Warning to Yuba Owners - don't use large rotors

Just posting this up for the safety of others. I was using a large 203mm rotor on my Yuba Mundo on the standard issue forks (bike is here: http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=30679&hilit=+yuba )

I realise a lot of people will chime in with comments about using such a large rotor (I started with a small rotor, but ended up moving to a 203mm) on rigid forks like this, but I thought I would post this up for the possible safety of others.

Luckily I was not going fast when this happened, but whilst braking (not suddenly or heavily), the forks on my Yuba collapsed and I crashed. As I said, I wasn't going fast so was only bruised, but if I had been going downhill it could have been possibly fatal.

As I said, I can already hear the comments about using such a large rotor, but to be honest the forks felt like they flexed slightly even with the 185mm rotor.

By way of background I weigh 95kg, and I was carrying nothing other than the ammo cans bolted to the bike and 40ah of Lipo on board, so well within weight spec.

Just thought I would post it up for other owners' possible safety.

Cheers, Phil.

WOW! I would have never guessed that the front fork was made so weak for a bike like this!

Time for a surly fork! I've had 2 of their solid forks... and they were wonderful. 203mm stops from 42mph, no prob.

Yea that's very scary.. I have never felt like I had any flex in my front fork , but seeing this happen to you has me concerned.

I have a 185mm rotor front and back now.

Did you reach out to yuba ? I would like to hear what they have to say about their fork failing like this.
I don't know how this could be anything but a design failure on their part.

Glad you were not hurt.

I'm really glad you are OK. You are right that it could have been a lot worse!

Conventional rigid forks do not belong on any bike that weighs more than 30 lbs or that goes faster than 25mph!

I've got the rock shox tora u-turns on my test bike and it says not to run them with 203mm rotors and they're built like a tank. I run the 203 rotor anyway for wear reasons but I'm very careful not to mash on it because I'm scared of exactly this scenario. I can't wait to get my next bike done. I've got an 888 wc ti that will take anything I can throw at it waiting for it!

Lucky crash. Could have turned so much worse. I broke a fork 20 years ago and it is still painful today.
Send this fork back to the manufacturer, with your story.

Glad you are okay.

I agree with other comments - this seems like a manufacturing failure, not a too large brake disc problem. Extreme application of brakes with a smaller disc would create similar stresses. A crack may have started earlier. Any earlier events that might have caused that?

This is disturbing, and I'm very glad that you have posted this. I am still a fan of the Yuba frame, but I now agree with neptronix on using a Surly fork. Of course, with a solid fork, I'd also use a Thudbuster seat and really fat tires.

Normally I'm not a fan of regen, for me its just an unnecessary complexity. But on a heavily loaded cargobike on a downhill, regen would keep the brake pads cool, and lessen the load on the forks.

There were no prior events to cause this. In hindsight I did get a warning, in that as I left I heard a noise/felt a noise in my frame, but I thought I imagined it. But i have never had a front impact etc.. to weaken the forks. They always felt a little flexy, and I had actually raised it with my bike mechanic, who essentially said he didn't like large rotors on that fork, my gut feel was that I should replace the forks but it was one of those things I just never got around to. That is why I am posting this, because I want to warn others. I should have trusted my gut. Personally I think it is not a failure specific to that very fork, I think it is too underbuilt for its purpose.

Normally I'm not a fan of regen, for me its just an unnecessary complexity. But on a heavily loaded cargobike on a downhill, regen would keep the brake pads cool, and lessen the load on the forks.

Click to expand...

I would have agreed with you Spinning Magnets, but again, I offer this as a tip for others considering the Yuba, regen on the rear is problematic at best. I use Kiwi's torque arms which are awesome, but I think to really properly use regen you need to modify or bolt to the frame.

The problem is that although Kiwi's torque arms offer resistance both ways (so theoretically support regen), I found that the force of the regen would eventually force the rear axle down and out of the drop out (you need to appreciate that the dropouts on the Yuba are massive BMX drops, so the axle doesn't slot in, it is like the proverbial case of throwing a sausage down a hallway, if the Yuba's rear drops were a vagina, it would "hang open and loose like a tired dog's mouth" as it were). This was happening to me with (the name eludes me, the ratcheting washers, whatever they are called). I personally think if you want to run rear regen on the Yuba with a heavy wheel like the X5, you need to modify the frame with a bolt on torque plate. The photo below hopefully illustrates the problem I am talking about.

I have sent the picture and description to the designer (Ben) of the Yuba. I have 30 of these bikes turning up in a few days.
makes me super nervous.

Seems like the way that failed was not just a bad weld or something. My gut reaction is that if the forks are going to have disk mounts, they should be designed to be able to take the forces they will produce, regardless of the rotor size.

It's not a wallmart frame designed to fit the body of a 115 pound adolescent. It should be built for the braking forces it will encounter if descending a hill with a load on the rack.

Sure hope it's just a fluke of a tubing defect, rather than a design defect.

I wonder if that fork was originally designed for rim brakes only and that disk brake mounts were added later? Am I right in assuming that part of the braking forces of rim brakes are transmitted straight to the top of the forks through the caliper unlike disk brakes where all the force travels through the fork leg?

If that is correct it might help explain the failure or be a contributing factor.

Gary

Edit --- Wait, that force is pushing forward at the caliper, so would that have no effect. Sorry, I was never good at this kind of thing

I am currently building a disc brake version 4 Mundo (to be heavily loaded), this tread is disturbing.
Have you contacted Ben at Yuba? If so, please post your findings.

That's too bad.

If I have to guess, I'd just say that you got unlucky. In my opinion, you got a defective fork.

