Having to do With Court's New Review of the Biktrix Juggernaut Ultra FS

[reed scott]

You are absolutely wrong as far as a hardtail is concerned. I have personally broken (3) aluminum frames at the same point and some friends have had failures too. Drive side lower chainstay close to the front curve portion. All you have to do is hit the throttle and hold the brake to see the torque stress. And knowing aluminum it will flex, and flex until it cracks and then your done. My last hardtail ( Surly Wednesday ) was a steel frame with a 170mm rear horizontal dropout. I built a torque bracket for me and my friends to clamp to the motor housing and lay flat to the non-drive rear chainstay and we use a hose clamp ( painted black ) and have not had any frame breaks in over a year . My buddy has a Juggernaut FS Ultra and the rear dropout is 197mm! So I'm guessing a wider footprint means less stability and more flex? Not bashing at all just my opinion. More pivot points means less stress per pivot yeah? I got a frame from WW and the rear dropout is 148mm and I see ZERO flex in the rear end and shifting is silent and has so far never made any noise at all. Flex is about transferring energy through the complete spectrum and the wider it is the more deflection. Thats why the 150mm Rockshox Bluto noodles a bit more than it should. Running a 110 or even a 135mm front hub keeps everything tighter, in my opinion.View attachment 71642

View attachment 71643


View attachment 71644

"Not Luna" Now that right there is funny.

 

[Mike_V]

Court's video illustrated several limitations of this design which have been described here in comments.
I count (6) sets of pivots in this now common rear "rocker" suspension, 'noun?
Stack up the 'sloppy' loose fits between these bushings, machining tolerances, weldments castings , shock assemblies:
= ~ 8mm of play as shown in the video.
Then rigidly constrain the axle to hear the disk brake rub one brake shoe.
It's too much !

 

[reed scott]

Court's video illustrated several limitations of this design which have been described here in comments.
I count (6) sets of pivots in this now common rear "rocker" suspension, 'noun?
Stack up the 'sloppy' loose fits between these bushings, machining tolerances, weldments castings , shock assemblies:
= ~ 8mm of play as shown in the video.
Then rigidly constrain the axle to hear the disk brake rub one brake shoe.
It's too much !

Well then, how SHOULD a rear suspension be done? No criticism. Just wondering what might be better.

 

[reed scott]

This is how my Specialized XC MTB does it: Ten year old bike

I should add, there is absolutely zero side to side slop, flex or movement in this hinge whatsoever.

 

[roshan]

This is how my Specialized XC MTB does it: Ten year old bike

View attachment 71647

I should add, there is absolutely zero side to side slop, flex or movement in this hinge whatsoever.

It'll start if you add a 160Nm mid motor and put in a fat bike wheel (190/197mm hub).. Those two things is what makes it challenging.

 

[roshan]

Court's video illustrated several limitations of this design which have been described here in comments.
I count (6) sets of pivots in this now common rear "rocker" suspension, 'noun?
Stack up the 'sloppy' loose fits between these bushings, machining tolerances, weldments castings , shock assemblies:
= ~ 8mm of play as shown in the video.
Then rigidly constrain the axle to hear the disk brake rub one brake shoe.
It's too much !

It's no where close to 8mm of movement side to side.

 

[Art Deco]

If you watch closely at the first "flex" mention (24:50) you'll see that Court is wrong about the cause. The swing arm itself isn't deflecting, it's the center pivot arm (not sure what that's called) which is pivoting on its bearings. This is the arm that translates the swing arm up/down motion on one end into the in/out motion for the rear shock at the other end.
Here's an arrow pointing to the center pivot arm:
View attachment 71467

Here's a shot from the video:
View attachment 71468

When watching the video on your computer, go full screen and place the mouse cursor at the rear arrow (leftmost in the above photo), which is where the swing arm joins to this center pivot arm thing. As Court uses throttle and the shift interlock re-enables you'll see that point move laterally (up/down on the screen relative to the cursor). The swing arm itself doesn't appear to deform as much as there is play somewhere in this multi-pivot mechanism. Note that the distance from the center pivot to the rear swing-arm pivot is pretty big so any small play in the center pivot gets magnified out by leverage.
Maybe this is something that can be adjusted or maybe it's something in the quality of the bearings used, or maybe it's just this particular example.

I also note that in both this section and the later section, where Court is climbing a short steep hill, he's in the top or almost top gear. In the second section of the video, he's again using only throttle and is going too slow and up too steep for that top gear. The top gear (small sprocket at the rear) isn't meant for hill climbing, it's meant for high speed on level or downhill ground.

I'm also not understanding the rear brake "zing" thing, either. The wheel, the brake disc, and the brake caliper are all attached to the swing arm. So, even if it deflects (or pivots as shown above), that shouldn't affect alignment.

You have sharp eyes ...

 

[MartsEbike]

The issue for me is the linkage on the chainstay. These are always a weak point, with quite a few broken examples, especially on the AM1000 style frames, also M620 powered - Frey themselves on their frame don't have this hinge point. This joint adds the chance for the rear triangle to flex more than normal. The chainstay arms provide no vertical strength.

