slipping gears under heavy loads?

Quoted post said:

Originally posted by dirtypuke
when i peddal hard and shift at the same time my bike slips real bad and them makes some really bad noises. is this how mountain bikes shift? or do i have something that needs adjusted? i have deore derailers on my new bike. 🙁

when you're shifting, you need to take some weight off the pedals. spin them lightly when shifting. it's normal for it to make noise if your putting pressure on the pedals.

that kind of sucks

Quoted post said:

Originally posted by dirtypuke
when i peddal hard and shift at the same time my bike slips real bad and them makes some really bad noises. is this how mountain bikes shift? or do i have something that needs adjusted? i have deore derailers on my new bike. 🙁

Response:
While you are in the process of shifting, you don't want to be cranking on your peddles. Lighten up on them while you are shifting then you can start cranking. Also, if you have recently put on a new chain and have worn gears, it can cause chain suck as well as slippage. As gears and chains wear together, they may work fine. Replacing one without the other can get you into trouble sometimes.

The tooth pattern of your cogs and chainrings is fixed...meaning that they cannot match a stretched chain. What happens is that the stretched chain tries to wear them down to match their stretched shape, but the best the cog can do is have its profile rearranged, with the result that the parts that engage the chain are worn off. Eventually the chain begins to slip off the cogs under pressure, particularly on the smaller cogs. The problem is that, even if you replace the chain before it actually skips, you have done enough wear to the cog profile that a brand new chain will skip on the rear! At this point, your only option is to replace the rear cassette. The front chainrings rarely get so bad that the chain can skip over them (although I have seen this happen), primarily because there are so many teeth trying to hold onto the chain.

Also, make sure that you are now is a situation where your chain is on the inner-most front cog and outer-most gear in the rear cassette. This can cause the chain to bend (wear more) and slip.