Topic: General upside down (USD) fork, front and rear wheel, swing arm swap info

[InAquaVeritas]

This thread is meant to be general info dump on doing a front end swap to modern upside down racing forks and/or wheels. Anyone who has additional info, post it in the replies. Please correct me if I'm wrong, I am not an engineer and got to swap my forks with help from someone who builds racing bikes. I did a lot of research for my particular swap, because I couldn't find anything on the forum for what I wanted to do.
Make sure you check if your rake, trail and other parts of the geometry are still within rideable limits!
Parts are expensive where I live so I wanted to be sure that I got what I needed before I ordered a bunch of parts that I couldn't use.

This is the general suspension and forks FAQ (does this belong there?) http://forums.sohc4.net/index.php?topic=370.0

Last spring I swapped my '77 CB750 F1 front end out for a set of '05 ZX6R Ninja upside down forks. The reason I went for the Ninja forks was that I didn't want to mess with making the Ninja wheel fit another set of forks. I chose the Ninja wheel for the looks, so the forks were a natural choice.
This my build so far:

(http://forums.sohc4.net/index.php?topic=133411.0)

Compatibility
Alan has made the most comprehensible collection of swap info I have found in my search: https://sites.google.com/site/alansdocuments/

I found a thread that has compatibility info about swaps between different models of bikes, along with forks sizes for different models. This also lists steering stem bearing sizes
http://www.dotheton.com/forum/index.php?topic=18092.0
http://www.clubchopper.com/forums/metric-chopper-talk/77043-jap-bikes-fork-tube-sizes-neck-bearings-axle-diameters.html
http://www.customfighters.com/forums/showthread.php?t=29199

When swapping the forks, you might as well swap the bearings. This is a guide to installing these bearings: http://www.stephenbottcher.net/Honda/tapered.htm

This thread goes into specs on the different years and frames: http://www.dotheton.com/forum/index.php?topic=45379.0

Spoke wheels
The threads that got me started on my search were Industrial Cafe's 750 with GSXR forks (http://forums.sohc4.net/index.php?topic=63784.0) and Squirley's 550 build (http://forums.sohc4.net/index.php?topic=63784.0)
They both use spoke wheels with an adaptor hub on the front. For info on that swap, check the forums. Swapping it out like this means you need to figure out what hub fits the forks you'll use, along with rotors and callipers.
Not having to do this with matching wheels and forks was a reason I chose my set up, along with liking the look a lot more than spoke wheels.

Industrial Cafe goes into using the GSXR triple trees with a CB750 steering stem. Regardless of the type of swap you're doing, this needs to be done (alternative is a custom steering stem, but requires the same steps). I had a custom one made, since I had custom triples made. I'll take some decent close-up shots of that when I get it everything back when the fenders are done.

Squirley says he started with a front end to build the bike around. This requires tons of fab, like a hub he made, but makes it so you can make it to exact spec and looks.

Epskate uses the original triple from the sport bike and makes the rest fit: http://forums.sohc4.net/index.php?topic=102261.0

Elan used a HD front hub and GSXR forks: http://forums.sohc4.net/index.php?topic=79833.msg1375926#msg1375926

Modern front wheel and/or front fork info
These threads go into either making modern cast wheel work with original forks, specifically the CBR F2 and F3 wheels, or other options for forks like the R6. This requires fabrication to make it all fit: spacers, calliper mounts, etc.
http://www.caferacer.net/forum/technical/5795-modern-sportbike-forks-wheels-cb750.html
http://forums.sohc4.net/index.php?topic=99470.0
http://forums.sohc4.net/index.php?topic=22395.0
http://www.cb750.com/threads/180-New-Guy-Suspension-Question
http://forums.sohc4.net/index.php?topic=99068.msg1133048#msg1133048
http://forums.sohc4.net/index.php?topic=113011.msg1364918#msg1364918
http://www.dotheton.com/forum/index.php?topic=34920.0
http://www.fireblades.org/forums/honda-fireblade/103010-17-front-wheel-conversion-cbr-900rr-1999-a.html

RC51 SP1 swap: http://www.vfrdiscussion.com/forum/index.php/topic/56297-another-inverted-fork-conversion-6th-gen/

This is the swap I've done, but with an '09 ER6N swing arm: http://forums.sohc4.net/index.php?topic=68041.0
The ER6N has the same wheels a the ZX6R, just with a different rating (from what I could find).

