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Author Topic: Need help asap with rear shock: To Blackbird or not to Blackbird?  (Read 1531 times)
VintageHunter
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« Reply #60 on: June 30, 2017, 12:27:50 PM »

thanks Aaron.
I'll call/try the Racetech app...see what they recommend.
I understand this is a "trail and error" type scenario since we are mixing 900rr shocks with CB1 springs with potentially other springs with potentially other shocks....and so forth and so on, hence the coined "Frankenshock" (which by the way would a helleva name for a potential startup company............(hint).
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spacetiger
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« Reply #61 on: June 30, 2017, 04:50:04 PM »

So...while I appreciate all the "tech" and "R&D" being done on this rear shock issue.....I'd like to ask a simple question(s):
I'm a slow-witted person. I don't really understand too well all the charts, graphs, mathematics, damping, stroke length, etc....so again, if someone could simply explain the answer in simple terms.

1) If you acquire a 900rr rear shock and remove it's current spring, what weight spring can you put in it to be effective for a 200lb rider?
1300lb? 1400lb 1500lb?

2) if you stick with the CB1 rear shock and swap out that "2-stage spring", same as above...what spring can be inserted into the original CB1 shock assembly?
1300lb? 1400lb 1500lb?

that's all that I'm looking for.
you might say..."what diff does it make you already made the transplant" but I may want to swap out the current CB1 spring in the 900rr shock to a better spring, so which one? 1300lb, 1400lb or 1500lb spring?

thanks for all the research you guys have done. it's tremendous.


I guess a spring is a spring in the end of the day. Racetech have an app which helps you select springs, so I'd go there and enter cb-1 and your weight, see what spring they come up with. As the cbr shock is for a shorter spring, you then order a spring in that weight,  for the cbr shock.

Only potential problem is the damping not coping with that rate spring, idk

Amorti,

Its not quite that simple because the CBR900 shock has a different stroke length than the CB-1 (1.9" max vs. 1.5")  That means the factory had a different envelope to design the spring/damping for the mission of the bike.  So, while you could go to RT, they're recommendation would be based on the OEM CB-1 shock [stroke].  

I did a little thinking from my last post and think I need to explain a few things, words of caution.  VH, that might address some of the things you are asking about.  I'll post them to your CBR900 thread.

Jerry
« Last Edit: June 30, 2017, 06:03:08 PM by spacetiger » Logged
VintageHunter
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« Reply #62 on: June 30, 2017, 04:54:36 PM »

Thanks for your patience with my ignorance Jerry.
I'm that guy from "Days of Thunder" movie...I just get on a motorcycle and ride it.
I know not about diving, damping, stroke length, compression, rebound......I just "get on" and ride it but I'm making an effort to understand more of the tech and math behind all this stuff so that I may explain it better to someone else....when asked. thanks for being patient.
So...while I appreciate all the "tech" and "R&D" being done on this rear shock issue.....I'd like to ask a simple question(s):
I'm a slow-witted person. I don't really understand too well all the charts, graphs, mathematics, damping, stroke length, etc....so again, if someone could simply explain the answer in simple terms.

1) If you acquire a 900rr rear shock and remove it's current spring, what weight spring can you put in it to be effective for a 200lb rider?
1300lb? 1400lb 1500lb?

2) if you stick with the CB1 rear shock and swap out that "2-stage spring", same as above...what spring can be inserted into the original CB1 shock assembly?
1300lb? 1400lb 1500lb?

that's all that I'm looking for.
you might say..."what diff does it make you already made the transplant" but I may want to swap out the current CB1 spring in the 900rr shock to a better spring, so which one? 1300lb, 1400lb or 1500lb spring?

thanks for all the research you guys have done. it's tremendous.


I guess a spring is a spring in the end of the day. Racetech have an app which helps you select springs, so I'd go there and enter cb-1 and your weight, see what spring they come up with. As the cbr shock is for a shorter spring, you then order a spring in that weight,  for the cbr shock.

Only potential problem is the damping not coping with that rate spring, idk

Amorti,

Its not quite that simple because the CBR900 shock has a different stroke length than the CB-1 (1.9" max vs. 1.5")  That means the factory had a different envelope to design the spring/damping for the mission of the bike.  So, while you could go to RT, they're recommendation would be based on the OEM CB-1 shock. 

I did a little thinking from my last post and think I need to explain a few things, words of caution.  VH, that might address some of the things you are asking about.  I'll post them to your CBR900 thread.

