Tony Posted November 29, 2008 Report Share Posted November 29, 2008 I had a BMW customer who had owned his M3 for some years and has had tyre wear/ handling issues. He's had the Geometry done several times in different places and each time the car didn't feel right. So i measured the chassis and the rear cambers were twice the values they should have been, i asked if the car was intended for the track, the answer was no. So why are the cambers so deep? He had the Geometry reports from the other company's with him and they looked ok'ish..... so why the camber now? I asked has "any work" been done to the car since the last Geometry "no!" Then the penny dropped... The BMW needs the suspension preloaded by adding 68kg on each front seat, 21kg in the boot and a full tank of fuel.... none of the other company's had done this So in essence they had lowered the camber to the OEM positions without respecting the fact the positions assume the car is weighted.... I did add the weights, hence the deep cambers. Sometimes the measurements we gather, however strange cannot be explained but i personally feel happier knowing why the chassis is so distressed. Quote Link to comment Share on other sites More sharing options...
Bazza Posted November 29, 2008 Report Share Posted November 29, 2008 ok this has got me thinking !! if the measurements are done with the car loaded up then the car is unloaded and remeasured would this not give the data required to then measure the car unloaded ?? Quote Link to comment Share on other sites More sharing options...
CIH Posted November 29, 2008 Report Share Posted November 29, 2008 Must have made a right mess of the tyres. Did you measure it without the weights too ie; to actually see the shift ? I always mean to try but never have the time. Quote Link to comment Share on other sites More sharing options...
Tony Posted November 29, 2008 Author Report Share Posted November 29, 2008 ok this has got me thinking !! if the measurements are done with the car loaded up then the car is unloaded and remeasured would this not give the data required to then measure the car unloaded ?? Why would you want to do that though... Surly you would only load since this is the correct "moment" required in the suspensions range. Quote Link to comment Share on other sites More sharing options...
Tony Posted November 29, 2008 Author Report Share Posted November 29, 2008 Must have made a right mess of the tyres. Did you measure it without the weights too ie; to actually see the shift ? I always mean to try but never have the time. No the tyres where fine since the cambers were light... it was the handling that was impaired. Quote Link to comment Share on other sites More sharing options...
Bazza Posted November 29, 2008 Report Share Posted November 29, 2008 ok this has got me thinking !! if the measurements are done with the car loaded up then the car is unloaded and remeasured would this not give the data required to then measure the car unloaded ?? Why would you want to do that though... Surly you would only load since this is the correct "moment" required in the suspensions range. to save having to load it up if it is measured when loaded, surely when unloaded it must return to a static position, that could be used to set the cars unloaded Quote Link to comment Share on other sites More sharing options...
Tony Posted November 29, 2008 Author Report Share Posted November 29, 2008 ok this has got me thinking !! if the measurements are done with the car loaded up then the car is unloaded and remeasured would this not give the data required to then measure the car unloaded ?? Why would you want to do that though... Surly you would only load since this is the correct "moment" required in the suspensions range. to save having to load it up if it is measured when loaded, surely when unloaded it must return to a static position, that could be used to set the cars unloaded I see your point... Within the "complexities" of Geometry BMW decided that particular "preloaded" position would cater for most eventualities.... Like the 2.4 children, average fuel loads, motorway/ town dynamics and so on.... I agree with you, let's have the naked car and target "suggested data" then dial in the "average factor".... Quote Link to comment Share on other sites More sharing options...
Rich Posted November 29, 2008 Report Share Posted November 29, 2008 Then the penny dropped... The BMW needs the suspension preloaded by adding 68kg on each front seat, 21kg in the boot and a full tank of fuel.... none of the other company's had done this What I don't understand is if all that weight is added to measure the chassis when removed the angles will change. So how is it any different from measuring the chassis with no weight and then adding it? Quote Link to comment Share on other sites More sharing options...
Tony Posted November 29, 2008 Author Report Share Posted November 29, 2008 Then the penny dropped... The BMW needs the suspension preloaded by adding 68kg on each front seat, 21kg in the boot and a full tank of fuel.... none of the other company's had done this What I don't understand is if all that weight is added to measure the chassis when removed the angles will change. So how is it any different from measuring the chassis with no weight and then adding it? It's so that the chassis is at it's "mid moment" dynamically (although the cars static) From this suggestion you can factor the average loads (human) and average aerodynamics. The only plus from this method is that it will counter areas like coil sag.... whereas the Jap method is to measure the "sag" then use their "height dependant" scale. Quote Link to comment Share on other sites More sharing options...
Rich Posted November 29, 2008 Report Share Posted November 29, 2008 Then the penny dropped... The BMW needs the suspension preloaded by adding 68kg on each front seat, 21kg in the boot and a full tank of fuel.... none of the other company's had done this What I don't understand is if all that weight is added to measure the chassis when removed the angles will change. So how is it any different from measuring the chassis with no weight and then adding it? It's so that the chassis is at it's "mid moment" dynamically (although the cars static) From this suggestion you can factor the average loads (human) and average aerodynamics. The only plus from this method is that it will counter areas like coil sag.... whereas the Jap method is to measure the "sag" then use their "height dependant" scale. Think I get it now...so when the car is moving the suspension is under more load than what it would be stationary when it's measured. So by adding the extra weight you're compensating for this? So why does this not apply to all cars? Quote Link to comment Share on other sites More sharing options...
Tony Posted November 29, 2008 Author Report Share Posted November 29, 2008 Yes the weight simulates the suspensions articulation from that "loaded point". The method differs between marques, most German cars need loading, most Jap cars have a static height chart, most European cars don't give a flying duck. Personally i feel the Jap method is best mainly because any modifications to the car can be easily mathed into a height dependant scale, whereas the load dependant German method opens much more variables to the modified car. Quote Link to comment Share on other sites More sharing options...
89mustang Posted December 2, 2008 Report Share Posted December 2, 2008 Just to butt in on this thread, re European cars, Tony, how do you deal with Pug, Citroen, they require loads of weight to get to the measurement height. Saxo/106 etc sit on their arse at adjustment height? Quote Link to comment Share on other sites More sharing options...
Tony Posted December 2, 2008 Author Report Share Posted December 2, 2008 Just to butt in on this thread, re European cars, Tony, how do you deal with Pug, Citroen, they require loads of weight to get to the measurement height. Saxo/106 etc sit on their arse at adjustment height? Within reason we load them, fortunately most times you are given a trim height table of settings. Quote Link to comment Share on other sites More sharing options...
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