Spring rate TVR Vixen

[octanetorque]

Slow M said:

octanetorque said:

. . . Might be worth mentioning that varying speed from 50-70 didn't seem to make any noticeable difference. Even at slow speeds in traffic on those roads there is some noticeable fore-aft bucking. . .

In that case, while I am sure that the bucking is very unpleasant, the phenomenon cannot be "porpoising."

Best,
B.

My missus would probably say it's my driving...!

I reckon something is too hard/soft and needs to be tweeked with...or the ruts in the road are at just the right spacing to upset the car - doesn't happen on any other surface.

and if it's not porpoising - what else might it be? Anyone live near the A12 and fancies doing a run between the m25 & A130 junction?

[Slow M]

If the front AND/OR rear suspension frequency were such, that the frequency of the seams in the road coincided, with it, then you might see the effect i think you're describing.

Poirposing can occur after one bump, and is the effect of the front and rear oscillating in opposite modes. Usually, the rear frequency is 20% higher than the front, so that the front and rear do not jounce and rebound at the same rate (or even too close). I think the front is kept softer to help steering control.

Poirposing can also be brought on by a road ripply road surface, which, at certain speeds, will not only harmonize with suspension frequency, but add amplitude to the oscillations.

So, even if the frequency of the seams in the road (time relative) were to match the suspension frequency (a factor of spring rate, sidewall, damping, etc) at 60MPH, the frequencies could not match up at 50 or 70.

I think what you're feeling, is a stty road, in a short wheelbase sportscar.

Best,
B.

P.S. Far be it for me to so much as suggest any illegal activity, but try it at 80, and see what it's like.

[octanetorque]

Slow M said:

I think what you're feeling, is a stty road, in a short wheelbase sportscar.

I have a feeling this might be utterly correct.

just to revert to one other question:

I understand the balance idea across the pivot bars with 4x spring & damper - but what would the expected ride difference be between 4x spring & damper and 2 spring and four damper setups? Just a firmer ride?

[Slow M]

If you are thinking of doubling what you already have, yes, much firmer.

Not sure what advantage the "balance across the pivot shaft" would be, unless the upper AND lower a arms inherently flex a great deal.

Best,
B.

[octanetorque]

Slow M said:

If you are thinking of doubling what you already have, yes, much firmer.

Not sure what advantage the "balance across the pivot shaft" would be, unless the upper AND lower a arms inherently flex a great deal.

Best,
B.

I'm wondering why there's a general recommendation for the S3 to be moved to the S2 configuration?

Is there any particular way of turning the S2 rear (i.e. should everything be halved? I have a feeling it's way more complex than one damper set to 7/14 and the other set to 3/14 give that corner an overall damper setting of 10/28 or 5/14? Should all springs be at the same height when calibrating etc...?

Thanks as always!
J

[Dollyman1850]

octanetorque said:

I'm wondering why there's a general recommendation for the S3 to be moved to the S2 configuration?

Is there any particular way of turning the S2 rear (i.e. should everything be halved? I have a feeling it's way more complex than one damper set to 7/14 and the other set to 3/14 give that corner an overall damper setting of 10/28 or 5/14? Should all springs be at the same height when calibrating etc...?

Thanks as always!
J

james. What are you doing with the car?
It seems to me that you have purchased springs, ten dampers then put it all together without much thought as to what you want to do with the car.

A std vixen runs well on springs of about 160 -170lbs..Upgraded is a matter of use and personal choice.. You have obviously went to 200 lb all round which is hard.. Not massively hard but hard nevertheless.. You now seem surprised that the car is a bit stiff.

A vixen is known to handle well on a single spring damper set up. you can run a 2nd damper on each side and if you want to switch to vixen S2 then you will also find that you will go astray since the opposite configuration on an s2 regards spring location often works best.

Then you need to weigh up coefficients of friction when considering the merits of running single or twin springs on the rear. In theory 2 springs with the spring rates halved is the same as 1 with double but in practise it doesn't often feel that way.

Then you need to consider the merits of splitting the sprung weight to either side of the lower pivot rod…Both solutions have merits and again both solutions are valid if you have a specific application in mind.

Then you need to consider adjustable damping.. again having 10 clicks available for bump an re-bound, along with 2 or 4 springs, along with spring rates between road car to race will give you a different ride and feel.

it seems to me that you could do a lot worse than speak directly to Adrian. If you have bought from him it usually comes with lots of free advice regarding set up, bushes, etc etc which will save you a whole load of grief.

No one person on here can give you the advice you want!

My race car runs 600 lb front and 400 lb rear rates with less adjustability than your car! It doesn't have to contend with UK roads though!

