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Steel frame flex

Old 01-31-18, 12:00 PM
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Steel frame flex

I have a Soma Juice 29er that I recently built. It's the flexiest frame that I have ever ridden and I don't know where the flex is coming from. I'm not sure if it's just the nature of this frame or if it's due to the style of sliding dropouts and QR skewers/axle diameter. Would switching to a through axle in the rear stiffen things up much? Any thoughts or experience with this?
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Old 01-31-18, 12:27 PM
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A flexible frame is not necessarily bad. Stiff frames are not necessarily better. Is there something in particular about it that makes you think it could work better?

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Old 01-31-18, 12:52 PM
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I wonder how that bike would feel with a rigid fork? A lot of flex can come from a fork. Additionally those huge hoops have a lot of span to keep steady. It's tricky assessing a frame's stiffness when the forces are acting through other structures. Andy
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Old 01-31-18, 01:52 PM
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Originally Posted by Andrew R Stewart View Post
I wonder how that bike would feel with a rigid fork? A lot of flex can come from a fork. Additionally those huge hoops have a lot of span to keep steady. It's tricky assessing a frame's stiffness when the forces are acting through other structures. Andy
I have a rigid Soma steel fork on it and Hope Pro 4 Enduro wheelset, which is fairly stiff.
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Old 01-31-18, 03:33 PM
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It may just be the nature of the frame. To borrow a quote from Soma's own FAQ page, you could just be experiencing the "springy, lively quality that steel is famous for".

To be a little more specific, the frame's front triangle is made from Tange Prestige tubing, which is pretty thin-walled stuff. It's 0.7 mm at the butted ends and 0.4 mm in the middle of the tube. And it's not oversized tubing, which would add some rigidity.
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Old 01-31-18, 03:44 PM
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Originally Posted by SkyDog75 View Post
It may just be the nature of the frame. To borrow a quote from Soma's own FAQ page, you could just be experiencing the "springy, lively quality that steel is famous for".

To be a little more specific, the frame's front triangle is made from Tange Prestige tubing, which is pretty thin-walled stuff. It's 0.7 mm at the butted ends and 0.4 mm in the middle of the tube. And it's not oversized tubing, which would add some rigidity.
There have always been a few levels of Prestige tubing. Current "Standard" Prestige is 0.8-0.5mm DB, so that's almost certainly what this is. Available in OS and double OS diameters.

What's now called "Prestige Japan" is 0.7-0.4mm DB. Prestige Ultimate and Ultimate Keirin are 0.65-0.35mm DB. If the tubing decal doesn't specify anything beyond "Prestige" it's the 0.8-0.5mm stuff.

https://www.tange-design.com/tubing_list.php?type_sn=1
click on thumbnails for full tube specs.
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Old 01-31-18, 03:57 PM
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Thanks for the correction and the link, @Ghrumpy . Always glad to learn new stuff.

