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Author Topic: Need help asap with rear shock: To Blackbird or not to Blackbird?  (Read 1832 times)
a_morti
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« Reply #30 on: June 22, 2017, 05:04:46 PM »

Morti, can you send the link of Mike Fellows' facebook post regarding the blackbird shock?

Not that I dont trust you, But Id like to see if he mentions anything about mounting the thing in the CB-1.
You may need to join the group, which is no bad thing anyways.
https://m.facebook.com/groups/1119747858086718?view=permalink&id=1231250040269832

You re my hero right now.

That Mike fellow seems to be happy with it and answered the questions I needed answering in his facebook posts. Even our weight is almost the same. 160 lbs = app. 72 kg. Im 70 kg. so those 2 kilos difference aren t going to mess things up I reckon.

Could I be this lucky..?

Seems like just the thing to get you by.
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spacetiger
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« Reply #31 on: June 22, 2017, 06:46:24 PM »

Good luck. Still check to make sure the spring is right. Your lighter weight helps and there is a bit for stroke. Don't let the weight thing trick you.  The upper rate of the cb1 spring is more stout that the rear spring on my can am Spyder. That bike weighs a 1,000 lbs, 600 more than cb1. Leverage is king.

Jerry
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VintageHunter
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« Reply #32 on: June 22, 2017, 09:33:29 PM »

Remember though....the CamAm Spyder has 3 wheels and while it weighs in at 1000lb....divided by 3 is well, 333lbs per suspension. I know it's now quite that easy but...it's close.
Good luck. Still check to make sure the spring is right. Your lighter weight helps and there is a bit for stroke. Don't let the weight thing trick you.  The upper rate of the cb1 spring is more stout that the rear spring on my can am Spyder. That bike weighs a 1,000 lbs, 600 more than cb1. Leverage is king.

Jerry
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Sugs
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« Reply #33 on: June 22, 2017, 09:34:35 PM »

Checking racetech for spring rate on the Blackbird shows that it has a 16.8kg/mm spring stock, which converts to 940.8lbs/inch?  So might be an OK option for a lighter rider.
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VintageHunter
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« Reply #34 on: June 22, 2017, 10:07:54 PM »

So..here's me simple minded question.
Why not just take the 900rr shock and stuff a 1500lb spring in it from Racetech and be done with it?
is too simple of a solution?
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ModerateFkr
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« Reply #35 on: June 22, 2017, 10:46:45 PM »

Mf, the plastic tube is there to protect the shock shaft.  The blackbird isn't a real heavy bike is it?  I would have guessed it Only 60 lbs or so than the CBC-1. In any case the angle of the mount and linkage really doesn't drive you to a stout spring. Can-1 has no help so it needs a stout spring. At your weight, I'd say you need at least a 1,500 lb/in.

I'd guess the bb stroke to be similar to VTR - see side by pic. So say about 2"?

Sorry Jerry, I didn't read your reply properly before. I was distracted. So, according to your figures, the Blackbird will be underscoring by about 50%?

According to Mike Fellows' fb page, it raised his back end by 15mm. Assuming my far ass compresses that down to normal level again, it will only leave me 35mm of shock travel. And that's only enough with an adequate spring isn't it?

The cheapest one I can find in decent condition is 75!

So I need to look at another option don't I?

I know I've read it here but I can't find in via my phone. What is the spring rate of the oem CB-1 rear spring?
« Last Edit: June 22, 2017, 10:50:43 PM by ModerateFkr » Logged
a_morti
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« Reply #36 on: June 23, 2017, 03:43:14 AM »

Mf, the plastic tube is there to protect the shock shaft.  The blackbird isn't a real heavy bike is it?  I would have guessed it Only 60 lbs or so than the CBC-1. In any case the angle of the mount and linkage really doesn't drive you to a stout spring. Can-1 has no help so it needs a stout spring. At your weight, I'd say you need at least a 1,500 lb/in.

