olegosna

Hi,

I am new in this forum and hope I can add some valuable experience here. I will focus on the technical stuff of my P8. I already saw another thread, but I thought it would be ok to open a new thread. As I am from Germany, I hope all the technical vocabulary is applied properly. In the last point there's also a technical question to the communitiy in terms of the derailleur cage length.
I am owning the BYB now for one month and will use it as a commuter bike also in trains. My experiences are:

· Great folded size. With the steering wheel not folded, practically to push for longer distances, e.g. in bigger train stations. In the German trains you usually have to fold the steering wheel also to move between the seats, which is not that comfortable as I have to move bent.

· The big Ortlieb Back Roller's are too big in many ways. It can hardly be attached with the lower hook and I did not find a good setting w/o hitting it with my heels or not to create friction wear between the bags and the small trolley wheels. Furthermore it is quite close to the ground. I will try the small Sport Roller bags from Ortlieb, these should match I think.

· The TERN Pack Rack (PR) is a great addition, but w/o the strap included. I did not really get, how the strap should work, cheap elastic straps from any DIY store seem to work much better to keep my office backpack in place. Although the PR is quite thin, it can secure quite big objects, like the mentioned backpack using the elastic straps. The biggest problem mounting the PR was, that I had to change the wiring w/o any really good description. I had a look on some TERN Youtube video with the PR and saw how to do it approximately. In the end it worked out and actually I like it better than the original setup with the wires hanging in a long curve in front of the bike.

· Biggest pain which I already expected, when ordering it: The long cage of the rear derailleur. I was asking some experienced bike mechanic to adjust the gears, as they were not really good adjusted initially. He could not believe, that this is a serial gear for the bike. And I have to agree, that I do not understand, why TERN chose such a long cage. Depending on the position it is really a matter of Millimeters to hit the road. Maybe there's someone in the community here, who could explain, why I should not change the cage length with another derailleur. With 8 gears only I would think, that it should not be an issue to use a shorter cage and my mechanic also sees no problem. On the other hand the bike is really smart designed, so there must be a reason (maybe only costs), why TERN chose this solution.


As a newbie I am not allowed to post pictures, but - with exception of the Pack Rack - it looks like an original BYB P8 currently, check on the original TERN Page and you will also see the long cage close to the street.

Jipe

I think its just a matter of cot !

The Byb S11 is equipped with an Ultegra medium cage that accept a biggest cog up to 34t, i.e. bigger than the 11-32t mounted on the P8.

If you look for a cheaper solution, the 105 11s has the same characteristics as the Ultegra but slightly heavier and cheaper.

The problem with the P8 is that its rear hub probably doesn't support a 11s road cassette ?

olegosna

Hi and thanks for feedback. I also thought that the whole mechanics of the rear derailleur has to be flat enough, that you do not have a collision by folding it in any gear. That's a restriction usual bikes do not have and it seams, that the p8 Shimano gear is a little flatter than other gears.
But I agree with you, in the end the s11 has a solution with shorter cage. I also think, that the rest (frame and luggage rack with the trolley wheels) is the same to make it financially attractive for Tern to produce 2 different versions. I am still not sure if I should already change something and curious for other feedback, maybe some other byb owner already tried something.

Jipe

The derailleur cage on a small wheel bike is indeed much closer to the ground than on a big wheel bike.

But "a matter of millimeter to hit the road" seems to me too close ?

I do not see that on the pictures of the Byb P8 I see n the web and I also do not have that on my Birdy 3 Touring which has smaller wheels and is factory equipped by Riese & Müller with a 10s Deore RD-T610-SGS long cage derailleur and a 9-32t cassette. In the position where the cage is the closest to the ground, there is an about 25mm clearance to the ground with the factory mounted 40x355 tires and more with the balloon 50x355 tires that can be mounted/I have on the Birdy.

Now for the choice of the long cage, as said, it must be a matter of cost: there are few medium cage derailleur and they usually are higher end/more expensive than what is mounted on the Byb P8. It must at least have a medium cage because short cage derailleur (which are road derailleur mostly) cannot handle a 32t cog.

Now, Shimano has also special short cage derailleur like the Zee and Saint but I think its also more expensive?

tds101 

I thought the Tern BYB was supposed to have a Shimano Nexus 8 speed IGH model as well? Am I mistaken? Or was it limited run of production?

tcs

Perhaps one of our gear-experimenters can comment on the application of the Microshift SuperShort Acolyte derailleur here.

Jipe

There are different model of Byb available on different market, seems that there are only two Byb available in Germany, the P8 and S11.

tds101 

Same here. Oh well,...

Reddleman

Hiya.

If you want more ground clearance for your rear derailleur then either the Microshift Acolyte (8 speed) or Advent (9 speed) SuperShort groupsets would be fine. Both will require changing the shifter too. Acolyte can use the existing 8 speed 11-34T cassette for now. Advent will need a 9 speed cassette. Both can handle up to an 11-38T cassette.

olegosna

Ok I was a little unprecise with the clearance. The most critical situation is probably not on a flat road with the smallest gearwheel (smallest clearance vertically) but with the biggest gearwheel and the cage pulled more to the front (smallest clearance to wheel surface). Encountering a ramp maybe with a small curb and I think my derailleur is gone. However, that is probably a common problem with small Tyres, which I am not used to.
The mentioned fact, that smaller cages are more expensive makes absolute sense in this context, I never thought about it, as I never changed serial derailleurs so far.
I think I will leave it as it is and hope that I will not forget about the small clearance someday and hit a curb accidentally. If it happens I will change it to a more expensive derailleur with shorter cage. Thanks for your advice.

olegosna

Thanks for that advice. Do you have s feeling, if those setups will need more space in lateral direction, which could cause problems folding the bike? The derailleur is between both wheels when folded.