Who supplied your dampers?

N.

Edited by Dollyman1850 on Saturday 27th December 11:18

Edited by Dollyman1850 on Saturday 27th December 11:32

[octanetorque]

Hi Neil - thinks for your detailed response, I'll attempt to answer as best possible - and of course I'll speak to Adrian - I do like to hear others' opinions too and get a wider view of possibilities and get my own head around reasoning.

Quick question to you, what do you mean by:

Dollyman1850 said:

Then you need to consider the merits of splitting the sprung weight to either side of the lower pivot rod…Both solutions have merits and again both solutions are valid if you have a specific application in mind.

What are the merits and cons for each solution?

To answer your questions:

Dollyman1850 said:

What are you doing with the car?

Mainly everyday road use - with about 6-10 track days a year, plus tours (Le Jog/Le Mans, Spa etc.) I've moved to 4xspring/damper setup due to the overall consensus (as I'm aware) with safety over weight on tie-bars / pivot rods. General advice has been in the same direction from Adrian and seemingly a few others on here for mainly road-going cars.

Dollyman1850 said:

Who supplied your dampers?

Adrian supplied the springs & dampers which are AVO.

Dollyman1850 said:

A std vixen runs well on springs of about 160 -170lbs..Upgraded is a matter of use and personal choice.. You have obviously went to 200 lb all round which is hard.. Not massively hard but hard nevertheless.. You now seem surprised that the car is a bit stiff.

I'm not really surprised how hard it is...but the rear is practically static which I would propose is very stiff. I want to get the best from the setup with have some level of comfort and I'm happy to compromise. Things like porpoising should be easily dealt with if it's resonance calibration, or a slightly lower spring rate.

I'll have a chat with Adrian in the new year. I take your points, but I'm certainly aware of what I've purchased and the advice that's gone with it - however if I'm missing information for whatever reason I'd rather ask and listen to further advice.

I actually think that..

Slow M said:

Porpoising can also be brought on by a road ripply road surface, which, at certain speeds, will not only harmonize with suspension frequency, but add amplitude to the oscillations.

This might be what I'm experiencing.

Thanks for your reply,
J

[tomtrout]

Hi James

My vixen is set up for brisk road use. The point about a road car is that you don't have the luxury of nice smooth road surfaces on most of our rubbish roads and the last thing you want halfway round a bend is your rear end to go airborne every time you hit a rabbit turd. My S2 car has a matched quad set up with 90lb rated rear springs which gives the rear end enough stiffness but critically allows the tyres to stay in contact with the road (most of the time at least). I'm also not in any danger of losing my dental fillings or getting double vision when driving down bumpy lanes! As Neil has recommended, I think a conversation with Adrian is in order.

[GAjon]

At risk of being ridiculed, but I have seen this on two TVRs one Vixen and one M.

Have you checked your wishbones havnt been over tightened ?

[Dollyman1850]

GAjon said:

At risk of being ridiculed, but I have seen this on two TVRs one Vixen and one M.

Have you checked your wishbones havnt been over tightened ?

I would never ridicule you OBI wonky blokey.

Everytime you post though I think about buying one of those Cadacs for Better outside frying capabilities I hope Cadwell happens this year.

I think most of the issue is tyre pressures and ballooning tyres on skinny rims and an over hard rear end…things I have been afflicted with for many years

Have you tightened your wishbones yet??

N.

Edited by Dollyman1850 on Saturday 27th December 15:31

[Dollyman1850]

octanetorque said:

Hi Neil - thinks for your detailed response, I'll attempt to answer as best possible - and of course I'll speak to Adrian - I do like to hear others' opinions too and get a wider view of possibilities and get my own head around reasoning.

Quick question to you, what do you mean by:

Dollyman1850 said:

Then you need to consider the merits of splitting the sprung weight to either side of the lower pivot rod…Both solutions have merits and again both solutions are valid if you have a specific application in mind.

What are the merits and cons for each solution?

Depends on what you are doing with the car. probably for a road car 2 x spring with about 90lbs per spring, (my opinion only)

To answer your questions:

Dollyman1850 said:

What are you doing with the car?

Mainly everyday road use - with about 6-10 track days a year, plus tours (Le Jog/Le Mans, Spa etc.) I've moved to 4xspring/damper setup due to the overall consensus (as I'm aware) with safety over weight on tie-bars / pivot rods. General advice has been in the same direction from Adrian and seemingly a few others on here for mainly road-going cars.

Dollyman1850 said:

Who supplied your dampers?

Adrian supplied the springs & dampers which are AVO.

