recalibration for a new tire size

isutherl · **Posted:** Wed Dec 12, 2007 8:57 pm

how can you get your computer recalibrated for a new tire size? Does the dealership have to do it, and how much does it cost, or will they be nice and do it for free? I doubt that last bit but I can be hopeful.

tjkoen01 · **Posted:** Thu Dec 13, 2007 9:54 am

it depends on the dealer....some have gotten it done for nothing, some people had to pay and some where told it can't be done....go figure

jason thompson · **Posted:** Thu Dec 13, 2007 9:08 pm

I say why bother?
you know it is off get a GPS ,yours or borrowed
figure out the % of error and you will know how fast or slow to go

Like mine close to 10% off by GPS
so when the speedo reads 65 I am going 71
also applies to MPG figures if the computer thingy and the miles work out to around 20-21 then I know I am getting close to
22-23 so I feel better about MPG

tommudd · **Posted:** Thu Dec 13, 2007 10:30 pm

never had it done never worry about

C co Crusader 2/127 · **Posted:** Sat Dec 29, 2007 2:04 am

if your going faster then the rest of the traffic slow down..... really easy...

Rush345 · **Posted:** Sat Dec 29, 2007 2:11 am

I'll set one of the 4 guage setting to MPH, then I'll see how well it coinsides with the actual Speedo. Wouldn't surprise me to find the computer smarter then the factory guage :twisted:

cmohr · **Posted:** Sun Dec 30, 2007 10:11 am

It's not just about how fast you are going....

The ECU uses the info collected form all sensors for engine management, IE, fuel mix, engine timing, gear changing and so forth. If you change you tyre size by a large amount, the information the sensors collect will conflict with the engine management table that is in the firmware of the ECU, and that can translate as a very noticable loss of engine power, gears changing and the gearbox hunting around for the right gear (in autos of cousre) all the time. Cruise control will play up too. (Mine would suddenly accelerate as soon as i pushed the "SET" button, and never tried to decellerate by changing down a gear when going down hills.) After I had the speedo reset to the correct tyre size, ALL the power came back to the engine, my fuel consumption decreased, the gearbox behaved itself again (no more hunting up and down for gears) and the cruise control worked again as it did before my tyres where on. These are modern computer controlled engines and if the information the ECU gets is incorrect it makes a whole lot of difference to the rest of the car, Its not just about how fast you are going. I did not have mine reset to have the speedo read the speed I was going, I had it done to give me back my Jeep as it was before.

Guest · **Posted:** Sun Dec 30, 2007 11:26 am

Rush345 wrote:

I'll set one of the 4 guage setting to MPH, then I'll see how well it coinsides with the actual Speedo. Wouldn't surprise me to find the computer smarter then the factory guage :twisted:

Won't be any different, rush. the Scanguage reads from the same sensors as the stock cluster, so it'll see the same information...

MiniDevil · **Posted:** Sun Dec 30, 2007 3:14 pm

C co Crusader 2/127 wrote:

if your going faster then the rest of the traffic slow down..... really easy...

+1

Just dont pass everyone, and no matter how fast you are going you won't get a ticket because you wont be the one standing out that the cops say "Wow that guy is flying, lets get him".

Just blend in and youll be fine

dloc_jeep_KJ · **Posted:** Sun Jan 06, 2008 11:54 am

here is a good link to calculate this. not sure how accurate it is but im sure its close.

http://www.miata.net/garage/tirecalc.html

hope this helps

recalibration for a new tire size

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