That detailed background of the history sure does explain why bumpsteer is inherent in the design of the M3W front suspension and I fully appreciate why the Suplex designed a shock and spring combo that minimised the impact. Clever use of spring and damper rates to minimise vertical movement about the static mid-point (where the track arms and wishbones are all parallel/horizontal) have clearly had the desired effect on Suplex-suspended cars.
I too have fitted the Spax adjustables, but due to header to shock interference, I cannot lower the car far enough to get the arms all aligned, so I have no choice but to run higher and look for a solution elsewhere......
... Which will be the empire kit, as this is a geometrically correct engineering approach, which no longer relies on the spring/damper design to minimise the degree of bumpsteer present during suspension travel. I hope therefore that the improved quality of the damping available in the uprated SPAX units will compliment the zero-bumpsteer geometry of the new upper wishbone to produce just as nice a drive as the Suplex approach.
Thanks PJB for that background info - it all makes sense now!
In theory, I don't see why, with the use of adjustable or shimmed vertical spacers on the steering arms, the Empire Geometric Correction kit can't be used with any ride height or set of shock absorber/spring units, be they Suplex or Spax adjustables.
In pracitice, and being a mere amateur at these things, I find it very hard to differentiate between standard shock absorbers and uprated and vastly more expensive items, in terms of ride quality and road holding, and to know if I truly need to spend money on uyprating them in the first place. Maybe we need to arrange a day where we can meet up somewhere, and drive various cars with different combinations, on a back to back basis, to really see the differences.
In theory, I don't see why, with the use of adjustable or shimmed vertical spacers on the steering arms, the Empire Geometric Correction kit can't be used with any ride height or set of shock absorber/spring units, be they Suplex or Spax adjustables.
In pracitice, and being a mere amateur at these things, I find it very hard to differentiate between standard shock absorbers and uprated and vastly more expensive items, in terms of ride quality and road holding, and to know if I truly need to spend money on uyprating them in the first place. Maybe we need to arrange a day where we can meet up somewhere, and drive various cars with different combinations, on a back to back basis, to really see the differences.
You're right Paul - with the Empire kit, the change in geometry caused by the stock wishbones is removed, so it will move true throughout the suspension movement, with pretty much any static ride-height set. The SPAX (stock or adjustables) or SUPLEX units will have no impact if the Empire kit is fitted. I accept that the uprated Suplex shocks sound very good and by the same score, the adjustable SPAX units are (in my case anyway) only going to offer improved damping quality over the cheaper stock units, as much as anything else. Probably not necessary in hindsight, but hey, they're fitted now!
Once I have my Empire kit fitted it would be good to compare notes and passenger rides.....
R1NGA - the SPAX units are not really 'uprated' (except in that the std SPAX are quite basic items), these adjustable SPAX are twin tube dampers with I believe just a bleed hole past the valving to affect the damping - the dampers on the SUPLEX kit are monotube (better heat transfer to air), highly gas pressurised (less foaming and loss of damping when used hard) and the damping adjuster actually controls the preload on the damper valves directly so not with a simple hole and tapered needle.
Paul Hi - running at different ride heights affects the negative camber at ride height, you must consider the camber of the front wheels when hard braking, one doesn't want to induce too much negative camber under braking as then the tyres are not at their optimum angle (vertical) under max braking. I really am not saying that the Empire kit has a problem in this situation, but it should be a consideration when setting camber change in bump and at static ride height. IMO better to control tyre camber under braking and then increase roll stiffness to make the tyres also work in cornering - but then there are many ways to skin a cat.
Ride assessment/development - I have been lucky to be paid to do this over the decades as have many others of course throughout the industry. There are many scales to assess ride and handling, the measured/objective bit is easy enough - the subjective bit is a lot more difficult and as you so rightly say, will the customer (who pays the bill) actually notice and appreciate the difference that some clever so & so has set up?
Value for money v benefit: Look at the cost of the dampers on another sports car, the lovely Lotus Elise and those on our favourite three wheeled sports car. There is a cost difference of nearly four times. Those costs go into the technology in the dampers. I'll let you guess which marque pays more for their dampers. OK Lotus's are likely to be driven a lot harder than the M3W so they choose technology to match and there is always a cost:performance calc by Morgan, and that is what they have to do in all design features - for better or for worse. I believe that Morgan have a good grip on what the customers want. Cheers PJB.
Hi Peter, can you describe the differences an average owner is likely to feel on the road, [rather than the track], between a Suplex suspended car and one running on standard OE shocks, once the geometry correction kit is installed? In other words, taking out the issue of bumpsteer, what are the actual benefits of spending all that extra money? Not that I wouldn't be tempted mind you!
Agreed PJB - the £1600 Suplex replacements will be better than the £700 Spax adjustables, which in turn will be better than the £200 (maybe) stock Spax units. As I mentioned before, I put monotube Ohlins on my Renault Spider (outstanding suspension) as the car has a chassis to really make the most of them and I would probably have spent the £1600 on the Suplex units for the Morgan - had MMC perhaps let on that yet further improved and uprated units were just around the corner....
However, having spent my money I will stick with my height and damping adjustable units and look forward to enjoying the benefits of the Empire kit even more!
