Independent rear suspension

Independent rear suspension

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Discussion

ken46

18 posts

5 months

Sunday 31st January
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Well I think you should have listened to your mummy.

the av8er

Original Poster:

98 posts

87 months

Sunday 21st February
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A relative of a friend of a friend works at caterham.
I've been trying to find out what new design and developments are being worked on there.
Obviously they are working on electric, but I can also share this.
If this was offered in stead of, or as well as de Dion. What would you think ??

the av8er

Original Poster:

98 posts

87 months

Sunday 21st February
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DCL

1,141 posts

143 months

Sunday 21st February
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If that is the car I think it is, then I don't think we're going to see that go into production. But it was a well executed project that I believe worked very well, albeit that it did reinforce many of the earlier comments in this thread.

bcr5784

5,466 posts

109 months

Sunday 21st February
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To say that IRS good de Dion bad is simplistic.

Likewise you can say the double wishbones are better than Macpherson struts - but there aren't many sports cars that handle better than a Porsche Cayman.

And a rear engined car like the 911 "ought" to handle like a pig.

In practice development can overcome some significant theoretical disadvantages - and poor detail design undermine any theoretical advantage.

I don't want to be unfair to Westfield, but I can't think of an independent road test which didn't conclude that the Caterham has a more resolved chassis setup.

So with IRS you probably can ultimately get better results - but there are any number of cars with IRS which don't handle anything like as well as a Caterham so I don't think it sensible to dismiss the car because of its de Dion suspension.

The big theoretical (and often actual) advantage of a de Dion is predictability - because there is no relative camber change inside to outside wheel.

Glug69

65 posts

86 months

Sunday 21st February
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So with IRS you probably can ultimately get better results - but there are any number of cars with IRS which don't handle anything like as well as a Caterham so I don't think it sensible to dismiss the car because of its de Dion suspension.


I think you are correct that a Caterham handles very well, especially on smooth roads, but in the real world on uneven and bumpy roads they are out performed by most cars, talk to someone who has owned a CSR and a dedion car and independent rear suspension the main advantage they talk about on the road.

bcr5784

5,466 posts

109 months

Sunday 21st February
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Glug69 said:
So with IRS you probably can ultimately get better results - but there are any number of cars with IRS which don't handle anything like as well as a Caterham so I don't think it sensible to dismiss the car because of its de Dion suspension.


I think you are correct that a Caterham handles very well, especially on smooth roads, but in the real world on uneven and bumpy roads they are out performed by most cars, talk to someone who has owned a CSR and a dedion car and independent rear suspension the main advantage they talk about on the road.
I have no personal experience of a CSR so can't compare it with the other Caterhams. But outperformed by "MOST" cars I very much doubt. There is no particular (theoretical) reason a de Dion should perform much worse on bumpy roads - IRS generally has a bit of a unsprung weight advantage but it is a small advantage. As I say I've not seen any road test that would suggest that a Westfield would handle a bumpy road as well.

If I remember rightly the CSR was said to be set up softer than was the norm for de Dion cars and if it does handle bumpy roads better I might suspect that might be the reason.

The Caterhams I have driven in recent years have all been set up stiffer than the live-axled one I raced - which amazed me by having a supple (!!!) ride which was almost unbelievable considering what a hefty lump of Marina back axle it had.

Edited by bcr5784 on Sunday 21st February 16:34


Edited by bcr5784 on Sunday 21st February 16:40


Edited by bcr5784 on Sunday 21st February 19:16

Equus

10,831 posts

65 months

Wednesday 24th February
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bcr5784 said:
There is no particular (theoretical) reason a de Dion should perform much worse on bumpy roads
Yes there is: aside from the unsprung weight disadvantage, DeDion (or any other beam axle arrangement, unless you are very careful to ensure an effective ratio of 1:1 for spring base vs. track) will suffer from the issue that when there is a bump at one side, it transfers some of the impact to the other wheel, with consequent change in the load at the tyre contact patch. Google 'centres of percussion'. It needs a very trick beam axle arrangement to overcome this.

