Bazza Posted December 30, 2006 Report Share Posted December 30, 2006 dynamic index there i typed it again i have no problem typing it or saying it, what i do have a problem with, is understanding what it means can us simpletons have an "idiots guide" to what it is, how its measured and what effects it has nothing too technical, just a quick run down Quote Link to comment Share on other sites More sharing options...
nick the greek Posted December 30, 2006 Report Share Posted December 30, 2006 If it makes you feel better Baz, I don't even know what one of them is Quote Link to comment Share on other sites More sharing options...
TDIPLC Posted December 30, 2006 Report Share Posted December 30, 2006 My (very basic) understanding is that the DI is a factor of the relationship beween the vehicles mass and it's wheel base. Sam is off today, so unless he logs on from home this weekend, I will ask him to provide a substantive answer on Tuesday Quote Link to comment Share on other sites More sharing options...
Tony Posted December 30, 2006 Report Share Posted December 30, 2006 I think Sam made an excellent summary here:- http://www.wheels-inmotion.co.uk/forum/ind...c=642&st=20 Bazza you haven't been paying attention have you Quote Link to comment Share on other sites More sharing options...
Bazza Posted December 30, 2006 Author Report Share Posted December 30, 2006 I think Sam made an excellent summary here:- http://www.wheels-inmotion.co.uk/forum/ind...c=642&st=20 Bazza you haven't been paying attention have you well i was kind of paying attention, i think you missed the two key words "simpletons" and "idiot" as normal, both sam and yourself show your very in depth understandings of a subject unknown to the minions, but sadly loose a few of us on your way perhaps drawings on the board would be better ps.....if you read marks answer, he technically in an engineers type of way, says "i dont know either" Quote Link to comment Share on other sites More sharing options...
Tony Posted December 30, 2006 Report Share Posted December 30, 2006 I think Sam made an excellent summary here:- http://www.wheels-inmotion.co.uk/forum/ind...c=642&st=20 Bazza you haven't been paying attention have you well i was kind of paying attention, i think you missed the two key words "simpletons" and "idiot" as normal, both sam and yourself show your very in depth understandings of a subject unknown to the minions, but sadly loose a few of us on your way perhaps drawings on the board would be better ps.....if you read marks answer, he technically in an engineers type of way, says "i dont know either" Indeed.... Anyway a good boss simply needs to ensure a reasonable understanding for the overall Geometry topics... I have been setting Geometry for 25yrs only to realise it's just a derivative of dynamic indexing. Sam@tdi is way more advanced on the interior of the DI structure, hence why i rape him for information to feed my own inquisitiveness. Also i understand your question. I forget this club is an arena to enable members to learn about a complicated topic, i apologize. I must agree with Mark though and suggest that Sam@tdi to construct a more understandable version of the topic if only that i can read how to converse within this field..... In other words if i do it, it will read like Gobble-a-duke... Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted January 2, 2007 Report Share Posted January 2, 2007 Ok sorry for the confusion I’ll try to clear things up A Dynamic Index is the output of Inertia Match Theory Inertia Match theory describes the relationship between a vehicles Centre Of Gravity position (COG), the vehicles wheel base and then it's yaw inertia (mass squared). There is no voodoo, the hard truth of it is that a 50/50 weight distribution will always give the best Dynamic Index figure for a given yaw inertia and i'll cover the various techniques and tricks used to attain this in a moment. There's no doubt about it that Inertia Match Theory is much more important for a vehicle design engineer who is working for a OEM manufacturer than it is to us working in the after market, this is because vehicle wheelbase will always be pre-defined and indeed set in stone by the time we're actually dealing with a car. However simply by being aware of Inertia Match Theory and its various mechanisms we can gain valuable knowledge about a chassis by calculating it's dynamic index. The dynamic index or DI gives us a unique insight into the way the chassis will behave when maneuvered on a ground plane at speed, armed with this knowledge we are better equipped to then go forward with tuning the chassis to suit any specific needs. Below is a diagram showing the output of Inertia Match Theory after the theoretical length C has been calculated. Below is a diagram showing a car with a DI less than 1.00... a classic example of a car like this would be a classic VW Beetle which has a DI of around 0.48, these are so bad and so far past being "nimble" that they are pretty much un-controllable and un-drivable at the grip limit This is a diagram of a car with a DI greater than one, most modern production cars fall into this category in varying degree's, this makes the car feel sluggish to respond to steering wheel commands In many cases like my Civic it's possible to adjust the vehicles front and rear ride heights and therefore weight distribution in order to change the DI to something closer to 1.00, it's an everyday road car so certain ideal options listed below are unrealistic. Under motorsport or track day circumstances it becomes possible to seriously alter the weight distribution not only by a adjusting ride heights but also by relocating heavy items such as fuel tanks and batteries etc. The other major benefit under these circumstances is the ability to genuinely adjust the chassis mass (making the car either heavier or lighter) as this is a serious factor in calculating the DI. Hopefully this reads ok and makes sense, hopefully you can see that whilst it's important to understand Inertia Match Theory it only makes up one aspect of chassis dynamics... suspension design and calibration, static and kinematic geometry, braking and driving force variation are all equally important. And remember we only do all of this in order to control the tyre contact patch... the tyre is king! Quote Link to comment Share on other sites More sharing options...
