Big twitch accelerating on bumpy dual carriageway

[ScottR400D]

Neil, it's not necessarily the case that you need a high pressure to enable balancing. My wheel balancer is very sensitive and has quite a slow spin speed. It will balance accurately at 18psi. 



 

[aerobod - near CYYC]

Some tyres can require a very high pressure to mount, the 13" Pirelli slicks I have used on the Caterham required 100PSI for the specialist tyre fitter to seat the bead. He declared them as one of the most difficult tyres he has ever mounted, which was done with extreme caution within a safety cage due to the much higher pressure than normal. When I had worn them out, they were also difficult to de-mount, with bead breaker hassles to dislodged the very substantial and stiff bead.

[SM25T]

I had new tyres fitted and the fitter started the balancing process at 18psi, he kept adding weights all over the place. It was ridiculous. I had to get him to stop, remove everything and start again. This time at 34psi. The tyre was moving or flexing at the lower pressure ... perhaps the machine accelerated too fast ? All was ok at 34, with minimal balalance weights needed, then reduced to 18psi for driving.

[7 wonders of the world]

Assume yours is a hand spun balancer, much simpler and better, 

[ScottR400D]

A lot of interesting experience there. 

My balancer is quite old (maybe 15yo) but was top of the range then and is little used. It's not a hand spin, though I see where that comes from, some of the hand spun balancers had very accurate measurement, the spin speed being so low. 

Weight chasing can often be caused by the wheel assembly slipping when the balancer starts and a tyre can move a little on the rim if it's very under inflated. Usually only an issue with old or cheap balancers with high spin speed and fast starts. 

An interesting point about the slicks. I would never risk inflating to 100psi, cage or not. It's way too much for a race tyre. I can't say I ever came across a race tyre that had beads stiff enough to cause seating issues, not to say it's impossible. It's normally the rim profile. 

I've fitted and balanced my own tyres, including race slicks) for many years now, and regularly do them for local club guys and can't say I've ever had a balancing or seating issue except for perhaps the odd rogue rim, but even then nothing major comes to mind, especially with 7s. 

Here's what I have, apologies for the mess:

[Wrightpayne]

ScottR400D,

What is you take / experience on the red or yellow dots on new tyres and positioning next to / opposite the valve?

SM25T has mentioned this before, to aid balancing / minimise weights, but when mentioned to my usual tyre place they just dismissed it as unimportant.

Ian

[ScottR400D]

I would tend to agree with that. IIRC the dots mark the light spot and should be next to valve which is the heavy part of the rim?

The light spot, again IIRC, is opposite the heavy spot (!) caused by the overlap of breaker plies in the tyre (which can often be felt inside the tyre). That in itself can vary so the significance of the heavy spot can vary too and with many valves now being very lightweight it's all a rough calculation. 

Having said that, it does reduce the amount of weight needed if you can get the heavy bit of the rim next to the light bit it tyre, but whether it's significant is another question. I never bother about it. I might if I was having to fit very big weights  

The only people I've known pay real attention to this are the OE tyre fitting companies, who have limits on the max weight they can fit so occasionally it is important. 

Bear in mind I'm referring to my experience a decade or so ago!  

 

[Wrightpayne]

Thanks. I might ask them to humour me next time I need tyres and insist on them aligning the dots! 

[SM25T]

Yellow by valve or red 180 degrees from valve

[7 wonders of the world]

Yellow dot normally next to the valve unless tyre manufacturer says otherwise,

I certainly find a reduction in weight needed, with the added bonus of being able to monitor if the tyres are rotating on the rim.

Peter, nice kit, wish I'd taken an opportunity I had in a previous roll to acquire some too,