Also, the theory that DeDion keeps the wheels square to the road under all conditions is simply wrong; it only does so in pure roll and/or pure pitch... a single wheel bump upsets the camber relationship just as badly, or worse, than IRS and it does so to both wheels on the axle at the same time and to the same degree.

bcr5784

5,466 posts

109 months

Wednesday 24th February
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Equus said:
Yes there is: aside from the unsprung weight disadvantage, DeDion (or any other beam axle arrangement, unless you are very careful to ensure an effective ratio of 1:1 for spring base vs. track) will suffer from the issue that when there is a bump at one side, it transfers some of the impact to the other wheel, with consequent change in the load at the tyre contact patch. Google 'centres of percussion'. It needs a very trick beam axle arrangement to overcome this.

Also, the theory that DeDion keeps the wheels square to the road under all conditions is simply wrong; it only does so in pure roll and/or pure pitch... a single wheel bump upsets the camber relationship just as badly, or worse, than IRS and it does so to both wheels on the axle at the same time and to the same degree.
While not strictly wrong it's misleading on both counts. Side to side load transfer will be much less than would be the case with a typical antiroll bar.

It would be a very odd double wishbone arrangement that didn't cause miles more camber change than a de Dion on bump. Put it this way for 6 inches of wheel travel a de Dion will produce little more than 1/2 (half) a degree camber change whereas a typical double wishbone setup might produce 3 or 4 degrees.

Equus

10,831 posts

65 months

Wednesday 24th February
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bcr5784 said:
Side to side load transfer will be much less than would be the case with a typical antiroll bar.
That's a spurious argument.

You shouldn't need an ARB on the back of such a light car, if you design it correctly, but of course you can't say that a beam axle obviates the need for an ARB where IRS dictates it, so its a quite different and unrelated issue. You might, of course, find that you need an ARB for your deDion, in which case you'll end up with BOTH load transfer due to percussion centres on the beam AND due to the ARB.

Whether the load transfer due to the one is greater than that from the other depends on a number of factors, but it's certainly not truthful to say that it is less for the beam axle in all cases (if you do fit an ARB at the back, it's likely to be quite a light one).

Whatever, the load transfer across the axle on single wheel bump is one of the main downsides of beam axles (just as, yes, degradation of grip due to load transfer is one of the main downsides of ARB's... but let's not try to distract from the truth by conflating the two issues), so it's certainly not 'misleading' to identify it as a problem; certainly less misleading than saying that 'there is no particular (theoretical) reason that deDion should perform much worse on bumpy roads', which is just plain wrong.

Equus

10,831 posts

65 months

Wednesday 24th February
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bcr5784 said:
Put it this way for 6 inches of wheel travel a de Dion will produce little more than 1/2 (half) a degree camber change whereas a typical double wishbone setup might produce 3 or 4 degrees.
Oh... and you're wrong on the camber change, too:

A 6" single wheel bump on the Caterham's rear track of 1334mm. would result in a camber change of about 6.5 degrees on the both wheels (I've just checked it on CAD), which is much worse than you'll get on an IRS (and the point is that IRS only experiences camber change on the wheel that's deflected, not on its opposite number as well). How much you get on IRS will depend on the amount of camber gain you design into the geometry of course, but a figure of 3 degrees is reasonable.

You also get what Arthur Mallock (a fierce proponent of beam axles, but not blind to their shortcomings) called the 'stagecoach effect' of a lateral displacement of the whole axle relative to the sprung mass (or, looked at the the other way, a lateral displacement of the sprung mass relative to the tyre contact patch, which the contact patch then has to react against the road).

bcr5784

5,466 posts

109 months

Wednesday 24th February
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I stand by what I said about the rear AR bar - it's pretty normal to fit them on Caterhams - and I think all the racers have them - so weight transferance on that score is a red herring.

But you are right about camber change (never trust a mathematician with arithmetic).

Fact remains that there is no reason to dismiss a Caterham because it has a de Dion rear end - any more than there is to dismiss a Cayman because it has struts. The proof of the pudding is in the eating.

Equus

10,831 posts

65 months

Wednesday 24th February
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bcr5784 said:
I stand by what I said about the rear AR bar - it's pretty normal to fit them on Caterhams - and I think all the racers have them - so weight transferance on that score is a red herring.


