Sprockets

[LordShaftesbu...]

With decent weather finally here it's time for me to get the summer bike out. Before I put it away last year I remember thinking that if I could I would like more acceleration, even at the expense of top speed.

As I understand it, you can do this by swapping the front sprocket for a smaller one. I kind of remember reading somewhere that it's fairly trivial to drop one tooth, although you can drop more (and increase the teeth on the rear sprocket) if you're prepared to mess about with chain tension (and possibly other things, can't quite recall).

Anyway, I mentioned this to a friend (who works for the Parkalgar racing team) and he strongly recommended that I not change any sprockets at all due to safety reasons.

Has anyone played with their sprockets and if so, in what way and what effect did it have? How easy was it to do?

[.....]

Don't know why he said it would be unsafe?

Have a play on here

https://www.gearingcommander.com/

To see what might work for your bike.

Changing sprockets is an easy job. You'll be putting on a new chain as well so need access to a chain tool really if your using a soft link unless you want to use the hammer method.

[DrDonnyBrago]

Unsafe? Hows that then?

Is a very common thing to change, only mechanical differences are that your speedo can overread if it is driven from the crankcase (it'll be fine from the front wheel) and a smaller front sprocket can increase chain wear rate. You will also be running around at higher revs so will use more fuel.

In real world terms it is probably irrelevant but I also heard that the more times the same link passes over the same tooth of a sprocket the faster they wear. If you change the number of teeth on the sprocket then you will alter that rate.

[jimbothe]

I remember putting a -2 and +2 respectively on a bandit 1200 and it turned into a animal
Struggled to keep the front down under acceleration and I'm no lightweight. Lost roughly 20mph top end. Not for the faint hearted,


Thats my mum on it before she fell ill, sorry, it's the only pic I have showing the sprocket.
Check out the gold dinner plate on the back


https://i22.photobucket.com/albums/b342/jgillard/maonthebandit.jpg















But I'd do it again in a jiffy
____________________
Check out our tackle shop on Facebook:
https://www.facebook.com/#!/JklTackle

[Rogerborg]

I've gone the other way (bigger fronts) on my 125 and 250 to stop them revving their nuts off. It's cheap, easy, effective, and as for safe: when you buy a used bike, do you actually count the teeth on the sprockets to make sure they're stock? Don't create worries for yourself based on vague "Bloke Said" warnings.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[yen_powell]

I changed the front sprocket on my DR350 so if I was paddling through severe clag offroad I could leave the clutch lever all the way out. It also made it easier lifting the front wheel over fallen trees etc.
____________________
Blackmail is a nasty word........but not as nasty as phlegm!
XT1200Z and a DR350 in bits

[G]

I hope your friend doesn't work on the mechanical side as the team will probably be changing sprockets on their race bikes most weekends!

Only 'danger' is you can get more acceleration in lower gears (higher gears, you could just have been in a lower gear before) - but when that's the desired result, hardly something to stop you doing it!

[Bendy]

Did 1 down, 4 up on my CBR6 and in 20,000 miles I appear to have not been killed or maimed.

Had to take the centre stand off as the chain rubbed, but otherwise no issues.

[LordShaftesbu...]

Ah music to my ears. He did mention the change in speedo reading ... if it over-reads rather than under-reads will it still pass its MOT (not that I'm too bothered as it wouldn't pass anyway with the exhaust that's on it)?

Sounds like some people went to extremes, -2 on front and +2 on back. Doesn't it increase the risk of the chain coming off the more you change it? Or is that why you have to get a new chain?

At the moment my bike can get up to 85mph in 2nd gear. Ideally I'd like to get to a maximum of 75mph in 2nd. According to that calculator (which is brilliant by the way) I could go with -2 on the front or -1 on the front with +3 on the back. I suppose the 1st option would be cheaper, but are there any other considerations?

[DrDonnyBrago]

[LordShaftesbu...]

Excellente ...

Anyone know any good brands for sprockets/chains? I don't want to repeat the mistake I made when I allowed the dealer to choose my heated grips for me ...

I was thinking about getting a Scottoiler Esystem fitted at the same time as this gubbins so that should keep chain wear down hopefully.

[.....]

I like DID X ring chains, I've had them on my dirt bikes and they hold up extremely well to the abuse they get. Sprockets I just go for any old steel sprocket.

Go for a Scottoiler V System - the E System is £150+.

[Bendy]

You can get a device called a Speedohealer that'll put your speedo back to correct.

Remember, your odometer will also be wrong, so you could be racking up 'mileage' you didn't really do - possible future sales issue.


Changing sprockets doesn't risk the chain coming off. It supposedly can increase wear a bit (particularly if you make the front sprocket smaller) but I didn't experience anything that I would consider ridiculous wear and (from memory) did about 15,000 miles on the first c&s with that -1 +4 setup. DID chain and Renthal sprocks, if I recall.

[Bendy]

This is the +4 on the CBR - it's hardly a dinnerplate but you can see the chain is a bit lower than normal and how it could rub if there's anything in the way.

https://dl.dropbox.com/u/3523115/bcf/sprocket.JPG

[LordShaftesbu...]

[DrDonnyBrago]

[DrDonnyBrago]

[Bendy]

[prawny1]

Smaller front sprockets wear out quicker (less teeth same load) but a bigger back sprocket should wear out slower.
____________________
hellkat wrote:

Some people are only alive cos its against the law to kill them.

[LordShaftesbu...]

How do I know what length chain to buy? Stock is 116 links, but if I go for a -2 front and +1 rear will this mean the length changes?

[DrDonnyBrago]

[prawny1]

Just buy a much longer chain then if it's too long you can just cut some off.

But to be honest minus -2 +1=-1 so you should only be a link out anyway and your adjusters should handle that if not cut a link out.
____________________
hellkat wrote:

Some people are only alive cos its against the law to kill them.

[Kickstart]

Hi

The only real safety concern with changing the sizes is the chain catching on things. Go too small on the front and the chain will chop into the swinging arm for example. A smaller sprocket will wear more quickly, and this might be noticeable but a fair chance the chain will be dead before it is an issue.

Other than in first you can gain much the same effect by just not changing up a gear so soon. And in first you are probably not using full throttle and revs to make full use of what you already have.

Rough guess, going down 2 at the front and up 1 at the back will knock 20~25mph off the top speed and will result in 6th gearing being the equivalent of something between 4th and 5th.

Email me a dyno chart and your gearbox ratios (or if you haven't got them the model and year of bike so I can look it up) and I will sort out the charts of rear wheel thrust for you.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[LordShaftesbu...]

[Kickstart]

Hi

Here you go:-

Bike thrust graph

Red line is the rear wheel thrust on stock gearing, blue line is the rear wheel thrust with 2 down on the front and one up on the back.

On stock gearing you run out of revs limiting top speed at about 143, with the lowered gearing you would run out of revs at about 123.

With the lowered gearing you have a load more umph in first gear (but doubt you use what you already have) but need to change up at about 53, while on stock gearing you can hang on in first until about 62. 2nd on the lowered gearing gives you an advantage from 62 until about 75. After that 3rd on the lowered gearing is pretty much the same as 2nd on the stock gearing, same for 4th / 3rd, 5th gives you about the same as half way between 3rd and 4th, 6th is about the same as 4th while on the stock gearing you still have 2 more gears to play with.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing