Serious wobble at 40mph with aero rims

djhep

I had a bit of a heart stopping moment last week while out cycling, and wondered has anyone else had a similair experience to the following?.

I was out on my old Joe Waugh 531c bike equipped with Mavic Cosmic aero rims, and while descending at about 40mph got into a pretty bad wobble.
It started very gently, and gradually got worse to the point where i really thought i was off.
Luckily i was able to very gently get on the brakes and pull to a stop. (the wobble continued almost to the point where i stopped)

The day started out with a slight breeze blowing, but up at around 700m it became fairly blustery with gusts probably around 20mph.

As the road surface was extremely good, I can only assume that one of the gusts had caught the deep section rims and was the cause of the wobble.

I've ridden the same setup in similar conditions before and never had a problem.
Will definitely be a bit more cautious in similar conditions next time out, maybe even start carrying a spare pair of shorts

Cheers.

Dave.

sungod

it's a nasty effect, to control it braking is probably not the best idea, instead...

- press one/both knees against the top tube

- unload weight from the saddle

- move weight forward a bit

keeping a relaxed grip can also help - human reactions aren't fast enough to correct wobble, if you attempt it the lag in reaction time may even reinforce it

i've had it once, seemed to be triggered by change in yaw angle as i went down a fast road with a gradual curve, once i was at the critical angle to the wind it started, but knees on the top tube damped it out fast

djhep

Hi Sungod......
Thanks alot for the advice.....hopefully i won't have to take it though .
My reaction to get on the brakes gently probably comes from motorcycling on sand/dirt roads where you can have a bit of a wobble, but definitely have to slow down for one reason or another

The scenario that you mention definitely sounds right. I was going around a very gradual but fast downhill curve and was changing angle to the wind.

Actually I'm amazed that the cross secional area of the aero rims can have such an effect, compared to that of normal rims.
I'll definitely pay more attention to weather conditions in future and leave the aero rims at home when the wind is blowing.

Dave.

ugo.santalucia

The solution is to get some shallow rims... which also look less ridiculous on a 531 frame

djhep

Oops.....
Sorry all... just realised that was my first post since 2011 when i joined this forum. :shock:
Can't believe it's 3 years ago.
Anyhow I promise to be more active on the forum from now on .

All the best.

Dave.

ugo.santalucia

Can't believe you still remember the password...

djhep

Nooooo Ugo......they look really cool and the colour even matches my bike

Dave.

ugo.santalucia

Let's be clear... when it comes to period bikes, this is cool


This also is cool


This is not cool


However, this is very cool...

djhep

Can't disagree with any of that Ugo......

ugo.santalucia

djhep wrote:

Can't disagree with any of that Ugo......

However, you were doing a "Tommasini/Bora"... hence uncool... for this time I'll let you go, but if that happens again I'll have to send you a formal warning...

djhep

Ugo....I promise i would never do something like that!!!!

The Mavics that i had on the 531 at the time, are the same as the front wheel on the Yellow Look bike that you attached (early 90's i believe)....hence only a few years younger than my bike (1989).
I know that is perhaps not strictly acceptable, but not in the same league as the Tomassini with modern Bora wheels.

Cheers.

Dave.

IShaggy

Check out your headset. Only time I've had serious speed wobble like you described was when my headset was loose.

butcher of bakersfield

Happens with normal rims too. Have very shallow rims on my bike, and I can think of at least two occasions where I've had major speed wobbles triggered by crosswinds. One of those times was very much like you describe...it felt not like a matter of if, but when, and I was preparing myself to go down. Thought the tyre must have blown.

One consistent factor every time I've had the wobbles (and there's been a number of other times too!), is that I've been quite tense. One time was my first ride on a road bike in adulthood, and feeling completely alien on the bike I was very nervous. Another was my first ride on the road bike after winter (I often ride MTB through winter) on a damp road and a big descent. Again, I was nervous. In the windy example I described above, the crosswinds on a fast descent were making me nervous.

My advice would be to try and relax.

nweststeyn

Had speed wobble once, coming down from Glenshee approaching 48mph. Absolutely terrifying, I tensed up and grabbed brakes and as you say, it keeps wobbling right up until you stop. This was on shallow rims. I think, in my case, the problem may have been caused by loose hubs?

Anyhow, it's never happened again and I am told the leg against the top tube whilst you relax your body is the way to go.

mfin

As a couple of people have hinted on here, not being tense is the best way to stop any speed wobble from happening in the first place.

djhep

Thanks for the responses guys......
I'm pretty good at keeping on top of maintenance on my bikes, but will definitely check out my wheel and headset bearings a bit more closely.

I agree that it's important to be relaxed on the bike, and i usually am, but i guess the fact that the wind was gusting and that i was hitting some high speeds probably did make me tense up a bit.
Once a wobble starts, i guess it's catch 22, and natural instinct is to tense up even more in anticipation of hitting the road...Ouch!!!
I must admit, i don't even like thinking about that lol......

Cheers.
Dave.

Grill

If you have the Cosmics I'm thinking of they're only 30mm which neither qualifies them as deep-section or aero. It's unlikely the wobble was due solely to the wheels as I've descended faster with stronger winds on 80mm with those issues.

itsnotarace

Someone tell this guy to get some shallow rims :roll:

https://www.youtube.com/watch?v=JuHsgAX3TBY

Brant

Simple solution... don't ride if it's windy, breezy or if the leaves on the trees are moving even the slightest.

djhep

Hi Grill.
I can't be sure but i think the old Cosmics are around 50-60mm deep.
I do know that the inner tube valve is 80mm lg.

Listening to all the comments including your own, i think there is a definite possibility that i have a slightly loose/worn wheel or headset bearing.
Unfortunately i'm sat in a swamp in West Africa at the moment so a checkover will have to wait.

Dave.

Grill

Got it, I was thinking you had the Cosmic Elites.

djhep

Hi Brant.....
Luckily for me that would be most of the year where i ride now