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MG MGB GT V8 Factory Originals Technical - Independant Rear Suspension

Anybody know whether its worth the expense of going this route?
If so, do you know of a cheap setup, as the Walden (now no longer) and the Hawk (of kit car fame) appear very expensive.

That depends upon what you consider cheap.I don't think it can be done correctly for less than $3,000.There is alot of machine work to do and if done incorrectly to save costs,then you could end up with a suspension that is worse than the original system.
Dave D

Before I collected my senses and moved on, I considered trying to fit the IRS from a Datsun 510 (I know, it's as old as the MG). My reason for that car was the track was about 55", it was a simple tube frame work that looked like it would fit in the "B", and it uses the same differential carrier as the 280Z, which means it can accept all those incredibly cheap limited slip differentials in the salvage yards. Plus, 510's were pretty hot performers on the track for their class. The problem now is finding a suitable donor car for the parts. I also looked at the Suburu IRS, which uses the same Nissan differential and has a similar track.



My impression is that the NG/Hawk front and rear systems will be equal or slightly superior to a well sorted standard system. If starting from scratch the rear does offer LSD Discs etc for a price of £3k which may not be much more than similar setup for standard B system.

The alternative would be Jag Try this site for info

However the cost may take you into NG/Hawk range and that is vitually plug and play.



Where have you got £3k from for the John Hoyle IRS? That is about double the list price for the kit (and we can get it cheaper than list)

Itís equal or slightly superior to a well sorted system; it is vastly superior to the standard live axle and leaf springs.

Geoff King

I actually got £3k as a figure as well - direct from John Hoyle at the MG Show at Stoneleigh recently. This was the subframe, with Ford Sierra diff, shortened drive shafts, L.S.D., rear discs and a high ratio (which I think from memory was 3.1 and came from the P100. Hence the request for a cheaper alternative.
Reasons for considering are that not only must it offer superior ride and handling, but it should deliver the power to the road without axle tramping.

Aren't the kits designed by the late Trevor Taylor, and now marketed by ?NG Cars?, a whole lot cheaper and pretty effective? I thought they had them sorted to the point that they literally bolted into the shock absorber mounting holes. Seems clear to me that'd be the best bet. I do worry about the weight of IRS assemblies, though -- they look EXTREMELY heavy!


The late great Trevor Taylor only sold the systems but he may have been involved in testing and recommended systems.

I think John Hoyle and John Hawkridge designed them and are available from John Hoyle NG Hawk MG Owners etc.

Good point about weight but it is sprung.


You won't get far with just sub frame! The version I would look at is about £3k + VAT.

Superior handling is debatable with anti tramp and RTL available for live, but ride is diff as front standard setting is 300lb wheras I currently use 560lb. Opinions that I have heard are still divided but the Hoyle system has the edge certainly on ride but at a cost.

Going back to cost if starting your V8 conversion with say MGC axle LSD discs Koni's Anti tramp lowered springs or GRP springs Panhard Rod Prop, I reckon £2.5k so in same ball park as IRS, in these circumstances I would go IRS but be careful of race rally regulations if you intend to use car for Motorsport.



I had considered that I wouldnít get far just with the subframe, give me some credit please.

With the sub-frame, coilover dampers, wishbones, hub carriers, stainless steel flexi brake pipes, handbrake cables and all polyurethane bushes at £1,400 (including VAT), the total package with the diff, half shafts, CV joints, hub assemblies, brake discs and calipers and a propshaft will surely be less than £3k? I hope so anyway, I have just bought a new X type Jag and the bank balance is looking a bit out of balance at the moment and the order is in for the IRS.


The IRS sub-frame is attached in 8 places; the leaf spring, the damper and the check strap mountings, no modifications are required to the chassis rails; it is a bolt in kit.

The Ford diff casing and the custom hub carriers are aluminium and although the total weight may still be more than the live axle most of the weight is sprung. If the kits LOOK extremely heavy the existing MGB leaf springs, dampers and axle ARE extremely heavy! Add anti tramp bars and a Panhard rod to make the live axle work and I doubt there is much in it.

Geoff King


When I totalled up bits from advertised price list it came to just over £3k excluding VAT but I would use top of range Cossie LSD Diff at £600 so could reduce price by £300 by why buy a rolls royce system and spoil it for £300 quid.

I would guess on special terms say total £2,800 including VAT.

