IR view of front tyres

[eilonoz]

is it just me or that the inner tire is much hoter in most of the corners?

[ben]

Originally posted by exFSAE:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Warpspeed:
Try using teflon coated tires and tell me if it has any effect at all on tire dynamics.

Sure, it will do "something." There are some traditional Coulomb friction forces at work which would be reduced, and more importantly the thicker the layer the less tread rubber that can be engaged in shear. That in itself would be a telling experiment. Have one tire untreated, one built with a 0.001" thick Teflon layer, another 0.010" and one more at 0.030". If the only thing that matters is a nearly pure 2D interface, then the thickness would have no bearing. I think you would find that this is not the case.

Of course that's fairly academic to consider as neither you nor I will be building special tires any time soon. However, it's been pretty well established/tested/proven in industry and academia that a large portion (perhaps we should say the largest portion) of in-plane tire forces are created by energy dissipation through a depth of tread rubber.

What you have to ask yourself is whether or not what you see from IR measurement of the VERY surface of the tread is indicative of the "operating depth." </div></BLOCKQUOTE>

Figure 3 of this paper visualises the way energy is dissipated into the depth of the tread. A key point is that this depth (and therefore the grip) is related to the roughness of the road surface itself. Kind of obvious, maybe, but often forgotten when we're obsessing about the "accuracy" of flat track tests.

http://www.multiscaleconsultin...nd_tire_dynamics.pdf

Persson's work is really worth digging into, but is worth noting that he doesn't attribute any significant portion of grip to adhesion. This is specifically reasonable for road cars, but does acknowledge that it might be relevant for race tyres without really exploring it mathematically.

Ben

[Owen Thomas]

I'm not really sure what you guys are arguing about. No one is saying that surface temperature is a better performance indicator for your tire (unless I'm mistaken).

However, I do think that seeing surface temperature is much more useful than seeing internal. This is from the perspective of testing/tuning instead of tire engineering, of which I know practically nothing.

My reasoning is that in order to get the carcass hot, you need to see how the heat is being applied to the tire (ie, at the surface). A video of tire surface temps will tell you quite a bit about what's happening, without the black art of reading tire grain (get it, 'black art'?). It also applies to your typical short-run FSAE tracks like autocross where there isn't a significant amount of tire wear, but you still want to tell how the tires are heating. You could theoretically see, at a glance, if your camber setting is off, what kind of slip angle drag you are generating on the inside tire, if your driver isn't being aggressive enough or too aggressive on corner entry (would have to be pretty sensitive for this), and the list goes on! It's just another DAQ tool, and how you apply it is what's important.

[jlangholzj]

Originally posted by Owen Thomas:
I'm not really sure what you guys are arguing about. No one is saying that surface temperature is a better performance indicator for your tire (unless I'm mistaken).

However, I do think that seeing surface temperature is much more useful than seeing internal. This is from the perspective of testing/tuning instead of tire engineering, of which I know practically nothing.

My reasoning is that in order to get the carcass hot, you need to see how the heat is being applied to the tire (ie, at the surface). A video of tire surface temps will tell you quite a bit about what's happening, without the black art of reading tire grain (get it, 'black art'?). It also applies to your typical short-run FSAE tracks like autocross where there isn't a significant amount of tire wear, but you still want to tell how the tires are heating. You could theoretically see, at a glance, if your camber setting is off, what kind of slip angle drag you are generating on the inside tire, if your driver isn't being aggressive enough or too aggressive on corner entry (would have to be pretty sensitive for this), and the list goes on! It's just another DAQ tool, and how you apply it is what's important.

I've been wanting to do this with our car for the last few years but we're a bit....er....budget limited when it comes to commercial IR sensors. I've been trying to figure out a decent way to use a pyro sensor to make our own but I've been having issues with that lately. Also looking at building our own for a IR sensor + goodies.

I was actually just wondering, for those of you who have data on our tires (namely the 13's) do they fluxuate that much as well? I'd be inclined to think that ours would be much more....stable? (maybe not the right word)...for temperature gradients than those smaller tires. Granted there's a lot more going on there but it was just a passing thought in my noggin.