I'd guess the bb stroke to be similar to VTR - see side by pic. So say about 2"?

Sorry Jerry, I didn't read your reply properly before. I was distracted. So, according to your figures, the Blackbird will be underscoring by about 50%?

According to Mike Fellows' fb page, it raised his back end by 15mm. Assuming my far ass compresses that down to normal level again, it will only leave me 35mm of shock travel. And that's only enough with an adequate spring isn't it?

The cheapest one I can find in decent condition is 75!

So I need to look at another option don't I?

I know I've read it here but I can't find in via my phone. What is the spring rate of the oem CB-1 rear spring?

Raising the back end by 15mm is due to about 5mm extra length on the shock body. If the shock has 2" travel, that's around 6" at the real wheel. It's "approx" 3 times multiplied.
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ModerateFkr
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« Reply #37 on: June 23, 2017, 09:14:01 AM »

Mf, the plastic tube is there to protect the shock shaft.  The blackbird isn't a real heavy bike is it?  I would have guessed it Only 60 lbs or so than the CBC-1. In any case the angle of the mount and linkage really doesn't drive you to a stout spring. Can-1 has no help so it needs a stout spring. At your weight, I'd say you need at least a 1,500 lb/in.

I'd guess the bb stroke to be similar to VTR - see side by pic. So say about 2"?

Sorry Jerry, I didn't read your reply properly before. I was distracted. So, according to your figures, the Blackbird will be underscoring by about 50%?

According to Mike Fellows' fb page, it raised his back end by 15mm. Assuming my far ass compresses that down to normal level again, it will only leave me 35mm of shock travel. And that's only enough with an adequate spring isn't it?

The cheapest one I can find in decent condition is 75!

So I need to look at another option don't I?

I know I've read it here but I can't find in via my phone. What is the spring rate of the oem CB-1 rear spring?

Raising the back end by 15mm is due to about 5mm extra length on the shock body. If the shock has 2" travel, that's around 6" at the real wheel. It's "approx" 3 times multiplied.

Thank you a_morti. That's a lot isn't it? My only question is how quickly will it be taken up by my 225 lbs weight? It seems the spring is 33% too light compared with the 1,500 lbs spring that Jerry's figures seem to clearly indicate that I need. I still need to compare them both with the oem spring capacity - just for reference. I can already see that lighter guys are happy with the BB shock - for obvious reasons.

This is why Jerry's research is so valuable (and why he needs our individual nylon washer data) because his Frankenstein solurions can be adapted to individual needs.

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a_morti
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« Reply #38 on: June 23, 2017, 09:23:25 AM »

ISTR Mike is around 150, which is 2/3 of your weight. Seems to make sense you'd need a stronger spring. It's not clear to me whether a blackbird shock with stock rate 1,100 and only partial damping control would work great with a 1,500 spring. Also not clear to me whether a Cbr shock with stock spring 800, even with full adjustability, could competently manage a 1,500 Spring without changing the valving. Space tiger certainly seems to be the man to work that out. (All those Spring numbers are guesstimated on the spot from rough rememberings)

I guess us skinny guys (I'm somewhere round 160) have the advantage in the search for a cheap replacement upgrade!
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a_morti
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« Reply #39 on: June 23, 2017, 09:33:47 AM »

Although adding preload isn't the same as using a stronger spring, the long threaded section on the blackbird shock body will let you add plenty of preload to avoid bottoming the shock out.
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Dash
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« Reply #40 on: June 23, 2017, 01:40:15 PM »

Aquired the shock for 50,-. Seems to be in good condition. Gonna try fit it tomorrow. Here's to hoping. Shocked
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VintageHunter
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« Reply #41 on: June 23, 2017, 02:26:51 PM »

which shock? the BB shock? give us the full report when installed and tested please.
  Grin
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ModerateFkr
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« Reply #42 on: June 23, 2017, 04:16:16 PM »

ISTR Mike is around 150, which is 2/3 of your weight. Seems to make sense you'd need a stronger spring. It's not clear to me whether a blackbird shock with stock rate 1,100 and only partial damping control would work great with a 1,500 spring. Also not clear to me whether a Cbr shock with stock spring 800, even with full adjustability, could competently manage a 1,500 Spring without changing the valving. Space tiger certainly seems to be the man to work that out. (All those Spring numbers are guesstimated on the spot from rough rememberings)

I guess us skinny guys (I'm somewhere round 160) have the advantage in the search for a cheap replacement upgrade!

