Tyre size/ speedo deviation calculator...

Submitted: Saturday, Apr 22, 2006 at 23:58
ThreadID: 33157 Views:5101 Replies:7 FollowUps:13
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Some time ago one of you lot posted a calculator which advised how far your actual speed would deviate from that displayed on your speedo as you increased/dereased tyre size from stock... I always sucked at math so I'm not even going to bother trying to figure it all out myself. Don't suppose a link is available...???
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Reply By: Voxson (Adelaide) - Sunday, Apr 23, 2006 at 00:17

Sunday, Apr 23, 2006 at 00:17
www.1010tires.com/tiresizecalculator.asp
AnswerID: 168524

Follow Up By: Voxson (Adelaide) - Sunday, Apr 23, 2006 at 00:21

Sunday, Apr 23, 2006 at 00:21
not quite what you wanted...
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Follow Up By: Member - Blue (VIC) - Sunday, Apr 23, 2006 at 00:39

Sunday, Apr 23, 2006 at 00:39
I already have that one Voxson... If I remember correctly, you would put in your stock numbers i.e. 225/75-16 and put in your new size i.e. 265/75-16 and it would say " your speedo will read "X"% over/under...
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Follow Up By: Peter McG (Member, Melbourne) - Sunday, Apr 23, 2006 at 00:52

Sunday, Apr 23, 2006 at 00:52
Try this one:

" target="EOF" class="lbg">www.miata.net/garage/tirecalc.html

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Follow Up By: Richard Kovac - Sunday, Apr 23, 2006 at 01:07

Sunday, Apr 23, 2006 at 01:07
this ones a good read
www.carbibles.com/tyre_bible.html

Richard
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Follow Up By: Bonz (Vic) - Sunday, Apr 23, 2006 at 12:29

Sunday, Apr 23, 2006 at 12:29
This is that one Blue the URL is " target="EOF" class="lbg">www.miata.net/garage/tirecalc.html

Try HERE fine person
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Follow Up By: Member - Blue (VIC) - Tuesday, Apr 25, 2006 at 15:45

Tuesday, Apr 25, 2006 at 15:45
Thanks for the effort there Peter that was the calculator I remember although the page came up as an error... Thanks Bonz for sorting the link to Miata... Richard, that is a good read, although my brain is somewhat foggy from a long weekend in Mansfield...
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Reply By: Richard Kovac - Sunday, Apr 23, 2006 at 01:04

Sunday, Apr 23, 2006 at 01:04
www.rochfordtyres.co.uk/tyrecalc.asp
www.catherineandken.co.uk/sti/tyres.html
www.go.jeep-xj.info/HowtoSpeedoGears.htm
www.tyretraders.com/tyrecalc.html
AnswerID: 168526

Follow Up By: Member - Blue (VIC) - Tuesday, Apr 25, 2006 at 15:48

Tuesday, Apr 25, 2006 at 15:48
Interesting pile of links there Richard, thanks...
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Reply By: rooscoota - Sunday, Apr 23, 2006 at 13:56

Sunday, Apr 23, 2006 at 13:56
hey hey g'day,

check this one out , it still works...

Tyre size calculator

___________________________________________________________

lifes a garden.......... dig it


AnswerID: 168587

Follow Up By: Member - Blue (VIC) - Tuesday, Apr 25, 2006 at 15:52

Tuesday, Apr 25, 2006 at 15:52
Thanks rooscooter, that's the one I was after and now have safely in my bookmarks until the next re-format, which shouldn't be too far away given the sites this computer takes me to(I swear I was looking up Saddle Club for my niece, crikey thank goodness she didn't type it in as I have no "net-nanny" to speak of)
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Reply By: Member - Norm C (QLD) - Sunday, Apr 23, 2006 at 15:32

Sunday, Apr 23, 2006 at 15:32
These web sites are great for calculating the speedo change in theory. I recently put on bigger tyres and the miata (I think that's the one I used), gave me a speedo variation of 7%. I made myself up a spreadsheet to calculate the difference across the full range, printed and laminated it for the 4B. By the calculation, when the speedo showed 100, I'd be doing 107; a tad fast.

