Tony Posted October 14, 2006 Report Share Posted October 14, 2006 wim wants to expand the current understanding in chassis dynamics and include corner weighting/pull downs into the overall race development experience, how valuable do you think this evolution is toward your cars set-up? Quote Link to comment Share on other sites More sharing options...
IanF Posted October 17, 2006 Report Share Posted October 17, 2006 wim wants to expand the current understanding in chassis dynamics and include corner weighting/pull downs into the overall race development experience, how valuable do you think this evolution is toward your cars set-up? I don't understand the question. So can't possibly answer Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted October 17, 2006 Report Share Posted October 17, 2006 Ok I’ll try and shed some light on the subject, lets concentrate on the process known as corner weighting at the moment. Before we can get into “how” corner weighting is carried out I think it’s important to understand “why”. One of the fundamental aspects of chassis design is inertia matching. It‘s a given that a chassis has mass and the centre of it’s mass is known as the chassis’s centre of gravity. The ideal chassis would have a low centre of gravity, an equal weight distribution on to all 4 of its wheels and it would have a wheelbase that gives the axles the correct amount of leverage upon the centre of gravity (dynamic indexing). The process of corner weighting is to place the chassis on four very accurate scales, one under each tire. This lets us know not only the exact overall weight but also the exact balance of the chassis whilst at rest. Once this information has been gathered it’s possible to make adjustments to the chassis’s mass distribution by either moving heavy components, ballasting, or for finer adjustments it’s possible to adjust the ride height at any one corner. Generally ride height adjustments tend to be more effective at adjusting right to left balance than the fore and aft balance simply due to the lengths involved. Quote Link to comment Share on other sites More sharing options...
Mark H. Posted October 17, 2006 Report Share Posted October 17, 2006 That sounds like it could be usefull. Especially if you plan on doing work that will change the weight/balance of the vehicle, eg installing a larger/heavier engine, a large sound system etc. It may also give you knowledge of which parts of the car have to carry more weight/do more work eg suspension tyres etc. Perhaps if done with every geometry check maybe 2 times a year could perhaps alert you do springs/dampers that are underperforming? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 17, 2006 Author Report Share Posted October 17, 2006 Ok I’ll try and shed some light on the subject, lets concentrate on the process known as corner weighting at the moment. Before we can get into “how†corner weighting is carried out I think it’s important to understand “whyâ€. One of the fundamental aspects of chassis design is inertia matching. It‘s a given that a chassis has mass and the centre of it’s mass is known as the chassis’s centre of gravity. The ideal chassis would have a low centre of gravity, an equal weight distribution on to all 4 of its wheels and it would have a wheelbase that gives the axles the correct amount of leverage upon the centre of gravity (dynamic indexing). The process of corner weighting is to place the chassis on four very accurate scales, one under each tire. This lets us know not only the exact overall weight but also the exact balance of the chassis whilst at rest. Once this information has been gathered it’s possible to make adjustments to the chassis’s mass distribution by either moving heavy components, ballasting, or for finer adjustments it’s possible to adjust the ride height at any one corner. Generally ride height adjustments tend to be more effective at adjusting right to left balance than the fore and aft balance simply due to the lengths involved. I love this topic There is nothing more satisfying than a chance to learn. What is obvious is that any Geometry set-up would be dependant of the corner weighting results and indeed solution... But i have a problem How would you suggest procedure with weighting/coil adjustment and Geometry positions? Let me explain at the moment i do not set coil positions until the Geometry is measured since if the Camber position is heavily negative it will lower that corners parallelogram and raise the diagonal partner, so currently i measure the positions correct the Camber then correct the trim height... then again correct the camber if needed, so do you feel the addition of weighting is a necessity during the overall set-up or something that could be a stand alone customer request? Quote Link to comment Share on other sites More sharing options...
Roger440 Posted October 17, 2006 Report Share Posted October 17, 2006 As you say, its good to learn! I've only done a few corner weighting jobs. Problem with it is, its quite time consuming, so not something most people will be interested in i suspect. Certainly not for most road cars anyway. Ive never assesed the difference between a car that just had the hieghts set up to the same car after corner weighting. Any one have any views on the scale of any benefits? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 17, 2006 Author Report Share Posted October 17, 2006 As you say, its good to learn! I've only done a few corner weighting jobs. Problem with it is, its quite time consuming, so not something most people will be interested in i suspect. Certainly not for most road cars anyway. Ive never assesed the difference between a car that just had the hieghts set up to the same car after corner weighting. Any one have any views on the scale of any benefits? I am sure Sam@tdi will summarize the value of weighting!.... Oddly enough Roger i get asked reasonably often if i do corner weighting, mainly by track day enthusiasts... Obviously this service would command a much higher price.... One that made me really think was a call i had for six S2000's to be weighted and set for the ring, since i did not serve that area i lost all six cars... This will not happen next season! Quote Link to comment Share on other sites More sharing options...
