Brake issues with 31" tires?????

Hinch068 · Post by **Hinch068** » Mon Jan 03, 2005 3:19 pm

Check out the following link......http://www.1010tires.com/TireSizeCalculator.asp...It recomends staying within a 3% diameter range when changing size of tires due to risk of break failure. Going from P235/70/15 to 31x10.5xR15 it calculates 9.76% difference which is too large, when going to 30X9.5XR15 it shows 6.81%. Do the breaks have to be upgraded when making this change? Will be driving my kids around so safety 1st......HELP!!!

Post by **HenryJ** » Mon Jan 03, 2005 3:32 pm

Notes:

* Tire diameters can vary slightly for each tire model. The listed diameters are from calculations based on the tire size.
* When changing tire sizes, we recommend staying within 3% of the diameter of the original tire. Any more than this and you face the risk of brake failure.
* This calculator is for information purposes only and we do not guarantee fitment based on this calculator alone.

Don't let it scare you. That is more of a legal disclaimer that anything else.

You get the same warning when you check the stock tire size , and compare it to the optional offroad tire size.

I would not be concerned for your safety. We have the same size brakes the ZR2 package has, and 31" tires are stock for them.

Our braking system is designed for a 5500lb towing capacity. I would be much more concerned if you were towing that much without supplemental braking.

While it is true that with the increase in rotating mass, and the leverage of the increased diameter , greater forces are needed to decrease the inertia. I believe that we have more than enough braking force than what will be required.

Upgrading brakes is a good idea, but would require larger wheels to clear the oversized rotors. There just isn't any room for larger. Now vented or slotted rotors could be an option, as would "high-tech" pads and calipers. Still I think that the stock calipers and ceramic pads are sufficient.

Hinch068 · Post by **Hinch068** » Mon Jan 03, 2005 3:44 pm

Great, thanks. Makes sense to be concerned more about towing weight that just increasing size of tire.

Hinch068 · Post by **Hinch068** » Mon Jan 03, 2005 4:02 pm

Hinch068 wrote:Great, thanks. Makes sense to be concerned more about towing weight that just increasing size of tire.

It also showed a speed reduction of 10.79%, moving up to 3.73 gears from 3.42...will that make up the difference?

Post by **HenryJ** » Mon Jan 03, 2005 4:14 pm

Hinch068 wrote:...It also showed a speed reduction of 10.79%, moving up to 3.73 gears from 3.42...will that make up the difference?

That will definitely help. 3.73's and 29" tires were the best combination IMO.

You do not want to try 3.42's and 31" tires. You will be disappointed.

F9K9 · Post by **F9K9** » Mon Jan 03, 2005 5:28 pm

Just my experience from driving a ZR2 from 97 until this past May is that their brakes were terrible

They were terrible when I drove it off the lot. According to some members on ZR2.com it was from the extra mass (tire wise) that the ZR2s using a stock brakes have bad braking!

Brake failure? Never had a problem and only had one pad change in 65k miles but, it was such an effort to apply enough foot pressure to stop it. Took my ZR5 for a test drive when I was looking at it and was thankful my seat belt was on

I know that our rear disks help alot but, it was like night and day between the two.

Yes I will step up to 31X10.5s on down the road:)

Post by **HenryJ** » Mon Jan 03, 2005 5:42 pm

f9k9 wrote:Just my experience from driving a ZR2 from 97 until this past May is that their brakes were terrible...They were terrible when I drove it off the lot. ...

There were indeed some problems in earlier models.
Perhaps some issues with the iron content of the rotors, in addition to some lining wear issues.

The first problem was the lack of mileage obtained from the brakes. Premature wear. I think they went to a harder lining composition. Then there were problems with the rotors wearing out , going out of round, etc.
This may have been due to the rotors being a little soft for the harsh pads.

They then made a change in the pads again, going to the ceramic pads. I am unsure what happened with the rotors, or if there was a change there.

Suffice it to say that things have improved, and you do not hear of those problems anymore.

Hinch068 · Post by **Hinch068** » Mon Jan 03, 2005 6:05 pm

This site is great, provides so much info, you all are very helpful....next question in regards to gears is being that it is a 4wd do I have to change both front and back when I get the bigger tires? and also would 4.11 gears match up better with keeping MPH the same on stock tires and 3.42 gears better then 3.73 with 31" tires. Gear ratio chart only showed Manual Trans, showed with overdrive transmission RPM in overdrive will be 15% to 30 % less.

Post by **HenryJ** » Mon Jan 03, 2005 6:51 pm

Hinch068 wrote:This site is great, provides so much info, you all are very helpful....next question in regards to gears is being that it is a 4wd do I have to change both front and back when I get the bigger tires?

Both axles must have the same diameter tires and the same gear ratios

... would 4.11 gears match up better with keeping MPH the same on stock tires and 3.42 gears better then 3.73 with 31" tires. Gear ratio chart only showed Manual Trans, showed with overdrive transmission RPM in overdrive will be 15% to 30 % less.

4.11 would be closer to ideal with 31" or larger tires. The 3.73's are not bad with a few performance enhancements though.

3rd gear in the auto is 1:1 as is 4th in a standard. overdrives may vary in ratio?