Bump steer measurements
06-30-2008, 08:37 AM
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Bump steer measurements
Has anyone measured the amount of bump steer on their cars? I've come across several topics where people are attributing handling problems to bump steer and reasoning that it is due to lowering, etc.
I did a measurement on my EG which sits at 3.5" ride height to the jack points on stock size tires. Per corner, I measured 0.1deg toe-out per inch of compression (i.e. 0.04" toe-out/inch compression measured at the rim edge). This is not a significant amount and I would estimate that the amount of toe-in compliance under braking would be greater than this (and yes, under braking, the forces and suspension geometry would suggest a toe-in behaviour - negative scrub radius).
If you've measured bump steer characteristics of your car, please share.
I did a measurement on my EG which sits at 3.5" ride height to the jack points on stock size tires. Per corner, I measured 0.1deg toe-out per inch of compression (i.e. 0.04" toe-out/inch compression measured at the rim edge). This is not a significant amount and I would estimate that the amount of toe-in compliance under braking would be greater than this (and yes, under braking, the forces and suspension geometry would suggest a toe-in behaviour - negative scrub radius).
If you've measured bump steer characteristics of your car, please share.
06-30-2008, 09:11 AM
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Re: Bump steer measurements (bsclywilly)
Will:
I spoke with Jonathan Speigal about this once. He was one of the founders or Progress group suspension and briefly ran a EF Hatch in SCCA F-Production. Jonathan said that with the EF at race height (which many observers thought to be too high on his car, despite that he's done the math and they hadn't...) there was little bump-steer affect and not much that could be improved upon. He thought the EF geometry (once lowered) was about as good as it could be without doing anything illegal in his class.
Bottom line, the Integras, EGs and EFs are pretty good in that area. The later strut cars, on the other hand... Well, a quick tie-rob inspection on any of the WCTC Acuras pretty well tells that story. They have issues.
I spoke with Jonathan Speigal about this once. He was one of the founders or Progress group suspension and briefly ran a EF Hatch in SCCA F-Production. Jonathan said that with the EF at race height (which many observers thought to be too high on his car, despite that he's done the math and they hadn't...) there was little bump-steer affect and not much that could be improved upon. He thought the EF geometry (once lowered) was about as good as it could be without doing anything illegal in his class.
Bottom line, the Integras, EGs and EFs are pretty good in that area. The later strut cars, on the other hand... Well, a quick tie-rob inspection on any of the WCTC Acuras pretty well tells that story. They have issues.
06-30-2008, 09:58 AM
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Re: Bump steer measurements (thawley)
Thanks for confirming my thoughts. I'll be at Mosport this weekend for an event but after, I plan on swapping UCA between left and right to gain more caster. I have heard some 'myths' that this will negatively affect bump steer. No doubt it will change it, i'll see by how much.
06-30-2008, 01:50 PM
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Re: Bump steer measurements (bsclywilly)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bsclywilly »</TD></TR><TR><TD CLASS="quote">Thanks for confirming my thoughts. I'll be at Mosport this weekend for an event but after, I plan on swapping UCA between left and right to gain more caster. I have heard some 'myths' that this will negatively affect bump steer. No doubt it will change it, i'll see by how much.</TD></TR></TABLE>
I would like to know results on this.
I have UCAs swapped on my DC2 (actually, caster adjusting UCAs swapped and max adjusted) with +4* of caster (stock was +1*). It feels like I have more bumpsteer than before, but I also added camber and raised the car 1" when I added caster so I didn't isolate a single variable.
I would like to know results on this.
I have UCAs swapped on my DC2 (actually, caster adjusting UCAs swapped and max adjusted) with +4* of caster (stock was +1*). It feels like I have more bumpsteer than before, but I also added camber and raised the car 1" when I added caster so I didn't isolate a single variable.
