Tires? Speed?

[jcsaleen]

The roads upstate can range from 2-15 miles long of very straight roads. By my school the road is about 4.5 miles long with almost no turns what so ever. It's all interstates really.

[curtis73]

Weight doesn't affect top speed. An getting a car from 180 to 200 takes A LOT more power than you think. I forget the numbers, but doubling top speed takes something like tenfold the power, so increasing the top speed by 10% might take 50% more power.

[GreyGoose006]

its a formula of sorts

i found a website that explained it very well once
here is a satisfactory one

http://www.pumaracing.co.uk/TOPSPEED.htm
and here is a "calcualator" of sorts
http://www.robrobinette.com/top_speed.htm

[jcsaleen]

Thanks man but it leaves out aerodynamic factors. Other then that it seems pretty right.

[GreyGoose006]

no it doesnt.
drag coefficient is a constant.

when your car is drag limited to a specific speed, and you increase the hp, the car will go faster.
the coefficient of drag wont change, so as long as you know the fastest speed you can possibly go in your car on level ground, it is correct.

[jcsaleen]

Sorry missed the tags thats robinette aka one of the top Rx7 guru's out there.

I'm adding the spoiler adding a diffuser (side generators as well), lip (won't do much) and maybe a new front bumper depending on the cooling layout I want to do. + The car is getting a fullbody FRP undertray and is being lowered 2.5 - 3.5 inches depends they are adjustable so...



The wing actually generates downforce depending on the set angle of course...

Also depends on the temparature (heatsoak/cool air = alot more hp) and air density as well.

[KiwiBacon]

Originally Posted by jcsaleen

Sorry missed the tags thats robinette aka one of the top Rx7 guru's out there.

I'm adding the spoiler adding a diffuser (side generators as well), lip (won't do much) and maybe a new front bumper depending on the cooling layout I want to do. + The car is getting a fullbody FRP undertray and is being lowered 2.5 - 3.5 inches depends they are adjustable so...

The wing actually generates downforce depending on the set angle of course...

Also depends on the temparature (heatsoak/cool air = alot more hp) and air density as well.

A rear spoiler generating downforce will create more drag.
Lowering your car will also create more drag.

I think you need a better technical advisor.

[jcsaleen]

Originally Posted by KiwiBacon

A rear spoiler generating downforce will create more drag.
Lowering your car will also create more drag.

I think you need a better technical advisor.

I know the wing will create more drag, only if it's angled to generate

How will lowering the car create more drag? That just means less space for air to travel under the car. The surface area is still the same.

[KiwiBacon]

Originally Posted by jcsaleen

I know the wing will create more drag, only if it's angled to generate

How will lowering the car create more drag? That just means less space for air to travel under the car. The surface area is still the same.

Less space for air means more interference between the two surfaces. In this case the bottom of the car and the road.

Your wing is going to drag regardless of how you have it set. I have seen CFD plots of splitter wings which can reduce drag, The photo you show is not one of them.

[beef_bourito]

the spoiler will create drag no matter how it's angled, changing the angle will increase or decrease the drag but it will always create drag (unless it's in an area untouched by oncoming air in which case it won't create downforce).

is the undertray a cover for the underside of the care that makes it smooth? if so it'll create downforce and you'll have more rolling resistance which will create more drag (not aerodynamic drag though)

edit: i didn't see the above post because i left this window open and only just got to it now.

how would a wing reduce drag?

[GreyGoose006]

the other reason that lowering the car will decrease your speed is that as you lower the car, there is more low pressure created under the car.
especially if you have a body kit with a front lip.

all this low pressure will create a vacuum and turbulence under the car.
turbulence is never a good thing when you want to go as fast as possible.

[jcsaleen]

Originally Posted by beef_bourito

how would a wing reduce drag?

I'm not saying the wing would reduce drag lmao. (Yes, I was wrong for stating that it would not effect the drag) I know that anything that is mounted onto a car will always create some drag/air resistance unless it's removed....

How would a completely smooth FRP undertray create drag??? It creates a smooth surface for the air to travel against at highspeeds instead air flying into the tranny tunnel, Diff, etc. Also how would it create downforce? The panel is completely sealed to the body no air will duct down on to it if thats what your thinking. I see your point of lowering = a tighter friction space for air to travel. I would still rather have more friction then having air get under the body and me paying the ultimate price like the racing beat Rx7 did. I know turbulent air will decrease the speed overall.

Now here's a question I've been wondering does torque play a huge roll in topend or is it all horsepower that really matters at those speeds?

Btw ~ Stock kit with a stock FRP lip.

[UncleBob]

back to the original question, tire speed ratings are for *sustained* speeds. All tires can go beyond their speed rating safely, but are not recommended for long runs at higher speeds. no one will define the time before safety is a concern, but it is much longer than most people would spend at higher speeds typically

This is why, for example, drag race tires would never survive a sustained high speed, but can see extremely high speeds safely for short distances

As for drag:

http://www.hotrod.com/techarticles/h...o_tricks_tips/

[beef_bourito]

Originally Posted by jcsaleen

I'm not saying the wing would reduce drag lmao. (Yes, I was wrong for stating that it would not effect the drag) I know that anything that is mounted onto a car will always create some drag/air resistance unless it's removed....

i was actually referring to kiwi's post about how he knows of a wing that will decrease drag.

Originally Posted by jcsaleen

How would a completely smooth FRP undertray create drag???

because it's smoother so the air can travel much faster. it's like a wing, the air on top of the wing is traveling faster so it creates lift, the air under your car will travel faster so it will create downforce.