Attack Adjustable Offset Tripple Clamps

[Murf99]

Long story short, I got a set. I'll do my best to record here the installation, tuning and effects.

Long story long: The Aprilia is a confusing beast to set up chassis wise. I am limited to the amount of rear ride height that I can dial in due to an inherent flaw in the shock linkage (if I make the shock any taller, the shock tops out against the lower suspension linkage).

For those of you that don't know, I'm a fan of rear ride height.

Anyhow, I got the bike to track reasonably well out of corners. It tracks quite well on the gas. Corner entry, however, is another story...

The Aprilia has a higher center of gravity than most bikes (read, I4s). Thus, it's more sensitive to ride height changes - as the center of gravity gets proportionally higher with respect to the wheelbase.

Traditionally, trail is tuned by front ride height. However, the Aprilia is overly sensitive to front ride height due to the above mentioned center of gravity issue. In other words, for a given ride height increase (say 5mm), the bike becomes much more difficult to turn. Part of that is the greater trail (good), the other part of that is the ever higher center of gravity. To add to this, a higher front removes some swingarm angle - making the bike track worse on the gas.

So, I decided to set the bike up for the best cornering behavior. This, unfortunately, leads to a lack of trail. Malik has been saying since I got this bike, that I ride like I don't trust the front end. I did, after all, learn a lot of what I know on the lotsa-trail Honda 600RR.

So - by getting this trick adjustable offset triple clamp, I am able to swap eccentric inserts, and by doing so change offset. Changing offset allows me to tune trail independent of anything else (COG height, ride height, swingarm angle). This should be fun.

I'll take the assembly into work tomorrow and try to get some CMM measurements to use as a baseline. Then, I'd like to get some additional eccentrics to allow finer tuning offset.

Stay tuned...

[gntbldr]

You know Todd, I'm not racing my '05 600rr anymore...
Just saying.

[Super Dave]

Originally Posted by Murf99

Long story short, I got a set. I'll do my best to record here the installation, tuning and effects.

What kind? What are your new options compared to stock?

Originally Posted by Murf99

For those of you that don't know, I'm a fan of rear ride height.

I'm asking all of this objectively, Todd, so don't take me the wrong way...

Why are you a fan of rear ride height?

Originally Posted by Murf99

Anyhow, I got the bike to track reasonably well out of corners. It tracks quite well on the gas. Corner entry, however, is another story...

What specifically don't you like?

Originally Posted by Murf99

The Aprilia has a higher center of gravity than most bikes (read, I4s). Thus, it's more sensitive to ride height changes - as the center of gravity gets proportionally higher with respect to the wheelbase.

We had similar set up issues with the 2001 GSXR600 using too much ride height.

Originally Posted by Murf99

Traditionally, trail is tuned by front ride height.

Or rear ride height. Or even springs too. But that would be secondary or operational trail.

Originally Posted by Murf99

However, the Aprilia is overly sensitive to front ride height due to the above mentioned center of gravity issue. In other words, for a given ride height increase (say 5mm), the bike becomes much more difficult to turn. Part of that is the greater trail (good), the other part of that is the ever higher center of gravity.

A lot of road racing is centered around increasing the CG to increase the leverage of the weight. That weight up high flops easier higher than lower.

Originally Posted by Murf99

To add to this, a higher front removes some swingarm angle - making the bike track worse on the gas.

Well, think that through again. As the front end of the bike is brought up, the chassis pivots up around the rear axle. Raising the front end via the forks would continue INCREASING the swingarm angle.

Originally Posted by Murf99

So, I decided to set the bike up for the best cornering behavior. This, unfortunately, leads to a lack of trail. Malik has been saying since I got this bike, that I ride like I don't trust the front end. I did, after all, learn a lot of what I know on the lotsa-trail Honda 600RR.

Most RR's struggle with front end feel from a lack of trail. Generally requiring a set up that lengthens the fork to increase trail.

Originally Posted by Murf99

So - by getting this trick adjustable offset triple clamp, I am able to swap eccentric inserts, and by doing so change offset. Changing offset allows me to tune trail independent of anything else (COG height, ride height, swingarm angle). This should be fun.

