[andy238]

A rolling circumference issue ..

My Jan 2010 T32 140ps LWB (panel van converted to Kombi, insulated, lined)
The label on driver pillar shows two 16 inch tyre sizes:
205/65/16 circ = 2114
215/65/16 circ = 2155
These have a circumference difference of about 2% (give or take all the maths rounding)
I have 205/65/16 fitted.

So for 18" alloys the closest matches for rolling c. are
205/65/16 matches 245/45/18
215/65/16 matches 255/45/18

For T32 everyone recommends 255/45/18, and it seems because these are 103 load rated, whereas the 245s are only 100/101.
This is what i find on a lot of the tyre seller sites.

My van is fitted with 205s, (load rated to 105/107) so to change to recommended size, 255, I have a 2% change to rolling circumference.
Speedo at 70 means I'm actually 71.5...
Or, cruise at 1500 revs to maintain same cruise speed revs will be 1470. (I like to rev low)

I am asking the insurer if I can fit 100 load rated to the T32, as I'm only SDP not a big load carrier.
This may give me more choice (confusion) even if there's not a big difference.

Is there any benefit of 245 vs 255 (e.g. less resistance, better mpg !) ?
In the real world will I notice anything different at all ?
Am I being too @[email protected] about this on figures ?

sarcasm is perfectly fine.

ps I set up the circumference calculator in a spreadsheet to check the rounding in on-line calculators. I like figures.

 

[robbi-wan]

100 Load index = 800kg limit

This is not enough for a T32. 1720kg is rear axle limit, therefore 103 rating is required (860kg min required / 103 rating = 875kg)
Also - 3% is allowed for in the rolling circumference calcs from std - so if you are within that; all is good
T:

 

[andy238]

thanks for the quick repl, Robbi-wan
I understand the numbers and appreciate 103 is the rating for the axle limit on T32.
But surely 100 is enough if the van is not loaded up, and insurers accept that, and I use it accordingly.
After all, the axle limit is a limit.

Are there any examples of getting lowered load ratings accepted ?

I'm asking the insurers too, I'm expecting a similar reply to yours.

 

[robbi-wan]

But surely 100 is enough if the van is not loaded up, and insurers accept that, and I use it accordingly.
After all, the axle limit is a limit.

From a VOSA (plod) perspective, wheels and tyres must match the axle rating - even if driven around empty all the time
Your insurers will see it this way also - they will run away in the event of a claim if they are less; so beware!

Are there any examples of getting lowered load ratings accepted ?

Vehicles can be derated to a lower GVW, and there are examples on the forum where this has happened - but it is a ball-ache i believe and has to be done via DVLA

Rob

 

[andy238]

cheers Rob.

That helps me rapidly reach the conclusion to stick with standard ratings and the circumference dilemma is just an interesting maths exercise !
Next van will be a T30 LWB, makes MOT easier too. (if I get a next van)

FWIW my chosen 18" wheels are
either
Wolfrace Munich, black/polished
or
Calibre Exile, black/polished

 

[krispringle]

T32 needs a class 7 MOT, according to the MOT handbook they check tyre load ratings, so it might fail on that.

http://www.motuk.co.uk/manual_410.htm


Also something to note, when i got my van it had a new set of dunlops on it, as it goes one of the back ones was a 99 load rating as apposed to 103 on all the others for some reason, now i only even cart my mtb around in it so never anything heavy, but after 6 months that tyre got a bubble in the side wall. its now a 103!

 

[wide]

Why did they go with 2 tyre sizes in 16" for the same vans ? Only noticed recently that some 16s get sold with 205s and some with 215s

 

[krispringle]

Suppose it depends on engine, think the 1.9's had 205's my 2.5 had 215's.

 

[andy238]

I checked my speedo against the sat nag (typo but that sounds about right)
I'm currently clocking about 2% less than actual, (28 vs 30 on speedo)
so I reckon my van should have 215/65/16 with the slightly longer circumference.

So I reckon the new tyres 255/45/18 will be spot on.

Wheels and tyres ordered .. delivery Monday.