Dollyman1850 said:

A std vixen runs well on springs of about 160 -170lbs..Upgraded is a matter of use and personal choice.. You have obviously went to 200 lb all round which is hard.. Not massively hard but hard nevertheless.. You now seem surprised that the car is a bit stiff.

I'm not really surprised how hard it is...but the rear is practically static which I would propose is very stiff. I want to get the best from the setup with have some level of comfort and I'm happy to compromise. Things like porpoising should be easily dealt with if it's resonance calibration, or a slightly lower spring rate.

I'll have a chat with Adrian in the new year. I take your points, but I'm certainly aware of what I've purchased and the advice that's gone with it - however if I'm missing information for whatever reason I'd rather ask and listen to further advice.

I actually think that..

Slow M said:

Porpoising can also be brought on by a road ripply road surface, which, at certain speeds, will not only harmonize with suspension frequency, but add amplitude to the oscillations.

This might be what I'm experiencing.

Does it only do it on 1 particular road? My polo does it on the A696 toward alston at Langley where the road has about 5 dips and ridges which promotes a harmonic rise and fall of the car… is the car happy everywhere else?

Thanks for your reply,
J

[GAjon]

[quote=Dollyman1850



Have you tightened your wishbones yet??

N.


[/quote]

Hello Neil, yes wishbones are tight and rotating fully.
This afternoon however I will be mainly flying my new helicopter and defending Rourkes drift with Micheal Cain

[Dollyman1850]

GAjon said:

Hello Neil, yes wishbones are tight and rotating fully.
This afternoon however I will be mainly flying my new helicopter and defending Rourkes drift with Micheal Cain

Is Zulu on again!!

My engineering inspiration this afternoon…Got to be a contender for best man gift of x-mas

[status]

Dollyman1850 said:

I think most of the issue is tyre pressures and ballooning tyres on skinny rims and an over hard rear end…

I've certainly experienced that combination in another car. I ran my XR2 on the road a couple of times to and from meets, with standard wheels/tyres but with semi-race suspension, and that could pitch and roll at the wrong surface/speed combination because of the flex in the sidewalls.

Definitely needs consideration

cheers
Nick

[Slow M]

octanetorque said:

. . . I actually think that..

Slow M said:

Porpoising can also be brought on by a road ripply road surface, which, at certain speeds, will not only harmonize with suspension frequency, but add amplitude to the oscillations.

This might be what I'm experiencing. . .

By "ripply," I was inferring bumps that are very close together. Think "washboard" road, where the bumps' peaks are approximately 30"-40" apart. In those low speed conditions, with my M behaving like a rocking horse, light throttle cured the problem. Imagine traversing the surface slowly enough, to sense the front moving up, as the rear moves down, and the converse.

As I mentioned before, if you can vary your speed from 50-70, with no discernible difference, I doubt that the effect you are sensing is "porpoising," but it depends on your definition. I would think that you are referring to coincident wave patterns between road surface inputs, into the suspension, and that suspension system's own (natural) harmonic frequencies (different front and rear). Think of it this way, you are changing the input frequency in a 40% range, not altering your suspension frequency, and expecting the output to remain the same. I think you are feeling a harsh bump approximately once per second, and the car's response to this input, but i also suspect, that each previous event does not effect the next, i.e. that you are sensing separate events, strung closely together, and occurring at a certain frequency (because the sections of . . . especially concrete . . . road are usually built in set lengths).

As Neil suggested, I would also urge you to have a conversation w/ Adrian, about this issue.

Best,
B.

P.S. How far apart are the bumps? Are they seams, in a concrete road?

[octanetorque]

Dear all - thank you for this flurry - I can tell the wives have brought you all back from shopping I currently don;t have the car as its having a new engine put in but soon as I'll get it back I'll check the below again.

Two particular roads: A45 (between Oxford and Bicester) and A12 stretch between A130 & M25. Car appears fine everywhere else. These are both concrete block seamed roads - and yes I would point to the issue being the seams not on the majority of surfaces - generally the ride is good otherwise. I'll try at different speeds as soon as I get the car back, but as I remember there was not a HUGE difference. But like I say, I'll double check.

1. Over tightening of wishbones is entirely possible; I'll check this.
2. Been running original setup of 22/24psi front rear tyre pressures - I've recently been recommended to run 26 on front - but any other suggestions?
3. Not aware of tyres skipping off the pavement, but the car does oscillate enough to be physically unconfortable.

Thank you all for giving this your 2d - it's very much appreciated. I'll take this all to the car when I get it back and report back (likely to be February)

Thanks,
J