Bosch Gen4 Perf Line CX stutters in Turbo after update - why? ('21Trek Rail 7)

AcerGT

New Member
I purchased a 2021 Trek Rail 7 in Aug 2020 knowing that Bosch planned an update for the bike's Gen 4 Performance Line CX motor which increases torque from 75 to 85 nm. I had fun riding during August and September, then returned the bike for the software upgrade through the dealer only to find that my bike stutters in Turbo now. By "stutter" I mean that the power pulses through the pedal stroke - turning on and off - and the speed indicator goes wacky displaying 14 mph one sec and 19 mph the next then back again. I use Turbo mode when pedaling on the paved roads to my trail area and this stutter is both annoying and unsafe. I brought the bike back to my Trek dealer and they verified that the the software upgrade was correct (it's Performance Line CX 1.1.2.0). They sent me home with my faulty bike and said they would investigate with Trek and Bosch. I used the bike for only a few more weeks last Fall before hanging it up for the Winter, and never heard back from the dealer. Fast forward to today and I picked up my bike from the dealer after a spring tune up, and it has the same problem - it still stutters at higher speeds in Turbo. The "low IQ" service rep said, "Yeah, all the Trek Rails do that". I've now left the bike with the dealer while they contact Trek and Bosch again, but I don't have confidence they'll figure out what is wrong. I know from reading this forum that a "stutter" in the pedal stroke may have something to do with a problem with the torque sensor. What's weird to me is that my new bike worked fine before the Gen 4 software update adding more torque. Anyone else have this problem or suggestions about how to fix it?
 

rich c

Well-Known Member
Only time I had a wild pattern of speed on the display was when the back axle nut was coming loose and the distance on the spoke sensor was changing as I rode. Not a Gen 4 though.
 

Dallant

Well-Known Member
Never had this issue with my Allant+7 CX. I also had the update and change from Sport to EMTB mode. I wonder if they have done a diagnostic since the update. Maybe they can change back to the previous software version.
 
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McCorby

Well-Known Member
Does it have a spoke magnet? If so, it may have come lose and/or is misaligned with the speed sensor on the chain stay.
 

William - Bosch Team

Active Member
The sporadic speed display points to speed sensor issue, as was mentioned above. A 2021 Rail should have Trek's proprietary speed sensor and rotor-mounted magnet combo, so mis-alignment of the magnet is less likely here, though was a common issue in the past. Some of the other things you shared don't necessarily support this though.

The new software update for the CX drive unit includes a feature that gives a little bit of extra "after-run" once you stop pedaling... this is designed to help you make it up wonky obstacles, through tough rock gardens, etc. I'd say this may be what you are experiencing, but the sporadic speed readout conflicts with this.

Something else to keep in mind is the nature of the Bosch system... it requires a certain amount of torque input from you to keep steady support. On the trails, this happens fairly easily, but Turbo-mode test-rides in the parking lot or on pavement in general can often make for a "pulse" experience. Turbo mode on the CX drive unit is designed for max. support, as you know, and often times in easier conditions the powerful engagement of Turbo support can give enough push that the rider is temporarily not applying enough torque. Happens to me with CX Turbo on parking lot test-rides. A very good test is to find a long, steep-ish hill, and to steadily pedal up it in Turbo mode.

If possible, push your shop to contact Bosch service. They can look at the diagnostic report your shop sends them, as well as guiding your shop through some more in-depth troubleshooting.
 

AcerGT

New Member
The sporadic speed display points to speed sensor issue, as was mentioned above. A 2021 Rail should have Trek's proprietary speed sensor and rotor-mounted magnet combo, so mis-alignment of the magnet is less likely here, though was a common issue in the past. Some of the other things you shared don't necessarily support this though.

The new software update for the CX drive unit includes a feature that gives a little bit of extra "after-run" once you stop pedaling... this is designed to help you make it up wonky obstacles, through tough rock gardens, etc. I'd say this may be what you are experiencing, but the sporadic speed readout conflicts with this.

Something else to keep in mind is the nature of the Bosch system... it requires a certain amount of torque input from you to keep steady support. On the trails, this happens fairly easily, but Turbo-mode test-rides in the parking lot or on pavement in general can often make for a "pulse" experience. Turbo mode on the CX drive unit is designed for max. support, as you know, and often times in easier conditions the powerful engagement of Turbo support can give enough push that the rider is temporarily not applying enough torque. Happens to me with CX Turbo on parking lot test-rides. A very good test is to find a long, steep-ish hill, and to steadily pedal up it in Turbo mode.

If possible, push your shop to contact Bosch service. They can look at the diagnostic report your shop sends them, as well as guiding your shop through some more in-depth troubleshooting.
Thanks for your reply. I've passed it on to my dealer and I am waiting to hear from them. I use Turbo when riding the 5 miles to/from my trail area, and during that time my pedal cadence is a constant 75 rpm. The stutter occurs during that steady cadence.
 

William - Bosch Team

Active Member
Thanks for your reply. I've passed it on to my dealer and I am waiting to hear from them. I use Turbo when riding the 5 miles to/from my trail area, and during that time my pedal cadence is a constant 75 rpm. The stutter occurs during that steady cadence.
Riding at a higher (ideal) cadence of 75 rpm, on pavement, and in Turbo can definitely cause some stuttering, or "pulsing on/off" of assistance as it may be hard to maintain the requisite 30 or 40 Nm (I forget which it is) of rider torque input at all times. Try the same thing in a lower assistance mode, or at a lower cadence, or on a steady uphill.