I'll take the assembly into work tomorrow and try to get some CMM measurements to use as a baseline. Then, I'd like to get some additional eccentrics to allow finer tuning offset.

Stay tuned...

Cool!

Sounds like BWW's could be fun with drawings and stuff...

[Murf99]

Okay, today I had the opportunity to grab some time on the CMM (in other words, our inspector was able to squeeze in 10 minutes of government work) and here's the result...

The Attack tripples include an eccentric insert marked "2". With this insert, I am able to install it in 2 positions. The first gives me 32mm of fork offset, the second gives me 28mm. SO - a central drill in the eccentric, or a "0", gives 30mm of trail, and every 'number' from that allows adjustment in that many mm + or - offset from 30mm. Thus, a "6" would give me the option of 24mm or 36mm. Additional eccentrics are $84 per set.

By way of comparison, the '04 Aprilia has 33.5mm fork offset as standard, the '01 had 35mm. I ran the '01 forks 2mm sank into the triples and dealt with the geometric side effects (the bike turned like a tank). For one reason or another, I chose to run the '04 a bit more plained out (I have 20mm of fork above the tripple - I know, big change).

Also, I know for speaking with Chip Spalding of KWS, that they ran thier bikes with 30mm-28mm of trail last year...

Anyhow, I'm pretty happy with the balance of the bike, and it's cornering behavior, but find the front lacks feel on turn in to apex. I'll install the tripples at the 28mm offset and see if the added trail is just what the doctor ordered...

BTW - I found these tripples for sale on the Aprilia forum for $500. Recognizing them as a good target of opportunity, I flopped. Time will tell if they're worth the price of admission, but I have high hopes.

Dave, good questions. I'll try to answer them all point-by-point.

Originally Posted by Super Dave

What kind? What are your new options compared to stock?

See above figures.

Originally Posted by Super Dave

Why are you a fan of rear ride height?

What specifically don't you like?

Traditionally, I have found that bikes come with too little. I shoot for 12 degrees as a starting point, and I find that OEM bikes seem to have 8-10deg.

I'm a 'keep it tidy' rider in the tradition of the European road racers - as opposed to the 'dirt track' spin-em-up style that likes a bike out of shape. I find that a ~12deg swingarm angle makes for a nice, tight carve transitioning from maintenance throttle to wide open, from the apex to track out. Make sense?

Originally Posted by Super Dave

We had similar set up issues with the 2001 GSXR600 using too much ride height.


Or rear ride height. Or even springs too. But that would be secondary or operational trail.

A lot of road racing is centered around increasing the CG to increase the leverage of the weight. That weight up high flops easier higher than lower.

Makes sense. Traditionally I have set the rear height where the bike tracks out well, and then dialed trail through front height. C of G be damned, I'll ride around it. But, the Aprilia seems much more sensitive to CG height than anything I've delved into before, so hence my resistance to dial trail with front height.

Originally Posted by Super Dave

Well, think that through again. As the front end of the bike is brought up, the chassis pivots up around the rear axle. Raising the front end via the forks would continue INCREASING the swingarm angle.

I think you're right, now that I think about it. One way or another, it's a secondary effect though. When I tune bikes, I do my best to seperate effects into 'primary' and 'secondary'.

For example, rear ride height has a primary effect on swingarm angle, and a secondary effect on trail.

I use the primary effects to tune that particular characteristic, and tune around the secondary effects - preferably using another primary effect. In the instance I offered above, swingarm angle and trail, I'd choose to use the front height to dial trail (accepting the secondary effect on swingarm angle, and perhaps tuning around it).

In the instance of my '04, however, the secondary effect of CG height becomes a significant contributor to handling. So, the tripples allow adjustment of trail via offset instead of fork height. I anticipate minimal secondary effects when adjusting trail through offset. Yeah, wheelbasw will change by a mm or two, but... meh...

Originally Posted by Super Dave

Most RR's struggle with front end feel from a lack of trail. Generally requiring a set up that lengthens the fork to increase trail.

