Diffs V tyres ??

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R

Rich

Guest
Good evening to all out there, could any one tell me if I was to change the
diffs in my classic Range Rover to series diffs how big would the tyre
diameter need to be to get back to the same overall gear ratio before the
diff swap with standard tyres??
Thanks
Rich

--
To reply remove " spam "


 
Rich wrote:

> Good evening to all out there, could any one tell me if I was to change the
> diffs in my classic Range Rover to series diffs how big would the tyre
> diameter need to be to get back to the same overall gear ratio before the
> diff swap with standard tyres??

Series Diff ratio is 4.7, RRC 3.54 so your engine will be spinning 32%
faster for any given road speed. To regain that gearing you will need
32% larger tyres - if your present tyres are 780mm tall then you'll need
to got to 1030mm tyres (which ain't going to fit).

You could look at 4.1 ratio diffs (Rover car) which gives a 15% increase
in engine speed, and with the above example would mean you needed 895mm
tyres which would fit with a body and suspension lift if you were really
lucky.

--
EMB
change two to number to reply
---------------

Old age is the outpatients department for purgatory.

-John Morton
 
On or around Mon, 13 Sep 2004 09:44:16 +1200, EMB <[email protected]>
enlightened us thusly:

>Rich wrote:
>
>> Good evening to all out there, could any one tell me if I was to change the
>> diffs in my classic Range Rover to series diffs how big would the tyre
>> diameter need to be to get back to the same overall gear ratio before the
>> diff swap with standard tyres??
>
>Series Diff ratio is 4.7, RRC 3.54 so your engine will be spinning 32%
>faster for any given road speed. To regain that gearing you will need
>32% larger tyres - if your present tyres are 780mm tall then you'll need
>to got to 1030mm tyres (which ain't going to fit).
>
>You could look at 4.1 ratio diffs (Rover car) which gives a 15% increase
>in engine speed, and with the above example would mean you needed 895mm
>tyres which would fit with a body and suspension lift if you were really
>lucky.

that's much more informative than my reply was going to be.

along the lines of "fecking enormous".

 

"EMB" <[email protected]> wrote in message
news:[email protected]...
> Rich wrote:
>
> > Good evening to all out there, could any one tell me if I was to change
the
> > diffs in my classic Range Rover to series diffs how big would the tyre
> > diameter need to be to get back to the same overall gear ratio before
the
> > diff swap with standard tyres??
>
> Series Diff ratio is 4.7, RRC 3.54 so your engine will be spinning 32%
> faster for any given road speed. To regain that gearing you will need
> 32% larger tyres - if your present tyres are 780mm tall then you'll need
> to got to 1030mm tyres (which ain't going to fit).
>
> You could look at 4.1 ratio diffs (Rover car) which gives a 15% increase
> in engine speed, and with the above example would mean you needed 895mm
> tyres which would fit with a body and suspension lift if you were really
> lucky.
>
> --
> EMB
> change two to number to reply
> ---------------
>
> Old age is the outpatients department for purgatory.
>
> -John Morton

IT IS THE CIRCUMFERENCE OF THE NEW TYRE and not the diameter which needs to
be increased by 32% to bring the ratios back into line!!
If you were to fit 1030mm tyres ( God knows what tyres or how they would
fit you would raise the gearing by far more than the 32%
I will post again in a while when I have worked out the sums as to what
diameter tyres you would need


David
LLAMA 4x4
www.llama4x4.co.uk


 

