an increase vs a drop made a distinction within the deflection. Whereas we had been capable of 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 seemingly inside the margin of error of the testing.
Notes about Stem Angles:
One different merchandise we wished to check was the distinction in like stems with completely different angles. We examined a few stems which might be out there in each 7 and 17 diploma angles and located that 17 diploma stems deflected a mean of seven% much less. The examined stems range 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 recurrently confused 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 path than within the others). If you attempt to lay up anisotropic carbon to cope with 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 talk. It’s true that composite buildings typically damp vibration higher than metallic ones, and there could also be real-world damping advantages to a carbon stem. One approach to take a look at stem damping can be to wire an accelerometer to the stem after which strike it gently with a hammer, studying the accelerometer information to see how shortly the vibrations dissipated. This ring-down take a look at could also be on the Truthful Wheel menu for a future article, however is outdoors the scope of this take a look at.
Blended supplies:
Hybrid stems, a carbon overlay on an alloy stem. We examined solely a few these however neither did effectively, we’ll do extra testing on others sooner or later to develop our ideas on this medium additional.
We examined two related 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, strengthened with carbon. Deflection was noticeably completely different, the complete alloy was considerably stiffer than alloy/carbon.
To take a position on why assessments put carbon/aluminum stems on the versatile finish of the spectrum, one may 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 may very well be plain epoxy. Neither materials is as stiff as aluminum, so that you’re taking a stiffness loss immediately.
Secondly, the market received’t tolerate a carbon-wrapped aluminum stem that’s each costlier and heavier than its plain-aluminum counterpart. So producers are pressured 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 satisfactory power however extra compliance (and presumably 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 affordable first move, however there could also be different elements at play that we haven’t thought-about and which might be additional explored in future assessments.
