Front end "chirp" | Page 2 | GTAMotorcycle.com

Front end "chirp"

suz1k3 said:
$1500 and no compression adjustment :(
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Yeah. At the time there was no other option other than going to new forks altogether. A set of Ohlins as on the Paul Smart would have been $3k back then, and they weren't exactly top shelf either. I think Traxxion has a kit for these forks now that has rebound on one leg and compression on the other (actually, that is how the OEM cartridges are valved too, though not adjustable). GP suspension also now makes a kit set up with compression on one side and rebound on the other.

Personally I doubt that the lack of compression adjustment is really the limiting factor at this point. Much faster guys than me have raced on these cartridges and done fine. I'm sure there is a setup solution, and I will find it.
 
Okay, more progress on this.

First, Gareth's advice to take all of the damping out prior to measuring sag was wonderful. With a high rebound setting, the apparent stiction in the forks (difference between the "stuck up" and "stuck down" numbers when measuring bike sag) was 14 mm. With the rebound wound all the way out, that number dropped to 5 mm! I had no idea. I just checked Trevitt's book and he doesn't mention this. When I spoke to Traxxion about my fork stiction they didn't mention it. The Dave Moss suspension videos I have watched did not mention it either...so very unique and valuable advice! I will make all my future sag measurements with damping set to minimum. Thanks Gareth!

Second, I removed a fork leg, took it apart and made a pile of measurements. As best I can tell, travel is not limited internally - I should have all 130 mm available that shows on the legs...so that means I have not been bottoming the forks after all. However, using all my weight on one assembled fork I can not get it to compress more than 100 mm. Not very scientific I know, but I wonder if the oil height / air gap might be limiting *effective* travel to something less than the mechanical limit. Not sure what to do with this idea.

Other measurements: free sag front 12 mm. Total sag front (rider in gear) = 29 mm. (Both sag measurements are "stuck up" because I was working alone and had to use a zip tie.) Rider weight in gear = 218 lb. Bike weight front = 192 lbs. Bike weight rear = 208 lbs.

So, I plan to give these numbers to Traxxion and ask what spring rate they would recommend for track riding, to see how it differs from the 0.925 I have currently. Other suggestions?
 
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Just got off the phone with Traxxion. They agree that I am not packing the forks given what the zip tie reads, and suggested that I could be confusing rear tire hop under braking with front end chatter. They think that changing the geometry is my best bet, and suggested dropping the forks 5 mm, and going back down to a more normal front tire pressure - i.e., exactly what Gareth suggested, and they also agreed that dropping the forks was a much better approach than reducing the rear ride height, for the reasons Gareth mentioned.

Also found out that if I send my cartridges to them they can now add compression damping adjustment for $75, so I think that is on the list for this winter - one more setup adjustment to play with, so then I can truly disappear up my own rear end in a state of confusion next season. I'll probably also up the spring rate a bit at that point since I'll be paying for shipping anyway, but as for now I am just going to change the oil and try the geometry change. Looks like I will be at TMP Thanksgiving weekend, so we'll see how all this works out.

Thanks again for the input.
 
YellowDuck said:
Just got off the phone with Traxxion. They agree that I am not packing the forks given what the zip tie reads, and suggested that I could be confusing rear tire hop under braking with front end chatter. They think that changing the geometry is my best bet, and suggested dropping the forks 5 mm, and going back down to a more normal front tire pressure - i.e., exactly what Gareth suggested, and they also agreed that dropping the forks was a much better approach than reducing the rear ride height, for the reasons Gareth mentioned.<br>
<br>
Also found out that if I send my cartridges to them they can now add compression damping adjustment for $75, so I think that is on the list for this winter - one more setup adjustment to play with, so then I can truly disappear up my own rear end in a state of confusion next season. I'll probably also up the spring rate a bit at that point since I'll be paying for shipping anyway, but as for now I am just going to change the oil and try the geometry change. Looks like I will be at TMP Thanksgiving weekend, so we'll see how all this works out.<br><br>
<br>
Thanks again for the input.
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Glad my 3 days with Max Macallister was of some help to you.Max is a great teacher of suspension and also a great jazz aficionado!!!

As usual I think you are answering your own question when you say that the oil capacity/ air gap maybe hindering your travel.
The addition of a compression adjustment will help show you this! Again the valves will have to be fully open too when you do a length of travel measurement as the length of internal components should compress fully and allow unrestricted transfer of the oil into the air gap.....Setting of compression and rebound comes afterwards. I watched Traxxion's lead tech do this on every fork leg that he serviced. Soon we will be able to wok on that rear ride height, etc and get the bike handling better than the Carl Fogerty Ducati and more like Ken McAdams. lol

Regards Gareth
http://www.trackdayhub.com
 
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PROBLEM SOLVED!!!

Thought I would report back. Made all of the changes described ad naseum above (changed fork oil, lowered oil height, dropped forks in the triples 4 mm, took some preload out).

Track day yesterday at TMP. Still had the "chatter" under hard braking going into 1. BLAST IT ALL TO HELL....

So, all those changes, front end acting exactly the same....unless it's not the front end....

Decided to entertain the idea that Dan from Traxxion posed - maybe I just *think* it is front end chatter, when in fact it is the rear hopping about. So I FORCED myself to keep my foot completely off the rear brake (hard to do because in both street and track riding I have always applied light pressure to the rear brake approaching corners).

No rear brake, no chatter. Problem solved. 100% totally and completely solved. It wasn't the suspension, it was rider error.

Spent the rest of the day with total confidence in the bike under braking, and dropped 2 seconds. :) One happy duck.
 
I was watching some of the fast bikes at the end of the straight yesterday. They were running 5 or 6 feet in from the outside of the track. I had noticed the I line was taking was very bumpy in the braking zone, felt like the back wheel was hopping (no rear brake), moving to the right helped out quite a bit.
I don't think it helped 2 seconds worth for me, but I won't know till I crack into the "under one egg timer" group.
I suspect it's a tough job to get the suspension right when it could be other factors; rider, bumpy track ...
 
The reason it added up to 2 seconds for me was because I had no confidence on the brakes going into either 1 or 2, and so had to just kinda halfway coast into both corners. The bouncing was a really violent thing...like, don't even *think* of turning the bike in until it stops.

Once the problem was solved I could concentrate on other things, like entry speed.

I expect that this will be the way it goes as I advance (slowly!) from being a raw novice to a decently competent track rider. At first any bike and any setup and any tires would be just fine. But then as I get a little faster things start to matter, and something about the bike becomes a limiting factor. So, you deal with that and go a little faster yet, then some other mecahnical limitation becomes important. Wash, Rinse, Repeat.

My big limitation currently, I think, is that I just don't have the courage to take enough speed and carry enough lean angle through the corners, especially the long slow corners like 9. The bike can do it but my brain can't. Seven track days in my life, and still no scrapes on the pucks! Point being, as I address that rider limitation, I am sure that some limitation in my (now "perfect") setup will emerge.

But that's fine with me. I enjoy the technical geekery part of it almost as much as the riding itself. What a great hobby!
 
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