How Stiff is Your Stem? Honest Wheel Updates Unbiased Street & Gravel Bike Stem Assessments

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

Honest Wheel Bikes exams actual highway & gravel bike stem stiffness

So why did Honest 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 wished to re-test, bars, stems and cranks and see how issues have modified.”

Sounds good to us.

I’ve personally recognized Honest Wheel since round 2001 or so. That’s after 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quickly after I headed to fulfill them in Tucson in particular person when touring out to race the 24 Hours within the Outdated Pueblo. Honest Wheel bikes has catered to each native on the lookout for trusted service, and bike nerds from far & huge looking probably the most unique elements and a number of the world’s lightest bike builds.

Though we didn’t get to it then, Honest Wheel just lately celebrated their Fiftieth-anniversary final yr by updating their highway crankarm and handlebar stiffness exams with some extra of the most recent & best trendy fashions. You’ll be able to try that Could 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 can we belief Honest Wheel Bike’s impartial element testing?

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

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

Try their unique 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, Honest Wheel introduced again their “favourite engineer” Jason Krantz to run the exams. He’s now a mechanical engineer at a worldwide firm growing testing & measurement gear. 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 pressure 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 potential. However the actual pressure/load/weight doesn’t actually matter, as deflection is linear, and they’re evaluating all stems with the identical forces.

Honest Wheel has tried to attenuate variables as a lot as potential. Their methodology says all stems needs to 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 actual 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 which will or could not matter.

What’s stiffness?

One thing of a disclaimer… neither Honest Wheel nor us at Bikerumor are essentially saying that larger 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 Honest Wheel check doesn’t even contact on the potential vibration damping that some supplies can present, independently of stiffness.

However if you’re on the lookout for cockpit rigidity for some discount of power loss or improved dealing with efficiency advantages, stem stiffness is definitely a superb place to start out in comparisons. And so, we’re fairly psyched that Honest Wheel is there out crunching these numbers for everybody to see.

Scroll right down to the underside of this text if you wish to learn Honest Wheel’s personal detailed description.

2024 Honest Wheel stem stiffness exams’ outcomes

High 5 Stiffest

1. FSA SL-Ok at simply 3.7mm deflection, fabricated from 2014 aluminum with metal bolts
2. FWB machined Ti prototype at simply 3.7mm deflection, fabricated from titanium with ti bolts
3. Ritchey Superlogic C260 at simply 3.7mm deflection, fabricated from 2024 aluminum with metal bolts
4. ENVE Carbon at simply 4.2mm deflection, fabricated from carbon with ti bolts
5. Uno Stealth at simply 4.5mm deflection, fabricated 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-Ok 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 in all probability fairly within the matter usually. For some bonus content material we determined to run a check of the identical stem in 8 completely different lengths. Chances are you’ll be stunned how predictable the variations within the outcomes actually are.“

My Bikerumor Takeaways from Honest Wheel’s stem exams

My first impression when trying 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 median 2.7% lower in stiffness:weight. Honest Wheel clarified a bit that we in all probability can’t so simply examine the figures general, as the person stems largely fell in comparable ranges. However they did word that new to the 2024 testing have 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 have been so stiff within the new 2024 batch (of 15). I take that to recommend that the business as an entire would possibly not likely be making an attempt exhausting to make stems stiffer, as a lot as they’re making an attempt to enhance aerodynamics & integration.

Then again, trying carefully although at like stems (Ritchey & FSA, for instance the place there are basically 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 element engineers are attempting to incrementally enhance efficiency, even on fundamental elements like stems.

Honest Wheel’s Takeaways

Jason Woznick of Honest Wheel Bikes did say that he sees, “that as an business pattern, stems have gotten disproportionally heavier than they’ve stiffer. That is doubtless as a result of 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 word exterior of simply trying on the numbers, Honest Wheel additionally provides that their testing reveals for highway elements “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 deciphering their information.

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

FairWheelBikes.com

Full Honest 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 centered on the intersection of composite supplies and finite aspect evaluation. Jason has labored for a number of corporations within the bicycle business and by no means fails to amaze us with the depth of his biking associated data.

Disclaimer: Loads of typing and numbers have gone into this text and we apologize prematurely 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 instances after which averaged. All stems examined have been 11cm aside from a couple of which aren’t obtainable 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 manner between a highway 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.

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 reasonable 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 could take a response pressure of 150lbs on the right-hand bar to counteract the pedaling pressure. This is identical 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 identical.

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 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 greater stresses). Nonetheless, normalizing to size inside a single stem make and mannequin is legitimate to a primary approximation, at the least with metallic stems. A composite stem is a distinct beast, as a result of layups (AKA laminate schedules) can fluctuate 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 could not be legitimate to extrapolate to longer or shorter stems, even throughout the similar mannequin, at the least in the event you’re on the lookout for absolute values.

When you’re concerned with relative values–for instance, if you wish to know whether or not stem A is stiffer than stem B–then these outcomes needs to be fairly helpful whatever the precise size you plan 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 have 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 should 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 Course:

We additionally wished to see if mounting a stem with an increase vs a drop made a distinction within the deflection. Whereas we have 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 throughout 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 obtainable in each 7 and 17 diploma angles and located that 17 diploma stems deflected a median of seven% much less. The examined stems fluctuate 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 cause for this: stems are recurrently pressured in 3 ways: bending, torsion and shear. In different phrases, the stresses in a stem are almost isotropic (uniform in all instructions). Carbon fiber is very anisotropic (stiffer/stronger in a single path than within the others). While you attempt to lay up anisotropic carbon to cope with isotropic stresses, you find yourself with what engineers consult 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 buildings 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 information to see how shortly the vibrations dissipated. This ring-down check could also be on the Honest Wheel menu for a future article, however is exterior the scope of this check.

Blended 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, strengthened with carbon. Deflection was noticeably completely different, the total alloy was considerably stiffer than alloy/carbon.

To invest on why exams put carbon/aluminum stems on the versatile finish of the spectrum, one would possibly take into account 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 instantly.

Secondly, the market gained’t tolerate a carbon-wrapped aluminum stem that’s each dearer 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 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 inexpensive first cross, however there could also be different elements at play that we haven’t thought-about and which will probably be additional explored in future exams.