Maybe on the '07+?? I found that my '05 was significantly resistant to turn - lots of trail. I'd actually aim the thing a foot to the inside of where I wanted to go, and rely on the understeer to place the bike where I desired. I think the '03-'06 bikes are pretty well documented as 'Not wanting to turn' (according to Josh Hayes). I verified this today by looking at an '06 and observing ~25mm of fork offset (by eyeball).

Does this make sense to you Dave? You've been around this a long time...

Originally Posted by Super Dave

Cool!

Sounds like BWW's could be fun with drawings and stuff...

Yup! Should I bring some graph paper?? (we might be banished to our own table...)

Thanks for the questions Dave, really makes me think and evaluate what I'm doing.

[Murf99]

If you listen really closely, you can hear the palm of Malik's hand hitting his forehead.

I called KWS today, and asked what offsets they were running last year on the their Aprilias in the AMA. One thing led to another, and Mike offered sell me (for a very reasonable price) an entire selection of eccentric inserts: 0mm, 1mm, 3mm and 4mm. Recall that the set came with a 2mm insert.

So, I will soon have the hardware to adjust the offset from anything from 34mm (less trail than standard) to 26mm (will turn like a buss).

Of all the things I've done to all the bikes I've had to date - I am probably the most excited about this particular modification.

[nickmick]

nice bit 'o kit!!

i just wish i had an adjustable rake....

[HerbigCBR]

Originally Posted by nickmick

nice bit 'o kit!!

i just wish i had an adjustable rake....

Me too!

Oh wait, I wish I was skilled enough to be able to detect a 5mm difference in ride height on the front end lol

[Super Dave]

Originally Posted by Murf99

By way of comparison, the '04 Aprilia has 33.5mm fork offset as standard, the '01 had 35mm.

OMG?!

We're talking the same measurement of center of the forks to the center of the stem?

I'll be using KZ750 twin triples on my H1 and their offset is like 30mm. I think one of the differences between my '99ZX6R and my '00 was an improvement in handling...going from 20mm of offset to 18mm.

Originally Posted by Murf99

Also, I know for speaking with Chip Spalding of KWS, that they ran thier bikes with 30mm-28mm of trail last year...

I'm assuming that would have been with the huge Dunlop.

And you mean offset rather than trail, right?

Originally Posted by Murf99

BTW - I found these tripples for sale on the Aprilia forum for $500. Recognizing them as a good target of opportunity, I flopped. Time will tell if they're worth the price of admission, but I have high hopes.

Yeah, that's a steal...

Originally Posted by Murf99

Traditionally, I have found that bikes come with too little. I shoot for 12 degrees as a starting point, and I find that OEM bikes seem to have 8-10deg.

Yeah, one can generalize that.

Specific numbers are hard to generalize with for a lot of reasons. Effective length of swingarm, CG, rotation of the CG, etc. I know that the first CBR600RR's of Honda America did best with extended fork internals (to increase trail in their supersport bikes) and colossal shock length to get 15 degrees. Some of the early millenium Suzuki's were good toward 11 degrees. Kevin Cameron told me that their H2R and KR750 Kawasaki triple GP bikes worked best around 13 degrees for some historical reference, but that doesn't account for a lot of other things...just interesting.

Originally Posted by Murf99

I'm a 'keep it tidy' rider in the tradition of the European road racers - as opposed to the 'dirt track' spin-em-up style that likes a bike out of shape. I find that a ~12deg swingarm angle makes for a nice, tight carve transitioning from maintenance throttle to wide open, from the apex to track out. Make sense?

Well...

A spin can come in many forms. So, it might be worth talking about it some. A bike hooked up is hooked up. So, all of the load from the tire holding everything into the chassis is put into the chassis. Thus, it can collapse the rear suspension. Sometimes, that can become so harsh that the spring has to release energy, and that causes the bike to bounce around. At some point, one must realize, suspension dampening cannot overcome the spring. It's a good rule to follow. The dampening is to clean things up, in general. The spring supports. Watch some old Daytona footage of the bikes coming out of T2 on the banking...watch all that load building up and then getting released violently.

All that load will collapse the suspension. The rear can collapse more under load of traction, bumps, and then adding in some acceleration. Thus, that can increase trail at midcorner and out.

