Roll Center??

cliff257 · 01-07-2007, 03:14 PM

Can anyone explain what bump steer is? how it effects the car and what downfalls the subaru's have in these areas and what is done to fix the problems.

JKonquer · 01-07-2007, 06:37 PM

is this same situation where you turn hard and it makes some kind of bump or bounces on the car?

cliff257 · 01-07-2007, 09:23 PM

well i found this if anybody is still curious. Bump steer is when the front toe setting changes as the suspension moves up and down. This happens when the arc that the hub travels on during a bump or a droop is not the same as the arc of the tie-rod end. If the toe changes more than a very small amount the front wheels begin to steer themselves without any input. making the car feel unstable on uneven and bumpy roads.

WRXSTi0487 · 01-08-2007, 02:42 PM

To add the the above...considering we just went over this in underbody at UTI, It is basicly caused by the car sitting too low and when you go over a bump there is no more travel left on the tie rod ends.

**SWortham** · 01-08-2007, 03:02 PM

^ Yep, camber affects toe and bump steer will occur as long as camber curves exist. Car manufacturers will try to minimize bump steer the best they can by designing the suspension geometry so that the car is resting at a mild part of the camber curve.

If you lower the car drastically as mentioned above, the car will be resting at a less-than-optimal position of the camber curve. This will increase positive camber gain through the typical suspension travel, therefore increasing change in dynamic toe, and increasing bump steer. If you have lowered your car, this is another thing a balljoint relocation kit could help with since the attachment points are changed to nearly restore the car's OEM camber curves.

cliff257 · 01-09-2007, 05:04 AM

nice thanks thats more or less what i have been hearing but what of this role center stuff. im an not sure exactly what that means at this point. i know that whiteline is coming out with a role center kit for the sti like the evo and was now wondering what role center is??

**fullerton** · 01-09-2007, 05:21 AM

fwiw- Six-Gun racing is working on upgrading their Ball Joint Extender to include a new tie-rod extender. This will help fix your camber curve back to normal (or better) on dropped vehicles and reduce bump steer.

**Turninconcepts.com** · 01-09-2007, 06:54 AM

Quote:

Originally Posted by WRXSTi0487

To add the the above...considering we just went over this in underbody at UTI, It is basicly caused by the car sitting too low and when you go over a bump there is no more travel left on the tie rod ends.

correct, but there's also the factor of the angle of the tie rods in relation to the rest of the angles of your suspension components. in our setup it's the relation of angle between the tie rod and the control arm.

There's been a "bumpsteer mod" being done by the UK shop powerstation for years that hasn't really caught on over here. Basically they shim the steering rack to help alleviate this bump steer problem. the thing is - the shim amount is not set and varies a little bit from car to car.

RainMaker · 01-09-2007, 09:57 AM

I really really am anxious for either 6-gun or Whiteline to release a roll-center kit (with bump-steer tie-rod spacer).

Anyone know what the time frame is on the Whiteline or the 6-Gun part?

Chris

***sciolist*** · 01-09-2007, 10:08 AM

^ Why don't you just email Tom?

cliff257 · 01-09-2007, 10:31 AM

not sure about the 6-gun kit but it is just to exspensive. i was told that the whiteline kit will be out shortly. the prototypes will be in testing within the month from there i dont know. but the whiteline kit (they say) isnt not for bump steer or the camber curve it is for the roll center that subarus dont have to many problems with. whether it will help with the camber curve and bump steer is what i am curious about.

**fullerton** · 01-09-2007, 10:48 AM

Quote:

Originally Posted by RainMaker

I really really am anxious for either 6-gun or Whiteline to release a roll-center kit (with bump-steer tie-rod spacer).

Anyone know what the time frame is on the Whiteline or the 6-Gun part?

Chris

The 6-Gun was released, but their tie rod extenders were faulty. They are working on a fix as I type, but no release date has been scheduled.

Whiteline has confirmed they are working on a kit, but state they are months off.

AnorexicSTI · 01-09-2007, 10:54 AM

Quote:

Originally Posted by Turninconcepts.com

correct, but there's also the factor of the angle of the tie rods in relation to the rest of the angles of your suspension components. in our setup it's the relation of angle between the tie rod and the control arm.

There's been a "bumpsteer mod" being done by the UK shop powerstation for years that hasn't really caught on over here. Basically they shim the steering rack to help alleviate this bump steer problem. the thing is - the shim amount is not set and varies a little bit from car to car.

Shim it in which direction? It mounts with a D bracket on the passenger side and a similar bracket on the driver side... do you mean putting washers underneath so the rack sits further away from the subframe it bolts to?

LOLSTi · 01-09-2007, 10:57 AM

Quote:

Originally Posted by cliff257

not sure about the 6-gun kit but it is just to exspensive. i was told that the whiteline kit will be out shortly. the prototypes will be in testing within the month from there i dont know. but the whiteline kit (they say) isnt not for bump steer or the camber curve it is for the roll center that subarus dont have to many problems with. whether it will help with the camber curve and bump steer is what i am curious about.

.....

cliff257 · 01-09-2007, 05:09 PM

oh yeah i like to cheat and get all the answers from you guys. kinda of like cliff notes.

01-07-2007, 03:14 PM	#1
cliff257 Junior STI Driver Car: 04 sti/08 335xi. Fav Mod: doug topspeed Location: spartanburg, sc Posts: 178 IWSTI Addict since: May 2006 Trader Rating: (1)	Roll Center?? Can anyone explain what bump steer is? how it effects the car and what downfalls the subaru's have in these areas and what is done to fix the problems. This ad is not endorsed by this member. Please register or login to hide this ad. Last edited by cliff257; 01-09-2007 at 10:39 AM.