More info on making a different steering stem work: http://www.xs650.com/forum/showthread.php?t=10383

AlanF. makes his CBR F2 (?) wheels fit his original swing arm and an updated front with a spacer. http://forums.sohc4.net/index.php?topic=46082.0

More wheel options for a GSXR fork: http://www.svrider.com/forum/archive/index.php/t-35903.html

Here is a lot of model specific info for dimension, rotor sizes and other sport bike measurements. http://www.vfrdiscussion.com/forum/index.php/topic/10129-swiffers-new-front-end/

jpfrk2001 has a diagram with all the specs on front forks from different makes and brands. http://forums.sohc4.net/index.php?topic=132472

Handlebar option instead of clip-ons and regular bars: http://www.sportbikes.net/forums/performance-customizing/296339-my-vfr800-w-rc51-front-end-2.html

Rear wheel swap
This thread goes into swapping the rear wheel. This isn't easy because of the original swing arm dimensions varying between models. My F model had a longer and wider arm over a K, but narrower than a Bol d'Or.
There's info on using the original and swapping out the swing arm to mount a modern wheel.
http://forums.sohc4.net/index.php?topic=82206.0
This thread goes into using DOHC arms in SOHC frames. Some of the DOHC arms fit the modern wheels. http://hondachopper.yuku.com/topic/35439/t/Swingarm-I-m-Skrewed.html#.VGogtZPF_mV
 This is one of the inspirations for my bike, most likely a Bol d'Or donor bike, since the wheel fits the original arm.
http://www.stinkyfab.com/blog/?p=310

I used an '04 ZX6R rear swing arm with the '05 wheel. I needed some spacers for the axle and calliper mount, but the rest fits like a glove. There is no modification to the frame or swing arm to make it fit. I went for the '04 swing arm because it's a simple box construction, where the '05 is one of those high tech looking ones. I got a chance to measure the width of the pivot point at a local Kawa dealer.
I gained about 4"/10cm of extra length, which in turn sorted out my rake and trail.
I'm running a 160/60/17 Michelin PilotRoad 4 because I will ride this all year and need some serious rain grip. Wanted a dual sport tire, but they don't go over 150. The wheel I'm using would NOT fit the original swing arm, it would mean lengthening the swing arm and possibly widening it.

This thread has all the numbers on the front and rear wheel bearing sizes for the Zx6r/ZX10R: http://www.zx-10r.net/forum/showthread.php?t=54599

My machineshop guy used the ZX6R axle and made it into a spacer/sleeve for the original axle. This means I don't have to make new spacers, use oddball bearings and keep my frame as is.



A list of rear axle diameters: http://www.dotheton.com/forum/index.php?topic=20952.0

Sprockets
Changing wheels means changing sprockets a lot of the time, along with a possible offset. The CB's used different types of sprockets and chains for different models as far as I could work out. My '78 CB750 F2 engine (most likely the F1 a well) uses a 630 chain, while my new '05 ZX6R wheel runs a 520 sprocket.
The wheel sprocket is brand new, so I will go off that to save some money. The chain is also lighter and quieter from what I've read. I will need to grind down the sprocket carrier to make up for some of the offset (0,43"/11mm). Make sure the chains clears your tire and swing arm before you start grinding!
The front sprocket needed to be replaced regardless, but it now also needs an offset. Honda used the same sprocket axle on a lot of different models with different offsets and chain sizes. Using a stock, and therefore cheaper, sprocket of a different model makes up for the rest of the offset and chain size.

Changing wheel sizes and sprockets will have an effect on how your bike performs compared to the original, effectively gearing the bike up or down. This causes power, top speed, acceleration and fuel efficiency to drop or peak.
www.gearingcommander.com is a site where you can select your original bike, insert the specs for the current set up and get an idea of the effects of changes to your bikes performance.
If I use my new rear sprocket and I go up 1 tooth on the front the performance will stay almost the same.

I will post a site that lists all the front sprocket axle diameters later on, as I can't find it right now.

[cougar]

InAquaVeritas ; Absolutely Super Coool of you to post such a wealth of information for others to use !!! I'm speechless other than to say THANKS !!!   IMHO this should be placed somewhere "PERMANENT" for others to always have access too.   ...cougar...

