Author Topic: question on shimano 7803 front mech with 48 38 28 chainring  (Read 4950 times)

question on shimano 7803 front mech with 48 38 28 chainring
« on: 26 April, 2018, 06:54:41 pm »
hello every one,

i've been looking for parts to build a touring bike recently, and all the parts now are in the LBS to be built.

Last night, the LBS sent me the picture which I attached to this post and said this is the best he can do with the parts I provide. which is a Shimano FD-7803 front mech with stronglight impact triple 48 38 28 chairing.

LBS reports that the shifting between middle and inner ring would be fine but not the outer ring for the setup from the picture. and if the front mech to be placed to the "normal position" (lower, close to the outer ring), then the mech would touched the middle ring.

my guess is maybe the 7803 front mech has taller cage due to the fact that 7803 chairing uses 52 39 30 combination, so when using 48 38 28 combination the height(or say gap) between outer and middle ring are too close for the mech cage. and the solution for it maybe is to replace the 48t outer ring to a 50t ring, or change to a mtb front mech.

any suggestions?


thanks!

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tiermat

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Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #1 on: 26 April, 2018, 07:07:56 pm »
Try to get hold of a 6603 mech, I ran one on my inbred 29er for a good few years, using just such a chainring combo.
I feel like Captain Kirk, on a brand new planet every day, a little like King Kong on top of the Empire State

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #2 on: 26 April, 2018, 07:30:01 pm »
The DA (and Ultegra) triple mechs work in a 12 or 13 tooth difference between outer and middle. Thus the inner cage side hits the centre ring if the mech is positioned as specified above the outer ring. A 105 triple mech will work with the 10 tooth difference I believe.  Check the mech specs on the Shimano tech docs.
We are making a New World (Paul Nash, 1918)

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #3 on: 26 April, 2018, 07:33:07 pm »
There's an Ultegra 6603 triple mech for sale here: https://www.bankruptbikeparts.co.uk/shimano-ultegra-fd-6603-front-gear-mech-derailleur-bottom-pull-31-8mm-50-bbp2210859

Are you using STIs or bar end/down tube shifters? If you're not using STIs, I'd be tempted to just go for a MTB front mech, gives you more flexibility of touring-suitable chain ring sizes.

On my tourer I'm now running 46/34/24 with an XT front mech, the only problem I have is when on 34/11 I get some chain rub against the pins of the outer Chinook chain ring, otherwise all good.



XT front mechs are discontinued, though and seem quite hard to find, Deore front mechs are still readily available, though then you're going down in quality a bit from Ultegra or XT
Old enough to know better, but young enough to do it anyway

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #4 on: 26 April, 2018, 11:21:38 pm »
I've encountered the same problem (not with DA gear though).
Higher than normal mech is not such a big issue as Shimano (and your LBS) would have you believe.  Yes, changing to/from the outer ring may not be as crisp as you'd expect from DA, but this is a touring bike?
Before you spend any more £ have them set it up so it just clears the middle ring and see how you get on.

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #5 on: 27 April, 2018, 04:09:58 am »
Try to get hold of a 6603 mech, I ran one on my inbred 29er for a good few years, using just such a chainring combo.

Thanks tiermat, if I can get hold of a set of 6603, will definitely give it a try.


The DA (and Ultegra) triple mechs work in a 12 or 13 tooth difference between outer and middle. Thus the inner cage side hits the centre ring if the mech is positioned as specified above the outer ring. A 105 triple mech will work with the 10 tooth difference I believe.  Check the mech specs on the Shimano tech docs.

Thanks for pointing the direction rafletcher!!!
I was trying to find the spec docs right after read the replies from here. I found FD-7803 spec from 2007 listed as Top gear teeth -> 52T,  capacity -> 22T, and chianstay angle-> 63~66 degrees. FD-6603 also share the same spec on top gear, capacity, and chain stay angles. I didn't saw the outer and middle chainring capacity in road series spec column, but I do saw it listed as "Top-Middle Min. Capacity" from ATB(MTB) section. And the 105 (5603) did has different spec on Top gear teeth (50T) and capacity (20T) while chainstay angles are the same.


There's an Ultegra 6603 triple mech for sale here: https://www.bankruptbikeparts.co.uk/shimano-ultegra-fd-6603-front-gear-mech-derailleur-bottom-pull-31-8mm-50-bbp2210859
Are you using STIs or bar end/down tube shifters? If you're not using STIs, I'd be tempted to just go for a MTB front mech, gives you more flexibility of touring-suitable chain ring sizes.
On my tourer I'm now running 46/34/24 with an XT front mech, the only problem I have is when on 34/11 I get some chain rub against the pins of the outer Chinook chain ring, otherwise all good.

XT front mechs are discontinued, though and seem quite hard to find, Deore front mechs are still readily available, though then you're going down in quality a bit from Ultegra or XT

Thanks for the "shopping guide" on 6603 Oxford_Guy. ;p
I am planing on (and already have a pair of SL-7900 in hand) use downtube shifter on this bike, and do considering to switch to MTB series of front mech to save some time/money on get a new crankset. the thing is with my limited knowledge( experience) I am troubled with choosing the suitable one.