A flattracker is a master of searching for traction. They aren't out there to slide. They just push to the limit and hang there looking to drive out over and over and over.

So, if you're Sheene, in the "traditional European style", one would get in good, then accelerate out as best as possible. Kenny was a flat tracker. So, in his acquired skill of pushing it to the limit, he would accelerate more and more and more until the tire would begin to loose some traction.

Some traction...

As the tire begins to loose some traction, it is reducing the load into the spring and the chassis. Thus, it can actually pick up a part of the chassis.

Case in point. When one crashes on the front, it usually happens in two ways, but the final result is basically the same. When the front it loaded too much and there is too little trail, the front tire will "tuck". It's sudden and abrupt. The end result is that the tire completely looses traction, the front springs unload, and trail is then increased dramatically causing the bike to run out of the radius that one was following. On the other side, one can "push" the front. Push to far, traction is completely lost and the front springs unload, trail is increased dramatically causing the bike to run out of the radius that one was following.

I'll hit on the other points later...gotta go eat here at the hotel while we have free breakfast.

Originally Posted by Murf99

Makes sense. Traditionally I have set the rear height where the bike tracks out well, and then dialed trail through front height. C of G be damned, I'll ride around it. But, the Aprilia seems much more sensitive to CG height than anything I've delved into before, so hence my resistance to dial trail with front height.

Some bikes are more sensitive. How to overcome it requires thought and then some experimenting.

Lemme go back to my 2001 GSXR600 that I raced in 2001/2002. We used the generally accepted numbers for front and rear ride heights and the appropriate springs. The bike was ok, but it lacked feel. The R6's worked better. We experimented with more ride height, and it kind of made it better, but, somewhat similarly to you, it was very sensitive to wheelbase changes. If I had a 45t rear sprocket and I wanted to change a tooth, I found that I needed to change my ride height to keep the chassis feeling at least ok.

Fast forward to 2003. I had an R6 now, but I had a problem that left me out with a repair. A friend offered his 2001 GSXR for me to race. Had good forks, but it had a stock shock which was substantially shorter than what we operated at and from the recommended length. This reduced swingarm angle, and it increased trail. It was almost a dream to ride. The shock lacked some of the dampening that I would have liked, but it was just much easier to get into a corner consistently lap after lap. I'll have to admit that I noticed that Mark Junge had been setting up his GSXR's like this the year prior.

Originally Posted by Murf99

I think you're right, now that I think about it. One way or another, it's a secondary effect though. When I tune bikes, I do my best to seperate effects into 'primary' and 'secondary'.

For example, rear ride height has a primary effect on swingarm angle, and a secondary effect on trail.

I use the primary effects to tune that particular characteristic, and tune around the secondary effects - preferably using another primary effect. In the instance I offered above, swingarm angle and trail, I'd choose to use the front height to dial trail (accepting the secondary effect on swingarm angle, and perhaps tuning around it).

In the instance of my '04, however, the secondary effect of CG height becomes a significant contributor to handling. So, the tripples allow adjustment of trail via offset instead of fork height. I anticipate minimal secondary effects when adjusting trail through offset. Yeah, wheelbasw will change by a mm or two, but... meh...

I separate primary into one thing. Actual geometry. It's one thing that IS. The suspension can only move to fully topped out. From there, one can move fork locations and shock lengths. They are what they are, and they will affect CG, anti-squat, trail, etc.

The bike in motion with springs of various rates and preloads I place in a secondary position. Literally, secondary geometry In addition to the rider.

One could have "perfect" geometry, but it can be ruined with over or under preloading, too little or too much spring rate front or rear or both, or a rider that sits on a bike in a specific way that is different from one that normally rides it even.

Originally Posted by Murf99

Maybe on the '07+??

I actually liked the later one, Ben's and others, compared to the early ones.

Originally Posted by Murf99

I found that my '05 was significantly resistant to turn - lots of trail. I'd actually aim the thing a foot to the inside of where I wanted to go, and rely on the understeer to place the bike where I desired. I think the '03-'06 bikes are pretty well documented as 'Not wanting to turn' (according to Josh Hayes). I verified this today by looking at an '06 and observing ~25mm of fork offset (by eyeball).