06-30-2008, 05:20 PM
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Re: Bump steer measurements (bsclywilly)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bsclywilly »</TD></TR><TR><TD CLASS="quote">Thanks for confirming my thoughts. I'll be at Mosport this weekend for an event but after, I plan on swapping UCA between left and right to gain more caster. I have heard some 'myths' that this will negatively affect bump steer. No doubt it will change it, i'll see by how much.</TD></TR></TABLE>
This is most certainly not a myth. Be prepared to switch the UCA back almost immediately. It is a waste of time and effort. I wasted a couple years with unnerving bumpsteer before I realized it was due to this swap. There was a thread where somebody did the measurements, but it looks to be gone.
It's too bad that the bumpsteer created by swapping the UCA actually creates a very tail happy car, it probably wouldn't be so bad if it generated understeer.
By swapping the control arms, you gain caster but by tilting the spindle back you lower the location point where the steering arm mounts to. Because the steering arm is now at a different angle, the line of action is moved upward and no longer aligns with the instantaneous center of upper and lower control arms. Because the line of action is moved upward, this means that the steering arm effectively becomes 'longer' than it was before, and causes toe-in during bump. This toe-in is sudden and upsets the car tremendously during cornering. And what do you think happens with sudden toe-in during bump? It happens that it ends up pitch the rear end around...my god I had this happen so many times during the autocross (especially in the rain).
I am so glad I figured out that it was this mod that caused the bump steer issues. That was like the biggest lesson I learned about cars and suspension. Bump steer is very very bad. And Honda did a ton of work making sure the EG6-DC2 chassis has almost none of it from the factory.
This is most certainly not a myth. Be prepared to switch the UCA back almost immediately. It is a waste of time and effort. I wasted a couple years with unnerving bumpsteer before I realized it was due to this swap. There was a thread where somebody did the measurements, but it looks to be gone.
It's too bad that the bumpsteer created by swapping the UCA actually creates a very tail happy car, it probably wouldn't be so bad if it generated understeer.
By swapping the control arms, you gain caster but by tilting the spindle back you lower the location point where the steering arm mounts to. Because the steering arm is now at a different angle, the line of action is moved upward and no longer aligns with the instantaneous center of upper and lower control arms. Because the line of action is moved upward, this means that the steering arm effectively becomes 'longer' than it was before, and causes toe-in during bump. This toe-in is sudden and upsets the car tremendously during cornering. And what do you think happens with sudden toe-in during bump? It happens that it ends up pitch the rear end around...my god I had this happen so many times during the autocross (especially in the rain).
I am so glad I figured out that it was this mod that caused the bump steer issues. That was like the biggest lesson I learned about cars and suspension. Bump steer is very very bad. And Honda did a ton of work making sure the EG6-DC2 chassis has almost none of it from the factory.
06-30-2008, 05:59 PM
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Re: Bump steer measurements (ginsu2k)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ginsu2k »</TD></TR><TR><TD CLASS="quote">By swapping the control arms, you gain caster but by tilting the spindle back you lower the location point where the steering arm mounts to. Because the steering arm is now at a different angle, the line of action is moved upward and no longer aligns with the instantaneous center of upper and lower control arms. Because the line of action is moved upward, this means that the steering arm effectively becomes 'longer' than it was before, and causes toe-in during bump. This toe-in is sudden and upsets the car tremendously during cornering. </TD></TR></TABLE>
Is that where you left it, or did you make any attempts to change the bump geometry by spacing the tie-rod away from the control arm mount?
Is that where you left it, or did you make any attempts to change the bump geometry by spacing the tie-rod away from the control arm mount?
06-30-2008, 06:17 PM
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Re: Bump steer measurements (thawley)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thawley »</TD></TR><TR><TD CLASS="quote">
Is that where you left it, or did you make any attempts to change the bump geometry by spacing the tie-rod away from the control arm mount?
</TD></TR></TABLE>
Are you running a bumpsteer kit?
Is that where you left it, or did you make any attempts to change the bump geometry by spacing the tie-rod away from the control arm mount?
</TD></TR></TABLE>
Are you running a bumpsteer kit?
