YES I think this is the first time I have seen someone actually do the sit bone measurement properly i.e. actually on the saddle! Why have so many people spent so many years telling people to do this on the stairs or on a chair?
I have been watching cycling/fit videos for 7 years (including this channel on occasion). This is the first time I saw someone taking seat bone measurements. I will definitely try this out.
I appreciate you and your channel. I started waxing my chain and really enjoy the process. The Connex Link is a MUST…a true game changer. Thanks for all the tips. Now my New Year’s Resolution is to find carbon wheels that won’t require a 2nd mortgage. Grace & Peace!
Love the foil method. Definitely going to try that to measure my sit-bone width before I buy another saddle. As a bonus you get a silver bird after you've drawn the eyes on @3:33 too! 😄
a tip. if you have more than one saddle or intend to do this test, get extra seatposts so all you do is change the SP without having to re-do the measurements. of course there is the cost factor. up to you lol
I highly appreciate this video! A real 👁-opener! 👌 @13:02 saddle tilt is indeed a fiddly one. Many saddles have cogs to keep them in position after tightening. However, the cogs prevent fine adjustment. 🙄
It'd be really handy to rig up an Excel spreadsheet that did the math for you on the fly as you wanted to change things like reach/angle/etc. They are all related for sure, it'd be helpful to see it in the moment as you say want a new bike, or have integrated bars on one bike vs the other and are determining if you can make it work. Great tips in this video.
Since the shape of the seat is affects tilt measurements, probably would be better to reference tilt based on sit bone location. If your saddle doesn't have marks, either a marker line for reference or adding a small tape marker will make it easy to make small accurate moves or return to original position if needed. Same for stem / seat post changes. adding a small mark makes it easy to return if needed.
Great content Steven! You're the master of cycling innovation DIY! Tried the tinfoil trick and couldn't find any idents even from different angles of light. Tried it on two of my saddles still no avail. Maybe my ass is too fat!
Ok. The points should be just before or at the widest part of the saddle. You can also put foil on a step, box or stool...sit up fairly straight and bring up your knees to about 90degrees. You should see the impressions. You can obtain your sitbone width from this.
And don't forget considerations for hemorrhoids, drape of the nuts alongside the saddle, length of toenails, and how each frame will be different. Some have mentioned the measurements vary with "Bite" on the saddle when suddenly confronted with an array of hazards. All things considered, "Close" is good enough for me.
My advice try a narrow saddle and try a wide one and figure which is better for you. Personally I ride narrow saddle and I’ve never found a wide one that doesn’t give me saddle sores. I like the way you figured out sit bone width in the video but for me I just tried different saddles until I realized I’m in the skinny bones gang
Nice to hear you're starting out on your bike. Best to start with a saddle with quite a bit of padding until your backside gets used to a bike saddle. Then in maybe 3-4 months you can go for a lighter,less padded saddle. Sorry I don't recommend saddles to riders as everyone is different shape....heavier riders don't automatically have wider sitbones either.
Thanks for the informative video! Ive been experimenting with different saddles over the last few weeks as the one i ride...Specialized Toupe is no longer available in the US. So i understand the sit bone measurements. My question is when putting the new saddle on how do you now where your sit bones will rest on that new saddle so that you can mark and measure accordingly? I saw that you made a template which I can do. But the video quickly passes over where to mark the new saddle. Can you be a little more specific as this really is key for set up of the new saddle. Thank you!😀
Hi, Great video once again! I measured my bike, and by pure chance, my measurements are within a tolerance of 0 to -5mm. My body shape is quite similar to yours, but I weigh 91kg and have a slightly bigger belly. I'm 184cm tall with a leg length of 88cm, and my crank length is 170mm. Could you share your body measurements so we can get a better sense of whether my (or our) bike adjustments are approximately correct? Greetings from Germany!
Try the extremely expensive yet comfiest 3D printed Specialized Power Saddle, they even come with a 30 day money back comfortable warranty. Comfiest saddle I’ve ever used.
Excellent videos. Please clarify this though.... I have always thought that the rear fit - i.e. sit bone to bottom bracket horizontal measurement -once determined is set in stone. Other adjustment - for example @ 15:24 where the reach is too long/short - should only be varied by bike size or stem length. Comments?