Well, Josh was riding a lot of FX bikes. Heavy 16.5's, huge rear tires.

I can't get on everything and ride fast. I have to rely upon being able to set it up and get it to give me feed back.

After the F3, Honda seemed to get away from what they had going with the F2/F3. The F4 marked a departure in that they sent the bike out into the public very undersprung and set up very lax on overall ride height, thus affecting rear geometry, anti-squat, etc. Similarly but different for the first F5/RR's. For me, a lot of the first generation RR's were excellent on the rear coming out of a corner. But they just really scared the daylights out of me going in.

Scared me going in? How? Ok, this gets kind of complicated and I'll try to draw in a lot of things together.

My aunt's boyfriend/NASA scientist/FIM GP racer from the 50's-60's/AFM riding school instructor/mechanical engineer and I used to correspond a lot about a lot of things. I don't have the engineering background, but I can give good feedback along with having a pretty good understanding of how I'm affecting the chassis...and how it scares me and when...Isn't being scared part of what slows you down or at least tells you that if you go further you end up binning all your stuff? LOL!

We know that a bike has a CG. Then we get on it and change it too. Would be different for different body types (personal weigh distribution [fat ass vs muscle head, right?], hang off style vs over the top, etc.), but let's just focus on the bike itself. Bob, my aunt's boyfriend, asserted that the CG moves around while the bike is in motion like an inverted pendulum. I agree with that. Where it gets dicey is this. What is the length of the pendulum and what is the origin of the pendulum? This hadn't occurred to Bob, but I had several cases where it was relevant.

My 2003 R6 was very easy to ride. The concept of a neutral handling bike was really apparent in our set up using rising rate Hyperpro springs and the geometry that we got from 4&6. When riding that bike, it wouldn't porpoise back and forth on the brakes and gas like most bikes. It was very simple in how it moved, almost as though it would just cause the bike to rise and fall. So, let's assume the location of the CG at some point on the bike below the tank. We could claim a similar point on every bike for discussion. Now, let's describe the handling with our inverted pendulum. The CG in this case would be directly above the origin of our pendulum. The distance between the GG and the origin of our pendulum we will claim as "long" in this case. Really, think of the origin of the pendulum as a long way below the riding surface.

So, as we are in motion on this R6 with this model of a long inverted pendulum. When one uses the brakes, the traction forces compress the front forks. The CG moves forward around the radius of our pendulum. But since is it long and centered directly below our static CG, its change does not dramatically affect the chassis nor do other inputs from the rider for braking, personal movement, acceleration, etc.

Dramatically different is the Honda CB/CR450 twin that I raced. It didn't really handle well at all. Low power, drum brakes (not that they are bad in and of themselves), and hard to get around a track with quick consistency. In fact, the braking performance was better...when I stayed on the gas!!!!

Yeah, really. So, here is the deal there. Place our static CG location in the spot assumed beforehand. The pendulum movement on older chassis is very different. Reduce the origin point for the pendulum in half, just for a more dramatic image. With that image, recognize that as the CG moves, it will move more dramatically from the longer pendulum of the R6 image. The R6 movement is more linear but not linear. We'd need a radius of infinity to be completely linear, right?

Next, move our CR450 origin forward. How about to directly under the front axle? So, while static, the bike has its CG. As the bike accelerates the CG moves back and down. Thankfully, it doesn't have a whole lot of power to spin the rear wheel, but as it accelerates, the CG is moving back and down because of it's lack of a lot of anti squat.

Braking. The bike doesn't make a lot of anti-squat, but when one lets off, it has no anti-squat or it even goes into squat. So, remember how our pendulum looked here...when trying to brake, the CG is moving UP! NO WEIGHT TRANSFER? Ever wonder why old bikes worked better while using the rear brakes? There ya go... So, to counter the movement of the CG on braking, I would keep the gas on a little to generate anti squat to keep the CG in a place where it would transfer something to the front to slow down better. The brakes on that bike were actually very good, but the geometry was pretty much ass. Similarly, from the period that Keith Code started writing, it was very much customary for riders to stop braking and go to gas to pick up the back of the bike to keep the trail reduced to aid turn in and following a reasonable line. A flat tracker could do it differently, but that's another story.