Jerry
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spacetiger
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« Reply #63 on: June 30, 2017, 06:06:43 PM »

Don't sweat it VH.  Suspension knowledge has advanced a lot, but it still is a black art to many riders.  I'm trying to post how I approach it.  I am sure some (many?) would question it, but I have acquired some good equipment to help guide me through the "black art".  I'll be the first to admit I'm learning as I go so don't get to wooed by the graphics.
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ModerateFkr
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« Reply #64 on: June 30, 2017, 09:27:45 PM »

Don't sweat it VH.  Suspension knowledge has advanced a lot, but it still is a black art to many riders.  I'm trying to post how I approach it.  I am sure some (many?) would question it, but I have acquired some good equipment to help guide me through the "black art".  I'll be the first to admit I'm learning as I go so don't get to wooed by the graphics.

I'm somewhat behind the curve here Jerry. Since our PM exchange I've had some legal issues to deal with.

Plus I've discovered that my CB-1 engine is smoking very badly when revved even when hot though. Only bought it recently and not got it on the road yet. Seems the PO overfilled it with oil. So I drained 500ml off - but that didn't cure it. He may of course have added a bore treatment to disguise the issue, and added the oil to mitigate for the effect/loss. Wouldn't be the first to do that. Looks like a possible ring issue. Could just be bad fuel. Will check that before assuming anything, or planning any major work.

Will catch up on the suspension story when I only have three things to think about at once.

BTW, your diagrams are epic. I've DL'd some to my iMac and studied them a bit. The study you did of rake and trail figures is a unique and very useful thing. It helps to explain the trends in thinking of various manufacturers over the various model types. If nothing else, unless I'm very much mistaken, it dispels the notion that dropping the front forks on a CB-1 just 43mm 'rakes them out' too much.

Plus, raising the back end seems to return the bike back to its standard rake. And despite the fact that the combined effect of both modifications raises the centre of gravity somewhat, our new friend who just went unlimited track racing his for three days (sorry, I've misplayed your name bro) (edit: I remembered) Dash found no ill effects. How much of that was due to his excellent tyre choice, or his light stature is another story.

You're taking this whole suspension thing to a new level mate. Very few people truly get 'inside' the real black arts. It's a calling. Some time back, I taught myself to make real wooden carriage wheels - the old way. It was like communing with 200 year old craftsmen who never saw an internal combustion engine. I worked with vernier callipers, routers and a calculator. But to get the job right, I still had to describe two arcs with Victorian dividers, and bash the heated iron tyre on with a heavy hammer. I couldn't teach anyone how I did it!

So, keep it up mate. One day one of us is going to actually find a nylon washer with a 15mm hole in the centre and produce some actual data...!;-))
« Last Edit: June 30, 2017, 10:28:34 PM by ModerateFkr » Logged
Sugs
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« Reply #65 on: July 01, 2017, 01:32:21 AM »

So, keep it up mate. One day one of us is going to actually find a nylon washer with a 15mm hole in the centre and produce some actual data...!;-))
I actually found something else that works pretty well, an old shock clip I had for ride height adjustment from one of my R/C 8th scale offroad buggies. Fit perfect and looks like this:


I just don't have a center stand and haven't come up with a way to measure it without one.

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1979 Honda GL1000 Goldwing - 1990 Honda CB1
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« Reply #66 on: July 01, 2017, 02:50:10 AM »

So, keep it up mate. One day one of us is going to actually find a nylon washer with a 15mm hole in the centre and produce some actual data...!;-))
I actually found something else that works pretty well, an old shock clip I had for ride height adjustment from one of my R/C 8th scale offroad buggies. Fit perfect and looks like this:


I just don't have a center stand and haven't come up with a way to measure it without one.



Excellent. They're perfect Sugs. Just roll your back wheel off the sidewalk or a concrete block lying on its side. All you're looking for is the bike's weight being dropped on its back wheel from the height it would be if you did have a centre stand. My understanding is that you're establishing a baseline for the bike on its own (which is actually likely to a constant on most standard CB-1s*), prior to adding the organic biped variable ;-)

* If you still have your original Honda toolkit (complete), and it's stored in the tail cowel, or if you've stashed some medication in the gap between the tool tray and the tail light, now might be the time to declare them...! We don't want to be throwing the baseline all over the place do we? ;-)

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