A word about cheap suspension forks w/disc brakes...

[neptronix]

...forget them!

I was running a 180mm avid BB7 on the stock front fork of my Trek 4300..

Car braked suddenly in front of me, i hit the car at about 3mph. Rear end lifts me up and almost over the handlebars, then slams me back down, i hear a crack.

I'm okay, but apparently 230lbs of rider + 55-60lbs of bike resting on one side of the fork was a bit too much for the stock RST unit.

I'm a bit frazzled honestly. And not sure where to go from now.
The local bike shops are offering up rockshox toras / recons in the $200 range, and those forks have thick as hell stanchions, almost twice as wide as what i have. The other option is a steel fork, which i wouldn't mind too much since i don't do offroad ( but do like the comfort of a suspension.. )

Any recommendations as to where to go? I don't have > $200 to spend on a fork right now.

 

[Ricky_nz]

Nasty
Glad you are alright.

I wonder if the failure was from the impact on already loaded forks though but even so it shows just how close to the edge they are.

 

[Hillhater]

I cannot see clearly but, has that failed at some sort of joint in the leg ?
I guess its a cast unit, or it would have bent rather than fractured.

 

[neptronix]

hillhater, the fracture happened about 5mm above where the Avid BB7 was mounted.
Ricky: thanks. The forks were already flexy to begin with even on a 160mm disc. I had beefing them up in the back of my mind for a while.

 

[liveforphysics]

Rigidity increases at the CUBE of radius.

This means, the forks with the largest diameter tubes are always the best choice.

 

[neptronix]

Yeah, diameter makes sense, but the thickness of the material.. i do wonder about that.
Am flip flopping between these two choices for a replacement:

Surly 1x1 fork.

or Rockshox recon ( 32mm stanchions VS my 25mm stanchions )

Here is another picture of the carnage:

 

[doc007]

WOW! Glad you are ok!

Check these deals out:

http://wheelworld.com/product/rockshox-09-tora-289-coil-oem-8377.htm

http://wheelworld.com/product/marzocchi-2008-mx-lo-fork-with-lock-out-7513.htm

http://wheelworld.com/product/marzocchi-2008-dirt-jumper-3-dj-3-oem-7246.htm

Both these companies make decent products. If you consider buying one of these, I would look up the reviews for them on mtbr.com or just google some reviews.

Good luck! Hope you get up and running soon!

 

[beast775]

wald makes a great heavy duty nonsuspension fork,i picked one up at my local bike shop for 10 bucks used.its better than a stock fork. im sure there not that expensive.try ratrodbikes.somebody may have a used one.

 

[yoyoman]

hmm, I have that Surly fork with my 408. I miss not having a front shock, but maybe be happy and get a fatter tire.

 

[neptronix]

doc: thanks for the recommendations!
yoyoman: what tires are you running?

 

[yoyoman]

err, I think they're Continental 26x1.95 tires. Not very cushy.

 

[full-throttle]

What was the travel on your old forks? The curved blade Surly is suspension corrected for 80mm. The Recon is adjustable from 85mm to 130mm. Personally I'd go with a rigid cromo over cheap sus, and italian made Marzocchi over RS - can send you a picture what happened to my RS Psylo so you understand why

Sorry to hear about your stack.

Oh and BTW a guy at work had recently cracked his Trek (7400 IIRC) near the bottom bracket, so watch out

 

[shinyballs]

Good to know that your ok.
I'm selling my Marzocchi All Mountain 3 Fork 2005 for $180 shipped. price brand new at that time is $500. Better saved up some money and get a higher model Fox or Marzocchi than a cheapo one.

 

[John in CR]

Scary about the fork and glad you're ok.

I must be missing something, but how can you not avoid hitting a car at 3mph? Don't ride directly behind cars or you'll end up a car sandwich at some point....gotta have an escape route at all times as well as always looking far enough ahead that his braking comes as no surprise be seeing his need to brake before he did.

 

[amberwolf]

I don't know how close he might've been, but I expect that the 3mph was simply how fast he was *still* going despite braking hard when impacting the car; after having slowed from whatever much higher speed he'd started from.

If I have to ride behind a large vehicle, or even to wait behind one at a light, I prefer to give myself at least a full vehicle's length between me and whatever is in front, positioned so I can see the driver's face in their mirror if possible.

 

[dogman dan]

Damn cheap fork kept you from tacoing the wheel. 8) Pretty clear that the spot just above the disk was getting metal fatigue. Now that I have a few bikes with disk, and a few with rim brakes, I have definitely noticed that there is more strain on the components with disk. You hear the spokes talking and such, and on front forks, the leverage on the fork tubes is clearly more, with the caliper located mid tube instead of on the top end on the horseshoe for v brakes.

The flip side of course, is that you'd have hit that car at 15 mph with rim brakes. Brings you to how I like to ride, out of the traffic in a bike lane or path for as much of the ride as possible, or on back streets that may take me miles out of my way but safe. I must mix with cars for a few blocks every day, and give em lots of space, just like I do in a car nowdays. Old fart driving style more and more.

Good idea about leaving some space ahead of you AW even when parked at a light. I witnessed a guy on a harley get sandwiched between two cars at a stoplight. More space ahead of him would have helped, he might not have been actually pinched between two bumpers with more space. Getting bounced into the front car would still smart, but not like metal touching metal snipping off legs.

