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wet vs dry?

Discussion in 'Technical and Troubleshooting Torque' started by emsie, Jun 12, 2006.

  1. So it occurs to me that the subject seems all wrong out of context, but let me fix that :)

    Brochures seem to talk about dry weights for bikes. What does this exactly mean, and, if my guesses are correct about what it means, how much weight can fuel and oil etc really add?
  2. Not sure about oils, but when I used to race cars we used a very rough guide of 1 litre of fuel equalling 1 kg.
  3. "Dry" can mean different things to different manufacturers.

    "Wet" items can include any of the following:

    Engine Oil
    Engine Coolant
    Brake Fluid
    Fork Oil
    Battery ('cos batteries have a liquid acid in them)

    Generally speaking 1 litre of any of these fluids is roughly 1.0 to 1.1kg of weight.

    Some manufacturers quote a "Half-Dry" figure, when means all fluids bar petrol.

    Some manufacturers take greater liberties than others with respect to quoting weight figures without two or more of the above listed liquids present in the bike.

    While petrol generally weighs about 1kg per litre, and no manufacturer quotes weight with petrol included, the sum of the rest of the items can be between 10-20kgs of weight, depending on the bike in question, and around 15kgs of weight for 600-1000cc super/hyper sports bikes.

    i.e. when a manufacturer quotes dry weight, it is rather ambiguous, and the actual fully wet weight of the bike (full tank of fuel) may be anything between 30-40kgs heavier than what is quoted.
  4. Dry is the bike empty with no fluids at all.


    brake fluid
    clutch fluid
    battery fluid

    Fuel weight is anywhere between 660-720 grams per litre.
  5. Dont forget chain lube!

    The difference between dry and wet weights on both my bikes is around 33kg, so yeah, it's quite a bit!
  6. oil based fluids are about 0.9 kg/litre

    I always get a little annoyed when bike mags or bike importers start quoting power to weight ratios.

    Add fluids, tool and a fully clothed rider and these days you adding more than 50% to any weight figure.
  7. wow :eek: I didn't realise it was all quite so much!! Nice to know though - the 150kg bike you sit on in the shop is gonna feel a whole lot different when you ride it away.

    Thanks guys :)
  8. Definately, especially bad when they then go comparing the figure to that of cars. Yes bikes are generally going to have a higher p/w but comparing a dry, riderless bike to a fully loaded car kind of biases the results a little bit. Reminds me of the time one of the Aussie carmakers got in trouble over claiming their car had a higher p/w than the competitor - only because they calculated their p/w ratio based on dry weight.
  9. This is where the motorcycle magazines should be doing us a favour, by weighing all their test bikes fully filled with fluids and fuel. This is the state that we will be using the machine in, anyway. The manufacturers have proved that they cannot be trusted to tell the truth with their figures, so we would finally have some useful benchmark figures to work with, if the mags provided them consistently.
  10. Indeed, power/weight ratios are a bit of a farce.

    Even today it is unlikely that a fully wet unmodified bike with rider will ever achieve a p/w ratio better than 1kW at the rear wheel per 2kgs, even though magazines like to pretend that manufacturers are rapidly closing on the hallowed 1kW per 1kg ratio (quoting ram-air assisted crankshaft kW vs fully-dry weight without rider).

    Used to be for a while there that AMCN did just this. Then they stopped. Wonder why? :roll:
  11. Hey Cathar, In my most recent issue of AMCN they have the Masterbike supersport shootout, and every bike has its wet weight measured, as well as rwhp output measured on a dyno.

    I think with some reviews they dont get to chuck the bike on a dyno, or measure its weight wil all fluids, but from my experience, AMCN will always tell you whether the weight/power in the stats column is claimed by the manufacturer, or measured by them.

    They had a little article awhile ago about dry/wet weights, and they explained that they try to provide measured 'real-life' power and weight figures for every bike that appears in the mag, however time and money and deadlines means it's not always possible.
  12. I knew someone was going to point that out! :grin:

    MasterBike is run by the EuroMags though. AMCN is just reporting the information that all the mags have access to.

    My point being that AMCN does not make it a regular practise with every review of a bike sold locally in Australia. Due to Euro emissions requirements being different to Australia too, as well as ADR reqs, it's not inconceivable that bikes sold in Australia will have different weights to Euro bikes.

    I doubt that time and money really prevents the simple task of wheeling a bike onto a set of scales.
  13. About the only manufacturers that can be trusted would have to be KTM & BMW. KTM list their bikes weight as everything minus fuel & I think BMW quote theirs with 1/2 a tank of fuel -not exactly sure on that though. But geez -don't they cop some stick over it. Every mag I've read whinges & whines about every extra gram when the real proof is in the riding.
  14. The only problem with forcing bike sellers to publish wet weights is that it then puts pressure on designers to reduce fluid tank sizes, in order to cook the figures.

    We run the risk of riding around on bikes with 1 litre fuel tanks, that have to have their oil changed every 100 km.
  15. Very good point. I can think of some new models that are getting closer to that already :roll:
    Cathar has hinted at some reasons why the local mags don't consistently question the importers/manufacturers claims. I used to work in the next cubicle to AMCN, and while I have no direct evidence of interference, I can believe that some importers definitely withhold test machines from publishers who do not play the game their way. (Noticed how a certain mag doesn't seem to have many local tests in it lately?) More importantly, they also "adjust" their advertising budgets.
    Roarin, I'd also (surprisingly) add Ducati to that list. For some reason the power and weight figures I've witnessed being measured seem to be much closer to the truth than any of the Japanese makers.
  16. Gross weight isn't as much of importance as weight distribution.
    The old Ducati 916/996/998's weigh substantially more than a modern 600 with roughly the same power output, but I know which I could put through the twisties more quickly and with greater ease.
    The Duc every time.
  17. Things must have changed a bit. Back around the time of the 851's and the first 916's Ducati made some pretty tenous weight claims