HP and chassis design - limits

[sbrats]

Purely a theory question...
At what point can one say that a vehicle will become un-drivable when dialing in additional HP and torque. What I mean is - is it predictable or calculable for a given wheelbase/tract width ratio and tire size to roughly estimate that above a given HP/torque there is a diminishing return in lap times.
Extending this question - can you over tire a car for a given HP/Torque - and how to calculate this estimate and at what point would a front-wheel-drive vehicle have a problem putting the power down when the front tires are loaded as much as they are already (vs. a 4WD or RWD design)

Thank u

S

 

[hemipanter]

You ask about Hp or Tq. Well, Tq number does not tell anything about how fast the car may become. There has to be an rpm number involved to specify work and then we talk Hp.
Ok, if Tq is to high an axle may brake and make the car undrivable.

Overpower, not really. If we look at it the other way around, will to efficent brakes create slower laptimes?

Overtire, I give this Q an no-answer, within sensible limits. Althrougt there IS situations where less rubber may be better.

Shortcut answer.
Goran

 

[GregLocock]

You can use a lap time simulator such as Bosch LapSim to estimate the answer. More power will always make you faster, dircetly because of improved acceleration, and indirectly because it allows you to carry more wing.

The maximum acceleration that a FWD can manage is fairly easy to estimate approximately, given cg height, wheelbase, and spring rates, and tire characteristics. However, changing the axle ratio with a more powerful engine will allow ou to benefit from the extra power, even if you are wheelslip limited at low speeds.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Thecardoc]

Having gotten to play on the vehicle dynamics pad a few times at BeaveRun, dosen't make me an expert at this but I do have an opinion. More HP/Torque is only going to increase your lap times, "IF" you can use it to increase traction (downforce), and also improve braking efficiency (cooling). All the "go" in the world won't help if you don't have the "whoa" to balance it. So for every 20 HP up, find a way to increase brake heat dissipation 10% and ground effect 5-10%.

 

[bikesrfast]

look at history for answers as well.

The Mazda MX6 turbo road car was about as much as is practicle for a street front drive car, look up test reports for its specs and drive reports.

English 2 litre touring racing cars had a formula the gave rear drive cars 100kgs extra and 4 wheel drive 200kgs extra (from memory)to make them equal in performance. The front drive cars were a handful with near 300hp even with F1 teams helping with the development.

Any car will immediately become faster but possibly more difficult to drive with increases in HP if the obvious - brakes, suspension, body ridgidity - are'nt kept in check.

 

[patprimmer]

If you loose nothing else in the process more power will reduce lap times, as even though you might have incidences where you are limited by traction, there will sometimes be situations where you can still apply full throttle.

You only need better brakes if you are going faster, so even without better brakes you will still be going faster when you have to apply the brakes.

The only truly overpowered situation if if there is no point on the track where your chassis will accept full throttle.

Re optimum tyre size, that is try it and test type tuning as there are variables and compromises.

Bigger tyres give more powerful cornering and better acceleration at the speeds that traction is the limiting factor, but smaller tyres give better aero and lower inertia or polar moment. The balance or break even point will be different for every track and car and driver and weather.

Regards

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