Yes, I hate you a_morti!!!;-)))) As recently as 1997, I was as skinny as you because I was cycling 20-30 miles a day - at speed. I was competing with commuter traffic easily. My bike had excellent road tyres on and I kept them inflated at 65-70 psi!! That makes a huge difference.

Anyway, the lesson is bro, don't get unfit, stay active. Limited rear shock options is only a small part of the downside of getting lazy - as I did.

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VintageHunter
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« Reply #43 on: June 23, 2017, 04:18:51 PM »

as recent as 1997? that was freakin 20 years ago mate. In 20 years....we all have gotten a bit, well......more.
A_morti is still a kid. Give him....Ohhh...I dunno....another 15 or 20 years and he'll be as round as hound, like the rest of us. Wink
ISTR Mike is around 150, which is 2/3 of your weight. Seems to make sense you'd need a stronger spring. It's not clear to me whether a blackbird shock with stock rate 1,100 and only partial damping control would work great with a 1,500 spring. Also not clear to me whether a Cbr shock with stock spring 800, even with full adjustability, could competently manage a 1,500 Spring without changing the valving. Space tiger certainly seems to be the man to work that out. (All those Spring numbers are guesstimated on the spot from rough rememberings)

I guess us skinny guys (I'm somewhere round 160) have the advantage in the search for a cheap replacement upgrade!

Yes, I hate you a_morti!!!;-)))) As recently as 1997, I was as skinny as you because I was cycling 20-30 miles a day - at speed. I was competing with commuter traffic easily. My bike had excellent road tyres on and I kept them inflated at 65-70 psi!! That makes a huge difference.

Anyway, the lesson is bro, don't get unfit, stay active. Limited rear shock options is only a small part of the downside of getting lazy - as I did.


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a_morti
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« Reply #44 on: June 23, 2017, 05:19:34 PM »

as recent as 1997? that was freakin 20 years ago mate. In 20 years....we all have gotten a bit, well......more.
A_morti is still a kid. Give him....Ohhh...I dunno....another 15 or 20 years and he'll be as round as hound, like the rest of us. Wink
ISTR Mike is around 150, which is 2/3 of your weight. Seems to make sense you'd need a stronger spring. It's not clear to me whether a blackbird shock with stock rate 1,100 and only partial damping control would work great with a 1,500 spring. Also not clear to me whether a Cbr shock with stock spring 800, even with full adjustability, could competently manage a 1,500 Spring without changing the valving. Space tiger certainly seems to be the man to work that out. (All those Spring numbers are guesstimated on the spot from rough rememberings)

I guess us skinny guys (I'm somewhere round 160) have the advantage in the search for a cheap replacement upgrade!

Yes, I hate you a_morti!!!;-)))) As recently as 1997, I was as skinny as you because I was cycling 20-30 miles a day - at speed. I was competing with commuter traffic easily. My bike had excellent road tyres on and I kept them inflated at 65-70 psi!! That makes a huge difference.

Anyway, the lesson is bro, don't get unfit, stay active. Limited rear shock options is only a small part of the downside of getting lazy - as I did.


I'm not sure I count as a kid any more, I'm from 1983. Weighed myself today though and I'm a few ounces over 11 stone, that's just under 155 in American and just under 70kg in modern money.

I certainly used to weigh less, but not sure I would even want to dip under 150.
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