Gears... 15/41 Stock v.s. 18/38 mod
 

I was thinking about making the bike faster by changing gears... I did a bit of research and with a 18/38 setup it looks like the bike would run alot faster and still keep lower rpms. according to the numbers i saw can anyone confirm or deny this theory all information is welcome. I wanted to make it slightly faster without killing it and the numbers i calc'ed are nice but I dont wanna spend money on something that i will remove if i think it will kill my bike.

also thinking about a 130 main jet a k&n air filter piped straight to the carb with no air box front (cold air effect) and a dual stock pipe setup... also any information welcome.



Ride with respect.
Respect the Ride.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

That suggested gearing will not work. The best you can do is go up one tooth on the front sprocket. The bike doesn't have the power to use that gearing unless you are "always" going down hill with a tail wind.
You would be changing the overall gearing by at least 25% and the bike won't do it successfully.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

how do u calculate the 25% I dont know how to calculate it

also don't you loose top end when doing this?

I was thinking about just a 15/38 to start... but that would change the overall length of the chain distance

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

I don't think there is enough room for that large of a counter sprocket???
I had a 16 and it is quite a bit larger than a 15.
Would probably have to shorten chain.

Playing with the carbs is a sure way to change the speed of the GZ...
No one has really gotten gains from carb work.

May have a little issue with shifter and or chain guard being in the way...
Be the first to make it happen.

But hey it is only time and money, keep us posted on the progress.

Not trying to be a rain on your parade, but, the GZ is what it is.
YMMV.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Ever 1 tooth up in the front = 3 down in the rear.

Be the same as going to a 30 tooth rear.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Simple, (18/38)/(15/41) = 1.294.... (according to the calculator on my phone).

So, the proposed gear ratio increases by more than 29%.

Just try the 16 tooth up front, which is a change of 6.7% you'll see the bike will already have more trouble with slight slopes up in 5th gear. And not go any faster.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

would that kill the bike ?

the 30 tooth rear?

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

18 divided by 15 time 100 = 120%
38 divided by 41 = 92.7%
An increase of 20% up front and a decrease at the rear of 7.3% is a total of 27.3% change in the gearing.
Just try a 16 tooth sprocket up front, you might like it and if you don't it is a cheap experiment.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

I am looking for top end really not fuel economy or quickness just nice torqued up top end pull the hills and such with a greater speed.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Only if you ride it.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

currently when i ride to my moms house in the mountains it gets top speed of like 47 uphill and i feel like i am gonan get run over

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Those two are on opposing ends.

Short answer...WRONG BIKE.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Regearing for more speed won't help. You wind up dropping the RPM too much to develop any power.
As was said, the GZ is a GZ. It is what it is.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

and hp gains wont help the rpm issue ?

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

If you improved the HP by 20%...

18+3.6= 21.6

My math is simple 2x0=0

It is a GZ.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Well you could switch down to 4th gear. At 65 mph in 4th gear the engine runs at 8,000 rpm which is not redline but the bike does not like to do such high rpms for a long time. At least in 4th gear you could easily go 50-55 and not blow up the engine.

PS WW - sorry but your 27% is kind of, um, off - you add where you should multiply. Look at my earlier post how to calculate the percent change in gearing, just multiply the two increases: (18/15) x (41/38) = 1.29... which is 29..% more. Moot though.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

So will a hp increase of 4hp suffice that kind of gear change ?

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

The GZ is what it is. The design has been around for years and Suzuki is getting just about everything out of a 4-stroke 1-cylinder 249 cc that one can get out without over-stressing it. Also, if it were a piece of cake to add 4HP, everyone would do it. Please take it for what it is and if you don't like it, and 4th gear will not get you up the slope any faster, consider another bike rather than trying to get more out of the little GZ.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Just for fun...

http://www.gearingcommander.com/

15/41= 2.733
16/41= 2.565
18/38= 2.111

The GZ has a hard time pulling the 16 tooth sprocket.
But if it could pull the 18/38 it would run 115 mph.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

No because again we are talking about a GZ with 18hp stock, so you still only would have 22hp to work with.


