Cyclist Down Cradle Today Sun 21 July

[love2fly]

1 hour ago, Mountain Bru said:

Sorry to hear about the incident. 

Speed wobbles can have many causes from what I've read/watched. A mate of mine had a huge wobble in front of me on the descent from Bidon towards the satellite climb, but was able to hold it up and come to a stand still. We tightened the headset compression a bit (after losening the stem clamps), and he took it easy for the rest of the lap but it never happened again. 

From the research I did afterwards, it seemed like the culprit is sometimes not a faulty part or installation, but more a combination of factors resulting in a vibration/wobble due to triggering a natural frequency of the bike and rider system. Some solve this by descending with a knee on the top tube which dampens the vibration and changes the stiffness of the system, and therefore the natural frequency. Others just slightly lift their bum off the saddle. Pedalling also seemed sometimes to change the stiffness characteristics and prevent the wobble, as did changing weight distribution on the bike, wheel stiffness etc. 

My point though is that checking the headset bearings, the frame for cracks, the wheels for trueness and balance, etc are all good and definitely things you should do, but at the same time, the culprit might be something completely different, like the bike fit resulting in a lack of front end downforce, or the alu frame having too much top tube flex, or lose pivots or something. So unless you weigh the same as your son, and sit in the same position, your tests might not give you reliable results. 
 

Here's a video of a guy intentionally initiating a speed wobble, and then stopping it by just touching the handlebars and weighting the front of the bike again for reference of what I mean about a single part not being responsible. 

 

Thanks. Nice interesting reading and video. We did do a quick loosen and re-torque of stem and bars but I plan on checking front to back carefully. Tyre had been coated with like a silicone spray that made the front - Ikon Race feel squelchy at home in that it didn't like keeping straight.

Just got to shake this chest cold and I'm riding his bike. Crash test dummy #2

[RobertWhitehead]

That's never nice to see / experience or hear, good luck for you and your family.

My money is on the headset, if I put my sciencey hat on the sealant will eventually stop being an issue as the rotation from the wheel will be greater. A loose headset on the other hand, the higher the speed the bigger the vibration. 

[love2fly]

1 hour ago, RobertWhitehead said:

That's never nice to see / experience or hear, good luck for you and your family.

My money is on the headset, if I put my sciencey hat on the sealant will eventually stop being an issue as the rotation from the wheel will be greater. A loose headset on the other hand, the higher the speed the bigger the vibration. 

Thanks Rob. Between hospital visiting hours and a chest cold I can't wait to have a look.

[Headshot]

Hard to imagine this kind of wobble on a far heavier less twitchy MTB with suspension. Interested to hear how the post accident test ride and mechanical check goes.  

[mazambaan]

On 7/23/2024 at 5:43 AM, RobertWhitehead said:

That's never nice to see / experience or hear, good luck for you and your family.

My money is on the headset, if I put my sciencey hat on the sealant will eventually stop being an issue as the rotation from the wheel will be greater. A loose headset on the other hand, the higher the speed the bigger the vibration. 

Agreed as a few weeks ago I went out on a motorised bike (Husky 501) and it felt very twitchy (no death wobble but it felt possible) at speed on a surfaced road, as long as that lasted. Steering head wasn't loose as such but very little resistance (normally set up to just let the bars flop over when the front wheel is off the ground). Needs some tightening I think.

[love2fly]

Some feedback. I'm still fighting a chest infection but decided to do some digging which rules out a ride. When riding in our complex the front felt very "squelchy"almost like the tyre was way over inflated with a definite middle mannetjie but it's a Reckon Race and at 1.7 bar

 

.

I put the bike on the stand and found the steering quite notchy.

Video attached without front wheel shows that the steerer didn't want to centre. New headset sorted that and I'll do a test ride at 70kmhr in the week but I'm pretty sure that was the issue.

Please excuse messy garage, we recently moved.

Edited July 28 by love2fly

[RobertWhitehead]

On 7/28/2024 at 2:02 PM, love2fly said:

Snip

Fantastic news man, I think you're golden! 

[love2fly]

Ok, took my son's bike for a ride and managed 59kmhr without any issues.

I also tried hard and soft hands and head down and all good, so looks like headset solved the issue. 

For ride #2 we'll start at Neck and Deck and go Caves and Back to limit the speed.

He checked his Garmin and found he fell off at 52kmhr. Lucky he got chucked onto the verge and not the tar.....he has a lot of tattoos.....

We got lucky and once again, thank you to the kind souls who assisted.

❤️ 

[ChrisF]

3 hours ago, love2fly said:

Ok, took my son's bike for a ride and managed 59kmhr without any issues.

I also tried hard and soft hands and head down and all good, so looks like headset solved the issue. 

For ride #2 we'll start at Neck and Deck and go Caves and Back to limit the speed.

He checked his Garmin and found he fell off at 52kmhr. Lucky he got chucked onto the verge and not the tar.....he has a lot of tattoos.....

We got lucky and once again, thank you to the kind souls who assisted.

❤️

 

Bike sorted 

 

Positive thoughts he recovers quickly and FULLY !!

[love2fly]

16 minutes ago, ChrisF said:

 

Bike sorted 

 

Positive thoughts he recovers quickly and FULLY !!

Thanks. Making very good progress. Hopes to ride in 2 to 3 weeks.