Paul, so what are the benefits of adjustable monotubes over the twin tube adjustables with a bypass bleed screw? Here are a few:-
1. Monotube damping levels do not reduce when used hard just when you need the damping to be consistent because: a. The viscosity & density of the oil does not drop much with hard use as it does not get over heated & thus degrades less in time. This should be noticeable. b. The high gas pressure in a monotube prevents cavitation and foaming that again reduces damping when used hard. This should be noticeable.
2. In monotubes the damping that is adjusted by adjusting the preload on the valves is more consistent throughout the range of adjustment than a simple bleed bypass. It is possible to maintain the relationship between bump:rebound and low speed bump:high speed bump throughout the range of adjustment, so you can get the same relationship at all damping settings. More difficult to assess subjectively, graphs will show this of course.
3. Monotube dampers respond quicker to inputs so better respond accurately to road surface irregularities, though can result in harshness. Should be noticeable on the road.
4. The montube damper valves are mounted on the end of the damper and thus see high oil flow rates so are far less sensitive to change over time. Twin tube valves see far less flow rate and are very sensitive to variations in leakage, valve spring creep, oil viscosity and density (both viscosity and density control resistance through the valves). This will be evident in time as the twin tube dampers may well need adjusting over the years to maintain damping levels.
5. Monotube dampers are lighter so less unsprung weight so better response to road imputs, a bit extreme this one I agree when you consider the weight of the rest of the suspension (cf with the Caterham front wishbones eh Paul?)
BUT if one is not sensitive to this degree of ride/handling then stick with what works for yourself. If you look at dampers on rally and race cars then even these adjustable monotubes are somewhat basic. Pays your money and takes your choice.
I must say that I was impressed with the Empire modifications on your M3W, very well done and thought out. The inherent problems with the std Spax units did, in my view, detract from the benefits of the geometry mods.
Thanks for the added information about your procedure of testing for the bumpsteer. I understand that as the spindle sweeps up/down the steering may be better in portions of that sweep arc. In this case, with the new shocks getting you lower, the bumpsteer deflection was more in it good part of the arc versus the bad part of the arc.
Thanks.
Peter,
Your very in depth explanation was great.
I understand the roll and COG of these cycle cars. What makes this worse is that all of the body roll control is transferred to the front suspension as the rear being a single contact point is no help against body roll in hard cornering as opposed to four wheels with the wider track width.
When I stated the “normal” setup of 2/3-1/3 I was referring to a more street driven non auto course weekend racing setup. We have some pretty big bumps on our roads here and with an 8:1 compression/rebound setup, our tires would be grabbing some air when going into pot holes or coming off of larger bumps.
With the 2/3-1/3 setup, I see how the M3W inner wheel would go down further with my setup than what you have in the M3W’s. But for normal street driving and conservative cornering, wouldn’t the 2/3-1/3 setup still give better overall ride comfort, but as we know, more body roll? Now this of course still relies on a good quality damping coil over. Trust me, I know the difference in quality shocks. Most late model CVO Harleys have lowered suspensions by 1” and the rear shocks are so harsh that it’s back jarring to say the least. Without air, they will support the bike, but the ride bottoms out a lot. Two up we run with around 40psi in the rears to get the non bottoming taken care of, but the ride is very poor. I upgraded to non air Progressive 440’s, but Ohlin’s are one brand people are using as well as Bitubo, Progressive and a couple other custom brands.
I’m trying to learn from some of you guys that obviously know their way around a car and suspension specifically. So I have some thoughts that I would like to run by you.
On the control arms and steering linkage, if you were to draw an imaginary line between the upper and lower control arm mounting points and then a similar imaginary line between the ball joints centers, shouldn’t the steering tie rod measure the same horizontally? So as an example you go up parallel from the lower control arm 3”, the tie rod should be the same length as it would intersect the two imaginary vertical lines. Is this correct? Because of the steering arm on the spindle allowing for the Ackerman steering, the tie rod would be slightly offset inward relative to the two imaginary lines.
Even though the tie might be the correct length as described above, if it’s not parallel to the lower arm, the vertical motion of the spindle would cause a fluctuation in toe creating bumpsteer. Is this correct?
Does the length of the control arms mean as much as long as the ratios are kept correct between the steering linkage and “A” arm length? Obviously the longer the arms the larger the sweep radius is, but I’m not sure I understand the how you find the sweet spot for their length.
Sorry to ramble, but when I have a possible chance to learn, I will always ask questions.
I find this very interesting and your way of telling the story is great.
Dan, had to read that a few times! Effects of limited rebound travel - any negative effect on ride comfort is minimal on most vehicles including the 4 wheelers (SUPLEX RS kit) and the three wheeler in my experience and by the guys at SUPLEX; the benefits in increased roll stiffness far outweigh any detriment to ride. Ref off road/potholes performance; SUPLEX have set up a lot of rally cars (including Colin Mcrae's) and Paris/Dakar trucks (incuding Jutta Kleinschmidt) with very limited suspension droop, both very successful of course - winning their classes so set up. The limited droop tends to reduce the likely hood of the wheel leaving the ground over a crest as all the weight of the suspension is hanging from the vehicle rather than the suspension pushing the vehicle even higher. Ok they still fly but have to go faster! A quick test to show the effect of limited/zero droop. Fit a damper that is fully extended at ride height, then the rubber bushes in the damper eyes are the rebound springs. Then feel the effect on ride and rolls stiffness - 'we' did this on my friend's MGMidget to great effect.
