1994SEV6 Posted November 10, 2011 Share Posted November 10, 2011 I bought my HB about 6 months ago now. It has 30x9.50r15lt tires all the way around. I had looked at the sticker in the door jamb 2 or 3 times for general information, but I never really payed attention to the tire size. It says the stock tires, the ones the truck was originally equipped with by Nissan, were 31x10.50r15. I never noticed this. If the stock is 31, and I'm running 30s, how far off is my odometer? Are there other consequences to this? Link to comment Share on other sites More sharing options...
Slartibartfast Posted November 10, 2011 Share Posted November 10, 2011 It won't be off too badly, if you've got GPS you can check the speed against the speedometer, or you can use highway mile markers and the trip odometer. Smaller tires will make it feel a little torquier, but limit top speed/cruising efficiency. I don't imagine a 1" difference will change that much. Pathfinders came on 31s or 29s, so apart from your speed sensor being a little off, 30s shouldn't be hurting anything. Link to comment Share on other sites More sharing options...
Trogdor636 Posted November 10, 2011 Share Posted November 10, 2011 http://www.powerdog.com/tiresize.cgi In the little box on the right enter 30/9.5/15 and then under it enter 31/10.5/15. 1 Link to comment Share on other sites More sharing options...
1994SEV6 Posted November 10, 2011 Author Share Posted November 10, 2011 It won't be off too badly, if you've got GPS you can check the speed against the speedometer, or you can use highway mile markers and the trip odometer. Smaller tires will make it feel a little torquier, but limit top speed/cruising efficiency. I don't imagine a 1" difference will change that much. Pathfinders came on 31s or 29s, so apart from your speed sensor being a little off, 30s shouldn't be hurting anything. Ahhhh ok. So, my speed odometer would say that I was going slightly faster than I really was? I might borrow a GPS unit from someone. That speedview app doesn't work on my phone. Damn Samsung captivate. So...small tires make for faster acceleration, but lower top speed. This kinda goes against everything I thought, but would bigger tires give me better gas mileage on the highway? Up to a point. I know like 40" tires would be very counter productive. Link to comment Share on other sites More sharing options...
Slartibartfast Posted November 10, 2011 Share Posted November 10, 2011 (edited) So...small tires make for faster acceleration, but lower top speed. This kinda goes against everything I thought, but would bigger tires give me better gas mileage on the highway? Think of it this way. A small tire covers less ground per revolution. It does less work, so it doesn't require as much torque to move. A big rim covers a lot of ground, so it's harder to move. Ideally, the rim/tire size is matched to the diff gear ratios, the ratios in the trans, and the engine, so that the engine isn't straining at low speeds or revving too high at high speeds. Either extreme will return lousy milage, and somewhere between the two is the 'butter zone.' Look at the tires as the last stage of gearing from the engine to the ground. With the O/D off, my truck does 50 at somewhere around 3k rpm. With O/D engaged, it gears up and engine RPM drops. If I didn't have O/D, I could compensate with bigger tires, and have the same ratio at speed that I do now. However, in first gear, I'd still be running a higher ratio due to the tires, so the truck would struggle to accelerate. Or, with smaller tires, I could be doing 50 at 3k with the O/D on, but I'd be working the engine harder. I haven't messed with any of this, so I don't know where the butter zone is. Adamzan said his milage dropped when he went to 33s, so that's clearly outside the butter zone. I suspect the rig was designed around the factory tire sizes of 29s and 31s. I haven't heard anyone compare milage between trucks on 29s and trucks on 31s, so I don't imagine the 1" difference in your tires is having a huge effect. TL;DR: I don't think 31s would change your milage appreciably. But they would make your gauges work right. Edited November 10, 2011 by Slartibartfast Link to comment Share on other sites More sharing options...
sewebster Posted November 10, 2011 Share Posted November 10, 2011 The engine applies a torque to the wheel. The force that is then applied from the tire to the ground to propel you forward is that torque divided by the radius of the tire. Bigger tire, less force. Link to comment Share on other sites More sharing options...
