wider tyres on rims

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swamper
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wider tyres on rims

Post by swamper »

im currently running 245's on the rear......but yesterday i went into my local tyre place and was having a chat with him about the rears and he reckons i can put up to 265 on with no problems........anyone else done this?
the badness makes me do it...!

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c_w
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Re: wider tyres on rims

Post by c_w »

A 265/40/17 will fit on the rear rim but it will look massive and not just in width - it will look very tall too and this makes the rim look smaller relatively.

Go up to 255/40/17 max but I prefer the look of the factory 245/40.
swamper
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Re: wider tyres on rims

Post by swamper »

is it safe CW to go up in size like that?...ie giving it some stick on track
the badness makes me do it...!

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c_w
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Re: wider tyres on rims

Post by c_w »

255/40 are fine in all conditions and a popular tyre size to go for on the rear 9" rim as road tyres at 255/40 sit quite well and only slightly taller over the 255/40

The arches are big enough to take a 265/40 too but it is noticeably taller/chunky so gearing slightly altered too.
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Re: wider tyres on rims

Post by swamper »

i really like sightly stretched look of the 245....i think im going to have to have a look out for someone with 255 so i can make my mind up.
cheers for the input CW :wink:
the badness makes me do it...!

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Gazza
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Re: wider tyres on rims

Post by Gazza »

I had 255/40's on previously, no problems, speedometer will read slightly faster



EDIT- on the rear
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TitanTim
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Re: wider tyres on rims

Post by TitanTim »

The Ac Schnitzer alloys I've just taken off were 225/40 fronts slightly stretched and 255/35 rears, I now have 225/40 all round and have to say the Zed has thanked me for it. I would seriously consider not stretching the tyres.

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swamper
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Re: wider tyres on rims

Post by swamper »

Gaz have you any pics please?

Tim 225 all round?
i take it its not a staggered fitment ?
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TitanTim
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Re: wider tyres on rims

Post by TitanTim »

swamper wrote:Gaz have you any pics please?

Tim 225 all round?
i take it its not a staggered fitment ?
Yepp 225 front and rear on 8x18s

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swamper
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Re: wider tyres on rims

Post by swamper »

ok Tim thanks.....had me going there foe a mo.... :D
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Gazza
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Re: wider tyres on rims

Post by Gazza »

swamper wrote:Gaz have you any pics please?
I'll check tomorrow :wink:

Come to think of it, I still have 255's now, Michelin PS2's
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Brian H
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Re: wider tyres on rims

Post by Brian H »

There is a good tyre size calc on the link below, theoretically a 265/40/17 is 16mm larger in diameter to the standard 245/40/17.

tyre size calc
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Gazza
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Re: wider tyres on rims

Post by Gazza »

This pic shows Goodyear Eagle F1 GSD3 255/40/17

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c_w
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Re: wider tyres on rims

Post by c_w »

A taller tyre like the 255/40 will in theory make the speedo read slightly slower, the reality is the speedo is DEAD accurate with this size fitted. My car was within 1mpg of a GPS at all speeds well in to 3 figures.
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c_w
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Re: wider tyres on rims

Post by c_w »

TitanTim wrote:The Ac Schnitzer alloys I've just taken off were 225/40 fronts slightly stretched and 255/35 rears, I now have 225/40 all round and have to say the Zed has thanked me for it. I would seriously consider not stretching the tyres.

Tim.
I don't think swamper is proposing to stretch tyres unless you mean "squashing" bigger tyres on to a rim?

A 255 is too wide for an 8J rim and won't be a "permitted rim width" by an tyre manufacturer so you will find the 225 is nice fitting and driving.

However the rear M rim is 9J and 245/255/265 are all permitted sizes, the factory 245/40 in some cases has a slight stretch, a 255 sits square and a 265 slightly overhang but all officially OK to fit according to tyre manufacturers.
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Gazza
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Re: wider tyres on rims

Post by Gazza »

c_w wrote:A taller tyre like the 255/40 will in theory make the speedo read slightly slower, the reality is the speedo is DEAD accurate with this size fitted. My car was within 1mpg of a GPS at all speeds well in to 3 figures.

Interesting, my speedo was 8mph faster than my TomTom GPS at 70mph with 255/40 :?
Gazza

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swamper
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Re: wider tyres on rims

Post by swamper »

cheers for the pic Gazza....i can see they look more square on than the 245s iv got on at the moment
the badness makes me do it...!