 

[reed scott]

The issue for me is the linkage on the chainstay. These are always a weak point, with quite a few broken examples, especially on the AM1000 style frames, also M620 powered - Frey themselves on their frame don't have this hinge point. This joint adds the chance for the rear triangle to flex more than normal. The chainstay arms provide no vertical strength.

Agree but I am still very curious why Frey adds the vertical piece that ties the chain stay and seat stay together. It is quite beefy with massive weld. As you say, can't see how it could add in effort to counteract the type of movement we have been discussing. Although it would make the entire rear triangle a solid piece. Regardless, what I have determined through this discussion will be to use judicious use of throttle and use of correct gears when my bike finally arrives. Full throttle in high gears from stop or very slow speed is like laying rubber with your hotrod. Sooner or later your rear end is gonna blow up.

 

[roshan]

The issue for me is the linkage on the chainstay. These are always a weak point, with quite a few broken examples, especially on the AM1000 style frames, also M620 powered - Frey themselves on their frame don't have this hinge point. This joint adds the chance for the rear triangle to flex more than normal. The chainstay arms provide no vertical strength.

That hinge point depends on the suspension design. With a solid rear triangle like what Frey has, you'll see that when you start moving from standstill, the rear end would push the suspension hence making the seat move upwards several mm. This is not desirable.

 

[MartsEbike]

Actually I should probably say "Frey no longer use this themselves"... I'm not too sure about the older versions. I know the newer ones don't.

 

[greeno]

Where can you access "Courts new review" video?

 

[MartsEbike]

That hinge point depends on the suspension design. With a solid rear triangle like what Frey has, you'll see that when you start moving from standstill, the rear end would push the suspension hence making the seat move upwards several mm. This is not desirable.

I know, but its a poor design. Everything is a compromise, I'd rather the extra strength as this isn't really a noticeable effect that has been observed and stated by owners - at least with any real negative consequence.

 

[MartsEbike]

Agree but I am still very curious why Frey adds the vertical piece that ties the chain stay and seat stay together. It is quite beefy with massive weld. As you say, can't see how it could add in effort to counteract the type of movement we have been discussing. Although it would make the entire rear triangle a solid piece. Regardless, what I have determined through this discussion will be to use judicious use of throttle and use of correct gears when my bike finally arrives. Full throttle in high gears from stop or very slow speed is like laying rubber with your hotrod. Sooner or later your rear end is gonna blow up.

View attachment 71652

I think its because they have an upper (3 point) and lower (2 point) linkage. If you removed it you'd have the same issue as I point out with the chainstay joint, weak rear triangle that could flex. I don't think the carbon based bikes are quite as restricted in this regard with the design.

 

[greeno]

Im pretty sure ALL e-bike's flex in the rear triangle when hitting the throttle. Here's what mine looks like.

I think the tighter (narrower) the width equals less flex. Again where can I view the video in question?

 

[reed scott]

Im pretty sure ALL e-bike's flex in the rear triangle when hitting the throttle. Here's what mine looks like.
View attachment 71656View attachment 71657View attachment 71658

I think the tighter (narrower) the width equals less flex. Again where can I view the video in question?

View on EBR review page.

 

[reed scott]

Where can you access "Courts new review" video?

View on EBR review pages.

 

[smorgasbord]

You have sharp eyes ...

Mostly I have a big monitor. Like I said, use the cursor as an index position.

 

[smorgasbord]

This is how my Specialized XC MTB does it: Ten year old bike,,,

I should add, there is absolutely zero side to side slop, flex or movement in this hinge whatsoever.

I'd like to see your dial caliper/video recording setup while riding by which you determined that there is "absolutely zero side to side" movement. Otherwise, you have no backing for your claim. Not to remind everyone that your bike is not even an e-bike and most riders are not capable of applying 160nM of torque without a motor.

You can't tell by moving parts with your hands. This happens under load, and as Roshan points out, with fat tires and the 160nM of torque suddenly and quickly being applied to the furthest from the center sprocket. Not proper riding technique.

 

[greeno]

Finally found the vid thanks.

But a non-e-bike can still get jacked. I used to race road bikes back in the early 90's and I had a teammate who was a sprinter totally crush his rear end by gettin on it to hard. And no he didn't win the sprint, his rear end stopped dead and he flew over the bars and into the crowd, not his best day. The mechanics figured his QR was a little loose and allowed a bit to much play and pow. Oh well just glad it wasn't me.

I did watch the video and you can definitely see the side pull flex when he hits the throttle. But its probably a non issue if you don't go with the level 5 and an 11 tooth cog on the rear. The Juggernaut's rear dropout being 25% wider than my bike and using the offset spider the chainring is mounted to on the motor to help with the chainline probably comes into play also. And the 8mm flex is probably measured at the rear end of the tire ( farthest point of travel ) just a thought. I wonder why they went with the 197mm dropout instead of a 170mm? Thats about an inch less span and I think that would help. My hardtail has a 170mm rear end and I have 4" tires and not even close to having a clearance problems.
Im not a designer so what do I know.