Ride Hieght

[gttouring]

provided one doesn't bottom out, how low is too low?
i recently put new higher rate springs on the car and it is a good bit low...
i have 3- 4 inches of clearance
it drives well, just go gingerly up those ramps!
but the exhaust scrapes no and again.

can i run a flat type exhaust (like NASCAR) to alleviate this?
or should i run it out the side like a cobra?

its a volvo amazon BTW
http://www.dropshots.com/fiorano3#da...11-08/03:55:49

[AU N EGL]

I run 3" between the ground and my front splitter or about 3 3/8" between the ground and bottom of the car.

If I could get drop spindles then I could drop the car an inch.

The shorter your exhaust pipes are might help you pick up some torque with the lower back pressure.

[gttouring]

oooh thanks for that i will measure the car to get the exact number-
the exhaust on there is not the proper one just a test pipe.
I will route the exhaust off the side i think, 3 3/8 off the bottom good reference
would a flat exhaust work? or can i run the pipe through the car? as long as it is enclosed form the passenger area its okay per VARA and SCCA rules (box it in i guess...) only the body can be recessed for the muffler though.

[AU N EGL]

If your running SCCA or VARA check with their rules.

The other things to look at:

suspension travel
do you need a bump steer kit

if your too low, then you many need both and bottom out with your suspension when you driver over some gaters

[KAM]

Can you increase the depth of the exhaust tunnel so the exhaust does not hang lower than the bottom of the car? Thats what I think I will end up doing on my car

[AU N EGL]

Originally Posted by KAM

Can you increase the depth of the exhaust tunnel so the exhaust does not hang lower than the bottom of the car? Thats what I think I will end up doing on my car

One could. Again look at your tech rules first.

My car has a tunnel for drive shaft and exhaust pipes. so the bottle is flat.

The other thing about exhaust pipes, has to do with the power out put. Long pipes hurts HP and TQ.

[gttouring]

i will keep them short and swing off to the side.
ok in the rules
the muffler can be recessed in the body...
bump steer seems ok- i drove the "****" out of it in some industrial lots on tuesday after noon and it did great, no scrapes only the exhaust tip which i expected, it wasn't angled properly. i would say it has been a successful change-
now i have to change the tire (VARA max is 15 inch-195mm width) they are currently 15 by 165/65 quite splashy feeling too.
but the suspension held up and kept the car shiny side up and no drama, those old volvos they built them right methinks
is it possible the suspension settled over a few days? it seems to have risen up a bit after driving.
my ground clearance is almost as good as my lowered street car which is very livable but i go sideways over sleeping policemen

[AU N EGL]

Suspension is settled after the first drive. Have you corner balanced the car yet?

[JohnD]

Have a look at Katz' "Race Car Aerodynamics", pp 49 and 193.
Lift decreases as the ground clearance diminishes, but drag increases.

A theoretical semi-ellipsoid will reach minimum lift AND drag when the ride height/length ratio is 0.05.
For even a generic open wheel race car (nearer to reality than an ellipsoid) the optimum ride height will be 0-5 cms for one with underbody tunnels (that's why F1 uses 'planks') and 0-10cms for a flat underbody.

The same work shows that ground clearance of 3-4" confers no benefit at all.

John

[AU N EGL]

Originally Posted by JohnD

Have a look at Katz' "Race Car Aerodynamics", pp 49 and 193.
Lift decreases as the ground clearance diminishes, but drag increases.

A theoretical semi-ellipsoid will reach minimum lift AND drag when the ride height/length ratio is 0.05.
For even a generic open wheel race car (nearer to reality than an ellipsoid) the optimum ride height will be 0-5 cms for one with underbody tunnels (that's why F1 uses 'planks') and 0-10cms for a flat underbody.

The same work shows that ground clearance of 3-4" confers no benefit at all.

John

John

Good info. Looks like I need to get those drop spindles then too get my car down to ~2" ( ~ 5 cm ) ground clearance.

Thanks, better re read that section

Tom

[dtype38]

I run a side exhaust and have tried ride heights down to 2" under the sump - that's about 2" on the front air damn and about 3" to the chassis. It's the lowest I'm allowed to go on my regs which say none of the car must touch the ground when one tyre is completely flat (supposedly so as we don't dig trenches in the tarmac if we get a flat!). Anyway, I haven't noticed any aerodynamic benefits, but the lower ride height certainly improves handling by virtue of the lower CoG.

I do have to run pretty stiff springs to stop it bottoming though (850lb/750lb F/R).

[gttouring]

cheers- i have not corner weighted the car in its final iteration
the battery cable and the new engine are still to be place- i have been running a stock location configuration for prelim testing

[VT-R]

Originally Posted by dtype38

I run a side exhaust and have tried ride heights down to 2" under the sump - that's about 2" on the front air damn and about 3" to the chassis. It's the lowest I'm allowed to go on my regs which say none of the car must touch the ground when one tyre is completely flat (supposedly so as we don't dig trenches in the tarmac if we get a flat!). Anyway, I haven't noticed any aerodynamic benefits, but the lower ride height certainly improves handling by virtue of the lower CoG.

