A while ago I bought 2 new front tires, now that I have completed the front end rebuild and alignment, I want to put the new tires on.
When I took the tires out of storage to put on, I noticed I had bought 255/35zr19
the tires that are on it now are 255/40zr19.
Will this mess up the computer and make it think it is having wheel spin on the rears? Will this trigger the DCS as its already very sensitive and likes to show the dcs light half the time?

 

The computer uses the reluctor ring on the axle bearing to get its speed readings. Tire width profile doesn't effect it.

 

The Tire Calculator shows 4% off, and a tire an inch shorter. Your car would ride a half inch lower on the front.

 

I would not use them. Can you exchange them?

The sidewall on 19" tires is thin enough already to put rims at risk. 12% less sidewall is even riskier.

Plus at 29 more revolutions per mile they will wear faster.

Less ground clearance was already mentioned and is particularly relevant for our cars.

Speedo will read higher than actual speed too.

Too many negatives IMHO.

 

Speedo will read the same. This just the 2 front tires.

 

+1 that is correct.

 

Not sure how the traction control would react, if it where the other way around (ie bigger front vs rear) the system would think you're rears are slipping. DSC would make it more complex, so I would not take any chances here and make sure you have similar sized tries front and rear.

 

the OP's tire change isn't in the width, it's in the height.

Z