Rim dimensions

[BigSkyBrad]

I’m looking to have super-single rims made here in the UK (Aspect Wheels so far) and just wanting to confirm the dimensions I have measured/gathered are correct for my FGB71. I was hoping not to take off the wheels til I need to.

Stud pattern – 6/222.2 (8.75)
Hub hole dia – 165mm
Stud hole dia - ?
New offset – 85-90mm

 

[SkiFreak]

Stud hole dia - ?

The studs are M20 and, from memory, the holes in a standard rim are about 31mm with a tapered seat.
The reason for this is that the standard rim needs the ability to be fitted on the front and rear, and on the rear it uses bud nuts to secure the outer rim (the bud stud is M30).

If you want the front and rear track to be the same, the offset will be determined by the width of the rim.
The diameter of the rim is often a point on contention on this forum, but I believe that a 17" rim will give you the widest tyre choice and less clearance issues.

Not that it affects the rim dimensions, but remember that on a Fuso there are right and left hand threads on the studs.

 

[gait]

maybe have a look at sea freight from Aus. You may be surprised. Then again, you may not.

Once upon a time I sea freighted a set of springs from Aus to UK. It was easier/cheaper than dealing with Mercedes in UK with an Aus spec Canter.

 

[BigSkyBrad]

Unfortunately my UK-spec truck has a 4.875 diff ratio instead of the usual 5.275. If I went to 17", I would need 33" (35" at a pinch) but there is nothing with a decent load rating in those sizes to match the rear axle. The truck will do mostly road/gravel mileage, so I will go for 17.5/19.5 rims. I'd like 17.5 with 265/70, but the only rims about are 6.75 wide and the only tyre around with decent meaty tread is Conti LCS at £900 ea (and 7.5 recommended rim width). So my only real option is 19.5 x 7.5 with 265/70 Toyo M608, which gives the same gearing as the usual 17" rim and 37" tyre. I totally get that the offroad ability will be crap, and the ride comfort is a bit concrete mixer, but short of swapping diffs (or at least heads) at great expence, life is a compromise!

Why would rim width alter the offset? - the centre of the rim (0et) is always in the centre, regardless of the width. The only reason width would need to be considered would be to clear shocks, balljoints etc, and that's backspace, not offset. A lesser offset than standard pushes the front rim outward, so clearance of stuff is not an issue. It does however change the kingpin position which increases bump-steer.

When figuring out the offset, I drew everything out on the garage floor, including the front and rear hub spacings and remembering the rear rims are turned inside out, to get the track the same for both axles.

 

[SkiFreak]

Why would rim width alter the offset?

My bad... I was thinking about something else.
From memory, the offset changes depending on the centre thickness of the rim. An 8" steel rim will have a different offset to an 8" alloy rim in order to get an equal track front and rear.

 

[BigSkyBrad]

yep, even factored in 10mm for the thickness of a beefy steel rim mounting plate in reverse mount on the rear.

 

[gait]

.... It does however change the kingpin position which increases bump-steer.
.....

not something I've noticed. I'd describe my truck steering as very stable. Maybe the beam axle, tie rod geometry, and limited suspension travel (even with parabolics) help. Roll steer also not noticeable.

 

[SkiFreak]

If, as you say, you are looking for a 19.5" rim, I agree with Gait that you should contact ATW and get a costing for supply and shipping of the rims they manufacture.
These are DOT approved and a known entity, so there should be no doubt that they are fit for purpose.

I suggested 17" rims only because that seems to be the most common consensus here; it's not the choice I made.
Initially I had ATW 19.5" steel rims, but have changed to ATW alloy rims, primarily because of the weight savings (about 90kg for me).

 

[BigSkyBrad]

I emailed ATW late last year but never got a reply, so started looking locally. I've sent another just now, so I'll wait and see.

 

[gait]

possibly worth a phone call.

 

[BigSkyBrad]

Got a reply back from ATW – the price for the rims is bearable, however the shipping, UK-VAT, and customs/import tax makes it too rich for our blood. However, will probably buy their flared fender kit.

So we are going with 265/70-17.5 140M on 17.5x6.75 (et90, 12mm mounting plate) custom truck rims from Aspect Wheels UK. Initially we’ll use TTS ZT-Drive premium remoulds to get us up and running then eventually go to Conti LCS tread if we have a windfall.

We’re dropping 200rpm@ 56mph/90kph and are only 100rpm above the 19.5s, so we still get the needed tyre width and ground clearance, keep the rear axle weight with singles and a fuel saving-relaxed engine, in a budget we can justify. The inch in ground clearance gained by using 19.5s won't be missed given the light off-roading it will see.

 

[BigSkyBrad]

My actual tyres being made today - TTS sent me pics of them going through the remould process, they are on Bridgestone M729 cases. They have been a super-nice company to deal with, the same for the tyre shop I'm getting them through, as TTS don't sell direct to the public, only trade and fleet companies. Here's hoping the tyres work out as lauded.

 

[BigSkyBrad]

I had forgotten to add a pic of the SRW wheels and tyres on the truck, for anyone who's interested. The tyres are 138 load rated, which keeps the GVW at 6500kg, but lowers the rear axle weight to 4500kg. However, there is 2000kg already on the front and 1000kg on the back in cab-chassis state, so still at the 6500kg, and gives 3500kg for the box and contents etc which is the norm anyway. The remoulds are downrated to K-speed though (68mph), but thats OK as UK trucks are limited through the tachograph at 56mph. New M rated tyres would lift that to 81mph for countries with higher speed limits.

If you're making or sourcing custom rims yourself, I can tell you the offset on the rims to get the tyres the same track front and rear on the Canter is +85mm. This offset is regardless of the rim width, because the centre of the rim is always the centre regardless of the width. I second-guessed my calculations (chickened-out) and had my rims made at 90mm, and ended up with my rears sticking out 10mm each side compared to the fronts, not enough to lose sleep over!

So my setup is - Tyres - 265/70-17.5, Rims - 17.5 x 6.5 +90