Author Topic: Rear suspension upgrades  (Read 4231 times)

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Offline afkrejci90

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Rear suspension upgrades
« on: July 31, 2016, 04:44:36 PM »
So the search results didn't turn up a whole lot of useful information as I would expect swing arm swaps to be a little more challenging than fork swaps.  That being said I'm looking into upgrading the suspension to more of a sport setup.  I recently acquired an 02 gsxr 600 fork to take care of the front suspension and really improve the braking performance.  I'm trying to keep the bike look period correct and don't want something that looks too modern.  So are there any swing arms out there that can be swapped to the 750 with relative ease besides a katana 600?  How much of an upgrade is there really with a stock K swingarm?  I know they tend to have some flex to them and it will have to handle a goal of about 100hp.  Will a good set of shocks be more of an improvement than a swing arm swap?
'78 CB750K http://forums.sohc4.net/index.php?topic=105327.0
'80 CB750C - Sold
'06 CBR600RR

Offline Retro Rocket

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Re: Rear suspension upgrades
« Reply #1 on: July 31, 2016, 06:04:53 PM »
If you want good handling you'll have to shorten any monoshock swingarm, they are way too long, I have a beautiful new Calfab aluminum arm I bought from Chris at Motogpwerks In Cali, He's making a new batch now, He's also doing some with an underneath brace, Give him a ring and ask...    ;)

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750 F1 970cc
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Offline seanbarney41

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Re: Rear suspension upgrades
« Reply #2 on: July 31, 2016, 06:55:26 PM »
whatever arm you use, make sure the pivot bushings are not sloppy and well lubed...that with a good set of shocks makes a huge difference

Most 70's jap bikes swingarm is total wet noodle city, I think the stock cb750 arm is slightly better than most so there is room for improvement but the gains are not as spectacular as with a 70's Kawasaki or others

Retro, is Motogpwerks Chris doing a tubular steel braced arm of some sort that might be cheaper than his Calfab?...because that could be awesome
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Offline slikwilli420

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Re: Rear suspension upgrades
« Reply #3 on: July 31, 2016, 07:12:09 PM »
If you want good handling you'll have to shorten any monoshock swingarm, they are way too long, I have a beautiful new Calfab aluminum arm I bought from Chris at Motogpwerks In Cali, He's making a new batch now, He's also doing some with an underneath brace, Give him a ring and ask...    ;)

I actually talked to Chris last week and he is out of the cb750 swing arm business. He said it was too much hasslespecially for our bikes.
All you gotta do is do what you gotta do.

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Offline dragracer

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Re: Rear suspension upgrades
« Reply #4 on: July 31, 2016, 07:53:55 PM »
A GS 1100 arm is about 3" longer than an SOHC arm. It's aluminum and strong. I've seen them used many times on Hondas. You'd have to use eye to eye shocks if I remember correctly.

Offline seanbarney41

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Re: Rear suspension upgrades
« Reply #5 on: July 31, 2016, 08:22:16 PM »
A GS 1100 arm is about 3" longer
and renders the bike useless for anything but straightline
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Offline dragracer

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Re: Rear suspension upgrades
« Reply #6 on: July 31, 2016, 08:38:04 PM »
A GS 1100 arm is about 3" longer
and renders the bike useless for anything but straightline

So the consensus is that a 3" longer arm will adversely affect cornering on an SOHC??

Offline Don R

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Re: Rear suspension upgrades
« Reply #7 on: July 31, 2016, 09:03:58 PM »
 Yes, but so do a lot of things we always did to them.  In this case I think the OP is turning corners a lot, even road racing. Things to do with cornering are very important to him, us drag racers just need to turn enough to get off the track and back to the pit space.
 
