Since the first day I've been riding my 749R, the bike has had major oscillation issues. I've adjusted, changed shocks and spring rate, no matter what I do, it either is a problem or REALLY bad = unridable. Also, I have major front end instability under power. Almost to the point of tank-slappers.
My configuration is;
- Dunlop 106/108 16.5"
- Rear wheel all the way back
- 30mm offset
- Stock spring rate in the shock, .95 rate in the forks
- Front ride height; fork tubes in-line with triple
- Rear right height; 250mm
- I weigh 160 with gear
What I'm looking for is perhaps somebody who has raced 749R's to give me there successful configuration, one thats been tested using the same config I've got (hopefully).
IMO, pointless doing anything until you've put the bike on a frame alignment jig.
If your front and rear contact patches are not in line and the wheel centre lines, in the horizontal and vertical axis, are not parallel then all kinds of instability problems will result.
IMO, pointless doing anything until you've put the bike on a frame alignment jig.
If your front and rear contact patches are not in line and the wheel centre lines, in the horizontal and vertical axis, are not parallel then all kinds of instability problems will result.
Ohh, I forgot to mention... the bike is fine on smooth tracks, its only rough ones where the problems occur.
Ohh, I forgot to mention... the bike is fine on smooth tracks, its only rough ones where the problems occur.
Not trying to sound flippant, but so what?
Why do you think the very first thing that top teams racing production machines do is stick them on a motoliner jig (that's a brand over here..guess you have acculign over there?) to check the alignment and then press them back into shape if needed..
Production frames, even ducati steel trellis frames, are not made to be that tight on production tolerances and what is fine for a road bike may cause problems on a track.
Until you know that all of the centre lines, pivot points, wheel contact points, relative angles and suspension travel paths are in line and true you might as well stop fiddling with the suspension and just burn a stack of $10 bills, because you will achieve exactly the same result.... a bike that still has handling problems and an empty wallet.
Just jumped off the phone with a friend of mine who received a bigger batch of KR slicks from Germanyīs IDM series (like CIV in Italy or BSB in the UK).
And he was complaining about the front end issues as well with the Dunlops. He spoke to his suspension tech and got told that itīs coming from the rear most likely.
Advice was: lower the forks and move the wheel all the way back and see what it does.
I know itīs a sucky advice, but maybe it helps - food for thought.
Did you try a Pirelli or Michelin rear to make sure itīs not the tyres?
Just jumped off the phone with a friend of mine who received a bigger batch of KR slicks from Germanyīs IDM series (like CIV in Italy or BSB in the UK).
And he was complaining about the front end issues as well with the Dunlops. He spoke to his suspension tech and got told that itīs coming from the rear most likely.
Advice was: lower the forks and move the wheel all the way back and see what it does.
I know itīs a sucky advice, but maybe it helps - food for thought.
Did you try a Pirelli or Michelin rear to make sure itīs not the tyres?
There ya go, thats good advice.
The catch with the 749R, 16.5" wheels and 30mm offset (all the way back) is that the front tire hits the fairing when you turn. The bike has been working very well in the past at the 36mm offset and I was about to leave it there because it works, the wheel doesn't hit, there is no front wobble etc... The only catch is, the bike does handle differently at extreme high speeds.
In terms of tires... If Dunlop went out of business tomorrow, I'd stop racing at the current series I race. Its not like I dislike Pirelli's, but for the track I race at, which is the fastest track in the west, you've gotta have tires that work for extended periods. Plus, I'm sponsored by Dunlop and Pirelli's deal was almost 2x the money.
I know MANY people from who've made this exact configuration work flawlessly. So its not like what I'm doing hasn't been done before. The previous owner of the bike, left the offset in 36mm mode, perhaps thats the golden goose? Lower the front a whole bunch and do the stink-bug approach.
NONE of this solves my rear end bumpy issues and rear tire wear. Those two things have been causing me to slow down. I actually went slower this past race weekend because the bike was so bumpy, then the month previous with identical setup, but the temperatures were through the roof. Obviously the suspension is very susceptible to major heat fluctuations.
So if we put the geometry, front head shaking aside for a moment because there is a definite fix for that, what about the rear?
Why do you think the very first thing that top teams racing production machines do is stick them on a motoliner jig (that's a brand over here..guess you have acculign over there?) to check the alignment and then press them back into shape if needed..
Because everybody else I know who rides Ducati's has had the same issues at this track. The solution (listed above) is to lower the front, fixes it almost instantaneously. Only catch is, 36mm offset is the best you can achieve with lowering the front because the tire hits the fairing/head and that means, your cornering abilities at high speed (150mph) are limited.
If the front is becomming unstable with 30mm offset and you are sure the frame/wheel alignment is good, it sounds like you may be squating on corner exits( did you raise the front when you went to 30mm offset? That would add weight to the rear on acceleration). This would cause weight to transfer to the rear lightening the front and causing a front instability over bumps. With the 30mm offset you should be able to lower the front and raise the rear with no problems, if you have contact at the front just raise the rear. The 30mm offset restores the trail and raising the rear would be good. I race a 1098 not a 749, but I had some major tire wear issues with the stock spring. The 1098 has a progressive rate spring, and I am thinking your 749 may also, not sure though, but the shock was unable to control the tire with that spring. Try some preload on the rear spring to help with the squat.Try it ,then you may need to add some compression and rebound to better control the rear wheel under acceleration. Just a couple of thoughts.