[InAquaVeritas]

InAquaVeritas ; Absolutely Super Coool of you to post such a wealth of information for others to use !!! I'm speechless other than to say THANKS !!!   IMHO this should be placed somewhere "PERMANENT" for others to always have access too.   ...cougar...

Thanks! My pleasure. When I was looking for info, I was hoping to come across a  thread like this. I hope this helps everyone with their swaps.

Again, any additional info is welcomed!

[70CB750]

Subscribed.

[Gman]

InAquaVeritas ; Absolutely Super Coool of you to post such a wealth of information for others to use !!! I'm speechless other than to say THANKS !!!   IMHO this should be placed somewhere "PERMANENT" for others to always have access too.   ...cougar...

I will second that.  Sharing is caring.
Peace,
G

[brandEn]

Nice post!

[InAquaVeritas]

Added a new site to the post.

www.gearingcommander.com

This will let you play around with different sprocket set ups and see the effects on top speed and rev's at certain speeds, along with a host of other features.

[Retro Rocket]

Don't just focus on rake and trail, you need to look at wheel sizes and their inherent qualities, eg; smaller wheel, faster steering than a bigger wheel, and swing arm length, the swinger on your bike is too long and will slow steering at the rear while the front mods will speed steering up, proper handling is a good balance of both front and rear and both front and rear effect each others performance...

[InAquaVeritas]

Yes, that as well! Did you refer to my bike specifically mentioning the swing arm? If so, I'd appreciate any input on handling, that part I'm fairly new to.
As I mentioned I had help from a guy that builds racing bikes. He is new to this setup as well, but has lot of knowledge and I know that knowledge is here along with the experience. So please, if anyone has anything to add, feel free.


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[Retro Rocket]

Yes, that as well! Did you refer to my bike specifically mentioning the swing arm? If so, I'd appreciate any input on handling, that part I'm fairly new to.
As I mentioned I had help from a guy that builds racing bikes. He is new to this setup as well, but has lot of knowledge and I know that knowledge is here along with the experience. So please, if anyone has anything to add, feel free.


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Look at drag bikes, they have long swingarms for 2 reasons, stops the front wheel from going skywards and adds stability in a straight line, on the street it makes the back fight the front when cornering, the 750/4,s handle best {K models} with between 1-2 inches of extra length, they were raced commonly with 1 inch longer swingarms, the F models had this mod as a stock feature as well as a bit more trail to match, they were noticeably more stable than the K models and nearly every bike test from the era stated this.

Modern bikes have noticeably longer swingarms mainly due to engine technology, making the engines more compact, therefore the swingarm pivot is much further forward, to maintain the handling balance the swingarm is much longer to get the desired wheelbase, thats why there are virtually no monoshock swingarms that work well on our bikies without modification {that is of course you are after good handling characteristics}. I have a GSXR1100J model swingarm converted to twin shock and i've had it considerably shortened to fit an F model frame, I'm also having a GS1100 alloy arm shortened to fit a K2  , My 3rd swingarm {which I will purchase as soon as I am cashed up} is 1 inch longer than the stock K model and is a production aftermarket item and based on the 1970's race bike specs...  Unfortunately, there is far more information on front end mods than rear mods and a lot of misinformation based on "what looks good", rather than what actually works...  We haven't even got to rear shock angle yet...

[MidnightLamp]

Have you considered at all that there is a fair bit more to swapping suspension on the front/rear of a bike than "does it fit?"

This would be like saying the front subframe and suspension from a honda S2000 fits into the body of a '92 honda civic, therefore I'll put it in in order to get the civic to handle like the s2000.

There is a large length change, a large change in wheel diameter (if going to sportbike mags from stock honda stuff), and there is a change in triple tree offset as well, all of those things have more than a small effect on the handling of the bike.

 

[InAquaVeritas]

The math has been done and it should work, but I'm always open to any suggestions.
I have a custom triple and the spring mounts are professionally welded by the guy doing all the math. I'm picking up parts next week and will talk all this over with him. Right now I can still make changes. I had taken into account the slower steering at the rear and was thinking of mounting a steering damper (fork to frame probably) to counter speed wobble.


