Surely F=uR holds? If you make all tyres out the same rubber you might be right, but in extremis (race bikes) you would select the rubber for the combination of grip and rolling resistance required (actually both as you have different compounds across the tyre).
Or have I missed something?
Straying rather OT now, but friction is only a small part of rolling resistance. Hysteresis losses are bigger.
tyre pressures.
I did not reply because I could see that the "test" was very badly set up.
It was a waste of my time to respond.
Besides it was an article in a magazine that sells advertising space !
I will continue to watch all the various cycle competitions knowing that they will use the best tyres for their event even if they are of the "narrow" type.
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Yes I mean I have not seen any such calculation as a subject with particular diy amps in solid state amps thread.
For the latter case, I use the amplitude/frequency statistics of classical and of rock music published in a few textbooks on acoustics. From these one might assume the reproduction of big chorus is the hardest test for amps and speakers. Even then if the original dynamic range is hardly ever recorded.
Heavy metal however is an easy job, besides the voice coil temperatures...
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OK, my initial interest in this topic was two fold - building my KSA-50 and fixing a mis-designed HP/COMPAQ Laptop.
There seems to be a rash of HP laptops made between 2007 and 2009 that have same problem...they eventually develop an issue where they go into a boot/reboot and never enter the bootup BIOS. Turns out the problem is the BGA (Ball Grid Array) video chip gets so hot that they de-solders itself from the socket (another issue was moving to a ROHS type lead free solder that has a higher melting point than the previously used solder in BGA chips).
Anyway, the main CPU and video processors are close enough proximity on motherboard that they are cooled by the same heatsink fan utilizing a flat copper tube to move the heat from both chips to the main copper heatsink / fan located about three inches away. The issue was that while there was good heatsink transfer tube contact to the main CPU, the video processor die to heatsink tube had a clearly visible air gap. This air gap had a silicone pad that "bridged" the gap. Eventually, the BGA chip would get too hot (since inadequate cooling) and laptop would fail to boot. HP was eventually recalled thousands of laptops for this little oversight. They have since "Closed" the recall.... the temporary fix is to reheat the video chip die to 390F for a few minutes, to allow teh BGA solder to melt and reconnect chip to socket, and re-install the heatsink, making sure there is better contact between heat sink and video chip die.
Question is - In this case, where there is NO contact or pressure on the heatsink to heat source (ie video chip), use layer of paste alone, or copper shim alone, or combo copper shim with paste on both sides? With paste/copper shim/paste, you now have four interfaces the conduct thru,
I have since fixed the last couple of laptops bending the copper tube to ensure some contact to the video chip die, with paste alone. Seems to be working a little better...
There seems to be a rash of HP laptops made between 2007 and 2009 that have same problem...they eventually develop an issue where they go into a boot/reboot and never enter the bootup BIOS. Turns out the problem is the BGA (Ball Grid Array) video chip gets so hot that they de-solders itself from the socket (another issue was moving to a ROHS type lead free solder that has a higher melting point than the previously used solder in BGA chips).
Anyway, the main CPU and video processors are close enough proximity on motherboard that they are cooled by the same heatsink fan utilizing a flat copper tube to move the heat from both chips to the main copper heatsink / fan located about three inches away. The issue was that while there was good heatsink transfer tube contact to the main CPU, the video processor die to heatsink tube had a clearly visible air gap. This air gap had a silicone pad that "bridged" the gap. Eventually, the BGA chip would get too hot (since inadequate cooling) and laptop would fail to boot. HP was eventually recalled thousands of laptops for this little oversight. They have since "Closed" the recall.... the temporary fix is to reheat the video chip die to 390F for a few minutes, to allow teh BGA solder to melt and reconnect chip to socket, and re-install the heatsink, making sure there is better contact between heat sink and video chip die.
Question is - In this case, where there is NO contact or pressure on the heatsink to heat source (ie video chip), use layer of paste alone, or copper shim alone, or combo copper shim with paste on both sides? With paste/copper shim/paste, you now have four interfaces the conduct thru,
I have since fixed the last couple of laptops bending the copper tube to ensure some contact to the video chip die, with paste alone. Seems to be working a little better...