CEBEP

My daughter has Tern BYB P8 though she rarely uses it. I didn’t notice derailleur being too close to the ground. Even though off topic I would strongly suggest to buy Pack Rack for this one which is very versatile and helps a lot carrying/driving the bike when folded.

Jipe

On the Birdy 3 with an Ultegra RD-R8000-GS medium cage derailleur and a 9-34t 11s cassette, the derailleur cage is vertical on a cog in the middle of he cassette. This is the most "dangerous" position because its the closest to the ground and also not very close to the wheel.

On the smallest cog, the cage is tilted to the rear, so higher from the ground and also at the biggest distance from the wheel.

On the biggest cog, its tilted to the front and it almost touch the wheel tire (with wide 50x355 tire). Because its so close to the tire, the chance to hit something like a stone in off-road use is very small, the stone should be touching the tire side to also hit the cage of the derailleur.

I have several small wheels bike with derailleur and never damaged one of them, even when riding off-road on trails (what I do often with the Birdy which with its full suspension and wide tires can be used as a gravel folding bike)..

Reddleman

As far as I can tell from photos, the super short derailleurs use the same upper arm as the medium length derailleurs in the same groupset. Checking by eye the width of the medium length Microshift Advent derailleurs installed on our two Tern Links, they appear about 20mm wide and no fatter than usual.

Personally, I wouldn’t worry about the distance from the ground on your Tern BYB as sold. As long as you keep away from grassy, muddy or rocky surfaces the derailleur’s distance from the ground should be fine. I would do the upgrade more to widen the gear range if you find your local hills too much rather than for the increased clearance.

olegosna

Thanks for your feedback, I will try to think about the curbs when using the bike in the city

Small plot twist:
I just figured out, that I have an Alivio deraillieur on my bike. Optically it looks like an Alivio RD-M3100-SGS, I found on the internet. However it's for 9 gears, but cassette and gear switch only support 8 (should be no problem, right?). On any other retailer page I can see the an Acera on the pictures which looks exactly like the one on the original TERN page (Shimano Acera, Shadow RD acc. to TERN HP). It seems that the Alivio is a little pricier. However, my mechanic mentioned that somehow the switching gap of the derailleur seems not to fit 100% to the cassette. Could that come from the Alivio? I would expect, that those gaps are the same for all Shimano gears but I really have no clue.
As I bought the bike quite cheap, maybe there was an issue with the original derailleur, which the retailer did not mentioned...

Ron Damon

Shimano Zee M640 RD, pictured here with a 45-305 wheel and 11-36T 10-speed cogset. The RD has been in service six years and still shifts crisply and accurately. Buy once, buy right.


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jfouellette

here is a picture of the Acolyte super short 8 speed I had installed. Worked well for two weeks until my bike was stolen. Better clearance with this derailleur and fast shifting.

Falconista

My Shimano XT derailleur rides a bit too close to the ground on my Dahon Speed 6 (now 11). It has not (so far) been an issue, except in winter muddy conditions when it sometimes acts as a scoop. Muddy puddles more than about 1" deep mean you get grit on the chain and you can feel it going round the system. It needs a quick hose off to avoid wearing out the teeth too quickly.

Fentuz

The cage used is based on the manufacturer specification and related to the cassette. Other 20" 8 speed with 11-32 cassettes often use the shimano Altus M310 rear derailleur which is the same size as a sora small cage.

shimano 7-8 and 9 are using the same mechanical ratio so, you can use any derailleurs with the trigger of your choice which itself define the number of speeds (with the cassette). Each trigger click pull the required amount of cable to shift.
When you move to 10, the ratios trigger/derailleur are different so you cannot mix and match.

I tested these in 7, 8 and 9 speeds configurations with either m310 or sora small cage derailleur , with 11-32, 11-36 cassettes without any issue. I manage to run 11-40 with some adjustments of the B screw.
With these derailleurs, the bottom pulley doesn't got much lower than the 20" rim giving about 2 to 3" clearance.

If you want to keep 8 speed, these Altus derailleurs are ~25€ and should be a straight swap. You may need to shorten the chain.
Then, if you are after upgrade like 9 or 10 speed, it is possible too but it would involve. With 9s, a altus M310 derailleur ~25€, a altus 9s or alivio 9s ~27€, a 9 s cassette (sunrace) ~30€ and a 9s chain~15€... easy.
if 10, I'd go for Ron setup with a ZEE but it more expensive

Ron Damon

Yeah, Zee ain't cheap. In my builds, the Zee RD ends up being the third most expensive component after the frameset and the wheels. On the other hand, it will last you with good performance for years.

Jipe

​​​​​​Seen the damages on its cage and body, even the Zee seems not safe with all riders !

Ron Damon

Despite knocks and scuffs over six years, three different bikes and three different countries, the Zee RD is still mechanically and functionally 100%. Worth every penny.

Winfried

€$£50 isn't the end of the world for such an important part on a bike

https://www.bike-discount.de/en/shim...derailleur-ssw

olegosna

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Thanks for that input, helps a lot. Also to the others in regards of alternatives for more gears. After doing some research that fits the plan of my mechanic. I have an 8spd 11-32 cassette as it seems and he wanted to put in an Altus with smaller cage. As I do not see a need to increase gears currently, I will probably follow this proposal (it's a commuter bike in the end currently).
However I still do not understand why my current configuration with the Alivio derailleur, Claris Switch and mentioned cassette change gears so bad. As the switch has 8 gears it should actually fit that Alivio which is potentially for 9 gears, as you described.

Fentuz

i am wondering if the derailleur hanger is bent.
when i crashed and bent the hanger, some gears worked but some were all over.

it might be worth taking it of and check its straightness.