Bump steer question

onanysunday

onanysunday

Well-known member
Joined
May 7, 2021
Messages
3,361
Reaction score
3,136
On my truck project I narrowed the front c5 corvette cradle 10". So I need a narrower rack. A Mustang 2 rack is 8" narrower. So starting point on each side would be about 1" wider where the tie rods start. Wonder how much bump steer that would create. Just 1" further out each side.  Anyone have an idea? Wheel travel on this truck is only about 3.5" with airbags.

20230403_121502 (3).jpg

 
I wouldn't think you have to worry about bump steer with only 3.5" of travel and on a road truck or car I dont think you would have to worry about it.  Not like it is going to be cycling though the suspension. 

 
If you orient the tie rods to be parallel with the combined travel arc of the suspension, should be liveable with 3.5” of travel and power steering if lap times and on tracktire life aren’t a priority.

Ackerman might be wonky at that position though, so check it and try to put things where both are compromised the least. To me, with 3.5” of travel, Ackerman would be the priority unless bumpsteer is crazy. 

That being said, since it’s a Mustang II rack, there are spacers available. 


Making this a non problem. :biggrin:

 
Last edited by a moderator:
44 minutes ago, Rockwood said:

If you orient the tie rods to be parallel with the combined travel arc of the suspension, should be liveable with 3.5” of travel and power steering if lap times and on tracktire life aren’t a priority.

Ackerman might be wonky at that position though, so check it and try to put things where both are compromised the least. To me, with 3.5” of travel, Ackerman would be the priority unless bumpsteer is crazy. 

That being said, since it’s a Mustang II rack, there are spacers available. 

Click to expand...
Yes, I was thinking about the ackerman as well. That will be interesting. Really don't want to change the spindles on this thing.  I am going from 104 wb which this is all designed for to 89 5/16 wb. Those rack extenders would not help since I would be to long with the Mustang 2 rack. I pulled the boots off the C5 vette rack and it is 33 1/2 from the ball on each end. The Mustang 2 rack is 25 1/2" long. I think a Honda Accord rack might be a little shorter but worried about the ratio. Might need to get ahold of each and do some checking on the bench. The factory c5s have a lot more travel and my guess is no bump steer on those.

 
Can it be made up with tie rod length? By moving the third arm out 1" on the spindle and making the tie rods the added 1" won't this correct? That is if there is room to move the third arm out.

 
onanysunday said:
Yes, I was thinking about the ackerman as well. That will be interesting. Really don't want to change the spindles on this thing.  I am going from 104 wb which this is all designed for to 89 5/16 wb. Those rack extenders would not help since I would be to long with the Mustang 2 rack. I pulled the boots off the C5 vette rack and it is 33 1/2 from the ball on each end. The Mustang 2 rack is 25 1/2" long. I think a Honda Accord rack might be a little shorter but worried about the ratio. Might need to get ahold of each and do some checking on the bench. The factory c5s have a lot more travel and my guess is no bump steer on those.
Click to expand...
Derp, read your post wrong and thought the Mustang rack was 2” too short, not long. 

richard h said:
Can it be made up with tie rod length? By moving the third arm out 1" on the spindle and making the tie rods the added 1" won't this correct? That is if there is room to move the third arm out.
Click to expand...
Alignment would be good, geometry less so. I think it’ll be fine unless you’re looking for lap times though. 

 
onanysunday said:
Yes, I was thinking about the ackerman as well. That will be interesting. Really don't want to change the spindles on this thing.  I am going from 104 wb which this is all designed for to 89 5/16 wb. Those rack extenders would not help since I would be to long with the Mustang 2 rack. I pulled the boots off the C5 vette rack and it is 33 1/2 from the ball on each end. The Mustang 2 rack is 25 1/2" long. I think a Honda Accord rack might be a little shorter but worried about the ratio. Might need to get ahold of each and do some checking on the bench. The factory c5s have a lot more travel and my guess is no bump steer on those.
Click to expand...
Derp, read your post wrong and thought the Mustang rack was 2” too short, not long. 

richard h said:
Can it be made up with tie rod length? By moving the third arm out 1" on the spindle and making the tie rods the added 1" won't this correct? That is if there is room to move the third arm out.
Click to expand...
Alignment would be good, geometry less so. I think it’ll be fine unless you’re looking for lap times though. If the rack is front mounted, it’ll toe in under bumps so at least it won’t dart to the outside. 

 
Rockwood said:
Alignment would be good, geometry less so. I think it’ll be fine unless you’re looking for lap times though. 
Click to expand...
LOL I only play with this stuff on sand cars and haven't noticed unusual tire wear.

 
Last edited by a moderator:
Just so I understand this. You draw a line from the lower ball joint and steering arm centerline. That is supposed to intersect with the center line of the rear end. In my case I have shortened the WB from 104 to 89 3/8. So I assume that will help the situation although I assume those lines will still cross each other before hitting the rear cradle centerline. Sure is easy to put a string on it tomorrow.  I also believe I read moving the rack forward or backward can change the ackerman as well. 

006-c5-corvette-upgrades-easy-bolt-on-diy.jpg

ackerman.jpg

800px-Ackermann_simple_design.svg.png

 
Centerline actually ends up intersecting towards the back of the truck past the center of the rear axle center line. So narrowing the cradle actually made it better. At this point I need to find a rack and build it.

20230411_144347.jpg

 
Whatever rack you end up trying make sure that when you steer right it turns the wheels right 🙂 

Some OE racks work in one direction and some work the opposite. Not fun to find out after its all fit up 😲

 
You must log in or register to reply here.
Back
Top