Tony Posted January 2, 2007 Report Share Posted January 2, 2007 Excellent explanation Sam@tdi, i thoroughly enjoyed reading that. Quote Link to comment Share on other sites More sharing options...
Roger440 Posted January 2, 2007 Report Share Posted January 2, 2007 Excellent explanation Sam@tdi, i thoroughly enjoyed reading that. Agreed, an excellent explanation. Quote Link to comment Share on other sites More sharing options...
peter026 Posted January 2, 2007 Report Share Posted January 2, 2007 So, by carrying a lot of weight in the back of, say my Hilux Surf, it dramatically alters the DI and therefore the handling somewhat. I find all this DI and geometry fascinating. Before joining this forum, a vehicle to me was a piece of metal resting on four bits of rubber. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted January 2, 2007 Report Share Posted January 2, 2007 Excellent explanation Sam@tdi, i thoroughly enjoyed reading that. Agreed, an excellent explanation. Thanks guys, glad it made sense So, by carrying a lot of weight in the back of, say my Hilux Surf, it dramatically alters the DI and therefore the handling somewhat. Yes definitely, try it, in a pick up normally you'll start with a low DI when empty (apprx 0.90) the DI would then get higher as you add mass, you'll normally feel the centre of rotation move rear-ward as you approach the chassis weight limit Quote Link to comment Share on other sites More sharing options...
Tony Posted January 3, 2007 Report Share Posted January 3, 2007 Excellent explanation Sam@tdi, i thoroughly enjoyed reading that. Agreed, an excellent explanation. Thanks guys, glad it made sense So, by carrying a lot of weight in the back of, say my Hilux Surf, it dramatically alters the DI and therefore the handling somewhat. Yes definitely, try it, in a pick up normally you'll start with a low DI when empty (apprx 0.90) the DI would then get higher as you add mass, you'll normally feel the centre of rotation move rear-ward as you approach the chassis weight limit Sam@tdi you have a fluid ability to communicate technical issues, i say again "excellent explanation" for a difficult topic..... Please continue Quote Link to comment Share on other sites More sharing options...
Continuity Posted February 8, 2007 Report Share Posted February 8, 2007 I find all this DI and geometry fascinating. Before joining this forum, a vehicle to me was a piece of metal resting on four bits of rubber. You mean it isnt Quote Link to comment Share on other sites More sharing options...
Tony Posted February 8, 2007 Report Share Posted February 8, 2007 I find all this DI and geometry fascinating. Before joining this forum, a vehicle to me was a piece of metal resting on four bits of rubber. You mean it isnt Tyre contact is a pin with the empierstatebuilding resting on it. Chassis dynamics encompasses all cars, all marques in all circumstances, by design or demand as an expedient for the developer so taken seriously in the indexing solution regime... Quote Link to comment Share on other sites More sharing options...
jon Posted February 8, 2007 Report Share Posted February 8, 2007 If i'm honest I still don't get why this forum has gone DI crazy. To me it reads a DI of 1 might be nice, but might not be the fastest way around the track. And if it's so important (and i realise this is, in part a stupid thing to say) why isn't it all over the chassis books I pour through and all over the net. Quote Link to comment Share on other sites More sharing options...
Tony Posted February 8, 2007 Report Share Posted February 8, 2007 If i'm honest I still don't get why this forum has gone DI crazy. To me it reads a DI of 1 might be nice, but might not be the fastest way around the track. And if it's so important (and i realise this is, in part a stupid thing to say) why isn't it all over the chassis books I pour through and all over the net. Because we are first to visually-verbally combine Geometry/ indexing/ chassis calibration/tyres in one forum.... "Why is D1" so prominent.... Because it's perfect! Any conversation can be graded from this position allowing realistic solution/ development from this path.... Tell me this jon? the "diffuser" you fitted aerodynamically evaluate the static DI for lets say.... simple throttle off corner in weight transition.. Inertia displacement.. maybe some simple Geometric gains, camber-castor.toe transitions... Books host past examples, wim hosts all examples "now".... History is an acronym of "His story" all books in truth are yesterdays news, today's chip wrappings. Quote Link to comment Share on other sites More sharing options...
jon Posted February 8, 2007 Report Share Posted February 8, 2007 Yeah wonderful. But, again, my understanding is we're simply putting a number on whether the car understeers or oversteers in a static yaw condition due to COG vs COR. That tells us what the cars weight should do if all things are equal but so what? They NEVER are!! Take for example the beetle. [please correct me if i'm wrong] Below is a diagram showing a car with a DI less than 1.00... a classic example of a car like this would be a classic VW Beetle which has a DI of around 0.48, these are so bad and so far past being "nimble" that they are pretty much un-controllable and un-drivable at the grip limit but, if i was to throw a pair of 335 section slicks on the rear and 135 space savers on the front, the car would still have a "loose" DI of .48 but I'd like to see you get it to oversteer. It would push everywhere and act as though it's DI was 10. I [think] I understand the principle of it, but to me as a driver and developer who wants to go as fast as the car will allow from where I sit it seems like a pretty pointless number. Quote Link to comment Share on other sites More sharing options...