 

[Thud]

They cracked at impact correct?
Nothing wrong with the forks..you just gave them a really weird load stress under optimal fail conditions. The fork broke right where the end of the tube was telescoped into it, that happend to coincide with it already being loaded from braking. A perfect storm.

The final fail force came from hitting a bumper much higher on the wheel than any bump obstical the designer ever allowed for the fork to contend with.

3 mph with 230+ pounds is a good deal of force.

I would think they performed beuatifly considering the circumstance.
Sucks they broke though, If you were happy with them I wouldn't hesitate to replace them. (but better ones are avilable for sure)
T

 

[MadRhino]

3 mph hit does not break a fork, even a cheap one. I bet yours was cracked already, and you are lucky that it broke in that ideal situation. Imagine it failed at 30 mph hitting a pothole in heavy traffic...

On the street, you'd rather have a good ridgid fork than a cheap suspension. In the mountain, a good suspension fork is your best insurance policy and even then, it needs to be inspected and serviced ponctually, according to your riding style.

 

[auraslip]

Glad you're ok. Lots of good advice here.

I personally would contact RST. I know they probably won't do anything, but IMHO it's not proper for them to sell forks that break under normal riding conditions. I might even go as far as to tell them you're considering filing a cpsc report. Might get them to give you a new fork..... and then report them anyways. frockers shouldn't be selling forks that fail with road riding.

Also, madRhino said a good rigid fork is better than a cheap suspension. And things like this are why. Any suspension fork under $300 is cheap in most peoples opinion.

 

[joe tomten]

Thud is right, of course. He knows what he is talking about because he is a mechanic, machinist, metalurgist who actually fabricates equipment and tests it to destruction.

I remember when i was a teen, and had completely overhauled my 10 speed bike, with brand new toe clips.

I was trying to get them adjusted, head down rolling along at 2 mph, and bumped into a car that never normally was parked there. Bent the head tube. Totaled bike. The forces were just right.

 

[nicobie]

I'd spend some time on Pinkbike.com

http://www.pinkbike.com/buysell/list/?region=3&category=8 triple crown forks

http://www.pinkbike.com/buysell/list/?region=3&category=9 single crown

 

[manitu]

I would recomend the Rockshox Argyle and Tora , or the Marzocchi Dirtjump or 4X series , those forks have heavy duty lower legs and steel inner legs.
A fork made for dirtjump will allways be stronger than one made for cross country.

The Marz Dirtjump 3 and 4 are cheap , strong forks and almost indestructible. They do need some service now and then , not to seize up , but they are really simple to service. The Dirtjump 2 & 3 and the 4X are brilliant, strong forks.

Argyle upper legs are often available used , as people who want a 4X but can't afford it often get a used pike and change out their argyle inner legs , making a "pargyle". most 32mm rockshox parts are interchangeable, only the materials used, length, and design on the lower legs differ. A rockshox can allmost allways be shortened and sometimes made longer. The cheap ones , Tora , Recon and I think sector too are ,depending on model year, 120-140mm inner legs. The expensive ones , Revelation and Reba are cut in the length they are sold and cannot be extended further.

.manitu

 

[FMB42]

Glad you're OK Nep.

Meanwhile, I think we should keep in mind that 3 mph is just a tic under walking speed for the average human being.

This, imo, positively indicates that the fork was previously damaged and/or that you were traveling much faster than the 3 mph you seem to recall.

Another factor to consider is the possibility that the vehicle you collided with was in the process of "rebounding" rearwards during the last moments of braking (at the exact moment when you contacted the rear bumper). The vehicular mass of this "rebounding" motion would certainly be sufficient to cause the damage incurred to your forks.

Having said that, I would (as other ES members have mentioned) thank your lucky stars and go out and buy another set of forks.

 

[TylerDurden]

"Perfect storm" is an apt expression.

I also agree with AmberWolf, 3mph was probably at the point a lot of force was being taken by the fork due to braking... the impact iced the cake.

 

[neptronix]

Scary about the fork and glad you're ok.

I must be missing something, but how can you not avoid hitting a car at 3mph? Don't ride directly behind cars or you'll end up a car sandwich at some point....gotta have an escape route at all times as well as always looking far enough ahead that his braking comes as no surprise be seeing his need to brake before he did.

I had been slowing down for a few seconds, but not as fast as a car overreacting to a yellow light . I was going 10-15mph, because all the cars were hauling ass to get through the short light, and so was full throttle until the driver in front of me decided that they should slam on the brakes because they thought the yellow was too short. There are red light cameras in that area.

Those bike brakes have to stop about 290lbs of mass. Let's be honest, unless you have 203mm discs all around ( and a frame that can handle that amount of braking force ), your brakes probably don't stack up to a car's either. Mine have always felt lackluster. Even when i was running a 160mm disc in the rear and 180mm in the front.

I essentially had all ~280lbs of me + bike sitting on the fork, with the majority of the weight on the disc brake side.

dogman: yeah, the wheel and disc brake are in perfect true!

Thud: they did crack at impact. The fork was a little flexy before the impact though ever since the 180mm disc was installed. I am sure that was not helping it.

Another thing that had been happening is kind of a knocking sound when i'd brake hard. I have had to tighten down the headset many times. It doesn't help that i am using a lot of extenders. I think i am going to find a bigger frame to avoid this, lest i risk frame problems too. I have a 19.5" but i think i need a 21"+.

Sounds like the eBike will be down again