Putting 305/35ZR20 on the rear of an 1LE.

[Arodr395]

Originally Posted by 2013 1LE

Will it throw off the speedometer?

Yes by 5 or 6 MPH's.

[Midnight Rat]

Originally Posted by Arodr395

Yes by 5 or 6 MPH's.

That seems like a lot.

[Arodr395]

Originally Posted by 2013 1LE

That seems like a lot.

That's what I was told by the people that work at the service department.

[Bauer2]

At 60 the difference from 285/35 to 305/35 is about 1 mph faster with the 305. Who ever told you 5-6 is crazy lol.

Sent from the future!!

[Matster]

Think the rubber compounds used in the tire and tread pattern have a lot to do with traction as well. After my build I had 305/35/20 P-Zero Ferrari and while it handle nice the traction was horrible, like grease pigs. I changed out to Nitto Invo's 315/35/20 and the difference in traction was night and day. The car has been lower 1.25" on all 4 corners and the tires fit without any issues although my rear rims are 11" wide.

[Dropspeed]

Originally Posted by Arodr395

I need a yes or no answer.

This is not a simple yes/no for a forum as I assure you know one here has done a back to back test with the exact same conditions.

Their are two many other variable that can affect your 1/4 mile time before the 285 or 305 would increase ot decrease your 1/4 time because of their negligible differences in size, weight and overall diameter. Everything from weather, surface prep, fuel volume, shift points etc can change the E/T.

For example. 15 gallons of gas weighs in the neighborhood (depending on ethanol content) 91lbs. 4 gallons, about 24 lbs. The 76lbs will make the car car slower, but wait a minute.....that is more weight over the rear wheels to aid in traction. The 76 lbs may help if the track surface is not prepped

Example 2. If you put two drivers in a the same car and one has 285 and the other has 305. The better driver will win a drag race everytime.

Bottom line. If you like the looks of the 305 and the coin to spend I would do it. But I would also spend more time learning to drive the car instead of worrying about the diff in tire size as seat time will far outweigh any 285/305 changes.

Matt

[willc1980]

if you road course it you can say hello to the problem the regular SS cars have....understeer

[2cnd chance]

Originally Posted by Bauer2

At 60 the difference from 285/35 to 305/35 is about 1 mph faster with the 305. Who ever told you 5-6 is crazy lol.

Sent from the future!!

Wouldn't it show a slower mph on the gauge due to the fact of less revolutions?

Also wouldn't the taller tire effect gearing negatively for the 1/4 mile.

[Dropspeed]

Originally Posted by 2cnd chance

Wouldn't it show a slower mph on the gauge due to the fact of less revolutions?

Also wouldn't the taller tire effect gearing negatively for the 1/4 mile.

Yes to both.

[Bauer2]

Yes the gauge would be slower so when it reads 60 your actually doing a little over 61. Guess I didn't explain it that well sorry.

Sent from the future!!

[Arodr395]

Originally Posted by Dropspeed

Yes to both.

How would it effect gearing negatively in the 1/4 mile?

[2cnd chance]

Originally Posted by Arodr395

How would it effect gearing negatively in the 1/4 mile?

Taller tire less revs = taller final gearing and weaker launch.

[Bauer2]

I could be wrong but the difference in diameter is only about 1 mph diff at 60 so the change in gearing it's going to be negligible.

Sent from the future!!

[Arodr395]

Originally Posted by 2cnd chance

Taller tire less revs = taller final gearing and weaker launch.

Seems like I shouldn't even bother going to 305's on the rear then .