1980 Suzuki GN400 - cafe conversion

[doc_rot]

Its a thread on a sweater - if you start pulling.... lol.

Thinner tires have advantages. all other things remaining equal - thinner tires mean less lean angle required for a turn, thinner tires also mean less rotational and un-sprung mass which means quicker steering (because less gyro) and better suspension reaction (less mass to move up and down).

mainly wider tires are used because they can handle more heat and load with a larger contact patch - you likely wont be generating lots of heat from excess power or braking and the bike is relatively light. I think your tire sizes are probably good picks for performance, but also consider the SR400 used 3.25/19 and 4.00/18 which commonly translate to 100/90/19 & 120/90/18. Those rim sizes you have picked OK if you decide to size up in the future as well

One thing to consider with the Borrani rims - you can see the differences in spoke angles on your existing wheels - this is because the hubs are different sizes requiring different angles. Rims are typically drilled for the application at hand because of the differences in hub sizes and widths. There is some tolerance for mixing and matching, but the hubs need to be pretty close. If you are buying pre-drilled rims on ebay this can be something to look out for.

The fun of buying these old Japanese bikes is its low stakes to chop one up. I would say if you are going to move the shock mount you might as well re-do the whole subframe to get the lines you want. You could also snake the exhaust behind the shock as well.

 

[Untame]

(Whether you pull the thread depends on who is wearing the sweater!)

Yeah, I'm leaning toward the skinnier tires as being "right" for this build. The further I get into planning it I feel my tastes evolving. In the end I want it to be a cohesive package and an honest tribute to the original vintage café racers. I won't get my way in everything because my daughter knows this is her project too, but she is primarily concerned with colors, accents, and style. She's likely to agree to whatever form I recommend to make it feel right.

So with the rims... I suppose I can ask the seller for more information on spoke angle or diameter of the hub for which it was designed. Maybe there is a narrow range of acceptable angles that have been specified for the rim.

 

[Untame]

From Borrani's USA website:

motorcycle

I measure the rear hub race diameter at 200mm and the front at 120mm.

 

[Untame]

Well, I got started.

 

[Untame]

Who are the best online retailers for custom motorcycle components? I've got my go-to's for car parts, but never ventured into motorcycles before.

 

[Untame]

Kickstand(s) question... delete the side stand and keep the center stand?

 

[Streetfighterkz]

Who are the best online retailers for custom motorcycle components? I've got my go-to's for car parts, but never ventured into motorcycles before.

That’s a broad question. What components are you looking for? Controls (clip-ons, bars, rearsets); electrical (battery, wiring parts); other?

A good place to start may be to look in the Vendor section. Speedmotoco, DimeCity Cycle, and some others are ones that come to mind sell a wide variety of parts. But there are companies that specialize in certain bits like electrical wiring and connectors.

Later, Doug

 

[Untame]

That’s a broad question. What components are you looking for? Controls (clip-ons, bars, rearsets); electrical (battery, wiring parts); other?

A good place to start may be to look in the Vendor section. Speedmotoco, DimeCity Cycle, and some others are ones that come to mind sell a wide variety of parts. But there are companies that specialize in certain bits like electrical wiring and connectors.

Later, Doug

Well, pretty much everything I will need to get from bare frame to street legal.

 

[doc_rot]

Partzilla is a good resource for OEM parts.

 

[doc_rot]

Kickstand(s) question... delete the side stand and keep the center stand?

Highly contested opinon. Any real cafe racer would certainly remove the center stand for weight savings, possibly the kickstand too depending on their commitment! If you have a paddock stand at home I don't really see the need for a center stand unless you are touring. Also on some bikes they will limit cornering clearance because they are often designed (seemingly) as an afterthought.

 

[Untame]

Partzilla is a good resource for OEM parts.

Cool.

They want me to pick between four different variations... but my VIN just says GN400.

 

[ridesolo]

Ha! Good question. I did a search of images using the four different designations you listed. At first glance I would have said the 400T because it looks like the 400TX has a more stepped seat and the XT and the XX look more like the TX than the T. I was hoping it would be something obvious like an entirely different tank or something else easy. But to make it more difficult I also found a TD and an L. Confused yet? Maybe do a search on the actual serial number of the bike and see what that brings up? Good luck!

