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Hardtail Bobing(9 posts)

Hardtail BobingPahana
Dec 2, 2003 2:24 PM
I'm a mountain biker but I figure you roadies must know a thing or two about spinning.On my hardtail I bob in a moderate gear at 100rpm.In order to stop the bobing I have to use a heavy gear that is hard on the knees. On my FS bike I can spin at 100rpm or more and not bob.I've move the seat down and that has helped some but still I bob in a moderate gear.I try to focus on the up side of the spin but still the bike starts bobing.The only way to stop bobing is spin at a lower gear and this burns out my legs.What am I doing wrong?
do both bikes have the same length crankarms? (nm)PmbH
Dec 2, 2003 2:27 PM
Check that your saddle height is the same on both bikes (nm)innergel
Dec 2, 2003 2:47 PM
Check that your saddle height is the same on both bikes (nm)Pahana
Dec 2, 2003 2:56 PM
Both crankarms are 175mm.I'm 5ft 4in tall. Is this size crankarm the cause of the problem? Should I go to 170mm will that help?
Check that your saddle height is the same on both bikes (nm)innergel
Dec 2, 2003 3:06 PM
Any difference in your setup between bikes can possibly cause bobbing. Measure the distance from the top of your saddle to the middle of your crankarms along the seattube. They should be the same. Also know that if you have different saddles, one may be softer so your effective length could be off a bit. Same thing with pedals and shoes. If you have different pedals or shoes, the stack height could be slightly off causing you to bob in higher cadences.

And 175 cranks seem a bit long for 5'4". It's probably more appropriate, at least on a road bike, to go with something shorter, like 170.

I would also agree with the other post that your FS could be absorbing your bobbing, making it only noticable on the HT.

Just make sure all your measurements are exactly the same, and if they are, practice your pedaling technique.
re: Hardtail BobingTriphop
Dec 2, 2003 2:54 PM
The FS bike is probably absorbing the bob so you don't notice it, but on the hardtail you actually bounce on the seat. You just need to practice pedaling circles. One legged spins on the trainer, or get slicks and ride rollers.
also try.....namaSSte
Dec 3, 2003 6:45 AM
keeping your heels low on the pedal stroke (flatter foot) and using a very round motion (you have to visualize this in your head as you pedal if you're not used to doing it). Another thing to do is relax a bit. I find that as i tire during a big effort, my pedal stroke becomes more of a mash (up and down rather than circular motion) and I lose any spin I had going. Allow the leg to travel in full range motion by relaxing a bit at the hip crease. This will bring your knees up as you pedal and allow you to spin a bit better. That all said, it won't feel natural at first if you are doing it right so just stay with it until it becomes second nature. Good luck and dry dirt to ya!

Scott (also a mtb'er)
Put more air in your rear tire. Practice! nmSpunout
Dec 3, 2003 9:42 AM
pretty typicalcyclopathic
Dec 3, 2003 11:05 AM
on FS bike suspension absorbs univen pedaling action. You have to practice: spin ups on downhill/trainer in easy gear, one leg work outs, etc. You're not doing anything wrong, you just need to work on it.