New tyres...chain almost fouling tyre in bottom gear...
Iain C
Posts: 464
This follows on from a thread I started in the general section about mud clearance (Supersonic's verdict was try it and see!) but I thought I should move it here as it's now a bit more workshop/techie!
Just fitted Bontrager Jones ACX 2.35 tubeless to my 07 Fuel EX7 and it certainly seems tight on mud clearance. Have not had a chance to ride it in anger yet as I am still getting over an injury. However, in bottom gear, the chain is running incredibly close to the side knobs of the tyre, so much that if you spin the rear wheel (bike stationary) and lean the bike over, the tyre just starts to rub on the tyre due to the weight of the chain falling in towards the centreline of the bike. Chain is very new and not worn.
My first thoughts were that clearly the tyres will not fit the bike, but on second thoughts, more or less regardless of the frame, the position of the sprockets, tyre, wheel, chainset and therefore chainline should in theory be constant no matter what frame they are mounted in. The tyres were sold to me as XC/trail tyres, it's not as if I am trying to get 2.7 DH tyres to fit a bike with 3 chainrings where there's only enough chain room for a single or double up front. Or are BB spindles available in different lengths to counter this and give a few more mm of room at the expense of a less desirable chain line?
Can a little bit of tweaking on the mech and tyre wear give me the room I need? How much should this be as a minimum? Or am I worrying about nothing as sometimes when you see stills of serious chainslap the chain is all over the place anyway...and if I was getting big chainslap I would not be in bottom gear anyway?
Help!
Just fitted Bontrager Jones ACX 2.35 tubeless to my 07 Fuel EX7 and it certainly seems tight on mud clearance. Have not had a chance to ride it in anger yet as I am still getting over an injury. However, in bottom gear, the chain is running incredibly close to the side knobs of the tyre, so much that if you spin the rear wheel (bike stationary) and lean the bike over, the tyre just starts to rub on the tyre due to the weight of the chain falling in towards the centreline of the bike. Chain is very new and not worn.
My first thoughts were that clearly the tyres will not fit the bike, but on second thoughts, more or less regardless of the frame, the position of the sprockets, tyre, wheel, chainset and therefore chainline should in theory be constant no matter what frame they are mounted in. The tyres were sold to me as XC/trail tyres, it's not as if I am trying to get 2.7 DH tyres to fit a bike with 3 chainrings where there's only enough chain room for a single or double up front. Or are BB spindles available in different lengths to counter this and give a few more mm of room at the expense of a less desirable chain line?
Can a little bit of tweaking on the mech and tyre wear give me the room I need? How much should this be as a minimum? Or am I worrying about nothing as sometimes when you see stills of serious chainslap the chain is all over the place anyway...and if I was getting big chainslap I would not be in bottom gear anyway?
Help!
0
Comments
-
in that case tyres are too big."Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools :?:SheldonBrown0 -
As nick said, it's simply a case of the tyres being too big for the frame.
You can adjust the front mech to your hearts content but it won't stop the problem unless it rubs on the mech instead on the tyre.Less gears, more beers.0 -
I was thinking more rear mech than front as it's the lower portion of the chain causing me grief rather than the top...I have about 5mm at the top.
Actually...that's just reminded me (bear in mind i have not ridden it since early August when I stacked it) it was overshifting past bottom the last time I rode it, chain was ending up between the bottom sprocket at the plastic disc...perhaps the mech hanger has had a smack or the stop screws need a tweak. I'll have a fiddle and see if I can improve it. What, realistically, is the minimum clearance in bottom gear that I need?0
