Maximum Tractive Force

[Edward M. Kasprzak]

Strictly speaking, every calculation we do as engineers is wrong. We always make assumptions and apply equations which are a simplification of reality. The key is to make assumptions and use equations which give results that are "close enough" to reality. How close is "close enough" is up to the engineer to decide.

Speaking specifically about the TTC tire data (or any laboratory tire data for that matter), we know tire performance is a function of both the tire and the road surface. Since the test machine and the road have different surfaces, the results will be somewhat different. Also, lab conditions do not exactly match on-vehicle conditions. Lab data is still useful (if "wrong"), and its accuracy can be improved through comparison with real-world performance (e.g., a change of friction coefficient).

[Mike Cook]

Dr. Kasprzak,

I appreciate all you have done for the FSAE community. But to start out a post with 'every calculation we do as engineers is wrong' is a little disingenuous.

If you look at the tire data you can see Coefficient of Friction values up to about 3. This is almost off by a factor of 2 from what we generally see in the field. Most of the calculations I make as an engineer, may not be 100% accurate, but are pretty darn close. I wouldn't consider this pretty darn close. The tire data may be useful, but without a lot of research on relating tire test results to on track results the ttc data is difficult to use and have confidence. It is also difficult to compare one tire to another, since different tire compounds may behave differently on the sand paper belt.

Tire data is fun. It gives us more answers to the questions surrounding racecar dynamics. Engineers love answers. But, they should be a little more concerned with if the answers are right.

Instead of spending more and more money on laboratory testing, why don't we figure a way to test the tires on real asphalt.

Mike

[Jersey Tom]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Instead of spending more and more money on laboratory testing, why don't we figure a way to test the tires on real asphalt.

Mike </div></BLOCKQUOTE>

As if lab tire data wasn't a difficult can of worms as it is... I'm not sure whether taking it to that level is the best call.

That said, there is nothing preventing teams from doing their own track correlation of the data.

Admittedly I have been out of the loop for a bit, but I got the impression that few if any teams were really using the lab data to the most of its potential... or even doing back-to-back construction/compound/manufacturer evaluations.

In my not so humble opinion, I think the best thing is more education on application (albeit hard to come by!) and focusing on basics rather than adding additional complexity.

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jersey Tom:

In my not so humble opinion, I think the best thing is more education on application (albeit hard to come by!) and focusing on basics rather than adding additional complexity. </div></BLOCKQUOTE>

+1. There is a LOT you can do to make a car faster without ANY tire data.

[Edward M. Kasprzak]

Mike: The respect is mutual. I'm familiar with your contributions to these forums--they are appreciated.

I will note, however, that the TTC has not tried to mislead anyone. The discrepancy in grip between the TTC data and on-track performance is documented, with most feedback placing the grip at Calspan about 35-40% higher than on-track. Whether its the TTC or our (MRA) professional customers, everyone faces the challenge of applying lab data to the road. The size of the discrepancies vary depending on the tire and the real-world road surface. Sometimes the correlation can be essentially 1:1 (non-FSAE tires).

I certainly agree that the TTC data is not easy to use, and that comparing tires to one another is difficult. Nothing is easy when it comes to tires. The TTC fills a hole by providing some engineering data on tires. This can be supplemented by student tests (driving their vehicle) and correlation work.

On-road testing has its own set of challenges. The resulting data is just as difficult to use. The TTC could look into running some on-road tests. We're always open to suggestions.

[Spetsnazos]

If we know for a fact that it is 30-40% off, generally speaking, then can we give it a correction factor based on the surface the tire will be used on?

As a future engineer, I rather have something that is 40% off that I can analyze with some kind of correction factor than nothing other than "how it feels".

Good discussion though Mike, if we could keep it going I think more people could learn about how to apply the data correctly

[Hector]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Instead of spending more and more money on laboratory testing, why don't we figure a way to test the tires on real asphalt. </div></BLOCKQUOTE>

Like this?

[RobbyObby]

I personally believe the TTC data is merely meant to be a starting point. Due to the nature of the tests (any laboratory tests for that matter), which try to minimize the total variables throughout the process, and include many assumptions, there will also be some difference between real world situations. For students/teams just beginning to grasp the complexities of vehicle dynamics, it is a great tool. However, once you move past that point and start to look for more realistic real world correlations, it forces you to start running your own tests, so you can start comparing results and determine certain correlation factors. This is where the top engineers excel and differentiate themselves from the rest.

Just my $0.02.

[Adambomb]

IMHO track testing and lab data are two entirely different things. Lab data is nice because the conditions are much better controlled, although looking at TTC data you can begin to appreciate different thermal effects, etc. by looking at the variation and funny effects that exist even under such controlled conditions. Based on what little testing experience I have I can appreciate how hard it is to get a test that is simple enough to not be blown away by un-intentional factors yet still provide meaningful results.

However, TTC is lab data, and absolutely can not be taken as gospel tire behavior. Anyone with any seat time knows the tremendous amount of variation between, say, a 30 year old asphalt parking lot in March and a completely sanitary concrete airstrip in July.

TTC data has its place, but I'd say that there are a very very small number of teams that know enough about their car's behavior (ie actual, not just what you designed it to do) to even make full use of TTC data. And clearly for 99% of the teams out there (including us), there are much larger gains to be had with track testing than with TTC data. That being said, TTC is great when trying to decide which tires you want to run, as I know that there is no way our team would be able to just plain buy that many different types of tires to do that testing, let alone put resources towards the actual testing (although that video Hector posted did look pretty awesome). It is also good for the "intellectual masturbation" half of the competition, in showing how your analysis of TTC data influenced your suspension design and what the results were.

Just my $0.02.

[RobbyObby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Adambomb:
IMHO track testing and lab data are two entirely different things. Lab data is nice because the conditions are much better controlled, although looking at TTC data you can begin to appreciate different thermal effects, etc. by looking at the variation and funny effects that exist even under such controlled conditions. Based on what little testing experience I have I can appreciate how hard it is to get a test that is simple enough to not be blown away by un-intentional factors yet still provide meaningful results.

However, TTC is lab data, and absolutely can not be taken as gospel tire behavior. Anyone with any seat time knows the tremendous amount of variation between, say, a 30 year old asphalt parking lot in March and a completely sanitary concrete airstrip in July.

TTC data has its place, but I'd say that there are a very very small number of teams that know enough about their car's behavior (ie actual, not just what you designed it to do) to even make full use of TTC data. And clearly for 99% of the teams out there (including us), there are much larger gains to be had with track testing than with TTC data. That being said, TTC is great when trying to decide which tires you want to run, as I know that there is no way our team would be able to just plain buy that many different types of tires to do that testing, let alone put resources towards the actual testing (although that video Hector posted did look pretty awesome). It is also good for the "intellectual masturbation" half of the competition, in showing how your analysis of TTC data influenced your suspension design and what the results were.

Just my $0.02. </div></BLOCKQUOTE>

+1
Completely agree.