Bronco Forum - Full Size Ford Bronco Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
17 Posts
Discussion Starter #1
Hi,

I just became the owner of a 89 Bronco, 302 Auto H9 axle. It needs tires badly, so I don't have a lot of time to do research. Can anyone here help me?

Apparrently I have two choices of size: P235/75R15.....or.....31x10.5R15/C.
It has the larger size on it now...but it has aftermarket rims so I don't know what size it was originally equipped with.

I went to Costco tonight and looked at the two sizes...the 31's are of course wider...but they are also quite a bit taller. I can't imagine how they both could be appropriate. It would seem that the final drive ratio of the vehicle would be quite a bit different from one to another. It would seem that the engine would rev higher at a given road speed with the P235's.....

My Priorities: I won't really be doing any off-roading to speak of. I plan to pull a smaller boat trailer on the highway. I would like a pleasant ride, quiet ride....within reason of course. And good handling. Cost and off-road performance would be secondary.

So; what should I do? Which size would fit my needs better? Thanks for your time folks...Chuck
 

·
Engineer
Joined
·
13,165 Posts
33x12.5's look good
 

·
FSB warrior
Joined
·
6,113 Posts
those 2 tire sizes your considering are big... for a car that is.

Go with 32's unless you will never use it offroad ever... then look at the sticker where you saw the H9 axle code, it tells you what size it came with. You might have to wide a wheel to run 235's on there again. (maybe??)


Just so you know 235's fit on a stock 4x4 ranger, they look like doughnuts on a fullsize.
 

·
Registered
Joined
·
245 Posts
go with 33's I have a '95 with 32's and stock rims and am cussing myself for not going bigger.
 

·
Premium Member
Joined
·
635 Posts
go with 32's. These are 32 AT's. They handle well on road and are a huge help in the snow. As far as riding quiet. I can't hear them, but then again, it is hard to hear much over the exhaust anyways.

[/IMG]

PS, almost 0 issue with rubbing the radius arms except at full lock; however, I have these on my 96 and different wheels and they don't rub at all.
 

·
Back in TEXAS
Joined
·
1,966 Posts
I have 32s on my 87 with a 302 and stock rims. The only time I rub is at full lock (radius arms). My speedometer is off by approx 10%, when it says 30 I'm really doing 33, 40=44, etc. To get a rough est of how far your speedometer is off get on the hiway and as you pass a mile marker check your odometer, when you pass the next look at it again. Mine registers .9 miles therefore approx 10%. If you have a friend with you go what you think is 60 for 1 mile, should take 1 min. Another option is have someone with a known good speedometer either follow (pace) you or you follow them to get reading.
 

·
Registered
Joined
·
17 Posts
Discussion Starter #10
Thanks for the replies so far...I have to admit...those 33's do look good.

Will they fit on my 31x10.5R15 rims...or would I need new rims also?

One thing keeps nagging me though...as I keep increasing tire size...isn't the final drive ratio shifting against the performance level? as in...wouldn't it be like running in overdrive because of the larger tire diameter?

Wouldn't acceleration be hindered by going to larger tires? After all...it's just a 302..I think it's maybe 185 HP or there-a-bouts.

As I see it.....the larger tires would give better gas mileage but worse performance...and the smaller tires would give worse gas mileage...but snappier acceleration. Am I wrong here?

Or is there a small enough difference in diameter as to not make much difference?

Thanks again, Chuck
 

·
Registered
Joined
·
444 Posts
I have 31/10.5/15 size tires on mine. So the 10.5 is the side wall right not the width. Any way I believe I have Ameican Racing 15 in rims. What is the widest and tallest tire I could put on? James
 

·
Engineer
Joined
·
13,165 Posts
78rangerbronc said:
I have 31/10.5/15 size tires on mine. So the 10.5 is the side wall right not the width. Any way I believe I have Ameican Racing 15 in rims. What is the widest and tallest tire I could put on? James

31 is the overall height, 10.5 is the width
 

·
Registered
Joined
·
27 Posts
ya already admit thta it is only a 302 after all so who are you going to be racing off the lights :smokin: thier will be a differance not that grand in scale going with 32" 33" inch tires more of a speedo calabation problem then any sorta acceleration isssue. Only thing i wanted to toss out thier is also match your tire to your rim width if their 15x7-8 the 32x11.5's match up better, if their 15x10 33x12'5-13'5 's match up better the width of the tire isn't the tread patten width ussually it's the widest part of the tire making the sidewall the width the of a tire unless it has huge side lugs on the tire. Any rate the basic idea is that your width should never exceed 4inches over your rim width. the radial belting and sidewall structure is made to work with-in that accomidation, although you can use a wider tire on a narrower rim it often causes a baloon effect wereing the center of the tread out first most often.
anyways i hope that this might help ya some .. 35 inch in bigger anouther story

as for the other guys question ya can run as big a tire as you can fit on your truck on 15'inch rims really wouldn't go past 38's ion a 15 inch rim cause it just looks wrong more width in the rubber then the steel.
:drinkbud : :beer
 

·
FSB warrior
Joined
·
6,113 Posts
chances are your aftermarket rims are 15X8, your stock ones were 15X7 and people do run 12.5 wide wheels on 7" wide rims. You can comprimise and go with 32's, but I wouldnt want to spend 450 on tires just to wish I had gone bigger.

effectively your right, smaller tires increase your final drive RPM, but its gonna probably be about 400 RPM's. The reason I came up with this complete guess is that 235's are 29" tall (approx) and 33's are approx 33". With my 31's (they were free, and they are my winter tires) I spin 3000 RPM's @70 MPH with my 36's I spin 2500 at 55 (on the speedo, which is actually 70MPH for real)

This is with a final gear of 1:1 and 3:50 axle ratio
 

·
Registered
Joined
·
4,684 Posts
As a comparison, I have 31s on my `94 5.0L, and they look a little small. I'd rather have 32s or 33s. You're not going to win any torque competitions with that 302 anyway, might as well put something a little meatier on it.

I turn 2000 at 75 (accurate by my GPS), but I have an OD gear (E4OD transmission).

Watch your wheel width, though. Don't get unsafe for the sake of looks.
 
1 - 16 of 16 Posts
Top