rpm speed cross reference

[trykemike]

here is a list of values that may be usefgul :

gear rpm mph kph

4 4500 35 55
5000 40 65
5500 43 70
6000 47 75
6500 51 83
7000 55 90
7500 59 97
8000 63 101

5 5000 49 80
5500 54 85
6000 58 95
6500 63 101
7000 68 115
7500 73 120
8000 78 125

[jonathan180iq]

What tach are you running?

[bigfour]

Hey thanks, I didn't know the GZ could go that fast in 4th without redlining, mine sounds angry if I get near 40 in 4th.

[Badbob]

Hey thanks, I didn't know the GZ could go that fast in 4th without redlining, mine sounds angry if I get near 40 in 4th.

I rode mine for a couple of hours once at 60-65 mph in fourth gear. It was the only way I could get over fifty in the head wind. Lots of vibration but that was about it.

[Water Warrior 2]

bigfour, the bike isn't angry, it is yelling for more throttle.

[Ofnoan]

Hmmm... My mechanic mentioned that I should not exceed 100 kph (60-65 mph) if I want my bike to last... After all it's an air cooled engine...

[Jordan310]

Heh.

Nah youll be fine.
I do 60-63Mph in 4th all the time.

Its fine.

[trykemike]

The figures quoted are calculated using the final drive ratio and gear ratio. I used a calulator that I found on the web. The values relect values that I have acheived on my speedo and have calculated using wheel circumference and rpm @ specified engine rpm.

Re: the 16 tooth mod . Here are some calculated values.

5 th gear
49 mph 4750 rpm
54 mph 5250
59 mph 5750

here are to same speed with 15 tooth sprocket

5 th gear
46 mph 4750 rpm
53 mph 5500 rpm
60 mph 6250

there seems to be a definite drop in engine speed in the 50 - 60 mph range which is the cruising speed for this machine.

[Jordan310]

Is this a good thing or a bad thing :P

[Sarris]

My bike seems to run better & stronger with the 16 tooth gear. My concern would be the clutch if anything. I wonder if Barnett or anyone else makes a heavy duty spring & clutch plate kit for it?
:??:

[Dirt_McGert]

How high of a gear should I be in for travelling 25-30mph? I'm usually in fourth to save gas and lower the vibrations, but what happens if I'm in too high of a gear if I'm travelling slow? (say, if I'm going 10mph but I'm in third - what happens with the clutch/tranny - any slippage/damage?)

With the 16-tooth sprocket now, I shift from 1st to 2nd at around 15mph, from 2nd to 3rd at around 25, from 3rd to 4th at around 35, and 4th to 5th at around 45. With the 15-tooth stock sprocket, I would shift a tad bit sooner than now. But I'm just wondering if it's ok to be in that high of gear when travelling slower, not sure if it would cause any damage. Plus, being my first bike, I'm not exactly sure of how fast the engine is going with how it sounds. Does anyone have any sound clips of their 250 at certain RPM's?

[Jordan310]

Hmm.

Ive posted, and read posts. My bike seems to be a bit odder then some others I guess because my gears work something like this..

1st gear, up to about 15Mph, then I flip to 2nd.
2nd gear will hold me to about 30-35Mph, then I kick it up to 3rd.
3rd gear will get me up to about 45-47Mph, and then I pull it up to 4th.
4th will take 45Mph all the way up to 65, and then I kick up to 5th.
5th goes on forever, but starts to scream at about 75+ Mph.

I have had this bike for some time now, and have had it checked several times.
As the engine is from the DR250S (a dirtbike motor), I sort of ride it like one. This bike is pretty forgiving with the shifting, and RPM range.

I have noticed a slight oddity though. in 5th the bike for sure looses its pull, and really, I do have to drop down and then back up from 4th to 5th when hitting inclines on the highway to maintain 75Mph now. It seems to be getting worse. Whats more odd, is that I seems to have gained some low end torque, and its running a little stonger in the lower gears!

Anyone?

All parts for the big bore kit im installing should be here soon.
Im excited.

Have everything laid out. Big bore kit, hidden LED lights, new EMGO shorty mega muffler (modded), etc ..

