7 replies to this topic

[kmidderigh]

My son bought a Suzuki swift 1.3 for his first car the other day - nice little car handles well - but it came with some non standard alloy wheels.

 

I'm trying to work out if the tyre pressures need to be adjusted from the manufacturers recommended values as the wheels are bigger :

 

Original wheels/tyres were 185/60 R15 with pressures of 33 front and 30 rear

 

current alloys are 205/40 R17

 

Is there a formula to work out if any change in tyre pressure change is required as a result of the differences in wheels size ?

 

Thanks.

[manus]

My son bought a Suzuki swift 1.3 for his first car the other day - nice little car handles well - but it came with some non standard alloy wheels. I'm trying to work out if the tyre pressures need to be adjusted from the manufacturers recommended values as the wheels are bigger : Original wheels/tyres were 185/60 R15 with pressures of 33 front and 30 rear current alloys are 205/40 R17 Is there a formula to work out if any change in tyre pressure change is required as a result of the differences in wheels size ? Thanks.

Weight = area x pressure weight doesn't change presumably the area increases by 205/185, roughly 10% suppose you decrease pressure by 185/205 (x 33 or 30), so try 30 and 27 and test it on the road

Edited by manus, 13 November 2014 - 07:12 PM.

[Ormes]

Maybe I should have listened more in my science lessons, but not sure why the pressure should change based on the area?  Manus can you explain (not challenging you just want to better my understanding )

[manus]

Maybe I should have listened more in my science lessons, but not sure why the pressure should change based on the area? Manus can you explain (not challenging you just want to better my understanding )

think the other way round. You can calculate the weight of a car by taking its footprint multiplied by tire pressure. If you inflate the surface area will be smaller. If you deflate, think flat tire, the area increases. http://exploratorium...ight/index.html In extreme situations, off-road or stuck in mud, not something to try with the VX, lower the pressure and maybe you get out.....

Edited by manus, 13 November 2014 - 07:41 PM.

[Ormes]

[anz3001]

I'm not sure that's right, or at least a few things are missing. volume is less in the new tyre so more pressure required to carry same load, no? Just taking the section width (205 vs 185) is too little information

[slindborg]

Having messed about with loads of cars with varying tyre sizes, the pressures have always been within about 5 psi of each other anyway. Same size as the chavvy 500 we have and that's running 2.3 bar upfront and 2.1 in the back, high and probably why its a sh*t to drive

[kmidderigh]

thanks for the replies - will just play it by ear