Road Bike chainring on a MTB Frame?

[Makizes]

Helo,

I bought a new MTB and would like to rebuild my old MTB as a Fitness bike. I'm planning to buy a Shimano 105 double Chainring but I have some doubts if it will fit on a MTB frame. For example if I take a double front chainwheel like: Shimano 105 (FC-5502). As per specification a Bottom Bracket with Spindle length of 109.5mm is recommended. Would the same size work on an MTB frame as well? I'm worried as the chainstays on an MTB is wider than on a road bike frame. Shall I go for a Spindle length of 118.5 mm?? Any experience with such a setup?

Thanks,
Daniel

 

[alfeng]

FWIW. You really need to measure the width of the chainstays where the ends of the crankarms will be to ascertain whether or not the 109.5mm Octalink BB will work on your particular frame ... on some, yes ... on others, no ...

This MTB frame required a 118mm BB spindle (either Octalink or ISIS) ...

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Subsequently, when I opted to put a MegaExo ROAD crank on the particular frame a few years ago, I needed to opt for a MegaExo Triple crank to achieve sufficient clearance for both the ends of the crankarms & for the 52t chainring ...

BTW. The Octalink Road cranks will work on the XTR Octalink BBs, and vice versa for the XTR Octalink cranksets on the Octalink Road BBs.

I found that on a STEEL Road frame that I could use a 112.5mm spindle to achieve sufficient offset for the Granny chainring on an Ultegra Triple; so, a 116mm XTR BB may be wide enough on your frame (you may need a spacer on the driveside of the BB shell if it is only 68mm wide), particularly if the frame will need a 73mm BB cartridge.

But, on this (below) particular frame, a standard Q-Factor Double crank could be used ...

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That's a long way of saying that if the intention is a 52t or 53t outer chainring, then the 118mm Octalink BB which is intended for a Triple will probably be the "safe choice" if you don't want to worry about it.

 

[Makizes]

Thanks for the replay. I have ordered a BB-5500 with spindle length 118.5 and it fits perfectly. (108,5 wouldn't be enough). The next step will be to sort out the front derailleur. I have a Shimano 105 FD-5600 on stock, but this one is bottom pull, and the frame would require a top pull model. Will either try to get a top pull model which can manage 53T, or I will have to look for for alternate solutions like a pulley or umlenker from www.speen.de ... Did you had any challanges with this?

 

[alfeng]

Originally Posted by Makizes
Thanks for the replay. I have ordered a BB-5500 with spindle length 118.5 and it fits perfectly. (108,5 wouldn't be enough). The next step will be to sort out the front derailleur. I have a Shimano 105 FD-5600 on stock, but this one is bottom pull, and the frame would require a top pull model. Will either try to get a top pull model which can manage 53T, or I will have to look for for alternate solutions like a pulley or umlenker from www.speen.de ... Did you had any challanges with this?

What TYPE of handlebars are you planning to use when you rebuild your old MTB?

WHICH shifters are you planning to use with the bike?

Do you already have them?

FYI. IF you are planning to use DROP handlebars, then IF you choose CAMPAGNOLO shifters you can use the front derailleur which is currently on your old bike BECAUSE Campagnolo shifters can be used with ANY cable-actuated front derailleur of ANY vintage ...

So, 'I' did not have any issues, per se, with the pictured configurations.

The second frame uses a bottom pull front derailleur.

If you already have a pair of Shimano Road shifters, then if the shifters are designed for a Triple (SRAM users need not apply!) then you can use it with a Double, too, with almost any front derailleur ...

I was able to use a Triple-capable 8-speed 105 front shifter with an 8-speed, top pull XT front derailleur [on the first bike, pictured above, prior to installing the Campagnolo shifters] ...

A Shimano MTB front derailleur can handle a 52t chainring ...

Although I have not tried one with a 53t-or-larger chaniring, I am pretty sure that a 53t chainring will not be a problem ...

Because the arc of the bottom edge of the outer plate of a Shimano MTB front derailleur isn't really any different than one will find on a Shimano Road front derailleur.

The front derailleur cable's tension was adjusted so that one of the extra "clicks" which would have normally moved the derailleur's cage to the Third/(Outer) Chainring now completed the shift to the Outer chanring on the Double chainring crankset ...

MINIMAL effort was needed to adjust the front derailleur cable's tension ... and, how you initially secure the cable may turn out to be good-to-go.

If you already have the shifters & they are only capable of handling a Double, then the UMLENKER would appear to be your best alternative OR simply sell the Shimano shifters & buy a pair of Campagnolo shifters ...

 

[LeoDing]

Tks for your info.