Evaluation of the bump steer phenomena on 928
01-12-2003, 10:34 PM
#16
Advanced
Join Date: Dec 2002
Location: Southern California
Posts: 81
Likes: 0
Received 0 Likes
on
0 Posts
I believe the tendency of the car to steer due to wide tires is called "hunting" and has absoultely nothing to do with bump steer which as some have pointed out here is due to dynamic suspension geometry changes and alignment issues.
Wider tires, when encountering uneven road surfaces such as ruts or a crowned road put higher forces on the steering system and do cause the car to "hunt" depending on all the variables.
I'm not sure if a 1/6th degree change in steering is reason to be alarmed.
Wider tires, when encountering uneven road surfaces such as ruts or a crowned road put higher forces on the steering system and do cause the car to "hunt" depending on all the variables.
I'm not sure if a 1/6th degree change in steering is reason to be alarmed.
01-12-2003, 11:19 PM
#17
Erik,
Perhaps you can get in touch with a German
928 Club, or any Porsche Club who has a contact within the Porsche Engineering office - not as big a stretch as you might imagine -.
There have to be engineering archives, somewhere, maybe a Porsche historian...
Give it a shot you could become "THE MAN" when it comes to 928 steering geometry.
The steering rut/tracking issue is as you can see a matter of personal experience. I only had one problem and after remorseless interrogation my wife finally admitted that she bounced the right front off a curb. Although, some folks who have gone to wider tires have made mention of the problem.
Hang in there, Erik. We 928 owners are equal to any 911 owner when it comes to being overbearing, opinionated, know-it-all's. sHARk bigots if you will.
You are on the right path, and we appreciate it even if the love doesn't show.
John S. 82', Weissach,Auto., 'Pattycakes'
P.S. We early model folks have only the single set of adjusters -unless we purchase the additional set of adjustable perches and associated hardware our adjustment parameters are limited - ride heigth - albiet the same 30 -33 mm
Perhaps you can get in touch with a German
928 Club, or any Porsche Club who has a contact within the Porsche Engineering office - not as big a stretch as you might imagine -.
There have to be engineering archives, somewhere, maybe a Porsche historian...
Give it a shot you could become "THE MAN" when it comes to 928 steering geometry.
The steering rut/tracking issue is as you can see a matter of personal experience. I only had one problem and after remorseless interrogation my wife finally admitted that she bounced the right front off a curb. Although, some folks who have gone to wider tires have made mention of the problem.
Hang in there, Erik. We 928 owners are equal to any 911 owner when it comes to being overbearing, opinionated, know-it-all's. sHARk bigots if you will.
You are on the right path, and we appreciate it even if the love doesn't show.
John S. 82', Weissach,Auto., 'Pattycakes'
P.S. We early model folks have only the single set of adjusters -unless we purchase the additional set of adjustable perches and associated hardware our adjustment parameters are limited - ride heigth - albiet the same 30 -33 mm
01-12-2003, 11:19 PM
#18
Cottage Industry Sponsor
Lifetime Rennlist
Member
Lifetime Rennlist
Member
When my car was lowered, it behaved quite strange on bumps in turns. I had to correct steering a lot - it felt as if the bumps would redirect the car.
Since the car's ride height has been brought back to a normal height, this is completely gone, and the car tracks like a on rails on pretty much any type of surface.
Check the DEVEK catalog for their Bump Steer Kit; the description might answer some of your questions better than I can.
Since the car's ride height has been brought back to a normal height, this is completely gone, and the car tracks like a on rails on pretty much any type of surface.
Check the DEVEK catalog for their Bump Steer Kit; the description might answer some of your questions better than I can.
01-12-2003, 11:23 PM
#19
Pro
Join Date: Oct 2002
Location: New Hampshire
Posts: 598
Likes: 0
Received 0 Likes
on
0 Posts
Erik: Please excuse my use of American slang. I do forget that there is a much broader audience to this forum than just here in the USA.
Not being familiar with a lot of these terms and concepts of suspension I am eager to learn, so when you mentioned "bump steer" I was naturally interested to know more.
