A new one on me, track width

[QtownTaxiGreg]

I selected wheels and tyres to get me off the stock summer rollerskates. 255/45/19 all season tyres and 19x8.5 45p wheels. An hour later I get a call from tyre guy.

According to the master wheel distributor I need to down my offset to make up for the skinnier 8.5" rim "because the decreased 'wheelbase' is going to affect my suspension loadings".

Yeah, nah! The track width aka "wheelbase??!!" is unchanged which is the whole reason I kept the stock offset and tyre size in the first place, so T couldn't complain I changed geometry.

According to the tyre guy the distributor is "strongly recommending" I get 38p instead, neigh, "STRONGLY RECOMMENDING to get the 38p".

Weird. If you put a magic wand to a stock wheel to shrink the rim by 1" moving each to the centre 0.5" you have a wheel with the same offset. If you did that with the tyre on and sitting on the ground the treads would have no shove on to either side. The tyre contact patch would be centered exactly where is was before the hocus pocus.

So what's really going on in these guys' heads?

I think they are so caught up in their own world of "fill up the wheel well with bitchin' wheels and tyres" that everything else goes out the window.

It's that or the distributor is concerned his 45p wheel is really too fragile for my wagon and making up stories. It is rare wheel that has 800kg rating but these do!

Do I back out of this deal quietly or plow on?

 

[Skavatar]

narrower wheel usually go with less offset, like +32mm or 35 or 38 are common, most 18x8 and 18x8.5 wheels i've looked at on Discount Tire's website.

you lose 1/2" (12.7mm) from the stock gemini 19x9.5

your wheel will actually go inside the wheel well more.

but if that's what you want, tell them you will sign a waiver and not hold them responsible for any future damages to the suspension.

also, wheelbase is front to back distance, which doesn't change. track width is left to right distance, can change with different offset.

here's a rough sketch i did to compare wheels about a month ago.

 

[QtownTaxiGreg]

The tyres already arrived. We measured the bead separation. Allowing for the rim lips it is near as dammit we see the tyre shape pretty much as it will mount up.

The new 255 tyres have a wider flat tread area than the 255 Michelins. That will put them closer to the guards by a fraction.

Tyre guy still says the circumference will stretch out and make the tyre taller than it would be when stretched onto 9.5" rim.

He had to agree the centre of the tyre is in the same location.

The only difference I can see is if they roll around more being on their natural rim width rather than stretched onto 9.5" rims. Won't be hitting any kerbs though.

We measured track at 1645mm with a bit of eyetrometer, inside bead extension to outside bead extension. Will be interesting to see what it measures after the swap. Will also check ride height.

 

[QtownTaxiGreg]

your wheel will actually go inside the wheel well more

Yes, but the tyre is still centred in the same location. No waiver required.

track width is left to right distance, can change with different offset.

yeah I know, as does tyre guy, that's what is weird about the situation. They wanted to change the offset, not me.

I reckon there will be slightly less clearance for the snow chains due to manufacturer variance in what constitutes a 255. Michelin half inch shy across the road going treads.

Looks like there is sidewall for Africa as well so no kerbing problems.

Strange yet comforting to see the M&S rating stamp on what looks pretty much like regular highway tread. They won't go hard as rocks in the -7 frosts.

Tyre is new on market so taking a bit of a punt. Nexen Nfera Supremo or something. Hyundai used to put Nexens on some OEM SUV as alternate to very good Hankooks, and that is about all know of the brand.

 

[Honda Convert]

This tire size tool is very helpful.

Wheel Offset Calculator

Use our wheel offset calculator to visualize the new tire position when changing wheel and tire sizes. Convert wheel offset and backspacing to calculate the correct setup for your vehicle.

tiresize.com