Larger Tyres and real distance travelled

drgtr
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Larger Tyres and real distance travelled

Unread post by drgtr » March 8th, 2018, 6:34 am

Hopefully someone can help.

2003 Td42ti Nissan Patrol Manual

32 inch tyres. compared to 31 inches
Last edited by drgtr on March 10th, 2018, 7:11 am, edited 1 time in total.

Peter Aawen
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Re: Larger Tyres and real distance travelled

Unread post by Peter Aawen » March 8th, 2018, 11:51 am

If the speedo 'indicated speed' has varied by about 10% then the chances are that the distance travelled shown on your odo/trip meter has also varied by pretty much the same amount!

Buuut, just for your interests sake, while your vehicle may have come from the factory with 265/70R16's fitted, Nissan originally designed the Patrols around running 750R16 tyres on their split rims (waaay back when they first designed that chassis & drivetrain!) and those were about 32.8" in rolling dia, and it proved to be quite a suitable combination of gearing and speedo/odo drives right across the range of wheels & tyres they've fitted ever since, so they have never changed that!! Which is a good thing for you, and pretty much why the nominal 35's you are now running are still so much within the 'right range' for driving, altho off road you might find you need to grab low range just a little earlier to avoid over-heating the clutch or at least too much slipping of the clutch in 1st gear Hi range! Before the change, your 'factory tyres' meant you were running at the high revving end of the ideal rev range, now with the bigger tyres fitted, you are running closer to the low revving end!

All that said, it WILL have made a difference to your fuel economy! But maybe not so much as you think... If you continue to drive at the same ACTUAL speeds (ie, taken off your GPS) rather than the same speed as indicated by your Speedo (which used to be somewhat slower than the indicated 100kph, but is now very much closer if not over that by a tiny amount!) AND you use the GPS 'distance travelled' instead of the trip meter or odometer (which was very likely formerly 'quite optomistic' about how far you'd gone!) you will be getting a much closer to 'correct' fuel usage reading, which might seem to be worse than it was, while before, when your odo/trip meter was being pretty optomistic about how many kms you'd travelled, it seemed pretty good!! But that was only because you were THINKING you were driving at 100 kph when you were actually only driving at something closer to 90 kph and you were THINKING you'd just travelled 110 kms when you'd probably actually only travelled something closer to 100 kms!! Sooo, if you drive off the speedo now, you'll actually be travelling faster (& therefore using more fuel than before) and driving fewer kms, ie, only 100 kms instead of the former possible 110.... and that will make your fuel economy seemingly take a hit! But if you use your GPS to drive at the same ACTUAL speed as you used to, ie about 90 kph, so you aren't working the engine any harder, and you use the GPS Distance travelled to measure each ACTUAL 100kms you've travelled, your fuel economy will at least be quite accurate, and certainly more realistic than it was in the past! However, if you do drive off the speedo at the same indicated speed as you used to with the old tyres (so you are really now driving about 10% faster) & you use the more accurate distance travelled from the trip meter now instead of the 'more than actual' it probably always reported before (so you are seemingly travelling 10% less kms than you were) then your fuel economy may seem to have taken a hit!! But when all things are equal except for the tyre dia, you should actually be doing a little better than previously due to the greater tyre rolling circumference & therefore greater distance travelled for each rev of the motor! ;)

Btw, modern GPS units read the satellite signal at least 3 times per second & will give you a much more accurate velocity reading than any speedo, and their distance travelled will also quite accurately reflect how far you have moved across the face of the Earth, and yes, that includes the ups & downs of hills & dips etc, not just a straight line record! Even the cheapest of GPS units that we get to use these days are pretty much waaay more accurate than any wheel driven speed or distance travelled indicator used in any motor car these days - hey, the GPS Units we have now are more accurate than the units that succesfully navigated a bunch of men to the Moon & back without any major hiccoughs! :thumb:

Enjoy, now that I've made all that sooo clear! :o
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

drgtr
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Re: Larger Tyres and real distance travelled

Unread post by drgtr » March 8th, 2018, 7:40 pm

Thank you Peter
Last edited by drgtr on March 10th, 2018, 7:11 am, edited 1 time in total.