I ride a CX bike, quite often over some very rough terrain, on a saddle that is generally comfortable. I have found that since buying the Redshift Shockstop seatpost, almost all the tenderness has gone. I think with such a seatpost most riders could tolerate even a very cheap saddle.
Seems like a revisit of the "Ass-o-meter" gimmick I remember from awhile back. Didn't the Big-S have this thing in their dealerships? After having some "undercarriage" work done I found I couldn't sit comfortably on saddles I'd used for years (after plenty of trial and error) so in a panic raced off to my LBS. Sat on their Ass-o-meter, tried the models suggested and hated 'em all. Went through a bunch of makes/models after that, in increasing prices. Only found relief when I got to SMP and even with those it still took trial and error. Back-in-the-day the shop I worked at loaned saddles...there were only 3 - Rolls, Turbo or Regal. SMP has test centers that offer the same idea...only trial-and-error really works IMHO. Start with the thing dead-level (women usually like a slight downward angle) and spend some time riding 'em before moving on to another. When I switched out my road bikes for gravel bikes, the slightly more upright position changed weight distribution enough that I needed yet another change in saddle shape. Still SMP, but a bit wider and more padded in the back. Happy pedaling!
I hate to sound old, but I reckon the whole "interface" was more comfortable years ago with a proper chamois (not a pad) and a decently padded saddle such as a turbo. The switch to thinner saddles and thicker pads changed the comfort variables somewhat. I'll admit I've surprisingly had luck with some turbo shaped copies, that bit of extra padding helps. Everything on a bike is so light now, a few grams of padding is worth it.
Great video, thanks. Wondering why you are measuring from the BB centre to sit bone, wouldn't it be better to measure from the peddle centre to sit bone and then take into account peddle centre to shoe?. As crank lengths vary. Or am I missing something?. Cheers
If you get a professional bike fit and make sure to take a measurement from the BB center, then you can easily transfer that to any bike. It isn’t any less accurate as long as you’re consistent and provided you keep the crank length and pedal/cleat setup consistent across your bikes
@@stevenleffanueAlex at Cycling Deal in Dandenong pranked me in 2020 , with an empty envelope . I will now have nothing to do with his team or recommend them .
I always find seats with no cushion very painful. So I don't know how someone can ride their bike a long distance without a sore a**. Do you have that problem too?
Saddle width discussed in these two vids... th-cam.com/video/QMy_2pR4Mzg/w-d-xo.htmlsi=oD1hYAgffg3LCem1 th-cam.com/video/B94mvr3mQec/w-d-xo.htmlsi=LopUMLtU3_z_ifgy
So quick questions. 1. Weight bearing capacity of the saddle. Do the saddles have and reference to this? I bought a Colnago and the saddle lasted 12 months or so before it cracked over a bump. It was a flexible seat but I was 84kg and apparently too heavy. 2. You didn't mention anything about saddle width. Your S saddle, I assume S for Specialised? It was the largest of the group you tested and mayhap the others were not wide enough? They looked narrower than the original, which might have meant you were sitting lower on the sides of the saddle than your original. 3. On replacing my saddle when the original went on the Colnago I went with a Fizzik. More your traditional materials over carbon, but that was because carbon was not that common at the time. Does carbon wear out more quickly because of fatigue from the flexing under the rider's weight and road surface impact?
I've never understood why we measure seat height from the center of the crank axle. This doesn't take into account crank arm length. I use 160mm so my measurement would need to be 10mm shorter than someone using 170mm.
If you want to get picky, neither is technically correct. The pelvis is actually 3 bones fused together: the pubis, ilium and ischium. Many people colloquially use “pelvis” to refer specifically to the pubis. “Sit bones” is the colloquial term for the ischial tuberosities. I dare you to record a video where you say ischial tuberosities repeatedly.
Both saddles 'appear' to be nose up slightly. My old saddle was set up this way with a level across the top resulting in a slightly nose up. New bike and saddle, when level the saddle this way results in too much nose up. Forget about how it looks and just focus on how it feels?