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[MidnightLamp]

I apologize if that came out rude! The things to check are to make sure your net rake/trail are reasonable, and also that you haven't deviate from the stock chassis specs too far in terms of axle heights, etc... It's not a linear relationship (where you change the rake to decrease the trail, but decrease the offset to increase the trail), as there is a lot of chassis balance that is disturbed (From CG placement etc...). As for the rear, same situation with adjusting the shock mount location as it changes the inclination of the shocks, which affects the spring rate of the rear as well as the response. The last thing you want is a front heavy bike with an increasing front weight bias under dive, as it causes the rear to feel loose as the front steering becomes twitchy. Couple that with a smaller front wheel and you've got a pretty finicky set-up to deal with.

[Retro Rocket]

The math has been done and it should work, but I'm always open to any suggestions.
I have a custom triple and the spring mounts are professionally welded by the guy doing all the math. I'm picking up parts next week and will talk all this over with him. Right now I can still make changes. I had taken into account the slower steering at the rear and was thinking of mounting a steering damper (fork to frame probably) to counter speed wobble.


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The way to avert "speed wobble" is to get the geometry right, a damper will help with road irregularities and pot holes, lines, grooves  and such, but good geometry is what you should be aiming for, front and rear....

[Retro Rocket]

I apologize if that came out rude! The things to check are to make sure your net rake/trail are reasonable, and also that you haven't deviate from the stock chassis specs too far in terms of axle heights, etc... It's not a linear relationship (where you change the rake to decrease the trail, but decrease the offset to increase the trail), as there is a lot of chassis balance that is disturbed (From CG placement etc...). As for the rear, same situation with adjusting the shock mount location as it changes the inclination of the shocks, which affects the spring rate of the rear as well as the response. The last thing you want is a front heavy bike with an increasing front weight bias under dive, as it causes the rear to feel loose as the front steering becomes twitchy. Couple that with a smaller front wheel and you've got a pretty finicky set-up to deal with.

The other thing is that if the trail falls in the stable category, the rake and wheel size are also essential to be right, the 17 inch front wheel on a slower steering front end will make the bike feel like its "falling" into corners.... When changing wheel size and triple clamp offset you must take into consideration you can't alter the rake....

[InAquaVeritas]

The math has been done and it should work, but I'm always open to any suggestions.
I have a custom triple and the spring mounts are professionally welded by the guy doing all the math. I'm picking up parts next week and will talk all this over with him. Right now I can still make changes. I had taken into account the slower steering at the rear and was thinking of mounting a steering damper (fork to frame probably) to counter speed wobble.


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The way to avert "speed wobble" is to get the geometry right, a damper will help with road irregularities and pot holes, lines, grooves  and such, but good geometry is what you should be aiming for, front and rear....

That's exactly what I'm hoping to achieve. If it turns out this setup won't be good to ride I'll definitely change it. I want a well riding awesome looking bike, in that order.
Thanks for making me this over this again, I will double check the measurements and maybe ask for help here if something is up. I'll quote all your info into the original bit if that's ok? This helps a lot for my builder and hopefully future builders, so people don't end up on super sketchy bikes.


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[Retro Rocket]

Use away. As I haven't started on the main bike I wish to keep, the one that will have all the best mods, I can't give specific exact measurements as I haven't used it myself, I'm in the ball park with everything but i want perfection, or as close as i can get so i can justify the cost of the build . I have a trail calculator that helps, but I also know a couple of  guys successfully racing very fast 750/4's, some of the best in the country , so when it comes down to my "keeper" bike i will be picking their brains, I want as close to modern handling as possible using the stock frame, braced of course... , I'll be using 18 inch wheels at both ends..

[RickRR]

This is something I would like to do eventually , thanks for the info.
Nice post !

[InAquaVeritas]

Use away. As I haven't started on the main bike I wish to keep, the one that will have all the best mods, I can't give specific exact measurements as I haven't used it myself, I'm in the ball park with everything but i want perfection, or as close as i can get so i can justify the cost of the build . I have a trail calculator that helps, but I also know a couple of  guys successfully racing very fast 750/4's, some of the best in the country , so when it comes down to my "keeper" bike i will be picking their brains, I want as close to modern handling as possible using the stock frame, braced of course... , I'll be using 18 inch wheels at both ends..

