Front wheel alignment
Discussion
Well, I don’t know, where are you all when a bit of technical nitty gritty is required?
I since found out how to determine the angle in degrees/minutes so I have something that is tracked ok now.
But the reason why I needed to know is because I have finally got round to adjusting my bump-steer, something that has been on my "To Do" list since I first found out about it a couple of years back. It took about 3 hours and I can now say it is well worth doing. No more unexpected directional changes when driving on rough roads and the steering seems to relay more and generally makes the car feel better rather than it being somewhat of an experience on some of my local roads.
I since found out how to determine the angle in degrees/minutes so I have something that is tracked ok now.
But the reason why I needed to know is because I have finally got round to adjusting my bump-steer, something that has been on my "To Do" list since I first found out about it a couple of years back. It took about 3 hours and I can now say it is well worth doing. No more unexpected directional changes when driving on rough roads and the steering seems to relay more and generally makes the car feel better rather than it being somewhat of an experience on some of my local roads.
pb3 said:
Well, I don’t know, where are you all when a bit of technical nitty gritty is required?
I since found out how to determine the angle in degrees/minutes so I have something that is tracked ok now.
But the reason why I needed to know is because I have finally got round to adjusting my bump-steer, something that has been on my "To Do" list since I first found out about it a couple of years back. It took about 3 hours and I can now say it is well worth doing. No more unexpected directional changes when driving on rough roads and the steering seems to relay more and generally makes the car feel better rather than it being somewhat of an experience on some of my local roads.
I since found out how to determine the angle in degrees/minutes so I have something that is tracked ok now.
But the reason why I needed to know is because I have finally got round to adjusting my bump-steer, something that has been on my "To Do" list since I first found out about it a couple of years back. It took about 3 hours and I can now say it is well worth doing. No more unexpected directional changes when driving on rough roads and the steering seems to relay more and generally makes the car feel better rather than it being somewhat of an experience on some of my local roads.
I would love to hear more about how you fixed it.
I had a rough idea what had to be done, but I found an article in a very old Ultimatum (the long gone Club, Issue No 002 I believe). But what it amounts to is having to either raise or lower the steering rack (or both) so that the wheel angle changes are minimal through full suspension travel.
In my case I had to move it down about 3.5mm on one side and 2.5mm on the other. I know from reading a post in the past that some have had new steering rack brackets/clamps made, but I did as the article suggested and slotted the original 4 fixing holes to allow for the required adjustment. Once complete it is necessary to adjust the tracking as in my case the wheels had been pulled in a little by my adjustmat to the rack height.
In my case I had to move it down about 3.5mm on one side and 2.5mm on the other. I know from reading a post in the past that some have had new steering rack brackets/clamps made, but I did as the article suggested and slotted the original 4 fixing holes to allow for the required adjustment. Once complete it is necessary to adjust the tracking as in my case the wheels had been pulled in a little by my adjustmat to the rack height.
v8owner said:
I cant believe a car capable of 200+ has bumpsteer?! anybody else with this problem?
I would have thought the ultina chassis jig accurate enought to not give problems?
PB3 was the problem steering rack arms inclined at normal ride height?
g
I would have thought the ultina chassis jig accurate enought to not give problems?
PB3 was the problem steering rack arms inclined at normal ride height?
g
Why? A car even when made on a jig will change/distort slightly when un-jigged. I guess you would only know how your particular chassis is when you hang all the front suspension and steering rack on it and measure it. Then you will know. All will be different in my opinion, and I have read, like I said earlier, that I am not the only one to find this a worthwhile exercise.
Yes the track rod arms are slightly inclined, but it is the arc that they follow when the suspension moves up and down that is important. The article said the "Ultima suspension is designed to have zero bump steer", providing you dial it out or you may be lucky in your case.
In response to V8Owner, I have the same issue. On country roads it feel like I am fighting the car to keep it in a straight line. It can be really bad. I have heard from a few ultima owners that they suffer the same problems. I had a conversation at the Brands hatch kit car event last year with the people from Z cars who are developing / developed the twin hyabusa engined 4WD ultima. They told me that they had to remake the front uprights as the KPI (King Pin Inclination) was all wrong and had an effect on the bump steer. They tell me, that they also added power steering. whether this was necesary is another matter. I would think that most ultima drivers say in normal driving it is not.
scuff said:
...They told me that they had to remake the front uprights as the KPI (King Pin Inclination) was all wrong and had an effect on the bump steer.
After a quick look, I estimate the KPI line on mine would just touch the inside edge of the front tyres.
IIRC the 'ideal' KPI line would pass thru the middle of the tyre, as this is effectivly the point around which the tyre rotates, so having the line in the center minimises the effort to turn, and the ability of the tyre to twist of it's own accord...
The length of the A arms may also have an effect, as they are fairly short, so they cause a lot of camber change for very little travel, but, as the tyres have only a limited space to move around in, that's perhaps not such a bad thing...
As for bump steer, isn't that also a factor of castor, which is 'usually' easier to adjust than the KPI?
It may be theoreticaly best to put the KPI in the centre of the tyre but that would result in almost no feel and thus not a nice car.
You can also definatelly dial out the bump steer without changing the uprights... my canam bump steered terribly which was completely dialed out by someone who knew what they were doing.
You can also definatelly dial out the bump steer without changing the uprights... my canam bump steered terribly which was completely dialed out by someone who knew what they were doing.
Hi Steve.
I don’t have the destructions that you are after, however I do remember this being discussed at some length on gt40s.com, either in the chassis section or under one of the build threads, try this link
www.gt40s.com/forum/builders-forum/13742-drb-5-a.html
the builder “Bill” was having trouble trying to work out where to put the steering rack, which will directly effect bump steer
www.gt40s.com/forum/gt40-tech-chassis-brakes-tires-wheels/19449-bump-steer.html
if you are looking for something in the forum, you will probably have to go down to the bottom of the page and select the display options to show since the beginning otherwise you only get posts from today.
Regards Ryan
Edited to note that Carrol Smiths book “drive to win” had a good write up on the topic from memory, you might see if you can find it.
I don’t have the destructions that you are after, however I do remember this being discussed at some length on gt40s.com, either in the chassis section or under one of the build threads, try this link
www.gt40s.com/forum/builders-forum/13742-drb-5-a.html
the builder “Bill” was having trouble trying to work out where to put the steering rack, which will directly effect bump steer
www.gt40s.com/forum/gt40-tech-chassis-brakes-tires-wheels/19449-bump-steer.html
if you are looking for something in the forum, you will probably have to go down to the bottom of the page and select the display options to show since the beginning otherwise you only get posts from today.
Regards Ryan
Edited to note that Carrol Smiths book “drive to win” had a good write up on the topic from memory, you might see if you can find it.
Edited by ezakimak on Wednesday 11th April 03:11
My guess would be:
Take off front clip
Set the car on stands so that it is level.
Remove Shocks and drop wheel to lowest point.
Lock steering wheel on centre
Get a spirit level with built-in laser and attach to wheel so that the laser line is level and runs through the centre of the hub and points towards a wall in front of the car.
Lock off the wheel against the front disk so it wont rotate.
With the wheel at bottom of travel, using another level, mark a plumb line on the wall close to the laser dot.
Using a jack under the wheel, move the wheel up and down and adjust the rack up and down until the laser line runs parallel to plumb line on the wall.
If the car is sitting exactly perpendicular to the wall, you could mark the centreline of the car on the wall and use the lasers on the wheels to do alignment at the same time.
DOH... just read the bump steer post on GT40.... the laser is not a good idea if facing forward as the hub prescribes an arc anyway...... the best advice is contained in later threads.... take the car and put it on wheel alignment machinery.
Take off front clip
Set the car on stands so that it is level.
Remove Shocks and drop wheel to lowest point.
Lock steering wheel on centre
Get a spirit level with built-in laser and attach to wheel so that the laser line is level and runs through the centre of the hub and points towards a wall in front of the car.
Lock off the wheel against the front disk so it wont rotate.
With the wheel at bottom of travel, using another level, mark a plumb line on the wall close to the laser dot.
Using a jack under the wheel, move the wheel up and down and adjust the rack up and down until the laser line runs parallel to plumb line on the wall.
If the car is sitting exactly perpendicular to the wall, you could mark the centreline of the car on the wall and use the lasers on the wheels to do alignment at the same time.
DOH... just read the bump steer post on GT40.... the laser is not a good idea if facing forward as the hub prescribes an arc anyway...... the best advice is contained in later threads.... take the car and put it on wheel alignment machinery.
Edited by crafty on Wednesday 11th April 04:51
I understand the technique.
The bit I'm missing is the amount of travel to take into consideration. You will never dial it out if you try and work with full extension to full compression. I seem to remember the notes I'm looking for talked of something like 2" up and 1" down from normal ride height. Until I know this there is little point starting.
