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MG MGB Technical - Coil spring rates

Can anyone confirm the front spring rates for the B?

My '71 roadster has a height of 10in, and a pair from a '78 GT has a height of 9.75, and I believe they are a higher rate spring.
So fitting them will lower the car a tad and harden up the front end?

Any thoughts?

Also going to the 3/4 anti roll bar from the GT.

Colin
Colin Parkinson

If the later spring is only 1/4" shorter, but stiffer, chances are it won't lower the car at all.
Dave O'Neill 2

That's strange
I was under the impression that roadster springs were 10" long and rated 350lb and GT springs were 9" long and I think 450 or 480 but both ended up the same length/ride height fitted
Any part No.s on them
William Revit

The R/B B's and all V8's had the higher ride height, down to a 1" spacer on top of the front cross member. The later length could have been down to tinkering with the finished height, the higher spring rate was probably down to dealing with the extra weight of the steel box behind the plastic bumper.
The 1/4" would be hardly noticeable but the 30% extra stiffness certainly would.
Allan Reeling

I have notes of five different spring specs ranging from 9.1" free height to 10.2" (excluding competition). They varied in wire gauge as well as free coils, and the loaded height ranged from 6.6" to 7.44". Load rates varied from 348 lb/in to 480, but the longest springs could be found on RB GTs as well as CB roadsters.

Table here http://www.mgb-stuff.org.uk/suspensiontext.htm#springs

71 roadster was 9.9" free, 7" loaded, and a rate of 348 lb per in.

RB GT was 10.2" free, 7.44" loaded, 373 lb/in.

So without the weight of the bumpers and the GT roof I think you would end up both higher and harder, been down that route myself. But exactly what spec you would get with new springs today is anyone's guess. A few years ago I bought a pair and when the chap put them on the counter they were different heights. I politely asked for two the same, and he obliged, but said "It won't make any difference". It didn't, the fitted heights were still different. They usually have paint splashes to denote the spec.
paulh4

Thanks paulh4 a really useful table you gave a link to.
But that only confuses me even more as the springs from the rubber bumper GT are 9.75, the table suggests 10.2.

Guess they have sagged over time????

Colin
Colin Parkinson

Possibly, also possibly the wrong ones if they had been replaced, and as I found both old and new springs are very variable, as in the attached which relate to four different sets I have had over two cars. The three on the right should all be to the same spec.

From left to right they are 'original' CB roadster spring, CB GT spring I tried in the roadster as an experiment, 'original' spring removed from the V8, and new spring ready to go in the V8. The original roadster spring is barely any shorter, but sagged quite a bit when loaded. The CB GT springs had been on 10 years and about 23k but are quite a bit shorter than spec. I put new correct spec back on, but don't have a measurement for them. The original V8 spring is longer than spec, and the new V8 spring a lot longer!

On first fitting the V8 gave a ride height of 16.25" right and 16.5" left. After a couple of miles over sleeping policemen and the like to settle them they had come down to 15" and 15.5", and two years later they were 14.5" and 14.625".


paulh4

I replaced the front springs on my 71 B about 15 years ago and within 2 years it had sunk so the ride height was lower than it had been with the 30 year old springs. The car handled great but my exhaust caught every sleeping policemen. I replaced them again about 10 years ago, this time with rubber bumper spec springs. It took a while but the front ride height looks about right now that they have sunk. The lower arms are sitting slightly upward towards the wheel end. About 5 years ago I replaced the tyres with 175-70, the previous ones were 185-65. I have had the opportunity to drive my car on the Gaydon test track with both sets of tyres and noted a marked difference in the cornering speeds. I have since replaced the anti roll bar with a 3/4" and it now feels much more stable. My new rear springs have settled too.
Paul Hollingworth

This thread was discussed between 18/10/2017 and 29/10/2017

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