While this particular flavor of Prestige might not be quite as thin as I was thinking, it could still be flexy when compared to other frame types. Or "compliant" if you want to paint it in a positive light. "Noodly" if you're not being so complimentary. ;-)
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Old 01-31-18, 08:50 PM
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A large part of flex depends on riding style. If you are in the habit of low revs, especially on acceleration, then you will experience flex on most bikes. It is extremely difficult to provide vertical compliance for comfort while providing lateral stiffness. Even then as noted by others extra stiffness is not necessarily in itself desirable. I had a very stiff Jackson Rake 16 criterium bike and even with that it was possible to get some flex in an out of the saddle sprint.
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Old 01-31-18, 11:19 PM
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Would converting to a thru axle stiffen the rear end up much?
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Old 02-01-18, 12:38 AM
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How are you perceiving the lack of stiffness? Would make it easier to conceptualize where the problem is. Thru axles will probably help a little bit if your primary issue is how the rear wheel tracks while a lateral load is applied to it.
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Old 02-01-18, 08:09 AM
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Originally Posted by bigbubba76 View Post
I have a Soma Juice 29er that I recently built. It's the flexiest frame that I have ever ridden and I don't know where the flex is coming from. I'm not sure if it's just the nature of this frame or if it's due to the style of sliding dropouts and QR skewers/axle diameter. Would switching to a through axle in the rear stiffen things up much? Any thoughts or experience with this?
What crankset and bottom bracket do you have?
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Old 02-01-18, 01:37 PM
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Originally Posted by ColonelSanders View Post
What crankset and bottom bracket do you have?
I have the current spec Shimano XT crankset and bottom bracket.
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Old 02-01-18, 01:39 PM
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Thanks everyone for your input. I have come to the realization that it's just a flexy frame.
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Old 02-01-18, 01:56 PM
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Originally Posted by cpach View Post
How are you perceiving the lack of stiffness? Would make it easier to conceptualize where the problem is. Thru axles will probably help a little bit if your primary issue is how the rear wheel tracks while a lateral load is applied to it.
It seems to be most noticeable when I am seated, pedaling or not and apply torque to the handlebar. It feels the the frame is twisting. It's unlike any bike that I've ever had or ridden before. It feels excessive and it's my first experience with IRD Tange sliding dropouts and SOMA, so didn't know if I should attribute the flex to the frame or to the several bolted connections in the dropouts vs. welded or a combination. I am realizing that it is probably more the frame than anything, but I may try swapping the standard QR skewer and dropout to a 12mm thru-axle.
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Old 02-01-18, 03:25 PM
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I very much doubt that you can twist the frame in any direction by merely torqueing the handlebars. Perhaps it's bars or stem.
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Old 02-01-18, 05:25 PM
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Originally Posted by bigbubba76 View Post
It seems to be most noticeable when I am seated, pedaling or not and apply torque to the handlebar. It feels the the frame is twisting. It's unlike any bike that I've ever had or ridden before. It feels excessive and it's my first experience with IRD Tange sliding dropouts and SOMA, so didn't know if I should attribute the flex to the frame or to the several bolted connections in the dropouts vs. welded or a combination. I am realizing that it is probably more the frame than anything, but I may try swapping the standard QR skewer and dropout to a 12mm thru-axle.
Have you been able to determine if the flex in the frame slows you down at all?
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Old 02-01-18, 06:19 PM
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It's not clear (to me) if you have ridden this bike and found the flex in the frame to be negative. Stiffness in a bicycle seems to be the considered 'good' in today's thinking. But in the 'old' days, we looked for a 'responsive' velo. For a bike to be responsive in must have an appropriate amount of flex that matched the style, weight and power of the rider. This can be difficult to achieve. When a bike is too stiff for the rider it will feel 'dead', unresponsive. But a bicycle with the correct amount of flex will feel lively and responsive. You will actually sprint faster and climb better on a heavier but responsive bike than you will on a lighter but stiff bike. As someone else already pointed out, many of the old pros had very good success riding velos that were considered 'flexy'. And those guys crank out mega watts. If you have not given the bike a good test ride yet take it for a good ride. Ride the bike. Put it thru its paces and see how it responds. You might be pleasantly surprised. It's true, too much flex is undesirable, but the correct amount of flex gives you a bike you want to ride all the time. And for an 'off-road' machine this is probably even more desirable. If you have ridden the bike and found the flex to be a problem then we can start thinking about how that might be corrected.

Keep Pedalin'.
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Old 02-01-18, 06:47 PM
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The handle bigbubba76 might be a sign.
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Old 02-01-18, 07:30 PM
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Originally Posted by 02Giant View Post
The handle bigbubba76 might be a sign.
You're not funny and unless you have a productive contribution, go **** off and be a troll elsewhere. My handle has nothing to do with my size or stature.
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Old 02-01-18, 07:55 PM
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I'm only a cycling amateur, but I have maybe a similar experience to yours. Most of my bikes growing up were cheap steel (pretty heavy and stiff), and the bike on which I've spent the most time in the last few years is an aluminum hybrid, which is also pretty stiff. It has a suspension fork, but you can very much tell that the frame is stiff.

