14 to 15 inch wheels

Submitted: Sunday, Mar 02, 2014 at 20:54
ThreadID: 106509 Views:10291 Replies:5 FollowUps:11
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I have 2 questions
(1) I have tandem axle with 14 inch wheels can i upgrade to 15inch on the same 10 inch electric brakes, my vans GTM 2400kgs with 180 kg ball weight, the clearance in the wheel arch would be ok.
(2) replace my overlay axle with a straight axle
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Reply By: Ross M - Sunday, Mar 02, 2014 at 22:20

Sunday, Mar 02, 2014 at 22:20
Things to think about and check:

The bigger rims and tyres will have more leverage over the brakes and so less braking power will be felt with the same input.
On 4wd's increasing OD of tyres noticeably affects the braking.
You may have to ensure more braking signal is fed to the brakes to gain the same retardation you are used to. No good finding out "by accident" the performance is not enough.

Most times, larger rims also mean increased profile size/height and that combined with the larger rim may eat up the guard clearance you currently think you have. Different axle may allow for that though.

With larger tyres the treads of the tyres will be closer together and may have little or no clearance between the tyres. Just depends on the current axle spacing.

AnswerID: 527546

Reply By: Racey - Monday, Mar 03, 2014 at 09:43

Monday, Mar 03, 2014 at 09:43
Tessa, Al-ko data for 10" brakes part # 33120010 with 2.25" shoes, 14' wheels 800 kg per wheel and 15/16" wheels 700 kg per wheel, giving you 2800 Kg.

Part #33120210? the rating is 1600 kg and 1400 kg respectively

Al-Ko Brake data

Looks like you will be OK.
AnswerID: 527563

Reply By: Iza B - Monday, Mar 03, 2014 at 10:46

Monday, Mar 03, 2014 at 10:46
Rim size is only half half the question. What width and profile do you intend for the new tyres?

AnswerID: 527564

Follow Up By: tessa1945 - Monday, Mar 03, 2014 at 17:20

Monday, Mar 03, 2014 at 17:20
Details about 215-70-15 TOYO OPEN COUNTRY A/T ALL TERRAIN TYRES 215/70R15
FollowupID: 810004

Reply By: The Bantam - Monday, Mar 03, 2014 at 11:12

Monday, Mar 03, 2014 at 11:12
The over riding issue is how the diameter of the complete wheel and tyre relates to the rating of the axle.

There is some arguement...BUT... both All Trailer Spares and QLD Vehicle Components, advise that an axle rated for 14 inch rims ( typically running pasenger tyres in the higher profiles) must be de-rated if fitted with 15 inch rims and tyres as found on 4wds or light trucks......the derating from memory is about 20%.

If changing to 15 inch rims with low profile pasenger tyres...there is no issue because the tyre diameter remains more or less the same.

One assumes the trailer is running ford SL bearings a 45mm square or a 50mmm round axle....that would put the axle rating at 1500KG with 14 inch rims.

Applying a 20% detating that brings you back to 1200Kg per axle.....hmmm... running a bit close to the wind

And yes there may be issues with braking efficiency.

there will also be issues with raising the centre of gravity of the van......if fitting a straight axle in place of a drop and stepping up in wheel size it may lift the van 4 or more inches.

Then there is the issue of hitch alignment.

and yess stepping from 14 inch rims that will typically be 175 to 205/14s...there is an inevitable tyre width increase going to 15 inch rims most people will be running 235s or wider.

The rim offsets will most definitely be different.

NOW..while enforcement of trailer compliance is pretty damn slack, and there are things that are permissable on trailer that most definitely are not on cars.....I recon this is an engineering and recomplinace job.

SO this is a far more complicated issue than it first seems

AnswerID: 527566

Follow Up By: pop2jocem - Monday, Mar 03, 2014 at 22:11

Monday, Mar 03, 2014 at 22:11
As far as the braking efficiency goes, sure there will be some loss of effect by going from 14" to 15" rims and lets say a 50 mm increase in diameter with 10" drums, although as has already been pointed out AL-KO stipulates that 10" brakes are within tolerance for 15" wheel size.
Not sure I get the bit about de-rating the axle loads because of the increase in tyre and of course rim size.
Why would your load rating decrease, all other things, axle size and design, wheel bearings and whatever being the same. An inch bigger rim size isn't going to impose any greater strain and might just allow a reduction in tyre pressures from the 14" to make the ride a bit less harsh on the dreaded corrrrragations.

FollowupID: 810037

Follow Up By: The Bantam - Tuesday, Mar 04, 2014 at 23:54

Tuesday, Mar 04, 2014 at 23:54
It not the 1 inch increase in rim diameter, it is the 3 inch or more increase in tyre diameter and the weight considerable weight increase innthe rim and tyre.

