Idea for a guide : Downgearing / Chain and Sprockets

[zaknafien]

How about a guide on downgearing?
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02 Firestorm.

[G]

Ask and ye' shall get another half finished thingy:

Downgearing

Why?

Don't I want my bike to go as fast as possible?.. so why would I change the gearing to make it slower?

First, changing your gears to a lower ratio can actually make your bike go faster! Most bikes won't reach the red line in in top gear. By down gearing the bike can make more use of top gear: you will get more power at a slightly lower speed, meaning that it should be able to get to the redline in top. Thus it may have a slightly higher top speed, because although it's geared lower, it can make full use off the gears. The reason most people downgear their bike however is acceleration. A shorter firstgear means better launches and the range in mph of the gears being closer together means that you can get through each gear a bit quicker. For track riding this generally means better lap times. You rarely reach the redline in top gear and you may still be quicker even if you have lowered the top speed. The downgeared rider gets up to their lower top speed quicker than the normal geared rider. They may only reach say 150, but they will probably have got there a few seconds before the other rider has. So by the time the rider with normal gearing has reached 170 the downgeared rider is a way infront anyway. Obviously this has advantages if you want to do stunts as well. First gear often becomes a bit too flighty for normal wheelies on powerful bikes, but the bike can usually then lift in 2nd gear which is still taller than the previous first gear, so allows for smoother more easily controlled wheelies. For those that are less experienced with wheelies or on less powerful bikes it makes it a lot easier to get it up in first without a lot off effort. There's more power at lower rear-wheel mph for starting burnouts off as well.

That all sounds great... any reasons I shouldn't do it then?
If you're downgearing a lot or you don't have a very high geared bike to start with you may find that motorway 'cruising' speed is at quite high rpm in top gear. This can be annoying because not only is your bike screaming constantly, but you don't have much go left over if you do want to or need to accelerate. Fuel economy is also going to suffer, so if you're pinching the pennies it might not be the best option, but then it's a whole load cheaper than buying a new bike . You'll be skipping about the gear box more; as the gears are now closer together your left foot may get a bit more of a work out. Not too much of an issue unless you're going 20 up on the rear sprocket or you've got a fairly short geared bike anyway.


How to do it?
You're changing the chain and sprockets, so if you've done that before you can downgear your bike. If you haven't, this is an overview of what you're likely to have to do:

Split the chain; most chains these days are rivetted. This means you will need either a proper chain splitter or an angle grinder. Note that you probably could use a hacksaw or similar, but remember that these links are designed to take 100ft-lb of torque through them, so aint exactly soft. Angle grinders can be got from around £15 including cutting discs, so it's a worth while investment, even if you're only going to use it occasionally. If you've got a lower powered bike, you may have a split pin chain, if so it's a case of taking the split pin link off... just unclip it with a screwdriver.

To join a new rivet chain you will need a chain riveter. Cheap ones can be bought from around £40, though quality can be variable. Some rivet chains will come with a split pin link for you to use so that you can get your bike to a garage that has a chain riveter. If you do not have a riveter you will also need something to compress the plate onto the chain... a g-clamp will normally do the job.

Obviously you will need appropriate sockets/spanner to remove the sprockets, axle etc and any covers that may be impeding your progress. Depending on how worried you get, on some bikes you may need an air wrench to undo the sprocket nut, especially if one was used to do it up.


The first thing to do is to get all the covers off from around the front sprocket.

There may be a washer bent up around the sprocket nut/bolt, a clamp or nothing at all. If there is something holding it on undo it or bend it back. To undo the nut/bolt you will need to at least get someone to hold the rear brake on or clamp it down. If this doesn't provide enough friction to hold the wheel you can try wedging some wood or similar between the rear wheel and the swing arm... be careful though you don't want to damage either. An air wrench/electric impact wrench should shift it if nothing else will, I've never had much luck with manual impact wrenches. You may also need to use this if the chain has snapped and you don't feel like putting stupid amounts of force through your new chain.

Now that's off you should be able to get the sprocket off... but not until you've got the actual chain off.

Personally I would probably split the chain before taking the rear wheel off... if nothing else it's more easily accessible, floating in mid air, as it does .

I haven't used one of the 'proper' tools to split a chain before, so can't comment. I'm sure someone can explain though. To angle grind it, you just, well, turn it on (following all appropriate safety precautions... wearing full 2" thick steal-plate armour etc*) and press the spinney bit against the chain. (You probably want to try and make sure not too many of those hot sparky bits go towards explosive things, like your fuel tank.

*seriously though, at the very least wear some eye protection. I've heard from people that it's happened to that molten metal landing in your eye isn't a pleasant thing.


To get the rear sprocket off you will have to take the rear wheel off, unless you've got a fancy single sided swing arm possibly. So that's axle out while it's on a centre stand/paddock/abba stand etc. You then need to get the sprocket nuts off, shouldn't be too much hassle. Remember not to put pressure on the brake disk, such as while laying it on the ground... this can cause them to crack. Clean it up a bit for the tarty effect if you want and put the new sprocket on.

Now you need to do basically the same procedure in reverse.
Now would be a good idea to dig up that Haynes manual to check the torque settings required... or you could try Korn's bookshop on ebay for a factory manual if you haven't got one . If you have used an air/impact wrench to undo anything, put it away now and get a torque wrench out... then hopefully you won't need a spare one.

If you've got some thread lock, a bit to each of both the front and rear sprocket nuts/bolts is probably worthwhile.

Do up your rear sprocket nuts/bolts to the correct torque settings and reattach the rear wheel, making sure you remember all the spacers etc . Adjust the appropriate adjusters so the wheel is positioned as far forward as possible.

You will now need to thread the chain through. I usually find it easiest to do it from the rear sprocket then pull it through to the front. No reason you can't do it the other way around though. It's probably worth putting some newspaper down underneath the path of the chain so that when it falls the fresh grease doesn't get covered in the much on your garage floor/driveway/road.


...................

[zaknafien]

Cheers G.
____________________
02 Firestorm.

[EuropeanNC30R...]

You can also use www.walesbikers.co.uk/gearing.exe to calculate the speedo error after down gearing. Enter the standard sprocket sizes and then the new sprocket sizes. Obviously that's for bikes with a speedo driven off the front sprocket. I should really design it clearer and make some proper instructions, but I'm too lazy

[zaknafien]

[EuropeanNC30R...]

Which bugs would those be? Unless you're trying to crash it with text or whatever

[zaknafien]

Start it up and just click get new gearing for a start.
____________________
02 Firestorm.

[EuropeanNC30R...]

Oops, I'll have to add in a little disclaimer in the next version, "Not for use of the retarded".

[EuropeanNC30R...]

Ok, sorted the gearing program a bit more now. It's at www.mauriceb.btinternet.co.uk/Sprockets.exe cos my domain hosting sucks