New Suspension Internals Front And Rear

[ozfireblade]

Hi All,

 

I haven't been on for a while, so I hope everyone's doing ok...

 

To the question......

 

I just had all the internals replaced to Ohlin's on forks and shock revalved, new springs, shock spring etc... SAG was set in shop, on a cold bike mind you.

 

I did a track day on Friday and I hate it no matter what I did the bike feels like . If I set the oem settings they will be out because the springs are both stiffer, front Ohlin's 4744-10 and rear spring 1115N. There wasn't any suspension guys there just a few people that tried to help. Anyway after 2 sessions, in pouring rain, the back end came around on me and I took a closer inspection of the track surface. I was riding at about 60%. I repaired the broken bits and went out again when it dried up, after returning the settings to the ones the suspension guy applied thinking it was just the wet and poor throttle control, but no the bike still felt horrible and left me with no confidence.

 

Has anyone had a similar (not crashing though) experience after new suspension?

 

Thanks in advance

 

Dylan

[khp]

Dylan,

 

I'm sorry to hear about your crash. I have some experience with Ohlins parts, all of them very good (both the parts and the experience). replaced the front springs with Ohlins in 3 bikes, and added Ohlins rear shocks on two. My trackbike had Ohlins parts in both ends when I bought it, so I can't claim fame to that part.

 

First of all, can you be more specific about "the bike still felt horrible". What was feeling horrible? straightaways, over bumps, entry/mid/exit of corner, etc ?

 

Secondly, a -10 spring sounds very stiff to me. What oil level are you using, and have you taken a look at the oil-level/effective spring rate diagram that comes with the Fork internals manual?

 

The front suspension on my streetbike (R1 '03) is really stiff, and has been since I had my mechanic change the spring (the spring is so heavily preloaded that I couldn't fix it myself), and I suspect that there is way too much oil in the fork (a thing to be checked when I get it out on the street again).

On my R6 '08, I've played around with the oil level to generate the "right" amount of maximum fork travel. This was fairly easy. Do you know how much travel you used (out of max what)?

 

In general, you should have a softer suspension setup for rain than for dry (because you want similar travel, but will use less harsh input). Can you explain how/why the rear came around? - my initial guess would be that you don't have too much rebound damping, so the rear tire looses traction.

[ozfireblade]

Hi khp, No too fussed on the crash bit sore a few says later but nothing broken:) footpeg snapped at the bolt so new bolt, some filing of the footpeg, tape for the fairings and back on track

 

The main issues that I'm having is mid corner and exit the front feels like its walking away even when applying throttle control. Like you said I think too stiff on the front, the spring is about right as I'm 87kg and with gear about 95kg. I have 85 mm of oil in the forks. So if I did the stock settings I should go softer by a click or 2? to take in account the harder spring?

 

The rear came around because I thought the line had dried out and decided to use my dry line, getting on the gas to hard tried to back off the throttle slightly to keep it spinning and controlled, thought I had control then the rear came around and the sliding began. My fault nothing to do with the bike

[khp]

The main issues that I'm having is mid corner and exit the front feels like its walking away even when applying throttle control. Like you said I think too stiff on the front, the spring is about right as I'm 87kg and with gear about 95kg. I have 85 mm of oil in the forks. So if I did the stock settings I should go softer by a click or 2? to take in account the harder spring?

 

The rear came around because I thought the line had dried out and decided to use my dry line, getting on the gas to hard tried to back off the throttle slightly to keep it spinning and controlled, thought I had control then the rear came around and the sliding began. My fault nothing to do with the bike

Changing the compression & rebound settings is not a good way to compensate for a spring issue (and we're not sure that this is a spring issue to start with). Mentally, you need to divide the suspension into two parts: travel damping (comp & rebound) and sag & maximum travel.

The oil thickness (viscosity or sometimes called heaviness) can be a bit confusing, because affects both travel damping (by the oil thickness) and the travel (by the oil amount, which yields the effective spring rate).

 

Apologies up front if you are well versed in how a suspension works, but it appears to me that you are mixing the suspension parts.