Anyone know where I can get metal polished reasonably, and what K&N filter would work best on this carb?
As well, any suggestions on some slighty bigger or fattere tires for wet weather? Im always in the damn rain. Even when the engine gets water in the oil. (That sucks).

[jonathan180iq]

Did you swap the engine for a DR before the big bore kit or are you still running the standard GZ motor?

[Jordan310]

The DR is the same motor as the GZ. =)
No, Im running the stock 2007 GZ motor.

REVISION: I tested it after readinf the above posted gear topic, and on a straight away early on a very warm Miami street I started out and did this:

1st - up to 20Mph (shift)
2nd - up to 40Mph (shift)
3rd - up to 50Mph (shift)
4th - up to to 60-65Mph (Shift)
5th - 65Mph +

Is anyone else able to get the RPM's this high without making the engine bitch too much at you?
Im just wondinging even more what the big bore, and SPROCKET mod in particular are going to do.

[Easy Rider]

1st - up to 20Mph (shift)
2nd - up to 40Mph (shift)
3rd - up to 50Mph (shift)
4th - up to to 60-65Mph (Shift)
5th - 65Mph +

Is anyone else able to get the RPM's this high without making the engine bitch too much at you?

Im just wondinging even more what the big bore, and SPROCKET mod in particular are going to do.

Probably not. Most of us know it's not a dirt bike racer and would like the engine to last a while ! :roll:

Are you doing this with the stock 15 tooth sprocket?
If so, OUCH! :cry:

I don't even get to those speeds (1st - 4th) WITH the extra tooth.........and don't think I'll try either, based on the sound the engine makes at the upper end.

[Jordan310]

These I do all the time with the 15 tooth give or take 2-3Mph.
Yea, the bike really does not scream at me too much either. Im not sure whats up with owners who cant seem to get past 50-60Mph.

Could it have to do with the fact that from the dealership to 3000+ miles Ive been riding it super fast, and pretty hard? I dunno.
My bike seems pretty able to handle the high revs I give it. Im going to have it fully checked again soon to insure that after 3000 miles I havent fucked anying up.

So far, .. the bike is strong though. Only a slight noticable loss in the upper gears (5th mostly). Dunno what thats about.
Again, the DR250S has the same engine, just a bit different gearing I think. The big bore kit should fit perfectly.

In any case, I think a loss in power is occuring because of the rainy season, Ive gotten water in the gas a few times, and the open air filter has gotten a bit damp.
Time to change it from the stock to a K&N. I woukd be more than grateful to anyone who can tell me which adaptor / KN filter (air) to use on the stock GZ250 carb.

Anyone?

[Dirt_McGert]

Is it ok to be in 4th gear travelling around 25-30mph? Note, I have the 16 tooth front sprocket, although it doesn't make that drastic of a difference in engine speed.

[Jordan310]

Uh.. yes. Its fine. Why you would want to do 20 in 4th is the real question. =)
You can do 10Mph in 4th if you want.

[Jordan310]

The sprocket (16 tooth), Im guessing is going to lower the RPM's on the top end, and allow you to reach 80Mph where you were just barely getting 75Mph (crossing fingers).
Actually for me, it will be .. trying to maintain 82-85Mph when my current top highway crusising speed is 78-79Mph.

After the big bore kit is in place, Ill pe pushing about 340cc's, and no doubt Ill hit 90Mph. Just a guess.
More torque by far, and quicker accel. for sure.

A pretty decent cafe racer / small crusier / city bike Im hoping.

[jonathan180iq]

the DR250S has the same engine, just a bit different gearing I think.

Different transmission, different internals, different combustion chamber, different exhaust, different engine mounts....

[Jordan310]

Yes but the large bore kit is pretty compatible. Same thing.

[jonathan180iq]

I just really hope, for your sake, that your mechanic has either done this before or has done a lot of research on this.
So, far, just doing some quick searches, I haven't been too convinced.

I'd hate for you to have spent money on a kit that isn't as compatible as you've been told.

[Jordan310]

Yes, I did some research, and my mechanic is pretty sure that this should be no problem.
I am going to double check with the maker of the kit, and the parts in the kit once more before completely commiting to the upgrade.

Good looking out.