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Offline Retro Rocket

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Re: Rear suspension upgrades
« Reply #8 on: July 31, 2016, 11:16:32 PM »
If you want good handling you'll have to shorten any monoshock swingarm, they are way too long, I have a beautiful new Calfab aluminum arm I bought from Chris at Motogpwerks In Cali, He's making a new batch now, He's also doing some with an underneath brace, Give him a ring and ask...    ;)

I actually talked to Chris last week and he is out of the cb750 swing arm business. He said it was too much hasslespecially for our bikes.

Interesting, thats not what he told me a couple of weeks ago.... ;) I went back through My correspondence with Chris and unless something recently changed his mind, he's making them, Stevo was after the last swingarm from his last batch, but Chris told him he had to wait as he needed it to help with the new ones, He even sent me pics of the new block chain adjuster he's already made and pics of them half welded up, he was making a batch of 140 arms including ones for the Eddie Lawson replica, Suzuki GS, and triumph arms , amongst others...  I'll report back...   ;) 
« Last Edit: July 31, 2016, 11:45:03 PM by Retro Rocket »
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750 F1 970cc
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Offline 754

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Re: Rear suspension upgrades
« Reply #9 on: July 31, 2016, 11:42:32 PM »
A GS 1100 arm is about 3" longer
and renders the bike useless for anything but straightline
So when they went 1 1/4 or 1 1/2 inches longer in 77 on the 750, did it become 1/2 useless for cornering?
Maker of the WELDLESS 750 Frame Kit
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Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Retro Rocket

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Re: Rear suspension upgrades
« Reply #10 on: July 31, 2016, 11:53:25 PM »
A GS 1100 arm is about 3" longer
and renders the bike useless for anything but straightline
So when they went 1 1/4 or 1 1/2 inches longer in 77 on the 750, did it become 1/2 useless for cornering?

They also changed rake at the front to compliment the rear changes Frank, NO it didn't become "useless", but it did handle different. Its all about balance. 3 inches is a big change to one end, especially if nothing is done at the other to counter the change. I've seen 2 inch over swingarms on Honda race bikes, using the 550 arm as well as its longer, but the bikes I've seen with longer arms also has offset  changes to the clamps at the front. There are very specific reasons as to why this should be done properly, Try talking to a circuit racer, totally different to straight line stuff....  Frank {dragracer}, I have  real nice GS1100 arm but I'm having it shortened 40mm at the pivot end. 
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.

Offline dragracer

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Re: Rear suspension upgrades
« Reply #11 on: August 01, 2016, 03:56:30 AM »
Hey, you all know I'm primarily into the straight-line stuff. I've never cut a corner in my life except going to the store. I have no clue on the required geometry for a road racer. I'm a knuckle dragger, not a knee dragged. Lol. Just trying to learn something about the topic.

Offline livefast_dieold

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Re: Rear suspension upgrades
« Reply #12 on: August 01, 2016, 04:21:28 AM »
So the search results didn't turn up a whole lot of useful information as I would expect swing arm swaps to be a little more challenging than fork swaps.  That being said I'm looking into upgrading the suspension to more of a sport setup.  I recently acquired an 02 gsxr 600 fork to take care of the front suspension and really improve the braking performance.  I'm trying to keep the bike look period correct and don't want something that looks too modern.  So are there any swing arms out there that can be swapped to the 750 with relative ease besides a katana 600?  How much of an upgrade is there really with a stock K swingarm?  I know they tend to have some flex to them and it will have to handle a goal of about 100hp.  Will a good set of shocks be more of an improvement than a swing arm swap?

Last year I've considered swapping swingarm with one from a Kawasaki Zephyr 550. It's about the same length of the original one, and it's made of aluminium, not steel.