The larger the wheel diameter the greater leverage the wheel exerts on the bearing during side loads.

If you doubt the weight issue ...go ahead...pick up a 14x185 wheel and tyre....if you are reasonably fit you should have no problem lifting it over your head......now with a 31x10.5 15 inch rim...yeh a bit of a different story.

that weight is jumping up and down anchored to the big mass called a caravan ...that weight borne entirely by the Bearing......remember all that shock loading does not benifit from the mass of the trailer or the action of the shock absorbers...in fact they both increse it.

Remember it is not just the loads borne on the tyre that matters...it is the load the tyre places on the bearing.

FollowupID: 810105

Follow Up By: pop2jocem - Wednesday, Mar 05, 2014 at 11:37

Wednesday, Mar 05, 2014 at 11:37
I have 195x14" LT tyres on Ally rims on the van about 22 kg. 31/10.5x15" tyres on steel rims on the ute. Haven't actually tried pressing either above my head but I can lift either quite comfortably to a reasonable height. I am not sure what the 31/10.5 x 15 have to do with the present scenario as that size is not what either I or tessa are planning to fit to the vans in question. A 225/75x 15 tyre is about the size I will be looking at and is optional on my van with the same hubs axles and springs. Even Mr Al-Ko says the 10' brakes with 2 1/4 shoes meet the requirements for up to 700 kg load per wheel, a reduction of 100 kg from 14" to 15" wheel size. As an aside if I was to go to the 15" wheel I would probably go to the 12" brakes just for safety.
What is being proposed is not likely to cause the collapse of civilisation as we know it BUT, this is just my opinion and everyone needs to do their own research and make their own decision.
FollowupID: 810118

Follow Up By: The Bantam - Wednesday, Mar 05, 2014 at 19:00

Wednesday, Mar 05, 2014 at 19:00
31x10.5R15s are a very popuar 4wd tyre one could say a typical 4wd tyre...there are bigger and smaller tyres arround and similar ( a little smaller perhaps) in size to the 225/75/15s....both are considerably larger and heavier than a 195x14 light truck.

agian... the derating of the brakes, like the derating of the axle eats into the already slim engineering margins typical of the trailer industry.

If the larger tyre is optional on your van.....does that option include different hubs and bearings...and may be different brakes.

If the trailer as it exists, runs the larger wheels and tyres as an option on the same stud pattern, with the same hubs, axles and brakes......Um why is there a question.

The fact is, and the trailer parts catalogues bear witness to the fact, that when stepping from 14 inch passenger car wheels and tyres to 15 inch 4wd wheels and tyres ( which are clearly larger and heavier), stronger axles, hubs and bearings and bigger brakes are required.

The van in the original post...in my opinion is already running on the minimum reasonable safety margin.


FollowupID: 810133

Follow Up By: pop2jocem - Wednesday, Mar 05, 2014 at 22:50

Wednesday, Mar 05, 2014 at 22:50
Tell me something, do you actually read, understand and digest what anyone has originally or followed up posting?
tessa was talking about a 215/70Rx 15 and I was suggesting I may look at 225/75x 15. Neither, repeat NEITHER of us were contemplating a 31x10.5x 15 4WD tyre.
A 225/75x 15 tyre has a recommended rim width of 6"
A 31x10.5 x 15 which you keep banging on about has a recommended rim width of 8.5".
Totally different animals.
I have no idea what tessa has in the way of axles, brakes or whatever on their van.
What I posted was that with my van the existing components were in the manufacturers considered opinion quite adequate for the 15" wheels and tyres which were an option at the time of manufacture.
Once again in case you missed it the first time, I would seriously consider upgrading my brakes from the current 10' to 12" purely to increase the safety margin, even though Al-Ko themselves state that the 10" are quite adequate for the 15" and in fact 16" rim sizes.
"Um..why is there a question"...very simple my attention ally deficient friend..tessa asked if the 14" to 15" increase was practical.
As I have already pointed out my van manufacturer had the two options available at time of production.
Why my van was ordered with the 14" I have no idea, I bought it second hand.
FollowupID: 810165

Follow Up By: fisho64 - Wednesday, Mar 05, 2014 at 23:45

Wednesday, Mar 05, 2014 at 23:45
Pop-according ADR (and logic) a complete axle cannot be rated to higher than the lowest rated part.
Hence if the brakes are rated to say 700kg per rim then you cant rate it more than that.
Its a chain with the weakest link.
FollowupID: 810175

Follow Up By: pop2jocem - Thursday, Mar 06, 2014 at 10:47

Thursday, Mar 06, 2014 at 10:47
OK, I'll try one more time.

