bdcheung

My rear wheel lifts off the ground during sprints. What am I doing wrong?

botto 

too much weight forward.

bdcheung

Huh. My chest is usually above my steerer tube with my neck/chin above where the stem clamps the handlebar. I feel like any further back and my saddle hits my legs when I sprint--am I doing it wrong?

MajorMantra

I find the back more prone to lifting when I'm in a too-high gear - it kills smoothness. Spinning slightly faster and shifting weight back helps.

mkadam68

I was taught that the nose of your saddle should lightly touch your hamstrings as you sprint. Of course, I think this advice came from BF, so it must be correct.

ted ward

poor pedaling technique: pulling up at top of stroke

grolby

More likely a variation on this, which is still pushing DOWN at the bottom of the stroke, which causes you to rise up which unweights the rear wheel which causes skipping. Pulling up too hard in the middle of a sprint is all but impossible; the downstroke is so many times more forceful that it's more likely to be causing a problem. In any case, pedal stroke is a real possibility.

merlinextraligh

+1. Waterrockets wrote a pretty good explanation of this in another rear wheel skipping thread. Worth looking up if the search engine worked.

ridethecliche

You need to do form sprints and add more high cadence sprints to your training. You're overgearing and under spinning.

waterrockets 

Yep, most of it is pedaling down through the bottom of the stroke. When you reach the bottom, any down force from your leg results in your hips going up, which gets your center of mass going up. This results in the tire coming off the ground as your cleats and pedals pull the bike up with you.

You can have your weight really far forward if your stroke is correct. Here's a side view of Renshaw and Cavendish taking 1-2 on the Champs Elysees (clip from this video). Cavendish's helmet is almost even with his front wheel:

shovelhd

Throwing the bike excessively from side to side can also cause skipping.

waterrockets 

Though, when properly controlled, this is a valuable component to a sprint. If I sprint with a well-timed swing, I find I get another 100W on the top end. True though, it can mess up your form and send you skipping along.

ridethecliche

Hence form sprints in the little ring at 130+ rpm.

shovelhd

+1. The swing has to come naturally, from the bar push/pull. I was referring to the guys who are trying to emulate Cavendish.

bdcheung

The skipping doesn't happen when I do my form sprints--and those I normally wind up past 145rpm.

If I look at Sunday's sprint, my cadence starts at 93 and gets up to 138.

gsteinb

sounds to me like jerky form. I'm pretty far forward here

bdcheung

i wish i had video.

the sprint was also up a 4% grade - which I'm guessing changes a lot and I should have included in my OP.

MDcatV

WR good explanation. i've found as have others i've spoken to, that rear wheel skip is exascerbated by deep section rims. i assume this a rim stiffness issue.

my natural sprinting position is very much like mark cavendish's (and for you dip****s out there, please note that i'm in no way comparing myself to mark cavendish, only that we're about same size and look similar in sprint position), so i've got my head out over the front of my bike kind of far and low. i notice that when i jump really hard i have a tendency to invoke rear wheel skip, particularly when i've got the deep section rims on and even moreso when sprinting up a hill. if i immediately focus on smooth, the skip goes away. i practice this so that i can largely avoid it when i actually need to sprint.

waterrockets 

Which ring?



Yeah, it means you were likely at a lower cadence, which means higher pedal force, so a larger jump when your pedal hits bottom and you haven't let up yet. My guess is that during the race, you lost form a bit and don't have the same stroke you do during form sprints.

botto 

how come everybody has a photographer with a decent camera/light/lens but me?

kensuf

some of those pictures you posted to fb were pretty good.

botto 

shhhh.

grolby

Yes, exactly - I was thinking about WR's posts on this issue in the past.

bdcheung

more form sprints it is!

Dunce

I had this problem last year a lot, still do some this year.

I found for me it was this....

*EDIT*

Or perhaps it was at the bottom. Point is I smoothed out the stroke (mostly by increasing cadence) and it's rarely an issue now.