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Tyre diameter less than 680mm but bigger than 640mm, any ideas?

Luegolover

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I have nearly finished rebuilding my BN1 and have tyre issues which I would appreciate some help with. I have a set of secondhand Michelin XAS 180 tyres with a total diameter of 680mm and they just touch the bodywork on full lock which is frustrating because they look good and get good reviews. I was only ever going to get the car on the road with these tyres and then buy a new set once all the expense of the rebuild has settled down. Spending some time surfing for alternatives I note that they generally come in with a rolling diameter of 640-644mm which seems much smaller.

In an ideal world I would like a tyre that has the largest possible diameter as I think that the cars look better with the arches filled as they were when the car was originally supplied. I am not going to be driving hard or fast so road holding on the edge is not a priority but of course I don't want poor handling tyres either. Money is an issue but I would be prepared to save up for the right tyre so although lower cost is best it is not a game changer.

Does anybody know of a tyre with a larger diameter than 644mm but a tad less than 680mm?
 

Jack T

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I would check with Dougal at Longstone Tyres. They have a wide selection and should be able to answer your question.
 

steveg

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LL - what you want is a 175-15 or 175/85-15. They don't seem to exist anymore.

Some of us have settled on the 180-15 Michelins. They work well. Mine scrub a little on the air deflectors occasionally on sharp turns.

I like them because they look right, give a good ride and cruising speed and the best ground clearance.
 

gonzo

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LL - what you want is a 175-15 or 175/85-15. They don't seem to exist anymore.

Some of us have settled on the 180-15 Michelins. They work well. Mine scrub a little on the air deflectors occasionally on sharp turns.

I like them because they look right, give a good ride and cruising speed and the best ground clearance.

Steveg, do you have these mounted on 4.5in or 5 in wheels or does it matter? Just curious for future reference. Thanks, GONZO
 

vette

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A couple of interesting points relative to this subject. I found it interesting that in Bill Young's chart in the April Healey Marque Magazine about calibrating the tach, he listed tire sizes. In his chart it shows that the 185/65/R15 tire is 24.5" in diameter. And the 165/80/R15 tire is 25.4" in diameter. Almost a full inch difference. Goes to show you really have to read the manufacturer's specifications for each tire you are interested in. Also during my bedtime reading I came across some other interesting info about tire sizes and applications. Unfortunately the charts are dated in that they show very old tire size labeling but in the widths and rim application they are accurate. The one chart shows "Designed Rim Width" the other shows "Approved Rim Widths". A statement at the bottom of the one chart says in regard to rim widths, "Manufacturers standards allow variations of up to 7% of these dimensions". This is from the HP Book "How to Make Your Car Handle" by Fred Puhn.
See charts below:
 

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twas_brillig

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Check the date of manufacture of those XAS and don't use them for regular driving if they're ten or more years older; some recommend pitching them after seven years. Driving around the block to make sure everything is working seems fine to me, irrespective of age, but you can't afford the bodywork if they fail as a result of heat buildup at speed. Doug
 
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Steve, Your wheels are probably 5" or 6" rims; I've not seen Dayton make a 5.5" rim for Brit cars (Rudge spline drive). Too bad, really, I have 6"--probably made for Jags--and I think they're just a tad wide (I have 185/70 tires).

http://www.daytonwirewheels.com/britishcars.php

Also, there is some variation on actual diameters for the same nominal size between manufacturers and models.

Edit: For example, Longstone measures a Michelin 185/70 at 641mm, but a Pirelli 185/70 at 632mm (they used to have a table of diameters, but I couldn't find it).
 

steveg

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Steve, Your wheels are probably 5" or 6" rims; I've not seen Dayton make a 5.5" rim for Brit cars (Rudge spline drive). Too bad, really, I have 6"--probably made for Jags--and I think they're just a tad wide (I have 185/70 tires).

http://www.daytonwirewheels.com/britishcars.php

Also, there is some variation on actual diameters for the same nominal size between manufacturers and models.

Edit: For example, Longstone measures a Michelin 185/70 at 641mm, but a Pirelli 185/70 at 632mm (they used to have a table of diameters, but I couldn't find it).

Ok Bob, I was guessing as my car's in the body shop right now. Was thinking at the time 15+ years ago the Indian Dunlops were available in 6" and the Daytons were 5.5.

The 180-15 Michelins Longstone sells are 85 aspect ratio, giving an overall diameter of 681mm.
175-15s (85 aspect - not available) would give a diameter of 672.5mm
 
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LL--

You say the tires touch the bodywork at full lock--What part of the bodywork do you mean, or are you talking about them rubbing some place in the wheel wells/inner fenders?
If the rubbing is but slight perhaps you could have the tires shaved to eliminate the rub? How often do we go to full lock anyway?
FWIW I have the 180 XAS's on my car and they fit just fine
 
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Luegolover

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They were rubbing on the front shroud and I modified it yesterday. I don't think I should go into details of the modification but they now turn full lock in both direction without rubbing.

The tyres are old though so I am going to keep in mind the comments about them over heating, I had just assumed that the effects of old age would be in the grip and handling.

I know the XAS tyres are expensive but they get really good reviews and they look the best on the car in my view so I will get the car on the road and save like mad over the winter for a new set.
 
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