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overfedlonghairedgnome

Hi, happy holidays. I am writing this from my hospital bed. That's right. I had an accident on my SC on Saturday (three days ago) while downhilling a long steep straight hill at about 45 MPH. I detected a mild speed wobble without hitting any bumps but it settled out pretty much right away. I sat up a little for some aerobraking and shifted my weight, so I slowed to maybe 40 MPH when the front wheel shimmy began again. I shifted my weight onto the pedals and eased on a little rear brake and the shimmy sustained and then got worse. I kept light resistance on the bars even to brake but it eventually got away from me and I went down.

So I have seven broken ribs, a collapsed lung, broken collarbone, roadrash galore, and some unknown soft tissue damage to my left shoulder. The paramedics on the scene were able to put the 4" needle into my chest and re-inflate my lung. I had a helicopter ride from the canyons where I crashed to the hospital. A the emergency response was wonderful and I feel very lucky to have had a skilled paramedic on the scene. He will be on my Christmas list.

So my questions pretty much, what have been the experiences with early 70's TdF and SCs (60cm) from a speed wobble tendency? My son rechecked my steering head bearings after the crash and thought everything was tight. I will recheck myself. The front wheel is a taco according to my wife. So I won't be able to check it very well but my guess may be that I had a out-of-round condition, maybe? The wheel was a Module E on a 1st generation Dura Ace hub, built many years ago and ridden on many bikes recently. I have done many fast downhills on that wheelset but this was the fastest descent I have done with the SC since building it.

So that's about it. I hope to go home today. Maybe I will know more about the bike soon enough but I am interested in any experiences.

Thanks - Jim

sandranian · Site Admin

Oh my! I am so sorry to hear about your accident! I owned a similar vintage Super Corsa (now that I think about it), and never had a "speed wobble" issue. It did get ridden at speeds at or in excess of what you are talking about there. The only issue I saw was that the forks really moved to absorb shock on the road, which I figured was due to the extreme rake. Was the road smooth? Perhaps that could have done it?

I know that all of the gitane's I have ever ridden have been used at speeds at or in excess of 45mph and I have never had a "speed wobble" issue (and haven't gone down...knock on wood). I have heard that there are better cornering bicycles out there, but I am timid when it comes to down-hilling on S curves anyways, so I wouldn't know.

I wonder what the heck it could be. My first thought would be (naturally) the geometry. Also, check the front axle on the hub. I can't imagine it would be broken, but that might be an issue.

I hope that you have a speedy recovery. You sound really banged up! I have had some bad crashes (broken vertebrae & ribs and road rash galore) and have been hit by a car (broken left hand...off...and torn open neck which required 350 stitches), but have never gone down like that! I hope your wife let's you out again. Tell her that mine did!

verktyg

Jim,

First off, I hope you recover quickly and the discomfort goes away soon. Tincture of Time is the only cure for broken ribs... Crying or Very sad

On a humorous "online get well soon card" note, the first thing most people that I know have done when they've taken a spill is (myself included) is to check out the bike! Next is look around to make sure no one saw you dump. Last thing is check yourself for injuries! Wink

Again, sorry to hear of your misfortune.

High speed wobble is a tough one to diagnose. Here's a couple of things to check out:

I'd check the frame alignment. That's the first thing that I do when prepping a bike. I've found a lot of badly misaligned frames that came that way from the factory, even on top name Italian and British frames (Bob Jackson and Colnago for starters).

Mavic Module-E rims came out about 1975. They were designed in conjunction with Michelin to work with the Michelin Elan tires. These were an early attempt to provide sewup like performance in a clincher tire. Thus the name "Module-E".

The Elan tires had a 3/4" or 20mm cross section and used a thin nylon hairnet like casing that regularly blew out. Wolber W20 tires were the first successful tires to fit these rims. These narrow clinchers were pretty radical in 1975 when a 1 1/8" cross section was considered small.

The Module-E rims were narrower, 20mm wide vs. the prevailing 22-24mm wide rims of the day. That was the standard sewup rim width. They also had thin sidewalls and lips inside to hook onto the larger beads on those tires so that they could be inflated to higher pressures without blowing off as easily as the older style rims.

