This may be a “how long is a piece of string” question but anyway…

Fox RP23, 120mm travel full bouncer. Sag set according to manual. Propedal off.

When pedalling hard in the saddle I get approx 1cm oscillation peak to peak on the shock shaft. With pro-pedal on, it disappears.

Would you ride like this or increase the air pressure to run with less sag but less bob? Personally it doesn’t bother me but I can’t quantify the losses associated with the bob.

I am lost for words

Obviously not entirely lost…

What’s acceptable is learning to ride a full suspension bike.

The whole idea of selectabe propedal is so you can kill the bob when climbing etc and ‘open the shock up’ when the trail get rougher or goes downhill.
🙂

“What’s acceptable is learning to ride a full suspension bike.”

Thanks for that. Very useful.

So once I’ve learnt to ride my bike, I shouldn’t have any bob at all?

omg

Its what the propedal is for, surely? So that you can set the spring rate to offer best suspension and then tune out most of the undesirable bob.

Personally I set the propedal so that it works and then just leave the bike as is.

So once I’ve learnt to ride my bike, I shouldn’t have any bob at all?

Almost. You learn to get the best out of it. The SPECIFIC measurement of bob is meaningless. You can feel if the bike is performing well or not.
As PP says, Propedal is design to reduce the amount of bob, but most suspension designs these days are good enough to not really need it.
I’m sure my yeti “bobs” when going uphill but it climbs like a bastard.

Peter,

Thanks for your reply, I am aware of the function of the pro-pedal. So with the pro-pedal off, you would expect a decent amount of pedal-driven shock compression then. (less with a well designed frame)

I’ve had a think and now I do have 2 words:

hard tail

Simon,

If you keep this up, you’ll have a complete vocabulary by next Thursday.

So, Schwiez, what are you trying to find out? If 1cm of “bob” is acceptable as a quantifiable loss?

If you have the correct sag and set it on 3 , there is very little bounce , basically none unless you are spiking ,if you are worried about the bounce …. get a hardtail .

So with the pro-pedal off, you would expect a decent amount of pedal-driven shock compression then

IMO, it’s not so much pedal driven as more to do with 2 large oscillating weights moving up and down (You legs!) and as sure as eggs is eggs that weight will make the bike bob a bit. Upping the low speed compression (That’s what propedal does, in effect) tunes that out but still lets bumps move the suspension under high speed compression.

It’s a fact of FS life that it’ll bob a bit when you pedal for one reason or another. Trying to kill that by upping shock pressure is entirely the wrong thing to do (you might as well get a hardtail). Set the shock to the correct sag and turn the PP on and off as needed.
🙂

full bouncer

hmmmmmmm

set the bike so the dag is correct and it rides well; deal with the bob that provides

imo no point buying a full suss and trying to eliminate the unfortunate side effects through set up.

Dez,

Yes, that’s about it. The bike rides well, “climbs like a bastard” but if I look down and see the shock compressing with each pedal stroke then I have to wonder how much energy is being wasted. Sure I can turn on the pro-pedal but this does change the handling charactaristic quite strongly and on a technical climb it begins to feel rather rigid and doesn’t stick to the terrain as well. If I add more air, the bob is lessened, the bike behaves OK uphill (compared to with PP on) but I don’t get as much use of the travel downhill. I’m trying to decide where to make the compromise.

A lot of very useless and unhelpful replies you lot! Shame on you!

A smooth pedalling action helps a lot, but yes it is a fact of life that FS bikes bob. Pro pedal will help minimise it quite a bit, but unless you’re fully locked out you will bob. I wouldnt worry about it too muh, offroad you wont really notice that much.

back of an envalope calculation using a lot of assumptions,

you are wasteing 250W of power!

If it realy is bobing a full 10mm evry time you put pressure on the pedals, i.e. you are somehow able to observe the shock moving up and down at >120Hz (presuming your cadence is 60+).

I suspect most of it is in your head, and the bobing your observing is just you/bike reacting to changes int he angle of the groud etc (which pro-pedal also filters out).

Thisisnotaspoon

Cadence is measured per minute and therefore the shock movement is more in the range of 1-2Hz (I’m more like 30rpm on technical climbs)which is somewhat more noticable than 120Hz

Guys , unless you are a weight weenieing freak , who cares about a little bit of bob . at the end of the day thats what full susp does , if it didnt it would be a hard tail . trying to elimanate bob and still absorb bumps is nearly impossible , its a case of a happy medium .

