Chain Chatter Issue

I was always under the impression that the rear axle centre, swing arm pin centre, and sprocket centre were in line at about the rider sag level, but how wrong I was! It is actually in line when the suspension is compressed (dropped) about 20mm more than the rider sag level.

So a "tight" chain when in line is giving me about 20mm slack at rider sag level. (not that I think I got the rider sag level exactly correct. Something to do with a shock top out rubber or spring, or a wrong weight main spring, or the impact of linkage ratios is making it difficult..... I cant get the free sag down to the Racetech recommendation of 5 to 10mm)

Compression and rebound are working OK, but still getting setup. No suspension chatter
 
There is some impact with the angle of the swingarm from Horizontal, that's beyond my pay grade. I don't have a handle on that aspect of motorcycle chassis design. It has an impact on traction plus ride height changes when accelerating and braking.
 
My belief is that there needs to sufficient swingarm downslope angle to prevent squatting, but not so much as to encourage the rear wheel to jack up the suspension. This is all under acceleration, not steady state cruising.

Remember that as the rear ride height changes, so does the angle of the steering head as well as the trail.

When we built the first cheater GSX-R’s for AMA racing we first set the swingarm angle then pulled the steering head out to give back the rake and trail. 23.1* rake, 100mm trail and 13* downslope IIRC, it was many years ago. The Suzuki factory was stuck riding un altered chassis and thus Mat Mladin rode with wildly shaking handlebars exiting every corner! That boy had huge balls!!

American Honda won several Supersport championships with slightly curved forks so that Miguel DuHamel could vary the trail and front grip by using the brake to set front ride height. They planned to claim crash damage if they ever got caught…….

As the saying goes: “If you ain’t cheatin’, you ain’t tryin’”.
 
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Alzero said:
American Honda won several Supersport championships with slightly curved forks so that Miguel DuHamel could vary the trail and front grip by using the brake to set front ride height. They planned to claim crash damage if they ever got caught…….
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I'm baffled! Totally confused. Using the brake to obtain a beneficial geometry adjustment????
 
Trail braking allowed him to control the front ride height and the subtle curve in the forks exaggerated the effect. This was as per the American Honda chief mechanic at the time and was also a very big secret back then. Privateers could do a lot that the factory teams could not get away with because of their fear of bad publicity.

The quote is from NASCAR and is attributed to Smokey Yunnick IIRC……
 
piranha-bro2 said:
I'm baffled! Totally confused. Using the brake to obtain a beneficial geometry adjustment????
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Me too. I wouldn't have thought there would be many opportunities during a race to feather the front brake to achieve a particular ride height. Perhaps in the middle of a corner? Otherwise you're either braking to the max or looking for max speed.
 
Dellortoman said:
Me too. I wouldn't have thought there would be many opportunities during a race to feather the front brake to achieve a particular ride height. Perhaps in the middle of a corner? Otherwise you're either braking to the max or looking for max speed.
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Exactly, in the middle of the corner to increase trail to increase front grip. As to whether on not it worked: the rider thought so. And if that belief made him faster, then Job Done!
 
If you're on the limit of adhesion in the middle of a bend, applying the brakes adds another reaction force to the tyre's contact patch and could put it over the limit. Playing with braking to achieve a desired amount of trail doesn't sound like a good idea to me. The whole story sounds implausible to me. I'd be questioning the source of the rumour.
 
IMO, what's been said is partially correct.
When the craze was for antidive on forks the top riders didn't like it. Once it was thought about and put into language riders could understand it became apparent that they liked forks which dived at least somewhat on brake application. What was happening was that as the forks dived, trail reduced - and the bike turned easier.
The moral is that trail braking will reduce fork trail by holding them down - and help turn - in. Some dive is good.
 
Is that why Rob Holden (and others?) hated the Britten and its non trad front end, Greg? Seem to remember reading about it not offering good turn-in.
 
Yeah. All the funny front ends were better received once a little dive was introduced. Feel then became much more what riders were used to.

The problem with the Britten was John. He liked how it felt - but he wasn't fast enough to get out to the limits his other riders were reaching.
Then you had one of the test riders who simply rode around any problems - so they didn't get adressed. Lesson one - pick your testers well.
 
I did a suspension test on my Dirtbike once for a local suspension guru, There was zero chance of anything even close to good happening, other than my shortfalls being fixed. I struggled with any constancy for any length of time. Those race pros do huge numbers of laps within fractions of seconds. It's way more demanding than the magazine tests make out. Getting high-end results that achieve improvements is really tough.
 
GregT said:
Yeah. All the funny front ends were better received once a little dive was introduced. Feel then became much more what riders were used to.

The problem with the Britten was John. He liked how it felt - but he wasn't fast enough to get out to the limits his other riders were reaching.
Then you had one of the test riders who simply rode around any problems - so they didn't get adressed. Lesson one - pick your testers well.
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Undoubtedly very good riders, able to ride the wheels off a bike even when it's a pig (Stoner on the Duc vs every other GP rider who tried?!). Great riders don't necessarily make great test riders as you point out Greg.
 
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