[theTTshark]

Originally posted by exFSAE:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by theTTshark:
Really the most important part would be to see the outside

Oh, do tell why. </div></BLOCKQUOTE>

You can get a pretty good esitmate of carcass temp by using the good old tire pyro. Especially since we don't have to deal with pit lanes while testing and can get some pretty good hot temps of the carcass. Unless you've been dealing with significant full carcass overheating and you can't figure out why, then it's not going to give you very much of an idea of where to find gains in using your tires. I've only dealt with 13" tires on FSAE cars, but we've never dealt with overheating/blistering issues. If you are though, it's usually only on an edge of a tire due to camber and/or toe, which are pretty easy to work out without an IR camera. If you are overheating a whole tire either tell your driver to back off some/get a harder tire/get a bigger tire. Yes a IR camera will see this on the inside, but you'll be able to see it visually as well as with the tire pyro.

Surface temperatures give you an instant analysis of how the car was working the tire at the specific point on the track. Carcass temperature gives you the average of how the car used the tire during a lap/session/race. I can get the average when the car comes in. I can't see how setup changes affect the tire in real time if I'm just monitoring carcass temps. Obviously the car/tire combo is not going to work the tire the same way in every corner. There are going to be some corners that are better than others, and being able to see how that changes with different setups is invaluable. But yes, you do need to know carcass temps, but yet again tire pyrometer gets you close enough.

UNLESS! If we leave the FSAE realm for a second, an inside view would be very helpful at a track like Daytona(road course). The car has just come off the banking and has to roll down a very long pit lane. Terrible for getting any good tire data with a pyro. The left hand tires have been able to cool off since the bus stop, and the right side tires have been worked on the banking. In fact a couple of weeks ago I was dealing with just that problem. So yes in this case it would be very helpful, but still I would prefer IR sensors/camera on the outside.

[Pippo69]

Originally posted by jlangholzj:
I was actually just wondering, for those of you who have data on our tires (namely the 13's) do they fluxuate that much as well? I'd be inclined to think that ours would be much more....stable? (maybe not the right word)...for temperature gradients than those smaller tires. Granted there's a lot more going on there but it was just a passing thought in my noggin.

I don't have seen such a video of FSAE 13" tires yet, but a video of 16" wintertires on snow and the temperature changes even faster. There were about 30°C of change just between the rolling car an driving a straight with throttle.

I think surface temperature are quite interesting but it don't tells us anything about the reacted forces. What is producing more temperature a tire at its force limit or a sliding tire? The surface temperature will be higher at an sliding tire and core temperature of rubber will be higher at the force limit.

[BillCobb]

But the conversation is or should be focused on the type of tires on these cars. They are racing tires. They have traction and cornering mu's much greater than 1.0. Some racing tires can be greater than 2.5. The speculative comments so far here don't jive with the machanics, physics, or chemistry.

Look up "ablation". Some of you could be losing you're marbles, eh? (get it ?)

Running a F.L.I.R. camera during a tire test under manual control can be a great value. (I think I hear an echo in here). I wonder if my night vision security cameras outside the house would do a good job, too... You don't need color, just distribution.

[Neil_Roberts]

Here is my take on the subject, with supporting data.

http://thinkfastengineering.com/2012/08/solo-heat/

[Drew Price]

Neil, I was going to link to that post of yours for those reading this thread who missed it the first time around. The temp oscillation from the sun heating the top of the tire while waiting at the grid still boggles my mind.



And at Justin - What kind of engineers are these, not out trying to buy used FLIR's? Want! I was out in the desert by Barstow a few weeks ago with some CalTech lunatics who rigged up a FLIR on a gimbal with a visible laser sight centered in the field of view to the top of an expedition van. They drove off into the desert, shut down the van, and waited for little warm heat signatures of rabbits. Guy on the roof with a rifle aimed at the visible laser spot (in total darkness otherwise).

They didn't get any rabbits. But it was fucking awesome.

[BillCobb]

Try this instead:

http://www.youtube.com/watch?v=H0dPsMDif78