Suspension and tire wear

[headshrink]

This is a copy of my post over at the CBR forum.... that gets no traffic, so I thought I'd try here. It should apply to any bike here, as the rear shock is similar. Sorry the images or so big, but it's difficult to show what I'm talking about with photos.

My stock Dunlops are near the end of their life, and orders have been placed for upgraded replacement tires. I noticed, however, an unusual wear pattern on my rear tire. I consistently keep my psi at Honda's recommended pressure, and hadn't touched the suspension up to the point I noticed the unusual, to me, tire wear at 8K+ miles.

The trailing edges of the tread has a little lip, or is raised a little. This is more pronounced toward the edge of the tire. According to this article, it is a suspension issue.

"Are the edges of the tread raised? – If you have a raised area on either the leading or back edge of the tread, this is a strong sign that rebound damping on the forks or shock is set either too fast or too slow. Usually if it’s on the leading edge rebound is too slow, and if it’s on the back edge it’s too fast."

My understanding of suspension tuning is very, very basic, and only theoretical because I'd never actually done it. But, I knew the suspension wasn't very good on this bike, and often feels like a pogo-stick to me. So I took the opportunity at this point to increase the pre-load (one click) and see how things changed. I know this isn't exactly dampening, but it's all I can do and thought it may still affect suspension behavior.

It's been a couple hundred miles (max) since I increased the pre-load, and the result in handling was initially impressive. There is way less pogo feeling, and noticed I was subconsciously riding a little faster. I just inspected my tires again, and although I can't be certain, I think the raised edge on the trailing edge of tread MAY be increasing, not decreasing like I expected. I refereed back to some original reference photos, but they aren't great pictures, so it's a difficult comparison between the original and today's reference photos. I'll post them bellow for feedback (ignore the chicken-strips on my commuter with stock rubber).

ORIGINAL REFERENCE PHOTOS






FOLLOW-UP REFERENCE PHOTOS

[cuong-nutz]

mother of god. I can't see

[cbinker]

there is only one setting on a 250, preload.

[headshrink]

Originally Posted by cbinker

there is only one setting on a 250, preload.

I realize that... same with the CBR500r.

[csmith12]

Those pics look to be of your cbr right?

It's been my experience that Dunlops are very sensitive to rebound. You have 2 choices really... take it to a suspension tech at their shop or see the suspension tech at a track near you. It's normally cheaper at the track to get a baseline setup, but that is assuming your springs and such are close to your weight.

Problem with doing it trackside is you can't really ride it and give feedback unless you leave the track or ride the track day.

Either way, your lip on the back side of the sipe isn't too bad really. But don't try to solve that problem, start with a baseline and build on that. If you solve this now and baseline it at a later date, it will just undo all the work and you will have start over again.

Only having a preload adjustment isn't really helping you either... :\

[headshrink]

Yes, it is the CBR.

The Dunlops are on the way out... I'm trying the Michelin Pilot Road 4 next.

That's probably good advice. It also reminds me when I struggled with carb tuning.

[Motofool]

Originally Posted by headshrink

......... The trailing edges of the tread has a little lip, or is raised a little. This is more pronounced toward the edge of the tire. According to this article, it is a suspension issue...........

I humbly disagree with the article.

As far as I have learned, what your tires show is known as cupping, which has nothing to do with the suspension of your bike.

It is the result of the deformation that the rubber between two grooves suffers, about 1150 times per minute @ 80 mph, under the shear load of hard cornering, hard braking and acceleration.

Those little ripples indicate that the surface of the rubber has been stressed and heated to near its flowing point.

Please, read the "Cupping" section in this other article:
http://www.rattlebars.com/tirewear/index.html

https://www.ninjette.org/forums/show...7&postcount=53

On the other hand, pre-load only moves the middle point at which your suspension works on flat road up or down, reducing its useful range.
More pre-load lifts the back of the bike a little, making the steering more sensitive.

