Larger Tyres

I disagree with the categoric statement.

Braking will be reduced on some surfaces. braking is a function of 3 major forces - vehicle inertia, rotational inertia and grip - this is some of the crap you learn studying university physics .....and then dole cue economics :-(

All else being equal:

Vehicle inetria - up slightly
Rotational inertia - up significantly
Grip - dependant on surface type and area. Both of which are affected by tyre pressure, atmosopheric pressure, atmospheric pressure, surface composition, how many dolphins were in your canned salmon, blah blah blah

My Vitara stops better on many (but not all) surfaces on 30x9.5x15's with Muddies than it did with 205x75x15 AT's.

Increased surface area - possible increase in grip - but definately worse rotational inertia.

Also - if you change wheels to fit the bigger tyres they may have better or worse airflow (cooling) to the discs.

I plan on fitting bigger brake cylinders or discs to the front soon to ensure brakes are better on every surface. Stupidly I want to go faster before I can stop faster - LEMMING - although the exhaust is cactus......

Anyone know what to use on Vitara? Otherwise I'll start with Volvo 4 spots or Hilux 4 spots....

Andrew

Sorry Andrew. I'll put my bosses degree in mechanical engineering and his rally experience up against your mechanics trade papers any day. By fitting larger diameter tyres, the distance from the centre of the wheel to the road MUST increase therefore exerting greater leverage and greater rotational forces. ie if you had a lever 3 mtrs long welded to a disc rotor and a braking force was applied, it would be easier to overcome the braking force than if you had used a 1 or 2 metre lever. The same works in reverse. If you increase the overall wheel diameter and you want to maintain the same braking, you must proportionately increase the the rotor diameter. Toyota increased the rotor diameter of the 80 series GXL, series 2, over that of the series 1 for this very reason , henci 15" rims on the series 1 to 16" rims on the series 2 in order to get the rim to fit. Secondly, a winch pulls easier when most of the cable is still on the drum, Why, because of the greater leverage attained by the increased drum diameter due to the quantity of cable on it . And lastly, I could lock up my cruiser's standard tyres on the bitumen but since going to the 285/75's I can't.

Chopper,
With larger rubber you actually travel more km's than what your speedo reads. Have you tken this into acount in your calculation?
What kind of truck?
cheers,
cj

yes CJ i have

there is a 6% difference in rolling circumference.

Also remember legally you will need an engineers to go from 31x10.5 to 33x12.5's...

my wife says that too... too many beers and theres not enough pressure either.