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Tone

United Kingdom
35 Posts

Posted - 21 Nov 2019 :  17:20:16  Show Profile  Reply with Quote
Hi all,
Could someone please tell me what size radial tyres I need for my rapier V.
Cheers Tone.

pruyter

Netherlands
280 Posts

Posted - 21 Nov 2019 :  17:55:15  Show Profile  Reply with Quote
The standard size in the sixties was 165/13

Regards,

Peter
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Tone

United Kingdom
35 Posts

Posted - 21 Nov 2019 :  18:33:01  Show Profile  Reply with Quote
Great thanks, I forgot to ask, would the pressure be the same with a modern tyre, 25psi?
Cheers Tone.
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pruyter

Netherlands
280 Posts

Posted - 21 Nov 2019 :  21:14:38  Show Profile  Reply with Quote
The given pressure (27 lbs/sq.inc) for the tyres were for diagonal tyres because this type of tyres were original installed in the size 6.00x13.
We, at the local Rootes dealer,pressured the radial tyres up to 30 lbs/sq.inch which I still do both for my Rapier and my Tiger.

Regards,

Peter
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jeremyshaw

8 Posts

Posted - 22 Nov 2019 :  14:32:54  Show Profile  Reply with Quote
I looked into this for my own Series 5. It's getting the correct rolling radius which is important; it has quite an effect on the overall gearing. So its the height of the tyre which is more important than the width. Crosslplies where pretty much 100% ratio width to height, so a 6" wide tyre was 6" tall. Trouble comes when you fit a 6" wide (155mm) radial which is at most 80% of the height. (155/80) The rolling radius is too small and you end up with a speedo reading high and too many revs for a given speed. Also, it just looks wrong, the wheels don't fill the arches, a bad enough problem with 13" wheels to start with.
I ended up fitting 175/80 13 van tyres from Formula 1 Autocentes and they give, as near as dammit, the correct rolling radius. They look better, handle fine, reduced the revs at speed and the speedo is not (so) wildly inaccurate!
The correct rolling radius in the Rootes manual is 29.56cm for a C41 Nylon crossply. Somewhere close to that is what I wanted.
There are various websites that you can go to and put in your tyre details and it will give you the rolling radius, speedo error and all kinds of confusing data!
I'm sure there are other arguments against my reasoning but it works mathematically and that's good enough for me!
Happy motoring, Jerry.
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jeremyshaw

8 Posts

Posted - 22 Nov 2019 :  14:35:35  Show Profile  Reply with Quote
Yes, I run mine at the 30-32psi pressure which seems OK so far. Will watch for the wear pattern to see if it's about correct.
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