"David_LLAMA4x4" <[email protected]> wrote in message
news:[email protected]...
>
> "EMB" <[email protected]> wrote in message
> news:[email protected]...
> > Rich wrote:
> >
> > > Good evening to all out there, could any one tell me if I was to
change
> the
> > > diffs in my classic Range Rover to series diffs how big would the tyre
> > > diameter need to be to get back to the same overall gear ratio before
> the
> > > diff swap with standard tyres??
> >
> > Series Diff ratio is 4.7, RRC 3.54 so your engine will be spinning 32%
> > faster for any given road speed. To regain that gearing you will need
> > 32% larger tyres - if your present tyres are 780mm tall then you'll need
> > to got to 1030mm tyres (which ain't going to fit).
> >
> > You could look at 4.1 ratio diffs (Rover car) which gives a 15% increase
> > in engine speed, and with the above example would mean you needed 895mm
> > tyres which would fit with a body and suspension lift if you were really
> > lucky.
> >
> > --
> > EMB
> > change two to number to reply
> > ---------------
> >
> > Old age is the outpatients department for purgatory.
> >
> > -John Morton
>
> IT IS THE CIRCUMFERENCE OF THE NEW TYRE and not the diameter which needs
to
> be increased by 32% to bring the ratios back into line!!
> If you were to fit 1030mm tyres ( God knows what tyres or how they would
> fit you would raise the gearing by far more than the 32%
> I will post again in a while when I have worked out the sums as to what
> diameter tyres you would need
>
>
> David
> LLAMA 4x4
> www.llama4x4.co.uk
>
>

Just done some very quick sums ( in my head so I may be wrong1) and to put
the ratios right you would need tyres in the 38" tall bracket which give or
take 7" or 8" will not fit in the wheelarches of a RRClassic...
IIRC an overdrive unit is about a 30% ratio change - what about fitting an
overdrive as well so on the road you could run with the overdrive putting
you about back to normal and offroad you could run without the overdrive and
have the much lower gearing??

David
LLAMA 4x4
www.llama4x4.co.uk


 
David_LLAMA4x4 wrote:

> IT IS THE CIRCUMFERENCE OF THE NEW TYRE and not the diameter which needs to
> be increased by 32% to bring the ratios back into line!!

Yes, but as circumference = pi * diameter, the diameter will also need
to be 32% bigger (as pi is fixed). You can use either in your maths and
the answer will be correct.

Paul

--
Paul Everett
repton at repton dot org
http://www.repton.org/
 
Ah yes I thought they would be quite big, but 38" is quite tall. The body
clearance is not an issue as the body will not be a Range Rover :)
And it does have an overdrive already did not think of using that in the
equasion !!!!!!!!!

Thanks all for the quick advice
Rich

> Just done some very quick sums ( in my head so I may be wrong1) and to put
> the ratios right you would need tyres in the 38" tall bracket which give
or
> take 7" or 8" will not fit in the wheelarches of a RRClassic...
> IIRC an overdrive unit is about a 30% ratio change - what about fitting
an
> overdrive as well so on the road you could run with the overdrive putting
> you about back to normal and offroad you could run without the overdrive
and
> have the much lower gearing??
>
> David
> LLAMA 4x4
> www.llama4x4.co.uk
>
>


 
David_LLAMA4x4 wrote:
> > IT IS THE CIRCUMFERENCE OF THE NEW TYRE and not the diameter which
> needs to be increased by 32% to bring the ratios back into line!!
> If you were to fit 1030mm tyres ( God knows what tyres or how they
> would fit you would raise the gearing by far more than the 32%
> I will post again in a while when I have worked out the sums as to
> what diameter tyres you would need
>
>
> David
> LLAMA 4x4
> www.llama4x4.co.uk

The diameter and circumference have a linear relationship (circumference =
diameter*pi), so increasing one by 32% will increase the other by the same
amount. 1030mm is about 40" - suitable for those Icelandic jobbies, but a
bit OTT for the UK.

--

Rich

Series 2a
RR 4.6
V8 trialler
dog, wife, kids, whatever


 

"Paul Everett" <[email protected]> wrote in message
news:[email protected]...
> David_LLAMA4x4 wrote:
>
> > IT IS THE CIRCUMFERENCE OF THE NEW TYRE and not the diameter which
needs to
> > be increased by 32% to bring the ratios back into line!!
>
> Yes, but as circumference = pi * diameter, the diameter will also need
> to be 32% bigger (as pi is fixed). You can use either in your maths and
> the answer will be correct.
>
> Paul
>
> --
> Paul Everett
> repton at repton dot org
> http://www.repton.org/

Good thinking, fidm't bother working that through... either way you are
going to struggle with 38" plus tyres! It isn't just the clearances think
of how much inertia you will have to break halfshafts with!!

