F1 Tire width

[SS454]

I've been doing research to find the rear tread width of F1 tires, but found there is no regulation on it. At least that I could find. Here are the regulated measurements...

Front Tires: (when mounted and inflated to 1.4 bar)

Section Width - 305-355mm
Tread Width - 270mm
Groove Width - 14mm that tapers down to 10mm
Groove Depth - 2.5mm minimum
Distance between grooves - 50 mm center to center
Diameter - 660 mm (670mm for wets)

These are generally fitted to 12.7x13" rims

Rear Tires: (when mounted and inflated to 1.4 bar)

Section Width - 365-380mm
Tread Width - not specified
Groove Width - 14 mm that tapers to 10mm
Groove Depth - 2.5 mm minimum
Distance between grooves - 50 mm center to center
Diameter - 660 mm (670 mm for wets)

These are generally fitted to 13.4x13" rims


My first observation is the 270 mm tread width, Im quite certain that does NOT include the grooves. So effectively the tread width from inside to outside edge would be a maximum of 326 mm wide, but the grooves dont count as tread. Whats interesting is with the tapered groove, the tread width that may start out at 270 mm, but could climb to 286 mm. Remember in 1998 when they first used grooves teams reported they got faster with tire wear, and claims were because of less lateral flex in the grooves, but surely it has somethin to do with the increase in tread width as the tires wear down too. Also, remember 2003 with the big Michelin fiasco. It was claimed that a Michelin tire was found to be 286 mm in tread width after the race. And then Bridgestoneowns (i think) showed an article with Pierre Dupasquier saying they did not alter the width of the tire, they just gave a definative place to measure the tread width. Im not certain how they did this, but Im sure its related to the grooves and stuff. We know the FIA measure the tread width AFTER a race, which brings up an interesting issue. To come within the 270 mm maximum tread width post race, a tire would have to start out with approx 254 mm tread width. But what happens when a team like Renault or Bridgestone at Bahrain eats up the grooves and the entire tire now becomes the tread width. Theoretically this should be deemed illegal. Noteably this could also explain why there is no maximum tread width for rear tires, as the rears are the ones that wear out the fastest.

Though there appears to be no regulation on how wide the tread width is for the rear tires (anyone know the official reason?), I think I read somewhere that the tread width was 305mm which would give 361 mm including the grooves. However the front tires at the maximum would have about 29mm (14.5mm per side) of section widh from the outside of the tire to the outside of the tread width. And front tires have rounder sidewalls for camber angles and probably aerodynamics too. So the rears run a squarer sidewall and visually less width between outside tire edge to outside tread width, perhaps around 15 mm (7.5 mm per side) totallying 365 mm tread with including grooves for a total of around 309-310 mm tread width.

So this is what I found and what I think and what I dont know. I thought I would share it, and perhaps some of the other technical guru's can chime in to what they know that might give more solid answers.

[coysht]

My best guess would be that there is no specified rear tyre tread width (after the race) as it has never been an issue (same as there was never one for fronts untill Bridgestone complained. Plus, the two tyre companies have similarly shaped rears anyway).

With the direction that tyre compounds are heading these days, worn tyres (even with a wider tread) are actually slower than new ones.

This is beacuse the temperature generated in the tyres comes from movement of rubber. Since the ridges between the grooves are taller when new, they can flex more, and generate more heat, more quickly.

A tyre that has worn down so that grooves start to disappear will probably not generate enough heat to work at its optimum.

Renault showed on a couple of occasions in 2005 that if you wore your rear tyres out, the car could loose maybe 2 seconds a lap through lack of traction and lateral grip.

[SS454]

Actually that 270mm front tread width was around before the Michelin deal in 03, just measured when the tire was new. Its interesting there is no width rule for the rears at all (pre or post race), but I suppose ur right, that they just max out the tread width as much as possible to fit the section width.

Yeah tire compounds are very picky about temperatures now days. I dont think its a case of the tires getting too cold when worn, but a case of too hot. I heard it on television once or twice. Just not enough rubber to heat to transfer through, where as the with the new grooved rubber the temperature has a chance to cycle through hot and cold. Mark Webber was saying that the tires in 05 would be very fast for 1 lap or 2, then fall off, and then sustain a certain level of grip, and then begin to fall off near the end of its life.

Just to clarrify myself, am I correct to believe the 270 mm treadwidth does not include the grooves. 270 mm is about 10.6", which would look alkward on a near 14" wide tire. But I like to be sure.

[coysht]

The tread width does include the grooves, it is effectively the width of the area that is in contact with the track. The FIA doesnt really define what tread is and so any rubber parallel to the track is basically the tread.

[JustBringIt]

I don't actually know what the rules say about grooves relating to the tread width but I'd be very surprised if they subtract the total groove width from the width of the tyre to come up with the tread width value.

I believe the Michelin '03 thing was a case of them using some of the sidewall of the tyre in corners when the tyre is loaded to gain a bit more tread width.

[coysht]

The '03 thing was simply that the front tyres were the close to the maximum allowed width at the surface when new (- as required by the regulations) but due to being much squarer than the Bridgestones, when they wore down, the contact patch got wider.

This wasn't technically illigal at the time, but someone complained, so the FIA decided to set that the tyres must also meet the measurements after a race.

[SS454]

I certainly dont blame Michelin for exploiting a loophole in 03. But I agree with keeping the tires to a 270 mm limit as the rules say for the entire race.

