MTB drivetrain question

[mudman]

I've got a Shimano 2x10 setup, XT785 chainrings 24T and 38T. Currently living in NYC and I'm constantly running out of gearing
Biggest chainring set in XT785 is like 26T and 40T and I don't think that'll be enough for me.
Can I use the big and middle ring from a triple set like the XT FCM770?
Also should I be looking at other brands?

I love keeping up with the road guys doing laps around Prospect Park on my MTB but I'd love it even more if I was passing them!

Oh, also, any recommendations for slicks/road tires for my 27.5 wheels?

[Laneco]

Can't help you with the gearing question but I think it could be a little complicated. Reason - when you jump up to a significantly larger chain ring, you need more chain. But you also need a longer derailleur throw to handle the longer chain. This is something that a good bike shop can probably help you with though checking here on Pelican is always a good first. Seems like SOMEONE here has done pretty much anything most of us think up!

As far as tires go, THAT I can help you with. I rode a 27.5 with a set of Ritchy Comp Race Slicks on it. Terrific tires, narrow and fast as hell with good corner grip. There are probably other tires out there now, but I've ridden THIS one and its quite good.

angela

[mudman]

Thanks Angela, I'll definitely check out the Ritcheys.
I've always worked on my own bikes and have built and modified several but I got out of it a long time ago and have never dealt with a 2X drivetrain. If I go to something like 44T and 26T the derailleur will be just fine after adjustment.
As for the longer chain, I'm probably due for a new one anyway. I've really been putting on the miles here

[nota]

you may lose your hi- low gear ie big front to big rear
but likely not a big deal as you got 19 others

40t is small on a road bike48- 50 or 52t is common
and 38-40t is a common road bike low ft crank gear
bolt spacing is the big deal on swapping ft gears/chain-rings
is your fr derailleur fixed mount or adjustable?
as if fixed you can't move it for too big a gear

btw a 27.5 is a 700 rim and 700 road tyres fit most
700 tyres come in teen to 40+mm wide
if you want to mess with roadbikers get road style lite rims
as 27.5 mt rims should be heaver for offroad loads then 700 road rims
but fit should be the same

[mudman]

I've got 64/104 bcd, lots of options from mtb triples.
Derailleur is adjustable up and down, yes.
I thought 27.5=650B? I've been out of this for too long

[Otter74]

There are lots of really good 650b road tires available. I've used Grand Bois Hetres for years on my daily driver; Compass tires (e.g. Baby shoe Pass, which I think are about 42mm) in general are really excellent.

[nota]

Originally Posted by mudman

I've got 64/104 bcd, lots of options from mtb triples.
Derailleur is adjustable up and down, yes.
I thought 27.5=650B? I've been out of this for too long

27.5'' = 698.5mm or 700 rounded

26'' = 660

25.59 = 650

[LEAKYSEALS951]

If you have a spare double or triple front sitting around, throw it on and see what happens. You will "perhaps" need but maybe not need a front derailleur. You might get by just lifting yours. You might have to adjust the q factor with another spindle. As for rear derailleur length- just try the setup to see if it works. Even if the setup cannot handle a large/large ring or a small/small ring combo, these are extremes and you should probably not use those anyway. Same goes for the front derailleur- raise it up and the chain might bottom out on the derailleur in the small/small cog combo. So what? Again, just avoid that ratio.

Good luck. You found yourself a deep rabbit hole. Go play. Tinkering is cheap and will let you know if you are on the right track before you invest real $$$ into the idea.

Good luck,
Ron

[look 171]

No advice for you on your gearing on the MTB but a larger chain ring. Its worth a try. Why not just get a road bike if you are going to go through all the trouble changing out to road specific tires just to ride it on the road? A road bike is A LOT faster then the MTB. This way, they can just smell your dust. They will notice you on the fast MtB, but they will fear you on the road bike. I think that more fun when they fear ya coming out of a corner. I have been there many times coming out of a corner on full pop out of the saddle just trying to bridge the gap. The worst parts is, I know who's right in front of me and I have to do the deed to put everyone up to his wheel. OH, the pain. Hate that guy.

[Laneco]

Originally Posted by mudman

I've got 64/104 bcd, lots of options from mtb triples.
Derailleur is adjustable up and down, yes.
I thought 27.5=650B? I've been out of this for too long

The REAR derailleur is going to be your problem. When you had a few lengths of chain to accommodate a much bigger chain ring, you've got to do something with that chain at the back. Your rear derailleur may not be able to accommodate the add'l length and you may need one with a longer cage. Try and see.

As far as the tires go - you are actually correct... But the whole thing is about as clear as mud.

The 700c and 650b are old designations where the letter indicates the bead. They went with a standard at some point. 700c is a regular road bike wheel and if you look at the wee wee printing around the bead you will usually see 622mm. The 29er wheels are same size rim (usually wider but same height) as road bike 700c. On a 29er tire, you will also often see in the see wee printing 622. Because they are the SAME. I've got 700c tires mounted on 29er rims. Run and ride perfectly

The 27.5 is the same as 650b (the b indicating the standard that everyone went with). In the wee printing on those tires you will find 584mm. So big print on all these tires is the size that we are MARKETED with - and the wee print visible on most of these tires right at the edges of the bead indicates the true size. Oh and 26" mtb is actually 559mm.

Ok - so blah blah blah - here's the short version. 700c equals 29er - with the mountain bike rims being wider but readily accepting wide 700c "roadie tires." The 27.5 and 650b are the same interchange ideas. Just get a tire with compatible width - the height is easy. Ignore the marketing hype.

OK?

angela

[Joe Bob]

Change the free wheel.

[Laneco]

Couple of pics. This first one is my Focus bike with 700c wheels. It's actually a cross bike but I'm using it as a road bike right now so I've removed the Rocket Ron cyclocross tires and put on a set of 700c x 32 Continentals. Look closely at the picture and you will see the rim says 700c tire size and the black lettering on the tire shows 622 (the wee letters) AND the 700x32 marking.


This bike is my old 'cross bike. I took the 700c Rocket Ron's off my Focus and put them on these wheels. The wheels are Spinergy Xyclone 29er mountain bike wheels. 700c tires on 29er wheels - perfect fit as long as they are wide enough.



This is a 26" mountain bike tire. It's a kenda small block 8 - my fav. In this picture you can see both the 559 marking (fairly large here, but sort of blended into the tire color-wise) and the 26" marking.




Oh by the way... A lot of 27.5 bikes will actually accept a carefully chosen 29er wheel with a slick tire provided you are running disc brakes. I've seen that one done a few times as well for a pretty darn quick "roadie" mountain bike.

angela