Small wheel blowouts - options?

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Mick F
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Re: Small wheel blowouts - options?

Postby Mick F » 20 Oct 2019, 6:25am

Mick F wrote:1st was 11th April 2016 - bike was brand new 2nd March that year.
I was descending locally not far from home.
Been thinking ....................... as I often do! :D

I still have the 28h Moulton MT20 black rims, but I no longer have the calliper brakes or levers from back then. They were Tiagra STI and silver Tektro R539.

I may have sufficient spokes - I have some black ones and some silver ones somewhere - and I still have the original 28h hub (now have a dyno hub).

As the first time I had a blowout was locally, and I can remember exactly where it happened coming down Stony Lane into the back of the village, I could repeat the scenario. The tyre blew as I reached the bottom. I had to go into the pub to recover! :lol:
It's a three chevron hill and I rarely cycle down it, and only once up it to see if I could! Some people won't even walk it! :lol:
Screen Shot 2019-10-20 at 06.27.40.png


Any road up, if I have the right spokes to fit and can build a useful wheel, I can come down the lane and see if I get a blowout and if not, test the temp of the front rim.

Meanwhile, I can do the same test with the present silver rimmed front wheel. I don't have a thermometer to check exactly, but I'll do a subjective "Ouch :shock: " test.

Is this a valid experiment?
I don't have to go far, and if it blows, I've only lost a tube.
Mick F. Cornwall

gazza_d
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Re: Small wheel blowouts - options?

Postby gazza_d » 20 Oct 2019, 6:56am

I'd say it was an interesting thing to try, but too many variables to be valid.
I doubt that either brake manufacturer or rim colour would make a lot of difference, other than having so little confidence in the brakes that you have then on constantly.
I've always been of the opinion that these blowouts happen cos the extra heat places extra stresses on a tube that already has a weakness, be it from manufacturer or via a badly executed previous repair. I've known tubes blow when they've just been sitting there with tyres at pressure.
You can't replicate that pre-existing weakness

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Mick F
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Re: Small wheel blowouts - options?

Postby Mick F » 20 Oct 2019, 7:23am

You could well be right.
I don't know.

My point all along though, is that black rims heat up more than silver rims when braking hard and long. If I can build a wheel with the black rim, I can try the Ouch :shock: test even if the tyre/tube doesn't blow.

If I can demonstrate what I believe to be true, it's only a step further to get an overheated situation developing.
If the Ouch :shock: test shows nothing, I'll then know I was wrong .......... and I will say so.

The main thing, is do I have the spokes?
I'll be checking later come the daylight. I'm a habitually early riser and the household is still fast asleep.
Mick F. Cornwall

brynpoeth
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Re: Small wheel blowouts - options?

Postby brynpoeth » 20 Oct 2019, 7:31am

It is such a complicated situation with so many variables, I would wait awhile
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Mick F
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Re: Small wheel blowouts - options?

Postby Mick F » 20 Oct 2019, 9:23am

I have spokes. :D
28 of them.
I have suitable rim tapes too, as well as a few spare innertubes.

Dunno if the spokes are left over from the front or the rear from the original hubs and rims.
Whatever, I'm sure they'll do.



As for "variables" what am I going to prove - or not?
If I can show that black rims get warmer than silver rims .............. on the same bike with the same brakes on the same hill on the same day with the same bloke riding .......................... that will be enough to show that there is a trend.

It'll have to wait until mid-week or so. Busy today, travelling north and south Monday+Tuesday, so it'll be Wednesday before I even build the wheel.
Mick F. Cornwall

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Re: Small wheel blowouts - options?

Postby Brucey » 20 Oct 2019, 11:27am

if the contention is that 'black rims radiate heat faster than silver rims' (or similar) then it is easy enough to test this, provided you have two rims that are otherwise similar (both shape and weight) apart from the colour.

Just heat the pair of them up (to ~100C) (eg inside an insulated enclosure using a suitable heat source eg an incandescent light bulb of about 60W) and then let them cool in air. You will soon see if they cool at noticeably different rates or not.

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Mick F
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Re: Small wheel blowouts - options?

Postby Mick F » 20 Oct 2019, 2:23pm

Yes, but that's boring! :lol:

I've constructed a wheel ......... as well as done loads of stuff including helping Mrs Mick F with preparing some crab apple and chilli chutney.

The wheel is now laced but a bit wobbly with some plain gauge SS spokes, some double-butted, and one black-painted steel one and some of the spokes are shorter threaded on than others. There's a variety of nipples so I needed two keys and a screwdriver. If I was that interested, I may be able to find all 28 nipples the same but I think the single black spoke has different threading. Dunno, but whatever, it fits.

The 27 came off the original rear wheel and it was plain and shorter on the drive side, and DB and longer on the NDS. One spoke used to replace a broken one on the later wheel, so it takes me down to 27 from the full house.
viewtopic.php?f=5&t=128419

Any road up, there's a useful wheel in progress though it'll have to wait a few days before I true it up. It doesn't have to be a perfect long-lived wheel or beautifully made, just enough to get me through a day or two.

Beer o'clock now. :D
Mick F. Cornwall

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Mick F
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Re: Small wheel blowouts - options?

Postby Mick F » 25 Oct 2019, 4:30pm

Wheel made.
Tyre and tube on, and inflated to 80psi.
Weather horrible out there, and likely to be tomorrow too. Sunday should be nice, so I'll be off on trial runs some time in the forenoon.
(no doubt call into a pub after the runs)

I'll be up Gunnislake Hill and down Stony Lane twice. Once with Black and once with Silver.
May actually vary the route to make a reasonable ride first before descending the three chevrons.

Watch this space for my results.
Can't give absolute figures on temperatures, but the Ouch Test could possibly show something - or not. You'll have to take my word on the results.
Mick F. Cornwall

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Mick F
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Re: Small wheel blowouts - options?

Postby Mick F » 27 Oct 2019, 10:56am

Tests done.

Off on a nice ride of 15miles and then coming down the three chevrons.
Braking hard with both brakes all the way down.
Then home, swap the front wheel over and go for a short ride and coming down the three chevrons again.

Silver CR18 rims front and rear, and both were nicely toasty warm. Warm but not hot. I could keep my hands on the rims.
Silver CR18 rear and black Moulton rim front, and again they were both toasty warm.

TBH the front black rim was warmer than the front silver rim had been, but there wasn't much in it.
All in all, nothing proven ......... and no, I'm not doing it again! :wink:
Mick F. Cornwall