A-arm design opinions

[Desertbound1024]

Looking for input on a few center mount concept I drew up for my Manx. Will be based around a 31” tire so the KPI/SAI is about 15* at the spindle (0* camber).

1st concept:

24.125” lower control arm

21.75” upper control arm

6” separation between upper arm pivots at bulkhead

6” separation between lower arm pivots at bulkhead

7” vertical separation between upper and lower arms at bulkhead

8.5” between pivots at spindle.

0 scrub

-2* camber at ride height

-7* camber at bump

0* camber at droop

~3” lateral scrub (track width change) over 18” of travel.


2nd concept:

24.25” lower control arm

17.75” upper control arm

13.5” separation between upper arm pivots at bulkhead

5.5” separation between lower arm pivots at bulkhead

8.375” vertical separation between upper and lower arms at bulkhead

8.5” between pivots at spindle

.5” scrub radius

-1* camber at ride height

-6.3* camber at bump

-6.2* camber at droop

Less than 1” lateral scrub (track width change) over 18” of travel.

11.5” of up travel, 7” droop travel.

//

I figure the 2nd concept will be better based on the lack of lateral scrub.


This is my first time designing an arms and I’d appreciate input on the parallel design vs the short upper design. Also would love some feedback on where I can make improvements.

 

[Motiracer38]

I've always been a fan of minimizing scrub in the theory that is keeps the track change the same as the solid rear axle. Being a Manx with a trailing arm rear may be a bit different and allow for some. Side x sides usually have tons of scrub but I believe that is more for axle plunge and angularity issues. You will give up some traction on the inside tire as the body roll only furthers leans the tire.

Unless your trying to use a Kartek spindle I would increase the kingpin spread as 8.5" is not much so will wear joints out faster and make steering rack mounting tighter.

Also make sure you watch the crossover point of the camber curve so that you don't get much less than your 1deg at ride height. It's been a long time since I paid for Racing Aspirations but you should be able to produce a wheel travel vs camber curve.

 

[Desertbound1024]

I've always been a fan of minimizing scrub in the theory that is keeps the track change the same as the solid rear axle. Being a Manx with a trailing arm rear may be a bit different and allow for some. Side x sides usually have tons of scrub but I believe that is more for axle plunge and angularity issues. You will give up some traction on the inside tire as the body roll only furthers leans the tire.

Unless your trying to use a Kartek spindle I would increase the kingpin spread as 8.5" is not much so will wear joints out faster and make steering rack mounting tighter.

Also make sure you watch the crossover point of the camber curve so that you don't get much less than your 1deg at ride height. It's been a long time since I paid for Racing Aspirations but you should be able to produce a wheel travel vs camber curve.

Thanks for the info. I recently changed a few things, one of them being lengthening the kingpin spread to 10”. I’ll take a look at the camber curve and see if I have to make any more changes.

 

[Creed00]

Looking for input on a few center mount concept I drew up for my Manx. Will be based around a 31” tire so the KPI/SAI is about 15* at the spindle (0* camber).

1st concept:

24.125” lower control arm

21.75” upper control arm

6” separation between upper arm pivots at bulkhead

6” separation between lower arm pivots at bulkhead

7” vertical separation between upper and lower arms at bulkhead

8.5” between pivots at spindle.

0 scrub

-2* camber at ride height

-7* camber at bump

0* camber at droop

~3” lateral scrub (track width change) over 18” of travel.


2nd concept:

24.25” lower control arm

17.75” upper control arm

13.5” separation between upper arm pivots at bulkhead

5.5” separation between lower arm pivots at bulkhead

8.375” vertical separation between upper and lower arms at bulkhead

8.5” between pivots at spindle

.5” scrub radius

-1* camber at ride height

-6.3* camber at bump

-6.2* camber at droop

Less than 1” lateral scrub (track width change) over 18” of travel.

11.5” of up travel, 7” droop travel.

//

I figure the 2nd concept will be better based on the lack of lateral scrub.


This is my first time designing an arms and I’d appreciate input on the parallel design vs the short upper design. Also would love some feedback on where I can make improvements.

What website is this?

 

[2012SVTSC]

What website is this?

I believe it's "racing aspirations".