I apologize if that came out rude! The things to check are to make sure your net rake/trail are reasonable, and also that you haven't deviate from the stock chassis specs too far in terms of axle heights, etc... It's not a linear relationship (where you change the rake to decrease the trail, but decrease the offset to increase the trail), as there is a lot of chassis balance that is disturbed (From CG placement etc...). As for the rear, same situation with adjusting the shock mount location as it changes the inclination of the shocks, which affects the spring rate of the rear as well as the response. The last thing you want is a front heavy bike with an increasing front weight bias under dive, as it causes the rear to feel loose as the front steering becomes twitchy. Couple that with a smaller front wheel and you've got a pretty finicky set-up to deal with.

I'm so happy I started this post, because it made me go over all the measurements again and there has been a major miscommunication between my welder/fabricator and me. He told me my setup is right on the edge after I said I want a bike that handles as close to original as possible. Which I took as a direct answer to my request, turns out he meant that it is on the edge of rideable...hooray...
Retro, can I pick your brain a bit about those perfect dimensions? Mainly what I need to aim for in general terms. What wheels will you use? Custom spoked wheels or cast modern wheels?

Look at drag bikes, they have long swingarms for 2 reasons, stops the front wheel from going skywards and adds stability in a straight line, on the street it makes the back fight the front when cornering, the 750/4,s handle best {K models} with between 1-2 inches of extra length, they were raced commonly with 1 inch longer swingarms, the F models had this mod as a stock feature as well as a bit more trail to match, they were noticeably more stable than the K models and nearly every bike test from the era stated this.

Modern bikes have noticeably longer swingarms mainly due to engine technology, making the engines more compact, therefore the swingarm pivot is much further forward, to maintain the handling balance the swingarm is much longer to get the desired wheelbase, thats why there are virtually no monoshock swingarms that work well on our bikies without modification {that is of course you are after good handling characteristics}. I have a GSXR1100J model swingarm converted to twin shock and i've had it considerably shortened to fit an F model frame, I'm also having a GS1100 alloy arm shortened to fit a K2  , My 3rd swingarm {which I will purchase as soon as I am cashed up} is 1 inch longer than the stock K model and is a production aftermarket item and based on the 1970's race bike specs...  Unfortunately, there is far more information on front end mods than rear mods and a lot of misinformation based on "what looks good", rather than what actually works...  We haven't even got to rear shock angle yet...

I'm now looking for a swing arm that fits my massive wheel (does have the narrowest possible tire, 160/60/17). When I was initially looking for parts I have come across some 70's-spec swing arms, but never saved them. Can't find em now, anyone has any suggestions?
Shortening those GS1100 arms, does that change the width at the axle? Will those fit a big wheel?

Using my Koni shocks that were on it when I bought the bike, on a shorter arm will raise the rear of the bike. I'm thinking of using a stepped clamp like the modern racers have originally, this way the forks become relatively longer and closer to the original length. This way I can compensate for the lift in the rear.
Does this make sense to do or is it money down the drain? I already have a custom triple with the original offset.

Again, thanks for pointing all this out to me, this saves me a lot of trouble later on! I will add to the rear replacement later on, when I've got some time.

[Retro Rocket]

Ok, before we go anywhere, how much are you prepared to spend on getting this right, for me, even though i'm far from rich, am prepared to spend what it takes. I'm leaning toward spoked wheels but have looked at both PVM vintage wheels and Campognolo vintage wheels {both 5 spoke in gold}. There is modifying to do on any swingarm that didn't belong to these bikes, Motogpwerks are making new Calfab aluminum swingarms for our 750's, they are 1 inch over stock and I will be buying one very soon. The GS1100 arm i'm using soon, I'm having it modified at the pivot end, shortened and modded to fit the Honda frame, I have a guy that builds classic and vintage race bikes do it for me, he's done a GSXR1100 arm for me previously, you should really have someone thats familiar with these mods do the work, your "friend" sounds a little out of his depth, no offense intended. You should be able to fit a 160 in, i've had a 4.5 inchx17 Suzuki rim in a stock arm and it just cleared with a 180 racing slick on it, so a 160 should fit. If using spokes 4.25 inch will be about the right size, the only 4.5 inch rim i've seen was the campognolo vintage. I am using 18 inch rims front and back, these are the sizes {rim heights}that were most commonly used when racing these bikes, I will run a 4.25 x18wide rear and a 2.5 or 2.75x18 front width rim. You want to aim at making the trail as close to 4 inches as you can, this adds some stability, stock is around 3.75 inches and is a little nervous, most modern sport bikes are around 4 inches, rarely under that these days, and sometimes fractionally more., With the slightly more than stock trail {@4 inches} the 1 inch longer swingarm will compliment this well as it adds slight stability at the rear as well, this should give a nice balance to the modifications. The way to get the trail at the front correct is to use custom made triple clamps, thats what i'm doing, I have a trail calculator you can have a copy of but i'll need an email addy to send it to you, its in PDF format. before you get clamps made you need to know what wheels you are using, the tires fitted and some measurements taken, its all in the converter. If you are using USD forks there's a guy on the forum making adjustable offset triple clamps, they have 3 different settings for offset and may be just what you'll need... 

