Attn: DR2000

[12SEC SS]

hey, u still running those 275x50s? how tall are they?

[DR2000]

Here's a good link that I use to calculate that kind of stuff:
http://www.miata.net/garage/tirecalc.html

From that my tires are 27.8 inches in diameter. Hmm, I thought they were about 27.

Either way I will need new tires real soon, and I'm not sure what to get at this point.

[9C1LT195]

In reality they are around 28". They have a tall thread.

[DR2000]

I was thinking of switching to something in the area of 285/40/17 for the rear, but that's 2 inches shorter. My dilema is with the final gearing and RPM. Here's the situation:

T56 that I've got is one of then 93 models. The one with 400lb/ft torque rating. The gearing seems to be better then in 94+ since they are more equally spaced, however it's higher then 94. It looks like that my 93 with 3.73s produces results as 94 would with something in between of 4.10s and 4.56s, which is pretty cool. Also with this 93 the driveshaft rotation speed will be much closer to safe then with 94.

So by going to a smaller diameter tire I will be getting closer to 4.56s then 4.10s. However it doesn't seem to make that much difference. I'll be able to go 70 at about 2000 RPM in 6th gear which isn't bad at all, and lately I don't seem to be cruising at speeds higher then that anyway.

Another questions is how will 285/40/17 fit on the stock Impala rim? Is the tire going to be to wide?

I wish I could afford new rims and go with 315's on the rear. Or maybe it won't run me too much to widen the rear ones, considering I've already go a set of 2. What do you think? What options do I have here?

I haven't done tire research in quite a while now... Forgot most of the stuff.

[12SEC SS]

how much thread is left on your tires? i know someone who needs a pair, and he may have 285x40s, and they do fit stock rims.

[DR2000]

They are not completly bold yet, but close to that. About 2mm at some places.

However I don't see a point in trading for the tires which could be in the same condition. If I'll be buying tires, I'll be buying new ones.

[Incitatus]

Here's a little info I had on my computer, I'm not sure if if it's the same info you're using or if it's even relevant to your discussion:

Tire sizes are normally listed in 3 numbers, such as 205/55/16.
The first number is simply the width of the tire in mm (205 mm).
The second number is sidewall height as a percentage of the width.
For instance, in this case, the sidewall is 55% of 205 mm: 112.75 mm.
The third number is the diameter of the wheel (rim) in inches.
So to calculate the diameter of a tire:
(sidewall X 2) + wheel
Converting the wheel diameter to mm. gives:
(112.75 mm X 2) + 406.4 = 631.9 mm or 24.88 in.
To calculate the circumference of the tire (how far the tire travels in one revolution):
631.9 * pi = 1985.17 mm or 78.16 in.

[9C1LT195]

I am running 285/40 in the back now along with 275/40 in front. The tires are BFG KDW (not the crappy KDWS). These tires are considered good tires by Autocrosser and other autocrossers/road racers on the ImpalaSSForum.

My impressions with them compared to the 275/50 Nittos. The straight line traction is definitely worse with BFGs. The reasons are shorter sidewall and shorter tire diameter (= steeper gearing). They are about the same in the rain and a lot worse in the snow. The good thing about these tires is handling in turns.

DR2000, the overdrive for the 93 T56 is 0.62 which is not that far off the 0.699 of the 4L60E. The 94+ T56 has a 0.50 overdrive which makes a HUGE difference in a gear selection.

I would recommend either staying with the same tire height and getting 4.10 gears. Another option is getting 285/40 tires and 3.73 gears which would equal to the 4.02 gear ratio compared to the 275/50 tires. The second option will be a little cheaper since the gears are more common and you won't have to pay for a $100 for a custom reluctor. However, all the lower profile performance tires are A LOT worse in the snow than 275/50 nittos. Just something to think about.

[9C1LT195]

P.S. In case you're wondering, 285/40 tires and 4.10 gears will be equal to 4.42 gears compared to your current tires.

[DR2000]

I think you misunderstood me slightly there. I'm not planning on using 4.10s in the rear. 4.10s work well with 94+. My plan is 3.73s, since gearing in 93 tranny is higher.