Tony Posted February 8, 2007 Report Share Posted February 8, 2007 Yeah wonderful. But, again, my understanding is we're simply putting a number on whether the car understeers or oversteers in a static yaw condition due to COG vs COR. That tells us what the cars weight should do if all things are equal but so what? They NEVER are!! Take for example the beetle. [please correct me if i'm wrong] Below is a diagram showing a car with a DI less than 1.00... a classic example of a car like this would be a classic VW Beetle which has a DI of around 0.48, these are so bad and so far past being "nimble" that they are pretty much un-controllable and un-drivable at the grip limit but, if i was to throw a pair of 335 section slicks on the rear and 135 space savers on the front, the car would still have a "loose" DI of .48 but I'd like to see you get it to oversteer. It would push everywhere and act as though it's DI was 10. I [think] I understand the principle of it, but to me as a driver and developer who wants to go as fast as the car will allow from where I sit it seems like a pretty pointless number. Definition is the key question here.... In reality 335 rear and 135 front has no destination so the DI compassion is redundant. I think you need to detach domestic DI evolution and DI track evolution. For the track your DI is explosively critical to the chassis calibration and comparative examples above do not refer to the track car. Quote Link to comment Share on other sites More sharing options...
jon Posted February 9, 2007 Report Share Posted February 9, 2007 That's were we differ. In reality they do, just to a lesser degree. My MR2 has a DI of less than 1 due to the weight balance so should oversteer. Take into account the wider rear tyres, wider rear track and the rear aero and it understeers so the DI was of no use that I can see..? Quote Link to comment Share on other sites More sharing options...
Tony Posted February 9, 2007 Report Share Posted February 9, 2007 That's were we differ. In reality they do, just to a lesser degree. My MR2 has a DI of less than 1 due to the weight balance so should oversteer. Take into account the wider rear tyres, wider rear track and the rear aero and it understeers so the DI was of no use that I can see..? This is when chassis calibration comes into play.. I said a long time ago i have not finished with your cars Geometry.... As we know Geometry is a modifier allowing correction when the chassis cannot comply.. The need to officially set the DI then the chassis compliance gains/ losses/ pneumatic trail, then the Geometric attitude including known track requirements then adding a smattering of driver demands you might then have a constructed chance. Then you test it!.... Like before jon. On return the drivers feed-back commands fine-tuning of the chassis albeit DI, pneumatic or Geometric... Suppose my point is there is no absolute rule or route to the perfect car but there is a need to find a fingerprint, dynamic indexing is a powerful starting point for evolution. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted February 9, 2007 Report Share Posted February 9, 2007 Hey Jon I agree with you, I think at the moment we are spending far too much time thinking and talking about DI, it's one aspect, only one aspect! I think the reason you don't understand DI's relivence to your sw20 or to any other track based car is because you've mis-understood DI. It looks to me as though you beleive that a car with a DI less than one will have a rear first departure. And that a car with a DI more than one will have a front first departure... this is WRONG .... (notice I avoided the terms understeer and oversteer, but thats a discussion for a whole other thread some time soon) Think of the car as a system, and as with all systems it has 2 main features COMMAND and CONTROL (we're talking chassis not driver here). The steering wheels are the Command, the rear wheels are the Control. The "moment of instance" that the chassis rotates about dictates it's DI number, simple. The moment of instance that the chassis rotates about tells you how Command and Control are related in that particular chassis system... "does the rear tyre slip angle dynamically increase as i turn the steering wheel or does the rear tyre slip angle dynamically decrease as I turn the steering wheel?" that is the question that calculating the DI answers... nothing more, nothing less.... this has nothing directly to do with which tyres will saturate or "let go" first ... (as your beetle example graphically points out) but, it does have a great deal to do with the way the car will actually try to move, and therefore it has a great impact on the cars emotional relationship with the driver. I consider that car/driver relationship to be one of the most important things to get right, especially in a race car, especially if you want to go quick Quote Link to comment Share on other sites More sharing options...
jon Posted February 9, 2007 Report Share Posted February 9, 2007 Now that makes a bit more sense, thank-you Sam I'm sure I'll have more to say on this in the near future but now i have to work. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted February 9, 2007 Report Share Posted February 9, 2007 Cool Quote Link to comment Share on other sites More sharing options...
Tony Posted March 21, 2007 Report Share Posted March 21, 2007 jon... Sams comments here developed our set-up last week. His intimate knowledge enabled us to assume a platform for your driving appetite. Combining historic disadvantages of the MR2 with correctional calibration (however) foreign, like removing rear tyre saturation points developed a new platform for your cars dynamics.. The damper calibration you manipulated, and seemingly this resulted with a track car able to reply to your needs. I think now we can work on manufacturing the Geometric gains and tendencies...... Happy days Quote Link to comment Share on other sites More sharing options...
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