suspension talk (or why are my tires worn so funny?)

[Dirty Duc]

We got into an interesting discussion about rebound and damping in another thread on somebody's tires.

With no permission whatsoever and a whole bunch of aggrandizement with kudos and apologies to the ever helpful Slide Panda, Frankenduc, and stopintime, I quote things here for posterity to search more easily.

The talk is about reading your tire wear to draw conclusions about your suspension settings and (if you are smarter than me) do something about it.  And now for the quote-fest with some minor edits:

The raised rubber lip behind the grooves is a sign of too little rebound damping.

WRT the "too little rebound damping", what I can say for fact is, scalloped tread is a sign of rebound damping being less than optimal for traction. (mind you, not control, traction..  That "control" thing is a kinda personal issue...)

Me Thinks (i.e., I can't personally substantiate):
1) too little rebound - after bumps the tire extends quickly and hammers the ground, resulting in
- tire deformation, and resulting scalloping
- bounce due to high rebound forces, and resulting loss of traction
2) too much rebound - after bumps the tire doesn't fall right to the ground.  Gravity takes its course, and
- time in air means loss of traction
- resulting hammering of the tire to the ground due to gravity results in tire deformation, and resulting scalloping.

Either way, if the bike gives you confidence, it's right.  If it's stable to the point of floating (slow easy lazy drifting), turn it out a bit and see if the scallops decrease. Or, if unstable/twitchy/eager-to-lean as is, turn it in a bit and see if the scallops decrease.  If they increase in either case, you're probably losing traction whilst losing confidence, turn it back...

Oh! I can contribute a visual!



The bike comes with some factory suspension settings and the shop probably didn't touch it unless you asked them too. Manufacturers presets are usually decent, but will have room for improvement. And the bike will come sprung for some weight they feel like. Remember preload doesn't make the springs stiffer - can't do that. Spring force is a constant

SP,

Does that go for the front, also?

Yep. The dynamic is basically the same. With too much damping the suspension is packing down and you're driving that edge into the pavement harder. With too little the suspension's bouncing a bit all the time.

If you were to look at the tire with 'ideal' wear the height of the 'land' (sections that contact the pavement) on either side of the sipe would be even, so the tire would have as close to a perfect circle as possible. When things are out of whack, the land on one side of the sipe will be lower, more worn.

I don't recall center vs side relating to compression vs rebound. As *I* have absorbed it (and hope I'm right) it's all about rebound for that sort of wear. Having off compression will do all sorts of other crappy things for you, but it seems rebound the the arbiter of this flavor of wear.

And a generic solution to a requirement for more damping could be heavier fork oil?  With the understanding that re-valving is a better solution.

Heavier oil would make for more compression damping as well too, just keep that in mind. And of course not like clickers for adjustment. But if there's no clickers... Not much else easy to do.

[Slide Panda]

 

[Slide Panda]

Some tire analysis with Dave Moss - watch to the end to see the 'Tire from hell'  - what happens to a tire with a way over weight (for the springs) rider and waaaay under damped. Oh mah jebus.

http://www.youtube.com/embed/JutNhZw1TB0

[SDRider]

My tire wear tells me that I do way too much commuting or freeway riding.

[Vishwacorp]

My tire wear tells me that I do way too much commuting or freeway riding.

+1
Or not enough riding on the twisties. Another way to look at the same thing.

[lazylightnin717]

Some tire analysis with Dave Moss - watch to the end to see the 'Tire from hell'  - what happens to a tire with a way over weight (for the springs) rider and waaaay under damped. Oh mah jebus.

http://www.youtube.com/embed/JutNhZw1TB0

Dave Moss really knows his shit.

Thanks for posting. I learned a good bit from that 

[Slide Panda]

Indeed he does. I've learned a good bit from his videos and his site
http://feelthetrack.com/

[Dirty Duc]

My tire wear tells me that I do way too much commuting or freeway riding.

+1
Or not enough riding on the twisties. Another way to look at the same thing.

I also have this problem...

But school is done, so moto time will increase! (not as much as if work was done, but what can you do?)

[FrankenDuc]

My tire wear tells me that I do way too much commuting or freeway riding.

Move up to the mountains and keep your job in the city... Wear problem solved 

[Dirty Duc]

All right...

So, next question: What the hell is going on here?

These tires have about 4k miles (the rear is pretty badly square and needs a replacement) but the front is showing the same weird wear pattern as the stock tires. Most all of this set has been commuting 1-up, but the last 1200 miles were two-up fully loaded.  I'd like to remedy this and the annoying high speed weave when confronted with imperfect road surfaces at light lean angles (indented botts dots at 80+ indicated... before the nazis jump in, speed limit is 75 real MPH).



This is the Strom, but I hate the Strom forums as they are full of people arguing about some mythical clutch problem that is the root of all Strom evil.

In case you can't tell, this is the front tire and the worn points are the pointy bits in between the big blocks.  It makes for some peculiar handling characteristics that I don't really appreciate. The OEM tires did something similar which I initially blamed on poor fork brace installation.  The rear tire shows no abnormal wear.

[FrankenDuc]

you say bobbing and weaving when leaned at speed right?, how is your front rebound set?

[Slide Panda]

Hard to see in that picture - but the pointy bit is the portion of the block that strikes first yes?

if so you need some more rebound damping. A couple clicks should do. It won't be radical and that tire will probably always show odd wear as it's beaten up already.

And how old is the fork oil, seal set etc etc? Old oil and sticky seals can bollox up suspension settings as well.

Regarding the weave - rear wheel alignment good? Front geometry good? I've never had a bike that wanted to weave - but I'm OCD about my wheel installs and getting stuff lined up. Can't say my OCD is the reason fro no weave ever, but can't say it's not either.

[Dirty Duc]

The pointy bit is circled.  I asked because it does not seem to be doing either of the things described.  The main blocks down the center are worn pretty evenly front to back, and the side blocks are pretty even.  Just the funny shaped ones are worn more square-like than all the rest of the blocks.

Fork oil and seals are about 10k old and the bike was built in 2012.

I wish it had rebound adjust.  All I get is preload, although I might have rebound adjust on the rear. 

I said weave, and that may have been the wrong word.  It rides normal almost all the time... it is when I go over the bumpy kind of tar snake or the small pothole-like bumps in a lane-change type situation.  The problem is significantly less noticeable two-up, and I haven't noticed anything strange at greater lean angles around a particular pot-hole laden downhill u-turn. 

I'll check for alignment when I get home, but my chain isn't wearing strangely and I would anticipate some strangeness there.  I did suspect the forks because I neglected a step when installing the fork brace the first time that I remedied when I put these tires on.

I have resigned myself to throwing money at the forks and shock... I just want to make sure I am going in the right direction.

[Slide Panda]

I really can't tell what's happening on the tire, in that photo. 

[Dirty Duc]

OK.  I'll try to take better ones tonight.

Maybe if I fiddle with the camera settings.  I didn't ride today because weather underground said it was 12.7 this morning, so it'll be another garage shot.

Next step, of course is a new rear, and since these are the Full-bore version of the shinko 705... I will probably replace the front at the same time.