beaver34
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| posted on 22/2/13 at 10:22 PM |
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Bump steer gauge
Anyone made there own?
If so any pics!
Going to have a go at sorting and checking mine, might need some help along the way
Thanks
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mark chandler
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| posted on 22/2/13 at 10:41 PM |
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Get a laser pointer, strap it to the wheel or disc and point at a wall.
Lock the steering wheel
Remove the road spring so you can easily lift the suspension through its full travel.
As you lift the wheel/hub the point of light should only rise or lower with the hub, if it points in or out you have bump steer 
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ceebmoj
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| posted on 22/2/13 at 11:46 PM |
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Have a look on seloc. There are some nice guide on there wiki
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sdh2903
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| posted on 22/2/13 at 11:50 PM |
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As above.
First time I did mine I didn't have the laser pointer so I used 2 long pieces of ally angle cable tied to front wheels pointing to garage wall.
With springs removed Mark the wall at full droop then with a Jack Lower to full compression Mark the wall again. Do some high school trigonometry (or
cheat and use online calculator) et voila you have a bump steer angle. Mine was quite a lot, approx 1.5 degrees per wheel of toe in at full
compression. Shimming the rack by 6mm pretty much dialled it out.
Good luck!
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beaver34
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| posted on 23/2/13 at 07:42 AM |
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thanks guys,
seems quite easy
also want to check my caster angle. any tips for doing this?
what order do i need to be doing it in caster first then bump then camber then toe in/out? as i presume changing some affects others
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Daddylonglegs
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| posted on 23/2/13 at 07:57 AM |
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Maybe plumbline from the centre of the top balljoint, measure the dstance between the centre of the bottom balljoint and the plumbline, then centre of
lower balljoint to centre of upper balljoint, and finally distance of horizontal line through lower balljoint to plumbline and centre of lower
balljoint. Then a bit of trigonometry? Hope that makes sense, it's early 
Sounds doaable to me?
Someone with a quicker/simpler method will be along in a bit though probably
It looks like the Midget is winning at the moment......
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NeilP
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| posted on 23/2/13 at 10:46 AM |
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Neither Bump nor Toe-in will impact Caster - that's fixed by the positions of the wishbones...
Camber by the position of the ball joints (so the top mushroom if fitted comes into play)...
Don't forget trailing hub - that helps with self centring and is also impacted by the mushrooms.
I'd do Caster (wishbone shimming), Camber and trailing hub together (ball joints and mushrooms) then bump steer (rack shimming) - should keep
you busy!
HTH, N.
EDIT: And toe-in last (rack ends)
All of which can be done with with straight lengths firmly secured to the wheels/hubs, masking tape on the floor/wall and some basic trig (look up
'inverse Tan' and it will tell you how the maths works)
[Edited on 23/2/2013 by NeilP]
If you pay peanuts...
Mentale, yar? Yar, mentale!
Drive it like you stole it!
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Minicooper
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| posted on 23/2/13 at 03:23 PM |
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quote:
Originally posted by mark chandler
Get a laser pointer, strap it to the wheel or disc and point at a wall.
Lock the steering wheel
Remove the road spring so you can easily lift the suspension through its full travel.
As you lift the wheel/hub the point of light should only rise or lower with the hub, if it points in or out you have bump steer
I really don't get this, as the wheel rises it will draw an arc, so how can you tell what is normal suspension movement and what is down the
bump steering?
Cheers
David
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procomp
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| posted on 23/2/13 at 03:58 PM |
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Hi.
That is the problem with trying to measure it with this bodged method. It does not take into account the camber change, that's why some of the
readings are so high.
Also why are people trying to get rid off bump steer when you actually want bump steer to give better grip levels in braking and cornering
situations. It's more a case off tuning the bump steer to work with the geometry than actually trying to get rid of it.
People need to stop reading out of date books and stop believing all the crap on the WWW. ( something this forum is guilty of ) and get back to solid
basics like making sure the camber actually travels in the right direction in the first place, putting 1/2" bolts in 1/2" holes rather
than 12mm because it's a few £ cheaper, get the dampers and springs something like right before messing with things like bump steer.
Cheers Matt
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sdh2903
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| posted on 23/2/13 at 05:00 PM |
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Matt, I accept that you are vastly knowledgeable as you should be as this is your profession but sometimes I wish you would be a bit more positive
with your posts. I've spoken to you on the phone a couple of times and you've been very helpful but sometimes your posts come across as
being arsey.