If you add 4 horsepower, you MIGHT feel it a little when you are poppin around town, and you MIGHT go 78 top end instead of 74 (just an example). So you are gonna do all that work and spend all that money to get 4 horsepower (which you would have to prove to me that you squeezed out), to get very very little reward from. I would have a hard time believing that you could even squeeze 4 extra horses out of the GZ engine without cracking open the engine and doing some serious internal work, I mean that is over 20% horsepower gain!!!

And before you say yeah that is a 20% horsepower gain, so I should feel a real difference in power, again, we are talking about a bike that only has 18 horses to start with. I have a push lawnmower that has almost 7hp, Most riding lawnmowers have 20+hp engines on them, so you are not working with much on the GZ, Just ride it like it is, and enjoy it for what it is.


See your gear ratios are a good idea for more top end, if you are dealing with a bike with plenty of horsepower, and you also have to have plenty of torque to give up, but on the GZ you have neither to play with, so it is what it is.

Not to mention the fact that the GZ is so light that even at 60ish, it starts feeling very sketchy, so why anyone would want to go much faster than that on one is beyond me, I went 71 on mine one time just to see how far I could go, and it did not feel very stable at that speed, so I can't imagine pushing it much farther then that.

All these ideas you have would be awesome to do to a bike with a bucket load of power to play with already, but the GZ just aint got it to give.

So we are not knocking your ideas or your enthusiasm, just the fact that you want to try and do it to a GZ.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Close is good for an old guy. :lol: :lol:

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

I know it is a gz I just want to get better performance for what I have while I am building my goldwing I also think that the gz has a lot of potential to be a really fun bike but I just wanna make it be comfortable to ride and be able to keep up with my buddies rebel

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Taken from: viewtopic.php?f=9&t=1058&hilit=modifying+the+gz
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~

Possibly the easiest mod that you can do which will have a pretty drastic change to the way your bike performs is to change the final drive gearing.

The final drive of the GZ250 is a simple chain/sprocket combo. The final drive ratio is 2.73. This number is easily calculated by dividing the number teeth on the rear sprocket by the number of teeth on the front sprocket. In our case, since we have a factory sprocket combination of 15 and 41 (15 teeth in the front and 41 in the rear) the calculation would look like this.

41 / 15 = 2.73333333 (or 2.73)
The lower the gearing, the lower the revs. The higher the gearing, the higher the revs.
You'll almost never want to change any sprocket more than one or two teeth sizes in any direction over the factory number.

By comparison, switching over to a 16T front sprocket lowers the final drive ratio to 2.56 (41/16)

What does this mean in practical application?
The 16T front sprocket lowers cruising revs in all gears and allows the lower gears to be used for a longer period of time. However, you will probably notice a drop off in your top speed. While the factory gearing allows the GZ to reach somewhere around 80mph, the 16T front sprocket will lower that to around 70mph+. The reason being that the internal gearing of 5th gear has a ratio of .818, which is basically an internal overdrive and seems to make the gear too "tall" for the mighty GZ to handle.

EDIT FOR THIS CONVERSATION: Imagine what this would be like with a 18T front sprocket.... On top of that, I highly doubt that an 18T front sprocket will even fit on this bike. There is a sprocket combo that should allow for decreased highway revs while also extending reducing the drain on the final drive and it is 16/42 or 16/43. The gearing ration on both of those works out to be 2.62 & 2.68 respectively. That falls on a nice medium in between the factory gearing and the overgearing of the 16T in 5th.


Where can I purchase a new sprocket?

The Suzuki factory part number for a 16T sprocket is 27511-37200
The JT Sprockets part number is JTF 434.16

Sprocket Specialists make both front and rear sprockets for the GZ250.
The front sprockets are available from size 10-16. Part number: 528-(number of teeth)
The rear sprockets are available from size 28-74. Part number: 461-(number of teeth)



How do I change my front sprocket?

http://www.gz250bike.com/viewtopic.php?t=317

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Interesting info. I think the smallest gearing change might be the biggest overall advantage.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

I completely agree. I wanted to try my suggested gearing combo but sold the bike long before the funds matched the desire.