1994SEV6 Posted November 10, 2011 Author Share Posted November 10, 2011 The engine applies a torque to the wheel. The force that is then applied from the tire to the ground to propel you forward is that torque divided by the radius of the tire. Bigger tire, less force. bigger tire is less force? By force you mean torque? well...then why do off-roaders have huge tires when they want more torque? Link to comment Share on other sites More sharing options...
Precise1 Posted November 10, 2011 Share Posted November 10, 2011 They change the gearing to compensate, just like they run huge tires to compensate for something else... B 1 Link to comment Share on other sites More sharing options...
sewebster Posted November 10, 2011 Share Posted November 10, 2011 (edited) I mean force, not torque. The torque is determined by the engine and is applied to the wheels via the transmission, driveshaft, diff, and axles, and is independent of tire size. The engine torque is different than the wheel torque by a factor of the trans and diff gear ratio. Big tires are good because they get you high off the ground etc etc. Precise is right, if you want to run big tires, re-gearing is a good idea. Of course you can get the same force with bigger tires by just increasing engine torque, usually by running at higher RPM. But this means you are going faster, which might not be what you want. Edited November 10, 2011 by sewebster Link to comment Share on other sites More sharing options...
adamzan Posted November 12, 2011 Share Posted November 12, 2011 Mine came with 235/75/15s but it got better mileage when I switched to 31s. But only on the legos, 31's on the stock chrome rims was a pretty heavy combo (they were bfg at) Link to comment Share on other sites More sharing options...
1994SEV6 Posted November 12, 2011 Author Share Posted November 12, 2011 Mine came with 235/75/15s but it got better mileage when I switched to 31s. But only on the legos, 31's on the stock chrome rims was a pretty heavy combo (they were bfg at) Hmm.. that's pretty interesting. Anything to improve mpg would be great. Where does it all go? 15-19mpg with a 3.0 = no bueno. I want to switch because I found 2 BRAND NEW BFG 31s under my dad's porch the other day. Still had the price tags on them, never touched pavement. They are probably pretty old, but the rubber looks great. 2 of my tires are getting kinda low on tread so I was thinking I could trade my good 30s for good 31s to get a complete set. Not working out so well so far. by the way, I'm getting the vibe that people around here don't like legos? Not a strong vibe, pretty mild. What's up with that? Not trying to go against the grain, but I love them. I lost my 2 front center caps within a week of ownership :'( still looking for replacements Link to comment Share on other sites More sharing options...
Trogdor636 Posted November 12, 2011 Share Posted November 12, 2011 Hmm.. that's pretty interesting. Anything to improve mpg would be great. Where does it all go? 15-19mpg with a 3.0 = no bueno. I want to switch because I found 2 BRAND NEW BFG 31s under my dad's porch the other day. Still had the price tags on them, never touched pavement. They are probably pretty old, but the rubber looks great. 2 of my tires are getting kinda low on tread so I was thinking I could trade my good 30s for good 31s to get a complete set. Not working out so well so far. by the way, I'm getting the vibe that people around here don't like legos? Not a strong vibe, pretty mild. What's up with that? Not trying to go against the grain, but I love them. I lost my 2 front center caps within a week of ownership :'( still looking for replacements There is a way to tell on the sidewall of the tire what year the tires were made in. I cant remember off the top of my head but you can google it. I think Legos are like anything else, some people like em, some would rather have the stock chromies, some would rather have custom. I like the Cragar soft 8's, but my Legos are cheap. Link to comment Share on other sites More sharing options...
schro Posted December 19, 2012 Share Posted December 19, 2012 So...small tires make for faster acceleration, but lower top speed. This kinda goes against everything I thought, but would bigger tires give me better gas mileage on the highway? Up to a point. I know like 40" tires would be very counter productive. Worse gas mileage. More wheel weight. Link to comment Share on other sites More sharing options...
silverton Posted December 19, 2012 Share Posted December 19, 2012 Holy thread revival! When I first saw it, I was like, I thought that kid was gone a long time ago, how he's back making more threads.... Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now