17 replies to this topic

[shaun979]

Why do Supercar V8s along with other touring cars run so much negative camber? Aren't they fairly stiff and not subject to lots of roll? Surely it isn't all just tire deformation? Sorry I don't know much about those cars.

Does anyone have some front angle photos of a Supercar V8 at high speed in a fast sweeper? I would like to see how their tires look. Thanks

[Wolf]

Probably, like F1, they don't have much of a suspension (aka. skateboards), so their 'static' camber could be optimized for cornering (since they don't roll much, or go up/down much, meaning not much camber gain- static camber is what they'll have in corners). That's just my uneducated™ guess...

[imaginesix]

Still seems to have an excessive amount of camber even under hard cornering. Maybe it is optimal for that tire, but if it isn't it would likely be because of allowable suspension changes in the rulebook. Anybody have insight on the rules?

[shaun979]

Originally posted by Wolf
Probably, like F1, they don't have much of a suspension (aka. skateboards), so their 'static' camber could be optimized for cornering (since they don't roll much, or go up/down much, meaning not much camber gain- static camber is what they'll have in corners). That's just my uneducated™ guess...

If a car is without suspension and completely rigid (no suspension travel, no roll, no camber gain) and there is a large amount of static negative camber, then isn't the tire never going to be flat on the ground unless the car actually lifts on one side. Low travel, stiff suspension cars are close to this aren't they? So likewise, what are they doing with the tires?

Imaginesix, thanks for the photo, actually the outside tires in that photo look pretty flat on the ground although the rim still looks way cambered. Maybe it is a lot of tire deformation along with some degree of roll and lack of camber gain that requires that much static camber? Maybe like you say it is what the tire likes (less patch area but more heat in that smaller area)? But I wouldn't think this would be so on a fairly heavy fairly powerful road race car. The rims also look a lot wider than the tires.

Anyone?

[McGuire]

The negative camber is run as a handling aid, in two ways: to generate camber thrust and camber torque.

Camber thrust works just as it does on a motorcycle, to help the vehicle turn. You would think that with both front tires at the same negative camber they would cancel each other out, but since the outer tire is much more highly loaded there is net thrust into the direction of the turn. Several degrees of negative camber in the front can provide a nice sharp turn-in response.

Camber torque works much like slip angle or toe to use the tire body's self aligning torque properties to corkscrew the footprint down into the surface as the tire rolls over the pavement. The wheel is turning true at the hub, but at the tread surface there is alignment friction. This is one of the ways a tire can have a friction coefficient greater than one -- the rubber grain is forced into a mechanical lock with the imperfections in the pavement. Just as a tire has a slip angle curve it also has a camber curve, and the grip will be somewhat higher on the negative side. Camber torque works on the front or rear of the car, so you will see some negative camber used on the rear tires too.

[shaun979]

Originally posted by McGuire
[B]The negative camber is run as a handling aid, in two ways: to generate camber thrust and camber torque.

Camber thrust works just as it does on a motorcycle, to help the vehicle turn. You would think that with both front tires at the same negative camber they would cancel each other out, but since the outer tire is much more highly loaded there is net thrust into the direction of the turn. Several degrees of negative camber in the front can provide a nice sharp turn-in response.

Thanks, then is it correct to say that the limit to how much one relies on camber thrust for sharp turn-in response is limited by how much the contact patch is compromised mid corner?

The racecars we see that do not have much static negative camber at all... what makes them not have to rely on it, and what is it about Supercar V8s and some other touring cars that makes them pick the camber route?

Camber torque works much like slip angle or toe to use the tire body's self aligning torque properties to corkscrew the footprint down into the surface as the tire rolls over the pavement. The wheel is turning true at the hub, but at the tread surface there is alignment friction. This is one of the ways a tire can have a friction coefficient greater than one -- the rubber grain is forced into a mechanical lock with the imperfections in the pavement. Just as a tire has a slip angle curve it also has a camber curve, and the grip will be somewhat higher on the negative side. Camber torque works on the front or rear of the car, so you will see some negative camber used on the rear tires too.

