Would a 225x75x15 (spare tire)be to much size difference for posi rearend with 235x75x15's for short time use?
Are you talking a limited slip , not really a posi, or a locker type or a spool? If it was to get you home or to the nearest tire shop or just to a safe place off the road I wouldn't think there would be no problem. That's not much of a difference, you could also lower the pressure a little ,might shorten the taller one a little. Alot of the muscle cars had space saver spares and limited slip , post, rear ends.
Hello, It was not clear if each of the rear tires are the different sizes. But, a simple search function of my favorite tire dealers across the USA for replacement tires and accessories brings up a lot of extra bits of information. Here is one of them showing your two different size tires. As you can see, the 235 is a little over 1/2 inch taller. So, if that is a worry, then get the exact matching size of tire with all similar sizes and tread. No mismatched tires are always the proper way to utilize tires and driving. If the distance is a flat tire emergency drive home, then not to worry. But, if longer distances or daily driving are in the future, get matching size and tread tires for the rear. Your tires should not be any less or cause any problems as you worry and drive. It is not worth it to have to think about that in the daily driving routine. We have had our share of Plus 1-2 tire size changes and drama, but we never used mismatched wheels and tires competing with/against each other. Jnaki When we were using the Bruce Slicks on the rear of our 1958 Impala, they were on 15 inch rims. The front tires were the stock 14 inch rims. It did not matter, other than the speedometer was off from the normal 14 inch rims and tires that were on for daily driving. But, the Chevy Positraction rear utilized the large Bruce Slicks with ease and nothing was wearing differently. The even fit inside of the rear wheel well and had plenty of clearance. But, we never had different height size tires on the rear. So, if it is a situation with two different size tires on the rear axle, then change them to keep from worrying about damage to something or another. But, if it is similar to our case, adjusting the speedometer was not going to help me in the long run, since we took those tires off after the Saturday night drags at Lion's Dragstrip. The longest runs on the Bruce Slicks for the street were to go over a hundred miles on a Spring Break down to Newport Beach/Balboa to Merle's Drive-In Restaurant scene and up to Downey to Harvey's Broiler. We never had to use our stock 14 inch spare on those Bruce Slicks nights. But, it was only a short distance to the nearest friend's house/gas station for a tire change/repair if needed.
The respective roll-out on each is 88.87" and 90.72". For each axle rotation, the larger diameter tire would travel 1.85" farther. Either smaller diameter one would need to turn faster, or the taller one slower, or some combination, to keep pace on a perfectly flat surface. I can ***ure you that there are no perfectly flat surfaces, and that even if you have matched sizes, your rotation differs by more than this during normal operation. Never forget that there are things called corners, and road crown.
Good info Also let us consider that the distance of the tread is much greater than what the distance at the axle hub comes to .
Its a 9" Ford posi-loc limited slip I got from Southwest Speed. What the no-no point for size difference, used for spare tire only
As long as you are within 5% rollout (cir***ference, as functionally observed under load) you should be fine. The diameter of a 31-spline Ford axle is about 1.34" at the splines. The ~2% in tire cir***ference between your spare and the regular tires equates to and under/over of +/-0.0268" measured on the cir***ference of the splines. As I have mentioned, the irregularities of the road, and the reality inexistence of straight lines is far greater than this. Run the spare at 5psi over what the larger tires are being run at. That will probably cancel out the difference. No, it does not make the tire appreciably larger in diameter, but it does push the "dent" from load farther out, increasing measured rollout.
No worries. Just consider the smaller tire as a "space saver spare" (as mentioned above) but not as a replacement tire.
On a long ago Sunday in South Dakota I blew out a rear tire on an O/T turbocharged 1988 Ford, and replaced it with the space saver spare. With no options or tire stores open anywhere nearby I drove it about 50 miles. It does depend on the type of limited slip rear you have. If they are of the torque sensing type, as long as you stay out of the throttle there really is no stress put on the LSD. If it is one of the spring loaded clutch types, they are always engaged and you'll likely generate a lot of heat and cause wear if there is too much difference in the tire cir***ference.
OK, corners yes, but road crown? I used to build roads, streets and freeways for a living, and on a straight road, how does crown affect distance? I have measured many miles of roadway for asphalt and rock quan***ies, and as long as the road was straight, didn't matter if I measured at the right fog line, the crown or the left fog line. When we would measure at curves, just measure down the crown and the short and long sides cancel out for distance. One of the few things that Caltrans makes easy, freeway lanes are flat planes at 2% slope from the #1 lane to the edge of the shoulder, or "grade break", then 5% on the shoulder, unless specified different, or in a corner that goes into what they call a superelevation aka a banked corner. On an undivided highway where where the opposite lanes meet in the middle, the high point is the "crown"- doesn't affect distance on a straight road
Never saw a muscle car (as we know them) with a space saver tire. Inflatable tires yes, but not one of those doughnut space savers.
I've got a dual pattern 5 on 4-3/4 and 5 on 5 space saver spare that came out of a 74 olds Delta 88 that I carried in my 48 for a long time. It's not tall enough to match a 235 though. I don't have posi in the 48 so that wasn't and issue.
Those contracted when empty expand-o-tires were a trip. I bunch of my Porsches had them. I always swapped for the real-deal.
I did , after attending 9 years of night cl***es to receive a degree & teachers certificate ,I found it to be the most unrewarding , frustrating , thankless , looked down upon ,underpaid foolish move in my life , most teachers were working towards retirement with whether or not they were actually teaching viewed as at best secondary & at worst irrelevant .
They are students I had a job for a semester in JC tutoring incoming students, only 3/4 at a time, and it was tough getting points across and trying to come up with examples/etc that they could relate to. Good teachers are a special breed.
And this is my point, it’s not an easy job for people who aren’t capable of doing the work themselves.
Well I am damned well not an engineer of any sort but logic says that the big part of the time if we stick the spare on at all on a hot rod or custom it is to get to the next tire store that can repair or replace the bad tire. The few miles we would normally drive probably won't be a big issue. If the distance was too far most of would figure out a way to work around it.
Boy did this thread get off topic quickly! I simply went to the wrecking yard with wheel pattern checker, and tape measure, and walked around checking diameters and bolt patterns. I was amazed at how big some of the SUV space saver spares are, and had no problem finding one that matched my pie crust slick's 29" diameter, and bolt pattern. It was brand new tire and rim, and at $15 a huge bargain.
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