01-08-2007, 03:02 PM	#5
SWortham Gold Member Car: 06 Subaru WRX STI Fav Mod: Ohlins struts Location: Mckinney, TX Posts: 759 IWSTI Addict since: Oct 2006 Trader Rating: (0)	^ Yep, camber affects toe and bump steer will occur as long as camber curves exist. Car manufacturers will try to minimize bump steer the best they can by designing the suspension geometry so that the car is resting at a mild part of the camber curve. If you lower the car drastically as mentioned above, the car will be resting at a less-than-optimal position of the camber curve. This will increase positive camber gain through the typical suspension travel, therefore increasing change in dynamic toe, and increasing bump steer. If you have lowered your car, this is another thing a balljoint relocation kit could help with since the attachment points are changed to nearly restore the car's OEM camber curves. Last edited by SWortham; 01-08-2007 at 03:42 PM.

01-09-2007, 05:09 PM	#15
cliff257 Junior STI Driver Car: 04 sti/08 335xi. Fav Mod: doug topspeed Location: spartanburg, sc Posts: 178 IWSTI Addict since: May 2006 Trader Rating: (1)	oh yeah i like to cheat and get all the answers from you guys. kinda of like cliff notes. This ad is not endorsed by this member. Please register or login to hide this ad.

New To Site?	Need Help?	More
REGISTER FOR FREE! IWSTI Rules/Signature Rules Create a Member Journal Bookmark IWSTI Tell your friends about IWSTI	Frequently Asked Questions Did you forget your password? Make a suggestion or report a bug Mark Forums Read Contact Us	Member Journals Forum Pictures & Photography Forum GR Series (08+) Marketplace GD Series (03/04-07) Marketplace Hot eBay Deals Forum Beyond Off Topic

01-07-2007, 06:37 PM	#2
JKonquer Spec C Club Car: AW 05 WRX STi Fav Mod: Recaro Racing Seats Location: CA-burbank and palm sprin Posts: 2,197 IWSTI Addict since: Sep 2004 Trader Rating: (2)	is this same situation where you turn hard and it makes some kind of bump or bounces on the car?

01-07-2007, 09:23 PM	#3
cliff257 Junior STI Driver Car: 04 sti/08 335xi. Fav Mod: doug topspeed Location: spartanburg, sc Posts: 178 IWSTI Addict since: May 2006 Trader Rating: (1)	well i found this if anybody is still curious. Bump steer is when the front toe setting changes as the suspension moves up and down. This happens when the arc that the hub travels on during a bump or a droop is not the same as the arc of the tie-rod end. If the toe changes more than a very small amount the front wheels begin to steer themselves without any input. making the car feel unstable on uneven and bumpy roads.

01-08-2007, 02:42 PM	#4
WRXSTi0487 Silver Member Car: 07 STi LTD #091 UGM Fav Mod: APS Exhaust Location: Elberta, AL Posts: 241 IWSTI Addict since: Aug 2006 Trader Rating: (7)	To add the the above...considering we just went over this in underbody at UTI, It is basicly caused by the car sitting too low and when you go over a bump there is no more travel left on the tie rod ends.

01-09-2007, 05:04 AM	#6
cliff257 Junior STI Driver Car: 04 sti/08 335xi. Fav Mod: doug topspeed Location: spartanburg, sc Posts: 178 IWSTI Addict since: May 2006 Trader Rating: (1)	nice thanks thats more or less what i have been hearing but what of this role center stuff. im an not sure exactly what that means at this point. i know that whiteline is coming out with a role center kit for the sti like the evo and was now wondering what role center is??

01-09-2007, 05:21 AM	#7
fullerton Halliburton Mercenary Car: AW GDF-D Fav Mod: Q-Rack Location: P&L 30R Land Posts: 17,078 IWSTI Addict since: Oct 2005 Trader Rating: (12)	fwiw- Six-Gun racing is working on upgrading their Ball Joint Extender to include a new tie-rod extender. This will help fix your camber curve back to normal (or better) on dropped vehicles and reduce bump steer.

01-09-2007, 09:57 AM	#9
RainMaker The Next Petter Solberg Car: 08 Z06 Corvette Fav Mod: Jack Jack Location: Portland, OR Posts: 882 IWSTI Addict since: Oct 2005 Trader Rating: (3)	I really really am anxious for either 6-gun or Whiteline to release a roll-center kit (with bump-steer tie-rod spacer). Anyone know what the time frame is on the Whiteline or the 6-Gun part? Chris

01-09-2007, 10:08 AM	#10
*sciolist* Spiteful Old Codger Location: Bend, OR Posts: 2,345 IWSTI Addict since: Jul 2003 Trader Rating: (1)	^ Why don't you just email Tom?

01-09-2007, 10:31 AM	#11
cliff257 Junior STI Driver Car: 04 sti/08 335xi. Fav Mod: doug topspeed Location: spartanburg, sc Posts: 178 IWSTI Addict since: May 2006 Trader Rating: (1)	not sure about the 6-gun kit but it is just to exspensive. i was told that the whiteline kit will be out shortly. the prototypes will be in testing within the month from there i dont know. but the whiteline kit (they say) isnt not for bump steer or the camber curve it is for the roll center that subarus dont have to many problems with. whether it will help with the camber curve and bump steer is what i am curious about.