I have a 18 speed malvern star bike with shimano gearing and i need to know how to the path for the chain

SOURCE: wont change gears 12or3

You don't state which operating system is fitted but this is the generic approach to adjustment of all front derailer systems.

If possible suspend rear of bike so that you can easily work your way through gears using hand rotation of pedals.

1. Put chain on to largest rear wheel cog.

2. Set front mechanism control to lowest gear position.

3. Make a written note of cable clamping to derailer mechanism. Disconnect cable at derailer - usually held by single clamp screw.

4. If cage of mechanism not over smallest chainwheel locate the low adjustment screw. This will probably be at the top front of the mechanism and is sometimes indicated by the letter "L" stamped nearby. If adjusting screws are unmarked you will have to find it by trial and error. Usually the high and low adjustment screws are about three quarters of an inch apart and are quite small so you should be able to identify them. Rotate the low adjustment screw until the cage of the mech is over the smallest chainwheel and the chain just clears the inside face of the cage as the pedals are rotated.

5. Move the rear wheel mechanisim throughout its full range to make sure the chain clears the front mechanisim cage for all of the rear gears. Tweek adjustment of low screw as necessary just a fraction of a turn at a time.

6. Put chain on to smallest rear wheel cog.

7. Now pull or lever the mechanism outward whilst rotating cranks to move chain on to the largest chainwheel. If it won't move don't force it over. Look for the high adjusting screw, perhaps "H", and adjust to give extra travel to the mechanisim.

8. Check that cage is parallel to chainwheel and it just clears chainwheel as it rises up and over. If the clearance gap is more than about one eighth of an inch it will have to be lowered.

If the mechanism is held on the bike with a clamp make a note of how much it has to come down to give a clearance of just under one eighth. Mark a line below the clamp for this adjustment and move the whole mechanisim down to the line. Now view from above the chainwheel and make sure that the cage is aligned parallel to the chainwheel. Take care not to align with chain as this is probably running at an angle to the chainwheel.

If mechanisim has fixed mount then there will probably be an adjustment screw. This should be the one remaining after you have eliminated the low and high adjustment screws.

If mech has been moved hand operate through gear range to make sure it clears all three chainwheels.

9. Now with chain on smallest cog at rear and largest chainwheel at front make sure that the chain just clears the cage as the chainwheel is rotated. Tweek with a fraction of a turn of high adjuster screw if neccessary and run rear gears through whole range to make sure that the chain clears the cage without rubbing anywhere.

10. Take the chain back down on to the smallest chainwheel.

11. Make sure front gear shift is still at low setting.

12. There is probably a barrel adjuster for the cable where it comes out of the gearshift. Screw this fully in. You may have to release a locking ring first. Check the other end of the cable sleeve for another barrel adjuster and screw this in if you find one. Check also for an adjuster at the derailer.

13. Take up all the slack on the cable and clamp it in position on the derailer mechanisim. This is when you need the note you made at 3 will save you hassle.

14. Put chain on nearest to middle rear cog.

15. Unscrew cable adjuster until mechanisim moves correctly up and down through all three gears. Check that chain clears cage throughout complete range of rear cogs.

16. If you get problems check lubrication of cable and mechanisim pivots. A very small tweek on the limit screws may be neccessary in difficult cases.

Happy riding.

SOURCE: shimano tiagra 9 speed shifters how to change gear

Go to http://techdocs.shimano.com/techdocs/index.jsp

Search in drop down list to go to all tiagra items and identify your particular components. Shimano are good at numbering their parts and you should find the number you seek on the bicycle component. You will usually be able to download an exploded parts diagram and service instructions. The service instructions are prefixed by the letters SI.

SOURCE: 18 speed bike 6 gear shift works fine 3 gear

If the cable is rusty or otherwise binding it won't let the derailleur fall toward the smaller sprockets when the control is moved. Likewise, it may not even let you move the control in the direction that pulls the cable (bigger rings).

If you don't know much about the process I suggest you read this:

http://coachlevi.com/cycling/complete-beginner-guide-to-bicycle-gears-shifting/

and take the bike to a Local Bike Shop for a look-see and maybe a tune-up.

SOURCE: clueless

My $.02...

To expand and maybe simplify the great advice offered by hgpilot...

The smallest cog in the rear and the largest chainring will limit the highest speed the bike can be pedaled. Divide the chainring by the cog (11t). Give some thought to the other (climbing/high torque) end of the problems as rarely do we max out our bike's speed capacity out of necessity but when that monster hill looms we dive deep into the other end of the cassette and smaller chainring because we HAVE to.

All else being equal, when comparing the typical compact crank of 50/36 or with a typical road crank (53/39) there is less of a limitation on the high end (2/50 or -4%) but an appreciable increase in low end torque (3/39 or +7.6%) from the smaller chainrings. A triple chainring can widen that performance envelope at the bottom only (typical 28t).

Cranksets and chainrings are generally a long term commitment. Cassettes are a piece of cake to exchange, or you can stock different wheelsets for even faster adaptability.

You don't say what gear ratio and wheel size you're (presumably) spinning out in with your buds. If you're topping out a road crankset and a 12 cog you're amazingly strong for an apparent novice.

Even a modest but unlikely 48 x12 pushing normal 700c road wheels at 90 rpm cadence would be 4 x 90 x 2.19 meters = 791 meters/min = 47+ kph or 29+mph. If you could maintain THAT forever I want to be right behind you. Higher cadence and a typical large chainring gets you into pro speeds.

Having a closer-spaced cassette might make more sense if you're having trouble matching your cadence to your requirements and keeping up at high speeds. The 11-26 8sp might typically go 11-13-15-17-19-21-23-26. At the high end you have a 2-tooth jump from 13 to 11 for higher speed. That's a 15.3% increase in load for the same speed. Imagine if you got rid of the 26 and had a 12 instead. The jumps in load from 13 to 12 and 12 to 11 would be 7.7% and 8.3%, respectively. Much easier to adapt to when the boyz put the hammer down.

SOURCE: Need to adjust the gears on 18 speed Next

Since you don't specify the make or model a manual is not likely to be recommended for you. However, gears adjustments are sort of generic within limits. Try this link and find your shifters...

http://parktool.com/repair/byregion.asp?catid=53