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Relocation bracket questions

Mad Hatter

Gotta go Faster
3,922
2,408
Santiago, Chile
Hi all. My brackets and LCA are arriving soon, what did you guys do with the steel weights attached to the axle? leave them on or take them off?? Other question is was there a recommended angle for the LCA? Looking at the BMR install instructions you can see that all three settings are more angled then the OEM lca is now. Is there a preferred angle for road racing?
 
My weights are still on the car. They are there for NVH.

If you use the brackets in the original position you wouldn't need them. ;). I'd start in the middle location and adjust from there.
 
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1
I personally wouldn't go too crazy on the angle unless you are after more roll steer.
Additionally, more anti squat (more lca angle) is less anti dive when adjusted from the bottom--translating to more rear end brake rise.
It's all a compromise, but it makes more sense in my mind for only mild changes in LCA angle for road race use.
 

Mad Hatter

Gotta go Faster
3,922
2,408
Santiago, Chile
Will try to keep sane! Does anyone have the angle of the original LCA? To try to get as close to it with the bracket holes as possible, even the middle hole seems quiet a bit more angle then oem was?? (looking at the picture, will not have the bracket till Monday). I should have measured the angle before I lowered the car!
 

Grant 302

basic and well known psychic
boro92 said:
I personally wouldn't go too crazy on the angle unless you are after more roll steer.
Additionally, more anti squat (more lca angle) is less anti dive when adjusted from the bottom--translating to more rear end brake rise.
It's all a compromise, but it makes more sense in my mind for only mild changes in LCA angle for road race use.

I think that's actually the opposite. With a lower LCA position, the body will squat as a result from rear axle braking force. The main problem from going too low on the bracket would be possibly getting brake hop if/when the rear looses traction under braking+engine decel if letting the clutch out too quickly in a heel-toe downshift.
 
Grant 302 said:
I think that's actually the opposite. With a lower LCA position, the body will squat as a result from rear axle braking force. The main problem from going too low on the bracket would be possibly getting brake hop if/when the rear looses traction under braking+engine decel if letting the clutch out too quickly in a heel-toe downshift.
I've been running mine in the upper of the two holes but wishing I had more squat accelerating out of the corner. Would it help or hurt to drop the LCA into the lower hole of the relo bracket?
 

Grant 302

basic and well known psychic
cloud9 said:
I've been running mine in the upper of the two holes but wishing I had more squat accelerating out of the corner. Would it help or hurt to drop the LCA into the lower hole of the relo bracket?

I've been trying to get you to change settings for a while now! ;D ;)

You should get more corner exit traction using the lower hole. The term 'anti-squat' is somewhat of a misnomer. A car can *actually* squat a little more as anti-squat geometry is increased (when before and after settings are still under 100% anti-squat). Increased traction causes more weight transfer. When you're on P springs with the upper hole, I think that's the case.

It's just two nuts and bolts...you should try it. :)
 
Grant 302 said:
I've been trying to get you to change settings for a while now! ;D ;)

You should get more corner exit traction using the lower hole. The term 'anti-squat' is somewhat of a misnomer. A car can *actually* squat a little more as anti-squat geometry is increased (when before and after settings are still under 100% anti-squat). Increased traction causes more weight transfer. When you're on P springs with the upper hole, I think that's the case.

It's just two nuts and bolts...you should try it. :)
Will do :D
 

Mad Hatter

Gotta go Faster
3,922
2,408
Santiago, Chile
Great will try that too! I am putting the car on a truck with my three Camaro friends on Thursday and will be trying the car out on this track on Saturday, racing on Sunday. Its a 600km drive and a friendly police man took my license away for a week...

56939942.png


I will be installing the BMR LCA and bracket, thursday morning or at the track on saturday. Any other tips on the car set up? The track is almost 2.3km long and is supposed to be the best in Chile so far.
 

ArizonaBOSS

Because racecar.
Moderator
8,545
2,376
Arizona, USA
Be wary of what moving to the lower hole could do; the roll steer geometry of the rear axle is also going to change. Rehagen et al recommend that middle hole so the axle doesn't move into a "roll understeer" position. So, while you may get more corner exit traction, the car may not corner the same when it rolls heavily.
 
ArizonaBOSS said:
Be wary of what moving to the lower hole could do; the roll steer geometry of the rear axle is also going to change. Rehagen et al recommend that middle hole so the axle doesn't move into a "roll understeer" position. So, while you may get more corner exit traction, the car may not corner the same when it rolls heavily.
Thanks I'll have to think about it. Going to maybe have a 3 day at MPH in May where it could be slow one day and might experiment. When I threw the 315s out back last fall I had plenty of grip so may just need to keep running the fatties.
 

