H&R Sport Springs - spring rate measured
 

H&R has never disclosed the spring rates for their Sport Spring lowering springs (their coilover kit for our cars are 345/345, these are not those springs). They say its because there is no agreed upon means of measuring progressive springs. Some have argued its because they didn't want anyone to copy their design. Though that theory doesn't hold up, how progressive they are is equally important as the rate.

Anyway, I wanted a way to at least compare the front spring to the rear. And also to get an idea how they compare to the stock springs.

I built the rig in the photo. My design. It uses a regular analog bathroom scale, and the boom multiplies the rate by twice what the scale reads. So the 300 lb scale can measure up to 600 lb.

There is a ruler stuck to the side to measure how far the spring is compressed. The means of measurement was to jack the jack a little to initially compress the spring, then carefully jack it 1/2" at a time, and record how much the weight on scale increased from previous reading. By taking several such measurements, I was able to see how 'progressive' each spring was. How much more each half inch increased from the previous half inch. These readings also allowed me to get a one inch rate as well.

I determined the fronts increase at approximately 1.05x for each inch compressed, over the first 2.5" of compression. It probably increases more the more its compressed, but my scale wouldn't allow further compression. The rears are less progressive, at just 1.01x

To me a fair way to rate progressive springs would be what their 1" rate is at ride height. If you were driving down a level road and hit a bump, how stiff would it feel compared to say, stock springs. Since they are progressive, the bigger the bump the more the rate, but you gotta pick one inch somewhere, and ride height seems like a good somewhere. So I took the 1" rate from 1.5" to 2", and used the 1.01R and 1.05F progression to extrapolate an approximate ride height rate.

Oh, I also calibrated my setup using a stock spring of a known rate. I was able to accurately measure the correct rate of 262 lbs/inch using this rig. So there is some reason to think my design and my maths are not horribly inaccurate.

One last thing, my rig uses the stock top hat and stock lower spring mount removed from a stock shock. These cradle the spring, and immobilize one coil top, one coil bottom, just like real world. Twohoos likewise took this into consideration when he calculated the stock spring rates in his excellent dissertation. So basically my numbers allow comparing to stock spring rates from twohoos chart. But they do not allow direct comparison to aftermarket springs as measured on a professional spring compressor. In that config, the raw spring is measured, so its not a real world value (but it still allows comparing one aftermarket spring to another, which is the point. Bottom line, just be careful comparing aftermarket rate to stock rates, as they are measured differently. You can compare my crude measured rates to stock, but not to some other aftermarket spring rate, progressive or otherwise).

Ok, so get on with it man, what are the spring rates???

Measured H&R Sport spring rates: (in lb/inch)

F: 292 (H&R 29 417 VA)
R: 326 (H&R 29 417 HA)


Attachment 138625

Bellissimo!! :D :thumbup:

Next step is to expand the range, perhaps by figuring out a way to either a) extend the boom for a greater multiplier, and/or b) preload the spring such that the scale reads zero at a given compression (from there, you'd be able to compress a further 300*N pounds).

Regardless, I'd love to see what numbers you measure for other OE springs.

Very cool, bruv.

I have several other oem springs I could measure. I'll get on that...

I thought about a longer boom, the problem is it multiplies any inaccuracies by an equal amount. If the bathroom scale is off by 1%, well now its N%, whatever the boom multiplier is. Any imperfections in how well I line up the ruler hash marks, N%. Imperfections in how centered the jack is on its mark, or the spring mounts on their marks.

The preload thing wouldn't work. Any preload on the spring is still going to put that much weight on the scale. Say I preload a straight rate 100# spring 2", and want to measure compressing it another inch. The moment the jack starts moving the spring, its going to read 100# (half the 200# of spring resistance @2"). Add the second inch, it'll go up to 150# (half the increase in spring resistance). (150-100)x2 = spring rate.

I can directly measure straight rate spring up to 600 inch/#. Progressive are much more difficult. Ideally I'd compress such a spring to ride height, then add another inch and measure increase in resistance. But that would greatly exceed any bathroom scale's capacity, not to mention be very unsafe. If the rig failed, it wouod be catastrophic.

I chose the bathroom scale because they are cheap, yet relatively accurate.

Very cool!