Do we have any tyre experts on here?

[Demannu]

I want to increase the rolling radius of the tyres on my Moho.
Simple thing would be fit 16s, but 5 bolt 16s are like hen's teeth for my van.
So I thought about fitting 235 instead of 225.
However, the 225 are commercial, the 235 are SUV, but most importantly the load index is correct, so not putting undue loads through the tyres.
What's the worst that could happen?

[KungFooBob]

That would just increase the width not the radius.

You'd need to change the profile (45/55/etc...) which is the percentage of the width the side wall height is IIRC.

Whats the worst that could happen?

The insurance use it as a get out if you ever have an accident (and the assessor picks it up)

[Demannu]

It does change the rolling radius.75% of 235 is more than 75% of 225. 699 Vs 714 rotations/mile
As for insurance purposes, it's suitable for the vehicle weight, so not an issue afaik.
Guessing you're not an expert!
Best off speaking to a tyre shop for their opinion I think.

[Felix]

Find out the PCD as the same will be on other vans. I only have 14" wheels on my Convoy Bus. Mk1 and Mk2 Iveco Dailys are the same PCD and 16" so i will be changing them before my Croatia trip. I am doing it more for the MPG as apparently its worth an extra 4MPG. Might not sound a lot but when you are between 28 - 30 every bit helps.

[Demannu]

Find out the PCD as the same will be on other vans. I only have 14" wheels on my Convoy Bus. Mk1 and Mk2 Iveco Dailys are the same PCD and 16" so i will be changing them before my Croatia trip. I am doing it more for the MPG as apparently its worth an extra 4MPG. Might not sound a lot but when you are between 28 - 30 every bit helps.

They are 5 x 130 et75 with a centre bore of 84.1mm
Ssanyong wheels are a straight fit, but afaik, none of their wheels are rated high enough for my weight.
Fiat ducato are same PCD but wrong centre bore
Late VW crafter have wrong et.
Trust me, I've looked.
I'm doing it for the same reason, fewer revs and less juice.
Do you have a non turbo banana motor?
My convoy didnt seem to have the oooomph to pull longer gearing when heavy, constantly up and down the box on hills.

[Le_Fromage_Grande]

Just drive a bit slower and you'll save fuel and won't have to twat about finding wheels.
Also, how many miles would you have to do before you've saved the cost of the new wheels and tyres that, may or may not, save you fuel?

[wull]

It does change the rolling radius.75% of 235 is more than 75% of 225. 699 Vs 714 rotations/mile
As for insurance purposes, it's suitable for the vehicle weight, so not an issue afaik.
Guessing you're not an expert!
Best off speaking to a tyre shop for their opinion I think.

You didn’t mention what the aspect ratio was on your 225 versus 235 tyres in your original post, so in theory your 235 choice may not have a larger rolling radius if say the aspect ratio was 65, it all boils down to the aspect ratio of the width, so Bob is correct with what he’s saying it’s the fact you didn’t state what the aspect ratio was. I’m presuming from the later post that it’s 75.

As for width, find out what the rim width is and you’ll have a certain range of tyre width that can be fitted safely, if it’s originally fitted with 225 tyres then I’d say you’ll be fine with 235 as it won’t stretch the sidewalls too much, when I had fast cars years ago I’d go as much as 20mm up but I’d always find out what the tolerances were. Other issues could be clearance on the arch etc but I’d imagine it’ll be fine.

[Mussels]

Carefully check how much clearance you have now, with steering at full lock and between the tyre wall and shock.

I increased the tyre diameter in my jeep by about 1", the shocks were already firm and slightly lifted but I still noticed slight rubbing at extremes.

There was so little spare room in my transit that I couldn't even fit snow chains on the OE tyres.

[Demannu]

Just drive a bit slower and you'll save fuel and won't have to twat about finding wheels.
Also, how many miles would you have to do before you've saved the cost of the new wheels and tyres that, may or may not, save you fuel?

