Tire pressure and wobble over 32mph

[Randyc3]

Hi,
Looking for some collective wisdom concerning a slight wobble I encountered going down some hills yesterday on my V20c. It begins around 32 mph and is very pronounced at 40 mph almost feels like I will wobble out of control. Front wheel is new. My wheels:
Front-Astrial Veil3, 24spoke, DTSwiss 350- 32mm gran prix 4season-80psi
Rear -HED Flanders C2+ Disc, 24 Spokes -32mm gran prix 4season-76psi
Running tubes
Any thoughts?
Thanks in advance.

 

[Mathew Fy]

Possibilities include loose headset, weight shifted to the rear, loose spokes, loose thru-axle bolt, ...
There's also a gyroscopic / harmonic issue that can come up in certain conditions. I've never encountered it with mine, but when this occurs, it can usually be squelched by squeezing the knees to the frame. I do this when descending partly to feel more stable, also to reduce wind in my face. Could it be more aero?

 

[Jeffers]

Motorcyclists call that 'a tank slapper'. But that there wasn't a full tank slapper.

 

[Randyc3]

Possibilities include loose headset, weight shifted to the rear, loose spokes, loose thru-axle bolt, ...
There's also a gyroscopic / harmonic issue that can come up in certain conditions. I've never encountered it with mine, but when this occurs, it can usually be squelched by squeezing the knees to the frame. I do this when descending partly to feel more stable, also to reduce wind in my face. Could it be more aero?

Thanks. Checked the above and all seem fine. Will remove the rear wheel and tire to see if have missed something. Generally I ride with my knees close in, but will pay special attention on descents now. Cheers.

 

[Graham Mccollum]

I had the same on a decent recently. Was convinced my front tyre had defkated. Did an emergency controlled stop flintstones style and found nothing. I think comments above are bang on the mark. Probably slight movement within the front somewhere allows resonant motion to build. Knees on frame definitely helps control it.

 

[Art G]

I had a Cinelli Supercorsa with steep angles and SLX tubing which was prone to front wheel wobbles on steep downhills. There are many factors which appeared to control this, weight distribution, cross winds and frame geometry were all involved somehow. I, too, found that clamping my knees against the top tube always prevented the really, really scary wobbles. Maybe if you did the same with the front boom it would solve the problem.

 

[-don1]

So glad someone brought this up. I thought it was me being a scaredee cat. I reckon might be wheel balance issues? I will recheck the headset and all the bolts. Higher speeds on the v20 have never given me confidence.

 

[cpml123]

Randy... Probably should see if the wheel is true (should be since it's new) as well as balancing the wheel. I have a bunch of golf club sticky weights that I bought from Amazon to balance my wheel. I only used 2 and have like 15 left. I can give some to you next weekend, or you can buy from Amazon if you need them soon. Here is a YouTube video about balancing bike wheel.

Michael

 

[Randyc3]

Randy... Probably should see if the wheel is true (should be since it's new) as well as balancing the wheel. I have a bunch of golf club sticky weights that I bought from Amazon to balance my wheel. I only used 2 and have like 15 left. I can give some to you next weekend, or you can buy from Amazon if you need them soon. Here is a YouTube video about balancing bike wheel.

Michael

Thanks Michael and all! Had never done balancing but make perfect sense. Both wheels look true but sure they would benefit from balancing. Cheers and safe riding.

 

[Robert Holler]

This can happen sometimes if you have a tire that is not fully seated in the bead of the rim at one area. It might be hard to see in general - that might be something to check out.

Robert

 

[Randyc3]

This can happen sometimes if you have a tire that is not fully seated in the bead of the rim at one area. It might be hard to see in general - that might be something to check out.

Robert

Thanks! Will deflate and reseat the tire as a check. Cheers.

 

[Frito Bandito]

My V20 got the speed wobbles on a slight downhill once when I first got it and it had me worried that it was going to be commonplace. Not sure what I did before the next time but it doesn't get them now.

As for tires, I always give them a spin in my hand to ensure the tire beads are seated. If not, I will deflate and reinflate or inflate to 120psi or so to get them to seat. Its not scientific, but holding the skewers with your hands while the wheel spins should reveal an imbalance if there is one.

 

[Randyc3]

Thanks. Don’t have a truing stand…..yet. Will do my first wheel balance on the bike. Fairly sure the front wheel needs to be balanced at the very least. Cheers and safe riding.

 

[Jim Parker]

When Maria first started racing and going fast in large crowds of bikes, she got wobbles at high-speed. It turned out she was scared and her hands were trembling, causing the front to shimmy. Once she realized what was happening, she learned to get a steady firm grip on the bars.

I would check all the mechanical stuff mentioned above. Happened to me once when I forgot to re-tighten the skewer/axle.

 

[Randyc3]

When Maria first started racing and going fast in large crowds of bikes, she got wobbles at high-speed. It turned out she was scared and her hands were trembling, causing the front to shimmy. Once she realized what was happening, she learned to get a steady firm grip on the bars.

I would check all the mechanical stuff mentioned above. Happened to me once when I forgot to re-tighten the skewer/axle.

Thanks Jim. Have checked the mechanicals. Changed to a curved slider boom which seems to help. Just got my weights, so will balance the front wheel before my next ride. Also making a conscious effort to keep my legs closer to the frame. Safe riding.

 

[artchris0002@yahoo.com]

Hi,
Looking for some collective wisdom concerning a slight wobble I encountered going down some hills yesterday on my V20c. It begins around 32 mph and is very pronounced at 40 mph almost feels like I will wobble out of control. Front wheel is new. My wheels:
Front-Astrial Veil3, 24spoke, DTSwiss 350- 32mm gran prix 4season-80psi
Rear -HED Flanders C2+ Disc, 24 Spokes -32mm gran prix 4season-76psi
Running tubes
Any thoughts?
Thanks in advance.

I have experienced the same Phenomenon. It's scary. I was on a V20 with Boyd wheels 25mm rear & 28mm front. I just sat up to increase wind resistance which reduced my speed. Losing control at 40mph is not on my must do list. However, I did have a conversation with Maria Parker. Her thought was I was holding the handlebars so tightly that I was responsible to the oscillation. Just my 2 cents on the topic.
Art

 

[Art G]

This is an interesting thread. I'm 73 and began adult riding when I was 22. I've owned a lot of bikes over the years, logged a lot of miles in different terrains and had a lot of different wheel set ups. But I only had one bike that would get front wheel wobbles at speed going downhill, my Cinelli Supercorsa. I admit, it is super scary but once I learned the trick of clamping your knees to the top tube it never happened again. I'm still a newbie on my S40 and am not yet comfortable going over 30 but it would be interesting to know how common front wheel wobble is on a Cruzbike. Lennard Zinn has a series of excellent articles in Velonews about front wheel wobble and what causes it but none of it is for recumbents. Is this common or a rarity for the recumbent crowd?
Art

 

[chicorider]

I have experienced the same Phenomenon. It's scary. I was on a V20 with Boyd wheels 25mm rear & 28mm front. I just sat up to increase wind resistance which reduced my speed. Losing control at 40mph is not on my must do list. However, I did have a conversation with Maria Parker. Her thought was I was holding the handlebars so tightly that I was responsible to the oscillation. Just my 2 cents on the topic.
Art

Yes. I learned years ago, after tearing a tendon near my elbow, to relax my deathgrip on the V20. Once I did that, my whole body relaxed, my spin smoothed out, my line became much straighter, and, oddly enough, my speeds increased, up, down, and flat. I never had what others here are describing as a front wheel "oscillation," but I do believe that a rider's body tension can play into this sensation.