You should check this thread: http://forums.kz650.info/index.php?topic=1140.0 (need to be registered to access)

Offline Motogpwerks

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Re: Rear suspension upgrades
« Reply #13 on: August 01, 2016, 10:20:38 AM »
Hi,
I am doing a small run off swingarms For cb750's and A large batch off cb750f's dohc.The reason is more people are racing and building spencer replica's than Sohc bikes nowadays .
The new 750 redesigned swingarms are no longer $650 but $900 and full braced arms are $1200-1400 depending on axle material (titainuim or 4130 )
I am building replica Eddie Lawson S1 swingarms but they are triple the work (and welding,7.25 ft) & they will be $1400-1600 they will also come with caliper bracket/axle .
No 400-550 swimgarms as most owners don't want to shell out the $$$
Most swingarms from the other 3-4 company's cost approx $900-2200 (3-6 week wait) or Harris even  $1500 pounds for a XR69 .
Currently my shop is making 140 swingarms.
I do have 1x 750 swingarm which is spoken for by a forum member and 1x cb550 left ...all old style

Offline 754

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Re: Rear suspension upgrades
« Reply #14 on: August 01, 2016, 10:48:43 AM »
When the 750 went longer in 77 the rake changed slightly on theF , but I dont think it did on the K
I know the length affects the handling but I also think it depends on the track.. Tight , twisty track short wheelbase is preffered,  but I am thinking on a high banked oval endurance race, or track with higher speed corners, the extra wheelbase may not  bother things.. That is just my uninformed theory.

 Now I wilm report about something I do actually. Know about ..flattrack..
 They do lengthen the wheelbase for longer tracks..and tighten it up for shorter tracks.. ..that is a well known fact..

 So build to suit YOUR INTENDED USE..not simply the first thing you read on the internet..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Retro Rocket

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Re: Rear suspension upgrades
« Reply #15 on: August 01, 2016, 03:43:52 PM »
Hi,
I am doing a small run off swingarms For cb750's and A large batch off cb750f's dohc.The reason is more people are racing and building spencer replica's than Sohc bikes nowadays .
The new 750 redesigned swingarms are no longer $650 but $900 and full braced arms are $1200-1400 depending on axle material (titainuim or 4130 )
I am building replica Eddie Lawson S1 swingarms but they are triple the work (and welding,7.25 ft) & they will be $1400-1600 they will also come with caliper bracket/axle .
No 400-550 swimgarms as most owners don't want to shell out the $$$
Most swingarms from the other 3-4 company's cost approx $900-2200 (3-6 week wait) or Harris even  $1500 pounds for a XR69 .
Currently my shop is making 140 swingarms.
I do have 1x 750 swingarm which is spoken for by a forum member and 1x cb550 left ...all old style

Thanks for chiming in Chris.... ;)
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.

Offline Retro Rocket

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Re: Rear suspension upgrades
« Reply #16 on: August 01, 2016, 04:01:07 PM »
When the 750 went longer in 77 the rake changed slightly on theF , but I dont think it did on the K
I know the length affects the handling but I also think it depends on the track.. Tight , twisty track short wheelbase is preffered,  but I am thinking on a high banked oval endurance race, or track with higher speed corners, the extra wheelbase may not  bother things.. That is just my uninformed theory.

 Now I wilm report about something I do actually. Know about ..flattrack..
 They do lengthen the wheelbase for longer tracks..and tighten it up for shorter tracks.. ..that is a well known fact..

 So build to suit YOUR INTENDED USE..not simply the first thing you read on the internet..

Thanks for getting all technical there Frank {754}... ;D  Small changes for different tracks is quite common, SMALL CHANGES, whats not common is large changes in geometry, at the rear for instance, lengthening the swingarm too much, and that doesn't have to be a great deal, shifts the weight distribution, unloading the rear wheel with less weight, on a track, that takes traction away form the rear wheel making it harder to get power down, Thats just one thing it does to detrimentally effect handling, it also changes swingarm angle effecting suspension rate and without getting longer shocks, lowers the rear, it also effects turn in, these are "well known facts" . Mich Doohan used to make 1mm changes to geometry and notice the differences. There is a hell of a lot of great info on the net, {and a lot of rubbish}, you just need to know what you're looking for.... ;D

PS, Flat track, drag racing and circuit racing, the only thing they have in common is that they are all have motorcycles competing, they are all set up completely different....
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.