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06-30-2008, 09:13 PM
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Re: Bump steer measurements (ginsu2k)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ginsu2k »</TD></TR><TR><TD CLASS="quote">
This is most certainly not a myth. Be prepared to switch the UCA back almost immediately. It is a waste of time and effort. I wasted a couple years with unnerving bumpsteer before I realized it was due to this swap. There was a thread where somebody did the measurements, but it looks to be gone.
</TD></TR></TABLE>
I'd have to disagree. I have been running swapped UCA for 3 year now. No big mythical bump steer issue at all. Even when i destroy a berm i don't notice any abnormal bump steer.
This is on a 2,200lbs H4 93 civic SI ~700lbs front springs and OE SI front bar.
No spacing of the tie rod or anything. And i am looking to get my car looser thing still pushes.
This is most certainly not a myth. Be prepared to switch the UCA back almost immediately. It is a waste of time and effort. I wasted a couple years with unnerving bumpsteer before I realized it was due to this swap. There was a thread where somebody did the measurements, but it looks to be gone.
</TD></TR></TABLE>
I'd have to disagree. I have been running swapped UCA for 3 year now. No big mythical bump steer issue at all. Even when i destroy a berm i don't notice any abnormal bump steer.
This is on a 2,200lbs H4 93 civic SI ~700lbs front springs and OE SI front bar.
No spacing of the tie rod or anything. And i am looking to get my car looser thing still pushes.
07-01-2008, 04:19 AM
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Re: Bump steer measurements (essex)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by essex »</TD></TR><TR><TD CLASS="quote">Are you running a bumpsteer kit?</TD></TR></TABLE>
If you're asking me the answer is no. As stated earlier the EF's bump steer geometry is pretty much perfect. There's no need for it.
If you're asking me the answer is no. As stated earlier the EF's bump steer geometry is pretty much perfect. There's no need for it.
07-01-2008, 05:32 AM
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Re: Bump steer measurements (slammed_93_hatch)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch »</TD></TR><TR><TD CLASS="quote">
I'd have to disagree. I have been running swapped UCA for 3 year now. No big mythical bump steer issue at all. Even when i destroy a berm i don't notice any abnormal bump steer.
No spacing of the tie rod or anything. And i am looking to get my car looser thing still pushes. </TD></TR></TABLE>
same here.
I'd have to disagree. I have been running swapped UCA for 3 year now. No big mythical bump steer issue at all. Even when i destroy a berm i don't notice any abnormal bump steer.
No spacing of the tie rod or anything. And i am looking to get my car looser thing still pushes. </TD></TR></TABLE>
same here.
07-01-2008, 05:44 AM
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Re: Bump steer measurements (ginsu2k)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ginsu2k »</TD></TR><TR><TD CLASS="quote">
It's too bad that the bumpsteer created by swapping the UCA actually creates a very tail happy car, it probably wouldn't be so bad if it generated understeer.
</TD></TR></TABLE>
Did you measure your bump-steer or you just think that the change in handling was due to bump steer and not the increased caster? The idea of increasing your caster is to improve the camber-steer characteristics to gain more grip at the front. That will certainly make a car more oversteering (allowing you to run softer rear rates which will improve traction on that end).
Generally, bumpsteer, or it's negative effects, will be felt most on the straights, under braking. A toe-out under compression could result in a nervous twitchy sensation in braking and corner entry however, this could be a good thing in small amounts. When cornering at the limit, a toe-out under compression would generally be felt as an understeer reaction to bumps which is generally better than OS reaction and losing the rear. It is quite common to use bump steer as a tuning method on race cars but you need to measure it to know what you're doing!
It's too bad that the bumpsteer created by swapping the UCA actually creates a very tail happy car, it probably wouldn't be so bad if it generated understeer.
</TD></TR></TABLE>
Did you measure your bump-steer or you just think that the change in handling was due to bump steer and not the increased caster? The idea of increasing your caster is to improve the camber-steer characteristics to gain more grip at the front. That will certainly make a car more oversteering (allowing you to run softer rear rates which will improve traction on that end).
