[mtg]

More surface area clamping the steerer so less chance of twisting stem on steerer in minor crashes. Probably not a huge deal on a trailbike (without a dual crown to "stop"), I just have bad memories of running Thomson stems on my DH bike back in the day (before integrated) that would twist on the steerer no matter how hard you did them up. I know this will go against troy's classic friction theory (friction shouldn't have proportionality to surface area, only the normal force), but it's my experience anyway.

I think some opening is okay but some stems have very little surface area against the steerer and I don't really like that. It's probably not a big deal though so I'm flexible on it.

Are you sure about that? I understand the point, but that issue on the Thompson could very well have been from other factors, such as the gap between stem bore and steerer being a couple thou larger than ideal, or the stem being too stiff (such that the clamp bolts produce less normal force on the steerer per unit of tightening torque), etc.
Having not done any tests on that myself, my estimation would be that simply open/closed steerer clamp does not necessarily directly equate to spins/does not spin in a crash.

I ask because you may have actually done some some of testing on this.

 

[Sandwich]

My weight target (130-140) isn't actually all that light, there are way lighter stems out there, some are posted here - but virtually all of them fail to fit my criteria, which I suspect puts us closer to the same goals than you think. My thread title is a bit misleading.

I didn't have a problem with 31.8mm either, but I switched to carbon on both trail and DH bikes a while ago, and it seems to make good 800mm carbon bars they need to use the larger 35mm clamp. I have broad shoulders and feel uncomfortable on less than 800. I use SIXC and it maxes out at 785mm in 31.8, to get 800 you need to go 35 (own both atm). They're super stiff though - maybe too much by some people's standards - no complaints there. I think you might just have a particularly flexy 35mm example?

Just for a laugh, @toodles here did break his Thomson X4 (31.8) stem, just from normal riding I think. But he used it for quite a few years so I don't think it was a fault of the stem. I guess everything can break.

I do have some heavier choices on my trailbike though (coil both ends, switching to 203mm rotors both ends) hence it'd be nice to keep the weight down where it's not needed. If anyone is interested, the SIXC 800x35x35rise bar is actually lighter than the 785x31.8x19rise bar (~220g vs ~230g), so that's kinda handy. I'm mostly changing for the extra rise.


More surface area clamping the steerer so less chance of twisting stem on steerer in minor crashes. Probably not a huge deal on a trailbike (without a dual crown to "stop"), I just have bad memories of running Thomson stems on my DH bike back in the day (before integrated) that would twist on the steerer no matter how hard you did them up. I know this will go against troy's classic friction theory (friction shouldn't have proportionality to surface area, only the normal force), but it's my experience anyway.

I think some opening is okay but some stems have very little surface area against the steerer and I don't really like that. It's probably not a big deal though so I'm flexible on it.

You've specified your alloy, which already puts you ahead of most people running 6061, I certainly agree on that.

As for the 35mm, I agree- for carbon bars, there are significant weight savings with 35mm. I did the math looking for an 800mm carbon bar and all 35mm options were lighter than 31.8.

I had my thomson twist in a gentle crash. I believe it's because they use such small bolts, which don't allow you to get a lot of torque on them. I could be wrong, but I really have to hamfist my tiny allen wrench- never had that problem with any other stem.

 

[Udi]

Are you sure about that? I understand the point, but that issue on the Thompson could very well have been from other factors, such as the gap between stem bore and steerer being a couple thou larger than ideal, or the stem being too stiff (such that the clamp bolts produce less normal force on the steerer per unit of tightening torque), etc.

Nah, not sure at all. This was all a very long time ago, I just switched stems and never thought about it since.
You may well be right with your reasoning. I just wanted to broadly avoid the issue, which for me never seemed to occur with a traditional twin bolt clamp with a lot of contact on the steerer.

Curious though - how can the clamp bolts produce less normal force on the steerer for a given tightening torque? If the stem was stiffer, wouldn't it just deform less and thus potentially put the same force on a smaller surface area of the steerer - but not change the total force applied to the steerer?

I had my thomson twist in a gentle crash. I believe it's because they use such small bolts, which don't allow you to get a lot of torque on them. I could be wrong, but I really have to hamfist my tiny allen wrench- never had that problem with any other stem.

