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Discussion Starter · #1 ·
I bought my Z125 Pro yesterday. It is my 44th motorcycle (I've been motorcycling for over 50 years), and shares its parking space with a highly modified Yamaha R3 that has been lightened by 44 lb (which got the Yamaha down to 300.7 lb before gas).

My intent was to buy either the Z125 Pro or the Honda Grom, up the power just a bit, lighten the bike aggressively beyond its already low starting weight, and beautify it and improve its performance, making it into a "little jewel"!

I have been modifying bikes, from 50cc through 1800cc, all my adult life, and the models chosen have included standards, cruisers, and sportbikes. The brands have included Suzuki, Honda, Norton, Kawasaki, Yamaha, Ducati, Aprilia, and KTM (I may have forgotten 1 or 2). The bikes have included single cylinder, twin, triple, four cylinder, and 6-cylinder engines. Weights of the bikes have ranged from 275 lb to over 800 lb. Lately my fixation has been on small, lightweight, very nimble motorcycles.

Both my pre-purchase research and my first ride uncovered some really interesting things about this tiny motorcycle:

- It weighs 224.8 lb as delivered, BUT that includes 2.0 gallons of fuel, which means the bike itself weighs just 212 lb. before gas. The Grom is notably more: 229 with gas, and about 219 before gas.

- It is relatively easy to get LOTS of weight off of the 212 lb Z125, via simple removal of OEM parts and substitution of lightweight replacement parts. I'm pretty confident I will get the bike below 200 lb pretty quickly, and haven't yet determined a sensible lower limit!

- I have examined all the Z125 dyno charts available online, and using the overall most conservative one I could find (i.e. lowest hp overall through the rpm range and a peak rwhp of just over 8), I modeled the performance of the Z125 in my computerized performance modeling software, and the software says the bike will do about 66 mph = 106kph flat out before any engine modifications (assuming proper break-in, reasonable sized 175 lb rider, clean and lubed chain, flat road, no headwind or tailwind, etc). Headwinds, hills, and large or heavy riders of course have a dramatic effect on the Z125's modest power output.

- Doing some "what ifs" with the software, I also discovered that there is NO top speed advantage in changing the gearing. If I increased the size of the countershaft sprocket, the bike went slower. If I decreased the size of the countershaft sprocket, it went slower. The way to get more speed from this bike is to leave the gearing alone and simply enable better higher rpm breathing via a combination of GOOD exhaust, intake, and electronic retune.

- The potential for more engine power is lower than on the Honda Grom because the Z125 can apparently only be punched out to 143 cc via a big bore kit, before requiring machining the cases ($$$). (The Grom can be taken much further - to about 180cc or so - because it can accept larger diameter pistons without machining the cases). 143cc bog bore kits, 4-valve heads, higher compression piston designs, etc are available but costly. However, I don't think I need MUCH more power. Just a bit.

- It seems easy, although not cheap, to get roughly about 15% more power, via a combination of GOOD well-designed exhaust, the Chimera intake, and either a Power Commander V, Bizzaz, or direct ECU retune.

- You can't go much higher anyway without needing much better tires, as the OEM IRC tires are rated to only 74 mph maximum speed ("51L" rating)!

- There are carbon fiber body parts available (e.g. front fender, rear fender, undercowl)

- Ohlins suspension components, front and rear, are an absolute BARGAIN for the Z125 compared to almost every other bike - at least 30% less costly, and some 50% less costly than for other bikes!

- Fender eliminator kits, LED signals, rearsets, adjustable and foldable high quality hand levers, and a host of other small items are readily available form multiple sources at reasonable prices.

- BST carbon fiber wheels are available, and relatively speaking a "bargain" compared to the cost of BST wheels for more conventionally sized bikes (about half the cost).

- I refilled my fuel tank after my first ride of 30 km duration, and with only that 30km on the odometer, I refilled the tank "to the brim" and the fuel mileage calculated out to exactly 2.0 liters/100 km = 117.6 US miles per gallon! Remember, this is an engine fresh from the dealer, and still not broken in! (I had to resist the urge to allow the eager engine to seek higher rpm! It IS after all redlined at a lofty 9800 rpm).

- Riding this bike is a very different riding experience. The ONLY parts of the bike that I could see during my ride (without consciously looking down at the "dashboard" or at the mirrors) were the top TIPS of the mirrors. This made it feel like I was "flying" just above the road - like some caped crusader!

- Before my ride, I thought the bike would feel weak when accelerating, but it really does not. It feels peppy thanks to that "perfect" factory gearing.

- Before my ride, I thought the bike would be "hard" to get above city speeds, but that proved to be untrue. In fact, I had to WATCH the speedo and tech, as the bike seems to want to always go faster and the engine to spin higher.

