Wider track for wheelbase at the front or rear??

[RCduck7]

I'm a little bit confused if the front or rear should be wider for the best cornering and stability.

I see that the front op the Exige motorsport elise is wider.
See at the bottom of this link...

http://www.sandsmuseum.com/cars/elise/experience/c...

But i also see that the rear of the GT3 concept car is very wide... But do they have races with this?? With that wheelbase??

http://www.carfolio.com/specifications/models/car/...

Can someone with technical and racing experience tell me what these differences do and what is best??

[Sam_68]

Do bear in mind that if a car has wider tyres at the back, and the measurement across the outside faces of the wheels is the same front and back (which is often the case purely for packaging reasons), then the track will be narrower at the back, since it's measured from centreline of wheel to centreline of wheel.

Having said which, to answer you question... and sorry, but this is a bit complicated (I'll keep it in layman's terms, though, so apologies to Scuffers and other experts for the generalisations):

• Track affects weight transfer when cornering. Basically the wider the track the less weight will be transferred across the car from one side to another.

• TOTAL weight transfer is a function of the height of centre of gravity, cornering force and average track.

• The wider end of the car transfers a smaller share of this total, though, so in effect, the car 'leans' diagonally onto the end with the narrower track.

• More load on a tyre generates a higher slip angle, therefore, all other things being equal, wider track at the rear will make a car lean on its outside front tyre and cause understeer, whereas wider track at the front will make it lean on its outside rear tyre, which will cause oversteer.

...so track width is one tool that the chassis engineer can use to manage understeer/oversteer balance.

But there are lots of other tools/factors than can be used (tyre width, weight distribution, different front and rear spring/anti-roll bar stiffnesses to give different roll resistances, etc.), and it's a matter of juggling all these factors (many of which have other side-effects) to give the overall compromise you want.

Most designers strive for slight understeer, therefore if all other factors were equal and perfectly balanced you'd want slightly wider track at the rear. But other factors never are equal and perfactly balanced, so the short answer to whether front or rear track should be wider is 'it depends'!

(edited for crap typing last night after a bottle of wine...)

Edited by Sam_68 on Saturday 14th March 08:53

[Scuffers]

good stuff...

only thing I would add is that going wider is often used to tackle a high COG.

[RCduck7]

Sam_68 said:

Do bear in mind that if a car has wider tyres at the back, and the measurement across the outside faces of the wheels is the same front and back (which is often the case purely for packaging reasons), then the track will be narrower at the back, since it's measured from centreline of wheel to centreline of wheel.

Having said which, to answer you question... and sorry, but this is a bit complicated (I'll keep it in layman's terms, though, so apologies to Scuffers and other experts for the generalisations):

• Track affects weight transfer when cornering. Basically the wider the track the less weight will be transferred across the car from one side to another.

• TOTAL weight transfer is a function of the height of centre of gravity, cornering force and average track.

• The wider end of the car transfers a smaller share of this total, though, so in effect, the car 'leans' diagonally onto the end with the narrower track.

• More load on a tyre generates a higher slip angle, therefore, all other things being equal, wider track at the rear will make a car lean on its outside front tyre and cause understeer, whereas wider track at the front will make it lean on its outside rear tyre, which will cause oversteer.

...so track width is one tool that the chassis engineer can use to manage understeer/oversteer balance.

But there are lots of other tools/factors than can be used (tyre width, weight distribution, different front and rear spring/anti-roll bar stiffnesses to give different roll resistances, etc.), and it's a matter of juggling all these factors (many of which have other side-effects) to give the overall compromise you want.

Most designers strive for slight understeer, therefore if all other factors were equal and perfectly balanced you'd want slightly wider track at the rear. But other factors never are equal and perfactly balanced, so the short answer to whether front or rear track should be wider is 'it depends'!

(edited for crap typing last night after a bottle of wine...)

Edited by Sam_68 on Saturday 14th March 08:53

Thanks for your very helpful reply.
What you just mentioned confirms what i felt when i drove the car with the wider track at the rear that i now have... More understeer.
Time to get some wider spacers at the front of my car to compensate this.

Cheers

Edited by RCduck7 on Saturday 14th March 20:37

[Scuffers]

RCduck7 said:

Thanks for your very helpful reply.
What you just mentioned confirms what i felt when i drove the car with the wider track at the rear that i now have... More understeer.
Time to get some wider spacers at the front of my car to compensate this.

Cheers

that's not the best/simplest solution - it's going to cause other issues too..

I would suggest running a stiffer ARB would have the desired effect..

[RCduck7]

Scuffers said:

RCduck7 said:

Thanks for your very helpful reply.
What you just mentioned confirms what i felt when i drove the car with the wider track at the rear that i now have... More understeer.
Time to get some wider spacers at the front of my car to compensate this.

Cheers

that's not the best/simplest solution - it's going to cause other issues too..

I would suggest running a stiffer ARB would have the desired effect..

What is COG or ARB??

Sorry, my English isn't that good to know these shortened words

[Thumbs]

COG = Centre Of Gravity
ARB = Anti Roll Bar

Thumbs