Maximum Tire size 1968 continental

[Cole1968]

I am trying to figure out what is the largest tire/rim you could put on a 68 continental with out issues or modifications, not that I'm going put some massive tires/rims on, I just want to go slightly bigger. I'm just looking for parameters/allowable sizes

[TonyC]

Well, if you're looking for dimensions, the stock rims with 235/75R15 tires on them and a tape measure will give you a good starting reference. The wheel wells may look deceptively more accommodating to something bigger, but that's to factor in suspension travel. There are spots with very little slack clearance, which can also limit size options...and then, there's the weight factor, which I just know that wagon-wheel enthusiasts almost never factor in when fitting wagon wheels on these cars.

Personally, I think that the 15-inchers with 235/75R15s have an ideal-looking balance of size to the rest of the car, as well as being the largest stock tire one can fit without going wagon-wheel. They do look noticeably bigger than, say, wheels on a 1988 Lincoln; but they don't look too big for the car, either.

---Tony

[Cole1968]

Do you know what the factory backspacing is?

[Dan Szwarc]

Here: https://www.thelincolnforum.net/phpbb3/ ... =1&t=46562

Continental, not Mark III.

[frasern]

So, I put 235 75 15 tires on my '67, and have some very light contact with the steering box bolt when turning left.
The original tires, 915 15 are 9.15" wide and tall, 235 are almost the same width, but only 75% as tall, meaning they are about 6.9" tall, But they are wider at the tread than the old school bias ply designs. this is the part of the tire which is rubbing.
In short, your width may be more restricting than the height.

[Dan Szwarc]

I've seen the upper ball joint rub on 235s on my 66, just a tiny bit. It happens with the wheel all the way down.
This is with the stock wheels.

[TonyC]

I admit to seeing a tad of rubbing at the upper control arms too, but it's never been a hazard, never expediting wear to the tires' inner walls, so I keep rolling. Those Hankook 724s are actually quite good all-season tires, plus being M+S-rated, that means I'd even be legal for German roads in winter. I do recommend them.

---Tony

[Cole1968]

Thank you for the help guys, Im just going to stick with the stock rim size and maybe go up in tire size just a little bit.

What was the original stock tire size?

[TonyC]

Well, the original specs were measured by a now-obsolete method, applicable to bias-ply but not radial. That said, though, it is possible to convert the old formula to the current one. The tire size was 9.15 x 15, with rim width at 6". The modern conversion equivalent would place those tires between 225/75R15 and 235/75R15, the former of which is harder to find than the latter. The 225s would be slightly smaller than the original biases, and the 235s are slightly larger than original (hence, the lack of clearance and subsequent sporadic rubbing, which I still maintain from experience is not hazardous). Depending on the brand, 225s may be rated to carry the load a '68 Lincoln imposes...however, 235s will carry that load without a problem. And load rating is a critical factor for tires where cars like these are concerned, something I suspect that most people fail to consider, except for vets like us.

Now, Cole, if you happen to find 225s, or better yet 230s, go with them if their combined load rating is right. Otherwise, you should be just fine with 235s; I personally suggest Hankook 724s in the 235/75R15 size, being that they have more than enough load rating, are all-season, and are "M+S"-qualified.

---Tony

[frasern]

Not all tires are the same shape, even though they are the same size, the casings may have slight variance. you may have more contact, or less, but it is unlikely this will be enough to cause a problem. Check for signs after you install, just to be sure.
In cross section, the casings were round in the '60s, that is they were as tall as they were wide. In the "70s, they came out with "wide oval" designs, which is where the 75 comes in. It means the tire height is 75% of the width. As such, any tire of todays design, will be 25% shorter than what your car came with. Only repop 915s will give that height, but the 235 75 15 are a good compromise, I have the same tires on my '67 as Tony.
Another thing, the speedometer will read fast because of this. For some reason, my speedo is perfect, even better than factory, so I think the previous owner changed the driven gear in the transmission, to compensate.
What was your previous size, and what is the reason you want to go bigger?

[frasern]

Do NOT get anything with a profile less than 75, they are cheaper, but have lower sidewalls. (shorter overall).

[Cole1968]

I was going to go a little bigger but I'm not anymore, I've changed my mind. I'm going to get new stock size tires.

[TonyC]

I have heard about the speedos reading differently with radials and the however-slight dimension differences. Although it does make sense to me, I never experienced a discrepancy in Frankenstein's speedo. It's always registered dead-on-balls accurate, except when display radars are off-calibration, which is common on Fort Riley but hardly anywhere else. One day, a given radar will read 1mph lower than indicated or even dead-on, the next day that same radar will read 5mph lower than the same indicated. But outside Fort Riley, for some reason, display radars are more consistent. Anyway, my speedo has always done me accurately, even after I dug into it to fix a malfunction and freshen up the drum's colors. I may have just been lucky in that sense.

Cole, you'll be good with my suggestion, or an equivalent. I've had only one blowout my entire time with Frankenstein, and that was caused from an excessive oil bath on the affected tire degrading the rubber, not from rub damage. Plus, my tires then were not from either of my choice sources.

If you have a Discount Tire Co. shop near you, go there. They have always done me well, at least until I got to Kansas where they did not exist (that is, until last year). But Peerless Tires have done me just as well so far where I am now. Also, very important, if you still sport the bias-ply wheel covers, the ones with grippers set at the edges, remember to stress to them "static balance." Even though it's not exactly accurate terminology, they will know not to mount the balance weights on the outboards of the rims. Keep an eye on the techs as well, to make sure they don't slip up on mounting the weights correctly (i.e., on the inboards of the rims). Of course, if you're one of those privileged few who have a set of the radial-variant covers, then the above caveat doesn't apply.

---Tony

[frasern]

My solution to the balancing issue was to use "counteract" beads. The internal balance eliminates interference with the hubcaps. I still saved the old, weird type of obsolete weights, which extend past the grips, but I am a hoarder by nature, and I can't change!

[Cole1968]

What actually is the recommended load rating for this car?