I am helping a friend with a 1966 Austin Healey 3000. The original tires were 5.90x15 bias ply tires with an aspect ratio of 90. There aren't really current car tires that match that size. Modern car tires have a smaller sidewall, which results in the car being lower to the ground. The car has already lost 2 exhaust systems due to scraping, so lower is not better in this case. So I was wondering if it would be crazy to use motorcycle tires (at least on the front). I will probably ask this same question on a Healey forum, but I respect people's opinions here very much.

It seems that car tires on motorcycles is a bit more common than the other way around. So even though the rim's are designed differently, it must work somewhat okay.

The car weighs less than 3000 lbs fully loaded. And there are rear tires for cruising bikes designed for 1000 lbs load rating. For instance, Shinko sells a 150/90-15 or a 170/80-15, both of which would fit in the wheel well, and match the original diameter very closely. Their speed rating is also acceptable.

I know that even rear motorcycles have a rounded profile, but a very popular car tire choice for a Healey 3000 these days is a Michelin XAS 180-r15, which has a somewhat rounded profile. I guess wide tires make the steering heavy, so a narrow front tire can actually help the manual steering on these old cars. The XAS is shown here and costs $260 each:
https://www.cokertire.com/michelin-xas.html

Am I crazy? I just want to find a good tire for my friend which won't set him back $1000. The car doesn't see many miles each year, so I don't think longevity is a concern. But safety clearly is.

Thanks.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

I think the greater question here is the load index for the tire. So long as you can find ones that will carry the load (and remember it's probably not just 1/4 of 3,000 lbs because of vehicle weight distribution, so you should find that out for the Healey).

I think they should handle fine, though the contact patches from the rounded profile will be odd (as you note this may help steering response, though). I wouldn't do it if he likes to carve through canyons and explore the limits, but even at that modern motorcycle tires are probably overall better than car tires were in the 60s.

Here's some useful information, particularly about reading load indexes: Motorcycle Tire School | Maxxis USA

If it helps, the folks who have gone the other way and mounted a car tire on the bike are usually the fools on the cruisers with the huge rear tires. I think it's most often done for financial reasons, since car tires have a longer life for the kind of riding those guys do are typically lots cheaper, but the bigger danger is if they have to take evasive action since that big flat surface is going to tend to keep them going straight (those tires don't lean well!).

So to sum up, if it's just mild-mannered occasional drives in a classic car and you can get the right load index (upper 70s should do it depending on weight distribution) then I think it's a decent idea.

Good luck.

Coker Tire sells 5.90 x 15, if you don't mind selling a kidney to afford them.

Yeah, I saw that Lucas has a 4.25 as well (the 155SR15), but it's only $99 each. You're losing 1.65 inches overall in width, but that ultimately might be a better contact patch than a motorcycle tire. It might just look really funny. OTOH, it's a Healey, so...

A good motorcycle tire is going to run you close to $200

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Moss Gate Bed & Breakfast
1985 300 TD GG done in by a red light runner
1984 300 CD Sold
2008 Titian
2000 Cadillac SLS
1966 FLH Sold
2003 Harley Ultra

And only last a couple of thousand miles...

MV

Also worth mentioning is that nice(r) motorcycle tires might be multi-compound, and not grip as well without if you're just using the center of the tire.

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-Justin

91 560 SEC AMG - other dogs dd
01 Honda S2000 - dogs dd
07 MB ML320 CDI - dd
16 Lexus IS250 - wifes dd

it's automatic.

One of the reasons a few years ago I gave up on keeping my 1980 SAAB 900 ( owned since 86 ) running was access to narrow 15" tires. ( and not being able to get parts same day at the local auto parts as this was Mom and Dads daily driver. )

There was one maker ( Korean or something like that ) that made tires but the wear rate was pretty high. But, probably no worse than bias ply of the day. Have you looked on Tire Rack?

Your friends car at 3000 lb is pretty heavy for narrow tires.

have you looked into diamond back tires? Tire Catalog | Diamond Back Classic White Wall Tires - Vintage Tires - Redline & Redline Radial Tires for Antique and Classic Cars

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Alain
independant MBZ tech since 1981
http://www.motorsportlegendsks.com/

I'd get the proper size tires from Coker.

You might find a light truck tire will work too. I'd imagine you can find one that is close on height and a little too wide.

I tried this back when I had my 59 Ferrari and ended up buying Coker tires since the correct size for the F car was 600 16 and if you didn't use the right size the exhaust dragged badly.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.