Going off topic here, but do you recall around 1990 what the weight rules were? I've found 505 kg min weight or something, but I also recall hearing a 585 kg weight get floating around. Perhaps it was 505 kg without driver and 585 kg with driver?

Just to continue with the tire tech, In 1990 the teams used Goodyear 25.0x10.0-13 front tires on 11.75x13" rims, with 26.0x15.0-13 rear tires on 16x13" rims. Thats like a 12.5 inch front tire and a 17" wide rear tire. Does anyone remember those years and recall if the teams did infact have trouble getting the power down?

[JustBringIt]

Originally posted by coysht
The '03 thing was simply that the front tyres were the close to the maximum allowed width at the surface when new (- as required by the regulations) but due to being much squarer than the Bridgestones, when they wore down, the contact patch got wider.

This wasn't technically illigal at the time, but someone complained, so the FIA decided to set that the tyres must also meet the measurements after a race.

The "as required by the regulations" isn't entirely accurate. The rules said that the car had to remain legal throughout the race. It was just that those measurements weren't part of the post-race scruteneering procedure, so they got away with it for most of that year.

SS454, I believe that the car was weighed without driver in 1990. I think weighing with the driver only came in in about '95.

[coysht]

Originally posted by JustBringIt
The "as required by the regulations" isn't entirely accurate. The rules said that the car had to remain legal throughout the race. It was just that those measurements weren't part of the post-race scruteneering procedure

All tyre requirements were originally writen for a brand new tyre, mounted on a rim, inflated to 1.4bar.

Yes the tyre must remain legal throughout the race, but no-one said what legal for a used tyre actually was.

It was a grey area, hence no punishment was handed out, or even suggested.

Thats the problem with alot of the regulations, they specify one condition, but not all possible conditions, leaving the rest open to interpretation untill there is a problem.

[SS454]

Thanks JustBringIt for when the weight with driver came in. At ~505 kg without driver, the cars would have weighed only around 580-585 kg for the average driver.

[JustBringIt]

Originally posted by coysht
All tyre requirements were originally writen for a brand new tyre, mounted on a rim, inflated to 1.4bar.

Yes the tyre must remain legal throughout the race, but no-one said what legal for a used tyre actually was.

It was a grey area, hence no punishment was handed out, or even suggested.

Thats the problem with alot of the regulations, they specify one condition, but not all possible conditions, leaving the rest open to interpretation untill there is a problem.

Actually, I think the tyre rules stated regulations for any tyre - not new, not used - but it was possibly interpretted as "new" because at that stage, tyres weren't measured at the end of the race.

Definitely it was a grey area (as with many of the rules). Bridgestone asked for clarification because they thought it was against the rules and, therefore, didn't pursue that type of design. The FIA said it wasn't legal so Michelin (after much whinging) had to change their design. I believe there was no penalty because the cars actually passed scruteneering. Since they tyres weren't measured after the race, there would be no evidence with which to disqualify anyone.


SS454, that was an approximate year, btw.

[mm154]

Isn't there a contact patch regulation? (I cant off hand find one in the new rules)

If so that would keep the tires from becoming too wide.

[SS454]

Originally posted by mm154
Isn't there a contact patch regulation? (I cant off hand find one in the new rules)

If so that would keep the tires from becoming too wide.

Yes, for wet tires only though. As they cant measure "tread width" the same, due to all the grooves and tread pattern, they restrict it to a contact patch. I dont recall the measurements, but I believe it was square, not rectangular.

[SS454]

When did the FIA ban super soft qualifying tires? I know they were used in 1990, and Im quite sure 1991 also given the tire war between Pirelli and Goodyear. Then Pirelli pulled out in 92, and the qualifying speeds werent that much better, but the race pace was a good second faster. In 1994 the qualifying pace was much slower than in 1993, while the race pace was about the same. Fastforward to 1999, with Goodyear gone, the qualifying speed was again much slower than in 1998, but the race pace was pretty close to before.

So since 1990 it would seem there was 3 years (92, 94, 99) that seems like a qualifying tire was banned over the previous season, though no evidence a qualifying tire came into play in a following season.

In 1996 the FIA proposed some ideas to stop the use of qualifying tires, but Im not sure if/when they were ever implemented.

[SS454]

What happened to all you fans pre-96? Nobody seems to know. What about when the rules changed in that the teams had to select a hard or soft compound in practice, and that compound would be used in Qual and the Race?

[Greig]

Write to Ask Nigel at Autosport, he will know Personally I just watched F1 back then, never had the internet so basically all I got was the race on TV, with no info inbetween, never mind rule changes LOL, when I got the internet in 99 I was amazed to find that F1 did testing between races believe it or not, I just assumed they went from one race to the next with the same cars.

[coysht]

Originally posted by Greig
Write to Ask Nigel at Autosport, he will know Personally I just watched F1 back then, never had the internet so basically all I got was the race on TV, with no info inbetween, never mind rule changes LOL, when I got the internet in 99 I was amazed to find that F1 did testing between races believe it or not, I just assumed they went from one race to the next with the same cars.

Yeah, same here.

It was getting on for 2000 before I started really looking at how it all worked and following it as anything more than a Sunday afternoon sport on the TV.


I think the super soft quali tyres probably went sometime just prior to 98, if not as part of the 98 grooved tyre regs themselves.

[SS454]

I know what you mean. When i started getting into F1 in 1996, I only really watched the highlights the day after, it wasnt till late 97, early 98 that I started getting up at 5 am to watch the races, and never watched qualifying. I also never took in all the information about the cars and stuff like i do now, I just wanted to see Ferrari doing well.