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Terry Hay

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About Terry Hay

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  1. Terry Hay

    MX Tech AER leaf spring mid valve

    There are a number of arrangements that you could have that provide the ability to tune. A fixed shimstack. Recess the valve centre and install a conventional sleeve / cupped washer. (which is what we do to every AER) A belleville washer and sleeve ( which is what we discussed a few years ago on KTM Talk) As Mog mentioned the KYB trampoline style midvalve cup..........its all just a variation on a theme and all still utilising the leaf spring shimstack. DinoY nailed it when he called it marketing.......and that's just good business. Jeremy is a sharp guy and he will have that thing working well
  2. Terry Hay

    MX Tech AER leaf spring mid valve

    Isn't every shimstack in fact a leaf spring?
  3. Terry Hay

    Torquing triple tree clamps

    You will find yourself going back and forth trying to achieve even torque. Once you feel you are in the zone, do yourself a favour.......ride the bike and get a feel for how it is working. Then remove the upper and lower bolts and ride again. You may never use those bolts again. The 3 bolt lower never really worked that well.
  4. Terry Hay

    Race sag effected by heat

    Just out of curiousity. Would the general consensus be that the following link not be true? https://www.roveron.com/knowledge/impact-temperature So far everything I have seen in my tests would agree with this graph.
  5. Terry Hay

    Race sag effected by heat

    Gustl Bike YZf450 We started at 105 rider sag. Rider standing bolt upright on pegs, holding onto the side of the building. I don't like this method due to the fact that it offers no relevence to actual rider load, but it is very repeatable and suits this purpose. 1 lap 103mm. Full moto 108mm My son is a reasonable MX rider and Champion Road Racer. He knows his way around a track. We are running at or around 40C right now so its not exactly apples and apples. Naturally the level of demand placed on the bikes will also promote a variable. I value your insight and would love to sit down and go over a few things with you should the possisbility ever arise. Maybe next Intermot......So far this discussion has promted me into action and has been quite revealing. Not so much from a sag point of view but the thermal situation in general. It's easy to say that since the improvements made in suspension fluids, heat is of little significance these days, but it seems that we are not quite on top of things yet. Sure we can deal with things the way they are as the situation is tolerable.....or we could seek to improve them even further. No point standing still. Luxon A very easy insight into the level of friction is to find the boundaries. Whether your are checking rider or static sag try the following.... Push down on the rear of the bike and let it come up very, very slowly under your control until movement has ceased. Note the measurement. Now lift the rear of the bike a little and lower very slowly until movement has ceased. Note the measurement. A bike in good order will usually have a difference of 6 - 8mm. Less is exceptional and more is indicative of the need for grease. By averaging out the difference you will achieve a more accurate level of sag. Of course you could perform this act say 3 times and average it out even further for greater accuracy. Whether you condsider this a measurement of friction or simply a symptom is purely semantics. Its something you can work with and offers value.
  6. Terry Hay

    Race sag effected by heat

    The friction is still there when measuring static sag. Best to take steps to measure the amount of friction and account for it in your calculations.
  7. Terry Hay

    Race sag effected by heat

    More testing... Gustl I tested a WP shock by putting it in the spring tester and set the reservoir pressure to 10 bar. I then heated the reservoir up until it was 13 bar as per your outline. The pressure rise was 5.1 kg which is significant. Not quite the 72n you predicted but the shock was static and friction was obviously playing a part here. This turned out to be more than I was expecting. The shock had to be compressed appr 55mm to get it into the tester so the gain would have been greater than at normal sag position. I had my son cut some laps for me on our test track. After 1 lap we did see a loss of sag. After a 16 lap moto we witnessed a gain. This got me thinking.....there is more to this story. I have been back and forth over the last 2 days with different tests (yes....even Christmas day). I fired up the dyno and tried different gas / oil volumes. Different reservoir pistons (I machined my own). Bladders.....sorry Mog. I re-tested the heat effect on springs. This time by heating them in the oven rather than with a heat gun to ensure a thorough heat soak.....even greater loss. Women fail to see the scientific benefits of utilising kitchen equipment. I believe that the spring needs to be considered a mechanism rather than just a piece of steel when it comes to predicting performance. Conclusion....There is a sequence of thermal events occurring here that all bear relevence and come into play at different times/heat levels. Most importantly this discussion/testing has provided me with a more detailed insight into the effects of heat on a shock absorber and a better plan on how to best manage these effects for maximum performance over a moto. The effects are quite significant and I believe there is a lot to gain here. I definitely haven't placed as much importance on this as I should have...I don't believe anyone I know has. No doubt the performance degradation of a shock absorber over a moto is simply written off as rider fatigue or the track getting rougher. How much fresher could the rider be if we get on top of this. Thank you everyone for the discussion.....debate......inspiration.
  8. Terry Hay

    Race sag effected by heat

    Once again we are looking at the effect of heat on sag. If the spring force is yielding through heat, this yield will be assisted by the leverage of the swingarm. If the gas force is increasing through heat, this will be resisted by the leverage of the swingarm (roughly 3 to 1). The system is against you here.
  9. Terry Hay

