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Withershins

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About Withershins

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    TT Newbie

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    United Kingdom
  1. Withershins

    Dynorun on my WR450

    The octane rating has no relevance to performance or economy, it's there purely to stop the end gasses pre-igniting. It's only the energy in the fuel that matters - the bang for your buck. It may be of some interest that some higher octane fuels have slightly lower calorific value than regular unleaded. Using higher octane fuels in an engine that has not been modded in any way is much like using snake oil, or magic beans. The increased throttle response, improved fuel economy, etc. only comes to those people because they want it to (psychosomatic, almost). There is no actual gain, unless there was a problem with knock. There is only a couple of ways of increasing performance: More fuel/air getting to the combustion chamber, or getting more energy relesed from the fuel/air mix (by increasing compression ratio), and it's only the latter which benefits from a higher octane fuel overcoming any pre-ignition. It's the other additives that make the fuel burn more cleanly, or evenly, etc. that make different fuels 'feel' different. Not the octane rating. Sorry to rant, but people wasting money on expensive fuels for a standard engine bothers me. :ride:
  2. Withershins

    Dynorun on my WR450

    What do you mean by 'hotter'?
  3. onbaord!! Have you used the spell check button at the bottom?
  4. Terrible use of commas.
  5. Withershins

    My idea-tire related

    what about Avon Distanzia tyres. I have seen guys racing supermoto with these, so they clearly work as a compromise. Distanzia
  6. Withershins

    how can i lighten my bike up ??

    It needs too WR450's are not heavy. XR650's CCM's and LC4's are heavy If you spent a fortune on titanium/carbon goodies, loose the battery and starter motor you will shed maybe 25 kgs. You can loose that by eating less pies for a few months. I should know I have lost nearly two stone to get more performance from my WR400. It is a free modification that helps power, suspension, and about every other part of the bike.
  7. Withershins

    Braking force. Info please.

    Dunno if this is going to be too much/not enough or the right sort of info, but here goes: Like a bikes brake lever will assist your hand, the pedal gives a mechanical advantage to your foot depending on the ratio. A 3:1 ratio will mean yor foot travels a short distance but ony multiplies the force by a smallish amount. An 8:1 ratio is going to give you a heap big advantage but the pedal will have to travel in a bigger arc. more travel equals more feel as you have more control over how much force to exert, but too much can feel wrong and you may not have enough room to move the pedal that far. Also, too much force at this point can be bad, as panic braking will just lock the wheels up immediately. Next is the master cylinder, well not quite, a lot of vehicles use a HydroBoost system that gives more pressure from the power steering (I think?). Now the master cylinder is the bit most people get wrong, with master cylinders less is more. The pressure the master cylinder is worked out by dividing the pressure from the lever, over the area of the master cylinder bore. For example, I'll say that from the lever you are putting 200kgs of force to the master cylinder. The master cylinder is 19mm giving a surface area of 2.8cm2. So 200/2.8 = 71.4 kgs/cm. if the master cylinder was 15mm you would have 200/1.8 = 111 kgs/cm. The smaller diameter master cylinder gives more pressure, but, as it is smaller cannot move as much fluid in the same stroke as the bigger one. As cars and trucks usually have a lot of calipers coming off of one master cylinder there is a lot of fluid to move around so you will need a big master cylinder, but the trick is to keep it as small as possible. Finally comes the caliper, this is the reverse of the master cylinder where big is best. Essentially you have the pressure from the master cylinder multiplied by the area of the piston/s so the more, or bigger, pistons you have - will give you more clamping force. Again the downside is that more pistons need more fluid, meaning a bigger master cylinder, but the trade-off is worth it. It is very easy to get a lot of force to a caliper. eg (I may get this bit wrong as I am more used to metric ) in a car: Your leg provides 90lbs of force to the pedal, after the pedal ratio has worked its advantage you have 360 lbs going to a 1.25" master cylinder. So 360/1.23 = 292 psi. This pressure now goes to a twin piston caliper (the pistons are 1.5" diameter) So multiply the pressure by the surface area of both pistons meaning that: 292 * 3.5 = 1022lbs of clamping force, all from your original 90lbs from your leg However a car has four calipers, so you now need to know the piston area for the whole system, how big the master cylinder needs to be, how much lever travel you want, how much force the caliper needs to exert, will you need to use additional pressure other than your leg so that it all 'feels' right (with a car the answer will usually be yes). This is the easy bit compared to... ... Stopping the damn car. Stopping is simply accelerating backwards (every action has an equal and opposite re-action, so to slow down you need to provide a force in the opposite direction to that which you are travelling) Newton states that Force = Mass * Acceleration (F=MA) or Acceleration (deceleration in this case) equals Force over the mass of the car. To get all these bits of math you will need to know the friction co-efficient of the brake pads in order to get the rotor output force, which is simply the clamping force multiplied by the friction coeficient of each brake pad. Then there is the torque created by the rotor etc, etc, etc... the list just grows. In answer to the question; it all depends on how far you want to go. I hope I have given you some ideas, but there is loads that could be delved into.
  8. I changed my front tyre the other day. Realized the rim was possibly being worn by the bead of the tyre so I changed the rim. From there, of course I had to get a new hub, and seeing as having a new front hub get worn out prematureley by a worn rear I changed that too. Along with the bearings, Forks, swingarm and frame. Seeing as I have new bolts in the frame should I get a new engine? There is nothing wrong with preventative maintenance, there are a lot more moving parts in a 4-stroke after all. So you do have to check the tolerances on more things, but seriously. If it aint broke; don't fix it.
  9. I did a tarmac only supermoto day last winter so I took my road helmet. Problem was there was so much slow speed stuff (compared to road racing), and I was breathing so hard getting the bike round a twisty kart track, the visor was permanently fogged up. In contrast on a hot day I went on a practice MX track with the road helmet, and couldn't believe how much dust was getting to my eyes. In summary MX is relatively slow and hard work, so you want a well airated helmet with a good seal around your eyes. This is from what I have learned, I could be completely wrong as I have no MX background only SM.
  10. Withershins

    free sponsorship?

    You want to try and get any sponsorship at all in the UK. Look at James Ellison, very successfull road racer, bareley sponsored at all. In the UK it is more about who you are, not about how good you are.
  11. Withershins

    Calling all WR engine people

    Fair enough I'll let you know then. After I have done it
  12. Withershins

    Calling all WR engine people

    Thank you!! That's what I was thinking. Looks like an easy job. Right or wrong
  13. Withershins

    Calling all WR engine people

    Seeing as my usual forum is experiencing 'technical difficulties' I will ask the collective inteligence of this, fine forum. While letting my engine warm up for an oil change, I noticed a small leak, bubbling from this hole: There seems to be no mention of this hole in the workshop manual. So what's going on??
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