I would think with this set up you could use the same chain. But rear sprockets cost somewhere around $45 so you really have to be in committed to getting perfect gearing. That being said, if you keep this bike for any significant amount of time, it makes sense to invest maybe $100 total and get a gearing that you are completely satisfied with.

I didn't post this in the previous little bit, but the gear ratio that the original poster suggested is 2.11 final drive.

2.11....

I don't know that you would even be able to get the bike to move forward in 1st gear. It would stall out.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

The cost commitment wouldn't be so heart stopping if you wait till you need to replace the chain and sprockets due to wear. I would be tempted to wait till the parts were due for a R+R. You know you will have to do it eventually.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

well i am gonna be doing the rear tire and brakes this month some time so i figured that it would be a good time to do it for mine. Also I am just now really getting to parts that have either rotted due to sitting and such cause it sat so long. THe back tire was dry rotted on the surface but under that was still a good tire. The chain just needed to be cleaned and the brakes all together fell apart over the course of the last 2 months so I will have to replace them too. I am thinking about doing the drill on the exhaust and the 130 main jet. I cant afford all that other stuff and the k & n air filter so i don't know if i should do the rejetting until I get that air filter too. I like riding the bike and I like the fact that I have already found some other 250 riders to ride with but at the same time all the other 250's are faster than me and typically leave me and I have to catch up at the next stop. I like the looks ofmy bike and the cost to get started riding but I have never had a vehicle that had less power than those i was around and I just want to remedy it enough to keep up with the Jones' and enjoy the bike as I save money.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

I was just up the road from you Sunday at Dahlonega, GA.

That is one of our breakfast rides, right at 300 miles.

The easiest and cheapest way to get the GZ to be a fast bike is to become a better rider.

:)

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

If the front tire is as old as the rear it will have to go too. After 5 years the rubber dries out and will not grip nearly as well. Good tires are an excelant health insurance plan.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

I'll go ahead and warn you right now... drilling the exhaust is a waste of time. It doesn't flow better, it sounds like crap, and a 130 on top of that is going to leave you running rich.

For about $60 you can chop off the rear muffler section and install an EMGO universal muffler and get a much better sound and better flow. Then, you can add a 130 and it will be about right. For slightly more air flow through the intake, just pull the snorkle off of the airbox and leave it alone. The stock filter is better at trapping contaminants than anything aftermarket, although it is the most restrictive part of the whole thing.

If funds are limited, I think this is your best bet. You don't have to pay for an expensive exhaust set-up and you get better intake flow without having to replace the filter or hassle with removing and replacing the airbox and the corresponding air hoses.

I'll say it again: Punching holes in the exhaust, or puncturing the baffle will just leave you disappointed in the long run. Trust me. I have been there. I even posted a video of it on Youtube. (Marauder GZ250 Exhaust Comparison) I hated it so much I spent $600 buying the a brand new factory system.

After you do all that and get the bike running right and sounding how you want, then save up $100-$150 and do the gearing/chain upgrade that has been suggested.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Would you go with the 42 or 43 setup ? I noticed you mentioned both, But I was unsure which one would give more desirable results.

EMGO muffler is there anything bad about it or you just like the stock muffler as I notice you didn't get an EMGO after you drilled your exhaust.

funds are somewhat limited but not too bad since it is a daily driver I have more money to upkeep it since I save so much money in fuel. about 70 a week savings so far but i am still only getting about 56 mpg.

I added 1Amp neons to the back of the bike and and they seem to draw little enough power that it doesn't over discharge the battery and I rid normally early morning and dusk (to and from work).

I have been interested in adding a small tach just so I know what is going on in there. any suggestions?

The front brakes had been acting weird and i figured out that the pad positioning pin is missing and a pad shim fell out as were the pads themselves.

I cleaned the brake line and reservoir with fresh brake fluid. and i have EBC fa106 pads. Waiting on the Pin and shim that I am missing to get it back out there on the road. the rear brake bar seems to be pointing at the air filter instead of that small area in the back that is supposed to be the gauge for when they need to be replaced. is there a way to know or readjust that to make the usage scale read right ?

it has Metzeler tires on it i am assuming from factory and I was wondering... when i look up the tire it says tubeless. but on spoke wheels i would think that they needed tube tires. can anyone shine some light on that ?

