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ags
United Kingdom
275 Posts |
 Posted - 30/05/2008 : 00:57:47
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Hi All,
This is the area in which I think my knowledge is weakest, but to keep the buzz going, can anyone suggest a set of procedures for getting desired characteristics for the handling of our cars.
I think the starting point should be a trunnion sprung chassis in top mechanical condition - how can it be improved using only "period modifications"?
David A, has shown that the biggest improvements for an M type may turn it into something that is not an M type, but what about the later cars?
Hoping for some education
Andrew Smith MMM571 |
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Gordon
United Kingdom
691 Posts |
Posted - 01/06/2008 : 11:04:22
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Hi All,
Your point about top mechanical condition of trunions as a starting point is obviously sound. To that I would add that the chassis frame is accurately square. Then I would make sure the springs are parallel to the frame and that the spring pips that locate axles are correct. I was told that the official tolerance for the distance from the fixed eye to pip was +/- .1875". One might as well start with the axles also square. I know that Rolls-Royce cars had the individual spring leaves lapped together to ensure maximum area of contact as this maximises the natural damping of a leaf spring. It goes without saying that the locatiion clips must be set to do their job properly.
I always understood that the cording of springs was to address this problem but this also is said to 'stiffen up' the springs making them firmer but don't know whether this is true.
The most obvious ways of tuning have been tyre pressures, size and tyre, and dampers. The question of weight distribution front to rear, spring camber, spring rates are further possible areas.
You then come to the question of steering geometry, all of which could be modified, and divided track rods.
Other options that spring to mind are changes to track and wheelbase and position of engine/gearbox. Clearly whilst one is about the chassis the basic crossbracing could be changed.
The big question is whether any of these or a combination would have the desired effect! I have to say I have absolutely no idea! I can only suggest that you persuade those with the fastest cars to tell you their secrets! But perhaps the most rapid effect for some people would be to be taught how to drive their cars properly! I suspect that this would have more effect for me than anything else!!
On re-reading this I find it is all obvious stuff so appolgise if I have inadvertantly offended anyone. I am sure that you know far more about it than I do but perhaps it will get the discussion going!!
Gordon
Gordon |
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David Allison
United Kingdom
665 Posts |
Posted - 02/06/2008 : 12:23:57
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All of my knowlege is based on experience with the N type really which is a much stiffer chassis than the earlier cars.
Tom Dark has I think done a lot of work on the Q type single seater - strengthening the chassis and preventing chassis twist.
The K3 was heavily modified during the 3 years of factory involvement - the prototypes were little more than a modified L type - but by the time of the Mille Miglia in 33 the cars had bigger brakes, stonger front and rear axles, modified chassis frames etc..
In 34 they went to the Marshall supercharger - lighter body construction and also built a number of specials for customers like Eddie Hall (1933 500 mile race), George Eyston (EX 135), plus engine and other developments for other customers.
The heaviest modified pre-war MG racing cars were K3-021 (modified by Peter Monkhouse) the car was not completed in time to race before the war but raced in Formula 2 events just post war with a class win at Rheims (not sureof the date though). It was raced at VSCC and MGCC events in the 60's and 70's by Dad and Syd Beer among others.
This car was shorter and had modified front and rear axles - larger front brakes (coverted to hydraulic operation by Syd).
The car was very effective and quick to drive winning many races and punching well above its weight.
K3-009 the ex-Parnell single seater.
This car has IFS fitted from a Lancia - uprated brakes - twin cam cylinder head.
The car was never really sorted before the war although like the Monkhouse car punched a couple of suprise results and took some valuable scalps.
The Q type special raced by Geoff Monk and Ray Masters.
This car started as a Q type (now owned by Anthony Littlejohn I think) and the car was raced with a good deal of success in formula libre events - even a formula 2 class win I think (although I am not sure).
The new 500 formula 3 class meant that they needed another car and using a stroked unblown P type engine Monk developed the car using another chassis.
The Q type remains one of the most original Q's and turns up at many meetings every year.
The Q special was then fitted with a full house 750 engine and raced in VSCC and MGCC events - it now lives in Sweden with another body on it (although I think the new body is more attractive).
The car has IFS and the chassis is heavily modified.
The modification of MMM cars is the same as any other - use common sense and you cant really go wrong.
IFS - will get you turned down by the VSCC unless it was done in period or has historical interest.
Hydraulic brakes are not really worth it unless you are racing - I have just fitted new drums to the NA and the original cables brakes are no where near as scarry as they used to be!
