Postion on bike and tyre pressures?

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Old Tuggo
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Postion on bike and tyre pressures?

Postby Old Tuggo » Tue Sep 11, 2007 20:56 pm

I have set up my position on my MTB almost the same as my road bike with the bars a little higher is this correct? My tyre pressures are about 38 psi is this too hard for trail/XC in the Peak District? I have difficulty in climbing rocky tracks as I usually lose my steering when hitting a large stone. I was wondering if this was due to my bike set up or simply my lack of expertise.

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supersonic
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Postby supersonic » Tue Sep 11, 2007 21:25 pm

Much of this is personal preference. XC riders may like a long lower position, trail riders more upright. Same for tyre pressures: different terrains, styles and bikes have different pressures. 35-40 is a good start, see how it feels and experiment.

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alaric@epicmtb
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Postby alaric@epicmtb » Wed Sep 12, 2007 14:18 pm

Riding position is much less fixed than on a road bike, just experiment a bit until you find a good combination for the trails you ride regularly. It sounds like you're in a good starting position, but don't get to set on it and try a few different combinations of saddle height and position, and bar height.

Bar height can be difficult to adjust (depending on how much steerer tube was left when the fork was fitted) you may want to try a few different stems.

The loss of steering on climbs could be over hard tyres, but it is more likely to be technique. For difficult/technical off road climbs, you need to stay seated (or hover just over the saddle), slide forward on the saddle and try to get your forearms parallel to the ground by crouching forward over the bars.

This will both maintain traction on the rear wheel for propulsion and the front for steering control.

As SS says, tyre pressure is a bit of a "How long is a piece of string" argument. For optimum off road performance you want to be running the lowest pressure you can, 35-40 psi is a good starting point, and then reduce by 5 psi every ride until you start getting problems (mainly pinch flats).

For smoother trails you can keep your tyres harder for lower rolling resistance, but for rocky technical trails the lower pressures give better traction.

Alaric.

Old Tuggo
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Postby Old Tuggo » Wed Sep 12, 2007 22:02 pm

Thanks for your advice fellas, I will certainly start experimenting with a lower front tyre pressure. I was on a rocky climb near Hayfield, Derbyshire, this morning which I had difficulty riding and and a younger chap on a cyclo-cross bike passed me with no problem (he told me that he weas in training for the Three Peaks). So I have still have a lot to learn but I suspect I need to have more confidence which I think will improve on the new full suspension bike I have just bought.

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MarvintheAndroid
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Postby MarvintheAndroid » Fri Sep 14, 2007 19:09 pm

I think your problem is more to do with technique than tyre pressures, 38 psi seems fine to me. If you drop too much pressure you will not only have steering problems when you hit rocks, but punctures too.

Try to anticipate the trail by picking your line more carefully, perhaps by avoiding rock-filled gullys and big rocks as much as possible. Big roots can also be a problem. For climbing such tracks your gear choice is important too. It may be better to pick a slightly harder gear and slug it, rather than a lower gear where the spinning is easier but maintaining momentum is harder. As you get stronger this will be easier.

As far as bike setup goes, your method makes a lot of sense provided that you find it comfortable, and certainly some top XC riders use the same methodology. The big difference will be the width of the bar and the effective stem length. Generally for XC or trail riding the saddle is slightly higher than the bar, and the position more upright than a road bike, but this is only a rule of thumb and no two riders are the same.

You could try using some of the techniques outlined on the Park Tool website for measuring and recording your bike setup, this will make it easier for you to experiment and undo any changes that don't work. This can be easier with the help of a friend.

http://www.parktool.com/repair/readhowto.asp?id=131

Marv
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Old Tuggo
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Postby Old Tuggo » Sat Sep 15, 2007 13:34 pm

Thanks Marvin, you have me wondering now whether I slipped up in cutting down the width of my bars and replacing the stem with a 5cm one to reduce my reach.

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MarvintheAndroid
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Postby MarvintheAndroid » Sun Sep 16, 2007 18:00 pm

Yes, that would certainly make the steering more skittish. Try keeping your weight forward whilst ascending, keeping a good grip on the bar and shifting your weight around as you tackle obstacles. Riding uphill while seated, especially in a very low gear, will tend to have the front end wandering around all over the place - either move forward to the nose of the saddle, or rise out of the saddle altogether.

Marv
What tree ? ...........



Trek 8000 ZR XC hardtail.

Old Tuggo
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Postby Old Tuggo » Mon Sep 17, 2007 06:37 am

Thanks Marvin I will try to remember your advice when I am bouncing up the rocky trails.

shin0r
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Postby shin0r » Mon Sep 17, 2007 07:13 am

Hi

Remember when climbing over the slippery stuff it's always a compromise between outright grip and front wheel control. If your weight is on the rear wheel you'll get great traction but the front of the bike is likely to wander; transfer weight to the front of the bike and you'll lose rear traction.Over time you'll find the right compromise for yourself.

As far as seat position vs handlebar/stem height; this is often personal preference. Some people find it more comfortable to sit quite upright, others prefer to be stretched out. I don't think there is any "right" way.

Same thing with tyre pressures; too hard and you might lose some traction; too soft and you risk pinch punctures and even damaging your rims if there's not enough air in the tyres to absorb knocks on the downhill sections. I usually go for 35psi if I'm on a rocky trail, it seems to be a good compromise.

cheers

Sam

Old Tuggo
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Postby Old Tuggo » Wed Sep 19, 2007 10:26 am

Thanks Sam, I feel that my problem is that I do not want to be too stretched but I feel that I sometimes do not have enough weight on the front as my wheel has a tendency to lift. As you say it is a compromise and I will have to keep on practicing using all the advice given.

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L60N
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Postby L60N » Wed Sep 19, 2007 12:08 pm

Is it ok to run tyres at around 65psi for commuting, and then reducing down to 40ish for trails? or is this not good for the tubes?

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Me-109
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Postby Me-109 » Wed Sep 19, 2007 23:11 pm

Old Tuggo wrote:a younger chap on a cyclo-cross bike passed me with no problem (he told me that he weas in training for the Three Peaks).


I hope that was training for next since this year's has been cancelled with the ongoing foot and mouth kerfuffle. :roll:


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