Greetings
I am hoping that one of you mechanical geniuses out there might be able to help me figure out why my Specialized Ruby has a dangerous quirk. I find myself stopping frequently because the rear wheel gets that squishy feeling like the tire is flat but the tire is fine. A casual coast down a hill and the rear wheel will feel like it's wobbling irratically - sometimes severely enough that the rear wheel jerks out from under the bike violently and unexpectedly (always jerking to the left). This has led to several crashes and somesevere injuries. Ive taken the bike in to the mechanic repeatedly- everything checks out perfectly. I've had everything from the drive train to the rear wheel inspected and replaced. Recently a fitter moved the saddle forward almost 2 inches- effectively moving my center of gravity forward on the bike. The problem of the rear instability got much worse. Now either i've pissed of a possessing bike demon or i have a bike frame that becomes dangerously unstable when its front loaded.

I'm toying with the idea of getting a custom frame made. What details should the builer and I address to resolve this issue?
Many thanks for your ideas

I'm stumped, do you have pictures of this dangerous bike?

Several crashes w/ injuries from casual coasting and you still ride this demon-spawn?
That's dogged determination, or something.

Pics?

-Bandera

The only times I've ever had this feeling from a bike is when the rear tire is actually going flat, or a tube is cracked. If there's a cracked tube, I'd be surprised it got by the mechanic. Past that, I'm stumped.

I'm at work and Ruby is at home so a pic from the internet is the best I can do at the moment (51 cm 2007 Specialized Ruby Expert Triple). I have custom wheels with 'bullet proof' hubs (hand built MTB stunt hubs!), new rear derailleur, new cassette, fresh crank rings. Had the wheels checked out under a microscope last week and they are perfectly true, no indication of cracks or anything. At the same time, the bike was disassembled and the frame stress tested. Everything is fine- no cracks in the frame or obvious issues. Other than a small saddle bag, nothing else tricked out on the bike. I've had the bike checked out thoroughly by two top flight bike builders/mechanics and no one can seem to identify the problem. this issue has been going on in a minor way since I purchased the bike in 2008 but has gotten more noticeable in the last year (and reproducibly worse when I move the saddle forward)

it happened again this morning.... rolling passively ~14 mph downhill on a 2% grade, spanking new clean pavement. The rear wheel skipped quickly left/right and then hard left. I kept the bike upright but just barely.

this little quirk has cost me 6 broken bones this year- the crash happened under virtually identical riding and road circumstances as above. Having a tricky bike is one thing if I'm putzing around on a bike path. But I ride ultras- crazy distances- and the safety issue is forcing the issue about considering another bike.

maybe I should contact an exorcist

many thanks to everybody

I'd try a different rear wheel, sounds like loose bearings, or the interface between the rear wheel and frame is being allowed to move or flex.

Broken frame, dude (or dudette). Sounds like one of the chainstays is broken or a dropout is coming out. It might be related to putting MTB wheels (135 mm OLD) into a road bike (130 mm OLD) frame. Stop riding that monster. I'd have trashed that thing when I broke the first bone, not to mention started some sort of dialogue with Specialized. 14 MPH is pretty pokey for having control problems- I don't get shimmy on my carbon fiber bike even at 60 MPH (don't know about faster since I've never gone faster). And Specialized knows how to design bikes well, so I don't think it's a design problem.

I'm with UH, the problem is getting missed. If the wheels are fine, something has to be broken (besides your bones!) or bent for a bike to behave like this.

Exorcism 1st.

Your stunt hubs may have 135 spacing in a frame designed for 130 and a lousy QR design.
Sounds like your mech has left few stones un-turned but that smells like a possible rock to roll over.
That being said I've never heard of anything like your extreme problem, I would have expected frame components had come adrift. Chainstay, dropout not really attached........both.....?

I don't tolerate broken bones so well anymore, an immediate total permanent fix or get rid of it now it would be my plan.

-Bandera

Now THAT'S a good idea.
I assumed the wheels were 130mm when the op described them, but if they are 135's and the drops are a little misaligned from the bigger hub being forced in AND the qr is substandard....that might be the perfect storm of Jacked Uppedness(tm) to create this problem.

I installed a large amount of Jacked Uppedness(tm) on my central nervous system during the UT game on Saturday.
Jack of the Daniels persuasion is also a demon spawn product that can cause severe instability.
Perhaps Ruby simply needs a sponsor and a 12 step program.

-Bandera

I would get a straight edge long enough to touch both rims in two places and see if the wheels are seriously out of plane. I also would not ride this bike. Never broken a bone, and I am not going to do anything that would change that if it is under my control

Have you had anyone ride with/behind you to witness the problem? I don't understand how you could still be riding it all these years if relatively low speed coasting causes crashes.

If you are any where near southern Vermont shoot me a PM. I would love to see your bike.

Severe injuries??
Wow-is that an expensive frame?
It ALWAYS does the same things under the same conditions??
Not a sometimes it acts up sometimes it doesn't situation?

As someone else suggested-Switch out the rear wheel-see what happens-let us know
Why those hubs-are you heavy?
Normal hubs-never break on road bikes

Borrow a different wheelset from the shop or buddy and see if it makes a difference.
Process of elimination, if the problem persists with another wheelset then it is certainly something to do with the frame or geometry (which it points to if you have issues when adjusting seat position).

"this little quirk has cost me 6 broken bones this year-"

You're kidding right?!

Frame is cracked. Give it a good examination.