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2isbetterthan4
5th November 2004, 12:29
I want to make my bike(cbr250r) go faster and im not sure how. Ive been told to change the sprockets. Do i need bigger or smaller ones?,will it make a difference or is it just a waste of time?.also will changing the air filter and exhaust mean the carb needs to be re tuned?.
any advice much apreciated.

Hitcher
5th November 2004, 12:37
You're wasting your time. Leave it the way it is.

scroter
5th November 2004, 13:15
i agree with hitcher but if your really intent on finding more boogy then changing the sprockets can help, if you lower the gearing you will get more acceleration. you can do this by either dropping a tooth on the front sprocket or adding some to the rear bearing in mind dropping one on the front should be about the same as adding 4 to the rear. however i believe the 250s are already pretty low geared so probably no good anyway, also if you do this you have to consider the length of the chain. as for exhaust and air filter you would have to tune the carbs. I think your money would be better saved and spent on more CC's

Mr Skid
5th November 2004, 13:27
You haven't specified what you mean by faster.. Without getting into differential calculus (which I'm cramming today) do you mean faster as in faster acceleration or higher top speed?

As for the air filter, replacements are around $60, so your bike will probably have a skanky unloved filter residing in your air box, much like mine did.

Get some filter foam, filter oil and silicone sealant and make your own.
Having a clean filter will assist breathing. I haven't found any significant change in fuel consumption or power, but it can't hurt.

Then probably worthwhile cleaning, and balancing the carbs.

magnum
5th November 2004, 15:51
i agree with hitcher but if your really intent on finding more boogy then changing the sprockets can help, if you lower the gearing you will get more acceleration. you can do this by either dropping a tooth on the front sprocket or adding some to the rear bearing in mind dropping one on the front should be about the same as adding 4 to the rear. however i believe the 250s are already pretty low geared so probably no good anyway, also if you do this you have to consider the length of the chain. as for exhaust and air filter you would have to tune the carbs. I think your money would be better saved and spent on more CC's
or do lotsa track days,the skills transfer onto any bike :niceone: :niceone:

TwoSeven
5th November 2004, 16:21
I cant say for the R model but the RR is geared standard for top speed being delivered for 180kph, so you wont gain anything for changing the sprockets - since the speed limiter will kick in.

If you de-restrict it - you will need to change the rear sprocket in order to be able to use the extra 40kph available. The trade off will be losing a small amount of drive out of the corners.

The only problem is that you'd have to drop from a 52 to a 44 tooth sprocket - if just changing the rear - and it probably wont fit due to size issues (the chain will run against the swingarm).

You could try an best balance would be to use 18/49 (im not sure that combo is avial and its for an RR not R) and thats set for 220kph in 6th.

Peak power on the 250 is also set at 180kph in 6th gear, if you change the gearing (sprockets) you'd need to find another 4000 rpm to have peak power happen at 220kph in 6th (20,000rpm). Thats an awfull lot of tuning you'd have to do and your bottom end would suck big time - I think thered be nothing until at least 7krpm at best. You'd give up driving in town.

If you didnt re-tune the engine, you'd still get that extra speed -the rev limiter doesnt kick in til 20k rpm, which is where 220kph will happen but it would take the bike half the length of the country in order to get there (in otherwords - a long time) due to lack of power so it wouldnt really be worth it .

Its my opinion thats the primary difference between the cbiiby 250 and the cibby 400 in performance - the latter has the capability to get to that magic number at a lower rpm.

Thats just my throughts - and I might have got some of the math wrong.

Jackrat
5th November 2004, 19:52
I also think it's pretty much a waste of time unless the change you make is huge.I changed my rear sprocket from a 36 to a 32 in an effort to lower my rev's at open road speeds.It did drop the rev's by about 200RPM.
In other word it wasn't even really noticeable.
The Yanks change the front as well,going up 1 tooth,this does make a bigger difference but it takes you all day to get up to speed.
What ever you do with sprockets you will only ever gain at one end at the exspense of the other end.
The factorys get it pretty right I think.

2isbetterthan4
8th November 2004, 10:32
alright i understand now and it does sound a waste of time.I think il just wait to get my full!
thanks everyone

White trash
8th November 2004, 14:02
Dont worry about the gearing. Come for a hoon with us on a Thursday night.

Velox has no problem keeping up on her CB250 Jade. It's not the size of your hammer (top speed) but the nail you're throwing it at that counts. The more riding you do, the faster you'll go.

My reason for buying a Gixxer 1K has nothig to do with speed :shifty:

Wasp
6th February 2006, 22:30
hey 2isbetterthan4, come chill with us, I need a 250 to hang with (sorry 150s your just a *tad* slow for me) on thursday night rides!

Oh no WT nothing to do with speed at all............. (just that lil bit of extra grunt eh?)

EDIT: fuck just realised this was an old past, no idea how i got here, SORRY!