Install a 16 Tooth Front Sprocket

[bpdchief]

WOW what a bunch of replies.... I ordered the 16t sprocket Saturday evening - should have by Friday. Looking forward to giving it a run down these flat Florida Coast Highways

[Thumperville]

thanks to the OP for posting this handy info. i've put around 500 miles on my 2001 GZ250, all using the 15t sprocket. The motor has high revs going down the freeway, but rarely do i have problems maintaining 65mph, with the majority of the time i can get up to 70-75mph if needed to pass a car while driving on the freeway. The bike seems to do better than i expected reading others feedback about top end speed. the only problem i have with the bike are the high revs, it just sounds angry going down the freeway at 70mph.

if there were no 16t sprocket option i believe i would be happy with the 15t sprocket knowing its as good as it gets.

however, i've been reading thru the forums about 15t vs 16t sprockets, etc. i decided to order a 16t.

Today I swapped out my 15t sprocket for a 16t sprocket (after i built motorcycle stands that i also found how to make on this kick ass site) so after swapping the sprockets out, the first ride with the 16t sprocket i was pleasantly surprised. The bike seems to sound more at ease driving 1st thru 4th ; I only went on a 10 minute ride that by my choice had a 1/4 mile uphill section to test out the 5th gear. while driving uphill, i was only able to maintain around 50-55mph but i stayed in 5th gear.
towards the end of the 10 minute ride i was able to go 65mph but didnt seem to have enough umph to go any faster.

would mods to air intake / exhaust / carb be a step in the right direction if i want more top end speed?

for the time being, i am going to put some miles on the new sprocket.

[jonathan180iq]

Several people have suggested that some slight intake, exhaust and jetting tweaks have gotten them back over the hump with the 16T mod.

I was able to maintain my 80mph top speed even with the 16T with just a little tuning. By the time my ownership was over, the only mod I had done was a single lift of the needle jet. For me, 7/8 throttle was better than 100% full throttle. I probably should have just gone with a single size increase on the main jet, but whatever.

You can still get good speed out of the bike by using 4th gear to climb hills. I used to use 4th to get me into the 60 MPH range and then use 5th to finish it off. It may feel like the bike is really revving, but you're doing ok. I had a tach, and 65 mph in 4th is only a hair under 6500 rpm. It's not exactly pushing redline or anything. I wouldn't stay there all day long, mind you, as no vehicle needs to operate at 90% all the time. But it's fine for getting you over the hump.

[Skunkhome]

I think before I do anything with the gearing I would get a tach and FInd out just how many revs this bike is putting out at any given speed. Most of us are not used to listening to rpm's north of 4000 rpm. I have not seen a torque curve on the little engine but judging from the engine geometry (over square) I would bet that peak torque is somewhere above 5500 rpm and is made to scream. Anything else is just lugging the engine.

[cayuse]

Here's a posting I made over in the Gear Shifting thread:

Originally Posted by cayuse

I don't have a tach (yet) and I've never been sure of my rpm's so I thought I would exercise the noodle and came up with these charts.

There are some interesting figures here:
It confirms the tach results some are reporting in 5th gear: rpm's are ~10x mph
If you want to hear 8000rpm's go to 50mph in 3rd gear (!)
Seems to be OK, at least for short periods, to go 65mph in 4th (ie redline is just below 70mph)
Stepping up to 16-tooth gearing will bring you down below peak HP and torque at 70mph so don't expect to go faster with that mod.
I've always been impressed with the accel I get with this little motor when I let it wind out a little. Now, I've got some peace of mind that I'm not over-revving.

[jonathan180iq]

I was just about to post that.

[Skunkhome]

Just as I suspected, you can see by that chart that you are way down in the torque curve when you are in 4th and 5th with a 16 tooth sprocket. Those people complaining that the 15 tooth is reving too high at 65 mph are actually at only a shade over 75% on RPM. At 65 mph it has not even reached peak torque in 5th gear.

[Thumperville]

i took my bike on a ride today that was 40 miles one way using the 16t sprocket. it was good and bad.

the first part of the ride i was driving directly into a stiff wall of wind and was only able to it up to around 55- 65mph at best... but could not maintain the 65mph speed limit in section of the road i was on. 4th gear would get me up to 60-65mph, but typically i was full throttle in 5th going 55-60mph.

i was feeling pretty bummed until the 40 mile drive back on the same road i was able to get it up to 75 mph with no problem, whenever i wanted it seemed. i even got up to 80mph in a few spots. engine felt pretty smooth and powerful with that tailwind lol!

now i just need to mount an airboat fan on a trailer that i pull behind the GZ250 and i'll be set.

[cayuse]

Thumperville, that's exactly what I experience in wind.

Like your avatar, BTW!!! :tongue:

[Water Warrior 2]

Riding into the wind is a real power sucker on smaller bikes. The GZ does have it's limitations but overall it is pretty hard to beat. In a perfect GZ world we would always be riding with the wind and slightly downhill. :lol: :lol: