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Aug 15, 2006 12:19:02 GMT
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And of course beyond the issue of manufacturing you have the whole handling issue. By lowering the ride height of a car but retaining the orignal springs with the original rates then you increase the likelyhood of the suspension bottoming out. Where as most correctly specified lowering springs are uprated to compensate for this. But by shortening a spring do you not change it's rate? Shorter spring = stiffer spring It's physics, and you cannae change the laws of physics.... no, i always thought that shortening it makes no change whatsoever. The 'stiffness' is in the spring, not in its height/size. as you said, you cant change the laws of physics
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Last Edit: Aug 15, 2006 12:20:00 GMT by Keefy
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Aug 15, 2006 12:22:58 GMT
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Maybe you're right. I'm not sure now.
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filmidget
East Midlands
Mostly Lurking
Posts: 1,652
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Aug 15, 2006 12:23:14 GMT
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I though shortening stiffened as well?
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'79 MG Midget 1500 - Still patiently awaiting attention '02 Vauxhall Astra 1.8 Elegance(!) - Better than you might think '03 Mazda MX5 - All new and shiny looking (thanks to Antony at Rust Republic) '09 Renault Clio - Needs to go.
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MWF
Posted a lot
Posts: 2,945
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Aug 15, 2006 12:23:40 GMT
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And of course beyond the issue of manufacturing you have the whole handling issue. By lowering the ride height of a car but retaining the orignal springs with the original rates then you increase the likelyhood of the suspension bottoming out. Where as most correctly specified lowering springs are uprated to compensate for this. But by shortening a spring do you not change it's rate? Shorter spring = stiffer spring It's physics, and you cannae change the laws of physics.... Not as I understand it. You just end up with a shorter version of the original spring.
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Aug 15, 2006 12:29:55 GMT
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Well, in NZ, cutting the spring so it can't seat on it's own is illegal, using ANY method other than having the shock machined to then trap the spring within the smaller space, is illegal, so thusly, straps, belts, wires to hold the springs etc. Doesn't fly.
Being in the vehicle recovery industry, you do see a lot of retardation modification wise and a lot of that is down to either completely removing the spring or simply cutting it too far. I cut a few coils off the rear of my 910, but only enough to make it sit flat. With what I can only assume was still factory length springs, it sat with posi-camber, no-one wants that, it would make it unsafe unless it was under load to a point where it say without any positive camber.
I don't think MWF is attacking anyone personally, he's just voicing his concern at what level people sometimes go to in what is to a lot of people just for "cosmetic" value. There are safetly issues involved. Even if you cut the spring short but trap it with wire or some such, if you were to go over a severe bump or over a period of time, some nasty pot holes, if the shock wasn't shortened to accomodate the smaller spring, then it could push/stab through the strut top. Which would be a rather nasty and unwanted surprise which could lead to some dangerous manoevoures depending on what speed the incident happened at.
If you've chopped your springs and adjusted everything else accordingly, there is no large safety issues as long as you're aware that you have less shock travel than before (and maybe you can't go off-roading like you used to). Of course, regardless, chopped springs are illegal in NZ. Having said that, if they're seated correctly and not obscenely low (we're only allowed 100mm at lowest point before needing a Low Volume Certification) then generally the WoF man won't notice.
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Skyline: 1963 - 1973 - 1983 Sunny: 1982 450SLC: 1973 Navara: 1992 Gloria: 1992
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Aug 15, 2006 12:30:00 GMT
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Shortening a spring does make it marginally stiffer but that's dictated by the properties of the metal it's made from. Remember that a coil spring works in exactly the same way as a tortion bar. Under compression the wire is twisted. If you remove one turn from a ten coils spring the wire forming the remaining nine turns now has to twist a little further to accomodate the same amount of compression as before. The more you cut off the further the wire needs to twist to accomodate the same movement. Ultimately. if you were to cut enough off there's a possibility that the wire could be twisted beyong it's elastic limit and snap but in practice this is very unlikely. I think this is one the theoretical safety problem MWF is on about. Truth is that unless you go silly and cut half the turns off it should never be a problem.
