Spring rates and body roll ?? - Alfa Romeo Bulletin Board & Forums
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post #1 of 63 (permalink) Old 10-09-2015, 10:55 AM Thread Starter
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Spring rates and body roll ??

When you look at old racing photos of the GTA's their body roll is enormous and inside wheels are often in the air. When you see these cars today they are usually cornering flat in the modern boring way.

Which is faster?

Are we just seeing a lack of serious commitment (fair enough) with todays drivers compared to when it actually mattered back in their real racing days?
Pete

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post #2 of 63 (permalink) Old 10-09-2015, 07:16 PM
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Body roll

"Back in the day" the cars were not nearly as fast as they are today................
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post #3 of 63 (permalink) Old 10-09-2015, 07:29 PM
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Tire technolgy at work

Flat is definitely faster.

What you're most likely seeing now is the benefits of 40 years of tire technology. Those GTA's in the day probably ran on bias ply rubber.

One of the problem with vintage racing today, is that the incredible stickyness of modern radial tires, flexes the comparatively floopy unibody of older cars.

One of the reasons why newer cars are so heavy; is that they have incredibly stiff unibodies to match the incredible grip of today's radials.

Just my two cents
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post #4 of 63 (permalink) Old 10-10-2015, 12:32 PM
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The answer to your question is strictly technical and my English is poor enough to assure me the possibility of correct explanation of the problem. Basically, the phenomena, of rising the front inner wheel in fast curves with GTA, was connected to cars RC that caused (after the introduction of sliding block) the rear live axle to remain relatively parallel to the road and assure the contact of both tires to the surface. (Before the sliding block, the first series GTA, used to rise the inner rear wheel while cornering). This was necessary to guarantee the whole traction power to be downloaded to the road surface, but chassis was exposed to strong bending effect that caused the lifting of the inner front wheel, and the bigger camber angle was adopted (by adding risers in the front suspension) to preserve the perpendicularity of the wheel in cornering. Strange enough, even on three wheels, GTA cornered faster than its direct rivals did and that was not a serious problem during competitions. Then, with better spring system, with better multi stage bumpers, with better anti roll bars and mainly with much better tires that effect almost disappeared. That is why they seems flat in cornering today. The fact of better driving in the past is relative, and I think that the excellent pilots are still available for any kind of racing. I hope that my explanation contains some sense.
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post #5 of 63 (permalink) Old 10-10-2015, 01:31 PM
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Flat is definitely faster.

What you're most likely seeing now is the benefits of 40 years of tire technology. Those GTA's in the day probably ran on bias ply rubber.

One of the problem with vintage racing today, is that the incredible stickyness of modern radial tires, flexes the comparatively floopy unibody of older cars.

One of the reasons why newer cars are so heavy; is that they have incredibly stiff unibodies to match the incredible grip of today's radials.

Just my two cents
I agree, the tire technology has improved immensely, but as far as I know, most vintage organizations still require bias ply tires. They are wider, and depending on the organization can have an aspect ratio as low as 50.

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post #6 of 63 (permalink) Old 10-12-2015, 04:07 AM
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Howdy PSK.

Pretty simple... Everyone use much stiffer springs now for the modern tire compounds.

In the past soft springs use in the rears for traction combine with stiffer fronts will make you look like a hero with one the front wheel suspended high off the ground as the rear squats excessively under full power.

Not just a 105 phenomenon.... Many cars of the period did the same. I must say the alfa's were gloriously higher than most !

Last edited by davbert; 10-13-2015 at 06:38 PM.
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post #7 of 63 (permalink) Old 10-12-2015, 09:45 AM Thread Starter
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In the old days with such soft rear springs, would they not have ended up on the bump stops and therefore neutering the soft spring rate traction?

I've always understood that you should set your spring rates as soft as possible but ensuring you keep off the bump stops.
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post #8 of 63 (permalink) Old 10-13-2015, 09:31 AM
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We're using quite soft springs in U2TC racing here in Europe because we have to run old style tyres. You can see that things get quite exciting on some occasions-

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post #9 of 63 (permalink) Old 10-13-2015, 09:54 AM
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In the old days with such soft rear springs, would they not have ended up on the bump stops and therefore neutering the soft spring rate traction?

I've always understood that you should set your spring rates as soft as possible but ensuring you keep off the bump stops.
Pete
My racing mentor's instruction was to make sure the springs were soft enough to have the underside of the car touch the track once per circuit (and only once). That compliance allowed maximum traction for acceleration.

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post #10 of 63 (permalink) Old 10-13-2015, 06:37 PM
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In the old days with such soft rear springs, would they not have ended up on the bump stops and therefore neutering the soft spring rate traction?

I've always understood that you should set your spring rates as soft as possible but ensuring you keep off the bump stops.
Pete
We often forget today that the cars ran with pretty high ground clearance with long suspension travel compared to the slammed cars we see today. Look at the period pics in the late 60's and early 70's. Even a full blown lemans racer like the 917 looks like they can clear a speed bump at the shopping mall with ease.

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post #11 of 63 (permalink) Old 10-13-2015, 09:48 PM
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Are we just seeing a lack of serious commitment (fair enough) with todays drivers compared to when it actually mattered back in their real racing days?
Pete
Lack of comittment? Seriously?
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post #12 of 63 (permalink) Old 10-13-2015, 09:50 PM
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What? We can't link to youtube videos anymore? Nevermind, fixed it.

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post #13 of 63 (permalink) Old 11-14-2015, 05:21 AM
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spring rates

Off topic:
Thank you for posting this link to Goodwood, every one will see drivers quality today!!!! This race shows exact the situation of 1966 touring car events: mainly GTA better cornering and topspeed as Cortina, his Lotus engines acceleration is better , has more horsepower due modern engine, specially combustion chamber. Both cars are winners in the right hands, and an GTA never wins in england , so a Cortina never in Italy..........for me , the real heros are Christensen on Ford Fairlane Thunderbolt , starting from 29.place and going like a hot knife through the rest and the performance of Nick Swift in his little Mini !!!!! I just wonder , that the drum brakes of the Thunderbolt hold the whole race??? perhaps illegal changing to discs like the Galaxies from sweden?

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post #14 of 63 (permalink) Old 11-16-2015, 11:57 AM
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I wouldn't look to Goodwood for rigorous enforcement of FIA Appendix K regulations to be honest. There was very little that was legal about that Ford by all accounts but Goodwood allows all sorts of rule bending because the event is all about the show. There's a Giulietta that races there with glass fibre panels and a watts linked rear end and I supplied a flywheel and clutch kit to someone who was fitting a 2000 engine to his Sprint GT a few years ago.

In reality, that Mini should have been nowhere near Alex unless it was wet so he was either off form or (I suspect more likely) the Mini had an oversized engine dropped in as it was running in "Goodwood spec". The Great British Public do like a giant killing performance...

GTAs do win in England when the rules are being enforced properly and Alex is a front runner then, Alfaholics Victorious at Donington Historic Festival 2015 The two GTAs romped away with this one and we're usually ahead of the Cortinas.


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post #15 of 63 (permalink) Old 11-25-2015, 03:03 PM
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Isn't the following true....GTA knuckle risers lower the RC on front suspension, and as the car sits high up the lower RC and relative high center of gravity, cause the car to roll and press hard on the springs. Also the sliding block lower RC, and will therefore make the car push much harder on the springs, also on the front. Hence the car will lift the inner wheel on the front.

Spring rates are defined by RC and CG. Ideally you want to as low as possible on the spring rate, hence you want to raise the RC a bit and lower the car a bit, so both RC and CG come closer together which will allow for using lower springrate, without more roll.
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