S1000RR Rear Suspension

[Gryfon]

Hello,

I have an ex-CSS '15 S1000RR that I ride exclusive on track (Mid-Ohio, Grattan, GingerMan).  I was using Dunlop Q3s without issues, but recently decided to try out slicks (Pirelli, then Michelin).  I keep getting excessive wear on the right side of rear slicks.  I've received a number of tips from the tire reps at the track and riding coaches:

- it's my riding style, I need to pick up the bike more before accelerating hard.

- it's a hot tear, I'm running 2 psi too low (went from 24 psi hot to 26 psi hot on the Michelin.

- it's the rear suspension, it's too stiff and you might have your eccentrics (top of rear shock mount and swingarm) set wrong.

I did try to change my riding style and played with the pressure, and the tires did last a bit longer (up from 2 days to ~3.5).

The last point was the one that was intriguing to me - I've never looked at the eccentrics or thought about them.  Since I bought the bike used (and had the rear swingarm removed by a mechanic when I had a full exhaust put on), I don't know if they are set 'stock' or something else.

Can someone tell from the pictures whether I have stock settings?  Does anyone have experience with how the bike handling will change if set these eccentrics different?

[Hotfoot]

I asked our chief mechanic at the school, here is his response:

>>

The eccentrics are in the stock position. There is no "wrong setting".

Tearing like that comes from wheel spin. Depending on what mode he runs in or what his traction control is set to will vary the wear. Mid Ohio for sure has some straights coming off right handers and a kink so there's gonna be some serious drive in those spots. The position of the wear would indicate getting on the gas late and hard.

>>

[Hotfoot]

I'm not a tire or suspension expert by any stretch, but here are my thoughts:

1) Since it only is happening on one side (and you are riding multiple tracks) that would imply an issue with riding style - unless the tracks are all very right-handed - less likely that a suspension or setup problem would only affect one side. A rider that drives much harder while leaned over farther on right handers might experience different tire wear on that side, though, does your lean angle or body position look significantly different from one side to the other in photos?

2) I'm not a suspension expert but this does look like tearing, is this is multi-compound tire, and is the compound on that part of the tire super soft? Personally I have only seen that kind of wear when the tire was too soft for the for the track surface and/or if temps were out of range (hot tear or cold tear). You might try asking a tire vendor what compound they use on the tracks you run - especially since you didn't have the issue with the Q3s, could be the tire is just not appropriate for the surface, or that it has a super-soft compound at the outside edges and THAT is too soft for the surface.

3) The width of the worn area looks even to me, doesn't show the wave or wider/thinner areas that you might expect to see if suspension was the issue.

Do you run warmers? How much does the tire pressure change from coming fresh off the warmers to coming off the track after riding? What sort of outside temps were you riding in, and do you have to sit for long between coming off the warmers to riding at speed on the track?

Dave Moss's various websites and videos are a great source of info, here is one that might be helpful:

 

[Gryfon]

Thanks for the responses!

I would say the majority of the hard acceleration corners at MO and Grattan (Clockwise) are right handers.  I attached a data logger plot of MO - the highest spin at high throttle are the keyhole exit (turn 10 in the plot) and the thunder valley entrance (turn 4 in the plot).  I was surprised to see that the logger shows spin through the back straight kink, and this is also on the right side of the tire.

I haven't noticed a different body position from one side to the other, however, I do think I feel more confident with right turns - a lot more knee puck wear on that side!

I am using the Michelin Power Slick Evo.  The Michelin reps at the track have some buzzwords about it (Two Compound Technology (2CT) and Adaptive Technology (ACT)), the gist of which seems to be that there is only one compound and it's supposed to adapt to conditions.  I did try a Pirelli Diablo SC2, which I think is their harder compound, and I had a similar wear problem - tearing on the right side.

I do use warmers, and I set the tire pressure coming off the warmers; I haven't looked at what the pressure is coming off the track.  The outside temp has varied from low 70's to mid 80's.  At most, there is a 5 minute wait before coming off the warmers and heading out to the track, and I put the warmers back on within 5 minutes of getting off the track.

The Michelin rep told me to run 24psi hot off the warmers, so that is what I've been running.  When I asked a riding coach about the tearing at MO, he suggested I run 2 more psi, so I tried running 26psi - this seemed to help a bit.  He also suggested I flip the tire when I saw signs of tearing, so I also did that.  I did read the forum article here about tearing, but that was afterwards (:>).

