Really, do they?

Is an 65mm XC stem more flexy than a 65mm DH stem. Or is it that DH stems are chunky to better survive crashes?

I doubt its noticeable but I suspect there is some difference.

Everything flexes.

Everything flexes.

this man is wise.

have you ever known a stem to break?
not the plate or bolts but the actual stem?

OK. Within the range of forces they are normally put through, do they flex?

yes, swapped an OEM kona stem for a ritchey one of the same size and it was noticably stiffer

Went form a truvative XR to a pro somethign or othere (began with K) and it was night and day again.

I wouldn't say its improved my riding dramaticaly, but a big imporvement is the sum of alot of little ones so I think its worth it.

OK. Within the range of forces they are normally put through, do they flex?

yes. there is not a 'flexing threshold' which above they will flew – they will flex whether a horse fly or a gorilla sits on your grip, just a different amount.

i can see my stem flex, skinny stem and 710mm bars. twist them hard and you can see the bars move by about 25mm each side.

I replaced a 120mm no name 2 bolt (one top, one bottom) stum with a 100m Thomson and I noticed a surprising difference in the steering.

It might have had more to do with how tightly the bar was held in place by the clamp, rather than how much the metal was flexing.

Years ago MBUK did at test on bars with a long pole and weights to test 'stiffness'. They did find a difference but as I have a life I didn't pay too much attention to the findings. How much 'flex' translates, or is worth considering in the 'real world' of riding is debatable, when other factors involved in the frame/forks/wheels/tyre area are taken into account.

I would think the flex in the stem on your typical 4 bolt clamp width is tiny compared with flex in bars, even oversize ones.

have you ever known a stem to break?
not the plate or bolts but the actual stem?

Yes, not me but a guy with his arm in a sling and blood running down his face at a Gorrick Enduro a couple of years ago…

this one does: