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MG MGB Technical - weight of mgb rear

Does anyone know what the rear of the MGB weighs?
I am ordering up some coil springs and will need to know how much weight will go on them.
Has anyone ever parked the back end of their car on a weigh bridge?.
I know that the axle weighs 175lbs, the springs and shackels 30lbs, and the shocks 20lbs. So if I weigh the wheels and subtract all of the formantioned, I will have an answer.
Peter

Given the near 50/50 weight distribution isn't it half the weight of the car? Workshop Manual quotes 1418lb for the rear for kerbside plus driver, passenger and 50lb luggage for 63 to 71, 1362lb for 71 to 74. Rear spring loads are given as 400lb to 450lb for a CB roadster, with rates of 105lb/inch (that is for a CB GT).
Paul Hunt 2

Thanks Paul,
I had a look though the archives and found two figures for working load.
400lbs +/-15
and 510lbs +/- 15
Do you know how the working load translates to weight?
2 times 400 (or 510) doesn't equal 1400 obviously.
Peter

The rear corner weights of my car with fiberglass leaf springs & tube shocks is 546 left and 489 right, and that's with the battery in the right side battery box (and me in the driver's seat) LHD. That should be an accurate weight for figuring coil spring needs, as the 'glass springs are only a few pounds each.
Jeff
Jeff Schlemmer

Wonderful, thanks very much Jeff. I'll prevail on your good will and ask three more questions. Is your car a chrome bumper car or rubber?. Roadster?. Was your spare in the boot at the time?.
I should have specified earlier.
I would guess a chrome bumper early 70's.
Peter

Peter: I weighed my 74 chrome bumper car on some race car scales about two years ago. The car has been converted to a single 12 volt battery, it's in the battery box on the passenger side. Fuel tank was about 1/2 full. Components in the rear are stock. I have 14" LE wheels. Spare wheel, scissor jack, tire changing tools and a portable fire extinguisher in the boot. Weights LR 541 lb. RR 545 lb. Total rear weight 1086 lb. Total car weight 2228 lb.

Clifton
Clifton Gordon

Thanks Clifton,
Data so far


LR 541 lb. RR 545 lb. (race scales)

74 chrome bumper car, single battery. Fuel tank was about 1/2 full. Components in the rear are stock. I have 14" LE wheels. Spare wheel, scissor jack, tire changing tools and a portable fire extinguisher in the boot. Weights LR 541 lb. RR 545 lb. Total rear weight 1086 lb. Total car weight 2228 lb.


LR 546 lb. RR 489 lb,

and that's with the battery in the right side battery box (and me in the driver's seat) LHD. That should be an accurate weight for figuring coil spring needs, as the 'glass springs are only a few pounds each.



LR=557 lbs. RR=564 lbs.

'79 B V8 215 rubber bumper car w/ rollbar, no driver, spare in trunk.


LR= 577.5 & RR= 587.5
Ford 8.8, sway Bar,drum brakes> > 1165 #'s with spare and minimal traveling gear.
No Driver, 9 gal fuel. 1978 B rdstr. tires 205-50-16



Nick Smallwood's site provided the weights of the axle, springs and shackels (175 + 30 lbs)
I have changed over to chrome bumpers, but have a tow bar. 535 would be about right.
330 looks pretty solid. I think I'll need to go park on weigh bridge at some stage, peoples answers have shown some significant variation, however 330 is a good figure to use when phoning around to see if it is possible to get a spring to fit up into the bumpstop location that fits all the criteria. Whatever happens I'll have to cut out the old rubberbumper bump stop in the rail. I'll leave the sides as a spring pocket and just cut the centre. Even then that only leaves a compressed spring lenght of 3 inches. Loaded lenght 5 inches, free standing lenght 8 to 10 inches, Diameter 2.5 inches max. Its looking possible!
I might also need to work out a way of capturing the spring, don't want to depend on the bounce straps to hold it together.
Peter

Peter, my car is a '71 chrome bumper roadster with an empty boot and no bumpers. Just under a half tank of fuel. I also have a fairly heavy roll cage with 2" tubing, so that may make up for the lack of bumpers.