Thank you for your suggestion to investigate the Internet for more information. I did find a most thorough discussion about bump street at:
<a href="http://www.bakerprecision.com/longacr17a.htm" target="_blank">http://www.bakerprecision.com/longacr17a.htm</a>
I must now admit that this is more information about suspension travel and effect than I care to know. However I do know one small fact that should alleviate any concerns that you have about the 928 front suspension and that it is "based on Porsche's earlier Type 804 (1962 Grand Prix single seater) and the 904 race cars."
That's good enough for me, or at least to get me to and from the grocery store.
Gordon
Not being familiar with a lot of these terms and concepts of suspension I am eager to learn, so when you mentioned "bump steer" I was naturally interested to know more.
Thank you for your suggestion to investigate the Internet for more information. I did find a most thorough discussion about bump street at:
<a href="http://www.bakerprecision.com/longacr17a.htm" target="_blank">http://www.bakerprecision.com/longacr17a.htm</a>
I must now admit that this is more information about suspension travel and effect than I care to know. However I do know one small fact that should alleviate any concerns that you have about the 928 front suspension and that it is "based on Porsche's earlier Type 804 (1962 Grand Prix single seater) and the 904 race cars."
That's good enough for me, or at least to get me to and from the grocery store.
Gordon
01-13-2003, 12:43 PM
#20
Burning Brakes
Eric:
Something is definately wrong with your suspension. You say it was rebuilt. My SWAG is that is was not done properly. Maybe they installed either S4 upper or S4 lower control arms, but not both. <img border="0" title="" alt="[Eek!]" src="eek.gif" />
My GT's toe is about 0.5 degrees 'out' when on the flat ground. It goes out more when the supension gets unloaded (car is raised), and it goes out more when the suspension is loaded more (pulled down the weigh the front suspension more). Thus, it goes out more regardless of loading. YMMV.
Something is definately wrong with your suspension. You say it was rebuilt. My SWAG is that is was not done properly. Maybe they installed either S4 upper or S4 lower control arms, but not both. <img border="0" title="" alt="[Eek!]" src="eek.gif" />
My GT's toe is about 0.5 degrees 'out' when on the flat ground. It goes out more when the supension gets unloaded (car is raised), and it goes out more when the suspension is loaded more (pulled down the weigh the front suspension more). Thus, it goes out more regardless of loading. YMMV.
01-13-2003, 03:39 PM
#22
Racer
Join Date: Aug 2002
Location: Costa Mesa, CA
Posts: 399
Likes: 0
Received 0 Likes
on
0 Posts
I'm not sure, but could it be a bum steer?
Sorry, couldn't resist.
P.S. to Erik:
In American slang, a "bum steer" is to give misleading instructions to someone, to direct
someone in the wrong way (not always intentionally}
It has nothing to do with what you sit on...
Sorry, couldn't resist.
P.S. to Erik:
In American slang, a "bum steer" is to give misleading instructions to someone, to direct
someone in the wrong way (not always intentionally}
It has nothing to do with what you sit on...
01-14-2003, 12:55 AM
#24
Addict
Rennlist Member
Rennlist Member
KBlair,
I highly recommend:
Gran Turismo East
3306 Shallowford Road
770-455-0347
They have a great reputation and specialize in exotics. Although I haven't been there in about 10 years, a Google search yielded quite a few hits, many of which are enthusiasts recommending Gran Turismo.
It's a small place that doesn't look like much on the outside but they are very experienced and believe in doing the job right.
Ask for Harris or Jeff Mills.
Click here for an article showing Jeff aligning a Pantera.
I highly recommend:
Gran Turismo East
3306 Shallowford Road
770-455-0347
They have a great reputation and specialize in exotics. Although I haven't been there in about 10 years, a Google search yielded quite a few hits, many of which are enthusiasts recommending Gran Turismo.
It's a small place that doesn't look like much on the outside but they are very experienced and believe in doing the job right.
Ask for Harris or Jeff Mills.
Click here for an article showing Jeff aligning a Pantera.
Last edited by Scott G; 09-28-2004 at 09:45 PM.
01-14-2003, 04:53 AM
#25
Burning Brakes
Join Date: Dec 2002
Location: Airlie Beach, Australia
Posts: 870
Likes: 0
Received 0 Likes
on
0 Posts
Erik,
Good to read the "bump steer" exchanges.