Mark H. Posted October 17, 2006 Report Share Posted October 17, 2006 I suppose ultimately, if you want WIM to be the complete package, then you need to offer the complete package, if you don't have the equipment then you won't be able too. Of course if you would only get a 50% return on the equipment cost until it needs replacing then it may not financially make sense. However it would seem that people are interested and it would further enhance your portfolio for people interested in using your services. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 17, 2006 Author Report Share Posted October 17, 2006 I suppose ultimately, if you want WIM to be the complete package, then you need to offer the complete package, if you don't have the equipment then you won't be able too. Of course if you would only get a 50% return on the equipment cost until it needs replacing then it may not financially make sense. However it would seem that people are interested and it would further enhance your portfolio for people interested in using your services. Well i hope so... In any business there is a need to react to the customers requests and cater for them professionally.. for some years wim has encompassed beds-poke set-ups in all manner of classes so the one stop performance shop seems a reasonable reply to the customer. Means to facilitate this promise althougth painful in cost is belayed from the opportunity to complete the task set for the customer, wim will fulfill this request. Quote Link to comment Share on other sites More sharing options...
Roger440 Posted October 17, 2006 Report Share Posted October 17, 2006 Interesting. Probably my own fault as we have never really advertised the fact we have corner weighting equipment!! Its not that expensive either (the eqipment) - releatively speaking. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 17, 2006 Author Report Share Posted October 17, 2006 Interesting. Probably my own fault as we have never really advertised the fact we have corner weighting equipment!! Its not that expensive either (the eqipment) - releatively speaking. Mate myself included!.... Your operation in this area seemingly lacks customer awareness.... It would be hyprocritical for me to say open up the visibility, that's obvious..... food for thought though, maybe the lack of action in the weighting department is as simple as marketing Quote Link to comment Share on other sites More sharing options...
Noel Posted October 17, 2006 Report Share Posted October 17, 2006 Just out of curiosity... is the car weighed with the driver in it? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 17, 2006 Author Report Share Posted October 17, 2006 Just out of curiosity... is the car weighed with the driver in it? In absolute terms for track precision yes, or at least ballast equivalent to the drivers weight. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted October 18, 2006 Report Share Posted October 18, 2006 Just out of curiosity... is the car weighed with the driver in it? In absolute terms for track precision yes, or at least ballast equivalent to the drivers weight. Bearing in mind the average driver weighs somewhere around 70-80kg you'll find it becomes more important the lighter the chassis is Quote Link to comment Share on other sites More sharing options...
scorps Posted October 18, 2006 Report Share Posted October 18, 2006 If you've ever been in the pits at a race meeting (BTCC) you see them weigh the cars on seperate corner scales with driver on board.... @ Sam, ...what about when there are 2 drivers at a race how would the set up be acheived for 2 drivers (different weight) and 1 car like at Le Mans. Quote Link to comment Share on other sites More sharing options...
jon Posted October 18, 2006 Report Share Posted October 18, 2006 Mean driver weight, heaviest of the two, lighest of the two. When you dealing with the placement of a few kgs either way the laptime advantage would become non existant. Remember on nearly all cars fuel will account for between 60kgs and 5kgs and will rarely be fully central. Quote Link to comment Share on other sites More sharing options...
Bazza Posted October 18, 2006 Report Share Posted October 18, 2006 Bearing in mind the average driver weighs somewhere around 70-80kg you'll find it becomes more important the lighter the chassis is could you stretch that average to about 85kg how are these weights attached and what do they use as weights Quote Link to comment Share on other sites More sharing options...
jon Posted October 18, 2006 Report Share Posted October 18, 2006 Bearing in mind the average driver weighs somewhere around 70-80kg you'll find it becomes more important the lighter the chassis is could you stretch that average to about 85kg how are these weights attached and what do they use as weights I hope Sam doesn't mind me butting in (and my information is correct) but... With corner balancing you don't add weight unless you've a category minimum to make up to, you just have to make the most of what you've got in the car. On a pure race car you can do things like move the driver around, how the engine is mounted, where the battery is, where the fuel is but all this is a bit extreme for a road car. My understanding is you'll never get 25% of the weight at each corner and rarely 50% of the weight each side or end. The best you can hope for is adjusting the ride height at each corner to adjust that corners load through the tyre onto the road and get the car reasonably well balanced. For idea distribution the left side tyres must have the same front to rear distribution as the whole car, same for the right. IE if the car balance is 60f 40r then the left front should carry 60% of the left hand side weight. Quote Link to comment Share on other sites More sharing options...
