Wider is better?

[Adam Ginsberg]

Thanks Richard!
Cool stuff and, as always, written in a succinct NASA (the space guys, not the race guys), SAE kinda way.
I have a set of wheels that require me to run spacers up front for caliper clearance...as well as wider front track. Always liked that setup.

Todd....I don't think you fully understood the gist of RP's writeup.

[RichardP]

Yes! I have no friggin' clue how to tune a race car suspension.

The important part is that you don't need to understand the physics or do a bunch of math to do some very valuable tuning. You changed your car at the last event. Not only did you feel the results of the relatively subtle change, you were able to describe those changes to us and even break it down to different sections of a corner. That's the hard part. There are a lot of people who can't do that and studying a text book flat isn't going to solve it.

Write down what you changed and include a description of how it changed the feel of the car. Include lap time differences if you can. Also include any other factors that could have influenced the changes (weather, etc.)

Then go change something else to see what it does. Setting the car up with adjustable parts is of course a big help here...


Richard P.

[mitchntx]

Yes! I have no friggin' clue how to tune a race car suspension.

The important part is that you don't need to understand the physics or do a bunch of math to do some very valuable tuning. You changed your car at the last event. Not only did you feel the results of the relatively subtle change, you were able to describe those changes to us and even break it down to different sections of a corner. That's the hard part. There are a lot of people who can't do that and studying a text book flat isn't going to solve it.

Write down what you changed and include a description of how it changed the feel of the car. Include lap time differences if you can. Also include any other factors that could have influenced the changes (weather, etc.)

Then go change something else to see what it does. Setting the car up with adjustable parts is of course a big help here...


Richard P.

Exactly!

I'm no rocket scientist and really don't claim to know all the physics involved in tuning a car's setup.

What I HAVE learned is that when I make a change, I document the crap out of it. Detailed notes on the CHANGES in FEEL along with the hard data like lap times, tire pressures, tire temps, etc.

That yields a delta between point A and point B.

Get several of those deltas "plotted" and you can make a very educated guess about what to do and most importantly, HOW MUCH TO DO in order to help the car do what you want it to do.

I had 3 years worth of notes in my gear bag that was ripped off last spring. That was priceless information and wound up in a dumpster somewhere. :evil:

[AI#97]

Yes! I have no friggin' clue how to tune a race car suspension.

The important part is that you don't need to understand the physics or do a bunch of math to do some very valuable tuning. You changed your car at the last event. Not only did you feel the results of the relatively subtle change, you were able to describe those changes to us and even break it down to different sections of a corner. That's the hard part. There are a lot of people who can't do that and studying a text book flat isn't going to solve it.

Write down what you changed and include a description of how it changed the feel of the car. Include lap time differences if you can. Also include any other factors that could have influenced the changes (weather, etc.)

Then go change something else to see what it does. Setting the car up with adjustable parts is of course a big help here...


Richard P.

I get your point Totally! However, what I would like to get a good basic read on is the basics of "if the car is doing this, try this" so I am not going in the wrong direction given my available track time is pretty limited. I also need a "pit bitch" to help out with this as it seems I never have time, or the attention to take these notes. ops:

[marshall_mosty]

From the Mark Ortiz July Newsletter

(excerpts to give just the "good stuff")

If we have a live axle, and we leave the springs alone and add track width by moving the tires out, the car should get tighter (more understeer). The car will have the same amount of roll, the same angular roll resistance at both ends, the same amount of load transfer at the front tires, and the same amount of load transfer at the rear springs, but less load transfer at the rear tires, because the rear roll-resisting moment will be taken out over a wider base. The total load transfer will be less, and the reduction will all come at the rear. That should make the rear stick better compared to the front. Of course, the car can always be re-balanced using other changes.

So far, we have been analyzing effects of track width, and track width relationships, purely in terms of effects on load transfer. There are some other effects as well.

If we have a locked rear, and we are road racing, we generally have a greater tendency toward locked-axle push when we widen the rear track. With a limited-slip diff, there is a similar effect, only more subdued. However, if rear load transfer increases, that can make it easier to unload the inside rear tire in hard cornering, reducing locked-axle push instead, roll-resisting moment will be taken out over a wider base. The total load transfer will be less, and the reduction will all come at the rear. That should make the rear stick better compared to the front.

If we widen the front track by spacing the wheels out on the spindles, we increase caster jacking with steer. This can mean that the vehicle is tighter in sweepers yet freer in tight turns.

[BlueFirePony]

One thought on the last point about increasing the front track width in combination with rear track width....one of the side effects of increasing the front track width (as eluded to in the snippet) is that caster angle is increased and the impact of that is the addition of lateral mechanical forces that can tend to mask the tire breakaway.
In particular if both front and rear track width are increased without suitable adjustments elsewhere (ie. tire pressures, ride height, etc.) then the steering forces will generally be harder to read. That amounts to a tradeoff between performance and control IMO (but the math backs it up
Thats one of the reasons that while caster angle can be augmented on the S197 so I can make it handle more like other cars I've driven, I've avoided it because the feedback is much more valuable to me when I am driving on the limit of the tire.

So, I know it (track width) can make me faster - in some cases and to some extent - but if I spin because I don't sense the breakaway that the additional steering performance gives me, then its not really helping me is it ?