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From: Brian on 29 Jan 2010 12:17
Paul wrote:
> Dave Plowman (News) wrote in message
> news:50e1387868dave(a)davenoise.co.uk...
>> In article <1-GdnUSEbLNHKf_WnZ2dnUVZ8vudnZ2d(a)brightview.com>,
>> Paul <reply_through_group(a)first.ok> wrote:
>>> have a standard Megane diesel with the original 13" steel
>>> wheels
>>> fitted.
>>> have some 14" alloys, will fitting these have any negative
>>> effect
>>> on economy?
>>> what if I went up to 15"?
>> If you fitted larger wheels and pro rata tyres you'd raise the
>> gearing.
>> Generally this results in better economy. But difficult to
>> check because
>> the odometer would now give an incorrect reading.
>
> Thanks Dave, you set me thinking. The last time I changed some
> wheels on a car, I went from 13" to 15" and it was the first time
> since I had owned the car that the speedo reading tallied with my
> satnav, previously the car was always showing about 4mph faster.

I've used my Tomtom in several cars and it never agrees with the MPH.
The car always reads 2-3 MPH faster. I'll bet the Tomtom is correct.
From: Cicero on 29 Jan 2010 12:31
On Fri, 29 Jan 2010 12:24:54 +0000, Paul wrote:

> Paul Giverin wrote in message
> news:qv6ekqCforYLFwgu(a)giverin.adsl24.co.uk...
>> In message <1-GdnUSEbLNHKf_WnZ2dnUVZ8vudnZ2d(a)brightview.com>, Paul
>> <reply_through_group(a)first.ok> writes
>>>have a standard Megane diesel with the original 13" steel wheels
>>>fitted.
>>>have some 14" alloys, will fitting these have any negative effect
>>>on economy?
>>>
>>>what if I went up to 15"?
>
>> If you lower the aspect ratio of the tyres then there will be minimal
>> change to the rolling radius. If you don't change the aspect ratio then
>> there will be negative effects of gearing and speedo reading.
>>
>> More info here:- http://www.carbibles.com/tyre_bible.html
>
> Cheers Paul, particularly for the link.

=================================================

Don't forget to check your insurance. Changing wheels may be regarded as a
'modification'.

Cic.

--
=================================================
Using Ubuntu Linux
Windows shown the door
=================================================

From: Dave Plowman (News) on 29 Jan 2010 12:56
In article <j_udndcVT6lxlP7WnZ2dnUVZ7oudnZ2d(a)brightview.com>,
Paul <reply_through_group(a)first.ok> wrote:
> Thanks Dave, you set me thinking. The last time I changed some
> wheels on a car, I went from 13" to 15" and it was the first time
> since I had owned the car that the speedo reading tallied with my
> satnav, previously the car was always showing about 4mph faster.

> As my Megane speedo shows a similar difference, can I expect the
> same result?

Be easy enough to work out if you can find out the rolling radius of the
various wheel tyre combinations.

--
*White with a hint of M42*

Dave Plowman dave(a)davenoise.co.uk London SW
To e-mail, change noise into sound.
From: Mrcheerful on 29 Jan 2010 17:46

"Dave Plowman (News)" <dave(a)davenoise.co.uk> wrote in message
news:50e152643edave(a)davenoise.co.uk...
> In article <j_udndcVT6lxlP7WnZ2dnUVZ7oudnZ2d(a)brightview.com>,
> Paul <reply_through_group(a)first.ok> wrote:
>> Thanks Dave, you set me thinking. The last time I changed some
>> wheels on a car, I went from 13" to 15" and it was the first time
>> since I had owned the car that the speedo reading tallied with my
>> satnav, previously the car was always showing about 4mph faster.
>
>> As my Megane speedo shows a similar difference, can I expect the
>> same result?
>
> Be easy enough to work out if you can find out the rolling radius of the
> various wheel tyre combinations.

even if the speedo reads correctly after fitting different wheels the
mileometer won't read right.


From: Chris Whelan on 29 Jan 2010 18:04
On Fri, 29 Jan 2010 22:46:39 +0000, Mrcheerful wrote:

[...]

> even if the speedo reads correctly after fitting different wheels the
> mileometer won't read right.

It won't read the same, but surely it may be closer to reality?

Chris

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