Good to hear another golden oldie has a 928. I am 63 and have a MY89 928S4 Auto. My car tramlines a little with Falken 326 front tyres - its the tyres not the car. It tracks like on rails - especially at 180-200km/h. I lived in Taastrup in the 1960's and worked for Caltex/Chevron in Adelgade,Copenhagen. A New Zealander by birth I now live in tropical northern Queensland, Australia. I enjoy the 928 immensely along with my "hairdresser's" BMW Z3 2.8l and Subaru Outback 2.5
Doug H
Good to read the "bump steer" exchanges.
Good to hear another golden oldie has a 928. I am 63 and have a MY89 928S4 Auto. My car tramlines a little with Falken 326 front tyres - its the tyres not the car. It tracks like on rails - especially at 180-200km/h. I lived in Taastrup in the 1960's and worked for Caltex/Chevron in Adelgade,Copenhagen. A New Zealander by birth I now live in tropical northern Queensland, Australia. I enjoy the 928 immensely along with my "hairdresser's" BMW Z3 2.8l and Subaru Outback 2.5
Doug H
01-14-2003, 05:08 AM
#26
Drifting
erik, perhaps americans are not familiar with european roads and as such have no experience of bumps!
i can agree that 'tramlining' due to tyre choice definitely occurs sometimes making the car feel nervous or fidgety on uneven surfaces.
ed, have you seen the size difference between the suspension parts upper and lower from the different model years? it must be nearly impossible for the scenario to arise with mixed upper and lower arms.
i can agree that 'tramlining' due to tyre choice definitely occurs sometimes making the car feel nervous or fidgety on uneven surfaces.
ed, have you seen the size difference between the suspension parts upper and lower from the different model years? it must be nearly impossible for the scenario to arise with mixed upper and lower arms.
01-14-2003, 07:33 AM
#27
Burning Brakes
Thread Starter
Join Date: Apr 2002
Location: Denmark
Posts: 881
Likes: 0
Received 0 Likes
on
0 Posts
Hi all,
Sorry for late answering, but sometimes I have a job to do. Yesterday I went to Munich in Germany for a meeting with a supplier in oil and gas industry. I always stocked there due to heavy snow-fall but went back in the middle of the night.
Here you have my comments to your positive input to my project:
Jim: Thanks for your good and constructive answer – By the way I like your avatar
Delta: That’s is 1/6 degree per 10 mm!
John: Thank for your nice thinking – I do not if I want to be ‘The Man’ but I want to find the answer, and when I find I will gladly share my experience with other 928 owners
Yes I will certainly go in touch with Germans, I just became a member of Porsche Club 928, Germany
Nicole: I agree, when the car is lowered it looks smart, but ‘the cost’ is less driving properties – Thanks for the tip about Devek, maybe Mark has the answer, I will check
Gordon: No problem, that good for me to be familiar with American slang
Ed: How will you explain that the toe-in disappears if you adjust the toe when the car is ‘high’?
Old & New: It was a spelling/typing failure instead of ‘torn’ I meant ‘corn’ – And I do not think I hid yours
Rob: Thanks for the slang info – I think you are right, it seams that ‘Bump steer’ does not have a good impression in America and you explain the possible reason
Dough: Nice to hear from another ‘grown-up’ 928 owner – I do hope you have a good impression of your stay in Denmark – As you certainly remember, we Danish have only have two things to complain about: The weather and the tax!
Nich: I agree
Thanks to all of you, I still hope to meet a 928 owner who made similar test, and I am sure some of racing frecks did
I will also find another 928 and check the toe change on this/these – Best if I can find different models – Maybe a good subject for a Porsche Frenzy Event in Denmark with the German 928 club
<img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" /> <img border="0" alt="[byebye]" title="" src="graemlins/wave.gif" />
Sorry for late answering, but sometimes I have a job to do. Yesterday I went to Munich in Germany for a meeting with a supplier in oil and gas industry. I always stocked there due to heavy snow-fall but went back in the middle of the night.
Here you have my comments to your positive input to my project:
Jim: Thanks for your good and constructive answer – By the way I like your avatar
Delta: That’s is 1/6 degree per 10 mm!
John: Thank for your nice thinking – I do not if I want to be ‘The Man’ but I want to find the answer, and when I find I will gladly share my experience with other 928 owners
Yes I will certainly go in touch with Germans, I just became a member of Porsche Club 928, Germany
Nicole: I agree, when the car is lowered it looks smart, but ‘the cost’ is less driving properties – Thanks for the tip about Devek, maybe Mark has the answer, I will check
Gordon: No problem, that good for me to be familiar with American slang
Ed: How will you explain that the toe-in disappears if you adjust the toe when the car is ‘high’?