It would be interesting to weigh both systems, if you have the time , but the ride improves with sprung weight, and hence the use of De Dion keeping virtues of live axle but reducing unsprung weight.


I fitted the John Hoyle system to my 72 roadster with a mildly tuned V8. The results are impressive the feel and handling of the car has been transformed the stopping power of the rear discs is superb,and the power is transmitted effortlessly.I spent about £2k total,£50 for the back end of a 4x4 Sierra from which I used the diff,drive shafts,hubs and drive joints. I fitted new calipers and discs,bearings and had the propshaft altered to mate with the Ford.
Only minor fitting problems and well worth the cost and effort,the front end is RV8 and the combined suspension arrangements make a superb road car.

Can you to tell us more? £50 for a 4X4 back end is fine. Did this include a limited slip diff? Was that then O.K. or did that need reconditining? What ratio did it have? Are you using Cossie drive shafts? Did you have anti -tramp bars before hand, and is this what you are comparing it to?

I have'nt been on here for a while... still the perennial problem of live axle v IRS-is there anything else out there...?

Way back I have said this before-but what are you trying to acheive with IRS? I think that it is right to consider it when starting out fresh on a V8 conversion-as by the time the axle has been built correctly-you wont have much change from £1k

I've seen the hawk cars setup at several of the shows and also under Trevor Taylors car when it it was at Stoneleigh-unless the customer version is different I would make the following points;
The link bars from the front spring hanger points simply don't look strong enough to stabilise the bottom of the diff cage.
There is not enought suspension travel for that that kind of road where you need IRS most-the nice interesting slightly bumpy B with ripples mid bend which would disturb the average live axle set up.
The cost-I am not wealthy-but there is always a cost benefit scenario-is the car going to handle £2-3K better?-before you know it you should have gone out and bought a Lotus Elise or even an MGF in the first place...

However we all like a challenge-it's a hobby after all-Nick Smallwood has fitted a Jag IRS... of which more later...
I think that there is one fundamental problem with IRS under the rear of the B:
Unless you are going to completely remodel the chassis legs under the rear of the car you are stuck with the box sections sweeping over the live axle in its current position-ie the distance from the top of the axle tube to the bump stop is the total available axle travel. The B doe not really have enough axle travel to soak up big bumps anyway and cutting down the existing stops to accomodate barely adequate suspension travel for a squeezed in top wish bone is not good fundamental design and certainly not worth £3k.....

This means that any revised supension-assuming a drive shaft- flexible or otherwise-in the conventional position at the centre of the wheel-needs to have its location below or at the same level as the drive shaft.
This leaves three basic layouts that I can see working under the B
Jag type IRS-This ahs a very handy diff cage and the upper shaft is used as top location for the hub carrier. MGC hubs could be used on the front to bring the five stud pattern together. Hats off to Nick for getting it under there-but I have reservations -it is heavy!-because the sahfts are designed for a large car every thing is massive-the brake calipers for instance weigh a ton. The system also has some conflicting geometry which is countered by using voided bushes in the front locating arm-this has to be countered by a diagonal locating arm to the inner wishbone axis for true geometry.
A Macpherson strut type set up(I should really say Chapman Strut as it is at the rear)This could work if substantial remodelling were carried out on the chassis leg to provide room for the strut and of course a strut tower would have to be welded in. Plenty of hub/strut combos around tho' big V8 power may be a problem.
A de dion tube. I think that this has possibilities as some of the existing hardware could be used-you could use leaf springs and keep any existing panhard rod. Used with inboard discs it's unsprung mass saving would probably equal the heavy weght components of the Jag IRS. I am still scheming this one-but my existing live axle setup is doing pretty well and even just loacting a diff under involves a lot of cutting and welding.
In my view you have got to get at least a 30% reduction in unsprung mass to make it worthwhile. To analyse this you have to work out where the weight is at the moment.
My currrent live axle weighs around 166lbs(without wheels). I would have to achieve a min 30% decrease in this component by substituting it for a de dion tube. This tube would still have hub carrier/bearing assemblies and would still take half the weight of heavier tripodal jointed drive shafts. This means that the most weight saving has to take place in the diff assembly. I havent analysed this yet but I think you can see that max 40% over the whole assembly is a probable target-any one done this yet?
I haven't mention the component that goes up on any V8 conversion and that is the wheel/tyre-my 195/65 Goodyear Eagle toouring on a 14" GB alloy weighs a whopping 33lbs-two of these is a big percentage of the overall axle weight.
In my view the most important thing is to get the standard set up right with the softest springs and proper tramp /panhard location with max wheel travel and soft progressive bump stops. I am still looking forward though as I've got a Sierra 4x4 diff/ driveshafts/hubs salted away in the shed.....