Offline afkrejci90

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Re: Rear suspension upgrades
« Reply #17 on: August 02, 2016, 09:07:10 AM »
So the forks I picked up seem to be about 2 inches shorter than the stock forks.  So that may bring the front wheel in some so maybe a few inches in the back won't be so bad?
'78 CB750K http://forums.sohc4.net/index.php?topic=105327.0
'80 CB750C - Sold
'06 CBR600RR

Offline 754

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Re: Rear suspension upgrades
« Reply #18 on: August 02, 2016, 10:54:08 AM »
A 3 inch over arm would put you at about an inch longer than a BMW 1200 twin, and you would beabout 5 1/2 shorter than a Rocket Three..
 The 750 F is actually an inch longer than a Busa..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Retro Rocket

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Re: Rear suspension upgrades
« Reply #19 on: August 02, 2016, 06:30:33 PM »
So the forks I picked up seem to be about 2 inches shorter than the stock forks.  So that may bring the front wheel in some so maybe a few inches in the back won't be so bad?

A 3 inch over arm would put you at about an inch longer than a BMW 1200 twin, and you would beabout 5 1/2 shorter than a Rocket Three..
 The 750 F is actually an inch longer than a Busa..

afkrejci90, no, it just doesn't work like that mate, I've explained in a previous post why .   Those  comparisons are all over the place Frank, The op wants his bike to handle and you compare it to a Rocket 3... ???  It matters not what any other bikes dimensions are, a rocket 3 basically has a car engine sideways in a bike frame, the end result is a really long bike thats geometry is based on how the bike had to be built, it means absolutely nothing when compared to any other bike, not a single thing, apart from the fact that its a motorcycle. Ask yourself why all modern sport bikes are built to within a whisker of each other..? Similar rake, similar trail, similar wheelbase...?  Any modern sport bike has a longer swingarm due to 2 reasons, 1st is that the engines are so much more compact {piggy backed gearboxes], so to retain a good wheelbase the have extended the swingarm, and 2nd is that the longer swingarm {still in the compact wheelbase} makes the rear suspension perform better, its a balance, to get the same performance from a longer swingarm on a 750 Honda, you'd have to move the swingarm pivot further forward {which is impossible due to lack of room}, its as simple as that. A better change is changing the angle of the rear shocks like Pops Yoshimura did. To the OP, Your 2 inch shorter forks will decrease rake, changing the whole front end,  if you use the 17 inch wheel, which steers faster, you then need to calculate rake and trail to find a suitable offset for the triple clamps, {the GSXR clamps may work at that height, give me a few measurements and I can give you a close estimate of the trail you'll have} If you use a 19 inch front wheel, you'll still be an inch lower than stock, your trail will be less that stock which is right on the limit as far as trail goes, the bike would be more nervous at the front, more prone to tank slappers, just throwing on any swingarm and front end is NOT the way to make a older bike handle well. Adding a longer swingarm is going in the opposite direction at the rear, you'll have a faster steering front end and a slower steering rear end with a completely different front to rear weight ratio or bias, because you've effectively brought the front end in at the front and the rear end out at the rear {also watch clearance of you tire to the exhaust, you will be closer now}....  I assume when you say the you want a more "sport set up" you want to actually improve handling..? I'm going through all this at the moment, I'm currently waiting for a custom set of triple clamps to turn up in the mail to suit the 41mm forks I'm using, My front end will retain stock height and I'm running an 18 inch front and rear wheel combination and  a Calfab alloy swingarm with a inch extra length in the adjusters and a braced frame,  using the 18 inch front wheel quickens steering slightly, my clamps have less offset to keep the trail in an acceptable range for the street... I still have to work out spring rates for the front,  The bike will handle and stop very well  ;)
Anyone can just shove new parts on an old bike, I see it all the time, if that what you want to do then go right ahead, I responded because you said you want a good handling bike....