Steve
The bit I'm missing is the amount of travel to take into consideration. You will never dial it out if you try and work with full extension to full compression. I seem to remember the notes I'm looking for talked of something like 2" up and 1" down from normal ride height. Until I know this there is little point starting.
Steve
Crafty,
In one of the posts it mentioned putting the laser so that it pointed to the side of the car, that way you will not get the arc, and it just goes in more or less a line.
The angle of bump steer is not important, Its the amount of change that is. Or more importantly reducing it. If you clamp the steering column so that it cant rotate, and then make small adjustments to the rack height, and temporarily clamp it to the chassis and observe the changes in the movement of the laser pointer you should be able to see whether you are making an improvement or not. You will probably find that there is a sweet spot for it and after you go past it will get worse again, I think you would be fairly safe with the 1” drop 2”compression movement as a starting point. Of all the vids on piston heads that I have watched the wheels don’t tend to drop to much when going over rough or undulating ground, and even when they do they would be lightly, or less loaded, probably a good vid to watch might be one from the drag strip on launch as this might be where a lot of drop is generated, I think I remember Mark with the turbo LS1 Canam in the USA had this problem after upping the boost. Something about going all light in the front end when Blunstone met firewall.
At the end of the day it will not cost anything more than time to try, and maybe a bit of filling of the mounting holes if you decide to implement any changes.
ryan
In one of the posts it mentioned putting the laser so that it pointed to the side of the car, that way you will not get the arc, and it just goes in more or less a line.
The angle of bump steer is not important, Its the amount of change that is. Or more importantly reducing it. If you clamp the steering column so that it cant rotate, and then make small adjustments to the rack height, and temporarily clamp it to the chassis and observe the changes in the movement of the laser pointer you should be able to see whether you are making an improvement or not. You will probably find that there is a sweet spot for it and after you go past it will get worse again, I think you would be fairly safe with the 1” drop 2”compression movement as a starting point. Of all the vids on piston heads that I have watched the wheels don’t tend to drop to much when going over rough or undulating ground, and even when they do they would be lightly, or less loaded, probably a good vid to watch might be one from the drag strip on launch as this might be where a lot of drop is generated, I think I remember Mark with the turbo LS1 Canam in the USA had this problem after upping the boost. Something about going all light in the front end when Blunstone met firewall.
At the end of the day it will not cost anything more than time to try, and maybe a bit of filling of the mounting holes if you decide to implement any changes.
ryan
Edited by ezakimak on Wednesday 11th April 08:50
steve_d said:
I understand the technique.
The bit I'm missing is the amount of travel to take into consideration. You will never dial it out if you try and work with full extension to full compression. I seem to remember the notes I'm looking for talked of something like 2" up and 1" down from normal ride height. Until I know this there is little point starting.
Steve
The bit I'm missing is the amount of travel to take into consideration. You will never dial it out if you try and work with full extension to full compression. I seem to remember the notes I'm looking for talked of something like 2" up and 1" down from normal ride height. Until I know this there is little point starting.
Steve
Im with you.. I alwys thought the biggest thing was to get the car set at normal ride height, and then ensure that the steering rack/arms were all horizontally level / perpedicular. I cant see how you can ever dial it out completely.. as the steering arms are always going to follow an arc.
steve_d said:
Bump
Somebody must have the bump steer instructions.
If so please mail them or post them here.
Cheers
Steve
Somebody must have the bump steer instructions.
If so please mail them or post them here.
Cheers
Steve
Hi Steve, I have a copy of some bump steer instructions which appeared in the Ultima Owners Club newsletter from about 7 years ago. Unfortunately, they are in yellow type. so do not scan at all.
I would type them out myself but with a typing speed of approx 3-5 words per min, it could take me a whole day. I could post them to you or, pass them over at Stoneleigh?
The instructions that I followed suggested 25mm and 50mm above and below the normal ride height position.
On mine I could not achieve 50mm below, more like 42mm or something. So I took measurements at +50, +25, -25 and -full travel. As said below I was not able to dial it all out but it was very close (ie no bump steer) between +25 and -25mm. The actual travel that can occur on the road is probably a bit more but never +/- 50mm! so I was quite happy. But the proof is in the pudding, and I am pleased with the results.
On mine I could not achieve 50mm below, more like 42mm or something. So I took measurements at +50, +25, -25 and -full travel. As said below I was not able to dial it all out but it was very close (ie no bump steer) between +25 and -25mm. The actual travel that can occur on the road is probably a bit more but never +/- 50mm! so I was quite happy. But the proof is in the pudding, and I am pleased with the results.
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