Originally Posted by dtype38

I do have to run pretty stiff springs to stop it bottoming though (850lb/750lb F/R).

Dtype38 did you use any form of calculation to arrive at those spring rates?
I’m planning on running my car at around the same ground clearance as you and I’m unsure if the springs (spring frequencies) I’ve chosen are high enough to stop the car grounding.

[dtype38]

Nope, got there by trial and error. Started with springs at half that rate and progressively increased the rate and reduced the damping until it felt like a go-kart, then dropped it to the deck!

[speedsense]

Originally Posted by JohnD

Have a look at Katz' "Race Car Aerodynamics", pp 49 and 193.
Lift decreases as the ground clearance diminishes, but drag increases.

A theoretical semi-ellipsoid will reach minimum lift AND drag when the ride height/length ratio is 0.05.
For even a generic open wheel race car (nearer to reality than an ellipsoid) the optimum ride height will be 0-5 cms for one with underbody tunnels (that's why F1 uses 'planks') and 0-10cms for a flat underbody.

The same work shows that ground clearance of 3-4" confers no benefit at all.

John

Not all the statements and theories in the Katz book are correct. This is one that gets questioned. It is obvious that a decrease in the lift will increase the downward force "ability" of the body, but you are also decreasing frontal area by way of the lowered height, there by decreasing drag, but increasing the efficency of the aero devices (all non self producing downforce devices) that no longer have a high lift ratio to contend with.
How does a downward force producing device (non wing device) produce more drag by way of reducing the force it is acting against? Producing more drag by becoming more efficient? This doesn't make sense....

[JohnD]

I can't speak for the Prof, but I think he was looking in detail at one aspect, under-floor flow. You're looking aat the whole picture, good idea!

But, lowering the height of the car to reduce the frontal area - does that make as much difference as you say, whe the lowering is in the region of 100mm? When drag = 0.5 x density x velocity^2 x Cd x FArea, and the car's Fa is 1800 x 1000mm (say), and the area goes down 10% (100mm lower), then drag goes down 10%. Katz shows reductions in Cd (note, not just drag, but drag coeff) of at least that much.

As to drag increasing as the height lowers beyond a point, Katz is not the only one to find this. Many websites refer to aeroplanes and 'wing in ground effect' but aircraft just never fly that low!
See: http://www.hanleyinnovations.com/racecar1.html and the graph and chart for the results of the problem set there. Table goes from drag 2.08 lbs at 12" high, through 4lbs at 3", to 91lbs (!) at 1".

I suppose that the answer is turbulence. The air flow beneath the car will flow faster and faster as the height diminishes. When Reynolds is exceeded, laminarity is lost and turbulence occurs, vastly increasing drag.

So low is good, too low is bad! But how many non-F1 cars ride that low!

John

[THR]

i nearly choked when you said 3-4 inches!!
15mm is good!!!!!

[phoenix]

A warning against going too low.......

It is my understanding that if you run a front splitter device, then it will only produce down force (and allow the underside of the car to produce downforce) if air is able to pass underneath it. Once the gap between the splitter and the ground is lost, all downforce from the splitter (and underside of the car) is lost. This can happen instantaneously - as you hit a certain speed or when you hit the brakes, for example - and the resultant sudden reduction in grip could cause anything from locking wheels under braking through unpredictable handling problems to a major off.

[AU N EGL]

Originally Posted by phoenix

A warning against going too low.......

It is my understanding that if you run a front splitter device, then it will only produce down force (and allow the underside of the car to produce downforce) if air is able to pass underneath it. Once the gap between the splitter and the ground is lost, all downforce from the splitter (and underside of the car) is lost. This can happen instantaneously - as you hit a certain speed or when you hit the brakes, for example - and the resultant sudden reduction in grip could cause anything from locking wheels under braking through unpredictable handling problems to a major off.

Take off, Not quite, but I have hit a few crest of hills and the car feels like it did lift a bit.

I need an extractor hood.

[phoenix]

Originally Posted by AU N EGL

Take off, Not quite

I know this is an international forum, but in the UK an 'off' means going off the circuit/track - i.e. onto the grass or into a gravel trap - or if you are unlucky into something hard like a wall or a barrier. It doesn't mean geting airborne.

[Maurotoro]

McBeath talks about it when he discusses splitter and airdam height for a saloon in Competition Car Aerodynamics, the lower you go before blockage occurs the more downforce and the less drag that you generate just by forcing the air away from the messy underbody (don't know for ground effects cars) but he also says the ride height sensibility also increases the lower you go so unless you're ready for solid suspensions and "springy"tires I suggest to be moderate in regards to splitter height and try to achieve front downforce elsewhere (getting high pressure air out of the wheelarches for instance).