275 60 15 tire musings/head rebuilds

[triple_green]

My car is a 68 383 HP (H code) console automatic with 3.23 sure grip.

There are a couple of things that I realized lately after making some changes.

20 years ago I bought magnum 500s for my car front: 15x7 with 235 60 15 radial TAs and rear: 15x8 with 275 60 15 radial TAs. I knew from feedback on this site that these paring would give me no clearance problems and look "meaty".

So I haven't really thought about the tires being 20 years old and I still liked the look. I replaced the fronts last year because there was some edge wear on them.

I had noticed when I put the 275's on the back that I seemed to loose a little low end grunt, but I loved the "meaty" look of these 28+"  and almost 11" wdie tires. But lately they had been kind of slipping and not even hooking up as well as they used to.

Recently I replaced the back tires with 265 50 15s that I had in my shop, these were very low miles and had been stored out of the sunlight all then time.

Yesterday I went on a cruise with my son's mustang club and I noticed that the car has more low end grunt and will spin the tires longer and even chirps them on going from 1st to 2nd on hard acceleration.

So two things I credit with the new performance.

-The 275s were old and the rubber had actually hardened and shredded a little. There is a thread in another section where the 275 on the 8" rim is debated.
But I believe that using the 275 tires changed my effective gear ratio (from stock 26.4" tire) from 3.23 to about 3.03.

When I went to the 265 50, it changed it to about 3.50 and that made quite a difference.

Also having the heads redone has livened it up and seems to have helped with the cooling a little too.

So all this makes me very happy..the one downside is the 265 50s just dont look as "meaty" as the 275 60s. I know the height and tread width are both reduced. I measured the wheel well lip height from the ground on both sizes and with the 265s it lowered 1.5", so I guess that is why it looks less "jacked  up" to the eye.


3X

[Dano 1]

I tend to agree that the reduction is effective gear ratio is what you're feeling the most. Freshened heads and fresh rubber also help but those two tire sizes are pretty different.

Have you ever played around with https://tiresize.com/comparison/ it's really useful to compare tires if you're looking at different options etc.

Here's your 275/60 vs 265/50:



This is really good info to have as I'm planning to rebuild my 2.76 open rear with a new gear (likely 3.55 or 3.23) and was thinking of running 275/60's out back.

[triple_green]

IF you are going to run 275 60 out back I would def go with the 3.55, if you needed a little more grunt you could always have a spare set of rims with a shorter tire to utilize the 3.55s,

I actually bought an extra set of 15x8 magnums and am trying to decide what size I want to put on the ones with 275s on them now.

[c00nhunterjoe]

I would stick with the 275/60s. The 8 inch wheel will not hurt it. That tire looks best on 80% of the street chargers out there in my opinion.