Tony Posted September 9, 2006 Report Share Posted September 9, 2006 The included angle is the inclination/declination of the kpi/sai/sji depending on your preferred terminology, +- the actual Camber. KEY: White:- Tyre Blue:- Inclination/Declination Red:- Camber By manufacture there is a deliberate need to determine where the Camber and the kpi angles meet at the tyres footprint, this intersection is the 'scrub radius'. Within the actual contact patch of a 205mm front tyre at normal speed the scrub radius is an oval consisting of about 115mm width, 60mm length (consider the centricities) within this contact patch the steering axis, longitudinal axis and Camber angle projection must fall within that footprint. The driven position of the scrub radius actuating on the footprint changes with the steering actions and the cornering actions, if all chassis dynamics has been considered then the swapping of forces acting within the scrub radius are balanced and the car will drive are desired......but? wim asks you this?..... Lower the car, change the wheel off-set then what repercussions do you feel might happen. The reason for this prompt is that the consequences are often unexpected but does have a reasonably simple solution assuming the car is Geometrically adjustable. Quote Link to comment Share on other sites More sharing options...
discount tyres dan Posted September 10, 2006 Report Share Posted September 10, 2006 ohhh i think i know.. i learnt the hard way when i put 205/60 13 capri wheels on my escort mark3. the offset was totaly different.. tiny steering wheel didnt help much either Quote Link to comment Share on other sites More sharing options...
Tony Posted September 10, 2006 Author Report Share Posted September 10, 2006 ohhh i think i know.. i learnt the hard way when i put 205/60 13 capri wheels on my escort mark3. the offset was totaly different.. tiny steering wheel didnt help much either Well done dan...remember this is not a test only an observation of something that does effect a car if the suspension or wheels are modified.... In your example dan how did the car feel to drive? Quote Link to comment Share on other sites More sharing options...
discount tyres dan Posted September 10, 2006 Report Share Posted September 10, 2006 as if the wheels werent attached to anything, the car would tram-line in ruts, self centering of the steering wheel was non existant and i needed a crow bar to turn the steering at low speeds Quote Link to comment Share on other sites More sharing options...
Tony Posted September 10, 2006 Author Report Share Posted September 10, 2006 as if the wheels werent attached to anything, the car would tram-line in ruts, self centering of the steering wheel was non existant and i needed a crow bar to turn the steering at low speeds Perfect example and explanation of incorrect placement of 'scrub radius'... We have an under-written law on the position of the scrub, this is calculated from the wheel off-set and the Kingpin off-set. This law 'suggests' a scrub radius of 0?.... mechanically the KPI declination (perpendicular) and the Camber angle will correlate at the 0 point of the radius... very convenient for today's standards i welcome that The example you displayed moved the scrub to the outside of the contact target, 1" of displacement will open a catalogue of problems regarding directional and correctional control.... look at that image again? Respect the fact that the projected positions nowadays are almost surgical in the intended target. Geometrically we need to respect and understand the 'scrub radius'..... some years ago i recall a prominent plc company seeking resolve with a combined modification that did not work... wisly the reason was realized as the wheel off-set and simple testing with other wheels proved that. All happy reading but i ask you this dan..... If a miss-matched combination in the scrub radius area was in front of you.... how would you deal with this? Remember matey this is not a test only an exploratory question. Quote Link to comment Share on other sites More sharing options...
discount tyres dan Posted September 10, 2006 Report Share Posted September 10, 2006 if i hadnt seen a geometry report i would check to see if the wheels are the correct offset (including spacers if fitted) check for any signs of damage to strutt and hub assemblys (cracked paint could indicate a bend somewhere) also if the car has been lowered wthout being adjusted this could throw the IA out. if i had a geom report obviosly this would be a lot easier, the easiest to ajust would be camber to point the bottom of the wheel at the point the kpi meets the road. early fiesta's and golfs are great examples when lowered, the camber goes all over the place Quote Link to comment Share on other sites More sharing options...