The nicest MMM cars I have driven have all been the standard ones!
Horses for courses - the blown NA has admittedly spoiled me because it is heavily modified but because they were all done at Abingdon - the car is still standard!
All the trick bits that used to be on the NA have been moved across to the NB now owned by my sister - this car is lower, lighter and has softer springs.
We also fitted radius rods under the rear springs (similar mods for the front springs are also planned).
The MMM chassis needs a lower centre of gravity - this is done on the NB by fitting alloy blocks under the axles lower the car by approx 2 inches.
The chassis does need stiffening (see the begining) as the JPKLQ chassis are about as stiff as a blancmanche - the N chassis is an improvement but not much of one!
The R was the way forward - if they had persisted then who knows what MG might had of achieved?
My advice is to tinker with pride and gradually improve.
Radical modification never normally works unless it is well thought out and these radical mods will probably upset the originality lovers, eligability scrutineers and in some cases good engineering sense!
Gone on too long again havent I?
Regards David
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tholden
United Kingdom
1638 Posts |
Posted - 02/06/2008 : 14:53:28
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Hi David
Just to clarify, Anthony Litlejohns' Q was chassis number 0255 - the ex Dorothy Turner car. It was beautifully restored by Colin Tieche some years ago. I did quite a lot of work on this car last year for Anthony. It is a fabulous car and very correct complete with original Zoller blower. It has since been sold and I believe it now resides in Sweden.
Incidentally I see that BW has Tom Darks excellent Q replica for sale but it is now the real thing. I wonder what the story is there ?
TH |
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Peter Green
United Kingdom
1682 Posts |
Posted - 02/06/2008 : 15:10:47
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Terry,
Tom Dark's Q type is not a replica any more, it is now built on its original Q chassis. The story is to long to tell here.
Peter. |
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Bruce Sutherland
United Kingdom
1564 Posts |
Posted - 02/06/2008 : 15:36:19
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David,
Thank you for all your information, however my reading of the original question sought answers of this nature:
ò What are the modifications required to stiffen the chassis: hardware details, dimensions, pictures?
ò Suspension tuning mods: (from the original æbookÆ values).
o ? Changes required to spring rates?
o ? Changes required to suspension travel?
o ? Changes to bump and rebound stops heights and rates?
o ? Changes to ride height?
o ? Changes to suspension damper (colloquially called shock absorbers) bump and rebound settings?
o ? Changes to front axle camber, castor angles, etc?
o ? Selection of tyre size, tread type, carcase type, manufacturer?
o ? changes to steering ratio?
o ? Selection wheels û diameter, rim width, spoke-to-mounting face offset?
ò ? In what sequence would you tackle the above (plus any other factors IÆve missed out)?
The type of use for the car û general road/touring or track use û I would not expect to make a significant difference to the fundamental tasks as the physics of vehicle dynamics are the same, just the extent to which any individual tuning change would differ.
I hope this doesn't make things too complicated....just trying to drill down to the nitty-gritty. Yours in anticipation.
Bruce. |
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ags
United Kingdom
275 Posts |
Posted - 02/06/2008 : 15:43:42
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Thanks Gordon and David,
I was beginning to get depressed and thinking that I would need to do some pump priming by listing my starting point, but you saved that. Since nearly two hundred people have read the start item in about a week, I cannot believe that there is any lack of interest. Perhaps a lack of confidence in peoples' own experience/expertise? Come on in, the water is warm and the company is helpful.
The earlier two contributions have actually gone rather further than I thought of initially. I was thinking more of a setting up guide rather than clean sheet modifications. For example, IFS is too far for my originality conscience to allow me to go.
So, I think I will describe my start position after all. I agree with Gordon that the basic thing is to make sure that you have a chassis that is true. After my 1977 accident I know that this was the case, but I both went further and not so far as Gordon has suggested. I did not check that the springs were parallel to the frame, at least any more than eyeballing them without measurements. I can now see the importance of this and will do a proper check when next the body is off, so I hope that that will be a long time away. Indeed I did not even know about the 3/16" tolerance on the spring mounting points. However I did do some checks in the vertical plane as well. The flexibility of the chassis will allow it to conform to the unevenness in any flat(tish) floor, but that does not mean that its unrestrained shape is actually truly planar. I therefore supported the bare chassis on four axle stands on my flattest bit of floor, two at the rear of the front spring mountings and two at the front mountings of the rear springs. (Note no springs or axles in place at this time.) Then, with a suitably large spring balance on the ends of the front cross member, I checked the force to just lift the chassis from the front stand on each side in turn. I was aiming of course to get equal figures but there was actually about ten lbs difference. A quick think about the forces and masses involved persuaded me to accept this and pay the bill for chassis straightening and repair. So, I hoped that I now had a chassis that would transfer forces evenly to the wheels.
