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Eccentric positioning


gig

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 I'm working on dialing in my suspension, forks raised 10mm in triples, rear is raised with Penske ride height adjustment bolt approx. 12mm. Wanted to know if there were anyone that had experience and thoughts on eccentric positioning. I have run it in the lower left corner to try and maximize ride hight and shorten wheel base.

 

Thx 

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3 hours ago, gig said:

 I'm working on dialing in my suspension, forks raised 10mm in triples, rear is raised with Penske ride height adjustment bolt approx. 12mm. Wanted to know if there were anyone that had experience and thoughts on eccentric positioning. I have run it in the lower left corner to try and maximize ride hight and shorten wheel base.

 

Thx 

 

The lower position is right. 

I did try a shorter chain to bring the rear wheel to the front but didn’t like it. 

I also have the forks custom built and raised 8mm, and the rear with a JD rear shock and raised about the same. 

I found the front wanted to tuck in slow corners. 

Now have it at right length and like it a lot more. 

Not sure what tyres you’re using, but found the steep profile of the Rosso III’s made the bike feel a lot lighter and more responsive. They also wear very evenly with no loss of feel. 7000kms from the rear and 95000kms from the front. 

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7 hours ago, VFROZ said:

 

The lower position is right. 

I did try a shorter chain to bring the rear wheel to the front but didn’t like it. 

I also have the forks custom built and raised 8mm, and the rear with a JD rear shock and raised about the same. 

I found the front wanted to tuck in slow corners. 

Now have it at right length and like it a lot more. 

Not sure what tyres you’re using, but found the steep profile of the Rosso III’s made the bike feel a lot lighter and more responsive. They also wear very evenly with no loss of feel. 7000kms from the rear and 95000kms from the front. 

 

Also running pirelli, the profile is the best.

Ive been struggling finding the perfect set up this year, but 8mm raised also was the sweet spot for me last year. The front was feeling a bit high / light mid corner and was easier dropping the front then raising the rear. Would there be any difference other then losing ground clearance by changing the geometry by lowering front vs raising the rear?    

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10 hours ago, gig said:

 

 

Also running pirelli, the profile is the best.

Ive been struggling finding the perfect set up this year, but 8mm raised also was the sweet spot for me last year. The front was feeling a bit high / light mid corner and was easier dropping the front then raising the rear. Would there be any difference other then losing ground clearance by changing the geometry by lowering front vs raising the rear?    

 

If you have the correct springs it won't make much difference to ground clearence.

I did find raising the rear was very good for front end feel.

As stated, my front is 8mm lower than stock, and rear is about 15mm higher.

I wasn't really happy with my set up until I got both ends moving the same (damping).

I originally had too much front end rebound damping, so the front was coming up too slow compared to the back lifting out of corners.

I took me a couple of years to get it right.

I'm now happy with it considering the limitations of the conventional 41mm forks and CBR929 rear shock.

If I had my time again I would have gone for the F4I forks and a quality rear shock with slightly softer springs.

I weigh 74kg and have 0.95kg/mm front springs and 21kg/mm rear.

 

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I'm limited on how much i can raise my rear due to the Two Bros header is directly under the dogbone. I thought it was raised to the maximum adjustment of Penske shock, but Im only able get 5mm at the shock. I weigh 74kg also. 90 front spring rate with adjustable inserts made by DMr, and had the shock serviced valving adjusted slightly last spring. Everything should be set up the same, sag, ride height, etc. but after winter mods the front feels high, not planted as before.       

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5mm at the shock will be about 15mm at the rear.

Just make sure your oil height is not set too high on the front.

I like a bit of dive on my front to load the front wheel but not too much that it bottoms too easy under brakes on bumps.

0.9kg should be spot on.

I'm using 18Cst @40°C oil.

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i was going to double check the oil height tomorrow. i raised it by 10mm, i think stock height is 130mm, and i set it at 120mm, which is where i though it was before but that could be different. I don't trail brake, but to see if that helped the high front feeling was experiencing, it did give me more of the planted feel i was looking for, like it could use a bit more dive, but thought that would be more related to compression. The lower oil level will give me more of that feel?

Im using motul 5wt fork oil, 19.5 viscosity

 

Thank You, for taking the time to work through this with me

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120mm should be fine. 

I did try 10mm higher than stock, but I went back to stock. 

Dive is controlled by the slow speed compression bleed, which is adjustable on the F4i forks, and oil height. 

Think of oil height as a secondary spring, the less air you have, the more it affects fork dive and bottoming out resistance as it builds pressure quicker during fork compression. 

To complicate things, slow speed compression adjustment affects both slow and high speed compression.  

Also if your compression damping is too hard, the forks will pack up and not dive enough. 

I tried JD's damping set up recommendation on the rear shock he sent me, but found it way too stiff for my liking. 

Everyones riding style is different, and personal preference has a major affect on your confidence. 

Dont be afraid to try different settings. 

If you haven't tried it already, you can back off the compression damping on the front first to see how you like it. 

It is always better and safer to have slightly not enough damping than too much. Both at the front or rear. 

Happy to help, but don't forget they are just my preferences, others might not agree with me. 

 

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I am involved as a technician with an MV Agusta F3 that we race in Supersport in both New Zealand and in the MotoAmerica rounds last year.

I mention this as the MV also has an eccentric and we use a ride height gauge and adjust the shock length to make the ride height a standard measurement when changing gearing.

 

I made a ride height gauge for my VFR and also adjust the shock length when adjusting the chain etc.

 

The effect of changing the eccentric is quite dramatic on the geometry especially if you are working in either the front or rear sectors where the height change is quite great compared to when it is in the centre position.

 

Well worthwhile measuring and trying to maintain the same ride height when dialing in your suspension.

 

Here is a photo of the gauge I made up in position. You measure from the axle to a known point on the gauge.

 

Cheers

Phil

Ride_Height_Tool.jpg

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I did mot measure it, but the 848 eccentric looks to be more centered, moving it more forward slightly toward a 8 o'clock position from VFR 7 o'clock, with the same chain length. Im running 17/45, i may try 16/43 to pull it back to a 6 'o'clock position    

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I was able to raise the rear a couple more mm = 7mm ride hight, felt better. So went back to 8mm in front since that is where it felt best before. Not thinking about it while ridding so its much better. I'll try the 6 oclock position and see how that feels.

 

VFROZ seems we have similar set up, do you know where is your Sag is set? My rider Sag set at 28 rear 34 front.  

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1 hour ago, gig said:

I was able to raise the rear a couple more mm = 7mm ride hight, felt better. So went back to 8mm in front since that is where it felt best before. Not thinking about it while ridding so its much better. I'll try the 6 oclock position and see how that feels.

 

VFROZ seems we have similar set up, do you know where is your Sag is set? My rider Sag set at 28 rear 34 front.  

 

I go for 38mm front and 30mm rear, so not much different, but the front is hard to get accurate.

 

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I've aimed for 29mm free sag and 37mm ride height on the front.

And 6mm free sag and 30mm ride height on the back.

 

The main point I was trying to make is about the ride height induced by the rise and fall of the eccentric.  this has really nothing to do with the dialed suspension ride height.

It is all to do with the geometry of the overall bike.

 

The rise and fall on the eccentric is in the order of 15mm and this is a large change in the geometry.

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This was one reason HRC apparently went with a conventional swing arm on their WSB RC45s towards the end of their reign.  SSSAs allowed for fast wheel changes in endurance racing, but other manufacturers eventually found ways to make quick wheel changes using regular swing arms, too, so that advantage was negated--leaving mainly the disadvantages (e.g., weight, difficulty in making changes--and the geometry changing all the time).

 

Still looks sweet, though!

 

Ciao,

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Yeah, you won't see SSSA in motoGP.

But for road bikes, it's the bees knees.

It was the biggest problem I found when trying to cheat and shorten my wheel base.

It only feels right when the eccentric is in the middle lower position.

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