Peter Aawen
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Re: Larger Tyres and real distance travelled

Unread post by Peter Aawen » March 8th, 2018, 8:22 pm

No wories! :thumb:

The interesting thing abougg all this is that while most manufacturers didn't care too much about the accuracy of their vehicles speedos just so long as the reading fell somewhere within the 'speed indicating devices may read anything up to 10% higher than true speed' with any of the factory option tyres fitted, so the vehicle could actually only be travelling closer to 90 kph while the speedo showed 100 kph (ie, speedos could show anything up to 10% over true speed - to make it difficult to blame the speedo for that speeding ticket!) AND they weren't allowed and were really hot on making sure that none of their standard sized tyres ever let a speedo show 100kph when the actual true speed was even just 101 kph; let alone any higher than that; there was even less strict control over odo/trip meter accuracy except for buyer/owner perceptions, altho funnily enough, most people objected to having an odo/trip meter ever read ANYTHING but fairly accurate (after all, they might service it too soon, or lose some of their 100,000km warranty!!) and besides, 'distance travelled' can be fairly readily measured and roughly checked!! So while many speedos read anything up to 10% fast on stock tyres, very few odo/trip meters are ever anywhere near the same percentage out... but they are still usually out at least a little !!

All of which means that you just can't assume that cos the speedo read 10% slow on the std wheels, it'll mean the odo was also 10% out.... it MIGHT have been out that much, and some certainly are, but chances are that it wasn't ever quite so much out if at all; so unless you KNOW what percentage your odo/trip meter was out on the stock tyres, then you are much better off to check it very carefully against a measured distance (& btw, using those roadside 1-5k markers or any roadside distance to/from towns against your Mk1 eyeball on the odo/trip meter dial often isn't anywhere NEAR carefully enough! It's just too easy to be maybe 100 meters or so out, & that's 10% @ 100k's) or use &/or compare the odo/trip meter against your GPS determined distance travelled!

Set your GPS 'Distance Travelled' to zero when you fill with fuel next, reset your trip meter at the same time, drive until you need to refill with fuel again & check to see if there's any difference between the GPS & Trip Meter when you reset them & work out how many litres of fuel you used so you can calc your fuel economy. The more your GPS is on & receiving a good signal while your engine is running, the better your GPS 'distance travelled' reading will be! :thumb:

Please tell us how accurate it is. And while you are on this stuff, be aware that Jaycar sells the makings for a 'Speedo Correction Box' fairly cheaply, & Marks 4WD Adaptors sell a Speedo Match Box that can be set to correct your speedo & odo/trip meter readings - the Patrols work off an electric impulse sent from the trans case to the dash, where that signal pulse is converted to a signal that the dial speedo & odo/trip meter can use. You can adjust them to suit whichever tyres you are running, road tyres, off road tyres, play tyres, whatever - and if you set the switching up right, it can be just the flick of a switch to correct the speedo for the different tyres!! Funny how whenever my Sons drive my Patrol they seem to go waaay slower than anyone else on the road, but they dare not go faster or they'd get booked for massively speeding - they just can't understand how everyone else gets away with it?!? Good thing they haven't heard about Speedo Correction boxes, isn't it! :D
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

drgtr
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Location: Campbelltown , NSW

Re: Larger Tyres and real distance travelled

Unread post by drgtr » March 8th, 2018, 8:34 pm

guess i got to buy another GPS unit. It doesnt have distance travelled

Its just an ebay Item that has heads up display on the windscreen for speed lol

drgtr
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Joined: March 5th, 2010, 3:32 pm
Location: Campbelltown , NSW

Re: Larger Tyres and real distance travelled

Unread post by drgtr » March 8th, 2018, 8:36 pm

So in simple terms. On highway speed now. because my revs are lower I should be getting better fuel consumption? Rather than have it revving so high at 110kmh
considering same road and same conditions?

