Some Tyre Help Please

[Big Kev]

Not wishing to upset you Kev

The aspect ratio dictates the height of the sidewall so a wider tyre will have a higher sidewall and the overall diameter will increase affecting the speedo.

Hope that makes sense!

But is that not somewhat disproved by such as the Ultra Low Profiles fitted to cars like those classed as "supercars" with very wide tread widths, but ridiculously low (tooth shattering) profiles like 40....??? In other words, the wall height does not automatically increase due to tyre width......have never quite got ma heid round tyre bumph. Anything under 55 profile I consider to be an instant cure for hemma.....haema......hemmy.....PILES....especially on totally underfunded Scottish roads.

Roll on Independence, when Alex Salmond will use all the oil money to fix our roads.....what a complete rectum...!!!!!!

Watch out Dorset if he wins....ah will be flittin'......

Big Kev.

Hi BK,

I think it is all to do with overall diameter of wheel & tyre combo, i.e. if you reduce the aspect ratio you need to increase the wheel & tyre diameters so that you get back approx to the overall diameter you started with.

Dorset's nice.

Comprehendicated, Seamus, but cannae see where actual tyre width comes into the equation of diameter.....?

[firemac]

Not wishing to upset you Kev

The aspect ratio dictates the height of the sidewall so a wider tyre will have a higher sidewall and the overall diameter will increase affecting the speedo.

Hope that makes sense!

But is that not somewhat disproved by such as the Ultra Low Profiles fitted to cars like those classed as "supercars" with very wide tread widths, but ridiculously low (tooth shattering) profiles like 40....??? In other words, the wall height does not automatically increase due to tyre width......have never quite got ma heid round tyre bumph. Anything under 55 profile I consider to be an instant cure for hemma.....haema......hemmy.....PILES....especially on totally underfunded Scottish roads.

Roll on Independence, when Alex Salmond will use all the oil money to fix our roads.....what a complete !Removed!...!!!!!!

Watch out Dorset if he wins....ah will be flittin'......

Big Kev.

Hi BK,

I think it is all to do with overall diameter of wheel & tyre combo, i.e. if you reduce the aspect ratio you need to increase the wheel & tyre diameters so that you get back approx to the overall diameter you started with.

Dorset's nice.

Comprehendicated, Seamus, but cannae see where actual tyre width comes into the equation of diameter.....?

It doesn't as far as I can see. The only relative point is that the really low-profile stuff comes in silly-wide sizes - more like glorified rubber bands than tyres. Makes for good after-market business for the alloy wheel trade though given the appalling state of most UK "roads".

[Ex Tiff]

Kev

The aspect ratio is found by dividing the tyre ride height by the width and multiply by 100 to express as a percentage. To get the effective diameter of the wheel/tyre combination add twice the tyre ride height to the wheel rim diameter. As an example the standard tyres on my car are 225/65R17 the tyre height is 225 x 65 divided by 100 which is 146.25mm or 5.76inches the diameter of the wheel /tyre combination is 28.52inches. If I fitted the same width tyres with ultra low profile say 225/40R17 the tyre ride height would be 225 x 40 divided by 100 =90mm(3.54inches) giving a diameter of 24.08inches. Changing either tyre width or aspect ratio will alter the effective diameter.

For pedants these calculations are always inexact because of other factors such as tyre pressure, tyre wear and vehicle loading will have minor effects on the tyre ride height as will the rim width. Hope this makes sense!

[rogsmith]

Thanks for all the replies.Although im a bit confused can i assume that no real difference will be made if i switch from the 4 215/70 on my car to 4 235/60 tyres.

[Aycee]

Just checked the tyre calculator and there is no noticeable difference in tyre diameter between the two, 2.6% or 19 mm less on the new tyres so you should be fine.

[rogsmith]

Great stuff thanks mate.I assumed they should be ok because when i first typed my reg into one of they tyre places it gave the 235/60 but when i looked it was the 215/70 that were on the car.

Thanks again all.

[Big Kev]

Kev

The aspect ratio is found by dividing the tyre ride height by the width and multiply by 100 to express as a percentage. To get the effective diameter of the wheel/tyre combination add twice the tyre ride height to the wheel rim diameter. As an example the standard tyres on my car are 225/65R17 the tyre height is 225 x 65 divided by 100 which is 146.25mm or 5.76inches the diameter of the wheel /tyre combination is 28.52inches. If I fitted the same width tyres with ultra low profile say 225/40R17 the tyre ride height would be 225 x 40 divided by 100 =90mm(3.54inches) giving a diameter of 24.08inches. Changing either tyre width or aspect ratio will alter the effective diameter.

For pedants these calculations are always inexact because of other factors such as tyre pressure, tyre wear and vehicle loading will have minor effects on the tyre ride height as will the rim width. Hope this makes sense!

Cheers, John.....now in a darkened room contemplating.....

Big Kev

[Ex Tiff]

Sorry Kev tried to help!, I've found an Islay malt helps all contemplation. Not that it's easily found this far south

John

[Big Kev]

Sorry Kev tried to help!, I've found an Islay malt helps all contemplation. Not that it's easily found this far south

John

Aha...Islay Malts......BG244 with diet coke and filtered peat bog......try some of the Grant's Speysiders like all the Balvenie family.....

[firemac]

Sorry Kev tried to help!, I've found an Islay malt helps all contemplation. Not that it's easily found this far south

John

Aha...Islay Malts......BG244 with diet coke and filtered peat bog......try some of the Grant's Speysiders like all the Balvenie family.....

Speyside grog is for jessies! Not real malt!

[Mike JD]

Sorry Kev tried to help!, I've found an Islay malt helps all contemplation. Not that it's easily found this far south

John

Cheer up! Waitrose in Okey this week have 20% off Lagavulin 16 and Bunnahabhain 12

[MarsKy]

baptise your new rav on saturday, big kev - possible snow on saturday

do you still have your yokos?

[Hoovie]

baptise your new rav on saturday, big kev - possible snow on saturday

do you still have your yokos?

Is that right? I am coming to Scotlnds 2nd ( ;) ) city today and staying overnight but was not planning on bringing the RAV. Maybe I should do?!

[MarsKy]

The BBC forecast showed snow falling over Glasgow/ Lanarkshire area... but said on the hills.

But we can still hope :)

WeatherOnline tends to be more accurate than the BBC and they are showing light snow on Saturday evening:

http://www.weatheronline.co.uk/weather/maps/city?PLZ=G71&PLZN=Glasgow&LANG=en&CEL=C&SI=mph&CONT=ukuk&LAND=SCO&REGION=0003&WMO=u3155&LEVEL=52&R=0&NOREGION=0

[Big Kev]

baptise your new rav on saturday, big kev - possible snow on saturday

do you still have your yokos?

Yokos left on SR180, BUT KEPT BRANNY YOKO SPARE FOR NEW CAR AND WHEEL.....sorry 'bout catapult letters.

What is it aboot some foax and bliddy snow......? Ah hate it with an old Hillman car built at Linwood (no more....)

big kev