[Jkilla71]

Is the front sprocket for the CBR250 the same as the 300? I want to give a 15t a try to see if I like it. I found the PBI 382-15 - front sprocket is this a match for the 300?

 

[kiwi rider]

I'm wondering the same. I run a 15t on my 250 and will probably do the same on the 300.
From what ive read it sounds like only some internals like the connecting rod and crank etc have been changed to stroke the motor and the rest is same as before.

 

[Jkilla71]

How do you like the 15T on your 250? Do you have to slip the clutch much more or is it pretty much the same for 1st gear?

I bought the 15T sprocket already and if it doesn't fit $15 is not a big sacrifice.

 

[MotoMike]

Going up or down one tooth on the front sprocket isn't very noticeable in the lower gears, but it does make for a significant difference in the upper gears. I run a 13T front sprocket on my 250R, which gives me a lot better acceleration in 3rd, 4th, 5th, and especially 6th gear.

With that change to a lower final drive ratio, I sacrificed about 5 MPH of top end speed, which for the majority of riding that I do (30 - 50 MPH on fairly twisty mountain roads) isn't an issue. But roll on acceleration is much improved... on exiting slower corners in 3rd gear is where I can really notice the difference of having the lower ratio. I didn't see much of a decrease in fuel consumption either, maybe 2 or 3 MPG, again due to the type of riding I'm doing.

 

[Jkilla71]

Sounds good, I only use the CBR300 to ride to work it is a lot of riding at the same rpm in high gears but only about 5 miles. I enjoy my vintage bikes on the twisty roads on the weekends but no doubt the CBR handles better than any of them. I was surprised that there are no threaded holes on the swing arm for spools. I am going to have to move the wheel forward with the 15t but I will figure out how to lift the bike with what i have when the sprocket comes.

 

[kiwi rider]

I found with the 250 that I needed to whittle away a little of the plastic on the inside of the sprocket cover to get it back on. Its still a bit of a jiggle but it does fit. And yep, the back wheel will be right forward in the swingarm slot but it quickens the handling even more!

No bother with first being too tall but a) I live in the country with no traffic light stops and b) I only weigh 60kg.

 

[Jkilla71]

I found with the 250 that I needed to whittle away a little of the plastic on the inside of the sprocket cover to get it back on. Its still a bit of a jiggle but it does fit. And yep, the back wheel will be right forward in the swingarm slot but it quickens the handling even more!

No bother with first being too tall but a) I live in the country with no traffic light stops and b) I only weigh 60kg.

I installed the 15T front sprocket and I am wondering if the sprocket cover is different on the 300. I had to leave out the metal reinforcement gasket on the sprocket cover because it wouldn't clear the front of the sprocket with it on. It just is held on to the plastic cover by 2 plastic pins and it just pops off/on the plastic cover. Without the metal gasket (lack of a better word) I was able to slide the cover back on without a problem. I like the difference in gearing so far it seems much better for riding in town traffic and cruising at 50mph.

 

[kiwi rider]

Thats good to hear, yes I know the metal gasket bit you refer to. I managed to not have to remove this on the 250 but it is a bit of a fiddle to get it over the front of the chain. Will see how I go with the 300.
I just sold my 250 last night and ordered a red 300 about an hour ago so I'm pretty excited. Have to wait till November tho, they havent reached New Zealand yet even tho Australia has had them since July.

 

[MotoMike]

That metal piece which is part of the front sprocket cover is there to protect the LH crankcase cover in the event of the chain breaking. From what I understand, those who have installed a 15T sprocket have filed or ground off the location pins on the plastic sprocket cover, which then allows the metal protector to move forward enough to get the clearance needed.

 

[Jkilla71]

Once I popped the metal guard off the cover, I tired to see if I could fit it in place without the cover and there was not enough room between the engine and the front of the chain on the sprocket to get the metal guard behind it.




I am not worried about breaking the chain but it occurs to me that it could act as a guide to keep things nice for a chain with too much slack in it too. I am going to leave it off but I won't be lazy about checking the slack in the chain every couple weeks until the bike gets a couple thousand miles on the chain.