Generally, bumpsteer, or it's negative effects, will be felt most on the straights, under braking. A toe-out under compression could result in a nervous twitchy sensation in braking and corner entry however, this could be a good thing in small amounts. When cornering at the limit, a toe-out under compression would generally be felt as an understeer reaction to bumps which is generally better than OS reaction and losing the rear. It is quite common to use bump steer as a tuning method on race cars but you need to measure it to know what you're doing!
07-01-2008, 05:49 AM
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Re: Bump steer measurements (slammed_93_hatch)
ginsu2 and slammed_93,
Did you find the increase in steering effort dramatic? Or are you guys running p/s still?
Did you find the increase in steering effort dramatic? Or are you guys running p/s still?
07-01-2008, 05:52 AM
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Re: Bump steer measurements (bsclywilly)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bsclywilly »</TD></TR><TR><TD CLASS="quote">you need to measure it to know what you're doing! </TD></TR></TABLE>
So speaketh the recently deported, Canadian engineer...
Hey Will, you still have all the measurements we took off my car?
So speaketh the recently deported, Canadian engineer...
Hey Will, you still have all the measurements we took off my car?
07-01-2008, 06:22 AM
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Re: Bump steer measurements (thawley)
Yup, I never emailed it to you? I was using some demo software at the time. I'll dig it up and send to you again. Never got to do a writeup on it but I remember the main thing I was looking at was roll centre behaviour at different ride heights and the conclusion was that the ride height you were runnign at the time was about as low as i'd want to go...so, just right!
By the way, our beautiful country is celebrating it's 141st birthday today, Canada Day, it is so aptly named
By the way, our beautiful country is celebrating it's 141st birthday today, Canada Day, it is so aptly named
07-01-2008, 06:53 AM
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Re: Bump steer measurements (bsclywilly)
I've measured the bump steer on an EG with swapped uca's after resetting toe to zero. IIRC it was 1/4" of toe in per 1/2" of bump or something exceedingly horrible. I'd have to find and check my notes on it again, but it was horrible.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch »</TD></TR><TR><TD CLASS="quote">
I'd have to disagree. I have been running swapped UCA for 3 year now. No big mythical bump steer issue at all. Even when i destroy a berm i don't notice any abnormal bump steer.
This is on a 2,200lbs H4 93 civic SI ~700lbs front springs and OE SI front bar.
No spacing of the tie rod or anything. And i am looking to get my car looser thing still pushes. </TD></TR></TABLE>
You won't feel it from the drivers seat unless you have an incredibly sensitive butt-o-meter. The tape measure doesn't lie. Oh, and to fix your push, put some narrower rear tires on that thing, bring up your front spring rates and dial out your rear camber.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch »</TD></TR><TR><TD CLASS="quote">
I'd have to disagree. I have been running swapped UCA for 3 year now. No big mythical bump steer issue at all. Even when i destroy a berm i don't notice any abnormal bump steer.
This is on a 2,200lbs H4 93 civic SI ~700lbs front springs and OE SI front bar.
No spacing of the tie rod or anything. And i am looking to get my car looser thing still pushes. </TD></TR></TABLE>
You won't feel it from the drivers seat unless you have an incredibly sensitive butt-o-meter. The tape measure doesn't lie. Oh, and to fix your push, put some narrower rear tires on that thing, bring up your front spring rates and dial out your rear camber.
07-01-2008, 07:31 AM
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Re: Bump steer measurements (bsclywilly)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bsclywilly »</TD></TR><TR><TD CLASS="quote">By the way, our beautiful country is celebrating it's 141st birthday today, Canada Day, it is so aptly named </TD></TR></TABLE>
Happy Birthday
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x »</TD></TR><TR><TD CLASS="quote">I've measured the bump steer on an EG with swapped uca's after resetting toe to zero. IIRC it was 1/4" of toe in per 1/2" of bump or something exceedingly horrible. I'd have to find and check my notes on it again, but it was horrible.</TD></TR></TABLE>
Nate, what else did you learn? Do your findings confirm the second hand info I mentioned above?
