Riser bars and 'pressuring the front wheel'

[legrandefromage]

Typical pinkbike answer, at least mine had pictures

And probably said the same thing

*I forgot add a smiley from my phone*

**yeah, thats what HE says**

Moron.

Your mum!

 

[My_Teenage_Self]

Some of you know me a bit, some of you don't. those that know me know I'll not argue things I'm not confident about :facepalm: :facepalm:

But it's all meant in good fun.

I've just performed a physics experiment.

2 different sized tyres (a 1.7 x 26" and a 2.4 x 29"). Both at 30psi. I've measured the contact patch with a consistent weight (me) applied. Who'd like to make a prediction?



in other news, lockdown can't finish soon enough...

 

[legrandefromage]

My mum?

 

[My_Teenage_Self]

This is just to annoy Hamster.

the test subjects;


some high density foam, with a layer of tin foil. I put a front wheel onto it and rested all my weight onto it.



At this point I marked the furthest points of the tread depression with sharpie, and measured the maximum length, and width. I tried not to flatten the sheets at all.







Apologies for the angles of the photos, I know it will throw off the perspective, but foil is hard to photograph

the WTB was a full inch longer, and 0.75" wider.

I flattened out the foil, and the Zmax gained 1/8", the WTB1/4" width.

they were both at 30psi.

 

[d8mok]

Re:

So lots take this to the limits of tyres width and rim

If we take a 3inch tyre and fit it to a 18mm wide rim it will have the shape of a ballon. Really narrow at the rim , with a rounded profile.

Same tyre on a 35mm rim will be squared off.



I can’t see how at the same pressure they will have the same contact patch. First one will be narrow as the tyre is having to curve to fit the rim.

If you Google this exact thing there are lots of articles written regarding it and they all say the same.

https://www.mtbr.com/threads/tech-why-w ... e.1170103/

https://m.pinkbike.com/news/rim-widths- ... -bike.html

 

[My_Teenage_Self]

The irony is I know Hamster is *technically* correct, when using a perfect scientific model. A 'perfect' tyre on a 'perfect' substrate will act in exactly the way he describes.

 

[hamster]

FABULOUS, what a brilliant experiment - the foil and foam is an absolutely inspired way to get the print.

It does raise an interesting question about the effects of such big tyre knobs on the contact patch, as the tyre will hang between them.

 

[legrandefromage]

But on the modern bike the wheel is way out in front so the weight is not coming directly from above and will be distributed almost evenly with the back wheel

The older shorter bike will have the weight bias shifting in a more measurable way as the rider shifts back and forth

So with the tin foil (mine is on my head as usual) shouting 'send it!!!' try each bike with weight front and aft as if you were on some gnarly singletrack in 1999 and 2021