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Old 23 Oct 2018, 20:24 (Ref:3858693)   #1
Overlap777
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Pitch Optimisation - yes or no

Firstly hello! I was drawn here by an informed discussion.


https://tentenths.com/forum/showthread.php?t=85269


Currently, I am helping someone prepare a vehicle in Historics. What struct me was how many cars (Front Engine RWD) seemed to be running that age-old combination of very stiff front springs and soft rear, therefore abandoning pitch optimisation in forward travel.



I personally don't like it - I think wheel frequency ought to suit the car and the purpose and then weight transfer should be managed on the anti-roll bar. However, I'd like to see what others think. Clearly if someone is winning with a setup that is "wrong", it's not necessarily wrong.
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Old 24 Oct 2018, 08:54 (Ref:3858796)   #2
zefarelly
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My post was 12 years ago . . . . . I haven't changed my car in 3 years, it runs a 24mm ARB, 500 lb front, and the same rear leaf springs . . . . weight distribution is 55/45 . . . feels fine to me. It's still a mk1 Cortina.

If its right or wrong, I don't know . . . . you'd have to talk to those who use a wind tunnel and a 7 post shaker rig . . . there's plenty of them out there, or are you just fishing ?
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Old 24 Oct 2018, 09:30 (Ref:3858800)   #3
Robyn Slater
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I've always thought the hard front/soft rear set-up was the prefered option when using CR65 crossply ditchfinders. I found softening up the rear of the anglebox worked for me. Too stiff and the rear would break out on exit acceleration.
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Old 24 Oct 2018, 09:51 (Ref:3858802)   #4
Gerard C
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Overlap, may be you could tell what car you prepare assuming its use is track only and what series you will enter (pre '66 ou Group1, 2…). If you use a Mac Pherson, the ARB has several uses. In any regulation, the ARB diameter is free but must not be hollow design. And you're not allowed to move any suspension attachement, chassis or cross member. You can also take in count the ride height, front and rear balance, and if you have a live axle is it cranked or not?
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Old 24 Oct 2018, 11:04 (Ref:3858818)   #5
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Originally Posted by zefarelly View Post
My post was 12 years ago . . . . . I haven't changed my car in 3 years, it runs a 24mm ARB, 500 lb front, and the same rear leaf springs . . . . weight distribution is 55/45 . . . feels fine to me. It's still a mk1 Cortina.

On a not quite FIA Cortina with 52.5/47.5 F/R distribution I ran 600lb front coils and single rear leaf springs of indeterminable poundage (I doubt no more than around 225/250 lbs). Front ARB was 1 inch (25.4mm for you youngsters). Handling was great though it tended to lift inside front wheel a tad - particularly so at Silverstone's Brooklands corner.
Also played around with an FIA Cortina which didn't handle anything like as well. It had around the same as your weight distribution of 55/45 with a 15/16th inch ARB (23.8mm). Front springs were 600 lbs and multi leaf rears were unknown poundage - probably around 250 lbs. This car sat higher than the other car by around threequarters of an inch at the front and just over an inch at the rear and we were in a 'development' stage changing one thing at a time when the car was destroyed so we never got to know just how well it might have handled.
I agree with Robyn that the rear needs to be fairly soft on touring cars.
To answer the OP's point pitch was never a major problem with either car.
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Old 24 Oct 2018, 11:23 (Ref:3858823)   #6
Gerard C
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Interesting numbers and experience. During unofficial practice you can also use what modern technology offers, like a box on the windshield or dash. To my knowledge, illegal use during Q and race in Historics. But once you're happy with your settings and have taken note of the influence of any change…
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Old 24 Oct 2018, 12:33 (Ref:3858846)   #7
Geraint Owen
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A question on the original post.......What is pitch optimisation?

If you are concerned with the amount of "dive" under braking, this is not purely a function of the spring rates, it is a geometrical issue.

Changes to spring rates front and rear will have a far greater effect on the cornering behavior than they will the pitching effects. Further to this, any ARB will have no effect on the pitching of the car in acceleration or braking
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Old 25 Oct 2018, 08:57 (Ref:3859044)   #8
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This may not help but i recall seeing the Bastos Rover 'porpoising' or pitching around Redgate at Donington earlier this year.
It didn't seem like it was doing car or driver much good...
To me it suggested the car was too stiff at the front?
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Old 25 Oct 2018, 10:39 (Ref:3859063)   #9
Gerard C
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Interesting chunterer. You collected videos from the Tricentrol RAC '81 year, it took you over ten years if my memory serves. Thanks again for that.
It seems the front running Capris had a higher rear end ride height in period than they have nowadays. May be Overlap can tell more about car, series and tires?
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Old 25 Oct 2018, 18:54 (Ref:3859146)   #10
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Originally Posted by chunterer View Post
This may not help but i recall seeing the Bastos Rover 'porpoising' or pitching around Redgate at Donington earlier this year.
It didn't seem like it was doing car or driver much good...
To me it suggested the car was too stiff at the front?
I met someone years ago who was involved with the racing Rovers and he said the rear axle's were rather special e.g. they weren't actually straight?
If that was the case presumably using a standard axle wouldn't help the handling?
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Old 26 Oct 2018, 19:12 (Ref:3859327)   #11
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They were cranked. But not too much, otherwise you ran the bearings. As were the Capris too.
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