7 replies to this topic

[rexy]

Doing a bit of fiddling around putting some 17s on the hatch. As part of this it became blindingly obvious that a 275 wide tyre varies a lot in both tread and total width even from the same manufacturer.
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The 275/50/15 BF Goodrich on a 10 inch Hotwire is approx 12mm wider overall than the 275/50/15 MT ET Street on a 8.5 inch Convo Pro. The 275/40/17 ET Street on a 8.5 inch wheel is another 30mm narrower again.
Total difference from narrowest to widest was 42mm!

Interestingly the overall width has no direct relationship to actual tread contact width.
The widest BFG has 245mm of tread contact.
The 275/50/15 MT has 260mm of tread contact.
The 275/40/17 MT has 240mm of tread contact.

Makes a big difference in the narrow Torana arches.

[Rockoz]

Was explained to me by a tyre guy years ago.

He called it the difference in the bag of the tyre.

There was an optimum width of rim for a tyre even though they can fit on a range of widths.

The correct width gave the best tread width and flattest contact patch at the recommended pressure.

[76lxhatch]

Yes there are differences between brands and sometimes batches, but you're not comparing apples with apples - different wheel widths, diameters, profiles are always going to give different results. When it comes to the tread width itself the pattern is going to cause variations too.

When you look at tyres like the cheater slicks (ET Street etc) the manufacturer even provides specs on the different widths you will achieve depending on the wheel you fit it to.

[rexy]

That's my point. When it came to the front end of the car I spent lots of time searching out sectional data and I am glad I did. There was at least 20mm variation in the quoted section width of the 235/40/17 tyres I was looking to get under the front.

[rexy]

15x8.5 with 5 inch backspace.

[myss427]

I found the same differences just using the 17 inch rim, 3 different brands of 275 tyres all same profile varied up to 25mm.

[Dave6179]

My rear Hankook Dynamic RA03 are 15mm narrower on the floor than the Hankook Super Dynamics on the front. Both 235/60. Oh the NEW RA03 are crap! Been on for about 6 months now, daily driver, useless. I've reduced the pressure to 26lb to find some form of traction. Might need another reduction. Had GoodYear VR Eagles down to 22 for the drags.