paizesb

Hi Guys

Need some clarification please. A couple of months ago i changed tire sizes in front up to 235 from 225 and in rear up to 265 from 255 while keeping the profile the same on the stock tires front and rear. there after I took it to our local tuner and had the v-max done up to 280km/h. It still was governed to 256km/h but the other day I dragged against a motorcycle and past 150km/h i pulled him bad. we both took the same exit off the highway and stopped at the traffic light and had a few quick words. He said he was doing 270km/h and i was still pulling away so im a bit confused has the v-max being effective and has the tire size change messed up my speedometer. Thanks for any input

stangxs

Not understanding the topic; but yes, an increase in diameter in the tires will change the speedo reading, not enough that you'd have to worry about, though.

C63newdude

Before when I had my OEM 255 rear tires my car would read 2100 rpms at 75mph in 7th gear(just like every C63 owner in the world with stock 18" and 255).
Ater I changed the tires to 275/35/18" now my car reads 2000 rpms at 75 mph in 7th gear so, yes, I think it changes the speedometer a little.

obsidian05e55

http://www.1010tires.com/TireSizeCal...?action=submit

DuaneC63

Yes it will throw your speedo off. Check out the difference in revolution per mile in the manufacturers specs for each tire. You can calculate the difference by comparing these numbers.

DD GT3 RD

Here is a calculator for tire sizes
http://www.discounttire.com/dtcs/infoTireMath.dos

it is the overall diameter/circumference that matters. The 2nd # on the tire 255/35/18 is a percentage of the first #. So a tire 285/35/18 will have a greater diameter/overall circumference than a 275/35/18

speedometer, revs and mileage get effected by this.

paizesb

thanks for the help gents

HuangYiChao

So is there a way to calibrate the speedo to make it accurate?

DuaneC63

Only your MBZ dealer would know. Back in the day you couldt change the little nylon gears that ran the speedo cable, but with all the new electronic, I don't they use that system.

Fatrat2

Hi guys,

Am wondering if the sensor reads off from the axles or the tranny? If axle, front or back?

Thanks!

cyberorth

Every manufacturer has data sheets for each model of their tire that gives you specific info like thread width or rev per mile etc. calculating only based on the size on the sidewall gives you a general idea but not an accurate one. This is especially important with oe tires that are made for the car.

S2000 for example came with oe tires bridgstones that were as wide as most 245s but were marked 225 on the sidewall.

Mort

Probably needs to be done in the ECU if you can find someone to do it. Ask at the dealer maybe the Star Tech can do it as MB offers slightly different tire options for any given model.