Suspension Upgrades

[EMS]

As they say, Phil: Rome was not built in one day! I think you deserve a little break and do some riding!

[Syscrush]

As they say, Phil: Rome was not built in one day! I think you deserve a little break and od some riding!

Man, if I could work my mechanics like Rome worked its slaves, this bike woulda been built in a couple of weeks, anyhow. ;)

It is starting to warm up, and I've managed to put a few hundred km on so far. It's good to have it back, for sure.

[Syscrush]

I continue to dial in the shocks, having taken a fair bit of damping out of them, they feel much better. Still needs the preload backed off a bit, which is complicated by the fact that I stupidly misplaced the little rod provided with the shocks as a tool for adjusting preload. It's in my apartment somewhere, I'll dig it up soon.

There's not much action in the thread that I started for my RFID keyless ignition, but some in here might find it interesting. Here's a vid of it in action:




More details in the thread here.

[Syscrush]

I continue to dial in the shocks, having taken a fair bit of damping out of them, they feel much better. Still needs the preload backed off a bit, which is complicated by the fact that I stupidly misplaced the little rod provided with the shocks as a tool for adjusting preload. It's in my apartment somewhere, I'll dig it up soon.

I found it tonight, under a stack of my wife's study materials on the dining table. Backed off preload about 4-5mm and wow - huge difference.

I think that there's some fine-tuning left to do, but as it is now, I'd characterize it as "compliant but not cushy". Except for the worst potholes & speedbumps, I no longer have to put all of my weight on the pegs to deal with road irregularities. Now, I spend almost all of the time just in the seat, enjoying life. That makes life a lot easier on my knees, and it also makes it easier to keep my arms loose. I can keep everything a bit looser now and kinda let the bike do its thing under me, which is a much better/smoother/safer/faster way to go.

Once the front end has been brought up to the same level as the rear, I think this is gonna be a pretty special bike.

[Syscrush]

OK, getting down to the nitty gritty now, and finalizing the design for custom triples.

As I understand it, the stock trail is 120mm and the stock triple offset on the twinshock bikes is 35mm. From my playing around with this calculator, it looks like increasing the offset by 10mm will bring the trail down to ~105mm (same as a Bandit 1200 or CB550).

Can someone with more practical experience and/or expertise weigh in on what offset change at the triples will get me to the 105mm trail I want?

[EMS]

With a rake of 27.5°, a change in offset of 10mm, will produce a reduction in trail according to the formula:

cos (27.5°) = x/10mm, this means cos (27.5°) x10 = x, with x being the change/ reduction in trail. I don't have a table handy or a calculator that does trigonometry functions, but assuming the cos (27.5°) is somewhere between 0.90 and 0.89,
this would give you a trail reduction of 8.9 to 9mm.
Turning the formula around, trying to get to a 15mm reduction:

cos (27.5°) = 15/x, means x = 15/cos(27.5°) and again using 0.89 to 0.90 for the cos of the rake angle, you would need a 16-17mm increase in offset.....

I may have that totally wrong.....

[jkotsi]

You have increase the ride height at the rear so the rake should be less than stock, less trail. Adding 10mm in offset would be about 9mm less trail.

If my math is right going from 27.5 to 24.5 degrees rake should give you close to 105mm of trail. If you have a digital angle finder you can confirm the current rake. Lowering the height of the axel reduces trail, Confirm from ground to mid point of front axel.

You may have enough ride height adjustment to meet your number.

[Syscrush]

With a rake of 27.5°, a change in offset of 10mm, will produce a reduction in trail according to the formula:

cos (27.5°) = x/10mm, this means cos (27.5°) x10 = x, with x being the change/ reduction in trail. I don't have a table handy or a calculator that does trigonometry functions, but assuming the cos (27.5°) is somewhere between 0.90 and 0.89,
this would give you a trail reduction of 8.9 to 9mm.
Turning the formula around, trying to get to a 15mm reduction:

cos (27.5°) = 15/x, means x = 15/cos(27.5°) and again using 0.89 to 0.90 for the cos of the rake angle, you would need a 16-17mm increase in offset.....

I may have that totally wrong.....

Thanks Mike.

In return for this helpful information about rake, trail, and offset, I offer you some information you will hopefully find helpful one day... Google has a calculator built in:

Click here to see

As it turns out, the cos of 27.5 is 0.887 - your estimate was very close. :)

Also, I double-checked your equation, and it fits with what Wiki says:



Of is the offset. So to see the change in trail due to a change in offset, it ends up being (-Of1 - -Of2)/cos(Ar) where Of1 is the original offset, Of2 is the new offset, and Ar is the rake angle.

