Taller front tires to reduce windshield angle

[NeilBlanchard]

You need to step back and think about the whole car.

The attitude/angle of air flow of the whole chassis matters most, and you cannot change the attitude of the whole chassis and see an over all benefit from just the windshield.

[Frank Lee]

The whole notion is false. Somewhere here is a link to an aero article Hot Rod mag did, complete with wind tunnel experiments. They said windshield angle is not critical.

[dmac257]

Originally Posted by Frank Lee

The whole notion is false. Somewhere here is a link to an aero article Hot Rod mag did, complete with wind tunnel experiments. They said windshield angle is not critical.

Frank,

I'm no expert and I agree with you about angle not being "critical" but I do have a question about the windshield transition. We are really talking about many small changes that add together to reduce overall Cd so while not "critical" a little here and little there still helps. Would it just be better to put a fairing in front of that transition angle to start air upward a little sooner?

There is usually a set of wipers there and many recommend removal (I won't do that) or a fairing. If you put a fairing in front of the blades would it be "better" to angle the fairing from the hood at angle halfway between the existing transition angle or from under the hood at a sharper angle.

Cycleguy,

As for changing the angle of the entire vehicle, I would say that we ALL need to see the vehicle before we can decide. ie: my truck sits higher in the back by 4 inches than the front and the overall underside of the body is already 3degrees higher in back. Dropping the back (changing entire angle) may make sense for my truck BUT after I put full belly pan on bottom, it might NOT make sense. I will have to see what the rear angle underneath looks like when done.

I would say no to the bigger wheels in front as you would likely get much better results from other things first and likely also to make overall combined Cd worse if you already did some mods and then put bigger tires on.

Don

[Patrick]

One possible advantage is that it will increase your effective gear ratio and might put your engine into a more efficient point on the BSFC curve.

[Frank Lee]

Originally Posted by dmac257

Frank,

I'm no expert and I agree with you about angle not being "critical" but I do have a question about the windshield transition. We are really talking about many small changes that add together to reduce overall Cd so while not "critical" a little here and little there still helps. Would it just be better to put a fairing in front of that transition angle to start air upward a little sooner?

There is usually a set of wipers there and many recommend removal (I won't do that) or a fairing. If you put a fairing in front of the blades would it be "better" to angle the fairing from the hood at angle halfway between the existing transition angle or from under the hood at a sharper angle.

Cycleguy,

As for changing the angle of the entire vehicle, I would say that we ALL need to see the vehicle before we can decide. ie: my truck sits higher in the back by 4 inches than the front and the overall underside of the body is already 3degrees higher in back. Dropping the back (changing entire angle) may make sense for my truck BUT after I put full belly pan on bottom, it might NOT make sense. I will have to see what the rear angle underneath looks like when done.

I would say no to the bigger wheels in front as you would likely get much better results from other things first and likely also to make overall combined Cd worse if you already did some mods and then put bigger tires on.

Don

You are correct in saying it is the windshield TRANSITION that is more critical but you are focused on the wrong transition- it is the one from the top of the windshield to the roof that has more influence on good flow and drag than the one at the base of the windshield to the hood. Too bad as that bottom one is the easy one to play with. Do whatever you want there; I'm quite sure you won't see any measureable results.

It is generally accepted that a slight nose-down rake is the most aero efficient.

Big front tires on this RWD won't change "gearing"!

[ShadeTreeMech]

I assume that cycleguy would be referring to his 94 Metro that he has listed. If this is the case, bigger tires may help a bit with making the gear ratio a touch better. Thing about the metro is, he won't be able to get much bigger than stock without some serious mods, so it would make little difference. My suspicion is the change in gearing ratio will make a bigger difference. However, I have noticed many cars, especially the fuel efficient ones, tend to lean a bit forward. Is this possibly by design?

[Vekke]

In huchos book he said after 60 degrees the gains are minimal.