Yeah my experience was similar, but I've used stems since my Thomson that use a more traditional / boring steerer clamp with the same size bolts (M5 thread, 4mm hex head, not sure if that's changed) that didn't twist anywhere near as easily in crashes. I'm not sure exactly why that is - I kinda just jumped ship and forgot about it.

Now that @mtg brings this up, I wonder if it's a function of the smooth pristinely machined surface having a lower coefficient of friction against the steerer compared to the slightly rougher bead-blast type finish that cheaper more traditional stems have. I'm running an el-cheapo kore cubix atm and it rarely moves.

 

[Gary]

@Udi.
things I remember about older Thomson parts

Seatposts and stems that slipped. their 30.9 seatposts were definitely undersized. and yeah that smooth finish isn't gonna help with that.
poor stem clamp designs.
stem face plate breakages

For a manufacturer who (at the time) only made seatposts and stems. Thomson weren't very good at either.

 

[mtg]

Nah, not sure at all. This was all a very long time ago, I just switched stems and never thought about it since.
You may well be right with your reasoning. I just wanted to broadly avoid the issue, which for me never seemed to occur with a traditional twin bolt clamp with a lot of contact on the steerer.

Curious though - how can the clamp bolts produce less normal force on the steerer for a given tightening torque? If the stem was stiffer, wouldn't it just deform less and thus potentially put the same force on a smaller surface area of the steerer - but not change the total force applied to the steerer?


Yeah my experience was similar, but I've used stems since my Thomson that use a more traditional / boring steerer clamp with the same size bolts (M5 thread, 4mm hex head, not sure if that's changed) that didn't twist anywhere near as easily in crashes. I'm not sure exactly why that is - I kinda just jumped ship and forgot about it.

Now that @mtg brings this up, I wonder if it's a function of the smooth pristinely machined surface having a lower coefficient of friction against the steerer compared to the slightly rougher bead-blast type finish that cheaper more traditional stems have. I'm running an el-cheapo kore cubix atm and it rarely moves.

Clamp bolt torque vs stem/steerer normal force: think of it in extremes. If the stem was infinitely stiff (hypothetically you have one without the pinch slot machined into it and they used a fantasy infinite modulus material), you could let He-Man tighten the pinch bolts and there would be no effective pinch onto the steerer tube. The purpose of the pinch slot is to effectively severely reduce the stiffness in the desired direction.

You may be onto something with the surface finish.

 

[Udi]

@mtg
That makes sense, I see what you mean now.

@Gary
Agree 100%. I bought my stem brand new (at exorbitant cost), and after finally giving up on it and switching to a cheap stem, all my problems went away. I've never bought any of their parts since - probably not really fair, but some very expensive and very nicely made parts miss the mark on simple functional design choices.

Another classic example was Chris King headsets, which for years creaked and came loose because CK was too tight to spend a nickel of his theivings on the FSA / Cane Creek split compression ring patent. As soon as the patent expired he switched to the obviously superior design, and marketed it as some kind of upgrade or improvement. At least Thomson could be excused for perhaps just honest mistakes, but the Chris King scam was enough to justify an intergalactic BDIU nomination.

 

[Gary]

Wasn't Thomsons main business something entirely unconnected to the bike industry back in their early days. Aerospace engineering IIRC?

If so. You'd hope they were slightly better at that.

 

[jonKranked]

Wasn't Thomsons main business something entirely unconnected to the bike industry back in their early days. Aerospace engineering IIRC?

If so. You'd hope they were slightly better at that.

their bike division is still a subdivision of the parent company, LH Thomson

http://www.lhthomson.com/

 

[Gary]

Chris King was indeed an evil genius... sell a $10 component for 20x the price and every sucker who buys one automatically looks after it like no other component they've ever owned. Ergo all those mugs are happy to spread their belief that their expensive purchase has superior reliability and durability whilst all the time they've treated it like it's a golden egg.
You'd even hear these idiots defending the products steerer scoring feature.

