Caterham Chassis Limitations

Caterham Chassis Limitations

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analog_me

Original Poster:

287 posts

128 months

Wednesday 9th August 2017
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Hi all,

I am relatively new to caterham ownership, 9 months about 5k miles fast road use on the mountain roads, and come from an S1 elise.
I adore the car, and all that goes with it and find it so much better suited to me than my 100% custom tuned nitroned, 180hp elise.
However i found the car k-series 1.6 superlight has limitations which i never experience during the 10 years of ownership of the elise.

The weakest point is the unstability/sensitivity of the rear axle over non perfectly flat road surfaces.
I always allow a generous margin allowing for the rear to cope with non flat surfaces so to avoid nasty non recoverable situations.
Something which was never needed to that extend with the elise since its suspension could cope with all kind of crap thrown at it despite how close you drove to the limit.


Second limitation is break efficiency which i found considerably lower than the elise on similar tires 048s despite the AP 4pot upgrade and RS14 on the caterham.
It has now happened twice to lock the front although i was expecting much more grip prior that.

Combining the above two how come the higher powered cars with +200 and +300hp cope and maintain a balanced experience?
You could easily have +300 and +400hp on the S1 elise without really feeling short of something else. (although much more boring to drive)
I guess the answer is it all comes together on track when conditions are more predictable and repetitive.

What do you think, what is your opinion regarding limitation of the caterham chassis when pushed hard?


HustleRussell

24,602 posts

159 months

Wednesday 9th August 2017
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Both are possibly partially symptomatic of the lower load acting on the tyres. The Elise is 50% heavier and with weight, by and large, comes directional stability. The Elise is also more aerodynamic. The Elise probably has wider track too which tends to reduce body roll. The engine being in the back might enable the rear axle to do more braking in some circumstances. Finally if you consider unsprung weight vs. sprung weight as a ratio the Elise will come out on top because of independent rear suspension.

Of course that 33% weight saving vs. the Elise compensates for all of this to some degree.

It's important to run low tyre pressures on a 7. Your brakes should be capable of locking the tyres if you push them hard enough- if they can't you have a problem. You can tailor brake pedal effort and friction coefficient by changing the master cylinder / brake pads.

V7SLR

456 posts

185 months

Wednesday 9th August 2017
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You've answered your own questions ... your Elise was fitted with Nitrons. Speak to Simon at Meteor Motorsport and do the same to your Caterham, it'll transform it in all the areas you've mentioned.

analog_me

Original Poster:

287 posts

128 months

Thursday 10th August 2017
quotequote all
V7SLR said:
You've answered your own questions ... your Elise was fitted with Nitrons. Speak to Simon at Meteor Motorsport and do the same to your Caterham, it'll transform it in all the areas you've mentioned.
Yes, thinking about it and the difference the Nitrons did, this could be a good reason to believe

Equus

16,767 posts

100 months

Thursday 10th August 2017
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Even with Nitrons, the Caterham is up against the fundamental limitations of its chassis technology. The sprung:unsprung weight ratio of the rear suspension is unfavourable, compared to more modern, IRS designs, and the chassis is woefully lacking in torsional stiffness by modern standards (so acts as an undamped spring itself).

It will never feel as composed as an Elise on normal (bumpy) public roads, though the limitations are less serious on a nice, smooth racetrack.

Having said which, the higher power outputs don't necessarily impose as much of a problem as you might expect, for the simple reason that the rear tyres constitute a 'fusible link' between that power and the road.

Caterham themselves have tried to address the worst of the limitations with the CSR, of course, but it hasn't quite caught on, hence perhaps suffers from a lack of development vs. the 'traditional' cars (so is yet to fully exploit its potential advantage).

griggsy2

126 posts

279 months

Thursday 10th August 2017
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Maybe you have other issues as the experience with my Elise (S2 on Nitrons and 48s/888s) was very different. The Elise was always very crashy over bumps compared to the Caterham and also very snappy on the limit, catching oversteer moments also far trickier and the high COG very noticeable.

From a couple of your points, pagids are known for being quite snatchy on the Caterham, maybe the initial bite is too strong and locking the tyres prior to you having decent weight transfer?

The rear instability could be a couple of things.. When was the car last flat floored/geo'd? Are the 48s old as they give up grip over time and heat cycles quite dramatically? 48s have very stiff sidewalls, maybe you need a softer sidewall? I run CR500s and don't have the comparative problems you outline. Do you have a rear ARB? Having that too stiff will also give a sketchy rear (ooh-err), on the road fully soft is probably where you need it or even disconnected.

Sure there are many other things to consider but maybe a few more details about your car would help.

analog_me

Original Poster:

287 posts

128 months

Thursday 10th August 2017
quotequote all
I can see all the points mentioned above and accept them.
First of all let me clarify once more i prefer the caterham to the elise but i can see some considerable limitations in the car's chassis and architecture as mentioned above.