So to decrease trail by 15mm, the offset should increase by 16.9mm, so your estimate was very, very close. :)

[EMS]

How does that saying about the blind squirrel go.....

There is a small side effect when increasing the offset: You will decrease the rake slightly. It is difficult to explain without an animated graph, but if you look at the rake/trail sketch and imagine increasing the offset, you will see, that the front end will be "lifted". Keeping the wheel on the ground means rotating around the steering neck and thus decreasing the rake angle.

[Syscrush]

You have increase the ride height at the rear so the rake should be less than stock, less trail. Adding 10mm in offset would be about 9mm less trail.

If my math is right going from 27.5 to 24.5 degrees rake should give you close to 105mm of trail. If you have a digital angle finder you can confirm the current rake. Lowering the height of the axel reduces trail, Confirm from ground to mid point of front axel.

You may have enough ride height adjustment to meet your number.

Thanks very much. The rear has been raised, but not enough to take out 3 degrees of rake - more like 1 degree. I'm still on the fence about if I want to get back to stock rake or leave it as is.

[Syscrush]

How does that saying about the blind squirrel go.....

There is a small side effect when increasing the offset: You will decrease the rake slightly. It is difficult to explain without an animated graph, but if you look at the rake/trail sketch and imagine increasing the offset, you will see, that the front end will be "lifted". Keeping the wheel on the ground means rotating around the steering neck and thus decreasing the rake angle.

Thanks for this pointer. To me this seems like a very small effect - as in a smaller effect than what happens when I move forward or backwards 1" in my seat. I think I'm just gonna add 15mm of offset and then dial in the dynamics I want by adjusting the front ride height, get it to where it feels good to me, and then stop worrying about millimeters.

[Syscrush]

Hey all.

I took all of my Pro-Link front end parts (triples & forks) out to the machinist's place on Sat, along with the new rotors & calipers and fork brace - things are getting exciting!

However, they're also getting a bit confusing. He pulled the original front end off the bike, and he says that both sets of triples have the same offset: 42mm.

This is very far apart from the following old post from EMS:

The result of my quick, office desk trigonometry calculation about the change in trail of 10mm, somehow did not make sense to me. It was just too small of an amount to produce such a difference in handling and feel as we experienced. I went home last night, took some dimensions on both my 79 and the 81 and on a seperate 79 fork assembly. I used the following data: Axle c/l above ground:320mm, trail 120mm, rake 27.5 degrees, offset in triple clamps 35mm, length of fork from lower tt bracket to c/l axle 565mm, distance between tt brackets 185mm. Upper bracket width 25mm, lower bracket width 42mm. I plugged all this into our chassis program, and came up with the following: Rake change to 29.5 degrees and unchanged triple tree would move the front wheel 35mm further forward and result in a trail of 149mm. In order to maintain
120mm, the adjustment in the offset of the lower bracket would be made, changing the fork angle to 34 degrees.
Putting this fork into the original 27.5 degree steering neck, will result in a trail of 45mm. Too low for comfort.
That's more like it. That's why we didn't consider the bike rideable. Now, I would really like to hear from somebody who did the change and likes it.
Maybe I am still looking at something the wrong way.

Can anyone else weigh in on this?

[EMS]

Hey all.


Can anyone else weigh in on this?

I guess I should:
Some of the original material released by Honda for the introduction of the Prolink models mentioned a different offset in the forks in order to compensate for a rake of 29.5° and maintain the same trail of 120mm.
This was confirmed by one of the technical experts from the U.K. CBX club.
My following investigation was done using a 39mm fork with - in hindsight - a lower fork clamp of unknown heritage.
Funny thing, the theoretical calculation confirmed the practical experience I AND some others had with plugging a Prolink fork into an early frame.
In following discussions, many did not share these experiences and confirmed that everything was O.K.
To this day, I do not know what lead me on the wrong track other than the technical spec of 29.5° rake, which seemed to be inaccurate. I still don't know where the lower clamp came from and what happened to it.
All I can say, at least here in the U.S., the frames have all the same rake and the fork triples have the same offset.

Mike

[daves79x]

I can also tell you that the early and late CBX have the exact same static front end geometry.

Dave

[Syscrush]

I guess I should:

All I can say, at least here in the U.S., the frames have all the same rake and the fork triples have the same offset.

Thanks a lot, Mike. That original topic is locked - maybe a moderator can open it or update it so it has the correct information?

I can also tell you that the early and late CBX have the exact same static front end geometry.

Thanks for the confirmation!