Trek Allant+8S crank resistance in turbo at top speed

Wakasacho

New Member
Region
USA
Hello, I bought a Trek Allant+8S a few weeks ago and like it a lot. I've had one issue with it, though, when riding at top speed in turbo. The crank becomes hard to turn and the speedometer jumps wildly from 35kph - 45kph. This doesn't cause the generation of any error codes in the app and the local bike shop techs didn't detect a problem in test riding it when I brought it in. I've petaled the bike at or above 45kph without power assist and this doesn't happen. Does anyone know what's going on? I asked the bike shop to open a ticket with Trek/Bosch in hopes there's a documented explanation. Thanks!
 
45 kph is the programmed speed limit for class 3 bikes like the 8s. No wonder it gets harder, the motor cuts out. The wild swings in speed are no doubt due to your speed dropping when the motor cuts out.
 
I'm having the same issue Wakasacho. Im thinking (hoping?) it might be caused by dirty speedometer sensors. Did you figure it out?

BTW, retinedNH, you have "no doubt" that the speed drops from 45 to 35 instantly because we reach top speed? Can you imagine how dangerous that would be!? Jesus.
 
actually power cuts out at a max of 27.5 mph but it starts dropping at 26 and often boschs are a mph faster than actual.
 
BTW, retinedNH, you have "no doubt" that the speed drops from 45 to 35 instantly because we reach top speed? Can you imagine how dangerous that would be!? Jesus.
Did I say "instantly"? Pay attention, and don't put words in people's mouth. fooferdoggie gave you a more nuanced (look it up if you don't know what nuanced means) explanation of "cuts out".
Guess you should have gone with a Bafang equipped bike with no restrictions?
 
Thanks for the input but again, the issue isn't that there is a speed limit on the assist, we're fully aware of that. The problem is that when we get close to that limit, the speedometer becomes erratic, like 7-10 kph up and down a few times each second. IE at 40kph, the speedometer will show 40, 48, 37, 43, 40 within a single second. If going at constant say 44kph, the computer will withdraw support every few seconds because it thinks we're going too fast. It's extremely annoying since the support is randomly withdrawn / brought back without any changes in effort. Issue seems to be with the speedometer...
 
If you post this question on the Bosch sub forum you will likely get some knowledgeable help from the Bosch team. This was the wrong sub forum on which to ask for help on this issue. The Bosch North America team is very active and helpful over there.

 
I'd check the speedo magnet/sensor. I think on these bikes it might on the brake rotor? It might be loose.. I don't have one of these bikes so guessing a bit!
 
If you post this question on the Bosch sub forum you will likely get some knowledgeable help from the Bosch team. This was the wrong sub forum on which to ask for help on this issue. The Bosch North America team is very active and helpful over there.

OK thanks will do!
 
Did I say "instantly"? Pay attention, and don't put words in people's mouth. fooferdoggie gave you a more nuanced (look it up if you don't know what nuanced means) explanation of "cuts out".
Guess you should have gone with a Bafang equipped bike with no restrictions?
Not helpful....
 
Thanks for the input but again, the issue isn't that there is a speed limit on the assist, we're fully aware of that. The problem is that when we get close to that limit, the speedometer becomes erratic, like 7-10 kph up and down a few times each second. IE at 40kph, the speedometer will show 40, 48, 37, 43, 40 within a single second. If going at constant say 44kph, the computer will withdraw support every few seconds because it thinks we're going too fast. It's extremely annoying since the support is randomly withdrawn / brought back without any changes in effort. Issue seems to be with the speedometer...
ok that sounds like something loose. well maybe but tis weird I only happens at that speed unless there is a lot of vibration.
 
ok that sounds like something loose. well maybe but tis weird I only happens at that speed unless there is a lot of vibration.
@Wakasacho It sounds like something that should generate and error code that would be picked up by connecting the bike to Bosch diagnostic software at a certified Bosch bike shop (which includes most if not all Trek shops as most Trek ebikes incorporate Bosch electricals.

I would take the bike in to the shop where it was purchased just a few weeks ago and let them figure it out and make it right. They should be happy to do so without charging you.
 
I got some of those issues when my nyon was not making good connections. but with the smartphone hub it wouldn't or be the same.
 
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