Trek 7.6 Gears-what a nightmare! Help wanted!!

weewillywinky

Hey all,

My girlfriend bought a Trek 7.6 FX for commuting on about a year ago.it has been used very little for various reasons but now is getting some use-or SHOULD be- Recently we have had loads of hassle with the gears-lots of rubbing on front mech. I spent a while trying to figure it out but got nowhere-its now been to 2 bike shops who have not made it any better (even after a full service!).

One shop insisted that there should never be a situation where she rides in the biggest ring on the front and the rear at the same time(this is when the rubbing is the worst)-is that correct? With all the money she spent on the bike she is absolutely devastated that they are telling her shes stuck with it like that and she can't simply ride round in whatever gear she chooses!

So-is anyone aware of problems with this bike or drivetrain setup (Shimano 105 rear mech, Bontrager Select Chainset, Shimano 9 speed front mech, shimano LX 9 speed shifters)??

Any help or advice appreciate as this is becoming avery frustrating problem totally destroying her enjoyment of the bike!

Will

riderjam

Using the two front and back biggest cogs at the same time just accelerates wear and tear because the chain is trying to go diagonally between the two- explains why the rubbing is worse

weewillywinky

thanks riderjam-I know it would speed up ware and tear BUT could the mech not be set up in such a way that there is no rubbing even though its running on diagonal?

supersonic

Yep, as above. You can get the same gear ratio in a smaller front ring and larger rear cog which will give a straighter line.

Have a read of this guide I put together:

http://www.bikeradar.com/forum/viewtopic.php?t=12647117

It concentrates on triple rings, but the principle of overlapping gears and angled chain still applies.

weewillywinky

I would have figured her smaller chainring to be the equivalent of a middle (in a triple chainset) and therefore thought there would be no rub issue when using it. And I just assumed that you could get the Larger ring operating with no rub-even if the chain is on a slight diagonal?

supersonic

It is not in the same place. There is no reason to use that gear.

probb66

Some bikes do this . I have a Boardman hybrid pro with only two front cogs on the crankset., but 10 gears at the rear. When in the largest front cog I wouldnt use the first 3 gears at the rear due to chain friction on the front derailler. Same for small front cog. I wouldnt use lowest three gears - 8, 9, 10.
Halfords are giving me a nightmare setting it up. They have fitted bottom bracket washers to help, but the fault just changes place.

My mountain bike- Gary Fisher Wahoo is different . It has three cogs on the front crankset and only eight rear gears. There is no friction at all on this.

Best to get a second opinion and do what your doing here. Try and get other Trek guys to chip in.

I also had a Trek 7200 3 front , 8 rear and no friction.

Hangie

All bikes with quality gears will rub on the front if you run with the chain diagonal (the Small Cog Front and Small cog Rear or Visa Versa). If they don't under normal use they certainly will if you push hard up a hill as the frame distorts.
It is something that you should not do, the instructions from Shimano and the likes will tell you so as it is inefficient and increases wear. I can see your point about not being able to use all your gears but this is taken into account when the gears are designed.

You can get access to the entire range of gears available without running diagonal as the ratios overlap to allow for this restriction.

High Ratio________________
__________________Low Ratio
Overlap

If you really struggle with the concept worth considering Hub gear (Shimano, Rholoff,Sturnley Archer all do them) The are very simple once fitted but I would suggest you trade in your current bike rather than trying to retrofit if you go down this route.

All the best.

BeaufortB

weewillywinky wrote:

...she is absolutely devastated that they are telling her shes stuck with it like that and she can't simply ride round in whatever gear she chooses!...

devastated? Is that not a slight over reaction?

Personally I tend to swap between the front rings for big drops rather than the rear.

bill_gates

I'd be keen to know the answer/outcome to this.

My missus also has a new Trek FX 7.x and when changing on an incline, there is a rattle when trying to get into the smallest chain-ring. There is also a lot of rattling from it.

The bike has had a check-over by the lbs but I would also think she would be 'devastated' to be told she would have to live with it.

BeaufortB

Theres a difference between a rattle from a badly adjusted gear, and misusing the gears.

It would be like driving around in 1st gear at 50mph in a car. No?

bill_gates

Is it badly adjusted when it will not go into the smallest chain-ring when under a but of pressure on an incline?

el_presidente

the front mech should shift under load but it will be more difficult and definitely more rattly / clunky. Sounds like you need to

a) fine tune the front mech and

b) learn to shift to the small chainring before the incline. This is not a fault with the gears, just good practice and more mechanically sympathetic.

BeaufortB

In fairness thats a different issue than the original poster.

Maybe I'm wrong but I thought with all derailleurs you have to ease off the pressue to change gears. Thats how I've always done it.

If you don't want to do this a hub geared bike might be better suited?

bill_gates

BeaufortB wrote:

If you don't want to do this a hub geared bike might be better suited?

I've got a Alfine Hub gear and was told that they don't shift that well under pressure which I agree with slightly but not having any major problems with it on an incline compared to the wife's standard derailleur setup which will jolt a chain out trying to get onto the granny spinner on a 1-2% incline.

BeaufortB

Get her a hub geared bike so

bill_gates

BeaufortB wrote:

Get her a hub geared bike so

I will next time but since her Trek is only a couple of months old, I would lose so much in depreciation on a trade-in.

Hub gears do seem to be the future.

MrChuck

The shop is right really, she shouldn't be using that combination- but since the same effective gear is available through other combinations I don't see the problem...? Nothing's been 'lost' by not using it.

Sounds a bit of a put down and it's not meant to be, but perhaps she just needs to get used to using the gears properly?

Of course this isn't to say that something might be slightly out of adjustment but if that's the only issue with it it sounds unlikley.

mudcovered

Bill Gates wrote:

I've got a Alfine Hub gear and was told that they don't shift that well under pressure which I agree with slightly but not having any major problems with it on an incline compared to the wife's standard derailleur setup which will jolt a chain out trying to get onto the granny spinner on a 1-2% incline.

So even on a slight uphill the front is reluctant to shift when pedalling under load. That doesn't sound right. Both my MTB's will drop to the granny ring pretty definitively even under load. Thats with current spec Deore LX and Deore mechs. The STX I was using previously was a little bit less definitive but would still shift under load. Its noisy but 100% reliable for me.

Mike

bill_gates

It will change on an incline but often needs a 'nudge'. It is very noisy also.

On the flat, it is smooth as it can be with very little noise.