Front suspension question

[rtj]

This is a photo of some old asphalt car (assumption). I see they have changed the axis of rotation of the upper a arm. I see in vette427sbc’s project thread, his lower a arms have this treatment. Is this give similar results and what is the benefit?


Vette427sbc’s Photos

http://www.vettemod.com/forum/showthread.php?t=10738&page=3

Post 72

I scanned through the thread and didn’t see an explanation.

 

[rtj]

It seems like setting the horizontal a arm position would be critical as it is going to tip the spindle.

 

[BBShark]

Just a guess but maybe the travel is more inline with the caster angle?

 

[rtj]

Just a guess but maybe the travel is more inline with the caster angle?

Well, I’m assuming that they are set up with the a arms horizontal. So as down force or braking occur, the seem to change castor angle opposite. The old race car with upper a arm mod would increase castor.

Anti dive was done slightly different, but maybe these designs contribute to anti dive too.


From google

“ Raising the front of the RF A-Arm, so that the front pivot is higher off the frame (ground) than the rear pivot, creates a an A-Arm arrangement that is identified as Anti Dive. So, lowering the back of your A-Arms puts Anti Dive in the car – it's an easy adjustment that you can make right at the track.”

 

[69427]

Just a guess but maybe the travel is more inline with the caster angle?

Well, I’m assuming that they are set up with the a arms horizontal. So as down force or braking occur, the seem to change castor angle opposite. The old race car with upper a arm mod would increase castor.

Anti dive was done slightly different, but maybe these designs contribute to anti dive too.


From google

“ Raising the front of the RF A-Arm, so that the front pivot is higher off the frame (ground) than the rear pivot, creates a an A-Arm arrangement that is identified as Anti Dive. So, lowering the back of your A-Arms puts Anti Dive in the car – it's an easy adjustment that you can make right at the track.”

From the picture it looks like there's multiple things going on. The angled up tilt of the upper A-arm shafts will create anti-dive, as the Google thing says, but the angled (relative to front-back) mount of the upper A-arms increases the positive caster during suspension compression, which increases the negative camber on the outside tire during cornering.

 

[rtj]

Just a guess but maybe the travel is more inline with the caster angle?

Well, I’m assuming that they are set up with the a arms horizontal. So as down force or braking occur, the seem to change castor angle opposite. The old race car with upper a arm mod would increase castor.

Anti dive was done slightly different, but maybe these designs contribute to anti dive too.


From google

“ Raising the front of the RF A-Arm, so that the front pivot is higher off the frame (ground) than the rear pivot, creates a an A-Arm arrangement that is identified as Anti Dive. So, lowering the back of your A-Arms puts Anti Dive in the car – it's an easy adjustment that you can make right at the track.”

From the picture it looks like there's multiple things going on. The angled up tilt of the upper A-arm shafts will create anti-dive, as the Google thing says, but the angled (relative to front-back) mount of the upper A-arms increases the positive caster during suspension compression, which increases the negative camber on the outside tire during cornering.

It might be an asphalt circle track car. I looked, both sides have the same setup.

I went back in case it was a one side only mod, but both sides are equivalent.

Now, it seems the lower a arm mod in the link above behaves opposite.

 

[69427]

Just a guess but maybe the travel is more inline with the caster angle?

Well, I’m assuming that they are set up with the a arms horizontal. So as down force or braking occur, the seem to change castor angle opposite. The old race car with upper a arm mod would increase castor.

Anti dive was done slightly different, but maybe these designs contribute to anti dive too.


From google

“ Raising the front of the RF A-Arm, so that the front pivot is higher off the frame (ground) than the rear pivot, creates a an A-Arm arrangement that is identified as Anti Dive. So, lowering the back of your A-Arms puts Anti Dive in the car – it's an easy adjustment that you can make right at the track.”

From the picture it looks like there's multiple things going on. The angled up tilt of the upper A-arm shafts will create anti-dive, as the Google thing says, but the angled (relative to front-back) mount of the upper A-arms increases the positive caster during suspension compression, which increases the negative camber on the outside tire during cornering.

It might be an asphalt circle track car. I looked, both sides have the same setup.

I went back in case it was a one side only mod, but both sides are equivalent.

Now, it seems the lower a arm mod in the link above behaves opposite.

Before I reply, what do you mean "opposite"?

 

[rtj]

Just a guess but maybe the travel is more inline with the caster angle?

Well, I’m assuming that they are set up with the a arms horizontal. So as down force or braking occur, the seem to change castor angle opposite. The old race car with upper a arm mod would increase castor.

Anti dive was done slightly different, but maybe these designs contribute to anti dive too.


From google

“ Raising the front of the RF A-Arm, so that the front pivot is higher off the frame (ground) than the rear pivot, creates a an A-Arm arrangement that is identified as Anti Dive. So, lowering the back of your A-Arms puts Anti Dive in the car – it's an easy adjustment that you can make right at the track.”

From the picture it looks like there's multiple things going on. The angled up tilt of the upper A-arm shafts will create anti-dive, as the Google thing says, but the angled (relative to front-back) mount of the upper A-arms increases the positive caster during suspension compression, which increases the negative camber on the outside tire during cornering.

It might be an asphalt circle track car. I looked, both sides have the same setup.

I went back in case it was a one side only mod, but both sides are equivalent.

Now, it seems the lower a arm mod in the link above behaves opposite.

Before I reply, what do you mean "opposite"?

I’m saying the castor angle for the asphalt car, if you assume that the a arm is horizontal in a neutral load, as the front end drops, the castor angle increases. That is the arc of the upper a arm moves the top of the spindle rear ward.

With the lower a arm as in the link, the arc of the lower a arm moves the bottom of the spindle assembly rear ward, decreasing castor.

 

[rtj]

The asphalt car might run on banked tracks.

 

[rtj]

I see you added in camber change that results.

 

[BBShark]

I'm confused. Does the suspension you showed on the top (red frame) also have an angled axis on the BOTTOM arm? If so, the bottom arm al the joint moves back slightly on jounce. The upper arm moves backwards slightly on jounce. If the upper arm is shorter there would be slightly increased caster.

I would really surprised if it increased caster unless the jounce was 4" or more. Also I think with both moving backwards your static caster is basically the same.

 

[rtj]

I'm confused. Does the suspension you showed on the top (red frame) also have an angled axis on the BOTTOM arm? If so, the bottom arm al the joint moves back slightly on jounce. The upper arm moves backwards slightly on jounce. If the upper arm is shorter there would be slightly increased caster.

I would really surprised if it increased caster unless the jounce was 4" or more. Also I think with both moving backwards your static caster is basically the same.

No it looks to me like factory lower a arms. I’ll try and find a better pic.