Best Regards

John Bourke
John Bourke

Hi John

Read your comments with interest. They caused me to look at the percentages and comparisons and I calculated the following.

The Jag set-up is around 35% heavier than the MGB live axle without limited-slip, panhard and anti-tramp etc.

56% of the Jag IRS's weight is sprung as opposed to less than 10% of the MGB's.

Minus wheels the unsprung weights for are Jag is 134lbs and the MGB just over 200lb.

I would do it again, but without the cage and solid mount it, as this limited coil over length and choice, as the top mounting position was restricted to the original position.

The void bushes on the forward locating arms are not a problem as long as diff is soft mounted. Otherwise as John says mounting to the forward lower inner pivot gets rid of any geometric problems, but you loose that bottom wishbone support.

Another way to approach that problem is to mount the forward arms off the standard wishbone position, but make the forward body mount inline with the inner wishbone spindle for better arc geometry.

Not expected to be on the road next till next spring, so donít ask me what it rides like.


Nick Smallwood

On other issue to consider is the performance you are trying to achieve with your suspension. I have spoken with a few Mustang owners that have upgraded thier cars to the Cobra IRS set-up from live axles. They all had similar comments/complaints.

IRS are designed for handling IE Cornering. That is were they shine. However like everything this comes at a price. They all mentioned they saw increased wheel hop in straightline acceleration. This is purely due to the way a IRS is designed to work. I bring this up becuase I thought everyone should know as it will affect the handling of your vehicles in a possibly unexpected way.
Larry Embrey

Has anyone in the US seen the 4 bar Link setup in the Summit Catalogs? To me this looks like it could be adapted to the stock live axle and then you could do away with the leaf springs. Cost is low too. Coilovers are the only other parts needed. I think it was made by Competion Engineering. Food for thought.
Mike Stemp

Not seen the Summit one but would be interested to find out more. In the UK Maidstone Sports Cars offer a 4-link kit but its very expensive.

To put a 4 bar set-up under a B,the bars will be very short.The result is that as the axle moves,so does the wheelbase length.Let the car roll a bit in a turn and you would get unsettling roll-oversteer.The Maidstone set-up touched on this and was masked by the use of stiff springs that are probably stiffer than the original leaf springs.Road racers that use a solid axle and 3 or 4 bar set-ups use very long bars.Most are so long that they go into the seating area.Look inside any Trans-Am/Grand American Road series car(tube frame Corvette,Camaro,Jag,etc...)and you will see the sheet metal box section used to cover the links.
I am currently building a B with an early 6 cyl E-type cage assembly.Everything is narrowed and ready to be mounted as soon as I work out suitable mounts,as I don't wish to mount the cage as some previous converters did.BUT.........After serious consideration and update work done to my other car(71 GT with NG Cars front end and British Automotive's fiberglass leaf springs with his newly recalibrated KYB shocks),plus a very accurate alignment (with the new frontend, I just HAD to by a new alignment machine),the car's ride was transformed!I really doubt that an IRS will feel significantly better.I most likely will continue with the Jag conversion due to the facts that 1.Most of the work and costs are over and 2.I just liketo build things that are different.I feel that people will always try new things just to say they tried it so good luck to all........
Dave D


Tony Bolton is selling Chapman Strut system for midget for about 1.5 with Ford parts, and can be widened for B.


It looks as if Moor Lane Garages's I.R.S. (with Chapman struts) for the 'B' is untried at the moment.
The five link set up looks interesting, but they suggest it can only take 150bhp? Perhaps you would like to comment on the other thread now started on Traction Bars.


I assume it could be developed to take V8 power.


While John Hoyle does not wish to contribute here as it could be perceived by some to be unethical, he does not mind if I pass on the following information that may be interesting to anyone considering the John Hoyle (Hawk/NG Cars) IRS system.

The main forces transmitted are not through the tie rods, but through the primary mountings to the existing shock absorber bolting points. Extensive testing was carried out on Trevor Taylorís car (over a 6 month period) including track work, the system is also well proven on NG's, one car is running with a 400bhp 5.2 engine.