I have reclined the handlebars back and adjusted the brake fluid and mirrors back flush will that hurt anything ?

Is there a place to get highway pegs on the Cheap?

also I seem to recall a post on a gas gauge for the gz is that thing reliable ? and is there an easier step by step guide to make these ?

The front fender looks like it is warped and is not sitting even and aligned with the wheel can that just be adjusted by the 4 bolts that are on it ?

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Muffler Swap
viewtopic.php?f=8&t=19

Tachometer:
viewtopic.php?f=8&t=533

If you just want to change one sprocket and keep the same chain just swap in a 40T rear sprocket and keep the 15T up front. That would give you a final drive gearing of 2.66. It would be an improvement on the highway over the factory setting (2.76) but won't be as drastic as the straight 16T swap (2.56).

I'm not really making a recommendation for one over the other. I'm just giving you ideas on what it out there. Doing just the rear sprocket swap would be easier and you won't have to change as many parts as you would if you went with a 16 & a 42/43.

Why I didn't upgrade the muffler at the time was simply because I got past the modding phase of my ownership very quickly. I just wanted a bike that was simple and reliable and I'm of the opinon that factory bikes are good enough for me, in most cases... (I've had to modify all of my Chinese bikes, but that's a different beast entirely.) I use motorcycles as daily drivers and beaters so for me, function is more important than form. And since I don't care about being loud, I just went with the factory exhaust system again.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Don't expect any of the mods you're considering to give you a significant increase in power, acceleration, or top speed, but they may reduce your gas mileage. You want a faster bike? -- get a bigger one.
There are innumerable threads on here about this, it has been discussed ad nauseum, so do a search on here and get educated before you mess up your bike.
Most people get 60-65 mpg. A dose of carb cleaner may increase your performance and gas mileage. Try that first.
There is no, nor has there ever been, a gas gauge for the GZ. Reset your trip odometer each time you fill up and refill at 150 miles or less and make sure the petcock is set to RUN so you have the 40 miles of RESERVE in the tank if you run dry.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Needle Shim Modification:
viewtopic.php?f=8&t=15

Sprocket Change:
viewtopic.php?f=8&t=317

Fuel Gauge Construction:
viewtopic.php?f=8&t=3823

Power Increase:
viewtopic.php?f=8&t=617&hilit=power+increase

Read all of the above threads. It should leave you with a very good ides of what our collective knowledge/opinons are in relation to what you want to accomplish. Some of them are quite long. But I still recommend you read all of it.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

That will keep him occupied for a while and maybe he'll decide to leave well enough alone, and try the carb cleaner for a starter.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

I have cleaned the carb alot! I took it off ans scrubbed the crap out of it and have run an entire can of seafoam through the carb as well as i use enzyme ethanol treatment on every fill up it takes 5.5 ml for 3 gallons of fuel so i do exactly that everytime i fill up i watch the gallons v.s. the price then add 5.5 ml with a baby medicine syringe. I have had the carb tuned in by a bike mechanic nearby. That is not it...

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

As far as people telling me to get a bigger bike.... If i wanted a bigger bike i would have gotten one already I want to see what I can get outta this little bugger. I figure that people have to try things to find out if it is gonna work and eventually there will be a means of doing things that you would have never thought possible. I have a passion for tinkering and a lot of other vehicles to drive when i am not using this one because i am modding. I don't care if it takes time nor energy I am up for it I have been a mechanic for a long time and I refuse to think that any manufacturer has ever gotten maximum performance outta any product.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Does anyone know if the EMGO shorty i think it is 12" long from what i have read provides enough back pressure not to have to go to a main jet bigger than 130 ?

http://cheapcycleparts.com/products/218 ... al-muffler

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Even with guys that run straight pipes, no one to my knowledge has ever needed anything bigger than a 135 on the GZ250.

We're talking open intake, open headers and everything.

Re: Gears... 15/41 Stock v.s. 18/38 mod
 

Thank you, for the information.