Thread: Quick question re tyre size/RPM - real world experience

You're dropping about 3 inches in height (32" to 29"), so i think the calculations would be the biggest factor (i believe that manufacturer sizes vary by a small amount - less than half an inch).

I've just done (almost) the reverse (29" up to 31"). There seems to be a drop in power, but since i rebuilt the engine at exactly the same time, i can't really tell (unless i put the old tyres back on).

I've never heard of someone being worried about engine revs when putting smaller tyres on... might be an issue if you went to 38" .

Thanks Pete...

By my calculations, and I know my maths can be unreliable :-)

235 x .85 = 199.75
225 x .75 = 168.75

So thats about 30mm difference in side wall, so 60mm difference in over height, not allowing for flex obviously. What I'd really want to know what the change is in rolling circumference...

The main thing I'm worried about is the engine rpms being a little high on the longer trips... but I think I'm worried about nothing by the sounds of it.

cheers

Dave

Whilst we wait for people with _real_ experience to chime in, my 2c worth.

* Not sure of your Vic laws, but in Qld, your vehicle would not be compliant as the diameter of the tyre will have changed by -62mm, more than the permissable -26mm allowed. Even with real world manufacturing differences, that's a big gap from -62 to -26mm

"The rim diameter may be varied from the standard size but the overall diameter of the tyre must not vary by more than +15mm or -26mm."

* You will raise the revs at 100k from around 2500rpm to 2700

Happy for someone to check my back of the envelope maths and keen to hear from someone who has actually done this

I'd be very surprised if anybody else has done it. They tyres may be a good deal, but at the end of the day they're the wrong tyres for the Defender, and you really need to be running a 31" tyre of some descript.

defender tryes are near on 32" not 31"

33" go really well on defenders and the speedo and oddometer start reading correctly as a bonus :P

there are quite a few threads on this on the site...

Thanks Guys,

Does anyone have any ideas then about what is a cheap AT/HT for a defer? They wont be going off-road. I'm about to return to study so I need to go back to one car, so the defer will be doing more of the general running around duties, and I don't fancy having to replace the MT's too often.

cheers

Dave

With a bit of calling around you should be able to get Kumhos for $150 - excellent price. I've run a set for just under three years and still have a bunch of tread on them.

Cheers
Simon

Cheap?
I can tell you the Nankang Conquerer has been a surprisingly good AT.
They feel ok on road, wet or dry, great in gravel & sand, and not too bad in mud & slop for an AT.
Kumhos had a bad reputation for many years (primarily separations), I don't know if they've lifted their game nowadays.