FIA rules for 1991

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CK
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Re: FIA rules for 1991

Post by CK »

According to Wikipedia, tires for 1981 to 1992 has the same size.

Front - 25.0" x 10.0" - 13"
Rear - 26.0" x 15.0" - 13"

I measured a 1990 Larrousse and Jordan 191, both kits front tires are close to that specification.
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Re: FIA rules for 1991

Post by gp-models »

notfound404 wrote: Mon Sep 20, 2021 11:37 am Lots of useful information on this link:

https://www.f1technical.net/articles/62
Thanks for posting this link, but i checked it before and i could not find the Datas im up for.
CK wrote: Mon Sep 20, 2021 12:09 pm According to Wikipedia, tires for 1981 to 1992 has the same size.

Front - 25.0" x 10.0" - 13"
Rear - 26.0" x 15.0" - 13"

I measured a 1990 Larrousse and Jordan 191, both kits front tires are close to that specification.
There must be a mistake on the rear tyre size CK, according to Wiki and also F1technical net the rear tyre size was reduced to 15 inch in 1993, so before it must have been 18 inch when i`m right.
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Re: FIA rules for 1991

Post by MPK »

1993
Rear tyre width reduced from 18 inches (457 mm) to 15 inches (381 mm) to reduce the grip and so the speed of the cars, overall car width reduced from 220 cm to 200 cm.
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Re: FIA rules for 1991

Post by CK »

So, after some digging, this is the story.

Wikipedia is correct on both occasions. Here's the text from Wikipedia.

Therefore, from 1981 until 1992, Goodyear supplied white sidewall marked Eagle tyres with the sizes of 25.0"x10.0"-13" in the front and 26.0"x15.0"-13" in the rear.[4] For the 1993 season, the complete wheel width of the rear was reduced from 18" to 15",[5] prompting Goodyear to change to yellow sidewall markings to correspond to the new, narrower rear tyres which were approximately 12.8" wide, down from the previous 15.0".

The reduction of rear tire from 18" to 15" is about the overall width. The 26.0"x15.0"-13" tire has a tread width of 15.0". The overall tire width is about 18". I have photo of 1989 Larrousse rear tire marked 26.0x15.0-13 on the side wall. Ferrari also specifies F1-91 (642) to have 25.0x10.0-13 for front tire and 26.0x15.0-13 for rear tire. There is also a photo of FW14B front tire that has marking of 25.0x10.0-13. The marking on the tires of the Tamiya 1/12 MP4/6 is also 25.0x10.0-13 and 26.0x15.0-13. This is consistent with what Wikipedia described.

A photo of Benetton B194 shows a partial marking of 15/660R13 on the rear tire. Assuming the missing number is 3, the full marking will be 315/660R13. 315mm is the width of the tread, which is 12.4". 660mm is the diameter of the tire which is 25.4". The tread width also matches what is described in Wikipedia (approximately 12.8").

Hope this information helps.
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Re: FIA rules for 1991

Post by MPK »

Yes CK, you are right. Race tyre markings differ from road tyre. TYRE DIA x THREAD WIDTH - WHEEL DIA.
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Re: FIA rules for 1991

Post by JamesB »

Never 220cm but 215 ;-) Yes, sorry :oops: front wing was already 140 by 1991.
Overall widths were never a fixed thing, as teams might vary it from race to race.
Wheelbase used to be more consistent.
Overall width used to be some 208 front, a bit wider, like 212, rear. Not THAT important. Tyres Would be some 32/44 cm wide fr/re.
Wikipedia will be wrong more than sometimes on things like that :mrgreen:
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Re: FIA rules for 1991

Post by gp-models »

I never noticed that there is so less info about the real car measurements around and that even with the tyresize so much confusion about it.
Ok, let`s resume a few things for 1991:
# maximum width of frontwing is 1400mm
# minimum distance between bottom and street on the frond end of the undertray is 25mm
# maximum rear wing hight is 1000mm

Now on to the tricky part with the tyre dimensions, 25x10x13 on the front and 26x15x13 which seems to be common at that season, but should the 10 on the front only be the tread of the tyre, missing the sidewall in overall size? Same for the rear, 15 inch only the tread without sidewall? Can the sidewalls be counted as 3 inch? personaly i think that the 18 as overall width makes more sence on the rear axle then 15 as total width. The only left over is the frontsize, also in total 13 instead of 10?
After all that years i`m a bit confused to find severall details about F1 cars from that period, but nothing about their real measurements, no blueprints or any hint to that excapt the FIA regulations.
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Re: FIA rules for 1991

Post by JamesB »

Forget the inches. They are quite confusing. The given cm numbers are correct. Tyred also could vary slightly as brands would make tests.

https://i.redd.it/yo4u6m4iyuf11.jpg
Download and make numbers for this pic. A quick check gave the forementioned for FULL width of front tyre at 32cm and 60,7 cm tall (diameter). You can figure yourself the share of tread, shoulders, etc. Easier than it sems.
Same for rear tyres. I might do teh maths tomorrow :wink:
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Re: FIA rules for 1991

Post by CK »

A measurements of Tamiya Jordan 191 tires and Hasegawa LC90 tires yield these numbers.

Front tire 25.0x10.0-13
Overall diameter: Tamiya - 24" (610mm) Hasegawa - 24.7" (627mm)
overall width: Tamiya - 12.74" (324mm) Hasegawa - 12.6" (321mm)
Tread width: Tamiya - 10.7" (271mm) Hasegawa - 10.6" (269mm)

Rear tire 26.0x15.0-13
Overall diameter: Tamiya - 25.6" (649mm) Hasegawa - 25.8" (654mm)
overall width: Tamiya - 17.8" (451mm) Hasegawa - 17.8" (451mm)
Tread width: Tamiya - 15.7" (400mm) Hasegawa - 15.5" (393mm)

The dimensions from 2 model manufactures with one in 1/20 and the other in 1/24 are so close. They should be accurate. Tire size could probably measured by Tamiya and Hasegawa. The delta can be due to different ware and tire pressure.
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Re: FIA rules for 1991

Post by steinietrabi »

Can someone say whether the rain tires had the same dimensions? Regarding tread depth and so on... That is also the case with the current tires.
Greetings Thomas
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