So, the other side is a bike that generates a lot of or enough anti-squat but lacks feel at turn in or under braking. My GSXR600, a lot of RR set ups, and kind of sounds like your Aprilia.

Really, it's just an inversion of the CB450. Probably not as dramatic, but...

So, we place our CG in our spot. As we accelerate with our modern sportbike, it generates anti-squat. In fact, it is generating anti-squat even off the gas. Should make it so that the length of our pendulum's radius is longer than the CB450, right? Anyway, as we're accelerating, it continues to make anti-squat and keeps our trail tight making the front carve through our exit very well. Can make the bike a little twitchy if it wants to go sideways as we don't have a lot of trail to work with. You run out of trail, you fall down, right? Changes in our steering are quick and snappy. Thus, if the rear hangs out, it can really lever the bike around too.

We're heading to our braking point, we let off, but it makes a whole lot of anti-squat yet. So much so that it pushes our CG forward and even down. That reduces our trail from static. Now we hit the brakes...might cause the rear wheel to come off the ground, might cause a lot of rear wheel bounce. Does make the brakes feel like they are very powerful, but there isn't a lot of slowing down going on. At the point of turning in, the suspension loads, and the nose gets loaded even more. Less and less trail, less feel as we follow our pendulum forward and down. Getting off the brakes and getting on the gas can help unload the front increasing trail more toward static... but probably not enough.


Regardless of the improvement of trail, less offset in triple clamps will pull the forks, front wheel, and brakes in toward the CG.

Was Chip using the offset steering head bearings too? Might want to ask. He might not want to tell. I think the AMA made them illegal at some point. I know people were using them yet for a while when they had lax enforcement, but after Jim Rashid ran tech, I'm betting that that pretty much had to stop.

I'm a little distracted right now, so I'm not happy with all of my responses here. I think I can do it better on paper. It doesn't mean that it is right, but I think it's something that you should consider on your set up.

Originally Posted by Murf99

Yup! Should I bring some graph paper?? (we might be banished to our own table...)

Thanks for the questions Dave, really makes me think and evaluate what I'm doing.

Hell yeah, bring graph paper! Just paper even...I have Wednesday in my plans yet.

[Murf99]

Thanks Dave, for taking the substantial time and sharing your thoughts and background. Lots there, it's going to take me a couple of times reading that over in order to generate the corresponding responses.

[Super Dave]

Originally Posted by Murf99

Thanks Dave, for taking the substantial time and sharing your thoughts and background. Lots there, it's going to take me a couple of times reading that over in order to generate the corresponding responses.

Hey, no problem.

It could be relevant to your thought process. So many things change, it gets hard to get solid answers.

These are the specs of your bike, right?
http://www.motorcycle.com/specs/apri...se/detail.html

Standard trail at 101+mm of trail seems pretty reasonable in that. 95 - 100 is usually considered the "sweet spot".

But that isn't always hard and fast either. The Buell XB12R, for example, http://www.sportrider.com/bikes/2004...ecs/index.html comes in at 83mm of trail. But it carries its weight so low, the CG doesn't move forward and down so much. It really just doesn't need so much trail. It's quite a study in making something so completely different from everyone else.

[HerbigCBR]

This is all good stuff guys. I enjoy reading about how the bike works and the comparisons between different bikes.

SD, I think I understand what you are saying about the inverted pendulum. It is the same as what would be called the pitch center on a racecar, right??? (makes sense that the pitch center is below ground...)

Originally Posted by Super Dave

Braking. The bike doesn't make a lot of anti-squat, but when one lets off, it has no anti-squat or it even goes into squat. So, remember how our pendulum looked here...when trying to brake, the CG is moving UP! NO WEIGHT TRANSFER? Ever wonder why old bikes worked better while using the rear brakes? There ya go... So, to counter the movement of the CG on braking, I would keep the gas on a little to generate anti squat to keep the CG in a place where it would transfer something to the front to slow down better. The brakes on that bike were actually very good, but the geometry was pretty much ass. Similarly, from the period that Keith Code started writing, it was very much customary for riders to stop braking and go to gas to pick up the back of the bike to keep the trail reduced to aid turn in and following a reasonable line. A flat tracker could do it differently, but that's another story.