- Before my ride, I thought that uphills would really slow the bike, and they DO! The power to weight ratio is not very good, especially with me aboard, as I weigh about 195 but also wear 16 to 20 lb of safety gear when I ride, so weigh about 211 to 215 lb when riding . . . :)

- Because I am breaking in a brand new engine, I was unable to run at "highway speeds" yet, so cannot comment yet on how much wind resistance I will feel because of (1) no fairing at all on the bike and (2) being 195 lb and wearing all thta additional gear, I am NOT a "small" cross-section exposed to the wind! I'll have to wait until I have broken in the engine before I can assess this realistically.

Those are my impressions so far . . .

I am looking forward to an exciting project over the winter, during which I will be upgrading components, reducing weight aggressively, and adding a bit more power.

Jim G
 

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Welcome Jim!

It's good to see feedback from a savvy rider/builder. It should be fun to watch your bike get faster and lighter.
 

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Discussion Starter · #4 · (Edited)
That fender has got to be good for at least 8 lbs!
Do you mean the oEM fender or the potential carbon fiber fender?

And which fender - front or rear?

Note that what I found on the Yamaha R3 is that the OEM plastics are thin enough that replacement carbon fiber ("CF") parts do NOT reduce the weight - they merely just about exactly match the OEM weights! On such bikes, you use CF not to save weight, but because it looks way better! When you see a WELL MADE CF part with a proper clearcoat for long-term protection, the texture will just captivate you. THAT's why I went CF for a couple of body parts on the Yamaha.

The OEM plastic front fender on the Yamaha R3, despite its bulbuous appearance, weighs only 0.93 lb. The CF replacement weighs 0.66 lb, but still adds the same OEM hardware so the net saving was only 0.27 lb.

Now if you are replacing METAL, the story is very different. BIG weight savings. 15 years ago, I redid a Ducati Monster S4, replacing virtually every metal part except controls with CF parts. That included even the fuel tank, the wheels, and even the headlight bucket. On that bike, I got the bike down to about 375 or 380 lb. A 916cc 4-valve twin with desmo valves in a 380 lb bike gave a very exciting ride. The bike also took 2nd place overall at a big Dallas motorcycle show.

Jim G
 

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I would assume he means the rear fender, with the big steel rod running down the spine. Then again I haven't closely inspected the front fender, maybe it's heavier than it looks.

I like the look of CF but I prefer it in moderation. The H2 is a nicer bike to look at despite the H2R being a completely mental track weapon.
 

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Discussion Starter · #7 ·
Year rear fender. There is a sub frame under that plastic.
1. Do you mean the LOWER rear fender that follows the radius of the rear tire, or the UPPER fender that holds the license plate and the signal lights?

2. Is the "subframe" permanently part of the fender or does the plastic detach from it?

Jim G
 

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The "upper" rear fender.

The "subframe" is attached to the main frame under the tail with 4 bolts. It's the spot that all the fender eliminators and racks and stuff like that mount to.

Subframe bolts to main frame, plastic bolts to subframe.
 

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Discussion Starter · #9 ·
The "upper" rear fender.

The "subframe" is attached to the main frame under the tail with 4 bolts. It's the spot that all the fender eliminators and racks and stuff like that mount to.

Subframe bolts to main frame, plastic bolts to subframe.
Ok, thanks for explaining it! The weight saving then basically becomes the weight of the big plastic piece that the license plate and signals attach to, minus the weight of the "new" license plate bracket in a fender eliminator kit.

To give you an order of magnitude on that weight saving potnetial, on the Yamha R3, which had a similar OEM setup, the NET weight saving after replacing it with a Vagabond kit and TST rear LED signals was 2.1 lb.

I just need 6 things like that to blow past the 200 lb weight milepost. :)

Jim G
 

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I would say to just change the exhaust, I bet you get a net 10 pounds right there. The tail section is probably about 2 pounds and only ounces to put on an eliminator and different lights.

You could shave a little with LED front signals, but by the time you put in the flasher fix it won't be very much.

You could eliminate the headlight and mount, replace it with a number plate, this would net about 3 pounds.

Battery needs to go, lithium would net you a couple of pounds.

As far as weighing individual pieces, a better way would be to get two larger scales and weight the bike at each end after doing everything. Also gives you an idea of the front/rear bias and how you may want to change things to fix handling issues.

Also keep in mind that aerodynamics play a huge role in these under powered machines, the more drag created by open framework can really offset any gains from lightening. A full fairing made from light fiberglass or CF might do better down the straight that no body at all, even if it weighs the same or more than the stock body.
 

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- The potential for more engine power is lower than on the Honda Grom because the Z125 can apparently only be punched out to 143 cc via a big bore kit, before requiring machining the cases ($$$). (The Grom can be taken much further - to about 180cc or so - because it can accept larger diameter pistons without machining the cases). 143cc bog bore kits, 4-valve heads, higher compression piston designs, etc are available but costly. However, I don't think I need MUCH more power. Just a bit.