Less than a year ago, I bought used my first "nice" steel bike, a 1997 Trek 750 with double-butted chrome-moly steel. This frame is super flexible, at least compared to what I'm used to. Holding the brakes on, and just putting weight on the forward pedal, the bottom bracket area twists down under the load. I've examined the bike thoroughly, and the frame is perfectly fine from the perspective of welds not being broken...it's just a sensation that I've never felt prior to now due to not ever owned this type of frame material. Its fork (in the same material) is also pretty soft/comfortable. Much more so than the hi-ten steel or alloy forks on some of my other bikes.

I've read how some people say that ride quality on certain steel is just so much more comfortable, but it never really hit home with me until I experienced a bike like that for myself.
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Old 02-02-18, 04:49 AM
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Originally Posted by bigbubba76 View Post
You're not funny and unless you have a productive contribution, go **** off and be a troll elsewhere. My handle has nothing to do with my size or stature.
I thought it may be pertinent, but then, my crystal ball wasn't working at the time.
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Old 02-02-18, 06:44 AM
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Originally Posted by bigbubba76 View Post
It seems to be most noticeable when I am seated, pedaling or not and apply torque to the handlebar.
I can't visualize this. Are you pushing forward, pulling back or what? I agree that it's hard to figure what you could do to the bars (while riding seated) that would cause your frame to flex. I once had a frame that seemed flexy but I only noticed it when standing to climb.
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Old 02-02-18, 07:58 AM
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I think you could brace the axles against something and push your foot against the bottom bracket and see where the flex is, if any.
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Old 04-02-18, 12:59 AM
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I happened to google Soma juice and this thread popped up.... I hope I can help.
I have owned a juice for 4 years now. I raced the SSWC on it and I have ridden tons of fun single track on it and I have recently converted it into a rigid commuter. I have used 135QR and 142x12 rear axle on it and it is a 19" frame. This is hands down the most flexy steel frame I have ever owned. It is not close. With wide bars, you can watch the front triangle twist when cranking up hills.

That said - when using it for cruising around, it is one of the best riding frames I have owned. Super chill and smooth. With a 100mm fork on it, had decent manners, but a 120mm made the front feel detached from the bike. The confidence factor plummeted quickly. Now with a rigid, it wa great around the neighborhood, but one you put any weight on the racks, it is a wet noodle again.

I see the OP concluded it is just a flexy frame and he is right. Just wanted to confirm.

I am comparing the ride to my other steel frames - my Vassago, Stanton and Salsa are significantly more confidence inspiring.
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Old 03-16-19, 10:13 PM
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Originally Posted by bloaker View Post
I happened to google Soma juice and this thread popped up.... I hope I can help.
I have owned a juice for 4 years now. I raced the SSWC on it and I have ridden tons of fun single track on it and I have recently converted it into a rigid commuter. I have used 135QR and 142x12 rear axle on it and it is a 19" frame. This is hands down the most flexy steel frame I have ever owned. It is not close. With wide bars, you can watch the front triangle twist when cranking up hills.

That said - when using it for cruising around, it is one of the best riding frames I have owned. Super chill and smooth. With a 100mm fork on it, had decent manners, but a 120mm made the front feel detached from the bike. The confidence factor plummeted quickly. Now with a rigid, it wa great around the neighborhood, but one you put any weight on the racks, it is a wet noodle again.

I see the OP concluded it is just a flexy frame and he is right. Just wanted to confirm.

I am comparing the ride to my other steel frames - my Vassago, Stanton and Salsa are significantly more confidence inspiring.
Thank you for your contribution and for validating my thoughts on this flexy
frame. I have the 21" size. Although, I enjoy this bike for the most part, I probably would not buy another one.
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