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Wheel/Tyre sizes etc....

Alloy wheels and tyre discussion
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AlanJ
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Wheel/Tyre sizes etc....

Post by AlanJ » Fri Jul 16, 2010 6:51 am

Found this website which may be of use - excellent explanations of wheel/tyre sizes and markings which people may find of use.

http://www.carbibles.com/tyre_bible.html
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Re: Wheel/Tyre sizes etc....

Post by chrisj900 » Sun Jan 08, 2012 11:40 pm

i was wondering if its possible to increase my sidewall. im running 225/40/18s right now and im thinking of changing to 225/45/18 when they need replaced. i have no clue if im alowed to do this
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Re: Wheel/Tyre sizes etc....

Post by gannet » Sun Jan 08, 2012 11:52 pm

your speedo will then be out even more...

not sure about mileage readers...
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Wheel/Tyre sizes etc....

Post by Half Colin » Mon Jan 09, 2012 12:24 am

My winter tyres are 255/40/18 and 225/45/18 and the speedo reads about 3% higher than the stock 255/35 and 225/40. This isn't really an issue as speedos usually read a little under speed anyway so it now reads the actual speed as checked by my GPS.
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Re: Wheel/Tyre sizes etc....

Post by Whiteknight » Mon Jan 09, 2012 1:22 am

Does anyone know the widest tyres that I can fit on my BMW/BBS 18" 107 Elipsode Alloys, I want to go as wide as poss to try & protect the rims when 'kerb parking'

At the moment they have:
225 / 40 /18
225 / 35 /18


Regards,
Paul
Last edited by Whiteknight on Mon Jan 09, 2012 7:26 pm, edited 1 time in total.
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Re: Wheel/Tyre sizes etc....

Post by mmm-five » Mon Jan 09, 2012 12:48 pm

Half Colin wrote:My winter tyres are 255/40/18 and 225/45/18 and the speedo reads about 3% higher than the stock 255/35 and 225/40. This isn't really an issue as speedos usually read a little under speed anyway so it now reads the actual speed as checked by my GPS.
Construction & Use regulations state that the speedo must never UNDER-read, but can OVER-read by upto 10% - but manufacturers usually work to a tighter tolerance of upto 5%.

Otherwise you'd have a defence for speeding owing to your speedo showing you doing 30mph when you were actually doing 33mph. It's also one of the reasons I don't have any pity for anyone crying about getting caught for being 'just over the limit', as you'd have to be speeding by your own speedo to have any chance of doing more than the speed limit.

If your's was under-reading previously, then you either had the wrong tyres on, or you have a problem with your speedo.
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Re: Wheel/Tyre sizes etc....

Post by Whiteknight » Mon Jan 09, 2012 7:25 pm

Whiteknight wrote:Does anyone know the widest tyres that I can fit on my BMW/BBS 18" 107 Elipsode Alloys, I want to go as wide as poss to try & protect the rims when 'kerb parking'

At the moment they have:
225 / 40 /18
225 / 35 /18

If I go much wider, will I need spacers?

Regards,
Paul

Maybe I should post this in a new topic, I have used the search, but can't find the answer :cry:
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Re: Wheel/Tyre sizes etc....

Post by mmm-five » Mon Jan 09, 2012 7:59 pm

Whiteknight wrote:Maybe I should post this in a new topic, I have used the search, but can't find the answer :cry:
Why are you running a 225/35 on the rear? I thought the options were 225/40/18 all around, or 225/40/18 and 255/35/18 on front & rear respectively. Simply fitting the 255/35/18 to the rear 8.5j wheel will protect it a bit more.

If it's just rim protection your after then find a brand with a wider protection strip. And don't forget that a 225 tread isn't the same from all manufacturers, some measure it differently and others just have a wider tyre. A bit of research on your part will be required to find out exactly who/what makes the widest and the one with the most protection.
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Re: Wheel/Tyre sizes etc....

Post by Half Colin » Mon Jan 09, 2012 8:45 pm

mmm-five wrote:
Half Colin wrote:My winter tyres are 255/40/18 and 225/45/18 and the speedo reads about 3% higher than the stock 255/35 and 225/40. This isn't really an issue as speedos usually read a little under speed anyway so it now reads the actual speed as checked by my GPS.
Construction & Use regulations state that the speedo must never UNDER-read, but can OVER-read by upto 10% - but manufacturers usually work to a tighter tolerance of upto 5%.

Otherwise you'd have a defence for speeding owing to your speedo showing you doing 30mph when you were actually doing 33mph. It's also one of the reasons I don't have any pity for anyone crying about getting caught for being 'just over the limit', as you'd have to be speeding by your own speedo to have any chance of doing more than the speed limit.

If your's was under-reading previously, then you either had the wrong tyres on, or you have a problem with your speedo.
No, came across wrong - I meant the actual speed was under what was shown on the speedo so yes of course you are right the speedo is reading higher than the actual speed. With the higher profile tyres the speedo is reading about 3% less with the overall effect of it now showing near enough the actual speed.
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Re: Wheel/Tyre sizes etc....

Post by chrisj900 » Mon Jan 09, 2012 8:56 pm

so im guessing its possible to change the speedo settings?
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Re: Wheel/Tyre sizes etc....

Post by Half Colin » Mon Jan 09, 2012 9:14 pm

Don't think that's possible - you just need to check with a GPS and mentally adjust. With stock tyres my speedo shows about 75 when the actual speed is 70 - with my higher profile winter tyres at 70 the speedo shows 70.
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