 

[4130biker]

First and only CK headset I owned I paid nearly full-price for. Installed on my bmx bike and the gigantic clunk each time I landed was instantly obvious. They wanted me to send in my stem to be machined “flat” on the bottom since everything else was reamed and flat. 7000 series S&M challenger stem with standard bolts, speaking of nice stems.... What a crock of shit..

Udi, if you had to throw out one of your wishes on the stem, which would it be?

 

[Udi]

Udi, if you had to throw out one of your wishes on the stem, which would it be?

Not super fussy about some of it:

• A bit of cutaway around the steerer is no big deal (just not too crazy, some stems have more steerer than clamp showing)
• Clamp width - not fussed, as long as it's not crazy narrow. I have a DH bike for big stuff, so forces here aren't huge.

The total dealbreaker is the 2-bolt faceplate because I can't fit a decent rise bar through it, and that's the main reason for this (otherwise pointless) upgrade. A good material is nice coz it somewhat reflects strength:weight ratio, and my weight restriction is pretty lax so I definitely wouldn't want it heavier.

If anyone remembers, I started the same thread for a DM stem (final decision here) and I was a lot more picky there because I care more about my DH bike, ride it way more, and run the same parts for years. The stem I was replacing in that thread (point1 splitsecond) I used for 8 years, on 4 frames, across 4 countries. The commentary in that thread is a lot more aggressive as a result, some cool info in there actually.

 

[toodles]

Not super fussy about some of it:

• A bit of cutaway around the steerer is no big deal (just not too crazy, some stems have more steerer than clamp showing)
• Clamp width - not fussed, as long as it's not crazy narrow. I have a DH bike for big stuff, so forces here aren't huge.

The total dealbreaker is the 2-bolt faceplate because I can't fit a decent rise bar through it, and that's the main reason for this (otherwise pointless) upgrade. A good material is nice coz it somewhat reflects strength:weight ratio, and my weight restriction is pretty lax so I definitely wouldn't want it heavier.

Turbine RF.

Actually, given how much you ride your trail bike, just get the lightest stem you can

Btw, my Thomson cracked at the top steerer pinchy thingy. Not exactly a reflection of the stem though, considering it was 8 years old and subjected to some interesting definitions of "clearing" jumps.

 

[troy]

Sure @Udi when You flip the 2 x 4 to the shorter side, it is 2 times easier to drag it across the floor. #udiphysics

Curious though - how can the clamp bolts produce less normal force on the steerer for a given tightening torque? If the stem was stiffer, wouldn't it just deform less and thus potentially put the same force on a smaller surface area of the steerer - but not change the total force applied to the steerer?

Here is another thing that will blow Your mind. Consistent torque does not equal consistent clamping force. You can tighten the same bolts 3 times with the exactly the same torque, using super precise torque wrench and get 3 different clamping force results, varying up to 100% in value. That is why even if You tighten the bolts up to spec, the clamping force may not be sufficient to keep the stem from slippage (ofc if the stem steerer bore was up to spec, although my experience with Thomson stem was exactly the same as Yours). Torque induced tension doesn't give the same results as tension induced tension. Mirror like, anodized finish on the Thomson stem do not help the case either, as the friction coefficient is much lower, than for a bead blasted/painted/roughly machined part.

Another thing is that this torque value is not meant to represent the friction needed to stop the bolt from un-threading or the clamp to stop moving, but it correlates with how much the bolt is physically stretched - therefore how much clamping force it will produce in given scenario. Also, 80-90% of the torque does not go to the clamping force, but rather to overcome bolt/nut and "bearing surface" friction.

Not sure if I do understand what You are trying to say in the 2nd sentence, but it seems like You do not see the difference between force and pressure, and use those terms interchangeably, and that would explain You confusion about "my theory" (which is the whole world theory btw., well, except Yours).

 

[Udi]

Yeah thanks, mtg already explained / corrected me.

Just to re-hash though, the time I actually didn't agree on this was when we were discussing a complex dynamic scenario of a hydrodynamically lubricated stanchion sliding in a bushing (on your torsional-flexbucket USD fork). I think there are many aspects of that application where classic friction theory is insufficient for describing all frictional forces generated - enough that there would be significant inaccuracies (and noticeable differences).