Ah, thanks.

[rhm]

Originally posted by imaginesix
Still seems to have an excessive amount of camber even under hard cornering. Maybe it is optimal for that tire, but if it isn't it would likely be because of allowable suspension changes in the rulebook. Anybody have insight on the rules?

That photo is a bit misleading. The bodywork is tapered towards the bottom of the car so both the front and rear wheels seem to have more negative camber than normal. The fronts have more than the rears, but then that's what you'd expect.

[Boro]

i'll do you one better.

here's a wheel cam of a v8 supercar at bathurst

that poor tire

[Lukin]

That tyre shot from under the 888 car was scary. One of the big things with new drivers at Bathurst is the case moving under load but no one had any real idea till we saw that. The drivers wouldn't watch it and I don't blame them.

Supercars do run a lot of camber compared to most other cars, but they aren't stiff in terms of roll stiffness that's for sure. There is a lot of wheel travel.

That pic isn't a V8 Supertaxi, it's a NZ V8. Less powerful, much closer to production than a V8. Our Car.

[shaun979]

Ok this is good, having both the commentator and Jason mention how much the tire deforms under load, something I originally considered.

Jason, when you say they aren't stiff in roll, what is very rough roll resistance in kg/cm, lb/in or however you measure it in Australia? How much wheel travel in total do you roughly have at the front and rear? They always looked like they sat almost touching the ground which is why I assumed they were low travel high roll stiffness cars. Is there a reason the tire suppliers don't design a stiffer tire ? What are typical slip angles in a series like that combination of tire and tire load? TIA

The commentator mentions peak tire loads of around 1020 kg (~ 2250 lb) . Indycars in medium aero trim at some courses run ~ 2500 lb tire loads and that's without bumps.

[Catalina Park]

The neat thing on the Aussie V8s is the camber on the rear with a live axle.

[zac510]

Originally posted by Boro
i'll do you one better.

here's a wheel cam of a v8 supercar at bathurst

that poor tire

Amazing! Brilliant camera shot.

[zac510]

Originally posted by Lukin
That tyre shot from under the 888 car was scary. One of the big things with new drivers at Bathurst is the case moving under load but no one had any real idea till we saw that. The drivers wouldn't watch it and I don't blame them.

Why do you say that - is tyre load significantly different at Bathurst?
Or is it the fact that part-time racers come in to race are not familiar with the tyre?
Do you have any figures for the tyre slip angle you can share?

[shaun979]

So many unanswered questions

Come on guys, you know we know you know

[Lukin]

I can't answer the questions specifically sorry.

To compare Bathurst to other tracks (in Australia at least) Bathurst is a more undulating (higher vertical load due to gravity at the bottom of the hills) and quicker (more downforce) than most tracks so yeah, you would expect more vertical load overall than most tracks.

[zac510]

Thanks Lukin. I suppose the control tyre reg precludes Dunlop from making a more suitable tyre for Bathurst

[shaun979]

Originally posted by Lukin
I can't answer the questions specifically sorry.

No problem, I understand. Had to try

====

Now separately, I recall some old BTCC cars running lots of negative camber on very low profile tires. In their case, I wonder what it was. They didn't look like they were softly sprung or had much wheel travel or roll at all - hopping over curbs, low ground clearance and all that..

Anyone know why?

[indigoid]

Originally posted by Lukin
To compare Bathurst to other tracks (in Australia at least) Bathurst is a more undulating (higher vertical load due to gravity at the bottom of the hills) and quicker (more downforce) than most tracks so yeah, you would expect more vertical load overall than most tracks.

I would like to see similar footage for a lap of Oran Park if they still run the V8s there. I think you'd see similar loadings through the final sequence of turns. I do so love Oran. Not a boring, technical track like Wakefield Park :-)