zmz0305

Hi guys,

I just bought a new Downtube mini b 16'' folding bike. It has a 8 speed Shimano nexus gear hub.

However, it has this problem that I am not sure if it is normal:

There is a huge resistance when I am trying to pedal backward, or stay still when the bike is moving forward, also when I am trying to move it backwards when I am walking on the ground, I can hardly make the wheel roll backward.

Does anyone know is it normal for a new bike to have such problem? Or is it just a feature of gear hub? I am new to this gear hub thing and I am generally a bike noob. Any help is appreciated, thanks!

blakcloud

You might want to put this in the mechanics section. Dan Burkhart in the mechanics forum is the resident expert on these hubs.

SkunkWerX

Also dealing with the Gates belt drive. It doesn't sound correct. The hub gears can "feel" a bit different, but should operate similarly to a standard free hub/freewheel set up. I'm sure Downtube will give you all the support you need to get it resolved.

Once it's taken care of, please come back and tell us about the Mini B. I am interested in the gear ratio, mostly at top end/top speed.

tds101 

I have an 8 speed Shimano Nexus hub, and it's nothing like you describe. The Gates carbon belt drive won't cause the issues you describe having. It sounds like the hub is either out of adjustment, or possibly faulty. Contact Downtube and get assistance. They're on point with customer service.

BruceMetras

Try loosening the axle nuts and slacking off the belt tension a lot .. then see if you can back pedal or roll the bike normally . if the belt is too tight, it will cause different kinds of grief..

Pinigis 

Contact Downtube directly. Yan is a helpful guy and a frequent contributor to this forum.

zmz0305

Hi guys,

I have tried loosen the belts, it does not help.

I have contacted Yan yesterday, here is the response:

We had a small number of mini's in which Shimano installed the "B" version dust cover. This dustcap rubs against the 22T gates cog. There are 2 solutions

1. Replacing the dust cover with the "A" version. Unfortunately Shimano is out of stock and the wait time is not short....I've been waiting for a few weeks and I still don't have an ETA. It turns out Shimano had a major problem in Europe with these dustcovers and they are backordered for a while.

2. By riding the bike downhill fast one mile or normal riding 5-7 miles the lip on the dustcover wears away and the problem goes away. The only problem with the dustcover is the lip.


So probably I will need to drive a bit more to wear away the dustcover. I'll keep updating. Thanks guys!

tds101 

Give her a spin around the neighborhood and let us know the results. I'd personally like to know, as I plan on getting an 8H in the future.

bhkyte

My nexus 8 is the same. It's better since a service but still stiff backwards.

SkunkWerX

Sounds like a minimal problem based upon Yan's answer.
If you want to expedite the fix, remove the rear wheel, get to the dust cover, and "machine" the lip off until you have clearance.
You could carefully use a dremel tool or even a hand file.

I would follow Yan's instruction first. If it doesn't go away completely, you will have wear/rub marks showing the portion of the dust cover that is still rubbing. The wear marks will indicate what will need to be removed should you pull the wheel/hub from the bike.

Sounds like a nice fast downhill run might do the trick.

ZMZ, where are you located?

zmz0305

Thanks for the suggestion! I live in Champaign, Illinois.

My leg was injured a few weeks ago playing softball, so I wasn't riding for a while. Hope the rubbing will go away soon as I start to ride it.

sslonkosky

I had a similar problem with an 8H that I discovered while Yan was still researching the problem and I tried several things that turned out not to be necessary. Yan finally suggested that turning the bike upside down, putting it in 8th gear and running the pedals for 5 or 10 minutes with my hands would fix things faster than simply riding it. The problem is now fixed. By the way, he offered to let me return the bike for a full refund even though it is past the 30 days. I am quite pleased with the bike and will definitely keep it. Without my asking, he refunded part of my purchase price which more than compensated me for the time I spent trying to fix the problem. It's nice to do business with someone who genuinely cares about his customers.

downtube

Shimano included their "A" type dust cover on a minority of our mini bikes, however they were installed on a majority of our 8H models. The dust cover problem is easy to resolve very quickly, however we have just dropped the price of the bikes to help the end consumer justify the purchase.

Thanks,
Yan