Turbo on CX is optimized for getting you up gnarly, technical trails, not necessarily steady spinning/cruising on smoother surfaces. My Gen 4 Performance Speed drive unit does the same thing unless I'm riding into a strong head wind, going up a slight hill, or somehow otherwise managing to keep sufficient torque on the cranks.
 

AcerGT

New Member
Riding at a higher (ideal) cadence of 75 rpm, on pavement, and in Turbo can definitely cause some stuttering, or "pulsing on/off" of assistance as it may be hard to maintain the requisite 30 or 40 Nm (I forget which it is) of rider torque input at all times. Try the same thing in a lower assistance mode, or at a lower cadence, or on a steady uphill.

Turbo on CX is optimized for getting you up gnarly, technical trails, not necessarily steady spinning/cruising on smoother surfaces. My Gen 4 Performance Speed drive unit does the same thing unless I'm riding into a strong head wind, going up a slight hill, or somehow otherwise managing to keep sufficient torque on the cranks.
Could you explain how eMTB is different from Turbo. I thought that eMTB mode monitored your torque and adjusted power up and down as needed. Steeper hills would get more torque without having to change modes. Turbo mode would be steady power. I'd really like to understand the difference between these modes better.
 

William - Bosch Team

Active Member
For the Gen4 CX drive unit: Tour mode is 140% on top of rider input, Sport mode is 240%, and Turbo is 340%. eMTB mode replaces Sport, and automatically varies, based on rider input, anywhere between 140% and 340%.

Steeper hills do require more energy expenditure to climb, but higher cadence would lessen the need for torque, so a steeper hill would not necessarily equate to max. support from eMTB mode. Keep in mind... at most, eMTB mode is equal to Turbo, but only when the rider input is at a maximum.
 

TroutRunner

New Member
Region
USA
I just got a new Orbea with the Bosch CX Performance motor and had the exact issue as the original poster. He described it perfectly. Best way to make it happen is on a steepish hill that with good cadence and pressure, it stutters like crazy. I can recreate it every time.

Did the OP or William-Bosch Team determine a fix?
 

William - Bosch Team

Active Member
I just got a new Orbea with the Bosch CX Performance motor and had the exact issue as the original poster. He described it perfectly. Best way to make it happen is on a steepish hill that with good cadence and pressure, it stutters like crazy. I can recreate it every time.

Did the OP or William-Bosch Team determine a fix?
Hard to determine what is happening remotely. Best course of action would be to have a Certified Bosch dealer take a look for you.
 

Dallant

Well-Known Member
I just got a new Orbea with the Bosch CX Performance motor and had the exact issue as the original poster. He described it perfectly. Best way to make it happen is on a steepish hill that with good cadence and pressure, it stutters like crazy. I can recreate it every time.

Did the OP or William-Bosch Team determine a fix?
Mine has a minor, gentle vibration but it’s seems quite rare and short-lived.
 

William - Bosch Team

Active Member
I just got a new Orbea with the Bosch CX Performance motor and had the exact issue as the original poster. He described it perfectly. Best way to make it happen is on a steepish hill that with good cadence and pressure, it stutters like crazy. I can recreate it every time.

Did the OP or William-Bosch Team determine a fix?
I just re-read the original post from March. If your speed is sporadic, it is a speed sensor related issue. Your Trek dealer can re-align the sensor based on some tech docs from Trek, as well as check a few other things. There is also a software update that specifically targets this issue on Bosch-equipped Trek eBikes.
 

TroutRunner

New Member
Region
USA
Thanks for the reply. I have an Orbea, not Trek, with the new rotor magnet instead of the spoke magnet.

I dropped it off at the dealer today, he did the updates and said he can't replicate the issue. I live 1 hour away. We'll see, I can do it every time before drop off.

Hope a computer upgrade does the trick but I'm dubious.

TR
 

William - Bosch Team

Active Member
Thanks for the reply. I have an Orbea, not Trek, with the new rotor magnet instead of the spoke magnet.

I dropped it off at the dealer today, he did the updates and said he can't replicate the issue. I live 1 hour away. We'll see, I can do it every time before drop off.

Hope a computer upgrade does the trick but I'm dubious.

TR
Ooops, that's my mistake, I'm sorry! Busy day, trying to juggle too many things. :oops:

Interested to hear what your shop says. If it is a rotor magnet, then it may have the new Bosch slim sensor. I believe it may also benefit from the software update, and there may also be room for sensor position adjustment, but not sure on the Orbea.
 

Dallant

Well-Known Member
I just re-read the original post from March. If your speed is sporadic, it is a speed sensor related issue. Your Trek dealer can re-align the sensor based on some tech docs from Trek, as well as check a few other things. There is also a software update that specifically targets this issue on Bosch-equipped Trek eBikes.
Do you have a link to this update? What version it is, what specific bikes it is for, etc?
 

TroutRunner

New Member
Region
USA
My dealer updated my bike to the latest editions of everything. He thought they came from the factory updated. The sensor needed an adjustment also and now my bike is running great again.

TR
 

AcerGT

New Member
My dealer updated my bike to the latest editions of everything. He thought they came from the factory updated. The sensor needed an adjustment also and now my bike is running great again.

TR
I’m the OP, and my bike is fixed, too. A seasoned tech at my LBS took over fixing my bike and told me he reset everything so the Bosch was calibrated to my Trek bike in terms of details like tire size. He thought my problem stemmed for a poor initial set-up. I’m back to having fun on it again, both on and off trails.
 

Dallant

Well-Known Member
I’m the OP, and my bike is fixed, too. A seasoned tech at my LBS took over fixing my bike and told me he reset everything so the Bosch was calibrated to my Trek bike in terms of details like tire size. He thought my problem stemmed for a poor initial set-up. I’m back to having fun on it again, both on and off trails.
So not vibration at all?