Peter Aawen
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Re: Larger Tyres and real distance travelled

Unread post by Peter Aawen » March 8th, 2018, 9:01 pm

Yeah, all other things being equal, you should get better fuel economy IF you drive at the same speed you were driving at before fitting the bigger tyres, but that's the ACTUAL 'same' speed, not the 'same' indicated speed!!

When you were on smaller tyres you were driving everywhere with a speedo telling you were going faster than your true speed.... now you've fitted taller tyres, you should be going further for every rev of the engine, which is fine, even good when the engine has the torque & power to push that, but if you push to travel at the same indicated speed as you were before, you'll be going faster & therefore working the engine harder to do it too!! And that will generally cost more fuel. Yeah, there is also likely to be some extra loading caused by the increased height the taller wheels bring, that makes the frontal area taller & so you hafta move more air as your engine pushes the vehicle along too, plus taking into account any increase in rolling resistance due to taller/wider/different tread on the tyres, maybe even different tyre pressures too, but if you try to travel at the same TRUE speed over the same ACTUAL distance & all other things are close to equal, then the chances are that you'll get better fuel economy doing it! So swapping from 31's to 35's on a vehicle with an engine & gearing that's designed to manage 33's comfortably shouldn't be too much of an issue..... ;)
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

drgtr
Been here a while
Posts: 248
Joined: March 5th, 2010, 3:32 pm
Location: Campbelltown , NSW

Re: Larger Tyres and real distance travelled

Unread post by drgtr » March 9th, 2018, 7:26 pm

Thanks Mate. Appreciate the info
Last edited by drgtr on March 10th, 2018, 7:12 am, edited 1 time in total.

Peter Aawen
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Re: Larger Tyres and real distance travelled

Unread post by Peter Aawen » March 9th, 2018, 8:20 pm

You are actually going to have to drive a set distance and see how much it differs between the trip meter/odo and the GPS; because the % variation or error on the speedo MAY NOT be the same on the odo/trip meter!! Like I said, manufacturers kept the speedo speed faster than actual by up to 10%, but they often worked to get the odo/trip meters very close to correct!!

So you just CANNOT ASSUME that the odo/trip meter error is the same as your speedo error!! It might be the same % error, but you'll never know for sure unless you check! Which means you need to drive a measured distance & compare!! ;)
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

drgtr
Been here a while
Posts: 248
Joined: March 5th, 2010, 3:32 pm
Location: Campbelltown , NSW

Re: Larger Tyres and real distance travelled

Unread post by drgtr » March 9th, 2018, 8:27 pm

lol Mate. The wheels are too heavy to swap and compare

Im done
I appreciate your input and advice.

Im just going to be happy and assume I get better fuel economy :lol:

Peter Aawen
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Re: Larger Tyres and real distance travelled

Unread post by Peter Aawen » March 9th, 2018, 8:47 pm

You don't need to swap wheels, but you probably should drive say.... a known 100 km and see what your odo/trip meter says!! Do that with the 35's on it, it hasta be them, so you can work out exactly what your distance error really is NOW! It doesn't really help you now to work out what the error WAS - you can take it as read that the speedo WAS reading faster than your true speed so those people passing you all the time back then may not have been speeding after all, but now you've got bigger tyres on this WILL be different, so you can use the GPS to show your true speed instead!! But you can't assume that just cos the speedo error is 10% or 15% or even 27% or any other % out , it isn't necessarily going to be the same error for your odo/trip meter!!

Ps: I sent you a PM with some fairly important stuff in it for your info, and hopefully you don't get sprung before you can follow the advice in it! ;)

Pps: the 35's are great, aren't they?!? It's as tho Nissan always intended us to make this change, it all just works SOOO well & drives SOOO well!! I enjoy my Patrol on 35's too! :thumb:
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

drgtr
Been here a while
Posts: 248
Joined: March 5th, 2010, 3:32 pm
Location: Campbelltown , NSW

Re: Larger Tyres and real distance travelled

Unread post by drgtr » March 10th, 2018, 7:07 am

Mate you are awesome. Thanks heaps

DIdnt even know you have a Patrol with 35s too!

Very true. It feels like its made for it

Will read the information you sent me

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