Anyway clearly this is not one of those cases, I posted and mentioned you pretty mindlessly and deserve this.
Thanks for gracing my thread with your presence and corrections.

 

[Udi]

Anyway - Ben (bucko) kindly offered to hook me up with a few of his Syncros stems so I'll probably just give that a go since I shortlisted it anyway.

Thanks everyone for their time, I'm sure many of the suggestions will be useful for future lurkers.

 

[Kanye West]

The lightest one is whatever one you decide to take an angle grinder to. You just have to believe in yourself. And in your insurance plan.

 

[Jm_]

I will never ever consider any of these data when I get my next stem

 

[norbar]

Spank Oozy Trail is 150 at 50mm but no 35mm bar clamp plus their alloy name is stupid and tells me nothing

Joystick components has something that could be light given they claim 125g for 35mm and they offer a 50mm version. The only problem is they call their alloy 8bit to be confusing. I assume it's not 6061 since they claim it's "better" but fuck knows what it is.

Also I'm not super fond of dartmoor but their trail v2 stem with 127g claimed for 50mm. No idea about material. I pushed their designer/enginer for 7075 some time ago but fuck knows if he went for it.


Also Pivot has something that may fit what you are looking for: http://www.pivotcycles.com/component/phoenix-team-enduro-trail-stem/

 

[toodles]

Also Pivot has something that may fit what you are looking for: http://www.pivotcycles.com/component/phoenix-team-enduro-trail-stem/

That is actually pretty awesome. I was looking for a 45mm stem for awhile. Cheers for the link

 

[troy]

I know, that You have already decided, but I will post it anyway:

135g - 35mm bar - 50mm long, local brand - Banana Bikes ~47USD , 6061T6 tho.

 

[William42]

Not that it's relevant anymore since we already established Thompson makes kinda shitty stems, but both of mine twisted, as did my buddies. 100% of the thompson stems (sample size: 3) I've ridden or had close friends riding were twisty shitters.

They were pretty good bar bike stems though.

 

[mykel]

+2 on Thomson stems.
Easy twist stems, even using crabon paste.
Retired.
No problems with either my Renthal or Point1.

Edit: Gamut who bought Point1 really should look at bringing back the Split Second stems, similar to what they did with the Podium pedals.

 

[Gary]

It's Daigoro, a local brand. I know the owner and I'm currently reviewing their 35mm cockpit kit. It's a generic stem he took from a generic factory in Taiwan. So far, digging it. It's affordable, plenty stiff, and I haven't had any issues once I clamped it hard enough to the steerer and bar.

Hey. does your friend have a website and does he ship internationally?
New bike incoming means I'm in the market for a new stem for 35mm bars.
Does his stem also come in 50mm length?

 

[slimshady]

Hey. does your friend have a website and does he ship internationally?
New bike incoming means I'm in the market for a new stem for 35mm bars.
Does his stem also come in 50mm length?

I know some folks from Latin America are buying his products, so feel free to contact him via Facebook:

https://m.facebook.com/DAIGORObici/

His name is Rolando, and he speaks English BTW.

 

[spocomptonrider]

Not super fussy about some of it:

• A bit of cutaway around the steerer is no big deal (just not too crazy, some stems have more steerer than clamp showing)
• Clamp width - not fussed, as long as it's not crazy narrow. I have a DH bike for big stuff, so forces here aren't huge.

The total dealbreaker is the 2-bolt faceplate because I can't fit a decent rise bar through it, and that's the main reason for this (otherwise pointless) upgrade. A good material is nice coz it somewhat reflects strength:weight ratio, and my weight restriction is pretty lax so I definitely wouldn't want it heavier.

If anyone remembers, I started the same thread for a DM stem (final decision here) and I was a lot more picky there because I care more about my DH bike, ride it way more, and run the same parts for years. The stem I was replacing in that thread (point1 splitsecond) I used for 8 years, on 4 frames, across 4 countries. The commentary in that thread is a lot more aggressive as a result, some cool info in there actually.