 

[kiwi rider]

Whats the standard gearing?

Can anyone tell me what the standard gearing is on the CBR300.
Is it 14th front and 38th rear, same as the 250?
Ive ordered a 300 but it wont be here for a couple of weeks yet.
Was wondering if I will need to go up a tooth on the front sprocket as I did with my 250.
Any thoughts on the gearing from new owners?

 

[MotoMike]

The 300R has a 14T front, and a 36T rear sprocket, for a final drive ratio of 2.571... a 15T front sprocket would give you a ratio of 2.400

So, it's slightly taller than the stock 14/38 final drive ratio of the CBR250R, which is 2.714... a change to 15T front sprocket results in a ratio of 2.533 on the 250R.

 

[kiwi rider]

Just put my 15 tooth sprocket on and this time I didnt file away any plastic and it fitted - just.
Was probably a bit hasty with the file when I did the 250. You need to have tension on the chain tho I found.
Now I can cruise without it revving its head off!

 

[kiwi rider]

alternative rear sprocket

I want to get a 34 tooth rear sprocket for my 300 but aren't seeing them listed being a new model and all.
I'm assuming they are the same as the CBR250 sprockets, the rear wheel looks the same etc.
Can anyone confirm this for me?

 

[commuter]

Sprocket mod question why 15T front instead of 35T rear?

Does anyone here know why a 15T sprocket in front is preferred over 35T rear sprocket option? Assuming stock gearing is 14T,36T both options would give the same result and for an absolute beginner like me, changing rear sprocket makes more sense just because of relatively large space available to work with. What am I missing?

 

[Jkilla71]

Does anyone here know why a 15T sprocket in front is preferred over 35T rear sprocket option? Assuming stock gearing is 14T,36T both options would give the same result and for an absolute beginner like me, changing rear sprocket makes more sense just because of relatively large space available to work with. What am I missing?

The front sprocket is less than half the cost of a rear sprocket and the front sprocket can be changed on the sidestand in about 15mins

 

[Joels_rody]

Also by increasing your front sprocket size you increase your chain life

 

[tonybell000]

just so you know, both your options don't give the same result. 1 tooth on the front is almost the same as 2 on the back. if stock is 14-and 36 teeth, its a 2.57 ratio. if you added 1 to the front, 15-36 then its 2.40 which is close to the same if you dropped 2 from the rear sprocket, 14 -34 its 2.42 to 1.
I guess which ever sprocket was available, or the cheapest would be good. but I kinda like a little smaller on the back because it makes the chain a hair longer, moving the rear tire back a little, looks good.

 

[commuter]

just so you know, both your options don't give the same result. 1 tooth on the front is almost the same as 2 on the back. if stock is 14-and 36 teeth, its a 2.57 ratio. if you added 1 to the front, 15-36 then its 2.40 which is close to the same if you dropped 2 from the rear sprocket, 14 -34 its 2.42 to 1.
I guess which ever sprocket was available, or the cheapest would be good. but I kinda like a little smaller on the back because it makes the chain a hair longer, moving the rear tire back a little, looks good.

You are right. I didn't realize this when I started the thread. Shows my lack of knowledge about motorcycles. I guess I am allowed to do that while I still have my noob hat on.

 

[louie]

Here is the recipe for dropping your rpm at 70 mph without losing little if any acceleration. Instead of going to a 15 tooth front sprocket go to Titanium sprockets and order a 33 tooth rear sprocket, Then lost the 16 pound rear tire and the 10 pound oem front tire. Replace with 12.7 pound rear and 9 pound front. The replace the sprocket nuts and bolts with TI replacements and last replace the chain with one that weighs about 1.5 pounds less than the oem chain. OH! Then replace the front 14 tooth oem sprocket with a 14 tooth drilled light weight sprocket. T%he bike then will become more competitive with the Kaw 300 and will cruise at 70 w2ithout running the RPM through the roof. I can advise as well. another thing, replace the rear fender with a shorter Yoshimura fender so it will not act like a parachute.