</TD></TR></TABLE>Happy Birthday
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x »</TD></TR><TR><TD CLASS="quote">I've measured the bump steer on an EG with swapped uca's after resetting toe to zero. IIRC it was 1/4" of toe in per 1/2" of bump or something exceedingly horrible. I'd have to find and check my notes on it again, but it was horrible.</TD></TR></TABLE>
Nate, what else did you learn? Do your findings confirm the second hand info I mentioned above?
07-01-2008, 08:00 AM
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Re: Bump steer measurements (thawley)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thawley »</TD></TR><TR><TD CLASS="quote">
Nate, what else did you learn? Do your findings confirm the second hand info I mentioned above?</TD></TR></TABLE>
Yeah, pretty much confirmed what you said. The bumpsteer with stock geometry was so minimal as to be negligible when lowered to race ride height. For my car, this applied to both front and rear. Did you know that the track gets narrower as you lower the car?
I never played with bump steer adjusters. The theory is sound though. As was mentioned before, swapping the uca lowers the point that the tie rod attaches to the knuckle. If you spaced the tie rod back up you should be able to zero out the bumpsteer again.
Nate, what else did you learn? Do your findings confirm the second hand info I mentioned above?</TD></TR></TABLE>
Yeah, pretty much confirmed what you said. The bumpsteer with stock geometry was so minimal as to be negligible when lowered to race ride height. For my car, this applied to both front and rear. Did you know that the track gets narrower as you lower the car?
I never played with bump steer adjusters. The theory is sound though. As was mentioned before, swapping the uca lowers the point that the tie rod attaches to the knuckle. If you spaced the tie rod back up you should be able to zero out the bumpsteer again.
07-01-2008, 08:27 AM
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Re: Bump steer measurements (solo-x)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x »</TD></TR><TR><TD CLASS="quote">
You won't feel it from the drivers seat unless you have an incredibly sensitive butt-o-meter. The tape measure doesn't lie. Oh, and to fix your push, put some narrower rear tires on that thing, bring up your front spring rates and dial out your rear camber. </TD></TR></TABLE>
Ehh i put them on like that
I run 225s up front, and 205s in the rear. The problem doesn't seem to be with the front, from were the push is. I am making one change at a time, but as of late i haven't been able to get back out to the track. First was the 225s up front, then it was a bump in rear spring, then it shock adjustment. Next I am going to pull out some rear camber, and the last thing im going to try is going 50lbs up on the front spring.
You won't feel it from the drivers seat unless you have an incredibly sensitive butt-o-meter. The tape measure doesn't lie. Oh, and to fix your push, put some narrower rear tires on that thing, bring up your front spring rates and dial out your rear camber.
</TD></TR></TABLE>Ehh i put them on like that
I run 225s up front, and 205s in the rear. The problem doesn't seem to be with the front, from were the push is. I am making one change at a time, but as of late i haven't been able to get back out to the track. First was the 225s up front, then it was a bump in rear spring, then it shock adjustment. Next I am going to pull out some rear camber, and the last thing im going to try is going 50lbs up on the front spring.
07-01-2008, 08:28 AM
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Re: Bump steer measurements (solo-x)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x »</TD></TR><TR><TD CLASS="quote">Did you know that the track gets narrower as you lower the car?</TD></TR></TABLE>
Makes sense. I've never bothered to measure mine. If I'm leaving anything on the table it would only mean more fender beating. No big deal on the front, but the rears were a PAIN to get what little clearance I've got.
Makes sense. I've never bothered to measure mine. If I'm leaving anything on the table it would only mean more fender beating. No big deal on the front, but the rears were a PAIN to get what little clearance I've got.
07-01-2008, 01:46 PM
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Re: Bump steer measurements (solo-x)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x »</TD></TR><TR><TD CLASS="quote">
As was mentioned before, swapping the uca lowers the point that the tie rod attaches to the knuckle. If you spaced the tie rod back up you should be able to zero out the bumpsteer again.</TD></TR></TABLE>
Since lowering raises the tie rod end compared to the chassis (or lowers the chassis relative to the tie rod end), wouldn't lowing further simply undo the bumpsteer created by the added caster?
