Tyre and wheel newbie advice for Vitara

[Undiplomatic]

I don't know much about tyres or wheels and trying to make the right decisions. I've always just been given suitable wheels and tyres for my car and never had to hunt my own! I'm also trying to keep my car engineerically correct as much as possible for a modified car so I want to know about offset and matching the tyres up to the rims.

Here's what I know.

I am currently running Runway Enduro AT tyres size LT235/75 R15 (equates to roughly 29"). I'd like to stick to this diameter tyre because it's big enough for off road use, yet not so big as to excessively slow down the car on the road or require gear ratio mods. I did try 31" wheels, great off road but didn't like them on road, too slow. Also, I removed the spring on my Vitara to check if these 29" tyres fully clear the wheel arches and they do, only just, with the wishbone pushed up against the bumpstops.

I'd like to move to a tyre that's more capable off road but ok on road. I like the look of the Goodrich KM2 below because it's ok on road (noise, fuel efficiency, according to my friend who uses it on his Cherokee), but still has some pokey-outey bits at the sides to get through mud. My car gets some farm use twice a year, occasional off road tours abroad, and also getting social use around London, but not high miles.

How do I match up a tyre size and a rim? And what tyre width to go for? I may buy new rims so I am not restricted to a tyre size that fits my existing rims, I can go for any combo.

And what about the wheel backspace or ET? I have a Calmini 3" suspension kit fitted, and Calmini have an advisory issued which says that for the correct leverage on their suspension springs, to give the correct ride height, and for correct componant life I should be running 30" x 9.5" tyres with 2" - 2.5" wheel backspace. But, get this, the Calmini website gives different recommendations! Links below. The website also recommends 30" x 9.5" tyres, but suggests 3" to 3.25" backspace. The website also recommends a rim size of 15" x 7-8", which the advisory gives no comment on. With backspace do I need to worry about keeping centre-point steering? Or is that too much over thinking? Maybe should just contact Calmini to see which of their backspace recommendations to follow and stick to that?

My current wheels are from a Daihatsu Fourtrak but can't find their offset online. Anyone know what it is?

Calmini backspace advisory: https://www.calmini.com/docs/bulletin-suzuki-whe...ce-disclaimer.pdf
Calmini tyre recommendations: https://www.calmini.com/tire-size.php

[Mr Tyre]

Sounds like you need to ask Calmini, what advice is right before you buy something you don't really need.
30.9.50R15 tyres (dependent on makes they all vary a bit.New ones come out at around 29.5 inches in diameter, 235/75's are around 29 inches as you say so there isn't that much between the 2 tyre diameters..You should tell Calmini what rims you already have, i 'm guessing it's the chrome ones from the fourtrak tdx.

[Undiplomatic]

It's the chrome Fourtrak wheels. Yes I agree that I should just go with what Calmini recommend. I also just spoke to someone that messed around with offset and says it doesn't make that much difference to the feel of the car and not worth worrying about. So maybe just stick to the Fourtrak wheels and fit the KM2 tyres to them.

Wouldn't mind knowing the width and offset of the Fourtrak wheels though so that I can see how close I am to Calmini's recommendations.

Will telephone Calmini USA tomorrow.

[Mr Tyre]

http://youtu.be/tYEWoG83Vsg

You can measure back spacing yourself have a look at the above link.
I expect you wheels to be close to 0mm offset.

[Undiplomatic]

I know I can measure it, just was hoping someone knew already as these are popular wheels and save me taking it off the car How do I measure the width, is it literally the distance from lip to lip?

[Mr Tyre]

The chrome TDX rims only came in one width and that was 7 inch.


To give you some idea most 7 inch wide rims with 0 offset have 4 inches of back spacing

[Undiplomatic]

Thanks Mr Tyre!