Back when I was cool enough to justify still having a dh bike that Point One Split Second DM was my stem of choice as well. I also ran it flipped (L to R) and it was stellar. I still have a non dm version with integrated top cap sitting in a box waiting patiently for a frame to be mounted on, it’s a great stem as well even if a bit fussy with the integrated top cap. I was bummed when Point One got gobbled up by Gamut, I feel they would be doing some really cool stuff if they weren’t forced to align with their new corporate overlords. Oh well.

 

[StiHacka]

Also Pivot has something that may fit what you are looking for: http://www.pivotcycles.com/component/phoenix-team-enduro-trail-stem/

I ordered one in LBS yesterday. They were really surprised I didn't get a whole Pivot bike as well.

 

[Jm_]

Another classic example was Chris King headsets, which for years creaked and came loose because CK was too tight to spend a nickel of his theivings on the FSA / Cane Creek split compression ring patent. As soon as the patent expired he switched to the obviously superior design, and marketed it as some kind of upgrade or improvement. At least Thomson could be excused for perhaps just honest mistakes, but the Chris King scam was enough to justify an intergalactic BDIU nomination.

You missed the part though where CK told all the users that reported this problem that it was their fault and that they installed it wrong

 

[norbar]

You missed the part though where CK told all the users that reported this problem that it was their fault and that they installed it wrong

I'm glad I was too cheap to buy an expensive headset back then since I was quite hyped about CK.

 

[toodles]

I'm glad I was too cheap to buy an expensive headset back then since I was quite hyped about CK.

The best part was people claiming that they were "a headset for life", like headsets were a consumable or wearing out headsets was a completely normal thing to do, or that 1.125" headsets were going to be relevant in 5 years time. Next up - "seat collars for life!"

 

[Jm_]

The best part was people claiming that they were "a headset for life", like headsets were a consumable or wearing out headsets was a completely normal thing to do, or that 1.125" headsets were going to be relevant in 5 years time. Next up - "seat collars for life!"

HubsAndBB4Life

 

[norbar]

The best part was people claiming that they were "a headset for life", like headsets were a consumable or wearing out headsets was a completely normal thing to do, or that 1.125" headsets were going to be relevant in 5 years time. Next up - "seat collars for life!"

My FSA Pig Headset lasted 15 years on my trailbike so that idea is not 100% wrong

 

[slimshady]

My FSA Pig Headset lasted 15 years on my trailbike so that idea is not 100% wrong

I caused a basic FSA headset to disintegrate within 15 hours of purchasing it. The upper cup got basically decapitated after nose landing a ~4ft drop .

 

[norbar]

I caused a basic FSA headset to disintegrate within 15 hours of purchasing it. The upper cup got basically decapitated after nose landing a ~4ft drop .

Well this is a trailbike so few hard crashes. Plus I'm pretty sure the Ellsworth frame will die before the headset

 

[StiHacka]

I caused a basic FSA headset to disintegrate within 15 hours of purchasing it. The upper cup got basically decapitated after nose landing a ~4ft drop .

Got any video footage from that event?

 

[rideit]

Well this is a trailbike so f. Plus I'm pretty sure the Ellsworth frame will die

' Murican Quality!

 

[slimshady]

Got any video footage from that event?

Didn't even had a camcorder at the time. I was a broken student at the time, I'm thinking of ~1998 IIRC. I put a 130mm RS Psylo I got extremely cheap from Jenson on an aluminum XC frame (a GT Aggressor if my memory serves me), grabbed a cheap loose ball FSA headset from the nearest bike shop (the previous one was toasted), and on my second ride I landed a small drop nose first (noob error, not enough speed), heard a CLANG!, tried to steer left, then saw the upper bearing holding rim hula-hooping around the steerer tube.

Clean cut, shortest lived bike component I ever had.

 

[kidwoo]

I know, that You have already decided, but I will post it anyway:

135g - 35mm bar - 50mm long, local brand - Banana Bikes ~47USD , 6061T6 tho.

Imma buy that just cuz the name.

 

[StiHacka]

Pivot 35/35

 

[Sandwich]

@Udi
how goes the syncros stem? Are you still on it? I don't want to run 35mm bars, but if I can find one in 50mm, I could be persuaded to replace my thomson.

I can't talk about saving weight on an easily replaceable part, so let's chat stem alloys again.

 

[manhattanprjkt83]

look no further.