 

[crazypj]

130 rear tyre is going to be too wide unless you get WM4 or wider rear rim, a narrower tyre on wider rim is more stable
The axle in front of fork was to reduce trail.
You'll probably have to do a search for recommended tyre size and rim width, I haven't posted the chart in probably 12 years and don't remember where it is.
I see someone posted chart.
Rim width is measured to inside edge so you remove tyre to measure it.
You measure PCD where spokes enter hub, it will be smaller than hub OD. It's a good idea to measure width between hub flanges as well as it affects spoke angle. With older steel hubs it was OK to build wheel then use a lead hammer to change spoke angle by 'give it a smack' but with old cast alloy hubs there is a chance of breaking a section out.
The suffixes are for trim levels, I would have to dig out paperwork to tell you exactly what they mean but XX is special.
This is what I do remember
G=street
N=single cylinder
L=lowrider/custom
T=touring

 

[Untame]

Cool.

They want me to pick between four different variations... but my VIN just says GN400.

View attachment 238259

Pretty sure mine is an XT. The T had alloy wheels, and the TX had a different stripe on the fuel tank.

 

[Untame]

Highly contested opinon. Any real cafe racer would certainly remove the center stand for weight savings, possibly the kickstand too depending on their commitment! If you have a paddock stand at home I don't really see the need for a center stand unless you are touring. Also on some bikes they will limit cornering clearance because they are often designed (seemingly) as an afterthought.

Well, my daughter knows what she wants, and she wants the side stand. Feels like it would require too much strength for her to operate the center stand. We can get a stand for the garage for storage and servicing.

Which brings me to a bigger issue. She wants this to be her bike that she owns, so she wants to build it with her own money. She also still wants me to get another bike so we can build them together. I was kinda thinking that I would pay for this project and own the bike, but let her make all of the design choices. This isn't what she wants. She is 15 and just got a part-time job at Caribou Coffee, so it is going to be slow going on her earnings. She is wanting to put 50% of her earnings toward the project. We'll see if she remains that focused, or if other "shiny" ends up cutting into that commitment.

We put together a spreadsheet with estimated costs for doing this project right. I believe best case scenario is about $2,000, and likely it will be a little more than that with incidentals, hardware, and miscellaneous.

Sadly, I just missed (by a couple hours) picking up another 1980 GN400 (except an alloy wheel T model) in excellent condition for $300 locally. Part of me says our project would be more fun if we were starting with identical bikes. But another part of me says that I would enjoy something a bit bigger like a 500 twin or 750 triple.

 

[Untame]

Found this 1978 Suzuki GS750, and it looks like it would be a good canvas for what I envision. Seller wants $600. It has 12,000 miles, 2-owners, and he says it needs front brake work. Unfortunately it is about 5 hours from home.

Compared to the GN400, it has the stance I'm looking for and the wheels would work perfectly with my vision (and tank shape isn't bad). Just reworking the wheels on the GN400 is going to run about $500. The less I have to modify, the more I can justify spending on the donor bike. The double cradle frame is nice, but engine tuning will be more complicated and potentially more expensive because there are 4 cylinders instead of 1.

 

[ex119x]

I have been following along and I have a few opinions on where this project appears to be going. I feel like there is lots of theorizing going on and not enough research and getting with it. Note that Suzuki uses lots of interchangeable parts so may pieces from other models will either bilt right on to yours or just require slight modifications. It is too bad that you already pulled the motor, since when it comes to suspension, I find it easier to make a change and then test ride it to see the results and modify from there.
Here is where I would start;
Replace the leading axle front forks with a set of inline axle forks from a GS450. They are both 35mm so the forks will slide right into your triples and the spacing will be the same so you can use your current front wheel. Replace the rear wheel with an 18" wheel from a GS400/425. Then ride the bike and see what you think. Too twitchy on the front? Consider a wider front tire, steering damper, taller profile front tire, 19" front wheel, shorter rear shocks, using the longer fork tubes from the GN etc. Steering too slow? Consider longer shocks, different triples, raise the fork tubes in the triples...
My point is, you can try and predict what your rake and trail will be, but my experience is that theoretical results likely will not match the actual results. I have built more than a handful of singles in my time, SR500, XT500, FT500, XL500 with front wheels from 23" to 16" and leading axle and straight line axle and the only way I have made them all work is to try them on the street so I have a baseline to work from.
I applaude you and your daughter wanting to work together and I am pleased that she wants this to be her bike. I would suggest that you try ro find another GN or related model, DR or SP, for yourself so you can try things out together and that you have a source of spare parts to use as you will need them.
Finally, what is your riding experience? If you have had some bikes and experience then getting that GS750 might be fine, but if you are also looking at a first bike then sticking with a 400 - 600 would make more sense to me.
Where are you located? This is a pretty hel[ful bunch here and if you are semi local to anybody, I am sure they would be a good resource.

