Bear with me on this one.

Just gone back to a ht after years of various fs bikes. Quick spec is, early Ragley Mmmbop, Flows, Hans Dampf on the front, Nobby Nic on the rear, Fox Float 32s, Reverb and a Charge Scoop. Both tyres around 32 psi.

First proper ride out last night and I was getting what I can best describe as ‘bobbing’ under power from the rear end, it almost felt like it was bouncing at times it was that bad. I’ve never had anything feel the same even on the fs bikes. Rear end is a 10mm qr axle and is seated in dropouts properly, no cracks in the frame I can see and spoke tension seems fine both on the front and the rear.

Am I going mad or is there a logical/sensible explanation for this?

Is the tyre seated on the rim? Or the wheel gone egg shaped?

If nothings broken I’d go with your going mad. 😆

tyre pressure is too low, or the wheel is radially out of true.

Saddle is too high or you’re spinning too high a cadence.

Tyres can develop bumps and bulges in them if threads in the carcass snap, but that should manifest itself all the time, not just under power.

Could it be the reverb? It’s just a locked out air spring (I guess) when all said and done.

Going mad would be the most likely option!

Wheel and tyre are both perfectly round when the wheel is spun with the bike on the work stand, tyre looks to be seated well.

I do have quite a bit of seat post showing but would have thought a a Reverb would be pretty rigid?

I was meaning more along the lines of a faulty Reverb in case that wasn’t clear!

Normally I would suggest Chainstay is cracked and only flexing under power. Maybe take the back wheel out and get the heaviest mate you have to lean on the axle! Otherwise wheel or tyre issues – but as someone else has said they would generally be all the time. In the grasping at straws section – How big is the rear tyre and how accurate is your pressure gauge? If it is 2.3 or 2.4 and the pressure is lower than your indicated 32psi it could bounce a bit under load. Try pumping it right up to 50ish then try an uphill.

I get this on my superfly from time to time. I narrowed it down to the rear axle being slightly loose, once I’d nipped it up tightly the bounce disappeared.

Try putting some power through a Boardman 29er Pro H/T…….I swore that I had snapped the chain stays first ride out…..but they are designed to flex….says so on the stickers 😆
But then the only bike I have that doesn’t flex is my Cove Stiffee 😆

Have you considered your pedal stroke? Going from FS to HT where previously mashing the pedals would be absorbed by the suspension to a greater degree.

Are you either spinning too low a gear or stomping too high a gear? Really concentrate on a smooth, all-the-way-round pedal stroke somewhere where you’ve noticed this and see if it feels different. Then buy a fixie to practice on 😉

I get this feeling whenever I go back to a hardtail after a long time on a full sus. If it’s the same as me then it’s purely pedalling technique. I must be bouncing up and down with each pedal stroke on my full sus. Not sure why?

woody2000 – Member
I was meaning more along the lines of a faulty Reverb in case that wasn’t clear!

Sorry I posted my reply just before I read your initial post, makes sense. Will put a cable tie at the bottom of the post and see if it moves up after a quick blast.

Tyre is a 2.25 from memory, checked the track pump gauge against my compressor and it seems bob on. I usually run an Ardent on the rear and the Nic does look a lot wider in comparison. It did seem worse when I was in a high gear giving it some beans. Will whip the back wheel off tonight and give everything a thorough going over.

At one stage early last year I did have a CX bike and another ht at the same time as my Spitfire and I never noticed the same feeling when coming off the fs onto either the CX or ht.

My soul does this. Saddle is pretty flexible and the seatpost was a use sumo with a lot of post showing. Together it was like being on a bouncy castle. On the downs it was quite a bonus. Now run a Thomson and much better.

On an alloy hard tail the fsa post and racing saddle made for a pneumatic drill like ride. So maybe go through saddle, post, tyres and wheels to see if any give.

I get this feeling whenever I go back to a hardtail after a long time on a full sus. If it’s the same as me then it’s purely pedalling technique. I must be bouncing up and down with each pedal stroke on my full sus. Not sure why?

maybe its the same phenomenon as people who spend a long time on ships getting land-sick – they’re brain has adjusted to the bobbing so non bobbing feels like anti-bobbing.

I had this after getting a hardtail after years of full suss. It was my pedal stroke. I had learned to accommodate the bob of the bike to smooth it out.

Took me a few weeks to get out of the habit. I was actually un weighting the saddle a bit during my pedal strokes.

The votes are in and it looks like we have a winner! pedalling action 😛

Get on a turbo (a couple of minutes will do) and pedal at the same cadence at which you experience the bobbing. If you feel like the bike’s going to throw you off …

Drop two gears I’ll bet it will go away!

Meh…you try spinning on wet slippy gravel roads at 190rpm on a fixie…. the rear end is all over the shop 😉

DrP

If you work on a ship for some weeks, one that rolls badly, you get used to it. Your body corrects automatically. Then when you get off, and try to walk on the dockside, you ‘feel’ the concrete pier moving under you.

Maybe there’s an element of this, in coming from only FS?

(edit)

As usual, too late, didn’t read everything.

Funny you should mention that, I used to do a lot of sea fishing with my Dad when I was a kid. He was fine on the boat but rough as a dog when we got off.

I’ve swapped the tyres over to my usual setup and had a good bounce about on the rear in the garage. There is quite a bit of flex on the saddle rails added to the fact I do run the saddle as far back as it will go so I’m sure my mammoth 10 1/2 stone on top will cause a bit of give.

I’m not doubting it for a second but I’m surprised to hear it might pedalling technique causing it, it’s something I’ve never given a thought to. Whitestone mentioned a turbo but I never had any issues using one when I had my CX set up on one, the only problem I had was not being able to move the bike side to side if I got up out of the saddle.

The bobbing was that bad I felt like I should be wearing a red nose and oversized shoes.

You sure you werent just going over some bumps ?

Seatpost flexing.

I do run the saddle as far back as it will

frame too small

I had an Mmmmbop dont remember any bob similat build hope flows thomson post 150 fox 32s had a 10mm RWS skewer. Great bike.

I’ve got a cunning theory which perhaps doesn’t boil down to pedalling inefficiency…

Perhaps when you ride your full suss and are sat down pedalling you bounce down on your saddle a bit not at the same time as pushing down on your pedal, but in-between pedal strokes. This way when you push down on the pedals the shock is rebounding and you some how are balancing everything out to some super efficient level pedalling. This obviously doesn’t transfer to hardtails. Sounds plausible?

I had the same thing going from a FS SB66 to a Cotic bfe earlier this year. First time HT rider and found the bobbing very odd. I was riding in a group of very experienced guys who had both FS’s and HT’s for different riding conditions. They said it was down to pedal action and having to be smoother on the HT.

I actually changed to an Absolute Black oval chainring and either this, or thinking smoother pedal technique helped me even it out. I’ve been swapping between HT and FS and I don’t notice a bob at all now.

Sounds like you need biopace
http://www.sheldonbrown.com/biopace.html
“Bouncing in the saddle generally results from difficulty with changes in leg direction, not speed in the middle of the stroke. Thus, as Biopace makes it easier on your knees, it also can help you spin faster without bouncing! ”

the tyre doesnt have any damping to its springyness so will feel as if its bouncing around a bit. always the case on any hardtail mtb iv ridden. especially if youre used to a full sus which still does this, but the damped suspension hides it

@smatkins1

You’ve just described pedalling inefficiency!

You have confused pedalling with chopping wood.