    Race sag effected by heat

    Gustl Sorry....one other thought. The spring yield is working to advantage given the leverage from the swingarm. Any opposing force being that of the gas pressure is now not only working to disadvantage (acting on the shaft) but this disadvantage is now multiplied by the swingarm / shock leverage ratio.
  10. Terry Hay

    Race sag effected by heat

    Gustl I will happily run that test.......but.... I have never seen a shock get less sag unless you simply heat it up. Hence the reason that I had to clarify the static test as opposed to a dynamic one. In the field you always get more sag. I have to admit I was unaware of the shear modulus figures prior to this. I was happy to think of the spring as simply more pliable. Turns out. I wasn't wrong. We always cycle shocks by hand once they are serviced. It is quite easy to stop an extending shock shaft. So much easier than trying to hold down a spring. The gas pressure certainly has force but as it appears, not enough to overcome the yield from the spring. Luxon It would appear to start at 20C which as you know is a measuring standard. Perhaps a lot more "Real World" that starting at zero. The guys are off on their Christmas break now. We have been developing a new balanced piston system on which we still have a lot of testing to do but I will be sure to include a spring temp test once they are back.
  11. Terry Hay

    Race sag effected by heat

    Luxon For what its worth, I really don't know how much track testing you have done, but the amount of times I have had to grab a rag in order to get a shock out of a bike because the spring was too hot is not insignificant. https://www.roveron.com/knowledge/impact-temperature A little bit of info. The spring rate decline as shown in the graph is significant from 20C to 100C. The graph extends well beyond this but.....you get the picture.
  12. Terry Hay

    Race sag effected by heat

    This is not a perfect test.... but it's still a test. Good enough to see a change in behaviour. The temperatures used this morning are far from what I have experienced with shock absorber springs. They get even hotter. We always account for system friction when setting sag and yet we still see the sag vary. Is this going to create a loose feeling bike? No but is does create a change. I do feel the OPs shock needs some fresh oil and a good going over. But the title of the post was "Does heat effect sag"? Paul Thede performed a simple demonstration with a old set of fork springs where he measured them (length) and then banged them on the ground. They grew by a little over 2mm. This probably wont be found in any table. Yet somehow this happened. This test happened and in spite of theory and opinion the results occurred.
  13. Terry Hay

    Race sag effected by heat

    Gustl As I mentioned, the gas force is working to disadvantage. If the reservoir piston is 46mm in diameter acting on an 18mm shaft then we will see that force reduced. It roughly works out to 6.5 to 1 . So an increase in force at the piston of 6.5 kgs only amounts to 1 kg on the shaft. Okay New test this morning. Ambient temp 23 degrees. WP 69/250 spring. Intercomp spring tester. Heat gun. Laser thermometer I placed the spring in the tester and compressed it to 100.17mm. There was appr. 12 - 15mm of clear space to allow the spring to be installed in the unit and to provide repeatability. I made sure each compression hit the final mark of 100.17mm each time. The tester was never switched off or reset during the test First reading 580.5 kg repeat. Second reading 581.5 kg Third reading 582 kg I would put this down to a small amount of spring growth. Heat to 34 degrees Fourth reading 573.5 kg Heat to 52 degrees Fifth reading 571 kgs The heating of the spring was done away from the spring tester so there was no corruption of the data. I have pulled shocks out of bikes for tuning immediately after a moto and the spring is much hotter than the temps used in this test. We could sit here and theorise all we like.......or......we could test. This is only my take on this but I feel that the excitation of the molecules in the spring wire (due to heat) somehow allows the material to become more pliable. Certainly not weaker. You don't need a gas torch for this to happen and you are not affecting the structual integrity of the wire.
  14. A lot of the latest 250 MX bikes are coming out with fairly heavy springs (.48 kg/mm) I am not surprised that the stock springs are still in there for a 90 kg rider. You should look at a lighter spring for your weight. It will also be a good thing for trail use. If the valving has been altered then I would certainly look at adapting it for your requirements as well. This will help you get the most enjoyment out of each ride.
  15. Terry Hay

    Race sag effected by heat

    Everything from the body of the shock to the spring is subjected to the changing effects of heat here. Whether the heat is effecting the spring, the gas or the effects of friction, the fact remains that the sag will alter pre / post moto. The significant heat soak that the shock is subjected to does not disregard the spring. It gets hot too. When accounting for sag it is advised that friction / stiction is measured and averaged out to provide greater accuracy. If you have done this correctly, you do your best to isolate spring force. After all it is the force that is opposing the combined mass of bike and rider. As mentioned previously and as stated by Luxon, the nitrogen (which is also a spring force) will also alter but this is working to mechanical disadvantage. It was stated that oil viscosity was the culprit for the change in sag. Very unlikely.... We can put forward every theory but the fact remains that the sag does alter. Does the spring remain cool while the rest of the shock gets stinking hot? Very unlikely. It would be interesting to cycle a spring in the dyno for 10 minutes or so and record the effects.
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