Gearing Guru's?

[WEAK_E90]

Looking for if anyone has information regarding gearing with larger tire setups.

Attempting to understand what gear change would be needed AND OR if anyone has recommendations to ratios on a 35 or 37" setup.

yes they cant fit - no i dont care about how 285s are all i need.:bolt:

 

[rdruss]

Looking for if anyone has information regarding gearing with larger tire setups.

Attempting to understand what gear change would be needed AND OR if anyone has recommendations to ratios on a 35 or 37" setup.

yes they cant fit - no i dont care about how 285s are all i need.:bolt:

Bigger tires result in lowered engine speed at the same road speed as before the change. So, if at 60 mph you were turning 2000 rpm before with 31" tires let's say, putting 35" tires on is a 12% larger tire diameter, 31/35 = .8857
So if you want the same rpm at 60 mph as before you would to change your gearing to 3.73/.8857 = 4.21, assuming you have 3.73 gearing now. 4.21 may not be available so 4.11 or 4.33, either one might be a choice. You can "google" tire gearing charts and plug in numbers and see what comes up.

 

[WEAK_E90]

Bigger tires result in lowered engine speed at the same road speed as before the change. So, if at 60 mph you were turning 2000 rpm before with 31" tires let's say, putting 35" tires on is a 12% larger tire diameter, 31/35 = .8857
So if you want the same rpm at 60 mph as before you would to change your gearing to 3.73/.8857 = 4.21, assuming you have 3.73 gearing now. 4.21 may not be available so 4.11 or 4.33, either one might be a choice. You can "google" tire gearing charts and plug in numbers and see what comes up.

Appreciate the information and the breakdown. Do you by chance have either installed that you would recommend?

 

[fourwd1]

A taller tire size will cause you engine to run somewhat outside it's normal powerband. You'd be running at higher RPMs to attain a MPH, using more gas which lowers your actual MPG. It also throws your speedo off which throws off your calculated MPH.

Changing to a lower (higher numerically) gear ratio will put you running back in the engines optimal powerband.

For example my '84 4 cyl/5 spd manual truck came with 28" tires and 4.10:1 gear ratio.
To get it back to the proper RPM range and correct the speedo error I went to 5.29:1 gearing.

The same vehicle with a 3 spd auto trans (like my '89) came with a slightly lower 4.30 ratio because it's an auto trans.

There's plenty of online gearing calculators you can use to determine the correct new ratio for a taller size tire.
Of course if you're only going an inch or 2 taller you may be able to deal with the slightly lower performance/MPG.

 

[rdruss]

Appreciate the information and the breakdown. Do you by chance have either installed that you would recommend?

No personal experience, I just know the math, but there are plenty of users on here who have regeared and I'm sure one or two will chime in.