Giving me a neat link to the wheels. Truing wheels is a job that I enjoy and find easy, and though I scrapped all the wheels that had been in use during the accident, the replacements had to be checked and I eventually passed them out with no more than 1/32" out of true at the rim in either the radial or the axial (wobble) directions. This is simple to do with no more equipment than a pointer on a stand, a piece of chalk to mark bad places and a spoke spanner. Incidentally you should check the tyre tread in the same way when they have been replaced, you would be surprised how far out they can be. However a few thumps with a rubber hammer on a nearly flat tyre will soon sort things out with the help of plenty of liquid soap.
The only modification which I ever tried to the chassis was to alter the front axle angles to lessen the positive camber on the front wheels. Here I was following the lead of the TCs who were going to the extent of getting negative camber on their wheels. Since the positive camber is such a noticeable feature of our front views I did not feel able to go that far, but I did reduce the camber to +1 deg. As noted earlier this was not a success. The intention was to decrease understeer in extremis on the track. What actually happened was that road behaviour under small or no cornering loads was made more lively (less understeer in those conditions) but the track response under heavy cornering loads was unchanged. I now believe that the basic problem is lack of roll stiffness at the rear, and I shall take the front axle back to standard and change the rear set up.
In actual chronology there was now a long pause while the chassis was reassembled and engine, transmission and body replaced but the next chassis tuning step needed all the usual masses to be in place. This was to check that the wheel hubs were all square in the loaded condition. No matter how carefully I measured, in a variety of different ways I was left with a 3/16" difference in wheel base from side to side. At the time I could not see how this had crept in, but now, spring length tolerances hmmmmm?. I gave up and accepted the situation.
So now on to readily adjustable things. First, shock absorbers. As I said in an earlier thread I have retained the standard Luvax set up at the rear. I could find little difference after adjustments here so mostly they stayed at the Blower setting of two or two and a quarter turns open. My front shockers were set progressively harder through the years. For the first meeting in 1973 I used a procedure credited to Nuvolari. This is to tighten the Hartfords right up to solid with the normal load on the front of the car. Then jack the car up so that both the front wheels are lifted but the axle is free, ie put the jacks under the chassis behind the front springs on both sides. Then, one side at a time, slacken off the front shocker until the axle just drops. Then by experiment on the road, tighten the shockers equally until the desired handling balance is reached. In general the resultant setting was one and a half or two complete turns from free. As time went on I tended to run them harder, and my final procedure was to use a torque spanner to take them up to a convenient starting point, I used 30 lb.ft. from mid 1976 on and then to adjust them on the road, usually backing them off one or two scale numbers from this start position. All these settings were for track events, for trials one usually runs everything as slack as possible, short of uncontrolled.
Lastly, immediately before a track event tyre pressures should be adjusted. These I found did make a noticeable difference. I started with them very hard, 45 psi all round for 450 x 19 tyres. After looking at tyre wear patterns I reduced these to 30 - 35 psi front and about 38 psi rear for dry weather. For wet I would run less still 28 - 30 front and 35 rear for a cloud burst. Though track practice sessions did not allow sufficient time adjustment of the pressures on the road taught me that the handling balance did respond quite well to changes of this degree. For trials the tyres, especially rears, should be run as soft as the event regulations allow, often 15 psi though 5 was permitted in prehistory.
There you are, my experiences. Please add yours and tell me where I can improve.
More technical ramblings from
Andrew Smith MMM571 |
Edited by - ags on 02/06/2008 15:49:46 |
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Gordon
United Kingdom
691 Posts |
Posted - 02/06/2008 : 19:39:09
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Andrew,
Your point about checking tyres for out of roundeness etc is a very good point. I got rid of a set of 4.5 x 19 Dunlops for this very reason and went to the Blockley 4 x 19. These are magic in being nice and true. I also found it lightned the steering noticebly and improved grip, again most notably in the wet. I must admit to having put the Luvax rears to one side with cracked casings and replaced these with Spax. This has transformed the ride not surprisingly and I am still experimenting with set up. Your comment about roll stiffness at the rear is interesting. I note that if you take a corner with no power on you get a sharp transition from understeer to roll? oversteer as the load builds up and this is shown by a significant increase in steering effort needed. Having the rear tyres 2 - 3 pounds harder improves this to some extent but applying power through the corner makes things even better! This was David's advice to me and very good advice it was!