These rims are 30-35 years old. I have 1 or 2 sets of them plus several sets of the poorly made Rigida 1320 copies. I use these wheels for casual rides only.

Modern rims and tires are much better built for high speed performance. Back in the day, only hard core racers (and inexperienced riders) (and people like me) attained speeds over 35 mph because most equipment wasn't designed for that kind of use.

Other things to check are: wheel balance (both front and rear), spoke tension (both front and rear), hub bearing smoothness (both front and rear), tire casing construction (lumps, out of line tread etc. both front and rear), wheel hop (both front and rear) freewheel trueness... (notice I mention rear wheels a lot, wobble can be caused by the rear wheel too!)

I've heard tell that shifting back on the seat and pressing one thigh against the top tube can help control front end wobble. Do a web search, there's lots written on the topic.

One other thing, I've seen changing to a shorter stem length cure high speed wobble problems but that tends to fall into dealing with the sacred for many bikies, like "let me take you mom out for a drink"... Twisted Evil

Hope your recovery is speedy, and like falling off of a horse, get back on a bike soon! Wink

Gtane

Jim,

I'm very sorry to learn of your accident and I wish you a full and speedy recovery.

I've never experienced speed wobble but have read about it from time to time.

Here's an article which may help (it also links back to an earlier article about high speed wobble in general - http://tinyurl.com/ycy2998), by frame builder Dave Moulton; - http://tinyurl.com/ycuyz57

All the very best and I hope you're able to fully enjoy the Christmas and New Year period.

Tim

overfedlonghairedgnome

Thanks for your support. I also re-read the section on shimmy in my "Bicycling Science" book. Dave Moulton's BLOG was helpful, thanks Tim, as were all the suggestions. My LBS has already been alerted and I will take the frame in for an alignment check. I will try to get as much a post mortum on the bike and wheels as possible. And I will update with anything that turns up.

The doctor just released me from the hospital so I will be going home today! Hurray!

I hope to complete a number of brevets and double centuries on the Gitane so I must be able to trust it.

Jim

greyhundguy

I thought Land Speed Records were conducted on the Bonneville Salt Flats. Wink

Get well soon Jim. Glad to know you will be at home for the Holidays.

Best regards,
Jay

scozim

Best wishes to a speedy recovery, Jim. My first thought when reading your post was possibly an issue with the fork but that would probably fall into Chas' frame alignment category.

I have Module E's on my Sprint and another bike of a different make and took them several times to 40 mph this year with no issues.

My TdF feels "twitchy" in the front - at least that's the way I describe it - but hasn't experienced a wobble. I believe in my situation it's the lightweight Super Vitus frame and the Mavic Gel 280 front wheel that make it feel real active on descents.

Scott

Wisey

Jim, I'm sorry to hear that you came down. Best wishes for a speedy recovery. Just take it easy and don't push yourself to quickly.

Big bikes and speed wobbles Confused

! I've noticed over the years that quite often guys with serious speed wobble problems are riding big bikes, 60cm and above. I have been curious about this for many years and have read everything I can find on the subject and talked to as many frame builders as I can etc etc. My observations:
1. A particular brand and /or model has no reports of speed wobble from any rider on smaller sizes, but multiple reports from riders on the really big sizes.
2. On investigation there seems to be no issues with the design or geometry of the bike. (I have done some pretty exhaustive research into the rake/trail issue)

I have personally ridden some of these bikes (having to put the saddle and bars down to my height, and can report that the wobble is real and barely controllable when you are expecting it to happen. I would hate to be surprised by it. I have also experimented with some of these bikes: changing each component to slowly eliminate each as a possible cause. Front wheel, fork, headset, bar height, stem length etc etc. Still the wobble persists.

The latest theory I have is that the shimmy is just caused by all the normal things that occur and have been well documented by more experienced people than me. What I am wondering about is the fore-aft weight distribution of the rider. Most big bikes have a fairly relaxed seat tube angle ~72 to 73 degrees. With the tall seat height, this means the seat is seat is so far aft it is almost over the rear axle. Thus there is very little weight over the front wheel. Could it be that this lack of downward pressure on the front end simply allows the front wheel to begin to shimmy more easilly than with smaller bikes? Anyone got any thoughts?

