Today I exchanged RM2213’s original split rim wheels with 9 x 20 tyres for a set of modern wheels with 10 x 22.5 tyres. The new wheels and tyres look slightly larger but otherwise the general appearance of the bus remains very similar. I was expecting the larger wheels and tyres would give a higher top speed and better fuel economy.

I have measured the circumference of the old and new wheels and tyres. I’d like to hear what people think the difference in circumference is and how much the top speed changed. (The speedometer reading will of course be the same but the speed can be assessed by a satellite navigation system). I’ll post the result in a week.

I’m also interested to hear what other people think about the pros and cons of new wheels and whether they would swap, given the chance.

My bus number (if any): RM471 and RM2213

Hi Chris, The slight downside to the larger wheels is that you may reduce your turning circle because the tyres may rub on part of the bus when on full lock. I would say there are more advantages to them , split rims are getting harder to come by whereas the the larger ones are readily available . My local tyre dealer quoted me £256 per wheel for new rim and tyre which seems fairly reasonable (including fitting etc). Some tyre places are not very keen on changing tyres on split rims-they have been known to explode when being put back together with resultant injuries (deaths as well) . As the larger wheels are tubeless they are a bit cheaper and you don't need the slipper in them that the splits have.
Not sure about the higher speed but I'd bet it would only be a couple of mph at most . Not sure if you can fit the "dustbin" lids on the back though with the larger wheels.
Did you do a wheel swap or just buy the new rims and do it yourself ?
I've just changed over to them as well.
Mark

My bus number (if any): RML2391

I just used the search: box above to dig out my post about tyre and wheel size from last April. Sorry I didn't reply to it sooner but the post in response to Steve's request for a speedo gear assembly reminded me of it. When I changed the wheels as above I measured the circumference of both sizes of tyres on the wheels and inflated to the correct pressures, the difference was less than 1 centimetre, less than 1%. When checking top speed with a SatNav there was no discernible difference and neither has consumption changed. A bit dissapointing really!

My bus number (if any): RM471, RM238 & RM2213

According to tyre tables, the listed difference in rolling circumference between a C20 (900X20) and a C22.5 (10x22.5) is 2 mm. I wouldn't get too excited about any noticeable gain in top speed.

It's a bit of a paradox, for fleet operators, split rims are old technology and required a degree of diligence and skill for safe use when checking and fitting.
That said, they have been a perfectly good wheel for many, many decades.

We changed our truck fleet many years back to one piece wheels and this was mainly for standardisation cost savings. Our latest lightweight wheels are yielding better efficiencies, but this is over volume and network.

On earlier vehicles, we did have problems retro fitting vehicles where a tyre size and diameter change ensued.

This ranged from incorrect speedo and mileage readings, variations on fuel consumption estimates and more seriously upsets to braking, suspension and bearing wear.
Front bearings and suspension components were taking different loads and vibrations which did flag up when the said vehicles service histories were noted.
Turning circles, wheel scrub and rubbing were all problems that also materialised. The list got longer so it was deemed uneconomic to modify so the 56 trucks were all refitted with original equipment and sold on at an earlier than planned date.

When I was at LT, I seem to recall a trial with a new type of wheel and alternative tyres to the then Standard Transport regroovable tyres.
I think the trial was on RT, RF and RM vehicles and at a central and country depot. I can't remember when or where (around 1973) but maybe someone else can recall. Noting changed but I have no idea what the LT findings were.

For a preserved bus or one on light duties, I would just ensure that the split rims are in the best possible condition and coated with an anti corrosion protective coating before tyre fitting, and fit the best quality tyre.

Every tyre fitter has to have split rim training for the ISO rating, so that should not be an issue. Laziness or unqualified labour is more likely prospect.
Supply of tyres might be the biggest problem