Jump to content

car weight and balance


aaronsti

Recommended Posts

so in a porsche 911 the rear has good traction because of all the weight at the back. and tires have more grip with more vertical load but it is non linear. so how come a car that is front heavy doesnt have excellent front end grip and instead pushes/understeers in corners?

Link to comment
Share on other sites

There are tons of factors that affect it. If you look at contact patch diagrams in your DE1 class book it will help to give you a visual of what is going on. Basically in the situation you're describing the (say your taking a right hander) front left tire gets too much of the weight and the front right and rear left tires don't have enough grip to rotate the car through the corner. You can lessen the affect through your braking prior to the corner and throttle inputs mid-corner and exit.

 

I take it you have an STi, judging by your forum name? Each car model is unique in how it handles stock and modified. If you're attempting to remedy your understeer I would find someone with the same car or engine/driveline layout to help you more specifically.

Link to comment
Share on other sites

The other thing to note is the "good traction" that occurs with a rear engine layout is more of when the car is in a straight line or close to it. Think 'track out and down the straight'. Up to apex, the rear end weight can hamper you if you are not accustomed to the ease of rotation allowed by swinging the weight around your "polar moment". Both layouts have their advantages/disadvantages.

 

BTW, I am not an automotive engineer. But I did sleep in my own bed last night and have been fortunate to drive quite a few different cars. I am certain someone on here can give you a more scientific and definitive response. Visualize what Reaper posted and you can get the idea.

Link to comment
Share on other sites

so in a porsche 911 the rear has good traction because of all the weight at the back. and tires have more grip with more vertical load but it is non linear.

 

Porsche has been perfecting a bad idea since Noah came off the ark

Link to comment
Share on other sites

so in a porsche 911 the rear has good traction because of all the weight at the back. and tires have more grip with more vertical load but it is non linear.

 

Porsche has been perfecting a bad idea since Noah came off the ark

 

true, though not all P-cars are bad (Cayman, Carrerra GT have the engine in the right spot )

 

to the OP - you nailed it with the non-linearity idea. Once you "overload" the tire it's going to slip. Very easy to overload a front tire with a front-heavy car.

Link to comment
Share on other sites

From what I understand, the more weight or mass moving at a certain velocity, the more momentum it object has:

 

kg * m/s = momentum

 

The more momentum that certain object has, the more force is needed to change the direction of the momentum, i.e. turning the car. True, front end heavy cars have more mechanical downforce applying a load on the tires, thus adding certain grip (only if the tire is right of course), but the tire is also having to work more to change momentum of the car.

 

I think for the most part, most tires under mechanical load might grip better moving in a straight line, like acceleration, but will lose some grip when cornering. Weight reduction of course helps with corning grip, while aerodynamic downforce puts load back on the tires without having to deal with momentum forces.

Link to comment
Share on other sites

  • 4 weeks later...

Well another way to think about it, so that a lot of cars off the production line are setup for understeer because its "safer." Second, as mentioned before, its easy to overload the front tires of a FWD car because of the extra weight and also because the driver might try and give power to early.

 

I think most of the issue is because of how the manufacturer tunes the suspension. Most of the "sporty" FWD cars aren't very pushy, and I have driven some Neons that are super oversteery with some simple suspension modifications.

Link to comment
Share on other sites

  • 1 month later...
...some Neons that are super oversteery with some simple suspension modifications.

This is very true. My cousin had a Neon that was easy to oversteer. But geometry is the main element here. As mentioned before, manufacturers prefer that cars understeer rather than oversteer for safety reasons. My car, for example (VW GTi) will experience both because even though it's a FWD it also has a solid rear axle (beam) which allows a driver to rotate the rear more easily.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...