Do 18 inch tyres reduce tyre squirt?

[Zynerji]

With shorter sidewalls, wouldn't the lateral flex be greatly reduced?

I'm also guessing the drag inducing floor slots could be smoothed or as well.

Thoughts?

[Nickel]

I'd love to read the thoughts of someone actually knowledgeable but my gut feeling is that tire squirt would remain just as strong but would become a bit easier you model. Less sidewall to flex as well as a smaller undamped spring should mean less variability in the pattern of the vortices coming off the tire due to a more consistent shape.

[jjn9128]

The short answer would be no. 'Tyre squirt' is a result of the separated flow from the convergence as the front face of the tyre meets the ground at the contact patch, which rolls up and is jetted around the sidewall by the freestream. Where people are calling for 18" wheels in F1 is normally about removing the added complexity of sidewall compliance and displacement (sometimes for the aesthetic and modernity), which have to be accurately modeled - this is from Ogawa's Honda F1 paper showing the difference in the front wheel wake with and without a side load effect modeled on the tyre sidewall.

A stiffer sidewall means the aerodynamics of the wheel and tyre are more consistent, however more compliance is required in the suspension set up so the sprung car rolls and dives more, so there are negatives too.

However, there could be effects from a number of other factors, the sidewall and tread profile with an 18" wheel will be squarer than with a 13" wheel so the separation angle could be different. Tyre deformations with an 18" wheel will be smaller so the deformation of the tyre ahead of the contact patch may be different and thus affect the separation angle. The short sidewall will mean that the wheel vortex will be closer to the ground and will merge with the lower tyre vortex differently - I think this is what some Formula E teams are trying to avoid with their flanged wheels https://twitter.com/ScarbsTech/status/8 ... 9629416449
I can't recall a paper that compares 13" and 18" wheels, there are loads on Indycar and F1 wheels in CFD and wind tunnels - rigid tyres, rigid and conical tyres, pneumatic tyres, pneumatic with varying pre-load, steer angle... etc.

[gixxer_drew]

Just speaking from the point of view of an aerodynamics firm:

The effect of the tire on the test results is massive. We occasionally get customers where they provide us a CAD model of the tire, either hand drawn from the 2d cross section (manufacturer supplied) or CAD from the tire manufacturer. We warn them the accuracy of the CFD results becomes questionable. The CAD models almost always less round than if you scan the tire in real life and do not account for the distortion in cornering. We almost never do downforce work in a straight line test, all in corner attitude.

We would love to have some kind of a rig to scan a tire as deformed in a corner but we havent been able to achieve something like this. The best we can hope for is a wake rake behind the tire (very difficult on a closed body car) and move the shape until the flow structures look similar.

Me I see this as one of the major challenges in aerodynamic simulation. It is a huge advantage to wind tunnels that can model this properly. I theorized it is one of the common causes of discrepancy between wind tunnel and CFD.

If anyone wanted to work together on this sort of a project we would be interested.

[jjn9128]

I know TotalSim do 3-d scanning of tyre profiles, but I don't know if they do it loaded and/or rotating. Reading the Honda paper, t seems they used static deformations for to model the tyres for CFD (at least circa 2007/08). The go to for me on this is Adam Sprot's PhD thesis, but that could just be that he was the researcher before me so I read it a lot for reference. I think he scanned the rotating and loaded tyre profile on a wind tunnel rolling road using a laser distance scanner, but are faster tools with which to do that.

The problem is, to build a decent library for a wide variety of projects would probably require hiring a wind tunnel or rolling road facility for a few days, and taking a number of tyres and wheel sizes (depending on what projects you get) and scanning them over a number of pressures, vertical loads and a range of yaws. I suppose it might be possible to build a rotating rig to do it 'in-house' project-to-project, but that could be pricey. It might be a USP for a consultancy firm though - "our tyre models are more accurate than our competitors."

[gixxer_drew]

I know TotalSim do 3-d scanning of tyre profiles, but I don't know if they do it loaded and/or rotating. Reading the Honda paper, t seems they used static deformations for to model the tyres for CFD (at least circa 2007/08). The go to for me on this is Adam Sprot's PhD thesis, but that could just be that he was the researcher before me so I read it a lot for reference. I think he scanned the rotating and loaded tyre profile on a wind tunnel rolling road using a laser distance scanner, but are faster tools with which to do that.

The problem is, to build a decent library for a wide variety of projects would probably require hiring a wind tunnel or rolling road facility for a few days, and taking a number of tyres and wheel sizes (depending on what projects you get) and scanning them over a number of pressures, vertical loads and a range of yaws. I suppose it might be possible to build a rotating rig to do it 'in-house' project-to-project, but that could be pricey. It might be a USP for a consultancy firm though - "our tyre models are more accurate than our competitors."

Any time we scan the car if they have a wheel/tire available we scan that as well. We have a decent library of scanned tires but it is surprisingly rare to repeat the same size and make of tire twice.

Scanning moving objects is quite difficult, but that is just the start. The test apparatus seems even harder. You need to load a tire vertically then steer it, that puts all kind of forces on the moving belt system. Something common like a 20% scale wind tunnel wont accommodate a full size tire, so you are talking about trying to get a rented facility to install a hydraulic ram to force a tire into their belt with up to say one tonne, I almost don't dare ask. Much easier for an F1 team. It could all go out the window when the next customer comes along on a different tire on the car. That makes the cost quite extreme. I imagined the easiest way would be with some distance measurement instrumentation in the wheelhouse with a camera and just get things way better although far from perfect.

[Vyssion]

I wonder whether if you were to scan a loaded tyre to a high enough accuracy and resolution, you could pick up the shearing of the rubber between the rim and tread on the sidewalls and measure small aerodynamic vortex flow and separation over them I'll stick to sending my recommendations to the wind tunnel guys thanks!!

[infuriweike]

NSN, I have a set of 5 wheels and tyres ive just taken off my D3 265/70/17 in great condition tyres are BFGs ?500 any use to you?

[Fifty]

I thought BMW had a test rig for their suspension that used a wheel and tire. It ran at speed and had the tire turning etc etc etc.

It shows the tire flex at different steering angles and also at different pressures due to suspension loading.
I wish I could find a video of it.

[hollus]

Couldn't one measure this by painting a pattern in an actual tire, running it on an actual vehicle at the desired load, speed, radius, etc, while carrying some stroboscopic stereo cameras around the tire?
I mean, just run it in an actual large piece of tarmac or an actual race track.