jmX

I've been noticing that on hard *uphill* sprints out of the saddle the rear wheel is lifting up off the ground quite a bit. It feels like its getting an inch or two of air, and sometimes will jump right an inch or two as well. Anything above 800w at lower cadence (75rpm's) seems to cause it. It isn't an issue on flat sprints where I'm not leaning as far forward.

Am I just not smooth enough? Is it common and nothing to worry about? It doesn't feel dangerous, but it doesn't feel nice either.

It started when I sized down from a 58cm to a 56.5cm bike, however my crank-to-seat angles/distances are the same, but my bars are about 1.5" lower than before. New bike is 2.5lbs lighter, but I can't see that coming too much into play here.

mattm

Probably leaning too far forward, and also not pedaling smoothly. My guesses.

Actually it may be mostly due leaning too far forward given the new bike/setup.

hna

Use a higher cadence.

I managed to do lift the back wheel once in a road race. The speed into a climb was very high and I was in a good position, but there was an accident just after we entered the climb. All but one rider had to slow down. I didn't have time for a gear change if I were to catch the rider in front, so the first few pedal strokes resulted in a wheel lift.

Creatre

I actually have the opposite problem on hard steep climbs, I lift my front wheel off the ground! Only time I've had problems with the rear wheel coming off the ground is poor sprint form in fast, flat sprints. I would have a really hard time getting the back wheel off the ground going uphill I think, but then again my max 5s is about 950w so I'm not over 800w very much.

rkwaki

I would anticipate the following:
1. You have a much longer stem to ensure a proper fit.
2. When you pedal somewhere along the line you were told to pull up one the pedals while pushing down with the other leg
Now how to correct?
1. Get your weight slightly further back - I imagine when you sprint our arms are very bent to get your head down and closer to the stem thus creating a weigh imbalance. Move that butt back a little.
2. While sprinting focus on the pedal stroke - don't focus as much on pulling up but rather pushing out - that is where you generate your power

jmX

Ok, forced myself to move my weight back a bit, and the front end came off the ground for a split second 1 of the 2 attempts. I think I'm just manhandling things too much and need to smooth things out. I'm always pretty tired by the time I get to this very short steep incline and going "all out" for 10 seconds means I have very little elegance at that moment.

2005trek1200

Yea, i would practice doing efforts up these types of hill IN the saddle. You will teach yourself proper stroke ; its all to simple to thrash the bike around out of the saddle.

waterrockets 

+1

+1

Most of the time I've seen people lifting a wheel in a sprint, it's because they pedal too far down in the stroke. At the bottom of the pedal stroke, they're still pushing down, but the pedal can't go down any more. This sends the rider's hips up instead, and results in jumping the bike a little on every pedal stroke.

Moving your weight around is good from a handling angle, and to help address the symptom here, but it's not going to fix the problem of you jumping off the bottom of every pedal stroke.

bostongarden

Indeed, in the end it is likely smoothness. A variety of things are related to that. My sense is that a low cadence while driving/pulling-up hard will create enough jerkiness to bring about the effect you describe. I've been there.

You can smooth out your stroke by imagining that you're balancing a bowling ball (either ten pin or candle pin -- if too much weight for you, imagine a marble) on your head, that a couple of barnyard dogs are nipping at your heels and that your saddle is on fire while you sprint.

MDcatV

i like WR's thoughts on this.

for back side positioning, i like to feel the nose of the saddle just kissing the the back inside of my thighs (there's a softball for you rkwaki). i'm #92 in the image below (another softball for rkwaki), a little farther forward than i'm describing.

jmX

This is meant to be a short 900-1200w effort out of the saddle. I do get plenty of climbing in the saddle, but this isn't the right place for that.

Maybe this is more along the lines of what the issue is. When I swapped from a 58cm to a 56.5cm bike, the crank also changed from 175mm to 172.5. After 2 years on a 175 maybe I still haven't adjusted. 2.5mm doesn't seem like much though.

I definitely pull up a bit during sprints. I've probably trained myself to be reckless since I do almost all my intervals indoors on a trainer that is next to impossible to crash on.

I'll keep at it this summer. I ride this section a few times a week so its easy for me to try different things and see how it goes.

shovelhd

IMO, that's your problem. You can't develop good sprint form on a trainer if you want to be able to put out real power. Form sprints, sure, but the bike is fixed, and on the road, it's not. Good road sprint form means adjusting your center of gravity with every stroke so that you minimize your upper body movement, which will stabilize everything else. I suggest that you forget about the watts for now and do form sprint sessions on the road instead. Get your form down on the flats (a slight downhill is best so that you start at close to race speed), and then take that form to the hills. Once you have a good idea of what constitutes good form for you, then add jumps to it, practice some more, then add power.

KoolAidnPizza

I have found that my front wheel gets some lift when riding uphill when very fatigued. Typically that means my posture is getting bad and I need to adjust

jmX

Alright, I've been successful in keeping the wheels mostly on the ground on the last 4-5 times I've tried this. Moved weight back a little bit, and I try to pedal more smoothly. The later seems to put a cap on my peak wattage though.

Peak watts dropped from 1400w->1290w, but 10sec watts went up from 1040w->1160w, so maybe all I've really done is dose the effort a little better so its less brutal at the start and more maintainable. I'm not totally sure thats a good thing, but 10sec seems more important than peak.

I have a feeling in a race situation all this would go out the window and I'd be back where I've started.

waterrockets 

Practice spinning sprints. Small ring on flat ground, try to get up to 160rpm or more. That will smooth you out. Even more: do it on rollers.

Regarding pacing in a sprint: it doesn't actually help. Every pedal stroke should be maximal for any solo race-winning effort shorter than 1:15 to 1:30. My bet is that your average went up because your improved form lead to a more efficient stroke at higher RPM. The loss of peak is probably just being tentative when your cadence is slow enough to feel the pieces of it -- but that's when it's slow enough that you probably wouldn't have hopped your wheel anyway!

Nice work on the improvement though. Once you get it in your muscle memory, you can be all-out 100% and fatigued and still keep everything on the ground. It won't take much more work for you.