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Dropped in 4.11s and still have stock tire size, which is 25.4" diameter. Want to go to larger diameter tires, primarily to give me a little more clearance as I have to crawl over speed bumps so my headers don't rub. Running 4.11s now so stock tire size makes me feel like I'm stuck in second gear. What is the largest tire size I can run on stock suspension without worrying about rubbing? Want to keep the staggered look. I'd like to go at least 225/70/15 (27.4") and 275/60/15 (28"). From others on here looks like I should be safe with those sizes on stock suspension. Anyone go any larger in the rear on stock suspension (285s @ 28.5")?
F70-14s were 25.6 inch diameter
At 25.4 your 4.11s are more like 4.14s
Cooper Cobra factory equivalent is 215/70R 14 they are 25.8 inch diameter and weigh 23 lbs each. Effective ratio is 4.05
Cooper Cobra 275/60R 15s are 28.1 inches in diameter and weigh 30 lbs. Effective ratio will be 3.72 ( that should make for a nice noticable difference)
If I recall correctly, you have a beast with like double the factory power output and will still be a street sweeper.
But those size tires can noticabley slow down our cars when stock... I had a 66 442 A2 with 3.23 limited slip and swapped on those exact tires. Car went from nice wheelspin to a chirp when you gunned it. And felt sluggish throughout... (Felt like you went from driving alone to having a car full of people)
In my case I had BF Goodrich Radial T/As which are far heavier than Cooper's. 36 lbs each. 13 lbs over stock per tire is devastating on a mild stock set-up Horrendous unsprung weight disadvantage.
RPM is inversely proportional to tire diameter. Assuming the car really does have 25.6" tires, changing to the 28" 275/60-15s yields a drop from 4,000 RPM to 3,660 RPM, about an 8.5% reduction. If the current tires are actually close to the stock 26.5" diameter, the change will be 3,785 RPM, only a 5% reduction in cruising RPM.
Car came with 3.23s and the 25.8" tires, which was a nice combo. First priority is taller tires as I need more clearance. I have a little lip entering my barn and I need to go super slow to avoid rubbing. The 2 7/8" headers hang pretty low on these motors. I bought the 4.11 rear axle when I bought the race motor so I moved to that in anticipation of the larger tires. Just trying to see what my options are on diameter. I'm good with tires weighing a little more as I have trouble keeping traction with the current setup.
Stock tires on a 1968 442 were F70x14, which are 26.5" in diameter.
Joe P is correct as usual. My bad I was relying on Automobile Catalog for factory tire spec without double checking... Coker tire puts it in Joe's range as well.
So I’m reading this as you need more front end clearance for the headers, and not taller rear tires for RPM reduction. Is this correct?
Primarily being the operative word.
Originally Posted by teamwieland
so my headers don't rub.
Running 4.11s now so stock tire size makes me feel like I'm stuck in second gear.
want to keep the staggered look.
Teamwieland if your fronts are currently 25.4 diameter. The 225 70 15s will push the car up 1 inch. That has to help... (Long tube headers can be a pain in the ***, I've been there...)
275 60 15s will reduce RPMs no matter what.
Staggered look is the way to go in my book as well.
As far as going even larger on rear, proceed with caution. As it is if your rims are 15x7 you are 1/2 an inch short on recommended rim width for 275 60 15s. And they fill the wheelwell very well, in both directions. Assuming backspacing is optimal.
As far as going even larger on rear, proceed with caution. As it is if your rims are 15x7 you are 1/2 an inch short on recommended rim width for 275 60 15s. And they fill the wheelwell very well, in both directions. Assuming backspacing is optimal.
Those tires look great !! I have been following along on this thread and am also trying to decide what size tires I will be running the hurst dazzlers 15 x7 and they have a 3.8 back spacing , I was thinking 255/60 but if I could get wider without rubbing issues I’d do it , also running 501 cargo coils but it doesn’t look too high? Would 275s fit ok? My car is a 69
What are you running for rear axle ratio with the 275/60s?
I have 3:08 on my 68 and 3:23 on my 72
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Last edited by Gary's 2 442-S; Feb 24, 2022 at 12:01 PM.