The methods of measurement shown are fairly inaccurate esp the bar method for handlebar drop, because you are lying it along the saddle even the slightest change in saddle angle will create significant changes in the bar measurement. This will also not be reproducible with different saddles that may have different shapes for the same reason. I also consider handlebar drop a secondary measurement, it's a result of the primary measurements you should be taking and thus is relatively immaterial. Using a self-leveling laser level with X and Y beams centered on the bb is far superior and less prone to human error. You create coordinates for the hand and sit bone contact points relative to the constant location of the BB axis. For example the sit bone contact point might be 350mm(X) and 500mm(Y). While it's a slight bit more work to set up and ensuring the frame is level (using the laser to level the front and rear axles whilst in a stand works best for me) you get far more precision and repeatability across bikes and individual components. But I love the Al foil method for getting an accurate sit bone location. Nicely done on that.
The super team fizik Argo copy may be better run with some extra nose down. I have Argos on all my bikes and run the nose down a little due to the kick at the back. I know this is going to mess with your measurements though, almost looks like the nose it up in your vids.
I couldn't get comfy on it at all , best was with nose slightly up but still no good for me. If Argos fits you , you would probably find the copy works for you too.
I just cannot seem to find a solution to penile numbness and loss of feel issues, got a bike fit, testet probably about 20 saddles at every angle, height and setback possible. tried several styles of bibshort but just cannot seem to solve this.
Shouldn't adjust reach by adjusting saddle setback/offset. Pulling up when pedalling is not recommended, it's been shown to be inefficient and unneccessary. You didn't allow for saddle padding density/compressibility Pretty much impossible to adjust tilt by 1mm with most saddle rail clamps.
Most modern road bikes have micro-adjustable seat clamps now. Yes , saddle foam compression will generally affect height, but it's difficult to measure...if you suspect significant difference in padding compression between saddles you can take an educated guess.
Height/Length DIY tool video....
th-cam.com/video/8dPSmt9Z1iU/w-d-xo.htmlsi=DuEiSpeeQCpljdxL
Samassi saddles....
samassi.us/
Superteam saddles....
www.superteamwheels.com/collections/superteam-carbon-wheels-personal-items/personal-items
YES I think this is the first time I have seen someone actually do the sit bone measurement properly i.e. actually on the saddle! Why have so many people spent so many years telling people to do this on the stairs or on a chair?
Well this video proves you can teach an old dog new tricks. Learned a few good tricks from this excellent video.
Loved this video, especially the aluminum foil & chalk trick- brilliant!
I have been watching cycling/fit videos for 7 years (including this channel on occasion). This is the first time I saw someone taking seat bone measurements. I will definitely try this out.
I thought I was the only person in the world who still owned pedal cage straps! 😊
THIS VIDEO IS GOLD through and through
thanks for all the info !!
Gotta hand it to ya. You got some brilliant ideas. As sparky loving the utilization of conduit fittings!
Haha, good spotting...indeed, electrical could fittings.
I appreciate you and your channel. I started waxing my chain and really enjoy the process. The Connex Link is a MUST…a true game changer. Thanks for all the tips. Now my New Year’s Resolution is to find carbon wheels that won’t require a 2nd mortgage. Grace & Peace!
I bought the yoeleo pro 60 wheels in this video for 750 usd. Best bang per buck I have ever spent.
Love the foil method. Definitely going to try that to measure my sit-bone width before I buy another saddle. As a bonus you get a silver bird after you've drawn the eyes on @3:33 too! 😄
a tip. if you have more than one saddle or intend to do this test, get extra seatposts so all you do is change the SP without having to re-do the measurements. of course there is the cost factor. up to you lol
This one of the best fit explanations I have seen!
I highly appreciate this video! A real 👁-opener! 👌
@13:02 saddle tilt is indeed a fiddly one. Many saddles have cogs to keep them in position after tightening. However, the cogs prevent fine adjustment.
🙄
You’re a genius 😅 thanks for your help and knowledge
Thanks for sharing
Another very helpful vdo ❤
Love the use of the pedal strap but only old men have those. I have several 😢
In the UK we are getting caked with mud...and you are just getting caked lol. Great video.
Oz cycling : simply the best ever
It'd be really handy to rig up an Excel spreadsheet that did the math for you on the fly as you wanted to change things like reach/angle/etc. They are all related for sure, it'd be helpful to see it in the moment as you say want a new bike, or have integrated bars on one bike vs the other and are determining if you can make it work. Great tips in this video.
