# Alternative tyre choice for 22.5" rims



## Floozie2 (Dec 23, 2007)

Anyone swapped over from the very expensive Michellin 235R8022.5 to the much cheaper 255R7022.5. If so how did it go and were there any problems? The weight and speed ratings are good, the dimensions not much different; the only issue I can think of is dual spacing, but that can be cured with spacers if need be.
Look forward to getting some feedback
Richard


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## b16duv (Feb 14, 2006)

Richard,

As no-one else seems to be responding, I'll give you my thoughts - feel free to totally disregard them!

It should be possible to change tyre sizes within reason and your proposed change seems ok. there will be a 20mm reduction in the space betweeen the twin tyres on the drive axle before sidewall deflection - check and see how big the gap is at the moment at the bottom of the tyres (6 o'clock position). This gap will reduce and increase as you drive along the road going over bumps etc.

WHen changing tyres, you will need to do a complete axle at a time and on the twin wheels, the difference between tread depths should not exceed 4 - 5 millimmetres.

I'd suggest speaking to the local coach or hgv tyre fitting people - ATS Euromaster or Central Tyres or one of the independants. There is a huge variety of different tyre types for various applications and with different wear/roadholding characteristics. The major manufacturers also have specially compounded tyres that reduce rolling resistance and improve fuel consumption.

You may find that with a slightly wider tyre, there is a greater tendency for the vehicle to 'tram-line' more - get dragged into the ruts caused by the trucks. This was noticeable about 10 years ago when the fashion for using super singles on the steering axle first began (though they were 385 wide).

Hope this helps

David


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## apxc15 (Dec 1, 2007)

My advice to anyone contemplating switching tyre size's from the original size is to get expert advice.
You have to consider other things than twin clearance's. Wheel arch clearance and rolling circumference are just as important.
Getting the wrong rolling circumference for example will alter the gear ratio's and more importantly the speedo accuracy.

Pete


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## b16duv (Feb 14, 2006)

Found this http://www.etyres.co.uk/tyre-size-calculator.htm

Put in your current tyre size and your proposed tyre size and it will tell you the difference in diameter. They recommend no more than +- 2.5% change.

You will need to use either 22 or 23 as the wheel diameter instead of 22.5.

David


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## Floozie2 (Dec 23, 2007)

Thanks Pete and Dave for your input. I had considered all the pros and cons you pointed out; there is precious little difference in the tyres on paper. It all boils down to price and availability. The 255s are easier to get and cheaper to buy. I can more or less get a full set of them for the price of a couple of Michelins and as my tyres are aging and beginn to get hiarline cracks around the lettering etc, I'm thinking of replacing the lot. I'm just about to check out the website you posted Dave; should be very useful. BTW, Sinton have a document to the effect that 255R7022.5 are a fair replacement for 235R8022.5. I'll let you know what I decide and what happens.
Cheers
Richard


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## Floozie2 (Dec 23, 2007)

Thanks for all the posts guys, very helpful especially the spacer issue. Looking at the rear of mine, there's a chasm between the duals so I'm figuring I can lose half an inch. I won't know for sure until I'm off site and on the road again next week, when she's sitting with all her weight on the ground. I have clearance enough for the bodywork and the ratings all match, so maybe it's all looking good. The two reasons for doing this is availability (the 255s being easier to source abroad) and price. I can more or less get a full set of 255s for the price of a couple of the Michelins. As my tyres are beginning to age, it's something I'm looking at having to do in the not too distant future anyway hence the cost cutting excercise!!:Wink:

Spoke to Sintons and they have a document that seems to say that the 255s are a good replacement for the 235s, so long as the clearances are OK.

Cheers for now
Richard


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## Floozie2 (Dec 23, 2007)

*Update*

I ended up putting 275R70/22.5s on. Had clearance & they are lots cheaper. There is no noticable difference in rolling circumference, so speedo reads the same. Tramlining is no worse. The mean difference I can tell is that the RV feels more 'planed' and stable on the road. She doesn't seem to wander as much. Can't tell if it's made any difference to fuel consumption as I've hardly gon anywhere and I'm pulling a car & trailer now.
All in all, I'm happy with the choice made and I know now that I can get a replacement anywhere!


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