suspension linkage

[AlanC]

Question for the technically minded.

What is the effect of play in the rear suspension linkage and the shock mountings? Does it affect grip, or just delay when the power kicks in?

Does it matter after the chain has taken up slack?

And lastly, what is a normal amount of play with everything working correctly?

Thanks in advance.

[AlanC]

Any opinions on this?

[baldilocks]

A few issues with play in the linkage from my point of view but I'm not an engineer !

First of all some play is required for bearings to move. When this is multiplied by the length of the swinging arm yamahas handbook for the air cooled stated this would be 1mm when the bike was new.

Play of more than this is due to wear in the actual bearings. The bearing surface being worn will increase friction. The additional play will alter the ride height of the bike. The angles the linkage is working at will also change. Most of us are not good enough to notice these changes in terms of performance but none of the above are good things.

I notice it when jumping on and off rocks,  you can hear the "Clunk" which is off-putting.

I cant see it having a material effect on grip but you could break the linkage or shock if its allowed to go too far.

 

[AlanC]

Thanks for the reply. I have replaced all linkage bearings bar the swingarm bearings/bushings and one one the suspension bushings because it was out of stock. Everything is moving smoothly, but there still seems to be about 10mm of play at the wheel (no play in wheel). I was thinking, if you try to hop the back wheel, the play will make it really difficult for the wheel to leave the ground at the top of the stroke. 

I think I found where the play is still there, and I'm wondering if the bolt inside the bushing could have worn down a bit to cause this.

Or could the shock bushings wear out too? 

I'm just wondering because if you had that much play on a road bike, it would be like driving a canoe.

Off road stuff is not my field of expertise, as you might have guessed.

Edited March 23, 2021 by AlanC
addition

[baldilocks]

10mm is way too much. You will feel that when trying to hop certainly. Just as a guide if I drop the forks through the yokes 5mm I can tell the difference. 10mm at the rear wheel will affect the steering head angle.

Are we talking about sag in the shock or play in the linkage? 

[jonnyc21]

The barrings/bushings and bolts, (including shock bushings/barrings) all play into how much movement you have at the rear tire. 

When things are loose it will affect trials riding in a number of ways.  I would expect that a lack of traction and control for most riders would be the most common problems, however a good number of riders might not even notice the change in grip and steering angle because in most cases it has changed over time and they adapted to it without noticing.  I would also expect that unless they went from bad barrings/bushings/bolts/etc. to all new at once most likely wouldn't notice the change and even then some might not.   I would guess that the second most affected riding would be hopping the front or rear, though probably more noticed on the rear hops, and as on the grip wouldn't expect it to be something most would notice as it likely changes over time and people often adjust without noticing.   I would think the most apparent would be, as baldilocks indicated, on the bigger hits during drops, splats, zap's, etc. as it would make the most nose. 

Also, at 10mm I am wondering if your talking sag or slop. 

[AlanC]

Sorry for the confusion lads. When I was looking at the 10mm of play, I was pulling the rear of the bike off the ground by hand, so not 100% accurate, and so it would include the sag in the shock too. But you can feel the change from one to the other as you lift it up, and feel it on the swingarm with the bike on the home made paddock stand that I have. I think I need to take it apart again to find the root of the problem. Anyway, its an old bike so it won't be perfect anyway.

As it is, would it be causing the rear wheel to spin when taking off from a standing start? I'm not worried about dropping off heights or any big stuff. I'm not that good. And I'm only learning all the terms you use to describe all these moves. I'm happy enough to stay on the bike. One of the skills I like the most is learning to find grip where there is none by feeling clutch and throttle biting and using yourself as a counterbalance to shift the weight around. 

Maybe I'll enter a competition this year, if any go ahead. 

[baldilocks]

By lowering the ride height in theory you are increasing weight balance to the rear wheel but its marginal.  It will not impact on grip when setting off. Tyre pressure and condition is much more important 

[AlanC]

I would agree with the weight transfer theory Baldilocks. But I was thinking more about the shock working being delayed on acceleration while it waits for the play to be soaked up. I did have a problem with it spinning up before, but it might have been the worn tyre. The edges of the blocks are all worn in one direction. I'll just have to put up with it for now. I'm sure the bike is better than me anyway.

[al_orange]

16 hours ago, AlanC said:

I would agree with the weight transfer theory Baldilocks. But I was thinking more about the shock working being delayed on acceleration while it waits for the play to be soaked up. I did have a problem with it spinning up before, but it might have been the worn tyre. The edges of the blocks are all worn in one direction. I'll just have to put up with it for now. I'm sure the bike is better than me anyway.

In theory, it could impact traction but the effect will be negligible compared to tyre condition, tyre pressure, clutch/throttle control, and use of body weight, or even sag/spring settings, rebound setting etc. So no, it's not what is causing you to spin up. 

 

[AlanC]

Thanks al orange, you have a point. If you think about something long enough, you will find an excuse other than your own lack of talent 🙂

 

[al_orange]

2 minutes ago, AlanC said:

Thanks al orange, you have a point. If you think about something long enough, you will find an excuse other than your own lack of talent 🙂

 

We've all been there. I do like to make sure my bike is well up together, as then I know the issue is with me. But a little play in the linkage won't be a big issue. However, tyre edge in slippery conditions makes a huge difference. More so when we're learning as we rely on the tyre's performance more to make up for lack of skill. I know I do! 

[AlanC]

Agreed. I'll have to fork out for new tyres soon. Thats if I can find somewhere to use them soon!

 

[pschrauber]

Most play comes from the mounts of the shocks and any spheral bearing mountings and here an asthonishing 0,5mm can lead to several mm at the rear of the swing arm. The most important bearings sre the spheral ones as these are very expensive and if they have play and not working seals will grind themself in hours of use down.

When you thighten up everything there should not much play left.

Another hint to all mono shock type rear suspension, give them at least an annual maintaince and replace the grease, also use water resistant grease. 

[baldilocks]

Annual ? I do mine once a month