Classic cars forum & vehicle restoration.

[fordf350camper]

Hi on the vintage caravan i got it has wire wheels but with 125x15 R .But i would have thought they should be crossply.What size cossply would 125x15 be.Would they be the same size.Thanks Pete

[WLC4EVA]

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Probably 4.00 by 15 Pete.

I can only say probably because you are trying to compare chalk with cheese.

Crossplies are normally at least as tall as they are wide (in cross-section).

Radial are 80 (or 82) percent as tall as they are wide; UNLESS they have a different number written on the sidewall.
125/30 R 15, would be 30% of 125mm high, so about 40mm high, ie they would be ultra low profile tyres.

Anyhow, back to your question, if you want the same axle height from cross-plies as you get from your radials then use 4.00 by 15s.

However, it is (was???) usual in the trade to replace 5.00 15 CPs with 125 15 Radials.
Despite that 150R15 would maintain axle height (and speedometer reading) better.
Speedo reading applies when changing from CP to radial on the driven axle.

Axle height goes out the window unless you know how to work out the correct tyre pressure for your radial tyres.
Normally, if you use the cross-ply pressure, you screw things up both in terms of calculating axle height, and in terms of gaining the advantages that come from radials.

Believe it or not, I've simplified my answer as much as I can, and left out bits that I should put in in order to cross the Is and dot the Ts.
If there are bits I haven't made clear, please bung your questions my; it's my job to give a clear answer not your job to guess what I'm on about.

Answering an apparently simple question like yours always reminds me of trying to get a fat lady into her corsets, there are always wobbly bits escaping.

Kind Regards, WLC.

[fordf350camper]

Hi WLC thanks for you answers.I am not sure what should be fitted the wheels are spoked.Someone must have fitted them as they are radials.I have had a look on a classic tyre company and for 4.00x15 are £65 each but 5.00x15 are £165 each so if the 4.00 look ok thats the ones i would fit.

[WLC4EVA]

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Now for one of the wobbly bits I couldn't get in the corset on the first go Pete?

How much does your van weigh loaded please?

The load rating for your tyre must equal or exceed the plated max weight of your van.
Except that your van probably predates the specific regulation, which isn't back-dated, or at least wasn't the last time I looked.
There may be a weigh on your coupling, then again, there may not.

Anyhow, back to basics, what does your van weigh when it's loaded?

Incidentally, why are you considering changing from radial to cross-ply please?

Kind Regards, WLC

[fordf350camper]

It says the van weight says in the book i have 700 cwt.The reason for crossply i thought they hadle the road better on a small caravan more movement on windy days.Thanks Pete

[MVPeters]

I strolled over here from the other thread!

If these are vintage wire spoked wheels I wouldn't fit anything but cross-plies. The rim design & bead profiles for radials are very, very different.
The stresses that radials put on rims are also very different - not necessarily 'more', but different.

Having said that, if these radials have been on the 'van for a while without problems & are not worn out or life-expired, is there any particular need to replace them? Tyre pressures & nose weight will have a bigger influence on handling.

If you do replace them, 4.00x15 sounds about right, but I would check the load rating of whatever you fit & check the bead seat width too. Any of the classic tyre suppliers will be able to help.

Mike
MVPeters@comcast.net

[WLC4EVA]

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Err, would 7 cwt be the unladed weight or the laden weight Pete?

Do you know the load rating of the 400-15 tyres you found please?

Can you explain more clearly why you expect crossplies to handle better on windy days.
Partly because you wrote "i thought they hadle the road better on a small caravan more movement on windy days".

Incidentally, have you ever done any martial arts training, or for that matter any sailing?

Also, can you give us some idea of the van you've got, and what your wheels look like please?


Kind Regards, WLC.

[WLC4EVA]

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Can you compare and contrast the stresses on wheels from cross-ply and radial tyres for us please Mike?
Preferably briefly and simply.

Kind Regards, WLC

[lowdrag]

Having experience of both radial and crossply tyres over a number of years I would certainly stick with what you have got. Now I haven't towed a trailer on crossplies, but they have a great predilection for "tramlining" and follow the slightest undulation on the road, so you could find your caravan hopping about a bit behind you. There are people more qualified than be on load weights etc, but if you do take the plunge I'd certainly change the rim tape and also the tubes, since the former perish and the latter get used to a certain form after a few years and the crossplies will change their shape a small amount, possibly leading to a blow out. Oh, and crossplies do not last anywhere as long either. I get 7,000 on RS5 Dunlops (crossplies) and 18,000 on 185/15 Dunlops (radials).

[Swampthing]

All that I can say is my Stirling was a bugger for snaking at anything ouve 45mph on 185x15 8ply radials, it was certainly a case of the tail wagging the dog even with a anti snake bar and up to 65psi, it would make the zephyr twitch, changed back to 6.70x15 6 ply crossply's and it will tow at motorway speeds and even without the anti snake, its road manners improved over night. that's with it loaded the same , the same tow car on the same road's .
so for me it has to be good old crossply's. have met several other older caravan owners at rallies over the years, and many of them have had similar problems.cured by re fitting crossplys
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Nobody saw me do it, you can't prove a thing!!

[WLC4EVA]

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I'm not surprised if you inflated to 65psi Swampy.

Why on earth would you do that?
How much does your van weigh for heaven's sake?

Kind Regards, WLC

[old van man]

now you have done it swampy this is going to go on and on and on

[fordf350camper]

Hi all i have been give some very good 6.70 x15 crossply van tyres do you think these will fit as the ones should be 4.00x15 thanks if they would thats going to save me 100s

[Swampthing]

personaly i would go for 400x15. Xply. 670x15 might be a bit wide for the rim. And i personaly would not want to use 125x15 citoren 2cv6 radials on sutch a rare and valuable classic. Also OVM is right to advise on a sprung towbar
_________________
Nobody saw me do it, you can't prove a thing!!

[WLC4EVA]

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How wide is your rim INSIDE Pete?

Your rim probably needs to be at least 4-1/2 inches wide inside to fit a 6.70 by 15 tyre.
Max 6 inches.

Your 125R15 would just about sit on a 4-1/2 inch rim.
4.00 by 15 probably wouldn't like rims 4-1/2 inches wide.

Kind Regards, WLC