Model Railway Forum

Many thanks again MG for your extensive reply, and indeed everyone who gave their help and advice. I ordered a packet of Dapol wheels (20) and a packet of Hornby (10), so I can compare them before continuing. I'll let you know how I get on when they arrive.

Thanks once more, Ian Alan

I used to find that Dapol wheels were the only ones that ever derailed, I have no idea why. Loco wheels were/are fine.

The de-railments on Dapol wheels are likely to be caused by the wheel profiles being too flat where the treads are. If you happen to have any, take a look at the old Hornby silver seal wheels. The round axled wheels did not wobble like the more common square axled wheeled type.. But despite this, they held the rails well. Now it was not neccessarily the depth of the flanges. Take a look how the tread surface is. They have a pronounced curve with these old wheels and this is why they worked so well. The silver seal wheels profile are noticeably curved so it is why I give them as a perfect example. What happens is that the rolling stock slides towards the outer rail as it takes a curve. When the wheels do this, due to the profile of the wheel, the outer wheel will be on the highest point on the tread, and the inner wheel on the other side of the same axle will be on the lowest part of the slight curve of the tread. This will in effect tilt the vehicle slightly inwards so it leans into the curve especially when travelling at speed.
Now if we have flat treads the vehicles will again slide towards the outer rail and there is nothing to prevent the centre of gravity from tilting the vehicle over.

Then there are other things coming into play which can effect a wheels performance. The back to back measurement and the flange depth. (And also the slight curve towards the flange as if it is too much like a 90 degree corner here, it will not stay on the rails). The back to back measurement needs to be correct for the wheels to go through the flangeways on pointwork.
Also flange depths. The deeper the flange the more grip it has BUT obviously we want to run trains which look more like the real thing. So we are compromising by reducing flange depths, but we can't go too far, as scaled down models are lighter in comparisson to the gravitational pulls and the frictions etc. Also dep flanges need deep flangeways and shallow flanges need shallow flangeways.. As when a wheel passes a frog, if a shallow flange crosses a deep frog it will jump down the frog where the rails are not there and bounce causing a de-railment, but worse still, if the flanges are too deep compared to the flangeways, then the wheels will jump up on the flanges and be even more likely to jump off the rails!
Now there needs to be a curve between the tread and the flange. This helps push the wheel back onto the tread. If this curve was not there the wheel will slam into the flange when hitting a curve and the shock of this slam will topple the vehicle over. The curve reduces this sudden slamming effect. Too much of a curve will push the wheel to ride over its flange so it is a compromize.

But as for wheels, if the back to back is correct, and the flange depth is not excessive in either being far too deep or too shallow, I would take a look at the profile of the wheels that you are using, as this is often one of the "Unseen" reasons why ones rolling stock may leave the track. Of course there is the track itself, or the couplings, lack of weight, or the weight is too high etc., etc. Many reasons! But as for wheels, the hidden mystery often not noted is that one does need the wheels to have a nice profile rather then a dead flat tread. I hope I may have explains a few things!

You learn something new everyday.

Thanks again MG, WTD and SR for your continuing contributions.

The wheels arrived today and I've made a start changing them. I'm wondering about what I can use to clean the holes that the axles go into. My memory tells me that the YT video I watched said that lighter fuel was best because it doesn't damage any plastic it touches. Being a non-smoker, I don't have any lying around. Do you think that IPA* would do the job?

*The electrician's stuff, not the beer.

Thanks again, Ian Alan

Yes it is perfect for the job and the other version of it for after the job.

Many thanks for your prompt reply WTD. You are clearly a gentleman and a scholar.

Thank you. Bet some on here will disagree with you

Just for fun, I've posted some photos of the newly rewheeled rolling stock on my thread in Members Layouts. They're in The Shankly and Gdynia Railway, page 18, post 178. You can't really see the new wheels, of course, but to get functioning rolling stock is the reason for all these posts.