When designing a system such as this you are obviously constrained by the under body which John did not want to modify. The upper wishbone is very close to the drive shaft to maximise the amount of suspension travel. If the wishbone were to be moved even lower the drive shaft would then come into contact with the chassis first. The bump stop is built into the coil over damper unit. I would also comment that looking at the geometry and the position of the upper wishbone fulcrum points the IRS travel is likely to be more than the existing axle.

The ride quality is far superior to the live axle and will cope with our (UK) normal poor quality road surfaces without problem. Obviously if an owner wanted to set his car up with a very low ride height you would lose out on suspension travel (as you would with a live axle set up) and then if you also wanted a "soft" ride it would occasionally bottom out.

Regarding weight the following is very interesting, the data is in Kilos.

Total Sprung Unsprung
Frame, Tie Bars, Diff 46 46 0
Wishbones 8 4 4
Drive Shafts 11 5.5 5.5
Dampers and springs 8 4 4
Uprights, Hubs, Drive Flanges,
Discs, & Callipers 32 0 32
TOTAL 105 59.5 45.5

Nick states that the live axle unsprung weight is some 90 Kgs with less than 10% sprung, so total weight of the IRS is similar while unprung weight is almost halved. Wheel weights have to be added to both and in my case the 195/60x15 tyre/alloy wheel combination is just less than 14 Kgs.

Does anyone know the individual weights of the axle, leaf springs, damper links, dampers, anti tramp bars, Panhard rod and a prop (drive) shaft? Iíll weigh mine when I take them off but I donít have anti tramp bars or a Panhard rod and it would be nice to compare the total and unsprung weights.

Geoff King

Guys, why wouldn't a simple setup like a Lotus 7 or Lotus replacement Spyder chassis type rear end work? These use off the shelf parts with simple upper/lower arms and simple diff carriers. I note in the latest Practical Classics car mag the Spyder repacement chassi for the Elan looks so simple! And as for handling...its a Lotus need we say more! Any Aussie conversions out there? We seem to have heaps of Japanese IRS setups in our wrecking yards,

Well here is my take on this. Having developed an IRS setup myself for my car. In the US the Nissan cars are quite plentiful just as the Sierra apparently is in the UK.

I took the basic rear suspension from a 280ZX turbo. Built a rear sub frame that would bolt into the MGB rear with little modifications. I.E. removed battery boxes and a short section of the lower drive shaft cover. Fabricated a mounting system on the frame so that camber and toe could be adjusted with some ease. Used a set of coil over shocks found on most street rods. The Nissan system is a well tested system and used for close to 30 years in there wagons, sports cars, and family sedans. The problem is that when the rear of the car squats the rear camber changes hence the need for some adjustability that?s why Nissan went with the system on the 200sx that has trailing arms but adjusts camber as the arm travels upward. In a car that has 10" of wheel travel the change in camber is about .5 to 1 degrees on my setup with 6" of wheel travel I have somewhere between .05 and .25 degrees of change which is negligible. The reason I started an IRS was to get disk brakes in the back end of the car. I have not as of yet had a chance to put this setup on the road yet. It?s in its 4th version and I?m sure there is more to come. The cost is not for the faint of heart. I have probably 2K in all of the pieces I have made. I don?t see a mass market for these simply because it uses parts that are not made any longer. Cost was never an issue. I will update when I get the car to the road.
Todd Budde

You boys with the IRS setups will have to swap rides with me some day. I want to see what all the fuss is about. You may not like the way mine rides, it's low to the ground and is a bit stiff. But it still has that prized MG quality of handling well and being extremely easy to control plus being forgiving of gross excesses. Mine is by no means near the limit of what can be done with the stock axle. I don't have the glass springs for instance, and though the oil is light and the valves tight it still has the same old Armstrongs. No panhard or traction bars, and no limited slip, but you know what? I doubt I've spent much more than a couple hundred dollars total on it. So far it's spent better than 15 years behind built, turboed, and now a supercharged v8, and though the thrust washers have worn a bit it's held up admirably well. Just in case it breaks I have a couple of spares laid by, along with some shocks and stuff, so I must say the incentive to spend all that money to see if the same car with an IRS will handle like my brother's TR4A-IRS (Not something I'd like) is miniscule. But I wouldn't mind a ride just to see.
Jim Blackwood

I have some new photos posted of my IRS. PLEASE leave me email and tell me what you think!!

Todd Budde

This thread was discussed between 08/04/2002 and 25/04/2002

MG MGB GT V8 Factory Originals Technical index

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