M758

No you are right. Simply just think about brakes. Heavy car vs light car using same brakes and tires. Which will stop faster? Also think of a car towing a trailer. Which stops faster.

Light car right? It all as to do with energy. It takes more energy to stop a heavy object. That energy needs to go somewhere.

ltc

My manager has a new Elise. It's a neat little car with very good road manners and handling. Fun to drive.

That having been said, it is not a dedicated track car. It could be made into a dedicated track car, as could many other cars mentioned on this thread.

A dedicated track car should not be street legal. Rollcage, fire supression system, racing shells with side head protection, driver side net, window net, minimal glass, 6-7 point harness, no airbags. It will also likely be lacking driver aids like PSM, etc.

A dedicated track car will likely end up looking like/being a:
Factory delivered production based race car (Cup car, as mentioned)
Factory delivered prototype/spyder based race car.

Just my 2 cents. We now return you to your normally scheduled programming.....

BrandonH

I second the factory racecar proposal. Fully developed, especially in the safety department, easy parts/support, best resale value. My next choice, which someone else mentioned too, would be a really well developed stock class racecar with full safety equipment etc. It is hard to beat a 911 in this respect: surely no other car on the planet has been subject to as much track/racing development. There were a number of front running G cars for sale this spring that were bargains at $30K...

Sanjeevan

Brakes and tires are NOT the only variables...a few others that come to mind, rear engine with rear weight bias will stop faster, stiffer dampers should help stop quicker I think, etc., .....It's true that a lighter car will stop quicker than a heavier car, if all other variables including the chassis are the same,...only two identical cars can be that way, or only in computer simulations...

As a general rule I will never say all light cars are safer than all other heavier cars...simply not true.

EDIT: I may be wrong, the only reason I am voicing my opinion is to LEARN...

ColorChange

Ughh!!!! I WAS WRONG!!!! A LIGHTER CAR DOES NOT STOP NOTABLY QUICKER THAN A HEAVIER CAR

I know this doesn't make intuitive sense but it's true. Very simply, the heavier car pushes down on the tires and achieves more stopping force to offset the additional weight. This doesn't work at rediculous extremes, but it is roughly correct.

Here is a nice link.
http://hyperphysics.phy-astr.gsu.edu/hbase/crstp.html

So, no more Elise. Ughhhh!!!! I hate making such big errors!

Sanjeevan

WOW! stopping distance is totally independent of the weight, I never knew that, thanks for the link...a good trivia question, now that I know the answer for it ...elise may be out, but the hunt for a safer track car is still on, Right ? (surely you are not going to rip you TT, to install a cage)

ltc

https://rennlist.com/forums/964-forum/209753-excellent-article-in-pano-this-month-braking-systems.html

macnewma

Here is another explanation of the relationship between stopping distance and coefficient of friction:

http://www.msgroup.org/TIP125.html

Basically, if you want to stop faster, get stickier tires so long as your brakes are powerful enough to lock up your current tires.

theedge

So why no more Elise? Sure a heavy car and a light car can be made to brake the same... But the heavier car will need bigger pads, rotors, bigger calipers, etc and can fade earlier.

Ever seen the brakes on an MR2 Turbo? Tiny little one pot things, like what youd find on a Civic. Does 60-0 in the same or lesser distance than an Enzo, 102 feet IIRC.

How about that for a track car idea? An MR2 Turbo. Toyota reliability, mid engine, lightweight, 2 seater, good aftermarket stuff.

M758

Tim,
I looked at the link you posted. I am trained mechaical engineeer. The equations presented are correct, but not accurate. Reason is the friction does not really apply the form stated. It is in fact more complex. That same reasoning would also tell you that in cornering weight is irrelvant. We know that is not the case however. The way friction and grip work is more complex.

Just think real world examples. Pickup truck empty stops in one distance. Now load it with a bunch of crap, but don't overload it. It WILL take longer to stop. The reason is that the friction that goes into slowing the car is not the mu x normal force which is the basic friction model.

"How to make your car Handle" by Fred Puhn covers this at least with respect to cornering.

macnewma

Joe, could you explain how it is different? Should we open a separate thread? I think this is a very interesting concept and I would like the explanation of engineers although in relatively layman's terms. Thanks!

M758

It is time for new thread...


As for explaining....

Back on Topic


So should Tim get an Elise?

Geo

Perhaps. I've never believed that. Different skills from driving a big hp car fast. I know people are now going to jump up and down and disagree with me, but so be it. I had some karting people try to talk me into getting a B&S 5hp tater digger (mostly the people driving the tater diggers) because "it's slower and I would learn to be a better driver faster." I ran away and bought a 2 cycle Yamaha.

Slow is just slow. Driving fast with a lot of hp requires different skills (or perhaps techniques if you prefer) from driving fast with low hp. That said, driving a fast car doesn't make a driver better either.

ColorChange

Now, since the light weight does not help me, I will look at many other cars. Again, full race prep and all safety devices will be required. My current list is:

Miata (in the lead because it is highly reliable and almost expendable)
944
old 911
old M3

Geo

Tim, you're being a spaz. You started out this discussion over the energy of a low mass car vs a high mass car. Now you're concered more about braking distances. Perhaps I missed a change in logic/concerns?

Of the above lists, I'd go with Joe's suggestion of the NA 944 and expand a bit by saying, hey, get some fiberglass fenders and lexan windows and you'll be WAY down on the mass and MUCH cheaper than the Elise.