Very usefull video , thanks 👍
R7. Brilliant saddle name 😁
Since the shape of the seat is affects tilt measurements, probably would be better to reference tilt based on sit bone location. If your saddle doesn't have marks, either a marker line for reference or adding a small tape marker will make it easy to make small accurate moves or return to original position if needed. Same for stem / seat post changes. adding a small mark makes it easy to return if needed.
I'm so glad I MTB bike and just enjoy riding my bike. NERRRDS!
Best is to measure the distance between sitbones and the hoods.
Preliminary to all this is to know your physical measurements. Thanks, good info.
Yes , that would be "bike fitting ".
Great content Steven! You're the master of cycling innovation DIY! Tried the tinfoil trick and couldn't find any idents even from different angles of light. Tried it on two of my saddles still no avail. Maybe my ass is too fat!
Ok. The points should be just before or at the widest part of the saddle. You can also put foil on a step, box or stool...sit up fairly straight and bring up your knees to about 90degrees. You should see the impressions. You can obtain your sitbone width from this.
@@stevenleffanue Thanks! Will try it tomorrow! You are the GOAT!
And don't forget considerations for hemorrhoids, drape of the nuts alongside the saddle, length of toenails, and how each frame will be different. Some have mentioned the measurements vary with "Bite" on the saddle when suddenly confronted with an array of hazards. All things considered, "Close" is good enough for me.
Great video. Thanks for making it.
Great video ! Thanks !!
Successful video. I feel good with my saddle choices. Now going to measure them up using your method. HNY Oz
My advice try a narrow saddle and try a wide one and figure which is better for you. Personally I ride narrow saddle and I’ve never found a wide one that doesn’t give me saddle sores. I like the way you figured out sit bone width in the video but for me I just tried different saddles until I realized I’m in the skinny bones gang
thanks Oz
Oh yes, the legendary rider Wang Yoeleo.
Great video! Earned my sub! I'm just getting into cycling at 42 years old, 2 meters tall, 100kg and rather wide hips. Any saddle recommendations?
Nice to hear you're starting out on your bike. Best to start with a saddle with quite a bit of padding until your backside gets used to a bike saddle. Then in maybe 3-4 months you can go for a lighter,less padded saddle. Sorry I don't recommend saddles to riders as everyone is different shape....heavier riders don't automatically have wider sitbones either.
Hand numbing can also be caused by the seat sloping down which puts more weight on your hands
Thanks for the informative video! Ive been experimenting with different saddles over the last few weeks as the one i ride...Specialized Toupe is no longer available in the US. So i understand the sit bone measurements. My question is when putting the new saddle on how do you now where your sit bones will rest on that new saddle so that you can mark and measure accordingly? I saw that you made a template which I can do. But the video quickly passes over where to mark the new saddle. Can you be a little more specific as this really is key for set up of the new saddle. Thank you!😀
th-cam.com/video/B94mvr3mQec/w-d-xo.htmlsi=SH6k2YTSUA1dF9Fg
Hi,
Great video once again! I measured my bike, and by pure chance, my measurements are within a tolerance of 0 to -5mm. My body shape is quite similar to yours, but I weigh 91kg and have a slightly bigger belly. I'm 184cm tall with a leg length of 88cm, and my crank length is 170mm. Could you share your body measurements so we can get a better sense of whether my (or our) bike adjustments are approximately correct?
Greetings from Germany!
Try the extremely expensive yet comfiest 3D printed Specialized Power Saddle, they even come with a 30 day money back comfortable warranty. Comfiest saddle I’ve ever used.
greetings from türkiye
Ha ha noses, our’s and the seat’s !:)
Excellent videos.
Please clarify this though....
I have always thought that the rear fit - i.e. sit bone to bottom bracket horizontal measurement -once determined is set in stone.
Other adjustment - for example @ 15:24 where the reach is too long/short - should only be varied by bike size or stem length.
Comments?
Nothing is "set in stone" really as we need to taylor the bike to fit our body shape and type of riding we are going to do with that bike.
I would like you to do a video on the SQ LABS seats,like to know what you think and if there any cyclists out there who can provide input
This Video was Amazing. Do You Have wrench link?
Torque wrench?
Thanks, good video. One question what is the brand of the bikestand (for the aft wheel)?
Not sure what brand but bought from local hardware store.
I ride a CX bike, quite often over some very rough terrain, on a saddle that is generally comfortable. I have found that since buying the Redshift Shockstop seatpost, almost all the tenderness has gone. I think with such a seatpost most riders could tolerate even a very cheap saddle.
