Speed wobbles

[Al Kidder]

I bought myself a new you beaut everything carbon road bike (Helios A7) from bikes online a few weeks ago.
The bike is good, and faster than the old one with a carbon frame and alloy wheels, but I'm finding it scary on descents.
It seems to be verging on wheel wobbles above 50 and I'm touching the brakes when I get to 60.
The whole front end has a light feeling to it.
Does that have something to do with wider tyres, 28mm, instead of the 23mm I've been on since Adam was a boy?
I tried moving the saddle forward to put more weight on the front with no effect, so what should I do?
Is it possible that the wheel is slightly out of balance? Also, I notice that the rim is assymetric in cross section. Why?

[Andy01]

Just a complete guess - has the tyre been mounted concentrically to the rim ?

The last tyres I replaced (Schwalbe Almotion) were shocking until I just blasted them with my garage compressor (I tried a couple of times with the track pump first) to maximum rated pressure - then they popped into the bead like a firecracker going off.

[DavidS]

I would also look at whether the wheels are completely round, I've had that problem before and it was only noticeable once you got to about 60KMh.

DS

[blizzard]

Doesn't sound normal. I doubt it's the tyre width causing the issue. I would be looking at imbalance in the wheel and tyre, or potentially loose spokes. What tyre pressure are you running? Hoing from 23mm to 28mm tyres you should be on much lower pressures than what you ran previously. Tyre pressure also influences speed wobble.

Rims are sometimes made asymmetrical to even out spoke tension between the drive and non drive side of the wheel.

[Thoglette]

Funny, I’ve been chasing a little wobble myself this last week.
The standard list
1. Check tyre pressures (and seating)
This is the #1 cause if “emergent” wobbles, along with badly loaded luggage
2. Check skewers are tight & wheels are straight
3. Check for play in wheel bearings (grab the rim - can you wiggle it?
4. Check for play in the headset (usually accompanied by brake judder)
5. Check your weight distribution/grip/frame stiffness

The last is where we start to get into maths that’s almost indistinguishable from magic: a magic combination of flex and weight and energy just wants to shimmy. (Have you seen “The World’s Fastest Indian?)

There’s a few good articles out there on how this happens. I’ll see what’s in my bookmarks..,,
Ah, start here and then read the Jobst Brandt too

[Dodgy-Knee]

What’s your posture on the bike when you descend? Are you upright and holding onto the brake hoods or are you low in the drops? Lowering your body and centre of gravity makes a world of difference… descending in the drops allows much more control and stability … hopefully your bike is ok and safe to ride.

[Mr Purple]

Just a complete guess - has the tyre been mounted concentrically to the rim ?

The last tyres I replaced (Schwalbe Almotion) were shocking until I just blasted them with my garage compressor (I tried a couple of times with the track pump first) to maximum rated pressure - then they popped into the bead like a firecracker going off.

This is my bet as well.

When I upgraded my old bike I was suffering shocking speed wobbles down Cootha at about 60km/hr. Turned out the front tyre hadn't beaded concentrically to the rim.

Very easy to check for as well - just check the bead is even all the way around.

[foo on patrol]

If you have a death grip on the bars that will also cause grief.

Foo

[antigee]

Just a complete guess - has the tyre been mounted concentrically to the rim ?

The last tyres I replaced (Schwalbe Almotion) were shocking until I just blasted them with my garage compressor (I tried a couple of times with the track pump first) to maximum rated pressure - then they popped into the bead like a firecracker going off.

This is my bet as well.

When I upgraded my old bike I was suffering shocking speed wobbles down Cootha at about 60km/hr. Turned out the front tyre hadn't beaded concentrically to the rim.

Very easy to check for as well - just check the bead is even all the way around.

Most tyres seem to have a thin line of rubber just back from the rim edge and all the way around the circumference...when mounting tyres I check that this maintains a constant distance from/on/just under the wheel rim all the way round and is same both sides

I did once have a tyre (reputable mnfr can't remember who) that had a twist and lumpy bit in the construction and rode horribly...took it back and the mechanic gave me a box of them to look thru saying something along the lines of "throw the faulty ones in a pile...we get lots"

[CmdrBiggles]

A lose steering column can also induce wobbles that a rider may mistake as coming from the wheel or hub. This is something that bedevilled us as touring cyclists many years ago with the now-older style Shimano and Campagnolo headsets that would very slowly lose their grip set tightness and allow progressively more and more play (as in, wobble) in the steerer. This wobble manifested in this circumstance on my Zaskar MTB 7 years ago. While there was found to be slight play in the hub, the bigger problem was the headset's weakened grip.

[Al Kidder]

Thanks for all the helpful tips. Unfortunately, I won't be trying any fast descents for at least a few weeks after a heart attack last Friday about 5.30pm.
Let me tell you, when you do go, that must be among the best ways. Absolutely zero pain or symptoms leading up to it. All I knew was that I woke up on the floor 1/2 an hour later after falling off my chair with no warning feeling dizzy and sick, so if I hadn't woken it would have been an easy death.
Still, I managed to have fun in the hospital next day when I deliberately got the heart rate monitor to go off by moving from sitting with a pulse of 40-45 to lying down and dropping it to 37 so all the nice nurses came rushing into the room as the alarm went nuts.
The cardiologists expected that stenting would be in order, but the angiogram found no major blockage, so I reckon I've got nothing more than a pulled muscle which should recover over time.
And I'm not going to be as dumb (I hope) as the guy who came and joined the ward on Sunday evening who was fat, already had stents, yet had gone in for the bike leg of the Wollongong triathlon despite feeling sick before it started. He had another stent on Tuesday.
Cheers

[foo on patrol]

^^^^^ ^^^^^

Foo

[g-boaf]

Thanks for all the helpful tips. Unfortunately, I won't be trying any fast descents for at least a few weeks after a heart attack last Friday about 5.30pm.

Holy crap!

Wishing you the best for recovery! That's a massive scare.

[blizzard]

Best of luck with your recovery, sounds like you got off fairly lucky, all things considered.