Instead of telling us all how we are all doing it wrong why not throw us a bit of info (not too much granted to protect your business). I will openly
admit I know very little of this subject but i'm trying to learn a bit here and there (and on a budget) rather than just let an expert do the
work for me.
Just my 2p
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mark chandler
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| posted on 23/2/13 at 05:48 PM |
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quote:
Originally posted by procomp
Hi.
That is the problem with trying to measure it with this bodged method. It does not take into account the camber change, that's why some of the
readings are so high.
Also why are people trying to get rid off bump steer when you actually want bump steer to give better grip levels in braking and cornering
situations. It's more a case off tuning the bump steer to work with the geometry than actually trying to get rid of it.
People need to stop reading out of date books and stop believing all the crap on the WWW. ( something this forum is guilty of ) and get back to solid
basics like making sure the camber actually travels in the right direction in the first place, putting 1/2" bolts in 1/2" holes rather
than 12mm because it's a few £ cheaper, get the dampers and springs something like right before messing with things like bump steer.
Cheers Matt
That's great advice for someone who has all the equipment, however given that 'old book' cars had serious design deficiencies before
you even start getting rid of horrendous bump steer will make the car far nicer
My car may not be the best handling car that it could be, however using string, lasers and a bit of trig it centres perfectly, goes around bends well
enough and can travel across rumble strips and rough curbing on the track without trying to turn itself out of line.
I agree you will not get perfection, but if the car is badly wrong to start with then you will see a great deal of improvement!
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procomp
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| posted on 23/2/13 at 09:21 PM |
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Hi.
Your just not seeing the basic flaw with the method described, as raised by David.
Im all for joe doing it in his garage with basic equitment, but it helps if the method used actualy gives results that are something like acurate.
Cheers Matt
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sdh2903
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| posted on 23/2/13 at 10:08 PM |
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Matt, correct me if I'm wrong but from the various info sources I've read. Bump in is highly undesirable and should be dialed out. In roll
a very small amount of bump out can help stability in the twisties?. However the tiny amount of bump out that you would be looking for makes it beyond
the skills and equipment of an average Diy'er, well beyond mine anyway.
For now I have removed my bump in that I believe was contributing to my twitchy handling however any further adjustments to compensate for roll and
camber etc I feel I would need a bit more professional assistance.
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mark chandler
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| posted on 24/2/13 at 07:58 AM |
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So draw an arc on the wall which follows the camber change, you can now be precise, you only need three points, top bottom and centre as you cannot
control the inbetween areas.
Moving the wall out reduces the error ratio, if you have the wall say 2' in front of the car you will definately need to describe the camber
change on the wall as the ratio is 1:4 assuming 6" wheel travel, shine at a wall 10' away and the error ratio is now 1:40.
It's not rocket science to measure, the further away the wall the more accurate you can be
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whitestu
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| posted on 24/2/13 at 09:24 AM |
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Matt is right and wrong. If you intend to make your car as good as it can be spend the money and get it set up professionally. If you want to make it
massively better for almost no cost get a cheap laser pointer and follow the instructions for dialling out bump steer.
Being a tight arse I did the latter and my car is much nicer to drive.
Stu
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NeilP
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| posted on 24/2/13 at 07:48 PM |
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If you can't get it how you want it go and take your car to Matt and Ivan (Procomp in Brum) - they are mechanical magicians...
If you pay peanuts...
Mentale, yar? Yar, mentale!
Drive it like you stole it!
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indykid
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| posted on 24/2/13 at 09:19 PM |
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If you fix your laser pointers perpendicular to the disc face, you isolate all the camber change/wishbone arc effects and only see toe (assuming you
keep the wishbone pivot axes horizontal). Couple of boards stood next to the car with vertical lines drawn on and you're good to go.
Have I missed something? I doubt anyone is running antidive, so that shouldn't be an issue.
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beaver34
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| posted on 24/2/13 at 09:51 PM |
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quote:
Originally posted by NeilP
If you can't get it how you want it go and take your car to Matt and Ivan (Procomp in Brum) - they are mechanical magicians...
that i will, or somewhere more local TBH once ive iron out all the niggles and recovered from the cost of mapping tax and insurance this month!
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