[Hellmutt]

#1) I am glad you are replacing the tires as I see some dry splitting of the carcass in the tire profile pic. Seems age has caught up with those tires.
#2) I concur with Chris that proper suspension setup makes a difference in helping the bike react correctly under your weight, which should translate through to the tires as well. I've had the same effect you're having happen on Dunlops in the past, but I can't say it's the tires fault since my suspension wasn't sprung/set for my weight. Get the sag/springs setup for you, get the new rubber under it, and see where you are later this season - you may be surprised.

**Looking at the pics again, I'm not sure its a dry split happening or not, may be shear tearing the tire?

[headshrink]

This stuff makes my head hurt, but one thing I can do is follow directions... mostly.

I just got back from a test ride after re-tuning the sag by taking measurements this time, not just trying another click. I was surprised I had to add an additional 2 clicks (3 total) from Honda's default setting of 3 of 9 to get my sag down to 36mm... and I'm only about 145 LBS max!

I'll need more miles to fully evaluate, but so far it feels even better.

[InvisiBill]

Do you know what spring rates are used on the bike?

Keep in mind that preload/sag affects how the suspension acts within the spring's travel. It is physically impossible for a preload adjustment to make a spring handle more weight, as that's determined by the spring's rate.

Using preload to compensate for a weak spring just compresses it closer to the bottom ahead of time. It feels less squishy because it's compressing less during use, but you're getting that because you're removing some of the initial travel ahead of time. The same weight will always compress the spring down to the same point (based on the rate) regardless of where you start due to preload. The bottom will always be the bottom, and extra preload just starts you partway down instead of at the top.

This may or may not apply to you, but I frequently see posts about people trying to compensate for a weak spring by adding preload. I just want to make sure you're not doing that.

[headshrink]

Originally Posted by InvisiBill

Do you know what spring rates are used on the bike?

Keep in mind that preload/sag affects how the suspension acts within the spring's travel. It is physically impossible for a preload adjustment to make a spring handle more weight, as that's determined by the spring's rate.

Using preload to compensate for a weak spring just compresses it closer to the bottom ahead of time. It feels less squishy because it's compressing less during use, but you're getting that because you're removing some of the initial travel ahead of time. The same weight will always compress the spring down to the same point (based on the rate) regardless of where you start due to preload. The bottom will always be the bottom, and extra preload just starts you partway down instead of at the top.

This may or may not apply to you, but I frequently see posts about people trying to compensate for a weak spring by adding preload. I just want to make sure you're not doing that.

I sort of get what your saying.... I don't know the spring weight, but most people who tune the fork on this bike put heavier springs in. The adjusters arrived, so that will be my first order of business. After achieving proper sag I'll re-evaluate from that point, but I anticipate adding heavier fork oil to reduce a bit of the pogo. This has been helpful for others on that forum. If I want to go further I anticipate addressing the springs, but I don't want to get too far ahead of myself yet.

The rear shock is not serviceable, so preload is all I can do. I'm not sure if I can even replace the spring on the rear, but if I can it might be better to get an old CBR600r rear off ebay.

[InvisiBill]

Originally Posted by headshrink

I sort of get what your saying.... I don't know the spring weight, but most people who tune the fork on this bike put heavier springs in. The adjusters arrived, so that will be my first order of business. After achieving proper sag I'll re-evaluate from that point, but I anticipate adding heavier fork oil to reduce a bit of the pogo. This has been helpful for others on that forum. If I want to go further I anticipate addressing the springs, but I don't want to get too far ahead of myself yet.

The rear shock is not serviceable, so preload is all I can do. I'm not sure if I can even replace the spring on the rear, but if I can it might be better to get an old CBR600r rear off ebay.

Keep in mind that if the springs are too far mismatched from your weight, you won't be able to get a proper sag setting. It's simply physics that if the spring can't properly support your weight, you'll never be able to make it operate in the proper range of movement by tweaking the preload.

I have no idea how good or bad a job Honda did on spring selection. Kawasaki seems to be pretty incompetent at picking spring rates on their smaller bikes. The 500's rear spring is good for about 130lb, while the fork springs are good for about 10lb. According to RT's calculator, the NewGen's rear spring is good for 220lb while the fork springs are good for 100lb. Some years of the 650 had a rear spring good for about 140lb, while the fork springs were for 300+lb.