Seems like a revisit of the "Ass-o-meter" gimmick I remember from awhile back. Didn't the Big-S have this thing in their dealerships? After having some "undercarriage" work done I found I couldn't sit comfortably on saddles I'd used for years (after plenty of trial and error) so in a panic raced off to my LBS. Sat on their Ass-o-meter, tried the models suggested and hated 'em all.
Went through a bunch of makes/models after that, in increasing prices. Only found relief when I got to SMP and even with those it still took trial and error.
Back-in-the-day the shop I worked at loaned saddles...there were only 3 - Rolls, Turbo or Regal.
SMP has test centers that offer the same idea...only trial-and-error really works IMHO. Start with the thing dead-level (women usually like a slight downward angle) and spend some time riding 'em before moving on to another. When I switched out my road bikes for gravel bikes, the slightly more upright position changed weight distribution enough that I needed yet another change in saddle shape. Still SMP, but a bit wider and more padded in the back. Happy pedaling!
My old fav was the regular "Turbo" , can't get them anymore.
👍👍
I hate to sound old, but I reckon the whole "interface" was more comfortable years ago with a proper chamois (not a pad) and a decently padded saddle such as a turbo. The switch to thinner saddles and thicker pads changed the comfort variables somewhat. I'll admit I've surprisingly had luck with some turbo shaped copies, that bit of extra padding helps. Everything on a bike is so light now, a few grams of padding is worth it.
May I ask what you are using to protect your carbon frame from the withstand clamp in this video?
It's not clamped, just sitting there with jaws stopping it from swaying. Been doing this to thousands of bikes for decades.
🌀🌀🌀
Great video, thanks. Wondering why you are measuring from the BB centre to sit bone, wouldn't it be better to measure from the peddle centre to sit bone and then take into account peddle centre to shoe?. As crank lengths vary. Or am I missing something?. Cheers
Yes, you can measure from centre of pedal spindle provided the crank is in line with the seat tube angle. Much easier from bb centre.
If you get a professional bike fit and make sure to take a measurement from the BB center, then you can easily transfer that to any bike. It isn’t any less accurate as long as you’re consistent and provided you keep the crank length and pedal/cleat setup consistent across your bikes
@@danielakerman8241 Thank you
nice video; do you have a link for the torque wrench?
www.cyclingdeal.com.au/buy/venzo-bicycle-bike-1-4-inch-driver-torque-wrench-a/VZ-F33-031
@@stevenleffanue thanks
@@stevenleffanueAlex at Cycling Deal in Dandenong pranked me in 2020 , with an empty envelope . I will now have nothing to do with his team or recommend them .
How did you determine those dimensions? Saddle height, reach and drop !
Also how to determine saddle position to crank set back ?
Either a bike fit or you are happy with your set up from riding over time
I always find seats with no cushion very painful. So I don't know how someone can ride their bike a long distance without a sore a**. Do you have that problem too?
@oz cycle what do you think of that Yoeleo? Decent road bike?
A little heavy but very comfortable.
What about sit bone width?
Saddle width discussed in these two vids...
th-cam.com/video/QMy_2pR4Mzg/w-d-xo.htmlsi=oD1hYAgffg3LCem1
th-cam.com/video/B94mvr3mQec/w-d-xo.htmlsi=LopUMLtU3_z_ifgy
I have a tendency to slide forward on my saddle. Any tips to correct this? Too much reach?
Yes , could be too much reach or saddle needs to be tilted more nose up.
Increase your saddle comfort by buying an Aeroelastic AE saddle. No more testicle pain.
So quick questions.
1. Weight bearing capacity of the saddle. Do the saddles have and reference to this? I bought a Colnago and the saddle lasted 12 months or so before it cracked over a bump. It was a flexible seat but I was 84kg and apparently too heavy.
2. You didn't mention anything about saddle width. Your S saddle, I assume S for Specialised? It was the largest of the group you tested and mayhap the others were not wide enough? They looked narrower than the original, which might have meant you were sitting lower on the sides of the saddle than your original.
3. On replacing my saddle when the original went on the Colnago I went with a Fizzik. More your traditional materials over carbon, but that was because carbon was not that common at the time. Does carbon wear out more quickly because of fatigue from the flexing under the rider's weight and road surface impact?
