Tyre widths

[Dai-X]

Been trying to decide which tyres to get for a while now, so as you'd expect have been scouring the BC archives for opinions/info as well as making notes about which tyres come in which widths/profiles.

Obviously the opinions are subjective but the widths are spec'd in mm so they're easy to compare.

 

Are they B 😳LL 😳CKS ❗

 

I've got Yoko A021Rs on at the moment which are 185/60R13

I've just compared them to some CR500s which are 175/55R13

 

Now when I went to school I'm fairly sure that 185mm was longer than 175mm - So how come the 175 CR500s are wider than the 185 '21Rs 🤔

 

Or am I missing something fundamental - do different manufactures measure from different points on the tyre? If so where the blue blazes does one find out which points each manufacturer measures from 🤔

 

I even took a picture of both tyres next to each other.

 

(then I went out for a blat and my headlamp lens assembly fell out ❗ 😳 - didn't realise my brakes were that good 😬 )

 

Cheers,

Ben 😬

 

 

 

Edited by - Dai-X on 21 Apr 2007 18:08:10

[Bob Simon]

The "185" dimension refers to the overall carcass width as measured inflated on the specified test width rim. Tread widths differ wildly from make to make, model to model.

 

 

-Bob

94 HPC VX Evo III

 

[Dai-X]

OK, sounds reasonable - except that of those 2 examples in the picture / in my garage, it certainly looks like it would be all but impossible to make the carcass of the "185" actually wider than the "175", whatever (similar or dissimilar) combination of rims you mounted them on, or pressures (within reason) you inflated them to.

 

This also seems to manifest on fitting "205" "width" tyres to 8.5" rims.

I can't find the picture now but there's one kicking about on the interweb of "205" Toyo R888s on 8.5 rims which have the sidewalls sloping out from the tread to the rim at a really scary angle and at no point does any part of the tyre/carcass look wide enough for the rim. However I was in Caterham midlands the other day and they've got a car with "205" width CR500s on 8.5" rears and they look just about spot on, nicely the right width from tread to rim. I wish I could find the picture because again, in the case of the R888s I can't see how they can possibly be the same specification in width as the CR500s.

 

Still, I do appreciate the input must dash now as my lift t'pub is about to roll up (as in arrive not fashion something to ❗ )

 

Cheers,

Ben

 

[Alias]

I've got Yoko A048Rs 195x60x14 on the rear of my car. The outer 15mm on either side of the tyre does not touch the road, therefore my contact patch is 165mm wide. IMHO the tyre width can only be used as a "rough guide" (as it looks like you've realised)!

 

-------------------------------------------------------------------

1800 Supersport with 6 gears and clamshell wings.

[Delberts Wallet]

Ben, I seem to recall some tech info on the old Caterham Web site suggesting that stretching tyres onto rims that are too big is a good idea. I can't find it on the new look web site tho.

 

I have 205 R888's on 8" rims and Sandy has them fitted to his 8.5" SLR Rims.

 

Gareth

 

Blue and Carbon 6 Speed 1.8 Supersport here

[SLR No.77]

Ben, I'm running 205 CR500s on 8.5" rims, and to be quite honest I do feel the rims are a little "too" wide. Maybe this contributes to Caterhms latest wheel/tyre combi being 205 CR500s on 8".

 

IIRC the info that Gareth is referring to relates to the tyre being lightly stretched across the tread therefore making it more stable when cornering hard.

 

Stu.

 

www.superse7ens.co.uk..........the rebuild 😬

 

 

[Fathead]

I have a mate who bought a car (mk11 supercharged golf rallye) which was wearing 9 inch rims with 195, 40 r15s!! looked really dangerous. I have no idea how they could have possibly been seated

[Dai-X]

If it is good to stretch the tyre onto a very wide rim, then you have to wonder (and that's all I'm doing, wondering, not trying to contradict) why Toyo specify 7.5" as the maximum rim size for the 205 R888s.

Out of interest as well Avon seem to specify 8.5" as the max rim size for their 205s

 

Anyway, a lot of this may have just become academic for me, as after reading in afew places in the archives about instances of the SLR rims not running true I've just checked one of mine that I was intending to use. Initial inspection seems to suggest it's not as true as it should be. Want to check further, but looks possibly ☹️

 

Cheers,

Ben

 

 

Edited by - Dai-X on 22 Apr 2007 15:07:39

[Bob Simon]

To further confuse things, here's a (cr@ppy) piccy of a 9" wheel with a 225mm A032 on it. There is a slight sidewall taper imparted to the tyre.

 

I can't imagine how a 195 on a nine inch rim would be safe. I would guess getting those narrow tyres mounted on wide rims involves a shot of starting fluid and a match.

 

I think Avon may be a bit wider than the industry standard. They may have taken some liberties in order to find the closest road car tyre sizes that would align with their racing carcass sizes.

 

 

 

-Bob

94 HPC VX Evo III