Getting bigger tires, do I have to re-gear?
#12
Senior Member
Thread Starter
Join Date: Jul 2011
Location: South of Boston, MA
Posts: 177
Likes: 0
Received 0 Likes
on
0 Posts
There kind of weird because 3 of them have about 70% tread left then this other one only has about 50%, the one that has 50% tread was on the back of the truck so I was thinking just from burnouts but its only 1 tire? Lol
#14
Senior Member
Thread Starter
Join Date: Jul 2011
Location: South of Boston, MA
Posts: 177
Likes: 0
Received 0 Likes
on
0 Posts
#15
Senior Member
235/75/R15
(0.75*235/24.5)*2+15 = 29.4 inches tall
31x10.5x15 = 31 inches tall
you be going 5% faster than your speedometer reads and your rear will feel 5% taller. Not enough to worry about. What I mean by taller is a 3.55 will feel like a 3.37
(0.75*235/24.5)*2+15 = 29.4 inches tall
31x10.5x15 = 31 inches tall
you be going 5% faster than your speedometer reads and your rear will feel 5% taller. Not enough to worry about. What I mean by taller is a 3.55 will feel like a 3.37
Last edited by Ssls6; 06-12-2012 at 10:33 PM.
#16
Originally Posted by Ssls6
235/75/R15
(0.75*235/24.5)*2+15 = 29.4 inches tall
31x10.5x15 = 31 inches tall
you be going 5% faster than your speedometer reads and your gear will feel 5% taller. Not enough to worry about.
(0.75*235/24.5)*2+15 = 29.4 inches tall
31x10.5x15 = 31 inches tall
you be going 5% faster than your speedometer reads and your gear will feel 5% taller. Not enough to worry about.
#17
Senior Member
#18
Originally Posted by Ssls6
It's how they are spec'd. I have no idea what any particular tire actually measures or how it squats. Did you measure that on or off the vehicle? I like your bottom quote
#19
Salvage Yard Pro
If you measure actual tire height of a properly inflated tire on the vehicle with a normal load, then you can use a tire size calculator to determine actual speed vs. what the speedometer shows. A gps is allot easier to determine speedo errors though.
http://www.onlineconversion.com/bigger_tires.htm
You can still use this calculator using stated size, but like has been said, manufacturers don't always build tires to the specs they claim. The above site also contains other calculators to determine how far off your speedo will be off and final drive ratio. Final drive ratio is basically tires Vs. gearing. My 2.73:1 rear gear and final drive ratio are matched using 235/75R15's. If I swap to 31's, my new final drive ratio is 2.83:1 and at 70mph on the speedo, I'll actually be doing 72.5mph. The cool thing is, I'll be going a little faster at the same rpm that used to net me 70mph. In town, I'll be turning a little more, heavier tire and stop and go's will cost me some MPG. At highway speed which is where the majority of my driving is, I'll actually gain ever so slightly in MPG.
Here's another that will give you all kinds of info based on current gearing as well as changes that will occur with different gearing.
http://www.angelfire.com/fl/procrastination/rear.html
Here's a calculator for converting metric to standard tire sizes.
http://www.xtremeterrain.com/tire-si...on-metric.aspx
I want to go with 33" tires on my truck which will gain me 6mph at highway speeds. My final drive ratio will be 3.0:1. At an actual gps speed of 70mph, I'll only be turning 2000rpm vs. 2200 with the old tires. 200rpm less won't make a huge difference, but it'll help over time given my 42 mile drives on the interstate.
http://www.onlineconversion.com/bigger_tires.htm
You can still use this calculator using stated size, but like has been said, manufacturers don't always build tires to the specs they claim. The above site also contains other calculators to determine how far off your speedo will be off and final drive ratio. Final drive ratio is basically tires Vs. gearing. My 2.73:1 rear gear and final drive ratio are matched using 235/75R15's. If I swap to 31's, my new final drive ratio is 2.83:1 and at 70mph on the speedo, I'll actually be doing 72.5mph. The cool thing is, I'll be going a little faster at the same rpm that used to net me 70mph. In town, I'll be turning a little more, heavier tire and stop and go's will cost me some MPG. At highway speed which is where the majority of my driving is, I'll actually gain ever so slightly in MPG.
Here's another that will give you all kinds of info based on current gearing as well as changes that will occur with different gearing.
http://www.angelfire.com/fl/procrastination/rear.html
Here's a calculator for converting metric to standard tire sizes.
http://www.xtremeterrain.com/tire-si...on-metric.aspx
I want to go with 33" tires on my truck which will gain me 6mph at highway speeds. My final drive ratio will be 3.0:1. At an actual gps speed of 70mph, I'll only be turning 2000rpm vs. 2200 with the old tires. 200rpm less won't make a huge difference, but it'll help over time given my 42 mile drives on the interstate.
Last edited by unit505; 06-13-2012 at 10:51 AM.
#20
Senior Member
Thread Starter
Join Date: Jul 2011
Location: South of Boston, MA
Posts: 177
Likes: 0
Received 0 Likes
on
0 Posts