What I was saying was 93 + 3.73 will results in higher final ratio then 94 + 4.10. However there are tons of people that run 3.73s with 4L60E and again I'll be able to maintain lower last gear RPMs with my set up, so I think 93 + 3.73 is a really good combination.

On the tire subject. What are people saying about Yokohama AVS Sport tires?

[DR2000]

Some number:

1st: 2.66 2nd: 1.78 3rd: 1.3 4th: 1 5th: 0.74 6th: 0.5

Tire Diameter 1: 27 inches
Rear Gear Ratio 1: 4.10:1

 
RPM 1st 2nd 3rd 4th 5th 6th
1000  7  11  15  20  26  39 
1500 11  17  23  29  40  59 
2000 15  22  30  39  53  78 
2500 18  28  38  49  66  98 
3000 22  33  45  59  79 118 
3500 26  39  53  69  93 137 
4000 29  44  60  78 106 157 
4500 33  50  68  88 119 176 
5000 37  55  75  98 132 196 
5500 41  61  83 108 146 216 
6000 44  66  90 118 159 235 
6500 48  72  98 127 172 255 

Transmission Ratios:
1st: 2.97 2nd: 2.07 3rd: 1.43 4th: 1 5th: 0.8 6th: 0.62

Tire Diameter 1: 27 inches
Rear Gear Ratio 1: 3.73:1

RPM 1st 2nd 3rd 4th 5th 6th
1000  7  10  15  22  27  35 
1500 11  16  23  32  40  52 
2000 15  21  30  43  54  69 
2500 18  26  38  54  67  87 
3000 22  31  45  65  81 104 
3500 25  36  53  75  94 122 
4000 29  42  60  86 108 139 
4500 33  47  68  97 121 156 
5000 36  52  75 108 135 174 
5500 40  57  83 118 148 191 
6000 44  62  90 129 162 208 
6500 47  68  98 140 175 226 

[DR2000]

Now going from those numbers:

Say that we take 94 + 4.10 RPMs as ideal. Then to achive that or get as close to that as possible I'd go with 93 + 3.73s with the taller tire (275 50). However it seems that 94 + 4.10 is less optimal then 93 + 3.73s, sine final ratios are higher, yet low enough not to cause drivability problems. Therefore I conclude that I could go with 285/40 without having much problems.

Does that sound right, or am I complety lost? :doh:

[9C1LT195]

I've heard good things about the Yokohama Sport tires.

1993 T56 with 285/40 tires and 3.73 gears sounds like an excellent combination.

Below I've calculated some final gear ratios (trans gear ratio * rear gear ratio)

                               93 T56+3.73           94 T56+4.10     4L60E+3.73
--------------------------------------------------------------------------------
First gear final ratio             12.53                10.91           11.41
Overdrive final ratio               2.31                 2.05            2.61

Looking at the figures, I really like the 93 T56 ratios. The punch from the line is significantly better and the overdrive ratio is not steep compared to the 4L60E. Also, you can clearly see why many people with 94+ T56 go with 4.56 gears.

Sorry for the hard to read table, vBuilletin seems to ignore the whitespace.

[DR2000]

It seems that I was getting upset over nothing when I found out the tranny was 93. Actually looks like I accidently lucked out on this one.

[DR2000]

Heard anything about these: Kumho ECSTA Supra 712?

They go for $116 a piece as opposed to $252 for Yokohamas. And that's a big difference when you are talking about 4 tires.

[9C1LT195]

My friend has them on a crown vic and likes them. However, crown vics do not have traction problems like lt1 powered b-bodies.

[DR2000]

Sorry to bring this one up, but I was looking over the numbers again and something looks strange.

First gear on 4L60E is 3.08, and on 93 T56 it's 2.97. How can the initial ration on T56 be more then on 4L60E? What am I missing?

[9C1LT195]

According to BigFastCar.com it's 3.36.

[DR2000]

Oh, there are 2 types. 400lb/ft one and 350lb/ft. I seem to have the one rated at 400, and it's first gear ratio is 2.97 judging by the same table on bigfastcar. So what does that do for the final first gear ratio? It still seems to come up on top of 94 version with 4.10s, right?

[9C1LT195]

Just multiply the trans gear ratio by the rear-end gear ratio. I always thought that 93 f-bodies had the weakest t56, and the one in the middle was in earlier vettes. I could be wrong.