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bsclywilly »</TD></TR><TR><TD CLASS="quote">ginsu2 and slammed_93,
Did you find the increase in steering effort dramatic? Or are you guys running p/s still?
</TD></TR></TABLE>
I have the stock powersteering in my DC2, and +4* of caster. Steering effort is increased, but to a level that I prefer.
As was mentioned before, swapping the uca lowers the point that the tie rod attaches to the knuckle. If you spaced the tie rod back up you should be able to zero out the bumpsteer again.</TD></TR></TABLE>
Since lowering raises the tie rod end compared to the chassis (or lowers the chassis relative to the tie rod end), wouldn't lowing further simply undo the bumpsteer created by the added caster?
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bsclywilly »</TD></TR><TR><TD CLASS="quote">ginsu2 and slammed_93,
Did you find the increase in steering effort dramatic? Or are you guys running p/s still?
</TD></TR></TABLE>
I have the stock powersteering in my DC2, and +4* of caster. Steering effort is increased, but to a level that I prefer.
07-01-2008, 07:03 PM
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Re: Bump steer measurements (TunerN00b)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TunerN00b »</TD></TR><TR><TD CLASS="quote">
Since lowering raises the tie rod end compared to the chassis (or lowers the chassis relative to the tie rod end), wouldn't lowing further simply undo the bumpsteer created by the added caster?</TD></TR></TABLE>
Negative. The issue is not the tie rod end relative to the chassis, it's the tie rod end (or rather angle) relative to the upper and lower control arms.
Since lowering raises the tie rod end compared to the chassis (or lowers the chassis relative to the tie rod end), wouldn't lowing further simply undo the bumpsteer created by the added caster?</TD></TR></TABLE>
Negative. The issue is not the tie rod end relative to the chassis, it's the tie rod end (or rather angle) relative to the upper and lower control arms.
07-02-2008, 01:19 PM
#22
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Re: Bump steer measurements (solo-x)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x »</TD></TR><TR><TD CLASS="quote">
Negative. The issue is not the tie rod end relative to the chassis, it's the tie rod end (or rather angle) relative to the upper and lower control arms.</TD></TR></TABLE>
This answer tells me that I don't understand the causes of bumpsteer nearly as well as I had thought.
Research time for me.
Negative. The issue is not the tie rod end relative to the chassis, it's the tie rod end (or rather angle) relative to the upper and lower control arms.</TD></TR></TABLE>
This answer tells me that I don't understand the causes of bumpsteer nearly as well as I had thought.
Research time for me.
07-02-2008, 04:46 PM
#23
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Re: Bump steer measurements (thawley)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thawley »</TD></TR><TR><TD CLASS="quote">
Is that where you left it, or did you make any attempts to change the bump geometry by spacing the tie-rod away from the control arm mount?
</TD></TR></TABLE>
No I was not able to space the tie-rod from the mounting point on the spindle. If my analysis is correct, you would need to move it up to correct the bump steer, which would not leave enough thread on the ball joint. I believe you would have to buy some after market tie rod ends.
Is that where you left it, or did you make any attempts to change the bump geometry by spacing the tie-rod away from the control arm mount?
</TD></TR></TABLE>
No I was not able to space the tie-rod from the mounting point on the spindle. If my analysis is correct, you would need to move it up to correct the bump steer, which would not leave enough thread on the ball joint. I believe you would have to buy some after market tie rod ends.
07-02-2008, 04:50 PM
#24
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Re: Bump steer measurements (slammed_93_hatch)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch »</TD></TR><TR><TD CLASS="quote">
I'd have to disagree. I have been running swapped UCA for 3 year now. No big mythical bump steer issue at all. Even when i destroy a berm i don't notice any abnormal bump steer.
This is on a 2,200lbs H4 93 civic SI ~700lbs front springs and OE SI front bar.
No spacing of the tie rod or anything. And i am looking to get my car looser thing still pushes. </TD></TR></TABLE>
Yeah, I wonder why. You have probably 2.5x the spring rate that I'm running. You have very little wheel travel with 700lb springs, so that is why you are most likely not suffering as much. But, you are suffering from bump steer you just can't feel it as much.