Anyway, hope you have as comfortable holiday as possible under the circumstances Jim. Best wishes, Paul.

verktyg

Good articles by Dave Moulton.

I came to some of the same conclusions as he did about frame desigm but for different reasons. He back pedaled on his comment about flawed frame design being the cause of front wheel shimmy.

I should have mentioned tire size in my previous message. Another thing, many bikes and components were/are designed for 125 Lb. to 150 lb. riders. Many of us don't fit that category.

About the only times I've ever encountered any shimmy or wobble were with bags or other heavy weight on the rear of my bike.

Back in the Bike Boom days when Pletscher rear bike racks were a standard accessory (along with a kick stand) shimmy was pretty common when the racks were loaded with groceries, books or whatever, even on the flat at moderate speed. I had those accessories on my 1972 Gitane Gran Sport too. It was my main means of transportation for several years.

The mounting parts for Pletscher and similar racks were pretty flimsy.

I used some automotive wire harness clamps to attach the rack to my seat stays and I beefed up the way the riveted on rear legs attached to the rack. This cured that problem as the rack was now firmly attached.

I did some touring in the mid 70s on my 54cm Bertin racing bike with a modified Pletscher style rack without the "rat trap" spring loaded clamping device. I ran sewups most of the time and I can remember long descents from mountain passes, having to deal with shimmy plus kicking the bags with my heels all day long.

After a tour through a number of the passes across Northern New Mexico I built myself a touring frame to fix those problems. The design similar to some well know British touring bikes, 18 1/2" long chainstays, a 75° seat tube and lots of fork trail. Notice the space between the rear tire and the seat tube! I can run over a speed bump and hardly feel it! Even though I've never used it for touring, it handles just the way I expected it to.

During those days I built some large size frames. The largest was a 73cm (28 3/4") pictured below (that's a meter stick I'm holding). It had a 37 3/4" stand over height. I designed it to be stable handling and to move the rider's weight forward like Dave Moulton talked about but it was so big that there was no way to test ride it. We equipped this bike with 40 spoke Super Champion rims, 700x32c tires and 180mm cranks.

I started work on an 83cm frame but the buyer, a basketball player, back out of the deal.

Portrait of the artist as a young man ca 1976

I drew some lines on these pictures to compare my frames to what Dave Moulton wrote about.

BTW Jim, have you gotten back on a bike yet?

Glad to hear that you've gone home. Heal quickly!

overfedlonghairedgnome

Now I am home to begin recuperating and resting over the holiday. I have had a look at the bike now. The bars and stem are forced almost 90 deg from the fork which isn't too surprising, and both brake levers are ground down considerably. The front "Racer" brake contacted heavily with the downtube, bending the caliper and leaving a deep gouge in the paint in front of the front der shift lever. The frame looks OK, though, no obvious kinks. I does not look like the bars contacted the top tube hard enough to dent the frame. It looks like my shoe banged hard into the chainstay on its way out of the pedal.

I made sure to include the frame size in my original post because larger frames have more deflection for the same stiffness. I agree that this is a factor but just not the root cause. Most of my cycling experience has been on slightly smaller 56-58 cm bikes and that both of my larger (61 cm C-T Masi and 60 cm C-C Gitane) have exhibited at least some signs of shimmy.

The front wheel was obviously damaged in the fall so it's hard to tell whether it had any pre-existing problem or not. All I can say is that wheel had tens of thousands of reliable miles on it and many fast downhills. But I am willing to believe that it contributed to the shimmy. I will have my LBS evaluate the frame and rear wheel today.

Jim

vanhelmont

Jim,

Hope you and your bike have a quick recovery.

I've never cycled in any real mountains, and would be too chicken to go that fast anyway, but the only shimmy I've experienced was due to a bad headset or bags, as Chas. discussed. I've also heard of holding your thigh against the top tube to damp out the vibrations, but never had a chance to try it, and hope I never do.