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TitanTim
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Re: wider tyres on rims

Post by TitanTim »

c_w wrote:
TitanTim wrote:The Ac Schnitzer alloys I've just taken off were 225/40 fronts slightly stretched and 255/35 rears, I now have 225/40 all round and have to say the Zed has thanked me for it. I would seriously consider not stretching the tyres.

Tim.
I don't think swamper is proposing to stretch tyres unless you mean "squashing" bigger tyres on to a rim?

A 255 is too wide for an 8J rim and won't be a "permitted rim width" by an tyre manufacturer so you will find the 225 is nice fitting and driving.

However the rear M rim is 9J and 245/255/265 are all permitted sizes, the factory 245/40 in some cases has a slight stretch, a 255 sits square and a 265 slightly overhang but all officially OK to fit according to tyre manufacturers.
Sorry I probably wasn't clear, I was mentioning in relation to the ACS alloys I have recently taken off which were 8.5x18 front and rear. The fronts were fitted with 225/40 which were slightly stretched and the rears 255/35. I've now fitted 8x18 alround and the Zed behaves much better. I'm just thinking fitting the widest tyre humanly possible doesn't do the car any favours IMHO.

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Z3cade
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Re: wider tyres on rims

Post by Z3cade »

I agree with Tim..

Stop messing about with it swamps and stick to 245s as it should be.. :wink:

255/265 If anything will make it worse with the side walls flush/overhanging which will make the tyre less stable on the track.
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Gazza
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Re: wider tyres on rims

Post by Gazza »

swamper wrote:cheers for the pic Gazza....i can see they look more square on than the 245s iv got on at the moment

I have Michelin PS2 255/40 on now and they aren't as square.
Gazza

"Understeer is when you hit the wall with the front of the car, oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall and torque is how far you take the wall with you"

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swamper
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Re: wider tyres on rims

Post by swamper »

thats what i have on now Gazza but in 245s....i do like the look of them.
im trying to get some width on the back without ruining the look.
Liam the stability thing is why im asking :wink:
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c_w
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Re: wider tyres on rims

Post by c_w »

You won't notice any difference between 245 and 255 IMHO - and besides they'll be 245 of one manufacturer that will be as wide as a 255 from another.

The speedo in theory should under read with taller tyres as the wheels are turning slower for a give speed but the difference is so slight it won't be affect and in my experience it makes it dead accurate.
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Re: wider tyres on rims

Post by huntert »

I dont understand when folk are saying that a 265/40 will look taller than any other 40 profile? isnt it the 40 profile that gives the tyre its hight regardless of width...................
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Re: wider tyres on rims

Post by Brian4 »

huntert wrote:I dont understand when folk are saying that a 265/40 will look taller than any other 40 profile? isnt it the 40 profile that gives the tyre its hight regardless of width...................
The 40 is the height of the tyre as a percentage of the width ie 265/40 is 106mm tall, 245/40 is 98mm tall so this makes a difference in rolling radius and so speedo readings. It is more important to get the tyre sizes correct when changing wheel diameter.

Moving from my standard 225/50/16 to 245/40/18 increases the distance travelled per revolution by approx 100mm and if I went to 255/40/19 would be 200mm more - approx 10% increase

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Robert T
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Re: wider tyres on rims

Post by Robert T »

The usual rule of thumb with a staggered setup is that your rears will have 5 points down on the ratio than the fronts, as they will be 20-30 mm wider than the fronts and two times 5% of 245 or 255 is either 24 or 25 mm. A similar rule applies when you increase the size of the rim - you normally come down 5 points on the ratio for each inch of rim - so 225s are normally a 50 on 16"s, 45 on 17"s and 40 on 18"s and 245/255s are normally a 45 on 16"s, 40 on 17"s and 35 on 18"s. The difference in circumference is only 17mm when going from 225/50/16 to 225/40/18 and 6mm when going from 245/45/16 to 245/35/18. Also bear in mind that most tyres have about 7-8mm of tread and the legal limit is 1.6mm of tread, so during the lifetime of a tyre, you will lost 10-15mm of the circumference of the tyre just through wear alone!

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Re: wider tyres on rims

Post by huntert »

so on a 19" rim 265s would idealy be 35?
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