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1962 Datsun Bluebird Estate - 1971 Datsun 510 SSS - 1976 Datsun 710 SSS - 1981 Dodge van - 1985 Nissan Cherry Europe GTi - 1988 Nissan Prairie - 1990 Hyundai Pony Pickup - 1992 Mazda MX5
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filmidget
East Midlands
Mostly Lurking
Posts: 1,652
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Aug 15, 2006 12:32:39 GMT
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A coil spring is just a long torsion bar all coiled up... A long bar will twist more than a short one, therefore a long spring will twist (compress) more than a short spring? Yes? (my physics teacher would be so proud ) EDIT: Ah, beaten to it by Ratdat. But assuming linear rate (non-progressive) springs, if you cut one coil off out of ten, you are stiffening 10%? That's quite significant rate change?
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Last Edit: Aug 15, 2006 12:36:29 GMT by filmidget
'79 MG Midget 1500 - Still patiently awaiting attention '02 Vauxhall Astra 1.8 Elegance(!) - Better than you might think '03 Mazda MX5 - All new and shiny looking (thanks to Antony at Rust Republic) '09 Renault Clio - Needs to go.
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Aug 15, 2006 12:42:07 GMT
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Not as I understand it. You just end up with a shorter version of the original spring. That's the point, you're wrong. Your whole argument against cut springs is based on a completely incorrect assumption.
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Aug 15, 2006 12:47:32 GMT
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And sometimes it's blatent. I mean for instance in the Sunday Times this week there's a huge add by Halfords or PCWorld for I-Pod FM transmitters for your car. Yet underneath, in the small print, it reads they are ilegal to use without a broadcasting license. The law is about to be changed so they are legal, hence everyone openly selling them now. BTW, it`s no worse than the old radar detectors - it was legal to buy them but not to use them for their intended purpose ;D
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Aug 15, 2006 13:09:48 GMT
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curse word, i was doing something else when i wrote that and was just thinking that what i had written was wrong. Ignore me lol
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Aug 15, 2006 16:15:06 GMT
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Can you get these blue dots in orange?
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ILIKELURKINGME
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Seth
South East
MorrisOxford TriumphMirald HillmanMinx BorgwardIsabellaCombi
Posts: 15,538
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Aug 15, 2006 16:38:24 GMT
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The free length of a coil spring is not actually a factor that affects its rate. Factors that do affect the spring rate are coil diameter, wire diameter, number of active coils* and a couple of materials related constants. What this means is that when you chop a spring you do affect the spring rate as you reduce the number of active coils. The spring rate will go up in proportion to the number of coils you remove but not by a huge amount. *These are the coils that actually do the work so in the case of a normal straight spring with ends flattened and ground those end coils are not counted
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Last Edit: Aug 15, 2006 16:38:49 GMT by Seth
Follow your dreams or you might as well be a vegetable.
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Aug 15, 2006 18:00:17 GMT
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Even if you cut the spring short but trap it with wire or some such, if you were to go over a severe bump or over a period of time, some nasty pot holes, if the shock wasn't shortened to accomodate the smaller spring, then it could push/stab through the strut top. Which would be a rather nasty and unwanted surprise which could lead to some dangerous manoevoures depending on what speed the incident happened at. That would only happen if you removed the bumpstop, it has nothing to do with the length of the spring unless the standard spring is becoming coilbound and limiting travel........ think about it What it does do to dampers is Move them out of there Ideal operating range and depending on the whole suspension design, may well soften the suspension as it goes falling rate in bump The bigger Danger is in Droop with springs being uncompressed and coming loose, but this can be avoided by using a positive stop to limit droop as hotwire has done or Wiring the Springs into the cups top and bottom...... Big Tywraps are great for this BTW Cutting coils if done correctly is no problem at all, and springs do increase in rate as they decrease in length Remember kids that "Professional just means you get paid for it...... it doesnt mean you are any good at it" ;D I have bought "Lowered uprated" springs before and checked the rate to find they are lower but softer than before And that was from a "Professional Company" who would not accept it even when I took a scale in and did the rate check on their Press in front of them ..... to get the money back I had to explain that Trading Standards would be called if they didnt co-operate But they were nice and shiny..... Powdercoated too which they Kept saying....... very proud of it but had no Idea of the implications of the process obviously A little knowledge is a very dangerous thing ;D
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Last Edit: Aug 15, 2006 18:01:46 GMT by CR500Dom
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