Finbro/Monkeyfather has a 200cc complete motor they are selling. Not cheap... but neither are carbon fiber wheels...
 

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I'm sure you are already thinking this but definitely go with an integrated turn signal tail light. I did the MNNTHBX Basic fender elim and I don't think I lost any weight due to re-using the signals/license light. They were surprisingly heavy.

MNNTHBX sells an OEM looking integrated tail and TST has a cool design as well. Haven't heard anything negative about either of them, pick your favorite and you can't go wrong.
 

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Finbro/Monkeyfather has a 200cc complete motor they are selling. Not cheap... but neither are carbon fiber wheels...
0.o! What's the market like for selling a complete stock Z125 engine with ~200 miles on it? (asking for a friend)
 

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Discussion Starter · #15 ·
I would say to just change the exhaust, I bet you get a net 10 pounds right there. The tail section is probably about 2 pounds and only ounces to put on an eliminator and different lights.

You could shave a little with LED front signals, but by the time you put in the flasher fix it won't be very much.

You could eliminate the headlight and mount, replace it with a number plate, this would net about 3 pounds.

Battery needs to go, lithium would net you a couple of pounds.

As far as weighing individual pieces, a better way would be to get two larger scales and weight the bike at each end after doing everything. Also gives you an idea of the front/rear bias and how you may want to change things to fix handling issues.

Also keep in mind that aerodynamics play a huge role in these under powered machines, the more drag created by open framework can really offset any gains from lightening. A full fairing made from light fiberglass or CF might do better down the straight that no body at all, even if it weighs the same or more than the stock body.
Great analysis and observations! Here are some comments on them:

The exhaust savings I have found on line have surprised me by being a little low compared to my expectations. I easily dropped 9.7 lb on the Yamaha R3 by replacing the OEM exhaust. But the numbers I am seeing for the Z125 are a lot lower - around 4 lb for a quality exhaust system that preserves the ability to ride on a public street withoiut attracting police attention.

Your 2 lb number on the tail section sounds about right, as I got EXACTLY 2 lb net reduction on the Yamaha R3 using the Vagabond kit.

You are right about the LED front signals. While I would normally do them as a safety and aesthetic as well as weight reduction improvement, I do not like the idea of adding that TST device to the wiring. I strongly prefer to leave factory wiring unaltered for reliability and durability reasons.

I can't remove the headlight and mount as this will be a STREET bike, not a racebike or showbike.

Yes, replacing the OEM lead acid battery with a Lithium battery is a given, as there is both a surprisingly large ( 2 to 3 lb) weight reduction dependant on the exact Lithium battery chosen, PLUS Lithium batteries do a great job starting the engine quickly AND they tend to not lose charge as quickly as lead acid batteries. And, since the battery is located so high on the bike (right under the seat), there is a handling benefit too.

I have tried in the past on other bikes to use scales to weigh the entire bike at front and rear, and it does not provide accurate results even when done very carefully. The problem is that to keep the bike upright, you have to exert some force on it with your hands, and each time you nudge it to keep it roughly upright (no practical way of knowing when it is EXACTLY upright and therefore putting ALL its weight onto the scales) the scale readings shift. Also, to get anywhere NEAR accuracy, you need a set of racing scales, and those are about $1000 for decent ones.

I have found by all the past experience that the best method by far is, for each individual modification, to weigh the sum total of all parts removed for that mod, weigh the sum total of parts added to the bike to replace them, record both weights, and calculate the net difference (i.e. sum total of all parts added for that specific mod minus sum total of all parts removed for that specific mod = net weight change). This approach gives you BOTH the overall weight effect on the bike AND the individual effect of each mod.

When you add a column to the table that shows the COST of each mod, you can then add another column that shows, for each mod, the "pounds removed per dollar spent". This can help guide your, and other Z125 owners', priorities on which to do first.

I also make note of the relative LOCATION on the bike of each component change, so that the effect on front versus rear weight distribution can be calculated as well. On the Yamaha R3 for example, of the total of the net 44 lb removed, 27 lb was off the rear axle versus the front.

Your comments on bodywork are correct IF you actually remove any bodywork. I don't plan to do that. But ANYWAY, on the Z125, weight reduction will NOT have much impact on top speed or high speed performance, as the bike is so underpowered that it is wind resistance that almost entirely determines top speed and high speed performance EXCEPT when climbing or descending hills. The reasons for removing weight on the Z125 center on (a) slightly better acceleration and (b) notably better handling, and (c) the especially favourable moment of inertia reductions via reduced rotating mass in tires, wheels, sprocket, brake rotors, and primary gear. THAT is where the rider will notice big differences.