And I stand by what I said about them too. They're not necessary - and indeed are detrimental - on such light cars for road use (take the matter up with Gordon Murray, who chose not to fit one either front or rear on the LCC Rocket, if you disagree with me) and any detriment to grip from the ARB would be additional to the detriment to grip from the load transfer arising from percussion effect of the axle.

You've heard the saying that two wrongs don't make a right?

It's ARB's that are the red herring in the context of this discussion.

bcr5784 said:
Fact remains that there is no reason to dismiss a Caterham because it has a de Dion rear end
The fact remains that you claimed there was "There is no particular (theoretical) reason a de Dion should perform much worse on bumpy roads', which is entirely and absolutely incorrect.

No ifs, no buts - you were just wrong.

Furthermore, Caterham themselves demonstrated (with the CSR) that the proof of the pudding is that IRS will clearly perform better on bumpy roads than the very best, most highly developed beam axle suspension you can achieve on such a lightweight car, so the 'proof of the pudding' argument falls flat, too.

PH User

17,331 posts

72 months

Wednesday 24th February
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What we have here is 2 different opinions.

Does any of this matter? It isn't costing sales and people enjoy driving them.

Equus

10,831 posts

65 months

Thursday 25th February
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PH User said:
Does any of this matter?
I'm sure that people thought Karl Benz' Patent-Motorwagen was a real wheeze to drive.

Doesn't stop some people wanting to progress beyond 1885 (or 1955, in the case of Caterham) levels of technology, and it appears that the OP of this thread is one of them (hence it may very well be costing sales, if he and people like him - and I'm one of them - can't find what they're looking for in Caterham's current range).

There is a broader problem in that Caterham have proved themselves a 'one trick pony' with the Seven. Everything else they've done to try to move the business forward: the 21, the Caterola, the collaboration with Alpine, CSR, the Aeroseven) has fallen flat. Time will come - very soon, with EV's looming - where any company that is reliant on a customer base that is incapable of adapting, will die.

PH User

17,331 posts

72 months

Thursday 25th February
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I'm sure they will be fine.

Equus

10,831 posts

65 months

Thursday 25th February
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PH User said:
I'm sure they will be fine.
I'm not. biggrin

It's all very well having a solid customer base of enthusiastic owners, but when they're only prepared to be enthusiastic about something you're not going to be allowed to build in 9 years from now, you've got BIG problems!

PH User

17,331 posts

72 months

Thursday 25th February
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Equus said:
PH User said:
I'm sure they will be fine.
I'm not. biggrin

It's all very well having a solid customer base of enthusiastic owners, but when they're only prepared to be enthusiastic about something you're not going to be allowed to build in 9 years from now, you've got BIG problems!
Well let's agree to disagree.

Plenty of other cars available from other manufacturers, so good for you.

Equus

10,831 posts

65 months

Thursday 25th February
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PH User said:
Well let's agree to disagree.
If you like, but as per my post above, Caterham has a long list of failed projects behind it that say I'm right.

By comparison, Morgan have massively upgraded their underlying chassis tech and have done a lot of work on EV's (both with their 4-wheeler and their trike - the latter almost reaching production) and Westfield is now making more money from autonomous vehicles and EV consulting (on the back of it's own EV projects) than it is from building its 'Seven' type cars.

Caterham's approach to the future, by contrast, seems to consist of sticking its fingers in its ears and singing 'la, la, la, we're not listening' in the face of developing legislation and announced Government policy.

PH User

17,331 posts

72 months

Thursday 25th February
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Equus said:
PH User said:
Well let's agree to disagree.
If you like, but as per my post above, Caterham has a long list of failed projects behind it that say I'm right.

By comparison, Morgan have massively upgraded their underlying chassis tech and have done a lot of work on EV's (both with their 4-wheeler and their trike - the latter almost reaching production) and Westfield is now making more money from autonomous vehicles and EV consulting (on the back of it's own EV projects) than it is from building its 'Seven' type cars.

Caterham's approach to the future, by contrast, seems to consist of sticking its fingers in its ears and singing 'la, la, la, we're not listening' in the face of developing legislation and announced Government policy.
Like I said, let's agree to disagree. There is plenty of choice out there if you don't want a Caterham.