Really stupid and trivial suspension question

monkeylizard

Well don't say I didn't warn you...

If I stand next to my bike, hold the bars/stem so that the front end stays on the ground, lift the bike by the saddle so that the rear wheel is a foot or so off the ground and then drop it, the back end of the bike bounces a few times when it lands.

If I repeat the same with the front end (hold the saddle down, lift the bars, drop it), the front wheel lands and stops dead - no bouncing.

Hmmm.

Is this because of how the bike's weight is distributed and/or where it pivots when I lift/drop it in each case?
Is it a sign of a problem with my suspension (at least setup if not a fault)?
Am I worrying too much?

(In my defence, I noticed this after hosing the bike and was bouncing it to remove excess water - I'm not intentionally this sad )

bails87

Have you got a hardtail?

If so then basically it shows that your suspension works.

If you've got an FS then you might need more rebound damping on the rear.

But I suppose it's how the bike feels when you ride it that matters more

(assuming it's a hardtail) Essentially, the forks compress to absorb the initial impact with the ground, so the tyres don't take it all and then bounce back. When the forks extend, the rebound damping stops them springing back too quickly. So they absorb the impact without flinging the bars back up straight afterwards, which is pretty much exactly what you want suspension to do.

Barteos

What would we do without bike forums...

Actually I was wondering the same many times and now you made me seriously thinking.
My guess is that unlike with the fork, when you drop the rear of the bike the force isn't high enough (higher shock pressure) to activate suspension/damping and it's the tyre that makes your bike bounce. That's assuming that the bike is setup correctly.
I hope it does make sense.

monkeylizard

I knew I was bound to miss out the most important piece of information :roll:

It's a full sus.

I've tried to reason why both the front and back were doing what they were, but ended up making good cases for both. Although it did seem right that the front was absorbing the impact.

I agree that it's how it feels when I'm riding that's most important, but as a beginner it's often difficult to tell whether something is right or not. When you say that I might need more rebound, does that mean making it slower?

And thanks for tolerating my daft question and taking the time to reply

Barteos
What you've said makes sense as well. So now I'm confused again

bails87

More rebound damping. Which slows down the rate at which the shock extends or 'rebounds' from an impact.

If there's no rebound damping then you'll end up with a pogo stick type effect, which could lead to you getting thrown off the bike. If there's too much rebound damping then over repeated hits the suspension can 'pack down'. So it doesn't get time to re-extend after compressing to absorb an impact, so by the time you hit the next bump, you've only got 50% of the travel available, then when you hit the next one, 20% and so on. There's a point inbetween that's just right!

Barteos might have a point, although it's not necessarily to do with shock pressure, as that depends on leverage ratios. But it might be that 70% of your weight is going through the rear wheel, and 30% through the shock, so for that reason, the rear needs more of an impact to start working, because if it compressed as easily as the front, you'd go through all the travel as soon as you sat on the bike.

monkeylizard

Thanks again, Bails. I really appreciate it.

I shall add a bit more damping shortly and see what effect it has when I take it out for my lunchtime thrash

If it feels worse when I'm riding I guess I'll just have to go back to coping with it bouncing when I try and shake the water off it

handful

I would say it's due to the rear shock having to support more of your body weight than the forks when seated. When you bounce it around unloaded it has very little weight to compress the rear end. You need to experiment in actual use rather than drying off I reckon.

monkeylizard

It gets plenty of use - but when I'm riding I have to think about more important things... like trying not to fall on my backside, and whether I'm going to cough my lungs up or my legs are going to fall off

Cleaning the bike gives me time to think about stupid things like why one end doesn't bounce. Maybe I should stop cleaning it...

Northwind

The 2 ends do the same sort of thing but in totally different ways so it's not too surprising they act differently. Unless you have a Bimota Tesi 2 or something. Also you've got the rearward weight distribution, and of course the suspension isn't the only thing bouncing.

I wonder what would happen if I did the same with my rigid. Maybe I'll find out

monkeylizard

Northwind wrote:

Unless you have a Bimota Tesi 2 or something.

Must resist the temptation to go completely off-topic and start talking Italian motorcycle exotica...