Gordon
Gordon |
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Ray Masters
United Kingdom
568 Posts |
Posted - 02/06/2008 : 20:49:04
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| Hi. All For the sake of histoical accuracy can I correct David's facts regarding the cars that Geoff Monk and myself were involved with. Firstly, the genuine Q-Type. This is not the car that Anthony Littlejohn owned. The Chassis no. of Geoff's car was QA0252, Reg. No.JB 4231. Anthony's car is Chassis No. QA0255. Reg. No. PMY 586. This car is no longer owned by Anthony. The other car Geoff Monk had was built by him & his friend Alan Bell,as a single seater using a highly modified P-type chassis with I.F.S for the old 500cc Formula 3, & called the MBMG. My article in the 2001 Triple-M Yearbook documents this car. It was later fitted with a Q-Type engine & two stage supercharging (at 28lbs boost) & raced in that form by Alan Bell and ,from 1964 until 1979 by myself. It has since passed through a number of hands, being fitted with a different body, ''loosing'' a supercharger, and possibly a different engine. I hope this puts the facts right ''for the future''. |
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David Allison
United Kingdom
665 Posts |
Posted - 03/06/2008 : 09:13:12
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Ray - many thanks!
My defence is that I was very young when told the story and it was a long time ago!
Andrew
I think that the only thing that has really changed since the last time you drove the PB competitively is the tyres currently available.
The Blockleys are indeed a very good tyre - designed for racing but also a good road tyre.
However the tyres do wear quite quickly in comparison to Dunlop Gold Seal (although not as bad as the Avon sidecar tyres) and they do have a very stiff side wall which is inclined to make the ride very hard.
My advice to Gordon was to drive in a pre-war style (to say the same to you would be an insult since you were driving the PB when I was in short trousers) modern cars (front drive) are much more forgiving!
I saw a brilliant ditty on Top Gear wit J Y Stewart giving driving tips on rear drive cars - he said that for the smoothest and most comfortable ride, "the most important thing is to - never open the throttle in a corner until you know that you dont have to close it again" and that this rule was the same for the fastest route as well.
This had a lot to do with his style of driving in F1 I think - always smooth.
I dont like the idea of telescopic dampers on pre-war cars from a personal postition - the NA had them fitted during the 60's and I removed them.
I have fitted some Rotaflow dampers from a TD (because I had them - they fitted and were free) and these are just as good as the worn out telescopics that I took off.
When Dad fitted the "teles" - he was trying to go racing - I am not.
I have driven cars with Hartfords all round and these always seem perfectly stable and predictable - this is always a good start.
The Luvax dampers are a dead loss as far as I am concerned - the fiddling about and constant repairs to make them work properly on anything other than a gently driven car is frankly not worth the effort!
These dampers were only really effective at the larger sizes fitted to Lagonda Rapiers and Rileys - the small drum types fitted to the MG's are too small and fragile.
The speed at which the vanes have to rotate is too high and this overheats the oil - which in turn leaks out and then the damper is no good.
The way I set up the chassis each year is the same as Dads.
Every sping I roll the car out, jack it up on to axle stands (under the chassis frame) and let the wheels hang free.
I loosen all the dampers off and then clean the springs with parrafin.
I then oil the chassis with SAE 140 and grease all the chassis points, prior to re-setting the dampers.
Over the winter this year I replaced the tyres - putting the car back on 16" wheels all round again - this in an effort to return it to its Monte spec.
I fitted Excelsior tyres - these were less expensive than Blockleys or Dunlops and more than up to road use - the grip on the road tyres is good and then run quietly on the road - the wear is acceptable (I have done about 150 miles so far and they still have the pimples on).
The sidewalls are much less stiff than the Blockley - they also seem to ride better than the Dunlops and Avons they replace.
They also do a race tyre which is also cheaper than the Blockley.
I can send details of where I got them from for any interested parties (send me an E-mail)?
The only advice I can really give is to go with common sense and modify one thing at a time.
Andrew Bradshaws little P special goes very well - not sure what tweaks he uses - but I think that car is still Abingdon on Thames in the chassis dept.
I honestly think the best idea is keep it simple and safe!
Regards David
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