Driveability

289, FIA & Daytona topics
Colin Newbold
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Re: Driveability

Post by Colin Newbold »

Your humble servant here, happy to chip in with my two pennyworth...what a racer wants from his/her car is balance and predictability. Chronic understeer or snap oversteer make the racer's life very frustrating and tense. One reason why the vast majority of racing Cobras are leaf sprung is because they handle so well (the other is cause the cut-off for Appendix K is 1965). That said, I've never raced a Cobra, let alone a fire-eating 400bhp + race car, but I've sprinted and hill-climbed and done track days in my 300 brake (previous engine) and my 200 brake (current engine) leaf sprung Kirkham and it's all quite manageable. What's more the ride on mine is pretty compliant for road use (it's set up pretty soft anyway - despite rose joints in place of Roger's rubber bushes (as per street Cobras). Yes it does roll but that makes the car easier to control in a way... no surprises. When it breaks away it does so gradually and I can see why on the Dunlop historics it drifts controllably.

Back in the day I had a RAM 427 copy and that handled well on track but was a bone shaker on the road. The exact opposite was true of 2 Southern Roadcraft copies I owned (all three had Jag rear ends). I owned a leaf sprung BRA, and a leaf sprung Hawk (both MGB axles) before finally building my own Hawk with double wishbone rear suspension centred on a Quaife diff in a Granada Scorpio casing. The latter was nowhere near as improved as I was hoping for and it wasn't until I raced the FIA MGB that I began to appreciate that back axle (and learn how to drive it).

My personal opinion... with a lot of hindsight... pay for professional coaching in your own car on a track and learn how to maximise what you've got! Way cheaper in the long run :wink:

Colin
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Paul Blore
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Re: Driveability

Post by Paul Blore »

I want to pick up on one point made by Colin.

The reason that all Cobras currently racing are 289's is because the 427/Mk.III was never homolgated for GT racing.

Paul
Samthomasracing
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Re: Driveability

Post by Samthomasracing »

We are currently building a 427 coil spring car to race in FIA championships, FIA are happy along as a car competed in an International FIA event, so can't be a 10 lap sprint at Spa but more like 1000km of Nurburgring or Sebring etc etc. This is how TVR Griffiths race at an FIA level now. Note their reintroduction to Goodwood this year.

I'd stay away from sticky tyres on Cobras, even on slicks the power will always break through the tyres & if the tyres are too sticky the car will become very nervous on corner entry and it will twitch on exit, we set them up to slide which is the fastest way in these old cars, set the nose up before the corner, steer with the throttle. Blockley tyres are really good, a lot of people run the Avon tyres too, i can get serial numbers if anyone wants to try them out.

Shock absorber revalving, spring rates & anti roll bars are key on these cars, there's a weight percentage which can be calculated, and makes the car extremely planted especially on the roads.

Saying this, isn't all the fun in oversteer out of roundabouts ?
When racing was dangerous and sex was safe....
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Roger King
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Re: Driveability

Post by Roger King »

When we're forced into electric self-drivers, oversteer will be a dim, distant memory...

just sayin'...
Paul Blore
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Re: Driveability

Post by Paul Blore »

Samthomasracing wrote:We are currently building a 427 coil spring car to race in FIA championships, FIA are happy along as a car competed in an International FIA event, so can't be a 10 lap sprint at Spa but more like 1000km of Nurburgring or Sebring etc etc. This is how TVR Griffiths race at an FIA level now. Note their reintroduction to Goodwood this year.

I'd stay away from sticky tyres on Cobras, even on slicks the power will always break through the tyres & if the tyres are too sticky the car will become very nervous on corner entry and it will twitch on exit, we set them up to slide which is the fastest way in these old cars, set the nose up before the corner, steer with the throttle. Blockley tyres are really good, a lot of people run the Avon tyres too, i can get serial numbers if anyone wants to try them out.

Shock absorber revalving, spring rates & anti roll bars are key on these cars, there's a weight percentage which can be calculated, and makes the car extremely planted especially on the roads.

Saying this, isn't all the fun in oversteer out of roundabouts ?
I'll be really interested to see how that goes Sam. I believe the 427 Cobras raced in the FIA Sports category in period, which put them directly up against the likes of McLarens, Chaparrals and GT40's etc.