Old & New: It was a spelling/typing failure instead of ‘torn’ I meant ‘corn’ – And I do not think I hid yours
Rob: Thanks for the slang info – I think you are right, it seams that ‘Bump steer’ does not have a good impression in America and you explain the possible reason
Dough: Nice to hear from another ‘grown-up’ 928 owner – I do hope you have a good impression of your stay in Denmark – As you certainly remember, we Danish have only have two things to complain about: The weather and the tax!
Nich: I agree
Thanks to all of you, I still hope to meet a 928 owner who made similar test, and I am sure some of racing frecks did
I will also find another 928 and check the toe change on this/these – Best if I can find different models – Maybe a good subject for a Porsche Frenzy Event in Denmark with the German 928 club
<img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" /> <img border="0" alt="[byebye]" title="" src="graemlins/wave.gif" />
01-14-2003, 10:32 AM
#28
Burning Brakes
</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Erik - Denmark:
<strong>
Ed: How will you explain that the toe-in disappears if you adjust the toe when the car is ‘high’? <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" /> <img border="0" alt="[byebye]" title="" src="graemlins/wave.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">First of all, you shouldn't be adjusting the toe when the car is raised. <img border="0" title="" alt="[Eek!]" src="eek.gif" /> If you do, there will be lots of "toe-in" when the car is lowered (back to its normal ride height).
On my car, the toe setting never goes "in". When level it's "out" but nearly "zero". When loaded or unloaded it goes OUT more. YMMV.
<strong>
Ed: How will you explain that the toe-in disappears if you adjust the toe when the car is ‘high’? <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" /> <img border="0" alt="[byebye]" title="" src="graemlins/wave.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">First of all, you shouldn't be adjusting the toe when the car is raised. <img border="0" title="" alt="[Eek!]" src="eek.gif" /> If you do, there will be lots of "toe-in" when the car is lowered (back to its normal ride height).
On my car, the toe setting never goes "in". When level it's "out" but nearly "zero". When loaded or unloaded it goes OUT more. YMMV.
01-14-2003, 10:54 AM
#29
Burning Brakes
Thread Starter
Join Date: Apr 2002
Location: Denmark
Posts: 881
Likes: 0
Received 0 Likes
on
0 Posts
Hi Ed,
Correct the car should not be adjusted when it is ‘high’ – I said, IF you adjust (and that what many people are doing) then the toe-in will disappear or even go to toe-out with the result of bad driving properties and inside-tire-wear.
I think (But I have not finished my evaluation yet) – When the car goes down you get more negative camber (To give better corning performance) - I.e. wider distance between the two front wheels' lower part – I.e. less toe-in –
How? The lower A suspension is longer than the upper A suspension – But as I said: ‘I think it is like this’
Correct the car should not be adjusted when it is ‘high’ – I said, IF you adjust (and that what many people are doing) then the toe-in will disappear or even go to toe-out with the result of bad driving properties and inside-tire-wear.
I think (But I have not finished my evaluation yet) – When the car goes down you get more negative camber (To give better corning performance) - I.e. wider distance between the two front wheels' lower part – I.e. less toe-in –
How? The lower A suspension is longer than the upper A suspension – But as I said: ‘I think it is like this’
01-14-2003, 10:59 AM
#30
Rennlist Member
Join Date: Dec 2002
Location: Southern New England
Posts: 1,975
Likes: 0
Received 0 Likes
on
0 Posts
</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"> Old & New: It was a spelling/typing failure instead of ‘torn’ I meant ‘corn’ – And I do not think I hid yours
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Erik,
That sounds very bad. I think.
And I don't think I would want anyone hiding my corn.
It sounds kind of pornographic, but this is a family board, so we won't go there...
<img border="0" alt="[icon501]" title="" src="graemlins/icon501.gif" />
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Erik,
That sounds very bad. I think.
And I don't think I would want anyone hiding my corn.
It sounds kind of pornographic, but this is a family board, so we won't go there...
<img border="0" alt="[icon501]" title="" src="graemlins/icon501.gif" />