What are the advantages of a large frame? Back in the day we usually rode as big as we could straddle, which makes it work with standard seat tubes and stems. But the late Sheldon Brown suggested you could adapt a smaller frame for proper fit with longer seat tube and stem, both of which are pretty available these days. I'm currently playing around with a 57 cm Bringhelli, which I got off ebay when I lost out on an 80's Team Pro in the last seconds. It has the same length top tube as my '72 SC, and 73 degree seat tube and head tube, and the wheel base is also the same because the adjusters on my SC are rusted in place near the front of the dropouts and I never messed with them. So with a longish seat tube and stem I've got the same geometry with a 57 cm frame as a 61 cm frame.

Dave

m000ns

Jim,
I'd like to add my best wishes to you for a successful recovery. Your incident is scary to read about. Thirty-five is about my limit, can't imagine 40-45 much less going down at that speed. I like riding large frame bikes so I will be wary from now on. I have nothing to contribute on possible causes but will be very interested if you can pin it down.
Best regards,
Macon

overfedlonghairedgnome

By all means do not let me cast aspersions on larger frames as a whole! I think something like a loose spoke, out-of-round wheel caused the shimmy. But most of my experience has been with 56-58 cm frames where I have descended many big hills (some as high as 55 MPH, on Cuesta Grade, Hwy 101 near SLO) without a problem. I once descended my fully loaded 58 cm Eisentraut Limited for several miles with my hands off the bars when I was coming down Hwy 180 from Sequoia National Park on tour. Obviously my bike was balanced well with the packs.

All I am asking is that since I do not have as much experience with frames as large as 60 cm that I want to know what others think. I do not think or want others to think that 60 cm frames are in any way unsafe. Being an engineer myself, I am trying to analyze just what exactly happened, simply because I don't believe that it was normal. Bike frames are not meant to shake at that kind of speed regardless of it's size, so there must be some kind of defect that I am trying to identify.

Back in the day it was popular to ride a somewhat smaller frame to get the stiffest, lightest steel frame possible. I raced a 56cm Colnago Super that was made with Columbus SL tubing. It was the largest frame size made with SL tubing and was rated for a rider not more than 160 lb. At the time I weighed 157 lb @ 5'11". With full kit this bike weighed 19 lb 12 Oz. It had such cheap tricks as a Cool Gear titanium rail "The Seat" ass hatchet and Dura-Ace EX cassette with 12-tooth top gear straight block, Fiamme Ergal rims, and Suntour Cyclone derailleurs. I even used 42-48 chainrings to reduce weight a few grams. That bike was miserable to ride in a road race but brilliant in a criterium. But this "small frame" conditioning is part of my background, so I have to ask questions.

BTW, I am feeling better and backing off the pain meds. I hope to be back on a bike by February, in time for my 54th birthday.

Respectfully - Jim

Holger

Hello, first i wanna wish you all the best. ( you rode pretty fast on a bike
with Mafac Brakes!)

I am really no expert about frames and steel, but just like to say that i
only have 60cm frames except one Colnago wich has 58cm.
And i have never felt unsave on them, mostly i ride rough roads in the forest with lots of ups and downs.
In 2007 i rode the l`eroica 200km on a (still un-identified 70`s bike)
this year i made the 75km stage with my Team-Pro both 60cm frames.
I broke pedals, cranks,spokes, but I never had any trouble caused by the Frame.
To me such a road bike is a quite sensible instrument any changes in the set-up quickly causes trouble.
In my opinion the most important thing on a bike are the wheels and i think they can cause the biggest trouble.
One, only little loose spoke or headset can crash the whole buiding down.
(This happend to me several times, but thank god without such trouble like you have)

Wish you again all the best, and a happy and save 2010

Holger

Wisey

Hi again everyone

I just wanted to clarify what I was saying about big bikes.

I am not saying that big bikes will have problems. In fact, there is no reason whatsoever in the design, geometry or materials to suggest that they will have these problems.

My question is related to the position of the rider and in particular where the rider's weight is distributed in the fore-aft plane. I wonder if tall riders on big bikes experience problems when their weight is mostly over the back wheel, thus removing down force from the front which allows the natural forces of the front wheel in motion (as described by many experts) to develop a shimmy. ie These forces happen to EVERY bike, but smaller bikes have steeper seat tubes and shorter riders thus more weight over the front wheel preventing the shimmy from developing in the first place.

Hope you are continuing to improve Jim.
Happy and safe new year everyone.
2010 - The year of the Gitane.