Makes perfect sense now, but I always wondered why the rear brakes on old bikes work so much better than a modern sportbike's.

Originally Posted by Super Dave

So, we place our CG in our spot. As we accelerate with our modern sportbike, it generates anti-squat. In fact, it is generating anti-squat even off the gas.

Maybe I'm overthinking this... could you explain some more. I understand anti-squat on the gas, but not off the gas? Is it just because of the location of the origin of the pendulum of the newer bikes and because of the fact that you are technically decellerating when off the gas?

Also, anyone ever looked at this book?
Motorcycle Dynamics by Vittore Cossalter

[Super Dave]

Originally Posted by HerbigCBR

This is all good stuff guys. I enjoy reading about how the bike works and the comparisons between different bikes.

SD, I think I understand what you are saying about the inverted pendulum. It is the same as what would be called the pitch center on a racecar, right??? (makes sense that the pitch center is below ground...)

Good question. Not sure.

I know that there are many equations and data that people that make tires for cars. However, motorcycle tire ideology is still kind of mystical even to the tire folks, so I'm told. It's an art.

On the flip side, a car is harder to set up. A bike, well, if you're really talented rider, you ride around the issues. Schwantz struggled with his NASCAR Busch program...was always thinking, "If I could just move my body back to make it hook up..."

Originally Posted by HerbigCBR

Makes perfect sense now, but I always wondered why the rear brakes on old bikes work so much better than a modern sportbike's.

Also comes from a real lack of height in some older bikes too.

Originally Posted by HerbigCBR

Maybe I'm overthinking this... could you explain some more. I understand anti-squat on the gas, but not off the gas? Is it just because of the location of the origin of the pendulum of the newer bikes and because of the fact that you are technically decellerating when off the gas?

There's anti-squat in modern sportbikes off the gas. But the generation of anti-squat comes from the relationship between the countershaft, the rear axle, and the swingarm pivot.

Old race bikes with poor development in the chassis will go into a squat mode off the gas loaded up mid corner. Two of the Honda's I raced (CB400F and CB450) both had serious issues with this. The rear wheel decelerating against the compression of the engine would cause the front wheel to violently bounce. So, there you are trying to slow down heading into the corner with the engine cases nearly on the ground, now the front it hopping all over. Back on the gas, it would pull out and go back to mild anti squat. Relocate the swingarm pivot, change the length of the shocks, etc...all can help. Some old bikes have issues with the countershaft being a long way away from the swingarm pivot too. Makes it harder.

Back to anti-squat...slipper clutches are pretty common now to reduce some of the off the gas anti-squat with astronomical engine RPM's.

Originally Posted by HerbigCBR

Also, anyone ever looked at this book?

Never looked at that one.

[Murf99]

An update.

I installed the triple clamps with 29mm of offset. A big change from the 33mm offset which I had been running, but to roughly convert to 10mm of fork height (offset divided by the sine of the angle of rake -> 4 / sin(24.8deg) = 4 / 0.42 = 9.52mm), so nowhere I haven't been before. This is also right in the region of what KWS were running on their DSB Aprilias last year.

The goal was to get some more trail without raising the center of mass.

My desire was to install the forks at the same relative height as I had been running. But, instead of making up a jig to measure fork height to the frame, I decided to measure the difference in height between the OEM upper clamp and Attack. This includes the steering stem nut height, clamp thickness, and droop. I ended up with 14mm of fork above the triple instead of the 25.5mm I had been running on the OEM setup.

Gotta start somewhere, after all. So I decided to put the thing together and have a go at it instead of making myself silly with maths and calculations. I figured I'd have some track time to sort it all out.

I figured wrong. A last minute business trip to detroit precluded me heading to the 7/21 trackday, and the weather looked poor for Friday (in addition, I was waiting on a fork clamp to attach my steering damper). Come Saturday, morning practice was rained out.