Tony Posted September 10, 2006 Author Report Share Posted September 10, 2006 if i hadn't seen a geometry report i would check to see if the wheels are the correct offset (including spacers if fitted) check for any signs of damage to strut and hub assemblies (cracked paint could indicate a bend somewhere) also if the car has been lowered without being adjusted this could throw the IA out. if i had a geom report obviously this would be a lot easier, the easiest to adjust would be camber to point the bottom of the wheel at the point the kpi meets the road. early fiesta's and golfs are great examples when lowered, the camber goes all over the place Dan you are spot on! Manipulation of the Camber will change the position at the Scrub radius, but this is dependant on the area that allows the adjustment..... At the strut the correction is minimal to the KPI, inboard adjusters below the wishbone commands much movement in the target scrub... again look at the image displayed... you can see manipulation of the lower control arm will direct the actual placement of the scrub radius.... suspension modifications and indeed wheel modifications are easier to image if we understand the target area....... Where is the Scrub radius? and what value is it -10mm +10mm (shrug)... It is visible in this image, and it is realistic to image the position in advance of any modifications. Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted August 4, 2007 Report Share Posted August 4, 2007 Tony, you know me as Robbins on MEG. I understand most of what has been said in this thread, and I'm starting to think that perhaps the Eibach springs have made my car handle worse because they do not allow the maximum amount of scrub area that is normally used. Quote Link to comment Share on other sites More sharing options...
jammy Posted August 4, 2007 Report Share Posted August 4, 2007 i put pug gti wheel's on a 60mm dropped escort and it trashed the set up tatally... offset was well off and camber went real aggressive got shed loads of tramlinin and torqe steer and really unstable at speed's Quote Link to comment Share on other sites More sharing options...
Tony Posted August 4, 2007 Author Report Share Posted August 4, 2007 Tony, you know me as Robbins on MEG. I understand most of what has been said in this thread, and I'm starting to think that perhaps the Eibach springs have made my car handle worse because they do not allow the maximum amount of scrub area that is normally used. Welcome to wim.... The "scrub radius" is a hard language to grasp..... Maybe try this thread> http://www.wheels-inmotion.co.uk/forum/ind...?showtopic=1495 to see if it opens some more doors.. Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted August 4, 2007 Report Share Posted August 4, 2007 Thanks Tony, so what are your thoughts on my issue? Could I be correct in saying the lowering springs have spoiled the handling? Quote Link to comment Share on other sites More sharing options...
Rich Posted August 5, 2007 Report Share Posted August 5, 2007 Although mine is a MK2 I have lowered it 30mm on Eibach springs and it's improved the handling alot, more noticeably body roll and tramlining. Wasn't there some kind of handling issue on the MK3 with 18's anyway, I'm sure I read that somewhere? Welcome to WIM as well Quote Link to comment Share on other sites More sharing options...
Tony Posted August 5, 2007 Author Report Share Posted August 5, 2007 Thanks Tony, so what are your thoughts on my issue? Could I be correct in saying the lowering springs have spoiled the handling? I feel its a combination of the lowering and the wheels. The scrub radius is on the outside of the tyres. You need to test this theory by borrowing a set of stock wheels and see how this changes the drive. If my thoughts are correct then a set of camber adjusters will be needed. Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted August 5, 2007 Report Share Posted August 5, 2007 Thanks Tony, so what are your thoughts on my issue? Could I be correct in saying the lowering springs have spoiled the handling? I feel its a combination of the lowering and the wheels. The scrub radius is on the outside of the tyres. You need to test this theory by borrowing a set of stock wheels and see how this changes the drive. If my thoughts are correct then a set of camber adjusters will be needed. The car drives how it should on 16" wheels (205/55/16), could you give me a run down on the camber adjusters please? Quote Link to comment Share on other sites More sharing options...
Tony Posted August 5, 2007 Author Report Share Posted August 5, 2007 Thanks Tony, so what are your thoughts on my issue? Could I be correct in saying the lowering springs have spoiled the handling? I feel its a combination of the lowering and the wheels. The scrub radius is on the outside of the tyres. You need to test this theory by borrowing a set of stock wheels and see how this changes the drive. If my thoughts are correct then a set of camber adjusters will be needed. The car drives how it should on 16" wheels (205/55/16), could you give me a run down on the camber adjusters please? It's kind of good news we now know why the car handles pants.... The solution is to re-direct the SR within the steer axis. Depending on the year of the car Eibach make camber adjusters, part number 5.89675k Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted August 5, 2007 Report Share Posted August 5, 2007 Its as if when cornering the extra 2cm of each tyre is not making contact with the road! The part number you specified is for the Ford Cougar apparently. Maybe I'm a lost cause. Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted August 5, 2007 Report Share Posted August 5, 2007 I have just had a look on the Eibach website, they do not do alignment kits for my model (2003 Mondeo). They do however sell spaces, from 30 to 50. Would this help alter the camber in my favour? Quote Link to comment Share on other sites More sharing options...
