Ultra FS frame flex and armadillo fender on DNM upgrade

Slayer33

New Member
So still very new to my Ultra FS, I did my usual commute 50km round trip today. Used about 70% of my 52V 17.5Ah battery on PAS9. My morning commute started off poorly as my armadillo front fender broke off on the first little curb I rode off.. had to pick it up and toss it in my backpack. Emailed Biktrix about the clearance issue as I had the fender mounted as high as it would go on the DNM fork.

On my way home I started see how much power this bike had, and one thing with all the torque and a full suspension bike is frame flex, has anyone else noticed the motor flexes a fair amount on the frame? I'm wondering if this is normal and if there are any precautions an Ultra FS owner should look to do to ensure things are tight and don't cause premature failure...

Other than that, geez this bike is fun.. the new head angle really helps with flying around curves and soaking up bumps at high speeds!!! Loving it!!! I'm coming from an NCM Aspen 500W rear hub fatbike.

Not much to compare here.. it's like comparing a Ferrari vs. a Hyundai Pony
 

reed scott

Well-Known Member
So still very new to my Ultra FS, I did my usual commute 50km round trip today. Used about 70% of my 52V 17.5Ah battery on PAS9. My morning commute started off poorly as my armadillo front fender broke off on the first little curb I rode off.. had to pick it up and toss it in my backpack. Emailed Biktrix about the clearance issue as I had the fender mounted as high as it would go on the DNM fork.

On my way home I started see how much power this bike had, and one thing with all the torque and a full suspension bike is frame flex, has anyone else noticed the motor flexes a fair amount on the frame? I'm wondering if this is normal and if there are any precautions an Ultra FS owner should look to do to ensure things are tight and don't cause premature failure...

Other than that, geez this bike is fun.. the new head angle really helps with flying around curves and soaking up bumps at high speeds!!! Loving it!!! I'm coming from an NCM Aspen 500W rear hub fatbike.

Not much to compare here.. it's like comparing a Ferrari vs. a Hyundai Pony

Can you describe this flexing you mention. Doesn't sound good.
 

Slayer33

New Member
Can you describe this flexing you mention. Doesn't sound good.

Well when I feel the pedal assist come on I can see the motor almost the whole bottom bracket/frame area a half inch to the left.. almost like if there's too much torque.. I was on the smallest cog 11T and PAS5-9 at slow speeds when I noticed it
 

reed scott

Well-Known Member
Well when I feel the pedal assist come on I can see the motor almost the whole bottom bracket/frame area a half inch to the left.. almost like if there's too much torque.. I was on the smallest cog 11T and PAS5-9 at slow speeds when I noticed it

That does not sound right. Check the bolts mounting the motor to the bracket. Can you move the motor at all with your hand? Contact Biktrix.
 

reed scott

Well-Known Member
Well when I feel the pedal assist come on I can see the motor almost the whole bottom bracket/frame area a half inch to the left.. almost like if there's too much torque.. I was on the smallest cog 11T and PAS5-9 at slow speeds when I noticed it


You are going to do damage or at least accelerated wear at high pas, small cog, low speed.
 

Slayer33

New Member
Gotcha, checked it over, lower linkage bolts were a little loose. Feels a bit better now. I need to learn how to ride the mid drive properly and ride it like a normal mtb vs a hub powered ebike.
 

lordnox09

Member
Gotcha, checked it over, lower linkage bolts were a little loose. Feels a bit better now. I need to learn how to ride the mid drive properly and ride it like a normal mtb vs a hub powered ebike.
give it a week and try to ride you other bike it feels like you are getting on a trike the handle bars are so small and so close you your legs its weird as hell

on a side note that just seems insane that you got 50km on 1 charge using pas 9 i have only been able to get like 55km and it was in pas 1-2 99% of the time and 3 for the other 1% where you in a fairly easy gear the whole time what was your speed a majority of the time
 

roshan

Well-Known Member
A little flex is expected on an FS frame where the motor puts out 160Nm of torque. You should keep in mind that the better you use gears (larger/lower gears to start and smaller/higher gears once you get going) the flex will be minimal. The flex will be most noticeable if you put out full throttle from standstill in the highest gear.
 

Hintrod

New Member
I have a Ultra FS full Suspension and I felt the exact same thing when I accelerated especially with the throttle. I too also assumed that the frame was flexing. I was wrong, when I carefully examined the bike I noticed that the bolt nut and washer were all missing on one side of the frame nearest to the ground on the rear suspension, It really shook me that I was riding around at high speed on a brand new bike and it was missing key parts. On the other side the same hardware was also loose.

I called Biktrix and they sent me the missing hardware and I had my local bike shop check all the hardware on the bike and tighten all nuts and bolts with Loctite.

Ever since then there is no flexing in the frame other than the normal suspension play and I check that hardware regularly...with all that torque it would be a disaster if the lower frame came apart at speed.
 

reed scott

Well-Known Member
I have a Ultra FS full Suspension and I felt the exact same thing when I accelerated especially with the throttle. I too also assumed that the frame was flexing. I was wrong, when I carefully examined the bike I noticed that the bolt nut and washer were all missing on one side of the frame nearest to the ground on the rear suspension, It really shook me that I was riding around at high speed on a brand new bike and it was missing key parts. On the other side the same hardware was also loose.

I called Biktrix and they sent me the missing hardware and I had my local bike shop check all the hardware on the bike and tighten all nuts and bolts with Loctite.

Ever since then there is no flexing in the frame other than the normal suspension play and I check that hardware regularly...with all that torque it would be a disaster if the lower frame came apart at speed.

EMTB guys on you tube have a video on checking over your bike before every ride. Takes a couple minutes. Not hard to do at all. Good practice. It's like at least looking at the tires on your car or truck before you leave the driveway. I usually don't even. But then I'm a lucky bastage. :cool: