Mk2 Golf IHI track car... Rear body work and door catches

Hmm, so the tank will be coming out then? Mk4 axle? or IRS from Synchro?

 

Getting warmer...

Colder... (might be in the pipeline for the year after next though)

And we have a winner! Cuddly toy is on its way!

It is indeed, I've only made one at the moment just so that I can check the clearances and suspension travel. I've also checked the rear roll center movement which I'll cover later on when I get the plans 100% I'm still undecided on the amount of drop I can get away with at the front while still achieving the desired wishbone angles, scrub radius and suspension travel.


On another note I was doing a little bit more on the car tonight and found that the O/S/F shock was completely worthless as a damper. It has very little effect with or without max rebound. Looks like it's time to do my bit for the economy once again!

 

Spent Friday night in the workshop with my mate making a prototype ball joint dropper. Here is the result after about an hour or so....




Not very pretty but worked really well for what we wanted.

 

Nifty use of old parts there.
So I presume you have checked for bump steer and camber changes before you started this little project. Was there significant changes through the suspension travel?
You will need to check for bump steer and make sure the steering track rod end does not want to intersect with the steering arm off the hub at a level that is not possible.
When I converted my Rocco (mk1 platform) to mk3 5 stud hubs, this was easy as the mk1 steering arm comes off the hub a lot higher than the mk2 / 3, so I had room to adjust the track rod end height.

 

Errrrmm... No not exactly, it was more a spur of the moment kind a thing

The project started while talking about the ride height, then roll centers, then scrub radius and wishbone angles then all of a sudden I was cutting up an old hub and we ended up with this little creation.

I'm still in the design phase at the moment so yes I still need to check the bump steer. Ment to do it ages ago but never got round to checking it.

Looks likethere is a lot more camber change on compression but the position of the top mount has not been finalised yet so I'm not too worried about it at the moment. I'm hoping that when I get round to finishing the string computer I will be able to come to the best compromise and start making a bit of progress.

I noticed there was a height difference in the steering arms when I had the hubs side by side.
Fingers crossed it will all bolt straight on and I wont need to give it a second thought.



Well.... Tis the season of miracles after all!

 

I thought I'd treat myself and bought a few new workshop items for the up and coming rebuild...




Shrinker / Stretcher





19" Bead roller with 11 pairs of dyes





12" sheet metal roller





And last but not least, a 220amp AC/DC tig welder with foot pedal.



Now after Single-handly saving the UK economy again I had better get on with some work on the car....



Quick shot of where the new ride height is going to be. Wing is not bolted on and is sat on top of the tyre just to get a rough idea of how much I need to cut out.

meanwhile... I've still not have enough time to sort out the string computer I've been trying to finish for the past week. Fingers crossed I'll get the time tomorrow to get it up and running.

 

Ok string computer is now finally finished! Got a few more lines to draw on but is now useable. I have not yet tried it out as I ran out of time today so I'll save that for tomorrow.

Brief run down on components and functions...

String computer for plotting front Roll Center

Basebord on the right (for plotting wishbone mounting point and to change amount of body roll)

Hub + wheel on the left (for plotting bottom ball joint location)

Shock + top mount above wheel & hub ( for plotting top mount location and changes in bump)

Wishbone (to plot path + changes in length)





Looks quite straight forward but was trickier to make than I thought! Fingers crossed I should have some results in the next update.

 

Look forward to more, as I have not visualised what you're going to do with it yet!

 

Hmm, muchos shiny new stuff on this page.

So we have drop plates for the rear axle.

And this string computer shizzle must be for the front end then.
If it is going to run at that ride height. I am interested to see if you need to get the inner wishbone pivot points raised. Or will the balljoint extenders be enough?

 

Prepare to be stunned and amazed!

..... or not


Had to work late tonight so didn't get the chance to try it out today but tomorrow is going to be fun all the way!

Check! To lower COG while still maintaining usable suspension travel and maximum wheelbase

Correct To help locate the best all round achievable compromise in mounting locations for wishbone, top mount and bottom ball joint to try and minimise roll center movement.

If possible it will go lower but I don't think I will be able to go much lower while still hitting the the right angles. Unless I tube the front end and change the wishbone mounting completely which I would perfer not too at this stage. On first glance the prototype extender that we made up last week is only enough to bring the wishbone back to level which is not quite far enough as this gives a low roll center and very long swing axle length. Which is not ideal. It will probably need a combination of both IMO.

 

Only had a couple of hours to test out the string computer but it worked really well...

Here is the computer in action, I've highlighted the string as it was difficult to see in the first photo. I've also highlighted the main points of interest.



This is with all the OE mounting points and the normal ride height ...




Roll centre is aprox +50mm. I had calculated it at 20mm but I have later since discovered that one of the angles was a little out. All fixed now though!

This is after making a change to the bottom ball joint...

(the shaded area is a "NO GO" area because in reality that space is filled with wheel and tyre. The wishbone thickness is not to scale btw)




Roll center is now +140mm

The grid lines are to make it easier to plot the findings and to be able to replicate any setup rather than trying to remember what went where.

I still need to spend a bit more time on it to determine the set up I'll be using but by using the computer I can take a lot of the guess work out of the equation.

 

I was under the impression that raising the roll centre is going to cause the car to roll more in the corners, so you should ideally be keeping it as close to the ground as possible.

 

This is what I thought before I started looking into it.

Roll is caused by centrifugal force acting on the centre of gravity. This force causes the COG to rotate around the roll centre. The distance between the COG and the roll centre is what will affect body roll due to the amount of leverage the COG has about the roll centre.


Picture if you will a vertical 1m long stick being held at one end (the roll centre) and has 100Nm pushing side ways on the top (force acting on the COG) the amount of force needed to resist this moment is therefore 100NM

Force X Distance = 1m X 100Nm = 100Nm

If you move where stick is being held by 50cm (raise the roll centre) then you will half the force that the COG has on the roll centre.

0.5m X 100Nm = 50Nm

A low roll centre just means you will need a bigger anti roll bar or tougher springs to combat the fores being applied.

Maintaining controll over the movement of the roll centre is more important than the actual height. Big changes in roll centre location while mid corner will cause the car to be unstable due to large changes in geometry. If the roll center is located tightly the effects will be minimised and the car will be easier to predict.

 

I am wearing a rustic woolly jumper, brown cords and growing beard, it's like Open University on here these days!

 

Still plugging more data into the computer so not much in the way of exciting updates going on but I did have these turn up this morning....



Cheers Mike they are spot on!

Can't wait to get to get round to fitting them for real!

 

Great bulid and I love the look of you mk2. Keep up the great work

 

That all makes sense, and it has been more than 10 years since I was reading up on this stuff, but I'm sure there's something else. I had this discussion when we were looking into this sort of thing, and remember saying "Look at F1 cars, the upper and lower wishbones are parallel". Now if only I could remember what that did to the roll centre.
I'll see if I can find the book I read back then (although it's probably still in South Africa), and let you know if I find anything out.

If you really want to fry your brain, ask yourself this:
What happens when the CoG is BELOW the roll centre? Will the car lean in to the corner, producing more grip, meaning the faster you go, the more grip you have?

 

+1

Calculation of CoG is a pain in the ass though.
One way of doing this is the following: http://www.longacreracing.com/articles/art.asp?ARTID=22
Nice info here too http://robrobinette.com/cg_height_calc.htm

 

so do you work it all out as the car sits or, say half way up the wheel travel? Its good to see it all being worked out properly!