Yes my car now has 048s (i am on the second set) which are past their best, yes i have a rear antiroll bar set to one before stiffest setting, it was corner weighted to 2kg front left and right 3 months ago, the geo was re-adjusted 2 weeks ago with the same accuracy i was doing my elise for almost 10 years (String method),
I have tried the green and orange front antiroll bar as well as all settings of the rear including not having one.

I understand this is very sensible to weight transfer and time needed for this to happen but cannot see how the caterham can generate the same g- forces during braking, as the elise as it feels it can not put enough weight in the front to make use of the full potential of the tires and 4 pot AP brakes.

Similarly, the rear always jumps around and unsettles when over not flat tarmac and close to the limit this is not inspiring confidence.
Yes over a perfectly flat road it is the greatest.
Ah, the car has no noticiable bump steer so all is well set up in the front



Edited by analog_me on Thursday 10th August 09:20

upsidedownmark

2,120 posts

134 months

Thursday 10th August 2017
quotequote all
What tyre pressures?

analog_me

Original Poster:

287 posts

128 months

Thursday 10th August 2017
quotequote all
upsidedownmark said:
What tyre pressures?
16 psi all round cold

upsidedownmark

2,120 posts

134 months

Thursday 10th August 2017
quotequote all
Not that then..

To me what you describe is a car that is too stiff. While the points above are valid, there are lighter vehicles out there; fundamentally if the damping and springing is matched to the weight, it should ride bumps reasonably well.

analog_me

Original Poster:

287 posts

128 months

Thursday 10th August 2017
quotequote all
So none of you share the same opinion and find the braking efficiency and rear axle stability up to standards?

sfaulds

653 posts

277 months

Thursday 10th August 2017
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Your single biggest problem is the A048 - they're a bloody awful tyre on the road.

Syndrome280

272 posts

110 months

Thursday 10th August 2017
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I have a Superlight 1.6k clone (last of the K-series parts bin at CC I think, so no plaque for me) and took delivery of the car in early 2016 on the same rear ARB settings as you (second from hardest) with 6" fronts and 8" rears running CR500 and while it had tons of grip it was very snappy when it let go.
Switching the rear ARB settings to second from softest suited road driving much better, I then switched to 6" rears with Avon ZZS tyres (replacement for the CR500 tyre) as 8" rears on that engine was a complete overkill, it is now much more compliant and when the back end steps out it is much more composed.

Most people I chatted to who had done serious track and road time suggested second from softest for fast road and second from hardest for track, if you want to hot swap between the two for trackdays you can buy the lower half of a droplink for around £5 from CC and just install the ball, I think Daniel French the guy who runs the R500 blog did the same thing.

HustleRussell

24,602 posts

159 months

Thursday 10th August 2017
quotequote all
Rear ARB setting depends a lot on what bar you have on the front and the rest of your setup of course. No hard and fast rules.

upsidedownmark

2,120 posts

134 months

Thursday 10th August 2017
quotequote all
analog_me said:
So none of you share the same opinion and find the braking efficiency and rear axle stability up to standards?
In a word, Nope. Mine's only a standard K 1600, on (6 inch) CR500's, but (if you really step on the pedal) the braking is like a punch in the face - better than anything I've driven including elises (due to lack of mass mainly), and the back end seems to be pretty good at staying behind the front/progressive when it goes.

DCL

1,215 posts

178 months

Thursday 10th August 2017
quotequote all
I think a lot of this is just down to perception and certainly, from the braking point of view, the Caterham is up there with the best. If it is locking up or unstable you need to look at corner weights and the geometry setting.

Yes the rear is not the latest technology and they do like the smoother surfaces, but, again, they are up there with the best handling cars when they are set up properly.

However, I'm with Stuart, as soon as you say A048, then it probably explains much of it. Caterham's are sensitive to tyres (they are so light) and do respond well to good tyres and time spent getting the set-up right.

Edited by DCL on Thursday 10th August 21:48

analog_me

Original Poster:

287 posts

128 months

Thursday 10th August 2017
quotequote all
Thank you gentlement
I now have 8 inch rears and will soon prepare a set of 6inch all round to test.

Amris

157 posts

167 months

Friday 11th August 2017
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Definitely worth getting it professionally flat floored. I couldn't believe the difference it made on my car and would most likely cure all of the issues you are seeing. Only decision you have to make in my eyes if whether to get some shiny new nitrons too before hand too ;-)

analog_me

Original Poster:

287 posts

128 months

Friday 11th August 2017
quotequote all
Amris said:
Definitely worth getting it professionally flat floored. I couldn't believe the difference it made on my car and would most likely cure all of the issues you are seeing. Only decision you have to make in my eyes if whether to get some shiny new nitrons too before hand too ;-)
I am confident of my corner weighting and geo settings. However having experienced the before and after nitron on my elise i totally agree with you
😁

HustleRussell

24,602 posts

159 months

Friday 11th August 2017
quotequote all
analog_me said:
Thank you gentlement
I now have 8 inch rears and will soon prepare a set of 6inch all round to test.
Remember to adjust the rear ride height when you fit the smaller rears to keep the rake sensible.