If you are looking for a looser car, why don't you lower the spring rate? You would get a lot more traction in the front and the car wouldn't understeer nearly as much. Remember, stock type-R's come with 250lb springs I don't know why anybody would need to run 700lb springs unless they had a huge front splitter and were making tons of downforce.
I'd have to disagree. I have been running swapped UCA for 3 year now. No big mythical bump steer issue at all. Even when i destroy a berm i don't notice any abnormal bump steer.
This is on a 2,200lbs H4 93 civic SI ~700lbs front springs and OE SI front bar.
No spacing of the tie rod or anything. And i am looking to get my car looser thing still pushes. </TD></TR></TABLE>
Yeah, I wonder why. You have probably 2.5x the spring rate that I'm running. You have very little wheel travel with 700lb springs, so that is why you are most likely not suffering as much. But, you are suffering from bump steer you just can't feel it as much.
If you are looking for a looser car, why don't you lower the spring rate? You would get a lot more traction in the front and the car wouldn't understeer nearly as much. Remember, stock type-R's come with 250lb springs I don't know why anybody would need to run 700lb springs unless they had a huge front splitter and were making tons of downforce.
07-02-2008, 05:00 PM
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Re: Bump steer measurements (bsclywilly)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bsclywilly »</TD></TR><TR><TD CLASS="quote">
Generally, bumpsteer, or it's negative effects, will be felt most on the straights, under braking. A toe-out under compression could result in a nervous twitchy sensation in braking and corner entry however, this could be a good thing in small amounts. When cornering at the limit, a toe-out under compression would generally be felt as an understeer reaction to bumps which is generally better than OS reaction and losing the rear. It is quite common to use bump steer as a tuning method on race cars but you need to measure it to know what you're doing! </TD></TR></TABLE>
This is exactly what I was feeling, although I believe we are getting toe-in with compression by doing the UCA swap. I do most of my driving on mountain roads very late at night and they are not particularly smooth. I don't push the limits very much, but I do like to get up to speed and brake hard for the corners, which is where the bump steer would affect me the most. Honestly, I measure it in terms of fear factor. I was nervous while the car was nervous, it was really, really noticeable when I switched them back how much more smoothly the car behaved under braking. I mean night/day difference. Of course, I've raced for 5+ years and I'm old and I feel my car pretty well.
I know some people think the whole bump steer thing is a myth and doesn't affect you but they either aren't driving at/near the limit, or they don't have much suspension travel. Bump steer is a very big deal. Every single F1 car has all their steering arms aligned perfectly with their control arms, because that is the easiest way to ensure they have ZERO bump steer. Think about it, they do this when their wheels travel like 2inches at the most on many tracks.
Generally, bumpsteer, or it's negative effects, will be felt most on the straights, under braking. A toe-out under compression could result in a nervous twitchy sensation in braking and corner entry however, this could be a good thing in small amounts. When cornering at the limit, a toe-out under compression would generally be felt as an understeer reaction to bumps which is generally better than OS reaction and losing the rear. It is quite common to use bump steer as a tuning method on race cars but you need to measure it to know what you're doing! </TD></TR></TABLE>
This is exactly what I was feeling, although I believe we are getting toe-in with compression by doing the UCA swap. I do most of my driving on mountain roads very late at night and they are not particularly smooth. I don't push the limits very much, but I do like to get up to speed and brake hard for the corners, which is where the bump steer would affect me the most. Honestly, I measure it in terms of fear factor. I was nervous while the car was nervous, it was really, really noticeable when I switched them back how much more smoothly the car behaved under braking. I mean night/day difference. Of course, I've raced for 5+ years and I'm old and I feel my car pretty well.
I know some people think the whole bump steer thing is a myth and doesn't affect you but they either aren't driving at/near the limit, or they don't have much suspension travel. Bump steer is a very big deal. Every single F1 car has all their steering arms aligned perfectly with their control arms, because that is the easiest way to ensure they have ZERO bump steer. Think about it, they do this when their wheels travel like 2inches at the most on many tracks.