Hi Les…im supprised your haveing problems if your useing Boge unless they are old/faulty as they were the very popular choice by many here on the forum and i dont remember anyone haveing problems…have a look here the Girlings are getting good reviews…Steve Girling Shock Absorbers are back!
I am fascinated by this discussion. For my car, after reading about all of the fixed damper and spring problems, I put adjustable shocks front and rear with the rears having the adjustable spring perches.
For the first drive, I left the shocks on the softest setting and drove it around the block. The ride was like a cork bobbing around. After the next few drives, I played around with the spring perches and shock settings until I got what seems like a reasonable ride. After reading all this, I realize there’s quite a bit more that can be done.
Hang in there with Clive and Tom on the job I’m sure we’ll get an outcome that in modern parlance will be a “ plug and play” solution for today’s road driving ……it’ll just take time
Thanks Dave, that’s encouraging. I’d settle for “mild passing interest”.
I don’t know if this discussion will yield anything more than a better understanding of the car and its systems, but that seems a worthy aim in itself.
Hi Danny…we already have a plug and play solution…to get the best out of an E type…all discussed in the first dozen or so posts in this thread…they really will make a huge difference to handling/ride etc…tyres, adjustable shocks, suspensing bushings and correct alignment. …all things we can easily play with now…Steve
We can be confident on the last part of that…
For the first, there will be something but the constraints are tight. The original creators knew what they were doing but we do have a few things in our favour, such as -
60 years of accrued knowledge, progress in materials and analysis tools
relative lack of constraints in cost, manufacturing feasibility, commonality with other models and customer bandwidth (they’re optional)
Even so, considerations of originality and the sheer value of the cars do restrict the room for technical manoeuvre. Areas that would normally be addressed before we ever got to damper tuning would include the front structure, suspension and steering geometry. Then the rear suspension - complex, compromised but very hard to change in a meaningful way. I haven’t addressed tyres because their size and shape are limited by originality concerns - they’re powerful but can’t work miracles. Likewise bars and bushes, need to be looked at (soon) but they can’t fix the concerns listed above.
Hence the focus on dampers, potential miracle workers given access to parts and some luck. As others have noted, their tuning can make or break the feel and character of a car with no outward change. No way that I know to model, calculate or predict from what went before, just get in the car and pay attention.
We’ll be testing and studying Gaz and Girling dampers, trying to understand what’s already there and what scope there may be for improvement. If we’re successful that could adjust the effort / benefit balance for some other areas, it might be worth taking another circuit looking for small changes that didn’t seem worth the trouble first time round.
Regular reminder - everything I say is based on analysis, not actual driving of a real car. Please make your own judgment if you’re as comfortable with that as I am.
True +20 characters in here
Can anyone tell me the inside diameter of the upper and lower damper bushes please? From parts lists I’ve been able to find, I’m thinking the rear bolts are 7/16"?
Rear upper and lower…5/8 from memory without actually measureing…both lower dampers sit on a 5/8 shaft that has 7/16 threads each end…upper have 5/8 steel bushes through the rubber damper bush secured to irs with 7/16 bolts…Steve
That makes sense of the illustration, thanks.
An update to this chart from a few days ago, which showed how the rear becomes effectively softer relative to the front as the overall load increases. (Because passenger, fuel and luggage loads go mainly on the rear wheels). The rear (green) curve converges towards the front (blue), giving a possibility of pitching over bumps.
I’ve added a couple of rear springs stiffer than the nominal 262 lbf/in - 290 and 325 lbf/in.
The purple dashed line is a typical target of 15% higher than the front frequency +15% (higher).
The middle (dashed) green line (290lbf/in, 51N/mm) looks like a pretty good match to the purple line, while the dotted green line (325lbf/in, 57N/mm) looks unnecessarily high here. It might look more attractive from a roll / handling perspective, or when matched to a stiffer front torsion bar.
I’ll take those two springs as a reasonable working range to look at the cornering effects, while waiting for test results on the dampers.
An alternative approach to the rear spring, a progressive rear jounce bumper as Tom suggested. I played around with various sections cut from a Mercedes bumper, it is generally softer and more progressive than the ones that come with dampers for sports cars. The red dotted line is just a sample curve, the possible range is vast - both cut-in point and stiffness.
@CliveR could you expound on how a jounce bumper works. I know they are mounted on the shaft of the damper. I always thought of them as a device that under extreme compression loading of the spring/damper, kept the shock from going into a hard metal to metal contact. But I gather they are also a means to obtain a progressive beyond linear rate to the springs?
Exactly. I don’t think I can add much to that! Traditionally they were to limit extreme motion, today they’re often an integral part of the springing system. One possible reason is that cars tend to be lower and suspension systems have less travel so the wheel gets towards the end of its travel more often, hence the forces there need to be managed more carefully. More sophisticated dampers and bumper materials undoubtedly play a part too.
I’ll dig out comparison curves for traditional bumpers and modern ones like the Mercedes.
OK, good to know I was on the right track. To dig a little deeper, my phrase “proressive beyond linear” was shorthand for the fact that the stock springs have a single linear spring rate of “whatever” lb/in. I understand that springs can be wound that are non-linear. I guess there are several ways to do this but I would envision the spacing of the coils intentionally not being equidistant and tricks like that. And you can obtain a similar effect with the jounce bumpers. I also have read that some race drivers with really good “butt dynos” can tell the difference and that some like them and some don’t. I’m not sure if playing with the jounce bumpers falls within Danny’s original mission statement but they might be an interesting option for some. I’m not sure how they would be installed on the stock Etype damper. I only commonly see them on McPherson strut type dampers, where they just pop over the shaft when you have the spring/strut assembly disassembled.
Yes, that’s a common way to do it. I’ve only played with them once and found their value quite limited because the length of spring left working obviously reduces quite quickly as the coils begin to contact each other. Starting with a target stiffness for the linear range, the physics of load and stress put limits on the possible variation from that line.
I thought it worth following up with Tom’s suggestion because they’re probably easier and cheaper to play with than springs. A small box of inexpensive bumpers can offer a wider range of properties, although you’d still be pulling dampers and springs apart to install them.
Their value might be more apparent in road use with a wider range of events, slower transients and more time to observe and adjust.
If the damper top can’t be removed it’s common to cut and superglue them after sliding over the damper stem. Cutting off the old bumper might require a deep breath and confidence, although it should be possible to replace that with glue.
(Incorrect comment about jounce bumper removed)
Maybe a good time to look at system behaviour in cornering. I’m thinking we should ensure we’re all using the same vocabulary, so here’s a 2D sketch of basic cornering force and load transfer. We’ll go to 3D and introduce the numbers from the ride discussion.
Not intended to patronise, I just want to be sure we’re starting with the same viewpoint.
The important point in this 2D view is that the load transfer from inside to outside wheels depends only on the height of the Centre of Gravity and the distance between wheels. Suspension detail plays no part in side to side transfer for the whole car - the car could be a single solid block and the transfer would be the same.
Orange you glad we’re interested in this topic?
Citrus-fruit-as-jounce-bumpers: THAT’s why yer a papered engineer, and I’m a bus driver.
And yes: roll does not create weight transfer.
Great way to show us amateurs the basics Clive