[InAquaVeritas]

I have a guy that builds classic and vintage race bikes do it for me, he's done a GSXR1100 arm for me previously, you should really have someone thats familiar with these mods do the work, your "friend" sounds a little out of his depth, no offense intended. [...]
If you are using USD forks there's a guy on the forum making adjustable offset triple clamps, they have 3 different settings for offset and may be just what you'll need...

I really appreciate that everyone here is always looking out for each other and helping people not make mistakes, I do not feel offended at all regarding my friend. I talked to him yesterday and asked the same question I asked here and he came up with the same answers. He has shortened and lengthened swing arms before, so I'm confident about him doing this work.
He already gave me a slightly shorter offset to make up for the +/- 2,5 cm/1" (this is +/- with sag and wear) loss in fork length.

The mistake was because of me not being clear enough and him not thinking ahead when I suggest things. Now that I know that, I was able to get down to two options that will get me closer to my original wheelbase and dimensions (excluding wheel size and ground clearance).
We have now agreed on shortening my ZX6R swing arm by about 10 cm/4" or using a CBR600 PC31 swing arm which has the same stock length as a regular K-arm, 41 cm/16,1" from pivot axle to centre of wheel axle slot, 23,5 cm/9,25" OD pivot axle and 23 cm/9" ID at the wheel axle.
The ZX6R arm is most likely a basic box construction with the axle blocks slotted in at the ends and welded on. If this one gets used, the blocks will be cut off and the box frame shortened and the blocks welded back in.
The shock mounts need to be shortened and relocated as well, to restore the right angles and geometry for the rear shocks and the angle at the steering head. Right now it is slightly leaning forward and effectively making the angle shorter.

When I get all my parts back, I will extend the original post with all the comments and some close up photos.

Any suggestions to add to the original post, wether its tips, tricks or major pitfalls, post away and I will add it.

[Retro Rocket]

I've answered some of this in your other thread....

[Retro Rocket]

Just thinking out aloud here mate, Motogpwerks has a new 750 swingarm thats a work of art.... This is a pic of an unfinished one...



There are pics of the finished items on his facebook page...

[InAquaVeritas]

I've answered some of this in your other thread....

Appreciated and replied! Will use your info in this thread later on.

Just thinking out aloud here mate, Motogpwerks has a new 750 swingarm thats a work of art.... This is a pic of an unfinished one...



There are pics of the finished items on his facebook page...

That is a work of art! I'm going to gawk at it right now!! I'm assuming (although that being the mother of all #$%* ups) that this is a CB750 dimension race arm in big rear wheel size?
Off topic, I've made up my mind: welding and fabrication classes to be booked! I need to be able to make all this!!

[Retro Rocket]

I've answered some of this in your other thread....

Appreciated and replied! Will use your info in this thread later on.

Just thinking out aloud here mate, Motogpwerks has a new 750 swingarm thats a work of art.... This is a pic of an unfinished one...



There are pics of the finished items on his facebook page...

That is a work of art! I'm going to gawk at it right now!! I'm assuming (although that being the mother of all #$%* ups) that this is a CB750 dimension race arm in big rear wheel size?
Off topic, I've made up my mind: welding and fabrication classes to be booked! I need to be able to make all this!!

If you can fit a 4.5 inch rim into a stock arm the you should have no trouble fitting one into the Motogp arm, its also 1 inch longer than a stock K arm....