Tony Posted August 5, 2007 Author Report Share Posted August 5, 2007 Its as if when cornering the extra 2cm of each tyre is not making contact with the road! The part number you specified is for the Ford Cougar apparently. Maybe I'm a lost cause. The SR is incorrect hence your complaint.... It feels horrible. The part number according to my information is the same, Cougar/Mondeo. Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted August 6, 2007 Report Share Posted August 6, 2007 I'm struggling to find the part, every where keeps pointing at a Mercury Cougar. With my current alignment settings will my tyres wear unevenly, as I guess thats my main concern. I have a track day on friday and the weather looks like its going to be dry so I have a real chance of experiementing and seeing what it can do. Assuming the PSI is correct, will be tears wear evenly? Quote Link to comment Share on other sites More sharing options...
Tony Posted August 6, 2007 Author Report Share Posted August 6, 2007 I'm struggling to find the part, every where keeps pointing at a Mercury Cougar. With my current alignment settings will my tyres wear unevenly, as I guess thats my main concern. I have a track day on friday and the weather looks like its going to be dry so I have a real chance of experiementing and seeing what it can do. Assuming the PSI is correct, will be tears wear evenly? What are your current alignment settings? The part number i have for the adjusters is from demon tweeks. Maybe you should contact them direct 01978 664555 www.demon-tweeks.co.uk Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted August 19, 2007 Report Share Posted August 19, 2007 Lets expand on the original topic. A lot of this is new to me so forgive me if anything is wrong. Brown Line - The more tyre here the better? Blue Line - The scrub radius, on most cars the red and purple line should meet at the bottom? Green Line - Any tyre behind the KP is of no use when cornering? Have I go that right? Quote Link to comment Share on other sites More sharing options...
Tony Posted August 19, 2007 Author Report Share Posted August 19, 2007 Lets expand on the original topic. A lot of this is new to me so forgive me if anything is wrong. Brown Line - The more tyre here the better? Blue Line - The scrub radius, on most cars the red and purple line should meet at the bottom? Green Line - Any tyre behind the KP is of no use when cornering? Have I go that right? The objective is to have a zero S/R on modern cars. So the blue line is the target with the lines intersecting at or just below the road surface. A S/R in the brown area will make the steering feel very nervous..... As if the front wheels are trying to hug grandma. A S/R in the green area suppresses the steering reply... An uncomfortable numb feel.... Almost dead requiring a lot of driver input. As you can now see if you change the camber or the wheels off-set then the target S/R may miss the intended contact patch within the steer axis "Blue" Quote Link to comment Share on other sites More sharing options...
ek9moo Posted October 12, 2007 Report Share Posted October 12, 2007 I’ve done this on my ek4 works very well, was just wondering about the dynamics of this with the camber slope of the Honda, you state that you want the zero scrub centre to be in the blue area get that. Here is my Q taking into account the dynamic camber on fully loaded steady state corner, for the range of the camber window where would you favour the scrub radius centre for optimal lateral G. I want to check I’m not stupid on this. pez Quote Link to comment Share on other sites More sharing options...
Tony Posted October 12, 2007 Author Report Share Posted October 12, 2007 I’ve done this on my ek4 works very well, was just wondering about the dynamics of this with the camber slope of the Honda, you state that you want the zero scrub centre to be in the blue area get that. Here is my Q taking into account the dynamic camber on fully loaded steady state corner, for the range of the camber window where would you favour the scrub radius centre for optimal lateral G. I want to check I’m not stupid on this. pez Well, there are three possible conditions for scrub radius – positive, zero, or negative. Positive scrub radius can be used to add a resistance to turn and helps keep the car stable (often mentioned as adding “feel†to the car) and is what you would normally use in a setup. A positive scrub radius also slightly reduces castor applied camber and has small effect on inclination applied camber. Zero scrub radius essentially has no effect on the handling of the car, but without it the handling can be a little nervous, hence the preference for some positive scrub radius. Negative scrub radius would have the opposite effect of a positive scrub radius....encouraging the car to enter a turn and therefore making it shaky in a straight line or even begin to wander. To optimize lateral G i would be inclined to concentrate on pneumatic slip angles and camber-castor gains. Quote Link to comment Share on other sites More sharing options...
ek9moo Posted October 12, 2007 Report Share Posted October 12, 2007 thanks that makes, sense bang for buck and all that the slip angles are very well controled and are in the zone for the tyre, the camber caster could be worth and think mind, will need quite a lot more work than the basics all the best pez Quote Link to comment Share on other sites More sharing options...
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