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 Post subject: Bump steer
PostPosted: Sat Jun 02, 2018 9:37 pm 
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848cc
848cc

Joined: Sat Jun 02, 2018 8:24 pm
Posts: 3
Hi all, new to the forum. Just want to find out if anyone knows, or can measure, the amount of bump steer present on a std suspension setup.
Thanks.


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 Post subject: Re: Bump steer
PostPosted: Sun Jun 03, 2018 10:52 am 
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1275cc
1275cc

Joined: Sat Feb 09, 2013 5:44 pm
Posts: 2176
Location: Camden
Do you mean the change in amount of toe-in and toe-out of each front wheel as it moves up and down through its suspension travel?


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 Post subject: Re: Bump steer
PostPosted: Sun Jun 03, 2018 6:42 pm 
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848cc
848cc

Joined: Sat Jun 02, 2018 8:24 pm
Posts: 3
Yep that's it. Putting a honda engine in and have had to move the steering rack. Need to prove to engineer bump steer isn't any worse than original. Wasn't switched on enough to measure before I changed the mount.


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 Post subject: Re: Bump steer
PostPosted: Sun Jun 03, 2018 7:38 pm 
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1360cc
1360cc
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Joined: Mon Aug 23, 2004 10:07 pm
Posts: 10650
Location: SE Melbourne
There's no specific measurement for it that applies to all minis as there were different length arms and racks depending on production year. The other influence is ride height.

What i would do if i was you is put the rack in its stock location (or simulate) and take the measurements you need at the correct ride height then position it to where you will finish the rack and re-measure.

What wheels, brakes and hubs / arms are you running?
How far did you move the rack?


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 Post subject: Re: Bump steer
PostPosted: Sun Jun 03, 2018 9:48 pm 
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848cc
848cc

Joined: Sat Jun 02, 2018 8:24 pm
Posts: 3
Have moved the rack down the fire wall 20mm.
The car is a mini k, so Mk1 steering arms I think, has disc brake hubs, adjustable lower arms, steering rack is new from mini spares for Mk2.
Will have to see if I canmock up the original rack position.


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 Post subject: Re: Bump steer
PostPosted: Mon Jun 04, 2018 8:38 am 
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1098cc
1098cc

Joined: Tue Aug 24, 2004 3:57 pm
Posts: 1478
Location: queensland
Dan81 wrote:
Have moved the rack down the fire wall 20mm.
The car is a mini k, so Mk1 steering arms I think, has disc brake hubs, adjustable lower arms, steering rack is new from mini spares for Mk2.
Will have to see if I canmock up the original rack position.



I can see his concern, particularly if you lower the suspension height. I can almost guarantee this has increased your bump steer. In the sports sedan we lifted the rack to reduce bump steer to good affect. You have unwittingly gone the other way.

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 Post subject: Re: Bump steer
PostPosted: Mon Jun 04, 2018 10:51 am 
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1360cc
1360cc
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Joined: Sun Apr 11, 2004 11:32 am
Posts: 12390
Location: Sthrn HiLoLands, NSW, Australia
Suggestion: contact other Honda converters and ask if they addressed bump in their builds?? :idea:

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 Post subject: Re: Bump steer
PostPosted: Mon Jun 04, 2018 10:52 am 
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1098cc
1098cc

Joined: Wed Nov 24, 2004 10:23 am
Posts: 1488
Location: Armidale, NSW
There's geometric models for understanding virtual centres, and from these roll centre, and bump steer.

Put very simply if you draw a line from where the upper and lower ball joints pivot through the pivot for the upper and lower arms, where these two lines intersect is the virtual centre.
To have no bumpsteer at a particular suspension height the steering linkage from the steering arm to the rack should also point at this virtual centre.

If you've moved the rack down 20mm my brain is telling me you'd need to move the steering arm down more than 20mm to compensate.
Project binky had a bit where they delved into bumpsteer which is probably worth a look.

Here's some stuff on finding virtual centres called virtual pivots in this article,
http://www.autospeed.com/cms/article.ht ... n&A=112911

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