Just be aware that it's very possible for OEM springs to be very mismatched from each other and from an average rider's weight. Depending on how far off the springs are, replacing them should be considered fixing an incorrect setup, not as a pro racer's upgrade to eek out slightly better handling. I'm not suggesting anyone throw suspension parts at a bike assuming it will automatically improve the handling, I'm just saying to make sure you use the proper parts so that the suspension actually matches the weight that it needs to support. For some people/bikes, OEM might work well. For others, it might not. Due to my weight and the 500's soft OEM fork springs, the $90 I spent on RaceTechs was the best thing I've done for it.


Likewise, simply dropping the shock/spring from "a better bike" onto your bike isn't necessarily an upgrade. Read Shock Swap Myth for a lot of details. With that being said, it is possible to find shocks from similar bikes that will be an improvement over OEM. I currently have a NewGen shock installed, and previously had an SV650 shock. As they're from similar bikes with similar low-end shocks, the main change was the spring rate, which was much better suited to my weight. In the end, that provided a ton of improvement for minimal cost, without drastically harming anything else.

[headshrink]

Since just the static sag is 37mm I'd say the springs aren't even up to the job of holding the bike's own weight without rider.

[InvisiBill]

Originally Posted by headshrink

Since just the static sag is 37mm I'd say the springs aren't even up to the job of holding the bike's own weight without rider.

It sounds backwards, but static sag is with the rider on. http://racetech.com/page/id/30 Free sag is just the bike itself.

Depending on how the preload is adjusted, 37mm of free sag isn't necessarily bad (though it's probably not good). See if you can adjust the preload to give you ~6mm of free sag. If the spring is in the right range for your weight, that should put static sag in the 25-35mm range. If the spring isn't the right rate for your weight, it'll be impossible to adjust it to get both free and static sag in the right range at the same time (which is what I was getting at in the previous post).

That leads into using preload to compensate for a too-soft spring. If you add a ton of extra preload to get your static sag in the right range, it'll cut into your free sag, which means the suspension won't be able to extend as it should for lower spots. When you change the preload to make up for using the wrong spring, the improvement comes directly at the cost of worsening performance elsewhere. If it's close, you might be able to get acceptable, but not-quite-perfect, results out of both areas. If you're way off, you'll have to screw one area up completely to get satisfactory results out of the other. Using springs of the right rate will allow you to get proper settings across the board.

http://www.ex-500.com/wiki/index.php...ension_Preload is long, but it has tons of detailed info about how suspensions work and how to properly adjust them.

[Motofool]

Originally Posted by headshrink

....... I'll need more miles to fully evaluate, but so far it feels even better.

Consider readjusting the headlight beam after you find your pre-load's sweet spot.

http://www.motorcyclistonline.com/how-to-your-aim-true

That is the main use of adjustable rear shock, to keep the bike horizontal, so the steering geometry and light beam remains as designed for a medium weight rider and for when riding two up.

Regarding rear suspension, pre-load adjustment doesn't do much, as well explained above by @InvisiBill.

[headshrink]

Originally Posted by InvisiBill

It sounds backwards, but static sag is with the rider on. http://racetech.com/page/id/30 Free sag is just the bike itself.

Depending on how the preload is adjusted, 37mm of free sag isn't necessarily bad (though it's probably not good). See if you can adjust the preload to give you ~6mm of free sag. If the spring is in the right range for your weight, that should put static sag in the 25-35mm range.

I used the terminology differently, which I took from a YouTube video. Apparently I was calling free sag static sag.

What I was saying was the FREE sag was 37mm before making any changes to the bike, when my sag with rider ~48mm (what I was calling loaded sag), this was evidence to me the springs are crap. Adding predload got the rider sag to 35mm, but free sag is now at 29mm.

[headshrink]

Ride Report: Yeah, these preload adjusters are awesome. I didn't realize just how much my front end was diving before, and just how much I was compensating for it in spirited turns (especially ones that required a lot of braking). Although it isn't perfect, it feels like it rides level now, doesn't pogo like before, or overreact to bumps and undulations, and generally just feels smoother. Now I wonder what having the proper springs would feel like