Jim G
 

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If you get a pair of decent digital scales, you can get a fairly reliable weight out of them. But you are right, as you exert force on the bike to keep it balanced, you do indeed change the weight on both scales. It's a matter of trying to read each one fast enough during that moment when the bike is balanced. And also fudging a few pounds. Best way would be a strap around the middle and I high accuracy scale suspended by a hoist.

That said, I keep thinking about building something that will hold the bike by the axle(s) on my scales so it stays upright by itself, then just tare the weight of this support. Haven't gotten there yet, but probably will sometime in the future.
 

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Discussion Starter · #17 · (Edited)
. . .

That said, I keep thinking about building something that will hold the bike by the axle(s) on my scales so it stays upright by itself, then just tare the weight of this support. Haven't gotten there yet, but probably will sometime in the future.
That's a GREAT idea! But it will be hard to make the 2 supports (front, rear) small enough to fit on the scale platforms AND keep the bike reliably from falling, as the bike will have tremendous leverage over anything narrow enough to fit on a portable scale. It will also be a 2-person job to get it all set up each time you weigh the bike without dropping the bike.

I suspect the most practical way for an individual owner (not the well-resourced factory) to get an accurate overall weight would be to put the entire bike on an accurate local commercial scale large enough to accept both tire contact patches AND the sidestand, and accurate enough to accurately detect single digit weight changes as you add or remove stuff.

But this would still not give you the front versus rear weight distribution.

And most commercial scales that we ordinary people have access to only display weights to the nearest 10 lb, or worse, nearest 10 kg (like our local scales here on Vancouver Island, Canada), so as to make clear that they are NOT accurate beyond that range. Some will display to single digits, but the specs say the accuracy is NOT "single digit" but rather several lb or kg. :(

The most accurate commercial scales large enough to hold an entire motorcycle on its sidestand are probably the "counting" scales used when shipping or receiving large boxes of items (like metal hardware items, or machine parts) where each box contains dozens, hundreds, or thousands of identical parts. Those scales have to be pretty accurate, because some very small, lightweight parts can be very expensive, and invoices and payments are calculated based on their "count" of the number of parts in a bin or on a pallet.

30 years ago, when I was in manufacturing, I had access to those kinds of scales in the manufacturing plants I worked at. They are awesome scales.

Jim G
 

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OK, now it's a challenge. I'll have to break out my scales. Cost me like $80 for the pair and they claim +-6 ounce accuracy due to only being in the 0-300 each range. At approximately 1 foot wide, you would have a 3 to 4 inch stickout on each side of the axle. That should be enough to safely keep the vehicle upright, especially if you have a support at each end. if you are clever, I think this can be a single person job: Weight is the enemy!

You could get a larger footprint by turning the scales to a diamond position (in regards to the wheel).

Anyone have some aluminum scraps big enough to build something? Need like 3x3x.25 angle about 10 inches high. Some flat plate or bar stock for the "foot" and some bar stock to stabilize the V onto the plate. Then you need a good strong strap on each wheel to hold the V to the wheel so that it can't fall over. Almost an example is how I built my trailer: Trailer

Just need a wider base on the wheel chock to make this work. It would be easy to knock over, but I'm positive that I could get it stable enough for a quick measurement.

If anyone has access to the scraps of materials, I'd be happy to pay the shipping to get it here. Prefer aluminum because I need massive amount of practice welding it, just got an AC TIG and the only supplies I bought were for aluminum, though I could buy filler for steel if there was no other choice.
 

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Discussion Starter · #19 ·
OK, now it's a challenge. I'll have to break out my scales. Cost me like $80 for the pair and they claim +-6 ounce accuracy due to only being in the 0-300 each range. At approximately 1 foot wide, you would have a 3 to 4 inch stickout on each side of the axle. That should be enough to safely keep the vehicle upright, especially if you have a support at each end. if you are clever, I think this can be a single person job: Weight is the enemy!

You could get a larger footprint by turning the scales to a diamond position (in regards to the wheel).

Anyone have some aluminum scraps big enough to build something? Need like 3x3x.25 angle about 10 inches high. Some flat plate or bar stock for the "foot" and some bar stock to stabilize the V onto the plate. Then you need a good strong strap on each wheel to hold the V to the wheel so that it can't fall over. Almost an example is how I built my trailer: Trailer

Just need a wider base on the wheel chock to make this work. It would be easy to knock over, but I'm positive that I could get it stable enough for a quick measurement.

If anyone has access to the scraps of materials, I'd be happy to pay the shipping to get it here. Prefer aluminum because I need massive amount of practice welding it, just got an AC TIG and the only supplies I bought were for aluminum, though I could buy filler for steel if there was no other choice.
And so it begins . . .

I am SO glad that there are more crazy and motivated people on this forum besides ME!

Jim G
 
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