Tyres

Problem with your Megane? Can't find an answer? Workshop manuals and technical notes are in here.

Moderators: q292u, Ray, AndyAdmin, Stranger

tomalamix
F1 Driver
Posts: 1766
Joined: Thu Jun 03, 2010 3:15 pm
Currently Drives:: Megane II 1.5dCI 100HP

Re: Tyres

Postby tomalamix » Fri Nov 12, 2010 12:39 pm

davelowe wrote:
tomalamix wrote:rolling circumference = 2.pi.((17*25.4)/2+45) or rolling circumference = (2.pi.((17*25.4)+2*45)/2) :)


Yeah - like, whatever! :roll: :roll: :roll:

Be easier to write it out on MathCad.... I think the gist of it is correct though! :oops:


I think the correct is the one i've told you. You can try it out...

Cheers

joeishmather
F1 Driver
Posts: 1689
Joined: Wed Nov 25, 2009 3:22 pm
Currently Drives:: 57 megane with roof, engine, wheels, doors... All the usual things.
Location: Sheffield

Re: Tyres

Postby joeishmather » Fri Nov 12, 2010 4:00 pm

Hi I have bought 18" alloys now, would o be looking at tyre size 225/45R18 or 225/45R18
also is 225 ok or should I have smaller, speed wise the 40's are most accurate advice please :-)
cheers, Joe
Image

davelowe
Driving Legend
Posts: 3136
Joined: Thu May 10, 2007 3:40 pm

Re: Tyres

Postby davelowe » Fri Nov 12, 2010 11:30 pm

tomalamix wrote:
davelowe wrote:
tomalamix wrote:rolling circumference = 2.pi.((17*25.4)/2+45) or rolling circumference = (2.pi.((17*25.4)+2*45)/2) :)


Yeah - like, whatever! :roll: :roll: :roll:

Be easier to write it out on MathCad.... I think the gist of it is correct though! :oops:


I think the correct is the one i've told you. You can try it out...

Cheers


The circumference of a 17" wheel with a nominal 45mm profile is 2995.8228mm (4dp)

The circumference of an 18" wheel with a nominal 45mm profile is 3278.5661mm (4dp)

The difference is 9.438% bigger. Enough to upset your speedometer.
Silver 08 plate 5dr 1.5dci Dynamique 106 Tech Run (re-mapped)

Red 03 plate 5dr 1.9 Dynamique dci120

Best advice for Megane owners: sell it before it bankrupts you!

AlexB
Driving Legend
Posts: 4312
Joined: Tue Mar 22, 2005 8:17 pm
Currently Drives:: Renaultsport R.S.250 Cup

Re: Tyres

Postby AlexB » Sat Nov 13, 2010 2:16 pm

Strange formulae you are discussing. I hope everyone understands that the tyre profile is defined as percentage of the tyre width. It is a percentage, not millimetres.

The sizes 205/50R17 (standard) and 225/45R18 are different by 3.6%. So at 70mph the speedometer will be showing 72.5mph.

The size 225/40R18 is the exact match, 0.06% difference. Get Continental SportContact 3, Bridgestone Potenza RE 050 A or Pirelli P ZERO NERO, which exist in this size, and live happily ever after.

For 225/40R18 make sure your rims are 7.5-9 inch wide and have the correct offset.

Beware, these tires will start aquaplaning about 8mph earlier than the standard size.
AlexB
(no, a different AlexB)

User avatar
Anthony
Rally Driver
Posts: 842
Joined: Mon Jun 15, 2009 6:52 pm
Currently Drives:: 2005 Renault Megane 1.5 dci 100
Location: Preston

Re: Tyres

Postby Anthony » Sat Nov 13, 2010 5:45 pm

Alex, I'm interested in what you said about them aquaplaning 8mph earlier. Can you explain why they do that please?
2005 1.5dci 100 Sport Hatch -Gone!

joeishmather
F1 Driver
Posts: 1689
Joined: Wed Nov 25, 2009 3:22 pm
Currently Drives:: 57 megane with roof, engine, wheels, doors... All the usual things.
Location: Sheffield

Re: Tyres

Postby joeishmather » Sat Nov 13, 2010 5:53 pm

Wider surface area I should imagine, although would have thought that the tread was developed to counteract that?
Image

shawty500
Just Passed
Posts: 112
Joined: Fri Oct 15, 2010 11:18 pm
Currently Drives:: 2008 Megane Cabriolet 1.9 Dci

Re: Tyres

Postby shawty500 » Sat Nov 13, 2010 5:56 pm

Anthony wrote:Alex, I'm interested in what you said about them aquaplaning 8mph earlier. Can you explain why they do that please?


technically it depends on road conditions, but in the scenario the whole road is covered with a few mm of water, it is harder for the tyre to cut through it, as its wider, it will just slide.

Like a knife on butter, put the back of the knife through it, even though its not sharp, it will glide through, but you try putting the handle through it, and it will slide along.

User avatar
Anthony
Rally Driver
Posts: 842
Joined: Mon Jun 15, 2009 6:52 pm
Currently Drives:: 2005 Renault Megane 1.5 dci 100
Location: Preston

Re: Tyres

Postby Anthony » Sat Nov 13, 2010 6:30 pm

Sorry I should of been more specific. I understand why it would aquaplane more readily, I was wondering how he came to the 8mph figure.
2005 1.5dci 100 Sport Hatch -Gone!

joeishmather
F1 Driver
Posts: 1689
Joined: Wed Nov 25, 2009 3:22 pm
Currently Drives:: 57 megane with roof, engine, wheels, doors... All the usual things.
Location: Sheffield

Re: Tyres

Postby joeishmather » Sat Nov 13, 2010 6:35 pm

Would think that'd have been a guess!lol no way he could tell, all the conditions r too variable! For instance what tyres were we running before? Could be bald!
Image


Return to “Problems / Questions”

Who is online

Users browsing this forum: Google [Bot] and 41 guests