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MG MGB GT V8 Factory Originals Technical - Recent Hopkinson sway bar(s) on a CB GT?
|I have heard two groups of smart people give very different advice regarding sway bars. Which is right? |
At a car show 2-3 of years ago, I got a ride in Glen Towery's blue bgtv8, and I specifically remember him telling me that a matched set of sway bars, such as the Hopkinson kit, was absolutely crucial to achieving great handling in a CB v8 conversion. I do specifically remember how well that car rode.
Now, scanning the archives, I see knowledgable folks like John Bourke saying that fat sway bars are a dangerous no-no. In re rear bars in particular, I think it's fair to paraphrase him as basically saying that when you are dealing with a live axle setup, because the sway bar makes it much more difficult for the axle to articulate independently of the car's body, as the body rolls (which it will inevitably do at some point if you corner hard enough), it will lift the inside wheel and force the outside wheel to supply all the traction. So when the outside wheel decides to go, the whole rear end goes. That seems right to me, and without a posi/LSD setup it seems to me you could lose a lot of propulsion in hard corners because the inside wheel will just spin. So it seems to me that the only setup that makes sense with a rear bar would be having really wide rear tires and a posi/LSD.
That being said, a lot of people seem to absolutely love the Hopkinson bar kits, especially in conjunction with the fiberglass leaf springs(?). I think I understand that Hopkinson now makes a mellower version of their old Evolution II handling kit -- 7/8 bar in front, quite a bit smaller in the rear -- with rubber bushes to allow a bit of play. Has anyone tried this setup, esp. on a CB car? What was the upshot?
I have the Ron Hopkkinson installed under my 77 RB and Iam very pleased with it. I have not compared it to other cars but to me it rides and handles OK.
I have the 7/8 in front and small bar in the rear.
I also think that the tires play a very important role. Going to 15 " rims and low profile tires wil certainly help also.
|Werner Van Clapdurp|
the trouble is that every body may be 'right' and the magic word here is compromise.
There are four springs that influence the handling of a car:
The side walls of the tyres
The suspension springs-leaf or coil/torsion
Any anti-roll bar fitted
and to a much lesser extent-compliance in the suspension bushes and flexure of the chassis.
The side walls of the tyres are really the most important springs-given enough side wall and a smooth enough road it's possible to get a vehicle to handle well with almost no suspension travel eg go-kart.
The trouble is we don't drive on super smooth roads all of the time-road car suspension exists to create a wider range of compliance than is availible purely from the sidewall and to create the best camber/castor /toe conditions-and damped flexure- so that the chosen wheel tyre can work to it's best capability.
The relation ship between the tyre rim and the tyre contact patch is important here-more so than lifting of the rear wheel etc-under steady state cornering the rubber tread locks itself into the road surface and the axis of the patch is different to the axis of the rim-the tyre sidewall acts as a spring in accommodating this distortion-the main suspension spring also distorts so that the sidewall spring does not become overloaded-when this happens say during bump midcorner,excessive load due to weight transfer during roll,excessive camber change-the contact patch become wrenched from the road surface and we have a slidng tyre. The melting rubber acts as lubricant so the tyre at this point has approx 10-15% less grip.
Anti roll bars transfer load across the car to the other wheel by reacting against the body-this can work both ways-bumps on the other side can affect the outside wheel and this becomes important when we get into mega bars.The bar increases the spring rate on the loaded side-and increases the risk of the wheel rate going high enough to wrench the contact patch free if a bump is encountered on either side of the car.
I'v'e fitted the RH kit way back when it first came out-went out and tried the car on a nice wide round about and was impressed by the lack of body roll and the feeling of security . More aquaintance found me getting fed up with the front end crashing into bumps/manhole covers and the feeling that the rear was very loose over bumps at the rear-nice country back roads would have you hanging onto the steering wheel feeling not quite in control. Much was made in the promotional video of the increased control with Tony Dron whizzing in and out of cones on a FLAT slalom course-so it must be better must'nt it?
This where you kid yourself. Take the average soggy B and bolt these bars on and it will transform the car-esp the RB version. The real test is against a well set up CB car with good quality 65/70 section tyres 3/4 bar, poly bushes all around,suspension tolerances all correct and say 25% uprated damping and possibly springs. This is the true baseline against which to judge the kit.
The RH kit will work with big tyres on super smooth roads-just like a race track where you will find all these big bars being used. A race track represents a road with limited conditions where you can narrow the scope in which the suspension has to work. This does not work on the road where varied conditions will be found-including wet bumpy bends with possibly a larger bump/pothole/manhole cover which will throw the whole compromise into disarray.
I'd also argue that relly big bars can cause the front chassis rails to flex esp when RV8 headers have been used without adequate reinforcement of the inner wings.
In my view one needs to make the maximum use of the limited wheel travel on the B by using near std rate springs-possibly variable rate-in conjuction with soft bumps stops which come in to use much sooner as a spring helper and ulimately an anti roll device.
|From my experience, John is absolutely correct on his assemnt of anti-roll bars. My only additional comment regards Chris's statement that wider tires and a limited-slip differential would help off-set the problems caused by the rear anti-roll bar. If the inside rear tyre has lifted on a corner, applying more power to the small outer patch of the outside tyre still in contact with the road will more likely promote a spin, if not a roll-over. The lifting wheel can act as a safety valve, preventing power reaching the tyre still in contact if no LSD is used.|
|The original poster is correct ... the recent Hopkinson bar kit is considerably more supple than the old Evo II kit. I have a set on a CB bgt (a 1950cc 4-banger) and the suspension is still quite forgiving - doesn't ride uncomfortably firmly at all. I have stock leafs, Spax in the rear, and V8 bushings in the front. I would never want to go back! You more than offset any lost traction, IMO, by absolutely >perfect< controllability. Years ago I had Hopkinson's old kit, which was a bit too much for road use. Indeed, as somebody noted, I had a quaife LSD put in there ... anyway, whole setup seems to work extremely well.|
This thread was discussed between 24/11/2000 and 28/11/2000
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