Grant 302

basic and well known psychic
ArizonaBOSS said:
Be wary of what moving to the lower hole could do; the roll steer geometry of the rear axle is also going to change. Rehagen et al recommend that middle hole so the axle doesn't move into a "roll understeer" position. So, while you may get more corner exit traction, the car may not corner the same when it rolls heavily.

With the static rear of the arms lower than the front of the arms, a turn will cause the arm on the outside to 'lengthen' and the arm on the inside 'shortens' resulting in roll oversteer.

found this example to illustrate:
06%20Roll%20Steer%20Illustration-XL.jpg

from this article:
http://www.motoiq.com/MagazineArticles/ID/2802/PageID/5480/Project-Mustang-50-Optimizing-Weight-Transfer-and-Roll-Steer.aspx

One benefit I find is that as you unwind the wheel, your available traction really increases. So it's like having 4 wheel steering and drag car traction.

cloud9 said:
Thanks I'll have to think about it. Going to maybe have a 3 day at MPH in May where it could be slow one day and might experiment. When I threw the 315s out back last fall I had plenty of grip so may just need to keep running the fatties.

Fatties can mask geometry and traction issues! Didn't know how much I was giving up when I was lowered without brackets, but the change was night and day for both traction and steering.
 

Mad Hatter

Gotta go Faster
3,922
2,408
Santiago, Chile
Grant 302 said:
With the static rear of the arms lower than the front of the arms, a turn will cause the arm on the outside to 'lengthen' and the arm on the inside 'shortens' resulting in roll oversteer.

found this example to illustrate:
06%20Roll%20Steer%20Illustration-XL.jpg

from this article:
http://www.motoiq.com/MagazineArticles/ID/2802/PageID/5480/Project-Mustang-50-Optimizing-Weight-Transfer-and-Roll-Steer.aspx

One benefit I find is that as you unwind the wheel, your available traction really increases. So it's like having 4 wheel steering and drag car traction.

Fatties can mask geometry and traction issues! Didn't know how much I was giving up when I was lowered without brackets, but the change was night and day for both traction and steering.

What a great article Grant302!! Cant wait to put on my BMR bracket. Perfectly describes what I felt with the P springs alone. I was missing the apex for lack of turn in, and loosing the tail powering out of the corner. Many thanks for the link. The possibility of gaining a second on a 60 sec track would be fantastic (Ok, even 1/2 a second!)
 
367
1
Grant 302 said:
I think that's actually the opposite. With a lower LCA position, the body will squat as a result from rear axle braking force. The main problem from going too low on the bracket would be possibly getting brake hop if/when the rear looses traction under braking+engine decel if letting the clutch out too quickly in a heel-toe downshift.

If the bottom LCA changes angle to increase anti squat (ie: pushes wheels into ground under load). Similarly, brake torque pushes wheels into the ground so it actually produces a rear end lift effect. Perhaps I'm mislead, but in the 90s when full suspension bicycles were gaining popularity, many manufacturers added a ton of anti squat into the rear suspension to reduce the pogo effect under pedaling. However, this caused the rear of the bike to jack upwards under braking. So, doesn't the same concept apply here?

I will need to dig it up, but I read an tuning book on this topic and the gist was angling the LCA in the way we are speaking of will produce pro-lift under braking. The way to combat this is with UCA length and angle. Shrug
 

Grant 302

basic and well known psychic
boro92 said:
So, doesn't the same concept apply here?

I will need to dig it up, but I read an tuning book on this topic and the gist was angling the LCA in the way we are speaking of will produce pro-lift under braking. The way to combat this is with UCA length and angle. Shrug

Two issues here: Bicycles. Separate brakes.

Now it's been a while since I've thought much about two wheel suspensions, but all of my motorcycles were swing arm with shock(s) and no UCA. So I don't think much applies to our cars.

And again on motorcycles, I never really used the rear brake...and certainly not under racetrack conditions. Since we have brakes on both axles that act at the same time, front braking doesn't just drag the rear axle, the rear axle drags the car too. You also need to consider that brakes will still act upon the instant center and not just one set of the arms.

Mad Hatter (ex splatter) said:
What a great article Grant302!! Cant wait to put on my BMR bracket. Perfectly describes what I felt with the P springs alone. I was missing the apex for lack of turn in, and loosing the tail powering out of the corner. Many thanks for the link. The possibility of gaining a second on a 60 sec track would be fantastic (Ok, even 1/2 a second!)

I was just looking for an image to help describe what I was talking about...glad your question stirred some investigation and interesting discussion! Good luck and always looking forward to your updates. :)
 
So could wanting roll over steer be the reason that some 302S teams run without a roll bar in the rear? Does this give them a sneaky advantage? A Watts link will not change this behavior, just keep the axle centered, right?
 

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