Wow, glad nobody was hurt. This looks to me like a mandatory upgrade for ebikers. It might hold up for eternity under pedal-biking loads, but that's a bit scary.

i don't think ebike or disk brakes caused the failure. it is just a weak fork imo.

dnmun said:

i don't think ebike or disk brakes caused the failure. it is just a weak fork imo.

Click to expand...

Yup.
That's pretty sad for a steel fork.
On a bike designed to haul 400lbs + rider.

I'm so tired of underbuilt bike parts.

Almost criminal if you ask me. They advertise the bike for hauling 2-3 kids....yet make the bike in the same factory as walmart

Aside from hitting a wall or car at 40mph or something, a steel fork should never fail like that, and there is really not excuse for it happening.

They definitely owe you a new fork of good quality, DMR trail-blade is not a bad choice for a rigid fork.


Perhaps they had a batch miss the post welding heat treatment or something, or perhaps a bad batch of steel, they should figure out what went wrong and send customers of the defective batch new forks.

Glad to hear you didn't get hurt.

That fork is steel? That's supprising.

For what it's worth, a 203 mm disk isn't going to put any more force on that fork than a 160mm. Size gives better modulation and heat disapaation, but the stopping force is exactly the same. And all the stress of the rotor is transmitted to the fork at the point where the caliper bolts to the fork, regardless of rotor size. stopping force is a function of the tire, any brake that is capable of locking the tire is capable of maximum stopping force.

Uh oh.

That's not too comforting to hear/see since I was planning on a Yuba as my next frame. Maybe that's why they are currently not available in frame only kit?

EDIT: even more disconcerting is that their site is down currently. Hope it is just a coincidence.

liveforphysics said:

Aside from hitting a wall or car at 40mph or something, a steel fork should never fail like that, and there is really not excuse for it happening.

They definitely owe you a new fork of good quality, DMR trail-blade is not a bad choice for a rigid fork.


Perhaps they had a batch miss the post welding heat treatment or something, or perhaps a bad batch of steel, they should figure out what went wrong and send customers of the defective batch new forks.

Click to expand...

Yuba owes you a free fork. Yuba owes all its customers an investigation about the quality of their steel & manufacturing standards. The way the fork bent sure seems this is just what Luke is suggesting... poor grade steel and/or improper heat treatment.

Wow, and this is supposed to be the monster cargo bike take takes huge loads. Not!

Wow! looks like it got hijacked by one of those drive by "virus scanner" scam sites as we speak.

Anyway, you should be able to get the frame kit from a dealer. Toss the fork in the trash can. Put a suspension fork on it.. and a super tall/fat rear tire to help with the ensuing geometry change.

cal3thousand said:

Uh oh.

That's not too comforting to hear/see since I was planning on a Yuba as my next frame. Maybe that's why they are currently not available in frame only kit?

EDIT: even more disconcerting is that their site is down currently. Hope it is just a coincidence.

Click to expand...

I'm glad your okay Phil.

I remembered reading something about front forks on Yuba Mundo's and so after searching for it I found this in their manual.

'We strongly recommend rim and/or disc brakes, though these carry their own risks:
under severe loads (as when carrying a passenger or cargo at high speed a very strong front brake can lead to
failure of the front fork. For this reason, don't use the front brake by itself; the rear or rear and front brake
should be used in all braking situations.'

Click to expand...

That doesn't feel reassuring.

The front brake is the main brake on a bicycle - the rear doesn't have much stopping power in comparison and a lot of us have learned correctly to use the front brake only 90 per cent of the time.

Edit: Upon reflection I shouldn't have included a link to the source of the quote.

A Google search for Yuba Mundo will reveal the passage - you can also make it out from the Google's URL without clicking on anything. As the site is still hacked I wouldn't recommend opening the PDF.

http://www.google.ie/search?sugexp=chrome,mod=19&sourceid=chrome&ie=UTF-8&q='We+strongly+recommend+rim+and%2For+disc+brakes%2C+though+these+carry+their+own+risks%3Aunder+severe+loads+(as+when+carrying+a+passenger+or+cargo+at+high+speed+a+very+strong+front+brake+can+lead+tofailure+of+the+front+fork.+For+this+reason%2C+don't+use+the+front+brake+by+itself%3B+the+rear+or+rear+and+front+brakeshould+be+used+in+all+braking+situations.'#hl=en&safe=off&sclient=psy-ab&q=yuba+mundo+manual+failure+of+the+front+fork&oq=yuba+mundo+manual+failure+of+the+front+fork&aq=f&aqi=&aql=&gs_l=serp.3...2943.4497.6.5257.6.6.0.0.0.0.185.784.1j5.6.0...0.0._-WIUn705pw&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=d322edf94108f330&biw=1366&bih=653

'We strongly recommend rim and/or disc brakes, though these carry their own risks:
under severe loads (as when carrying a passenger or cargo at high speed a very strong front brake can lead to
failure of the front fork. For this reason, don't use the front brake by itself; the rear or rear and front brake
should be used in all braking situations.'

Click to expand...

That is interesting, I never read the manual. I was using only the front brake, as I had no rear disc mount on the motor, and the rim was too untrue to use rear rim brakes, and regen had the issues mentioned above. That is interesting.

I have contacted Ben and told him. As I said, I don't want this to be a bag Yuba thread because I have been nothing but thrilled and happy with my Yuba, it is an awesome bike, and I highly recommend it to people, I just think you have to be careful with the forks.

I just did a nice 20 mile ride on my yuba and during a break i was looking at my front fork.

Right where your's bent it looks like the metal does a type of indentation like the inside of the U rather then the opposite.

Thought that was a bit weird. Seems to me just going straight would give it more strength.

I don't know jack about these types of things tho just something I thought weird.. Will grab a pic in a bit.