All the original OP asked was if going up an inch in rim and of course tyre size was practical.
Someone, quite rightly, asked what size tyres were proposed. I believe the size was 215/70x15. NOT 31x10.5x15 which is a very large size best suited to 4WD type vehicles but could be fitted to a van for all sorts of reasons including interchangeability with the tow car. But yes, an upgrade of other components would be most advisable in this case.
I pointed out that while everyone needs to do their own research in my opinion and based on MY van this could be done without causing any safety issues. The latest model of my particular van does come with 15" wheels as standard and according to the manufacturer my van had the 15" wheels as an option rather than the 14" that came standard. Why mine was fitted with 14" rather than 15" I have no idea as I bought mine when it was second hand. Maybe 14" were considered quite adequate by the original purchaser and maybe a bit cheaper. Both wheel sizes were fitted without going to different hubs and the associated bearings, axles whatever. Not however the much larger 31x10.5x 15 as proposed by another poster. The rolling chassis as used under my van has a rating 360 kg heavier than the ATM as nameplated so the wheels could be upgraded to 15" without any changes to any other components. The ATM that I have is quite adequate for my needs so I am not looking to increase any loadings, in fact the 700 kg per wheel as is, is actually well over my existing ATM.
DiISCLAIMER; Do your own research and make a decision based on your own van and circumstances.
FollowupID: 810200

Follow Up By: The Bantam - Friday, Mar 07, 2014 at 21:17

Friday, Mar 07, 2014 at 21:17
pop2jocem...pull your head in chum.

In my first post I gave a comprehensive dsicussion of the matteris in question...this was before anybody discussed actual tyre size.

ANY discussion in this portion of the thread is a FOLLOW UP to my reply....not necessarily the wider discussion...particularly posts after mine.

My mention of 31x10.5s was as an example and not specific.

In the vast majority of cases where people are looking at changing from 14 inch rims they are talking about changing from passenger tyres on 14 inch rims to 4wd tyres on 15 inch rims.

In this sort of case the actual tyre size in immaterial....those trailer parts suppliers that specifically mention derating of alxle and hub assemblies intended for 14 inch rims when running 15 inch rims....do not discuss actual tyre size.......they certainly do not discuss the rim material....they care not if they are alloy or steel.

Because in general 14 inch rims shod with pasenger tyres are considerably smaller and lighter than 15 inch rims shod with 4wd tyres.

The only time this derating does not apply is where 15 inch passenger rims fitted with low profile passenger tyres are replacing wheels and tyres of a similar diameter to the 14 inch common or garden high profile tyres.

The engineering factors remain the same.

I have no interest in how the manufacturer of your caravan came to their engineering choice or justified their recommendations.

It must be remembered that the trailer industry, and that includes caravans..... regardless of price...is not the pinicle of engineering...and mostly driven by price...thus there is in general fairly narrow safety margins in hubs, axles and brakes.....it is very rare to find a trailer of any type that has hubs,axles or brakes any better than absolutely necessary.......often those choices can be considered marginal at best.

THus.ANY significant increase in wheel and tyre size......particularly one that crosses a catagory is very likely to consume the entire safety margin.....which on the basis of the figures provided seems to be the case

Neither you nor the OP have come back with any solid information about the hub and axle combination used under your vans.....so the rest of us are left with discussions of a general nature.

You can come on with all the piss and vinegar that you like...it does not change the recommendations of the parts manufacturers or the real engineering factors in play

without specific knoweledge of all the parts in question, it is unreasonable to say anything is safe or reasonable.

FollowupID: 810316

Follow Up By: The Bantam - Friday, Mar 07, 2014 at 21:23

Friday, Mar 07, 2014 at 21:23
Oh BTW pop2jocem...if you do not grasp the engineering factors that result in parts manufacturers derating hub & axles designed for 14 inch rims when fitted with 15 inch rims......you are not fit to make any recommendations about the safety of such changes.

FollowupID: 810317

Follow Up By: tessa1945 - Sunday, Mar 09, 2014 at 19:05

Sunday, Mar 09, 2014 at 19:05
Thanks I have that all sorted now next question,
I am using 15 inch alloy wheels or steel sunrasia the tire size will be 215 x 70or75 x 15/min 100 will be using mainly on highway 20% off road any suggestions
FollowupID: 810433

Reply By: tessa1945 - Sunday, Mar 09, 2014 at 19:08

Sunday, Mar 09, 2014 at 19:08
Thanks I have that all sorted now next question,
I am using 15 inch alloy wheels or steel sunrasia the tire size will be 215 x 70or75 x 15/min 100 will be using mainly on highway 20% off road any suggestions
AnswerID: 527986

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