 

Ideally, you want the spring+preload to determine the sag (it does), and together with the oil level, determine the maximum travel (all weight on the front wheel, hitting a bump in the road at the same time, etc). If we could statically balance the bike so parts of the weight is transferred to the front, the spring + oil level would determine the travel here too.

 

Ideally, you would want the compression & rebound adjusters to handle all the dynamic effects (movement in time).

 

But because the spring is always trying to return the fork to the statically equilibrium position, the (effective) spring rate also impact the dynamics of the suspension.

 

OK, back to spring rate: I don't know what the "standard" spring rate is for your bike (a CBR 1000 RR, I presume - which year?), but for my R6 '08, a spring rate of 0.90-0.95kg/cm is common. I'm same weight as you and on my R6, I have 0.95 springs I believe (I don't have my notebook here). Have you put zipties around the fork legs to gauge the amount of travel that you are using? If you haven't, put a zip around a leg and go doing some stoppies in dry conditions to measure the travel. You should be using most of the travel (but not hit the hard stop). If you do use almost the full stroke, then I would start looking at softening the compression setting*.

 

Just to confirm my understand of what you say, but when you say that "feels like its walking away" at mid-corner and exit, you feel that the front is going towards the outside of the corner, making the bike understeer?

 

My immediate thought is that when you are unloading the front (because you are applying throttle), the tyre is not pushed into the track enough, causing it to "wander". A remedy could try to reducing the rebound damping, so the fork can be extended quicker.

 

I grabbed my copy of "Sportbike Suspension Tuning" by Andrew Trevitt, and in the troubleshooting section it says:

EXITING A CORNER

Symptom:

Bike running wide or is unstable over bumps.

Likely cause:

Excessive squat is causing the front tire to lose traction.

Possibly remedy:

Reduce squat by adding rear low-speed compression damping, adding rear preload, adding rear ride height, raising the front fork tubes in the triple clamps, adding front rebound damping, or raising the swingarm pivot.

 

If you have other observations about the suspension, please put them up, because there are plenty of suggestions divided into entry/mid/exit-corner, straights, and braking.

 

*) Mind you, just to make things complicated, the general recommendation is to have more damping with a harder spring and faster riding.

 

Edit: Feel free to PM me.

 

Kai

[ktk_ace]

SAG pictures with zipties on the front forks will tell ALOT imho.

 

I do recommend a readup (link below) for getting to know the basics of your top shelf suspension imho~

or better, go to a school/workshop

http://www.gostar-racing.com/information/motorcycle_suspension_set-up.htm

[ozfireblade]

Thanks for the advice, I'm not too bad with the concepts of suspension tuning I guess its putting it into practice at the track and not trying to "get my monies worth and pull in during a session and make adjustments. A hot day would probably been good to really gauge where the current setup is at. I have the zip ties on and they're not using all the travel. I really need to get some heat into the oil first before I try and set it up so I'm going to have to wait till I'm at the track next and get the local suspension guru to help as well.

 

Thanks

[khp]

You're welcome. That you're not using travel is a major indicator to me at least, that the effective spring rate is to high.

 

Until your next track day, see if you can open up the forks and measure the oil level. It's the free-air level above the oil that's important.

Also, if you already don't have it, consider to get a funnel, some ml-based measuring glasses, and a thing to suck up the oil from the forks so you can adjust them on the spot.

Was there travel vs Force & oil-level diagram in your fork manual? It might be useful to study it to get an impression of the right oil level.

 

Kai

[ozfireblade]

You're welcome. That you're not using travel is a major indicator to me at least, that the effective spring rate is to high.

 

Until your next track day, see if you can open up the forks and measure the oil level. It's the free-air level above the oil that's important.

Also, if you already don't have it, consider to get a funnel, some ml-based measuring glasses, and a thing to suck up the oil from the forks so you can adjust them on the spot.

Was there travel vs Force & oil-level diagram in your fork manual? It might be useful to study it to get an impression of the right oil level.

 

Kai

The fork levels should be fine as everything was installed by a Ohlins approved technician, I think its mainly a combination of me, the settings being too hard and cold oil. Just keen to get the bike back out again.