Then after fitting the tyres we went for a drive. I used the GPS to check speed. What had actually happened was that the bigger tyres corrected the speedo error that was built in to the vehicle. Our speedo is now just about spot on and only get 1 or 2 KPH out when we get over 100KPH. We have checked this on three separate trips, and I reckon we have it right (GPS error notwithstanding).

So, I'd suggest you do a practical test as well to check how it compares with the theory.
AnswerID: 168598

Follow Up By: Member - Pezza (QLD) - Sunday, Apr 23, 2006 at 23:21

Sunday, Apr 23, 2006 at 23:21
G'day Norm,
I thought that only happened on the patrol, a few of us have found the same thing, when I went to the larger 265/75 from the standard 265/70, a 4% increase, the speedo now reads 100% accurate, on a recent trip the GPS and the trip metre were an exact match to the metre, and the speeds shown are the same aswell, yet with the standard tyres on the speedo would read 100kph and the GPS would read 96kph.
I wonder if the manufacturers are doing this on purpose.

Avagoodn
Perry
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Reply By: Member - Patrick (QLD) - Sunday, Apr 23, 2006 at 15:47

Sunday, Apr 23, 2006 at 15:47
OK, pardon my ignorance here, but if you fit a larger tyre say a 185 70 16 instead of the original 165 70 16, does this show less kilometres travelled on the oddometer??? There is less number of roataions per kilometre so does than mean a different reading???
AnswerID: 168600

Follow Up By: rooscoota - Sunday, Apr 23, 2006 at 18:12

Sunday, Apr 23, 2006 at 18:12
hey hey g'day

not sure if i duplicated the link in my post but it seems to work.... after entering your new tyre sizes it shows underneath the graph the percententage either faster or slower relative to speedo reading

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Reply By: Member - Darren T (VIC) - Sunday, Apr 23, 2006 at 21:11

Sunday, Apr 23, 2006 at 21:11
If you forget to carry the one or something while doing the calculations etc. , you could always try something a bit easier like this from Jaycar.
Site Link
I did see a glimps of a kit in the 2005 Jaycar catalogue for around $45 that will alter your speedo (recalibrate as it were) but unsure where to find it on the Jaycar site.
AnswerID: 168649

Follow Up By: Member - Blue (VIC) - Tuesday, Apr 25, 2006 at 15:55

Tuesday, Apr 25, 2006 at 15:55
Darren, Jaycar make some interesting kits... I think the speedo corrector was only for "fly-by-wire" speedo's, a step-up/down gearbox is required for cable speedo's.
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Reply By: Katherine - Sunday, Apr 23, 2006 at 23:14

Sunday, Apr 23, 2006 at 23:14
Those tyre calculators were great.
Speaking of tyres, what is the law in NSW re tyre sizes??. Been told you you can only go 15mm larger in diameter from standard to "put on what fits and looks good".

Katherine
AnswerID: 168665

Follow Up By: Member - Blue (VIC) - Tuesday, Apr 25, 2006 at 15:39

Tuesday, Apr 25, 2006 at 15:39
Katherine, there is much debate about how much bigger one can go and still be legal... On here(I think) and on www.outerlimits.com there has been some talk about a new figure of 50mm... The VicRoads website still clearly states 15mm but I'm willing to take the risk anyway, as I said I only have them on a few times a year...(Waits for Murphy to step in)

One part of your previous question I didn't answer was whether or not they stick out past the gaurds... Yes they do, by about an inch. When the axles articulate they don't foul the gaurds so I don't worry too much about it(although that's illegal also). A different offset rim may help you out there, mine are supposedly "standard Patrol" offset...??? There isn't a whole lot of room on full steering lock for a much shallower offset but if you speak to an expert they could probably steer you in the right direction.
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Follow Up By: Katherine - Tuesday, Apr 25, 2006 at 19:14

Tuesday, Apr 25, 2006 at 19:14
Spoke to few tyre shops and only one off them knew what the law is when fitting larger tyres. He said i should ask the RTA, which i did and 15mm larger OD over standard rule also applies in NSW. Which makes you think how many 4x4's and CARS out there are actually legal?????
Keeping it legal means no probs with insurance when you need to make a claim.
Knowing this, im off looking for the best deal on some wheels/tyres.
Thanks for the tips and advice.

Katherine
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