I ride uphill and the hartaillers overtake me , on the downs i overtake them , are you happy with your riding ? My fitness might be a factor too , just be happy and enjoy your rides , look too much into it and you need to cross to the dark side – ROADIE !

but if I look down and see the shock compressing with each pedal stroke

How do you know that the shock doesn’t compress when you are NOT looking down? It could be your head position causing the bob. You need to hire a datalogger or get someone to video you as they ride beside you to collect the correct information. It’s the only scientific way…

I_did_dab

Excellent advice. I will mount a mirror on my helmet to enable me to maintain my optimum head position and still observe my shocking bob issues. I assume that the effects of rolling my eyeballs to check the mirror will be negligable?

If it doesn’t bother you and climbs well, its not worth worrying about.
What I usually do is switch on propedal for steep climbs, long climbs and long flat sections (or road sections) and leave it off the rest of the time.
If it feels right, it doesn’t really matter exactly how much bob there is.

My old RM usd to have a silver linkage plate and my mate was always commenting on how twitchy it looked while I was pedaling. I never even noticed the movement though.

If you are a weight weenie XC man , hardtail is the answer . we dont know what kind of rider you are ?

Im a plodder , 50km rides , 2000m of climbing , cruise up the climbs , belt down the decents. bob ? yep …. i dont care .

RP23 , PP on 1 and 220psi , rider 205lb .

This may appear unhelpful, but if you are pedalling uphill at 30rpm then the remarks about learning to pedal the bike properly are probably quite valid. You need to smooth out your pedal stroke and spin a bit quicker.

Full suspension bikes bob, but as to how much power you lose is always open to debate. The fact that you can get rid of it with pro-pedal and as soon as you do the bike doesn’t surge forward suggest that it’s not a lot. In fact you say it actually feels slower as it doesn’t grip as well, so there is your answer.
I ride both a hardtail and a full suspension and the hardtail feels like it accelerates more, but loses traction quite easily, where as the bobbing full suspension actually climbs better because it maintains traction. It’s all a compromise.

ozzy, I’m probably very similar to you. 6’3, 209lbs, hardtail in the valleys during the winter, FS in the alps in the summer. When you are climbing 2000m in one go then you start to notice little things like pedal bob…. Highlight of the season is the Grand Raid – 121km, 5430m climbing (trying to get round before the cut-off…)

traildog, the most noticable bounce is the low speed technical stuff, hence the 30rpm average cadence. Of course on a normal uphill section I am trying to spin like Lance.

Im only 5’10 😀 yeah good climbs , i had a 8.2kg XC bike then my club went classes on times , so i now ride a AM bike and dropped a class , all good , im happier 😆

I can’t quantify the losses associated with the bob

Seriously then 😉 , any energy lost is transferred to heat, so go for a ride and feel if your shock has got noticeably warm. I doubt it will. (250W would be seriously hot!).
I only notice the small bob on my FS on the road. Off road the bumps in the ground cause bigger shock movement than the bob so it isn’t worth worrying about. Some suspension designs are more bobby than others, hence the development of propedal, others don’t need it as much.
You are probably wasting more energy just thinking about it.

ooops!

re-does calculation, 30W, arroundabout 5-10% of an average persons output

for anyone else to check………

1cm at the shock = 2.5cm at the wheel

assumed 2/3 of rider weight is on the rear wheel to achieve 30% sag,
rider weight is 90kg,
travel is 5″
therefore spring rate (at rear wheel) = 150 Ncm-1

force to move wheel 2.5cm = 375N

force x distance gives 15J

at 60rpm (2Hz bob fequency), that gives 30W

ohh, and that asumes that all the energy in the compression bob i absorbed by the rebound not the case if you keep the chain tesnion up as it will propell you foreward.

Hey spoon , i like your way of thinking but it probably mans JACK to 99% of us here , we need lay-mans-terms , that technical shit is for roadies and woofters. were talking bob and suspension happy mediums here . Sorry to be so blunt 😕

If you spin you should minimise bob significantly. Try using a higher cadence?

30rpm! Jeez. Even out of the saddle you should be doing no less than double that. No wonder you’re making the bike bob!

In MTB terms, a rider on a full sus could eat 20 slices of cake on a ride, the hardtail rider could only eat 19

I don’t think any pedal bob is acceptable on an XC-oriented bike – noticeable and frustrating waste of energy. Putting more air in will eventually make it a hardtail. Pro-pedal helps on smooth climbs but on bobbly climbs where you really need the traction, it’s all gone.

I test rode an Orange 5 the other week, and the sus was losing so much energy uphill and on the flat – made it feel like it was dragging an anchor (was fine downhill tho). All the Giants have very active sus but pedal like demons – it’s just a different design.

thisisnotaspoon, have you taken into consideration the affect of the fork compression in relation to the back wheel and front wheels & their position in relation to BB position?