MacRS200 Posted October 18, 2006 Report Share Posted October 18, 2006 When I set my coilovers up I did a very easy and probably not too accurate measure of the weight on each corner. Jack the car up and take any pre-load off the spring so that it is just "filling" the gap between to top and bottom seats. Measure from the top of the arch to the wheel centre, drop the car back down and measure the same distance again. Knowing that the spring rate is say 10Kg/mm on the rear you can work out the load on that corner. Bearing in mind the already mentioned fuel and "bodies" load could be anywhere between a driver + a near empty tank (85Kg) and five people and a full tank (470Kg), between 7% and 36% of my cars weight. Don't really see the point of doing things any more accurately for a raod car. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted October 19, 2006 Report Share Posted October 19, 2006 Bearing in mind the average driver weighs somewhere around 70-80kg you'll find it becomes more important the lighter the chassis is could you stretch that average to about 85kg how are these weights attached and what do they use as weights I hope Sam doesn't mind me butting in (and my information is correct) but... With corner balancing you don't add weight unless you've a category minimum to make up to, you just have to make the most of what you've got in the car. On a pure race car you can do things like move the driver around, how the engine is mounted, where the battery is, where the fuel is but all this is a bit extreme for a road car. My understanding is you'll never get 25% of the weight at each corner and rarely 50% of the weight each side or end. The best you can hope for is adjusting the ride height at each corner to adjust that corners load through the tyre onto the road and get the car reasonably well balanced. For idea distribution the left side tyres must have the same front to rear distribution as the whole car, same for the right. IE if the car balance is 60f 40r then the left front should carry 60% of the left hand side weight. I'd say that’s a fair summary But believe it or not, it is entirely possible to make a car too snappy by making it too light for its wheelbase. This effect is addressed as part of a dynamic indexing process Quote Link to comment Share on other sites More sharing options...
Tony Posted October 20, 2006 Author Report Share Posted October 20, 2006 Sam@tdi But believe it or not, it is entirely possible to make a car too snappy by making it too light for its wheelbase. This effect is addressed as part of a dynamic indexing process Sam@tdi The 'indexing', is it actually possible this could form a calculation from all the variables then call this data 'a matter of fact' for the track and dynamics.... in other words in your opinion how accurate do you feel this data is in real terms. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted October 20, 2006 Report Share Posted October 20, 2006 Sam@tdi But believe it or not, it is entirely possible to make a car too snappy by making it too light for its wheelbase. This effect is addressed as part of a dynamic indexing process Sam@tdi The 'indexing', is it actually possible this could form a calculation from all the variables then call this data 'a matter of fact' for the track and dynamics.... in other words in your opinion how accurate do you feel this data is in real terms. Yes dynamic indexing is actually explainable with an equation and it is possible to make a dynamic index calculator that works reliably. The thing to bear in mind is that having a car with a dynamics index of 1.00 (perfect) simply means that you are not forced to follow any particular direction when setting up the many other aspects of the chassis and suspension. Having a good DI gives you choices as to how to approach the set-up Quote Link to comment Share on other sites More sharing options...
TDIPLC Posted October 21, 2006 Report Share Posted October 21, 2006 The new TDi project car has a Dynamic Index of around 1.7, which is a very long way from ideal. I think we have a bit of a challenge with this project Quote Link to comment Share on other sites More sharing options...
Tony Posted October 21, 2006 Author Report Share Posted October 21, 2006 This is very interesting... A D1 index of 1.00 is this an actual or a theoretical (perfect) goal? By comparison what index would you consider the average modern domestic car to be at? And (sorry) what index position is considered the worst overall. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted October 23, 2006 Report Share Posted October 23, 2006 It's very subjective, the lower the Dynamic Index the more agile and lively the chassis tends to feel. It's a very subjective thing but it's powerful, history suggests that drivers emotionally identify cars with DI's between 0.90 and 1.10 as cars that handle well. This is because the car with a DI of 1.00 tends to handle in a linear and predictable fashion, so when at the grip limit tend to behave in a way that’s intuitive to the average driver therefore the required steering corrections or throttle/brake responses seem to come "naturally". The best technical summary I can give is to say that with the chassis at the grip limit, if you were to experience a variance in yaw demand from the front wheels (perhaps encountering a road feature that increases vertical load on the tire) this would "increases rear slip angle" if the DI is lower than 1.00 but the same action "reduces rear slip angle" if the DI is greater than 1.00.... I hope that makes sense Regarding family cars, most tend to be a little higher than 1.00 and tend to get a lot more so as they are loaded with passengers or luggage. You would be amazed how massively far out some cars are. For instance the classic VW beetle which believe it are not has a weight distribution not too far away from 50/50 actually has a DI of 0.48 and I think it's a well know fact that an un-modified one is just straight up dangerous when approaching the grip limit This is usually as a result of a project going to the design house before it goes to the dynamics engineers. Quote Link to comment Share on other sites More sharing options...
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