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BMX tyres are constructed differently to typical tyres. If you take two tyres of the same construction but different width, the wider one will have lower rolling resistance. Rolling resistance is also typically measured on smooth surfaces and test the tyre alone, whereas on rough surfaces with a rider, there are extra suspension losses due to the rider being vibrated, and those losses are higher with narrower tyres and higher pressures.
I know they're not the best source, but they have been the most influential recently, so they come up first in Google. There are quite a few other sources who have found similar results.
Professional cyclists have been using wider tyres recently. In the past it was common to see widths as low as 19mm, whereas nowadays 23-25mm is more common, and as much as 30mm where the roads are really rough. However they mostly use what their sponsors tell them, so you can't assume they always use the most effective equipment.
The larger the gap, the more likely that using a shim would be better. I think you would have to do some actual measurements to get an idea of how large. Of course no gap is better, and absolutely no air. Anything is better than air.
The best thermal transfer compound is no thermal transfer compound at all. But since the surfaces of chips and coolers are (usually) not 100% flat and even, some compound must be used to avoid air gaps. A thin layer of good thermal paste is the best for this purpose, and it really should be only very thin layer. Many people use way too much, which is counter productive.
I have worked a lot with air- and watercooling of overclocked computers, and for optimal heat transfer I would lap both heatsink (wet sanding) and sometimes also chip surface on very fine grit sandpaper to make them as flat as possible (on thick glass plate as level surface). Very time consuming proces
But it works wonders for heat transfer! For example the heat spreaders on Intel CPUs were (are?) notorious for being concave, so without sanding the heat sink would only have solid metal to metal contact around the edge (maybe try sanding the back of output mosfet also..).In your situation, I would think a nice copper shim with thin layer of thermal paste on both sides will work well. Just make sure the shim is flat and level.
The worst solution is silicone or similar type "heat pads", which really should not be used for hot CPU or GPU chips, but even so, is often seen in notebooks, as it is a cheap solution in production.
Some textbooks have actual measurements of case temp of output devices.
The case temp follows indeed the amplitude statistics, unfortunately most passive speakers have an impedance minimum right at the frequency which has the maximum amplitudes, statistically. I do not have a scanner , sorry.
the case temperature is Tc.
You need to know Tc to be able to temperature de-rate your devices.
Tc is the temperature existing when you are analysing a particular working condition.
It is important that you have a matching set of working conditions and the appropriate Tc.
If you know your heatsink is sitting at deltaT of 20Cdegrees above ambient in a winter temperature workshop, then you can model the summer temperature of the sink for a worst case operating temperature Ts.
You know the steady heat load through your device to sink interfaces.
That allows you to model the average Tc if all devices are identical and all the interfaces are thermally identical. You now have a good estimate for Tc average.
I allow an extra 5C degrees for worst case device and interface inequalities. Some will be cooler and some will be hotter than the average.
I then use a modified version of Bensen's spreadsheet to model the stresses on the output devices (and the drivers).
Look up David Eather's article since you can't be bothered finding and reading all the manufacturer's detailed heatsink guidance.
You need to know Tc to be able to temperature de-rate your devices.
Tc is the temperature existing when you are analysing a particular working condition.
It is important that you have a matching set of working conditions and the appropriate Tc.
If you know your heatsink is sitting at deltaT of 20Cdegrees above ambient in a winter temperature workshop, then you can model the summer temperature of the sink for a worst case operating temperature Ts.
You know the steady heat load through your device to sink interfaces.
That allows you to model the average Tc if all devices are identical and all the interfaces are thermally identical. You now have a good estimate for Tc average.
I allow an extra 5C degrees for worst case device and interface inequalities. Some will be cooler and some will be hotter than the average.
I then use a modified version of Bensen's spreadsheet to model the stresses on the output devices (and the drivers).
Look up David Eather's article since you can't be bothered finding and reading all the manufacturer's detailed heatsink guidance.
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