Did you watch Top Gear last night Roger? They test drove an electric car that was specifically designed to hang the tail out. :)
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Roger King
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Re: Driveability

Post by Roger King »

Paul Blore wrote:
Samthomasracing wrote:We are currently building a 427 coil spring car to race in FIA championships, FIA are happy along as a car competed in an International FIA event, so can't be a 10 lap sprint at Spa but more like 1000km of Nurburgring or Sebring etc etc. This is how TVR Griffiths race at an FIA level now. Note their reintroduction to Goodwood this year.

I'd stay away from sticky tyres on Cobras, even on slicks the power will always break through the tyres & if the tyres are too sticky the car will become very nervous on corner entry and it will twitch on exit, we set them up to slide which is the fastest way in these old cars, set the nose up before the corner, steer with the throttle. Blockley tyres are really good, a lot of people run the Avon tyres too, i can get serial numbers if anyone wants to try them out.

Shock absorber revalving, spring rates & anti roll bars are key on these cars, there's a weight percentage which can be calculated, and makes the car extremely planted especially on the roads.

Saying this, isn't all the fun in oversteer out of roundabouts ?
I'll be really interested to see how that goes Sam. I believe the 427 Cobras raced in the FIA Sports category in period, which put them directly up against the likes of McLarens, Chaparrals and GT40's etc.

Did you watch Top Gear last night Roger? They test drove an electric car that was specifically designed to hang the tail out. :)
Yes, I did. It wasn't driving itself though, was it? Can you imagine a self-driving car that allowed you to do that? Switching off the self-drive would probably automatically invalidate your insurance...
Nobody's thought this through, and until they sort out the legal aspects these things are dead in the water. The lawyers always, always win.

But please - I bow out of this discussion now as I know where it will lead and this is not the right place for it! A pub with padded walls and floor and no sharp objects might be best...
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agnoraan
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Re: Driveability

Post by agnoraan »

Thanks for the all the replies and insight into the different driving styles. This car is going to be predominantly for road use, though I may try a few sprints with it. I want a car that has good road manners and is predictable in what it's going to do when pushed hard, hence my initial question as to which is the best all round performer, the coilsprung or leaf sprung chassis, bearing in mind that this is an original style chassis and not a Hawk. I don't want a car that shakes your fillings out on uneven surfaces, or becomes too tiresome to drive on long journeys. Yeah, I know it's a Cobra, I must just be getting old I guess, but I want to enjoy the driving experience and not have a car that I have to fight with :wink: .

Nige
Paul Blore
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Re: Driveability

Post by Paul Blore »

Hi Nige,

If you're building a "replica" 289 from scratch, then you might as well try to get as close as you can to an original, which would mean transverse leaf suspension. There is no reason why it shouldn't be comfortable and civilised within the scope of what's possible. Colin took his 289 to Italy in 2015 and I didn't hear any complaints from him about his car in that respect.

Paul
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Roger King
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Re: Driveability

Post by Roger King »

I presume your decision comes down to 'what do I build a replica of?' I guess the choice is leafspring 289 (known as 'slabside') or later AC 289, with coil springs and different chassis design. Both are 'original' in design terms, and I'd say neither is 'better' than the other, they're just different.

The coil sprung car feels more 'modern', and my reasons for referring to the Hawk chassis are that as far as I am aware the chassis dimensions etc. of the Hawk are similar to the later AC289, although the Hawk frame 'kicks up' towards the front whereas I don't think the AC289 does. I am the first to admit that I know a lot less about the later AC289 than I do about the earlier cars so hopefully someone else can give more complete advice.
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db replicas
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Re: Driveability

Post by db replicas »

As far as I know, the AC289 coil sprung chassis is the same as the 427, but with different engine/chassis mounts for the smaller motor.
There are differences between the 427 chassis' in that the "Street" chassis has slightly different pick up points for the rear upper structure to allow room for the underslung exhausts to pass up behind the rear bulkhead and over the axle. (I am not referring here to the GRP boot internals, but the main steel chassis structure.)
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