Grip - what influences grip

[sbrats]

Very open question and not a simple answer - could someone outline what influences overall mechanical grip in suspension design and vehicle design for that matter. If you can give give some detail that would be helpful. I am just trying to understand some sports cars seem to do better than others.


Thank you

Steve

 

[patprimmer]

Keeping the tyre tread flat on the road under all circumstances.

A rigid body structure.

Regards

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[TestDriver]

And, adding to Pat's comment;

Keeping the tires (assuming same size tires) as evenly loaded as possible.

Cheers.

Ramon

 

[cibachrome]

And tires with wheels having structure and compound(s) which can sustain high coefficients of friction for the racing lap sequences. Not all tires have the same settings based on mileage, noise, mass, fuel economy, electrical conductivity, road feel, load sensitivity, speed rating, durability, cost, track granularity, wet traction, applied horsepower, and braking capacity requirements.

These are design parameters that go into the tire's development recipe.

You might be surprized at the range of performance (grip) available for tires in the same exact size, even in the same brand and running the same pressure but different formulations in just their construction details: wire angles, tread depth, rubber to carbon ratio, tread depth, breaker angles, sidewall parts, belt materials and silica content and compound matrix nano partical size.

Watch for the new carbon fibre tires that have started to appear in OEM and aftemarket fitments. They tend to push the boundaries for many of the listed properties.

 

[sbrats]

I recently was watching some footage of the Caparo T1 and it's lack of grip at low speed (tire temp a factor I would suspect) but the faster it would go the more the aero come into play - basically a road going f3 car - I was wondering - since it was designed by the same bunch as the road going Mclaren you would think that it has grip even as low speed - but it appeared to be quite a handful - back end stepping out, understeer

 

[hemipanter]

A suspension deigned for heavy downforce may show slightley
less grip at non aero influence, low speed.
Goran Malmberg

 

[sbrats]

And what would the difference be between a suspension designed for heavy downforce and one not?
In this case is it more about the tire contact not being flat at low downforce (because of the geometry at that point of the suspension travel) and tires that need downforce to get the heat in (hard compound) that otherwise wouldn't survive at high loads

 

[hemipanter]

sbrats, myself I use longer and more parallell A-arms, less camber compensation, along with much firmer wheelrate for heavy downforce cars.
Goran Malmberg

 

[murpia]

A suspension designed for downforce, but without any kind of heave-only 3rd element, will need higher wheelrates. This typically means greater load fluctuations as the tyre is excited by the road, and greater stiffness of the chassis in warp. Both hurt grip on anything except the smoothest and flattest of road surfaces.

Regards, Ian

 

[sbrats]

Can you describe a 3rd element or point to a illustration or ref material

Thank you

S

 

[murpia]

It's the opposite of an anti-roll bar, a mechanism that only deflects when both wheels of an axle move in the same direction. It makes the car stiffer in heave without affecting the roll.

Most high downforce single seaters and LMP cars have them.

Regards, Ian

 

[SusTestEng]

Proper Compliance
Body and Suspension link rigidity
Tire construction

These are the biggest 3 I deal with. Yes, suspension geometry also play a big factor, but as a development engineer, this is what I deal with on a daily basis. You would be surprised at the gain in grip and response by stiffening the chassis by only a few percentage points. I can notice as little as 1-2% changes, even in local areas. Tire construction is also a huge area to gain grip and response. I keep saying response,because sometimes people confuse the two.
Having all your compliances work together greatly affects not only the ultimate grip, but also the grip decay. As the case with the Caparo, I would bet that car has very little compliance, so the ultimate grip is very high, but the grip decay is very sudden. This makes the vehicle very hard to control at/near the linit. Low compliance vehicles tend to go from lots of grip, straight to over or under steer conditions with very little warning. Basically the difference between a go kart and a BMW sedan. The BMW has tons of compliance, but the kart has very little.

 

[hemipanter]

SusTestEng,
"You would be surprised at the gain in grip and response by stiffening the chassis by only a few percentage points."
Are you talking about torsional rigidity of the chassis?
This is interesting since I have been testing different chassis stiffnes over a fairly wide range of numbers 5000-20000 Nm/dgr using slicks. Not to sientific but anyway, driving tests while cornering over bumps in the track and regular skidpad.
Is it that the difference might show in "steps" as you notice a few percentage?
Also, you say "local areas". I understand Chassis stiffness is measured as a sum over the measuring points, no matter where in between those spot the chassis flex.

I would be happy if you could expand that chassis issue a little.
Regards
Goran Malmberg