84kg should be fine on the majority of saddles.
All about the same width...141-143mm.
I've never understood why we measure seat height from the center of the crank axle. This doesn't take into account crank arm length. I use 160mm so my measurement would need to be 10mm shorter than someone using 170mm.
Assuming both people are same leg length
Any particular reason why you are using the term "sit bone" and not pelvic bone?
Sit bone is commonly known , pelvic bone usually refers to the "girdle".
If you want to get picky, neither is technically correct. The pelvis is actually 3 bones fused together: the pubis, ilium and ischium. Many people colloquially use “pelvis” to refer specifically to the pubis. “Sit bones” is the colloquial term for the ischial tuberosities. I dare you to record a video where you say ischial tuberosities repeatedly.
Who cares ? 🤷🏼♂️
Your but will thank you
Nearly all bikefitters say sit bone , no need to get all fancy pants.
Both saddles 'appear' to be nose up slightly. My old saddle was set up this way with a level across the top resulting in a slightly nose up. New bike and saddle, when level the saddle this way results in too much nose up. Forget about how it looks and just focus on how it feels?
Exactly....how it feels. I have a permanent pelvic adduction due to back injury twenty odd years ago so slightly nose up for me.
Oz, where did you get that drawing of the cycle of pedal power and the muscle related to it? I would like to download that and print it. Thx
www.pinkbike.com/news/Which-Muscles-are-Really-Used-During-the-Pedal-Stroke-2012.html
@@stevenleffanue Steven, Thx..Your the man.. I enjoy your videos
The methods of measurement shown are fairly inaccurate esp the bar method for handlebar drop, because you are lying it along the saddle even the slightest change in saddle angle will create significant changes in the bar measurement. This will also not be reproducible with different saddles that may have different shapes for the same reason. I also consider handlebar drop a secondary measurement, it's a result of the primary measurements you should be taking and thus is relatively immaterial.
Using a self-leveling laser level with X and Y beams centered on the bb is far superior and less prone to human error. You create coordinates for the hand and sit bone contact points relative to the constant location of the BB axis. For example the sit bone contact point might be 350mm(X) and 500mm(Y). While it's a slight bit more work to set up and ensuring the frame is level (using the laser to level the front and rear axles whilst in a stand works best for me) you get far more precision and repeatability across bikes and individual components.
But I love the Al foil method for getting an accurate sit bone location. Nicely done on that.
The super team fizik Argo copy may be better run with some extra nose down. I have Argos on all my bikes and run the nose down a little due to the kick at the back. I know this is going to mess with your measurements though, almost looks like the nose it up in your vids.
I couldn't get comfy on it at all , best was with nose slightly up but still no good for me. If Argos fits you , you would probably find the copy works for you too.
@ nah I wouldn’t trust a flung dung seat under my family jewels 🤣
I just cannot seem to find a solution to penile numbness and loss of feel issues, got a bike fit, testet probably about 20 saddles at every angle, height and setback possible. tried several styles of bibshort but just cannot seem to solve this.
Try saddles with a perennial relief channel.
@ all I’ve tried have had one
ISM saddle?
@ I’ve tried them before but didn’t feel like the helped me. Didn’t quite understand how I am supposed to sit on them and still got numbness.
Have you tried a SQlab Ergowave?
😕 Phew. That was a lot sir.
Dude. Clamping the top tube and then leaning all over it!! Giving me anxiety!!
It's OK, it's not clamped
Semasi "arse heaven "
Shouldn't adjust reach by adjusting saddle setback/offset.
Pulling up when pedalling is not recommended, it's been shown to be inefficient and unneccessary.
You didn't allow for saddle padding density/compressibility
Pretty much impossible to adjust tilt by 1mm with most saddle rail clamps.
Most modern road bikes have micro-adjustable seat clamps now.
Yes , saddle foam compression will generally affect height, but it's difficult to measure...if you suspect significant difference in padding compression between saddles you can take an educated guess.
Clamp on the toptube while putting pressure on the bars. Sorry, but I'm not taking any advice from you
Not clamped, just sitting there....never clamp on carbon...even seatposts
@stevenleffanue don't put pressure on the bike when it's resting like that. That's exactly what clamping does.
It's not clamped
@@stevenleffanue it doesn't have to be. You're putting compressive load in a stress riser