We mooch about at 50-55 already. The sale of the old wheels should go a long way to offset the cost of the new ones. Or spunking £150 (just over a thankful) on a couple of tyres to test a theory isnt going to break the bank.

[mangocrazy]

I was thinking of doing similar on my VW T4 van, but my reasoning was to allow me to cruise at higher speeds while keeping sensible revs. For me at the time fuel consumption was secondary, now it's assumed more importance. But the downside is that your speedo will under-read, leaving you liable to fall foul of Plod, Gatsos etc.

[Le_Fromage_Grande]

You'd have to make a big change to the wheel size for the Speedo to under read, they're usually over by 10%, so you'd have to increase the diameter of the wheel and tyre by more than 10% for it to be a problem.

[Felix]

I'm doing it for the same reason, fewer revs and less juice.
Do you have a non turbo banana motor?
My convoy didnt seem to have the oooomph to pull longer gearing when heavy, constantly up and down the box on hills.

No i have the later Mk6 Transit 2.4 TDDi. Its not a standard convoy as its a coachsmith so plated at 4.2 tonne. As it was a bus the diff ratio is also different what helps the mpg over the van versions.

[mangocrazy]

You'd have to make a big change to the wheel size for the Speedo to under read, they're usually over by 10%, so you'd have to increase the diameter of the wheel and tyre by more than 10% for it to be a problem.

Motorcycles speedos are notoriously optimistic, but I've found that van speedos are pretty accurate. Certainly when I've been done for speeding in the van, the speed quoted has closely matched my memory of the speed at the time.

[Demannu]

GPS 55 is an indicated 60, so altering the gearing by 2-3% won't be an issue

[dern]

You can compare wheel/tyre size combinations with sites like these... https://www.willtheyfit.com/

We changed wheel and tyre sizes on our T5 camper van from 205/65R16 to 235/65R17. We did this to fit off road tyres to give us more grip on mud and snow and that has worked really well. It also looks a lot better in my opinion. The wheels and tyres have been on there for four years and the tyres are just getting to the end of their life. The wheels are obviously bigger but also wider. They must have the right load rating along with the tyres.

Our speedo error is 8.73% which is substantial and you do have to be careful of your speed, especially in Europe as many of the cameras do not give the same leeway as the UK ones do.

Downsides are noise will increase, steering will be heavier and less responsive, the load on steering, suspension and clutch will be heavier. These parts will wear out faster.

We have not found fuel consumption to have changed significantly but don't pay that much attention to it.

[Demannu]

So today I spoke to a tyre shop.
In their opinion, provided the load range is ok, then there are no legality issues. They did say that a 4ply tyre is going to have more corner roll and bump absorption than a commercial tyre.
There suggestion is to find a 16" wheel.

[mangocrazy]

So today I spoke to a tyre shop.
There suggestion is to find a 16" wheel.

I'd suggest you'll need four...

[Mr. Dazzle]

So today I spoke to a tyre shop.
There suggestion is to find a 16" wheel.

I'd suggest you'll need four...

Reminds me of the time I had a puncture in my old Ovlov. The RAC man fitted one of those generic spare wheels (really clever actually, cunning little adaptor thing in the middle to suit different PCDs), but it was 2" smaller than the standard wheel on the other side

This was on the front axle in a FWD car. I drove the ~15 miles home (with RAC man following me so he could get his wheel back) with a hugely mismatched front axle. The handling was surprisingly not that off, but the two wheels were of course spinning at quite different speeds. I had to keep it <40mph for fear of the diff blowing up, it was whining away like an 80's rally car gearbox

[porter_jamie]

Make a press fit collar for the nose of the hub to allow you to fit the larger diameter wheel with the larger centre bore diameter. I did this for someone's Audi A8 when he wanted some chavvy huge wheels off a cayeene or something

[porter_jamie]

Ps my mate is the wheel and tyre manager for ford commercial vehicles so is probably one of if not the most knowledgeable people on van tyres in the country.
What exact vehicle is it, what's the gvm and axle weights, and what is the wheel and tyre size?