I'd love to see Frank {754} add some technical details to one of these discussions, feel free to point out any errors I've made, with a detailed explanation, just bolting on miss matched parts is NOT the way to make a good handling bike, I don't care what anyone says, and this is the reason I now usually have these discussions via PM's....
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.

Offline afkrejci90

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Re: Rear suspension upgrades
« Reply #20 on: August 02, 2016, 06:38:47 PM »
So the forks I picked up seem to be about 2 inches shorter than the stock forks.  So that may bring the front wheel in some so maybe a few inches in the back won't be so bad?

A 3 inch over arm would put you at about an inch longer than a BMW 1200 twin, and you would beabout 5 1/2 shorter than a Rocket Three..
 The 750 F is actually an inch longer than a Busa..

afkrejci90, no, it just doesn't work like that mate, I've explained in a previous post why .   Those  comparisons are all over the place Frank, The op wants his bike to handle and you compare it to a Rocket 3... ???  It matters not what any other bikes dimensions are, a rocket 3 basically has a car engine sideways in a bike frame, the end result is a really long bike thats geometry is based on how the bike had to be built, it means absolutely nothing when compared to any other bike, not a single thing, apart from the fact that its a motorcycle. Ask yourself why all modern sport bikes are built to within a whisker of each other..? Similar rake, similar trail, similar wheelbase...?  Any modern sport bike has a longer swingarm due to 2 reasons, 1st is that the engines are so much more compact {piggy backed gearboxes], so to retain a good wheelbase the have extended the swingarm, and 2nd is that the longer swingarm {still in the compact wheelbase} makes the rear suspension perform better, its a balance, to get the same performance from a longer swingarm on a 750 Honda, you'd have to move the swingarm pivot further forward {which is impossible due to lack of room}, its as simple as that. A better change is changing the angle of the rear shocks like Pops Yoshimura did. To the OP, Your 2 inch shorter forks will decrease rake, changing the whole front end,  if you use the 17 inch wheel, which steers faster, you then need to calculate rake and trail to find a suitable offset for the triple clamps, {the GSXR clamps may work at that height, give me a few measurements and I can give you a close estimate of the trail you'll have} If you use a 19 inch front wheel, you'll still be an inch lower than stock, your trail will be less that stock which is right on the limit as far as trail goes, the bike would be more nervous at the front, more prone to tank slappers, just throwing on any swingarm and front end is NOT the way to make a older bike handle well. Adding a longer swingarm is going in the opposite direction at the rear, you'll have a faster steering front end and a slower steering rear end with a completely different front to rear weight ratio or bias, because you've effectively brought the front end in at the front and the rear end out at the rear {also watch clearance of you tire to the exhaust, you will be closer now}....  I assume when you say the you want a more "sport set up" you want to actually improve handling..? I'm going through all this at the moment, I'm currently waiting for a custom set of triple clamps to turn up in the mail to suit the 41mm forks I'm using, My front end will retain stock height and I'm running an 18 inch front and rear wheel combination and  a Calfab alloy swingarm with a inch extra length in the adjusters and a braced frame,  using the 18 inch front wheel quickens steering slightly, my clamps have less offset to keep the trail in an acceptable range for the street... I still have to work out spring rates for the front,  The bike will handle and stop very well  ;)
Anyone can just shove new parts on an old bike, I see it all the time, if that what you want to do then go right ahead, I responded because you said you want a good handling bike....

I'd love to see Frank {754} add some technical details to one of these discussions, feel free to point out any errors I've made, with a detailed explanation, just bolting on miss matched parts is NOT the way to make a good handling bike, I don't care what anyone says, and this is the reason I now usually have these discussions via PM's....

This is more complicated than I thought it was going to be.  :o   ;D  When it comes to suspension geometry I am lost. I'll send you a PM on those measurements.
'78 CB750K http://forums.sohc4.net/index.php?topic=105327.0
'80 CB750C - Sold
'06 CBR600RR