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Adding A Front Tooth?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by RobE, Oct 27, 2010.

  1. On the highway at 100 kph the Hornet is running at a bit over 4,000 revs in 6th.

    It makes me want to go up one more gear.

    What would be the performance consequences of adding one more tooth to the front sprocket?

    Are such cogs available?

    Would this make the speedo inaccurate? What else?
  2. Adding a tooth to the front sprocket will drop your revs at a given speed in every gear to a value calculated by dividing your original revs by the new number of teeth and then multiplying by the old number of teeth.

    You will find acceleration reduced in every gear, although you can get round this in every gear but first by dropping a cog or hanging onto the lower gears longer. However, this might negate any improvement in fuel consumption you might otherwise see.

    You'll also find that you won't be able to trickle along at low speeds in high gears so well, as chain snatch will manifest itself sooner, although this is less of a problem with a four than with a big single or twin.

    Alternative sprockets are pretty widely available for common bikes. I would expect there to be a selection to be available for the Hornet. The only limitation might be that, at big sizes, you may run out of clearance around the sprocket.

    Larger front sprox don't, generally, require a longer chain. Might do if the axle starts out as far forward as it'll go before the sprocket change though.

    Speedo accuracy will depend on whether it drives from the front wheel (no effect), the rear wheel (no effect but highly unlikely) or the gearbox. If it's the gearbox, the speedo reading will be dropped by the same proportion as the engine revs. However, as going from a 14 tooth to a 15 tooth sprocket (for example) will only make a 7% difference and as most speedos have getting on for 10% optimism built in, you'll probably get away with it. Would be worth checking against a GPS before trusting your licence to it.

    Front sprockets are relatively cheap. It's probably worth a go as you can always revert to standard if you don't like the effect, without having sunk a fortune into it.
  3. wot pat said.

    Also, 4000rpm on a 600/4 at 100 is not that busy. I would have actually expected 5500 or even higher.

    It depends on where you do must of your riding. If it's all on the HWY, then it might be worth trying. They only cost about $25 and it's not hard to do yourself.
  4. I reckon 4000 in 6th may even be slightly taller than stock. Can another H600 owner confirm? ZZR250's are spinning at 8,000 at that speed and they will do that all day so I wouldnt think you have much to worry about. Having said that my Bandit is doing 3,300 but its a torque factory. Even they work better on the north side of 4,000.
  5. I couldn't see running under 4000 rpm be a good thing.
  6. adding 1 tooth on the front will do just over 2/5th of **** all. if you really want to make a noticable change to the rpm. (ie more than 100rpm) you will need to also knock a few off the rear too.

    as above 4000rpm aint bad.
  7. Actually 1 tooth in 16 is over 6% and represents 250rpm at 4000. So not huge, but not insignificant.

    I should add that inline 4s tend to have annoying resonance around 4000 rpm. So that may explain why the OP finds it annoying and going the other way might actually solve the problem.
  8. I thought this too, but if it'll pull a bit higher ratio, I don't see any harm in giving it a go.