I can add:
574LF and 549RF, still taken with myself in the driver's seat at 185lbs. Yes - this was done on race scales as well.
Jeff
Jeff Schlemmer

Just realized I've made a couple of errors.
Axle plus springs is 205lbs. Half on each side. This of course also doesn't include the wheels and tyres! These also have to be weighed and subtracted. So in Jeffs case thats roughly 1123 minus 205lbs minus whatever 3 wheels weigh. Divide by 2 for each spring.
Pauls "400lb to 450lb for a CB roadster, with rates of 105lb/inch (that is for a CB GT)
is starting to look good again"!.
Peter

Peter,

Not sure what car you have but the following may help.

From a copy of the British Leyland Special Tuning manual, C1969 p17 and p35 (for the 3 bearing and 18GB, first of the 5 bearing engines):

Rear suspension leaf springs

Roadster working loads 400lb, early type and 450lb for later type (from car 11313?).

GT, both early and late types, 510lb.

Each plus/minus 15lb.

The 400lb w/l had a rate of 99lb/inch and the 450 w/l a rate of 93lb/inch.

The 510lb w/l had a rate of 99lb/inch.

There were also springs with w/l of 375 and 542 lb with rates of 100 and 124 lb/inch respectively.

I notice that the coil (front suspension) w/ls were 1030 to 1193lb, with rates of 348 to 480 lb/inch.

Paul, not sure what all this means contrasted with the Workshop manual figures for the GT?

The tuning manual also notes the above "...rate is effective at the wheel in the case of rear non-independent axles, but is a function of the independent suspension geometry in the case of the front spring." I can only guess that this explains the difference in the coil/leaf figures.

Regards
Roger

Roger T

Roger - re your last paragraph: The solid axle should mean that even though the springs are inboard of the wheels there is no leverage to take into account, unlike the wishbones at the front. I've accepted that as the reason why the load figure for the front springs combined is different to the weight of the front of the car, but that doesn't explain why the load of two rear springs is significantly less than the weight of the rear of the car. Also the load for the V8 springs is given as 50 lb each more than that of an RB GT, but their gross weights are only 28 lb different. I know the V8 springs are harder and so it rides higher, and deflects less under a given load, but don't understand what the load figure in the book actually refers to.
Paul Hunt 2

Thank you Roger T (and everyone else) for the hard data,
All of the above examples (taking this that and the other into account!) seem to fall into the categories of either 400 or 375 lbs. The first must ride about a quarter inch higher.

Wheels & tyres =16.2kg each i.e. about 100lbs of wheels. Springs 32lbs, axle 175 (I must check this, not sure if Nick was using an MGB axle)
That’s about 310lbs, plus (in my case) about 30kg of tow bar plus giant bag of tools.

No one (of the above) seems to fit the 450lb category. 900 +310 would put their back ends at 1210lbs.
I figure I should aim at 400 and expect the springs to settle just a little. Or possibly 375 and be prpared to shimm them up quater of an inch.

The point and purpose of this was to gather data to get some Coil springs made and fit them to the chrome bumper bump stop location. I’m setting up a three link trailing arm suspension much as used in the current Mustangs or early C type Jaguars. All that space above and infront of the diff' makes the MGB particularly well suited for this.

Reference points are from the base of the chrome bump stop to the top of the bump stop on the axle (now spring perch!). I drilled a small hole to measure the depth of the rubber bumper bump stop crescent and found it to be 38mm (1.5inches) deep.

Maximum Spring diameter- 3 inches (75mm)
Maximum height, unloaded “free standing” spring height, is greater than 24cm (9.5inches).

Ride height, is 5.5 inches. With a load of 400lbs.

Allowing 2.5 inches (approx 6.3mm) of upward suspension travel means that the compressed spring height may be no more than 2.5 inches. Allowing 0.5 inches to prevent spring binding.


When you consider the MGB spring rating of 99lb per inch you get an odd co-incidence. i.e. 99lbs per inch for 400 lbs gets you from 9.5 to 5.5 with precision. Almost as if someone designed it that way right from the beginning ;).



My cars a chrome bumper conversion. The chrome bumpstops (or more correctly spring locations!) are all still there under those welded in crescents of metal. Looks easy to cut out, there's not much holding them in place.
Peter

This thread was discussed between 27/06/2006 and 02/07/2006

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