Tire pressure...some newby questions (warning, patience may be required)

[DaveSw]

After massaging (and some beating) this old XT to the point where I don't fear for my life on it on the pavement, I found some time today to try some tame gravel roads.

As soon as I hit the gravel (Melrose Rd, Qualicum Beach - I did say tame) the front end of the bike started weaving around, almost like I was stuck in a sinusoidal track. (I wasn't) This was at a fairly slowish speed ~35-40 kph - a bit unnerving as I thought I'd killed the weave with new steering bearings and fiddling tire pressures.

So after a few moments of this at varying speeds, I stopped and dropped the front tire from 25 psi to about 19 psi. This was certainly more confidence inspiring (that means I was no longer fearing a bad end to the day's outing), but the weave wasn't totally gone. Hmm, did I need less pressure yet? A little, a lot?

Background: Front tire is an old (6-7 years), newish appearing IRC-GP1 (3.00-21). The back is a new MT-43 at 13 psi.

Given the traditional DS role, some pavement to get there, then gravel, etc. (for me, now, more gravel, less gnarly, rooty, slick stuff.)

I know folks run lower pressures off-road than on, is there a "typical" set of pressures (off/on road) for a tire like the GP-1 (obviously road biased). Would less than the 19 psi I ran be better? How low is too low?

Are there any obvious (or not so obvious) signs of "wrong" tire pressure I can watch for, or is this not a subject open to generalizations? i.e. "too much pressure leads to..." "too little pressure..." :help

Some good news from today's ride was that I didn't freeze, I might have my layers sorted out - but some new gloves will likely be on my Christmas list.

 

[LordEndo]

If you don't have rim locks I'd keep it to no lower than 15psi. With rim locks I run 11psi front and 10.5 in the rear for trail use, but that works well in the gravel as well. Personally I run a knobby and was really happy with the MT-21 Metzler on the front and rear. On my WR I ran those at the pressures noted. I'd jack it up to 20PSI for the road.

 

[DirtClunker]

Melrose eh? Are you going to venture onto the trails at Whiskey Creek? Nice riding!

As for steering bearings, put the bike on a centre stand/box, grab the front forks and wiggle it. See if you can get a little knock knock. If so, tighten it up a touch.

As for the weaving, could be all kinds of things. Just for a test, try 10psi. Dont hit any big rocks or logs, dont slam on the front brakes, just see if it feels better. If it does you know tire pressure will help. FWIW I often run 10-11 psi up front all day long on offroad trails and roads, the risk is pinch flats and denting the rims, but the gain is better traction and keeping that wheel on the ground.

It could also be crappy suspension, worn out suspension, or maybe just needs a fork oil change. If your suspension is bad, it will be skiddish on gravel, and even worse on rougher trails.

Wish I was up there, I'd like to give her a go and see how she feels. See if you can hook up with one of the guys up there to have them ride it a bit and give you an opinion.