[Dylan Code]

The slip % should be between 5% and 15%, which it is, and the traction control will keep it in that range. It looks like you are getting a lot of slip % at steep lean, which would suggest that your entry speeds are a little low for your liking and are being compensated for with somewhat aggressive throttle while leaned over far mid turn. I have no clue about Michelins, but would follow the suggestions of the local distributor for that tire.

[Hotfoot]

Ok first of all this is TOTALLY awesome that you have this data to post! The datalogger is fantastic, and I'm glad to see you using it, what a great application. That second chart is terrific, lots of information there.

At first glance at the second chart things look pretty even from one side to the other, your lean angle is not drastically different on rights versus lefts,  but on closer examination the throttle position versus lean angle does look somewhat different - that top red line showing around 75% throttle at 40+% lean angle and some of the yellow and orange at 45-50% are more apparent on rights than lefts, and the slip rate seems, in general, a little higher on the rights but not much (looks like more data points in the >10% range?)... and maybe the characteristics of the corners on that track are what is causing those differences. 

I think I see the problem - the Michelins are not "adapting" sufficiently to your situation.

Do you know if the tire damage is more within the first few laps or sessions or at the beginning of the day versus later? That might help determine if it is cold or hot tear, it sort of looks like hot tear to me (the tears look wider and shallower than I'd expect to see for cold tear) but for sure I am not an expert. But the fact that a 2 psi pressure increase seemed to improve the situation would support that as well - if you have a chance next time to check tire temperature and pressure before and after riding  (straight off warmers versus coming off the track) that should help tell you whether it is hot or cold tear, that article above has some specifics of what temp/pressure rise to look for, and/or the tire rep should be able to tell you what is optimum operating temperature/pressure for that tire, to compare to what you are actually getting.

If it were me I'd check the alignment on that rear wheel - not sure whether that would or could have anything to do with this type of uneven tire wear but it's a really easy thing to check, and a good idea to do anyway. Then, if the tire pressure and compound seem correct for the track (per the tire rep),  I'd next try softening the rear suspension and see if that helps, since that could contribute to hot tearing by making the tire work too hard because the suspension is not compliant enough. Also check the spring rate recommended for your weight and see if you are within range, if the rear spring is way too stiff for your weight that could be contributing to the problem.

Since you have good photos AND access to the wealth of information from your datalogger, you could try reaching out to Dave Moss to see what he thinks on the suspension side, I think he does analysis like that and it would probably be refreshing to him to have all that data available to work with. Dataloggers are such an amazing tool!!

 

[Gryfon]

Dylan brought up exactly the point one of the riding coaches at Grattan pointed out to me.  My entry speeds are too low, so I'm grabbing a handful of throttle to make up for it.

This is what I would like to work on at my next CSS visit (CODE Race in October)...

The plot below is also MO, but from my DAIR suit instead of the BMW logger.  It let me overlay my S1000RR lap (blue) with my other bike (red-Daytona 675R, running Dunlop Q3s). Sorry, the turn numbers are different from the BMW log.

I learned all the tracks on my Daytona, and I know I need to adjust my braking points and entry speeds for getting more out of the S1000RR and slicks, but you can see in the overlay that I'm basically riding the two bikes the same, just accelerating and braking harder on the straights with the S1000RR.  I'm actually faster through the chicane and keyhole (turns 10 and 11) with the Daytona, and this seems like a mental issue I need to sort out, as the S1000RR should be able to the do the same thing!

[AdamZisa]

Very cool and insightful read!!!! Got dang I need to get me one of them data loggers. This is really helpful for high analysis. Thank you for this post. 

[Hotfoot]

The data loggers are absolutely incredible in what they do, and small and easy to mount. If you really are interested in one, contact the school office at 800-530-3350.

Slicks are really expensive and tires are one of the biggest expenses involved in track riding. If the data logger helps you find the problem with your tire wear (or gives you the info you need to take to your suspension guy or tire guy), it will pay for itself very quickly. The additional riding info that you get that will improve your laptimes will just be a bonus!  

Edit - BTW if you have a friend that has one, too, you can download your data and compare, creating a "virtual race" type thing where you can overlay your laps and see the differences - where you or your friend is getting on the gas earlier, carrying more speed, braking later, etc., and you can use your combined positive points to improve each other's laptimes. Or just bench race. Anyway it is really great and I highly recommend it!