If the front is becomming unstable with 30mm offset and you are sure the frame/wheel alignment is good, it sounds like you may be squating on corner exits( did you raise the front when you went to 30mm offset?
Yea, the common thing to do is raise the front so the fork tubes are flush with the triple tree. I'm in 100% disagreement with that, but if you don't do that, the front wheel is too close to the fairing and it hits when riding around the paddock. Perhaps the Ducati Corse fairings have more space in that area where the sharkskinz don't?
Quote:
Originally Posted by duckracer
That would add weight to the rear on acceleration). This would cause weight to transfer to the rear lightening the front and causing a front instability over bumps. With the 30mm offset you should be able to lower the front and raise the rear with no problems, if you have contact at the front just raise the rear.
I've also not lowered the front a lot yet, perhaps there is a spot where the front tire won't hit the fairing when turning and I've not found it yet.. My rear ride height is between 250-260mm, which is quite a lot. I've experimented with greater ride height, but haven't come to any decent conclusions yet. Mainly because I can't seem to find anybody who's tuned these bikes to the level I'm attempting to do it. Most people ride these things stock and as I've said numerous times, on smooth tracks, the bike is flawless!
Quote:
Originally Posted by duckracer
The 30mm offset restores the trail and raising the rear would be good. I race a 1098 not a 749, but I had some major tire wear issues with the stock spring. The 1098 has a progressive rate spring, and I am thinking your 749 may also, not sure though, but the shock was unable to control the tire with that spring. Try some preload on the rear spring to help with the squat.Try it ,then you may need to add some compression and rebound to better control the rear wheel under acceleration. Just a couple of thoughts.
The 749R has a linear valve/spring setup. Its quite unusual, the shock travel is substantially less then an average shock's travel. I went out and bought an Ohlins DU301 shock from a buddy of mine because I thought the bike needed more travel in the rear. It felt better, much smoother over the bumps, but the side effect was a new wobble introduced from the rear, which was uncontrollable. Even after changing out the spring with the stock spring from my 749R, the new shock had too much travel which led to too much squatting. So I ended up selling the shock and putting that money into a lighter fuel tank.
I'll be honest, I've not messed around with the compression/rebound too much. I found a happy medium and stuck with it, but I will spend more time with it in a few weekends.
Quote:
Originally Posted by trussdude
I thought Tye knew everything.
The problem is, I stepped into a can of worms and they're crawling all over me. I had my 748 setup perfectly, but it was too slow. So I bought a bike I didn't know with suspension thats super unusual (not on any other production Ducati) and have been trying to figure out how to make it better ever since.
Everybody says the 749R rear suspension is the best production rear end they've ever made. So if thats the case, the issues I'm encountering, shouldn't be here at all.
I do know a great deal about geometry and suspension, but with the 749R there seems to be these set guidelines and going outside of those, seems to be almost impossible. These issues I'm having arn't easily fixed by dropping the front (wheel hits fairing) or decreasing rebound/compression in the back (shock is still too stiff) so there is something else going on...
Well sounds like you have been doing the ussual test/adjust/test. So I wonder if the shock just needs to be revalved for your style. The 1098/848 bikes threw a curve ball at all of us. The made the Chassis geometry in such a way that the conventional drop of the front rais the rear does not work. But if you change the fork offset to 30mm you can go back to the old way and it will work, you may be running into something like this. I still think it is in the front end set up and you are just loading the rear so much that the spring and shock cant handle the load. Give Jason at Department of Susspension a call he was really good with the 916 and 999 series bikes.
Why dont u just cut the fairing? Form follows function.
It surely is really hard to guess your problem thru the web. But then I think duckracers thoughts sound good. What spring rate is your stock spring? My R went well with a 90nm with me weighing 95 with all gear on. Mine had stock offset though.
Well sounds like you have been doing the ussual test/adjust/test. So I wonder if the shock just needs to be revalved for your style. The 1098/848 bikes threw a curve ball at all of us. The made the Chassis geometry in such a way that the conventional drop of the front rais the rear does not work. But if you change the fork offset to 30mm you can go back to the old way and it will work, you may be running into something like this. I still think it is in the front end set up and you are just loading the rear so much that the spring and shock cant handle the load. Give Jason at Department of Susspension a call he was really good with the 916 and 999 series bikes.
The 1098/848 are really weird bikes though in stock form. The 749R isn't quite that odd, though I am dealing with Dunlops and 16.5" wheels, so those two things are strange in of themselves. I have an 848 as well and have been so reluctant to spend a dime on it because of all the horror stories about setting them up properly for the track.
I'm in Vegas for the NAB convention right now, so later tonight I'll get a better response together...
Just jumped off the phone with a friend of mine who received a bigger batch of KR slicks from Germanyīs IDM series (like CIV in Italy or BSB in the UK).
I don't want to sound like a nitpicker and I know it's off topic but BSB is a very different animal compared to IDM, Ben
Need some suspension help
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