traction

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Jimbo
Posts: 26
Joined: Fri Feb 26, 2016 7:00 pm

traction

Post by Jimbo »

Is it the front spring hanger that is re positioned up closer to the body to improve traction from standstill if so how much closer to the body has it got to be for how much improvement ? My car is having 4 new spring hanger brackets welded on so its a good time to do this change. Ive got lowered leaf springs, uprated leaver arms dampers, rose jointed drop link, panard rod, LSD & competition half shafts to be fitted when ALL the welding is finished.
Big Daddy
Posts: 7158
Joined: Fri Jun 10, 2011 7:33 am

Re: traction

Post by Big Daddy »

A35 has high mass centre in relation to short wheelbase, resulting in significant load transfer (ie improved traction) to the rear tyres under acceleration. If wheel torque is sufficiently large, a limited slip diff will prevent spinning of the least loaded rear tyre. These factors allow Evo2 to storm off the grid at race meetings.

Unfortunately high mass centre to short wheelbase and narrow track ratios also work against you. Under braking, load transfer to the front 'axle' is increased hence further biasing F/R brake apportioning. Under cornering, load transfer to the outer tyres is increased limiting cornering force. But if high cornering force can be recovered using 'sticky' tyres, A35s are then prone to rolling over... :shock:

Longitudinal load transfer (acceleration and braking) is illustrated below:
Load_transfer.png
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Dave Clark
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Location: High Wycombe, Bucks

Re: traction

Post by Dave Clark »

Sorry Jimbo but I don,t understand the idea of "closer to the body" There is very little room to move the spring eye at all, and this would then move the axle forward. Is this what you meant ? (I don,t think so)

Raising the front spring attachment may help with traction, but will lower the car further of course.

Drag racers use a link to increase traction, Fixed to the U bolts and a link pointing downwards from the spring eye.The idea is to prevent the diff nose rising as power comes on.Leaf springs distort to allow this.

Best idea is to 5 link the axle - or, very simply, just add a traction bar(anti tramp bar) on the drivers side.
Big Daddy
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Joined: Fri Jun 10, 2011 7:33 am

Re: traction

Post by Big Daddy »

Dave Clark wrote:Raising the front spring attachment may help with traction, but will lower the car further of course.
Don't understand :? Surely lowering the car also lowers mass centre at the expense of traction :?:
Dave Clark wrote:Drag racers use a link to increase traction, Fixed to the U bolts and a link pointing downwards from the spring eye.The idea is to prevent the diff nose rising as power comes on.Leaf springs distort to allow this.
Leaf springs and drag racers ... :roll:
Dave Clark wrote:Best idea is to 5 link the axle - or, very simply, just add a traction bar(anti tramp bar) on the drivers side.
Recommend 4 longitudinal links, Watts Linkage (Panhard Rod imposes roll centre asymmetry), coil-overs, LSD and lowered mass centre. Traction is outstanding and tramp eliminated :thumbs: Even with limited wheel torque, 0-60mph in under 6 secs is easy. Could get into 3 sec bracket with more torque and 'sticky' tyres, just like RR... :mrgreen:
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Big Daddy
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Re: traction

Post by Big Daddy »

Here's how an A35 can storm off the grid. We qualified half way in the field, behind the sea of Caterhams but near front of the saloon cars... :thumbs:


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Dave Clark
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Location: High Wycombe, Bucks

Re: traction

Post by Dave Clark »

Raising the front spring mount alters whether the car will lift or squat on takeoff. Raising it promotes lift and therefore more traction.

Using wedges on the spring to axle mount in order to point the nose of the diff slightly downwards will also add to traction as the diff tries to move upwards,

Gives the universal joints a hard time though.
Big Daddy
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Joined: Fri Jun 10, 2011 7:33 am

Re: traction

Post by Big Daddy »

Reckon this exchange could get protracted, just like the good old days... :mrgreen:
Dave Clark wrote:Raising the front spring mount alters whether the car will lift or squat on takeoff. Raising it promotes lift and therefore more traction.
Load transfer to rear axle (and hence traction) is purely dependent on the mass centre / wheelbase ratio (ref diagram above). Amount of front lift or rear squat is simply a function of vertical spring rate to load. Stiffer springs mean less deflection. Anti-dive wishbone geometry has a similar effect to increased spring rates. But that isn't relevant on most A35s.

Making the rear end lift would impose an inertial effect during deflection of sprung body mass upwards, but it's very transient (<<1 sec). Also I'm intrigued how rearward load transfer can have an effect in the opposite direction (ie force downwards but deflection upwards) :?: :?: :?:
Dave Clark wrote:Using wedges on the spring to axle mount in order to point the nose of the diff slightly downwards will also add to traction as the diff tries to move upwards.
Uses driveline torque reaction to impose a vertical force, but all rather crude... :whistle:
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Dave Clark
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Re: traction

Post by Dave Clark »

You know me so well !
Big Daddy
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Re: traction

Post by Big Daddy »

Was that your last word :?: ... :mrgreen:
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Dave Clark
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Location: High Wycombe, Bucks

Re: traction

Post by Dave Clark »

Certainly not.

Although the effect may be transient it occurs at the most critical part of the launch, so may be significant,

Agree that the effect may be countered by the lowering of the mass and it,s consequent effect, but I contend that it could be worth it.

Back to Jimbo. I suspect he is not looking at extreme things like nose down diffs but may be looking at re-locating the front spring eye. From his specifications he is looking at a circuit racer response, not a drag strip special.

Be nice to hear from him on all this waffle.
Jimbo
Posts: 26
Joined: Fri Feb 26, 2016 7:00 pm

Re: traction

Post by Jimbo »

I meant as you say raising the front spring attachment the idea was to help with the first part of launch, The car is for road use but maybe the odd hill climb sorry but not into drag
Big Daddy
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Joined: Fri Jun 10, 2011 7:33 am

Re: traction

Post by Big Daddy »

Jimbo wrote:Is it the front spring hanger that is re positioned up closer to the body to improve traction from standstill if so how much closer to the body has it got to be for how much improvement ? My car is having 4 new spring hanger brackets welded on so its a good time to do this change. Ive got lowered leaf springs, uprated leaver arms dampers, rose jointed drop link, panard rod, LSD & competition half shafts to be fitted when ALL the welding is finished.
Jimbo wrote:I meant as you say raising the front spring attachment the idea was to help with the first part of launch, The car is for road use but maybe the odd hill climb sorry but not into drag
Forget relocating the front spring eyes - the effect at best is marginal and could degrade handling. Try your car with all those proposed modifications and see how well it works. Further changes may be unnecessary... :thumbs:

At all costs, avoid lowering blocks... :evil:
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Big Daddy
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Joined: Fri Jun 10, 2011 7:33 am

Re: traction

Post by Big Daddy »

Dave Clark wrote:Certainly not.
... :rol:
Dave Clark wrote:Be nice to hear from him on all this waffle.
I'm not Call Me Dave... :whistle:
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Jimbo
Posts: 26
Joined: Fri Feb 26, 2016 7:00 pm

Re: traction

Post by Jimbo »

no lowering blocks fitted just lowered springs.
Big Daddy
Posts: 7158
Joined: Fri Jun 10, 2011 7:33 am

Re: traction

Post by Big Daddy »

Jimbo wrote:no lowering blocks fitted just lowered springs.
Doing it correctly... :thumbs:

Only exception is when springs have been completely decoupled and all axle location is provided by rigid links. Otherwise lowering blocks are taboo :!:
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