David
LLAMA 4x4
www.llama4x4.co.uk


 
In news:[email protected],
David_LLAMA4x4 <[email protected]> blithered:
> "EMB" <[email protected]> wrote in message
> news:[email protected]...
>> Rich wrote:
>>
>>> Good evening to all out there, could any one tell me if I was to
>>> change the diffs in my classic Range Rover to series diffs how big
>>> would the tyre diameter need to be to get back to the same overall
>>> gear ratio before the diff swap with standard tyres??
>>
>> Series Diff ratio is 4.7, RRC 3.54 so your engine will be spinning
>> 32% faster for any given road speed. To regain that gearing you
>> will need 32% larger tyres - if your present tyres are 780mm tall
>> then you'll need to got to 1030mm tyres (which ain't going to fit).
>>
>> You could look at 4.1 ratio diffs (Rover car) which gives a 15%
>> increase in engine speed, and with the above example would mean you
>> needed 895mm tyres which would fit with a body and suspension lift
>> if you were really lucky.
>>
>> --
>> EMB
>> change two to number to reply
>> ---------------
>>
>> Old age is the outpatients department for purgatory.
>>
>> -John Morton
>
> IT IS THE CIRCUMFERENCE OF THE NEW TYRE and not the diameter which
> needs to be increased by 32% to bring the ratios back into line!!
> If you were to fit 1030mm tyres ( God knows what tyres or how they
> would fit you would raise the gearing by far more than the 32%
> I will post again in a while when I have worked out the sums as to
> what diameter tyres you would need
>
>
> David
> LLAMA 4x4
> www.llama4x4.co.uk

Last time I checked circumference and diameter were related by a constant .. Pi
!!!

--
UR SHGb02+14 &ICMFP
If at first you don't succeed,
maybe skydiving's not for you!


 
David_LLAMA4x4 wrote:

> IT IS THE CIRCUMFERENCE OF THE NEW TYRE and not the diameter which needs to
> be increased by 32% to bring the ratios back into line!!

David, any percentage increase in diameter has exactly the same effect
on the circumference, and vice-versa.

--
EMB
change two to number to reply
 
On or around Tue, 14 Sep 2004 08:17:16 +1200, EMB <[email protected]>
enlightened us thusly:

>David_LLAMA4x4 wrote:
>
>> IT IS THE CIRCUMFERENCE OF THE NEW TYRE and not the diameter which needs to
>> be increased by 32% to bring the ratios back into line!!
>
>David, any percentage increase in diameter has exactly the same effect
>on the circumference, and vice-versa.

alright, enough already, he's quite red enough now... :)

and we've all at times posted equivalent bollocks.


 

"Austin Shackles" <[email protected]> wrote in message
news:[email protected]...
> On or around Tue, 14 Sep 2004 08:17:16 +1200, EMB <[email protected]>
> enlightened us thusly:
>
> >David_LLAMA4x4 wrote:
> >
> >> IT IS THE CIRCUMFERENCE OF THE NEW TYRE and not the diameter which
needs to
> >> be increased by 32% to bring the ratios back into line!!
> >
> >David, any percentage increase in diameter has exactly the same effect
> >on the circumference, and vice-versa.
>
> alright, enough already, he's quite red enough now... :)
>
> and we've all at times posted equivalent bollocks.
>
>

I admitted earlier in the thread that my posting was not thought through to
its ultimate conclusion but at least the info was still accurate amd not of
the bollocks standards that some info posted stoops to!!.
A-level maths was a lot of years ago now!! I am still waiting to see a
RRClassic with 40" tyres that is actually useable, safe and worth the effort
of getting them to fit!

David
LLAMA 4x4
www.llama4x4.co.uk



 
David_LLAMA4x4 wrote:


> I admitted earlier in the thread that my posting was not thought through to
> its ultimate conclusion but at least the info was still accurate amd not of
> the bollocks standards that some info posted stoops to!!.

Sorry David....despite having several hours to do so, the other postings
hadn't managed to hit our newsserver when I replied, but they all
arrived about 10 minutes after I hit 'Send'. :)

--
EMB
change two to number to reply
 
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