 

[Untame]

I have been following along and I have a few opinions on where this project appears to be going. I feel like there is lots of theorizing going on and not enough research and getting with it. Note that Suzuki uses lots of interchangeable parts so may pieces from other models will either bilt right on to yours or just require slight modifications. It is too bad that you already pulled the motor, since when it comes to suspension, I find it easier to make a change and then test ride it to see the results and modify from there.
Here is where I would start;
Replace the leading axle front forks with a set of inline axle forks from a GS450. They are both 35mm so the forks will slide right into your triples and the spacing will be the same so you can use your current front wheel. Replace the rear wheel with an 18" wheel from a GS400/425. Then ride the bike and see what you think. Too twitchy on the front? Consider a wider front tire, steering damper, taller profile front tire, 19" front wheel, shorter rear shocks, using the longer fork tubes from the GN etc. Steering too slow? Consider longer shocks, different triples, raise the fork tubes in the triples...
My point is, you can try and predict what your rake and trail will be, but my experience is that theoretical results likely will not match the actual results. I have built more than a handful of singles in my time, SR500, XT500, FT500, XL500 with front wheels from 23" to 16" and leading axle and straight line axle and the only way I have made them all work is to try them on the street so I have a baseline to work from.
I applaude you and your daughter wanting to work together and I am pleased that she wants this to be her bike. I would suggest that you try ro find another GN or related model, DR or SP, for yourself so you can try things out together and that you have a source of spare parts to use as you will need them.
Finally, what is your riding experience? If you have had some bikes and experience then getting that GS750 might be fine, but if you are also looking at a first bike then sticking with a 400 - 600 would make more sense to me.
Where are you located? This is a pretty hel[ful bunch here and if you are semi local to anybody, I am sure they would be a good resource.

Thanks for this thoughtful and thorough post.

The bike was not running when I got it. Seller said "electrical problems" (CDI?). Also, neither tires held air.

I have zero experience riding motorcycles, so I get it that I'm better off starting with a smaller bike. Having another GN400 would be ideal for our mutual learning experience. I found a real scrapper on Marketplace for $200. I will give it another look.

So the GS400/425 is an 18in and will swap right into the GN400? Found one on Ebay. This would save some project money on rims and the hassle of relacing if I went 18in front and rear.

I'm in the La Crosse, WI area.

 

[Maritime]

Thanks for this thoughtful and thorough post.

The bike was not running when I got it. Seller said "electrical problems" (CDI?). Also, neither tires held air.

I have zero experience riding motorcycles, so I get it that I'm better off starting with a smaller bike. Having another GN400 would be ideal for our mutual learning experience. I found a real scrapper on Marketplace for $200. I will give it another look.

So the GS400/425 is an 18in and will swap right into the GN400? Found one on Ebay. This would save some project money on rims and the hassle of relacing if I went 18in front and rear.

I'm in the La Crosse, WI area.

Zero experience riding? As an MSF instructor the first thing I suggest is you and your Daughter sign up and take the MSF course. It will be the best $$$ you will spend in your life. As for that GS, Check out Murray's Carbs, He make a set of plug and play Mikuni's with 2 into 4 intakes that will make the bike run better and make more HP and Torque. Pretty sure he has GS750 ones but I can vouch for his CX500 ones and Irk can tell you the CB550 sets are worth every penny.

 

[ridesolo]

Zero experience riding? As an MSF instructor the first thing I suggest is you and your Daughter sign up and take the MSF course. It will be the best $$$ you will spend in your life.

As a former MSF Instructor I concur 100%. It's time and money well-spent. Year after year I had even the most cynical, experienced riders who were only taking the class because it was required by the military tell me they enjoyed it, learned things, and improved their skills.