Au contraire to the max!! This has put a spanner in the works.....big time. I have double checked my 280mm 5 stud (what strimmer will be using ) And it is 6.35mm. He used a Stanley Fat Max tape measure for his readings, so I think out subtle discrepancies will be lost in his calculations.
I've marked on the diagram lines to create triangles, using some measurements from the car and trigonometry I have calculated the scrub radius. Starting with the green line. Measure the distance between top mounts and the distance between the pivot point/ball joint. Deduct the pivot point measurement from top mount measurement gives the green line measure. Blue line next. A bit trickier to measure and required using a straight line across top mounts and although I didn't use one a straight line across joining the pivot point would help too, take the measurement of the blue line. Last measurements again a couple of tricky ones. Vertically measure from pivot point to centre line of hub, and horizontally from pivot point to face of hub. Also required are wheel diameter, offset, tyre width, tyre profile ratio, brake disc thickness of the non-friction part. Purple line. Use the radius of the wheel including tyre calculated from wheel diameter, and profile ratio deduct the vertical height measured from pivot point to centre of hub to give the measure of the purple line. And for the math. Using tan function of trigonometry calculated angle "a" using the known green line and blue line. This angle "a" is mirrored in the bottom corner of the smaller triangle that contacts the ground and known measurement of purple line we can again use trig calculate the red line. Now we know where the KPI intersects with the ground in relation to the pivot point. Measure of pivot point to hub face, plus disc thickness and less the offset of wheel we have the centre line of the tyre as it intersects the ground in relation to the pivot point. Take one from the other and we have scrub radius. Its all in a spreadsheet and now if it holds up to scrutiny I can play with raising/lowering the car ride height, widetrack with wider wishbones, changing wheel diameter and offset, tyre width and profile.
I could have saved you a lot of measuring as I already have all that data in my Pro/E model, and they're taken from drawings, not measured from a car
Hi Mickey, I don't suppose you want to share the factory dimensions of the mk1 with us would you? Gurds
Is this a working model, could it be accessible and open to be changed and tweaked for chassis upgrades and changes and will it calculate scrub radius? Can I have a copy? .... just noticed you have Mk1. Ignore above
No, I didnt mention it, but I hadnt forgot about it. All measurements were taken off my car, by me, with standard wheel diameters fitted Obviously tyre dia changes things, but Im more concentrating about offset, since the same rolling radius wheels are 'normally' fitted, but with incorrect et. Mickey, when setting up a car its the actual car you measure, and not the drawings. Drawings can be different to whats found on the actual car, as I found out once.
Im trying to get to grips with this. Im running ET24 15 inch wheels on my race car (mk1), I have to to clear the spring platforms - and I cant get even shorter springs with helpers, as I wouldnt have enough travel. A bit of toe-out. Im not finding bump steer on track, and all feels very good. Am I getting massive scrub due to the offset? Is the scrub mainly during cornering? Interested in learning, so thanks for posting your wisdom.
I've been mainly house-bound of late, so decided to draw up the MkII front suspension uber accurately. The scanner cut off the lefthand side of this drawing! They are 6 x 14 ET 38 on Audi 80 hubs. Using ME10 CAD I can draw separate parts, and superimpose everything on top of each other, to give an overall arrangement. I'm sure it's pretty accurate as I got the 0.50 degree negative camber by setting the ball joint at the mid point in the wishbone slots. As a design engineer, I had to assume that the German engineer thought as I did and used the same thought process as I do. ie. All design dimensions are base on 1000mm divide by 2, 4, 8, 10, 12.5, 25, .... 125, 250, 500, 1000, etc. I may be alittle out, as I found that the front track came out at 1435 instead of 1432!
Great work, if you are up for trying out new ideas what would the scrub be on a 195 50 r15 et35 be on a mk2?
Tom. I will produce a drawing for you. But. I guess you are interested in the scrub radius when the car is loaded? The drawing I did was for the static set-up, with the car at kerb weight. This, of course, is the arrangement when the car is being set up for camber. I did this so that I could ascertain the accuracy of my drawing by checking the camber angle. If you want me to check the loaded condition, can you arrange for the 'X' dimension to be measured when the car is loaded? Also. I got the rolling radius of the tyres from a web site which did not take the rim width into account. If you want a really accurate check, can you find the dynamic rolling radius for you exact tyre/rim combination? Dave.
SDad , how long did it take you to be able to draw like that? Or were you always artistic? and have you interest in helping me figure out a bump steer issue on my rally car?
Std MkI and II steering geometry Great thread with excellent information for us tekheds seeking to engineer changes rather than guesstimate same Confession: when rebuilding my MkII suspension a year ago I first loaded the car to simulate a 70kg driver and 1/2 tank gas on a level floor, then supported the body at that height after removing the wheels - - next removed the springs, substituted gutted gas shocks, and placed the wishbones at standard ride height for initial measurements - - then cycled the front suspension throughout its full range including steering, while using plumb bobs to register relevant pivot centres onto masking tape applied to the garage floor Idea was to obtain a set of static dimensions similar to Daved's for a local software engineer to create a 3D programme with which to model proposed changes Returned from work the next day to find a certain person had "cleaned up" the garage including removing said tape If anyone has a Mk II 3D or 2D suspension programme I'd really appreciate a copy - - PS If possible please include brake disc std location, as offset may require changing in order to remain centered over the tyre contact pivot point
I have been re-measuring, and, re-drawing, all of the front suspension components because I was unsure as to how accurate my first attempt was. I was concerned because I was unable to replicate the only two definative dimensions of which I am aware. Firstly: I was getting the front track out by about 3mm over wide. Secondly: I was unable to get the dimensions between gear box flanges, from the VWMS Manual, and found these were about 3mm undersize! So the differences are in opposite directions? Having re-measured everything, I was pretty happy with all of the body/subframe/strut/wishbone/topmount dimensions, but, I found the one thing difficult to measure was the front upright. If I had a proper metrology lab I might be happy, but I am struggling with a bench and a digital caliper. My concern is the position of the strut mounting hole relative to the inner bearing circlip groove. The inner face of the wheel bearing is utilsed to check the dimension between gearbox output flanges. So I drew it up as measured: Then re-drew it with a 1mm difference. The results are as below. I also wondered what effect an error in strut length would have, and drew a set-up to check. So. Errors in upright dimensions have a serious effect on the accuracy of scrub radius and kingpin inclination. Strut length (position ot top mount) have very little effect. My conclusion is that: Without uber accurate data drawing the arrangement proves of very little use. Sorry Tom and Tris. It looks like I can't help you. I recon LCT's idea of making a staniforth style string computer to investigate the geometry is about the only safe way to do it!