I entered the GTO to get some track time, but it became obvious the first lap that my quick shifter was misbehaving. That took over half the race to disconnect. After I went out, the bike steered really quick, but appeared to lack any sort of feel. In fact, I tucked the front in the buss-stop right in front of Ron Hix. Thankfully, things like my knee, the exhaust and footpeg got in the way of the bike falling. I mistakenly wrote my piss poor performance off to a green track. A slight preload change and I was back out for Supertwins.

Nope. No better. It seemed like I had all I could do to keep the front from tucking. I tossed it into the carousel on the first lap, to try and run down Rick Breuer, and the front end just seemed to fold. I limped through that race very very frustrated.

Turns out I was way off. I'm not sure if it was a measurement error, or simply a result of unaccounted for changes in chassis behavior resulting from the big change in offset... but way off nonetheless.

Feeling the lack of trail, Malik and I raised the front end 10mm and headed out for the late afternoon practice. Step in the right direction. Malik was nice enough to grab the preload wrench and stand in pit lane - the idea was to use preload as a quick substitute for ride height. 3 laps at a time, and 7 turns of preload later, we ended up with another 5mm of front height. We made that adjustment over night.

First warmup, more of the same. But, owing mainly to a conversation I had with Super Dave over BW3 legs and beer... we decided to take some rear height out. We were still in the 'Big Change' mode and took 6mm out at the frame. Much better. The bike didn't track as well out of turns on partial throttle, but it felt much more free at high throttle openings. It became obvious that the chassis was binding previously. The bike didn't seem to 'carve' as well, but it started to yaw on exit. Very cool. First time I've felt that. I understand the whole 'steer with the throttle' thing a bit better now.

You were right! Thanks Dave!

Anyhow, for my HWSB race Sunday, Malik dialed in 2mm more rear height (for a total change of -4mm) and a little more front preload - to make the chassis a little less of a departure from what I was used to.

The race itself is a whole other story...

The changes did the trick. A ways from my quickest laps, but it was at least in the neighborhood. As an interesting post script, my tire looked awesome! Gone was the 'tearing' that I had come to accept as normal wear!

I'm a sensative guy when it comes to setup - I rekon Boulder would have gotten on the bike and ridden the wheels off of it regardless of setup... but I'm not that guy. I really have to thank Malik for helping me sort through the chassis changes, in very limited time, to move the bike from something that was to me borderline rideable, to something that was pretty close.

There's lots of room to improve from here. It's kind of a whole new world. Talking with Chip at KWS on several occasions, about setup, the conversation always ended with 'but we had the adjustable triples - which pretty much changed everything.'

The Attack Triples were eefinately not the silver bullet solution I was hoping for, or rather they aren't yet. Lots of room to grow, to improve. It's evolving...

[Super Dave]

Neat to hear!

Missed your message last night...and my cell service at location number three is worse than at home...Ack!

Talk more about the "yaw" on exit. What are your compression settings at in back?

[ERB68]

Originally Posted by Murf99

I'm a sensitive guy

Ah ha!!! I knew it.

cool info here, keep it going

[Murf99]

Originally Posted by Super Dave

Talk more about the "yaw" on exit. What are your compression settings at in back?

The back end would seem to rotate 3-4degrees out-of-line with the front. This 'angle of yaw' could seemingly be controlled with throttle application - though I was definitely not spinning the rear up. Odd. But new.

Damping is pretty stiff, per Scotty, but not out of line.

I don't think this is a damping issue, though, because it's not in the transient. It's sustainable.

Thoughts?

I really need more seat time to comment more...

[Trackside S&E]

About 6 years back when Dave started explaining all of the specifics of squat - Anti Squat and geometry had my head spinning.. Not to mention the inverted pendulum....... It took me a while to mentally put it all together in my head... But once I did - It really gave me a connection/feel for the bike that I never understood before...

All of everything Murf and I have talked about makes sense with what is being said here... Sometimes I wish we have more opportunity at the track to work with everyone - as sometimes it comes down to multi faceted - Compounding issues that effect geometry while in motion....