grass trackers don't exactly need to slow down in a race....Quote:
Originally Posted by novarally
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grass trackers don't exactly need to slow down in a race....Quote:
Originally Posted by novarally
Braking efficiency is massively complex as it depends on the weight, CoG and geometry of the vehicle and the tyres grip levels etc, I do know someone who made a spreadsheet to calculate it as a point of interest but he's now somewhat busy for a year with Force India... lolQuote:
Originally Posted by novarally
Even the spreadsheet was fairly rough though, and it was a good 2 pages or so of various measurements which would be hard to collect without modelling the car from scratch in it's entirety.
Your main 'foe' against them working is the heat buildup though imo, no large brakes have totally fallen over because they cant exert enough force to stop to my knowledge.
Also the KE might not be huge, but the inertia you're fighting will be considerably larger than a bike.
short runs, maybe 10 braking efforts per run, only a couple of them will be full on.. as a guess.. keeping heat in might be more of an issue...
Standard 236mm solid disc is 2.9kg.Quote:
Originally Posted by mowgli
Yes, I think the bike disc would need some sort of mounting bell, which will add weight.
the discs are heated at the surface, and this is not a problem where you have some sort of thickness to it, the outside of the disc may well be hot, but it dissipates into the discs, the bike discs are just over 1.3rd of the weight and higher diameter, so they are considerably thinner, and imo you're going to get the heat from both sides combining in the middle of the disc instead of dissipating effectively through it's thickness, and from there the heat issue is going to be rough.
and if during braking in competition only 8 out of 10 are at full effort something is going wrong somewhere...
i mean, just slowing slightly, setting up for a corner as opposed to slowing to a full stop. i know each braking movement will be hard, but the effort to scrub 10mph off is a lot less than scrubbing off 100mph.
Ah ok, but still I think heat is gonna be an issue, for your example of slowing down 10mph, assuming a total conversion from KE to heat energy (i.e ignoring any that gets converted to sound etc) you heat the discs by about 40c, now I'm not sure what kind of temperature brake fade kicks in but brake fluid boils at around 300, after its travelled into the brake system, so assuming your 10 runs you haven't got any room for any high speed to low braking runs.
edit: and that's assuming the heat is dissipated perfectly.
the discs can get as hot as you like.... its the pads and fluid that will suffer if you dont get the right compounds.
The mass of the vehicle is mostly irrelevant as said the KE is what you are dumping as heat, and then the interia of the drive train (that might be a problem).
I reckon, give it a go with some high end pads and see how it goes
I would have thought it's the heat of the discs that largely decides how much the pads break down into the gas that iirc, causes brake fade? Kinda like touching water with a heated paperclip, or a lump of steel, both still bubble at their surfaces, granted the paperclip cools faster as well though.Quote:
Originally Posted by Stuart
The mass (as a function of velocity) decides the KE though and also I meant the inertia of the vehicle more than the rotating inertia, so that's 2 direct relationships to mass that effect braking, calling it irrelevant is a bit extreme imo, it's one of the main factors that effect braking requirements!
It may not have come across in my posts, but I'm all for giving it a go, but my prediction is heat is an issue, and either extra cooling needs to be employed, or a beefier disc used.
Colin
How about mocking up some fitting then trialing them on a breaker you have in on a long straight at lower speeds to start with, if it ccould handle say the speed/stopping of an xe nova weighing around 80kg's then it will cope with your lightweight model.
I wouldnt fancy trialing it in a competition!