I am fairly new to the cycling world with very little experience/knowledge. still digging, hopefully I can finish the project alright. Thanks for the suggestions and direction pointing! and sorry for not having visual guide on the specs docs, cause I don't know how to put the picture here via computer. I will try to put them on via mobile phone later today. Maybe also the pictures of the parts I already get.


Cheers!!

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #6 on: 27 April, 2018, 05:00:33 am »
I've encountered the same problem (not with DA gear though).
Higher than normal mech is not such a big issue as Shimano (and your LBS) would have you believe.  Yes, changing to/from the outer ring may not be as crisp as you'd expect from DA, but this is a touring bike?
Before you spend any more £ have them set it up so it just clears the middle ring and see how you get on.
Thank you Somnolent, I will try to take a look by myself from the LBS. hopefully it will be sorted out from my next trip to the LBS.


cheers

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Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #7 on: 27 April, 2018, 05:03:33 am »
here are the info from shimano 2007 spec docs I found. 7803,6603, 5603, and part of MTB section on front mech. hope this helps than the words.

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Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #8 on: 27 April, 2018, 12:31:39 pm »
If it is any help I've used both 6603 and 6703 with a 44/32/22 XT chainset on my Audax bike.  There is a gap of at least 10 mm between the front mech and the largest chainwheel as this is the lowest the front mech can go without fouling on the chainstay.  The only issue I've found is that you have to pause for a second or so if you want to change from the largest to smallest chain wheel or vice versa.  i.e click 1 -2 -3 click.  I've done at least 10,000km using 44/32/22 with 6603/6703 without any significant issue.

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #9 on: 28 April, 2018, 03:19:15 am »
my aged Suntour front derailleur (some sort of off-road branded unit, but is ok with being ridden on roads) handles 48-38-24 pretty well.

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #10 on: 28 April, 2018, 03:53:58 am »
If it is any help I've used both 6603 and 6703 with a 44/32/22 XT chainset on my Audax bike.  There is a gap of at least 10 mm between the front mech and the largest chainwheel as this is the lowest the front mech can go without fouling on the chainstay.  The only issue I've found is that you have to pause for a second or so if you want to change from the largest to smallest chain wheel or vice versa.  i.e click 1 -2 -3 click.  I've done at least 10,000km using 44/32/22 with 6603/6703 without any significant issue.
thanks freeflow, looks like the 6603/6703 can handle 12t differences between outer(top) and middle chainring. will give it a try to see If it handles 10t difference(48 38 28), IF I can get hold of a 6603. ;)


cheers

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Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #11 on: 28 April, 2018, 04:12:02 am »
my aged Suntour front derailleur (some sort of off-road branded unit, but is ok with being ridden on roads) handles 48-38-24 pretty well.
lovely! I am now waiting a deore mt60 to try on my bike. also an aged front mech. ;p

I think should list my setup here, I am now using 10sp downtube shifter, a stronglight impact triple(48 38 28), 7803 front mech, 11-32 cassette(maybe a tiagra), and XTR M971 rear mech, the frame is an off the peg BJ world tour.

it looks like this so far....


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Torslanda

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Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #12 on: 28 April, 2018, 10:03:47 am »
That is beautiful!

Now I've seen your bike it's occurred to me that you could use almost any triple front mech that's bottom pull and capable of running a 48 ring. From where I'm sitting I can see a Sora, RSX, STX and a Deore. All 28.6mm band and - with the possible exception of the STX - an elegant solution IMHO

Friction shifting FTW!  :thumbsup:

ETA That's assuming the seat tube is 28.6mm . . .
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #13 on: 28 April, 2018, 11:20:40 am »
my aged Suntour front derailleur (some sort of off-road branded unit, but is ok with being ridden on roads) handles 48-38-24 pretty well.
lovely! I am now waiting a deore mt60 to try on my bike. also an aged front mech. ;p

I think should list my setup here, I am now using 10sp downtube shifter, a stronglight impact triple(48 38 28), 7803 front mech, 11-32 cassette(maybe a tiagra), and XTR M971 rear mech, the frame is an off the peg BJ world tour.

it looks like this so far....

Very nice! If I was ever to build a (road) tourer from scratch, I would probably start with as Bob Jackson frame... Slightly jealous of your XTR rear mech, I couldn't find one at a sensible price, so settled for XT. What brakes are you going to fit? I've been very happy with the Shimano CX50 cantis (with Swissstop Flashpro pads in Ultegra shoes) that Brucey recommended to me recently.
Old enough to know better, but young enough to do it anyway

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #14 on: 28 April, 2018, 11:57:44 am »
.....it's occurred to me that you could use almost any triple front mech that's bottom pull and capable of running a 48 ring. From where I'm sitting I can see a Sora, RSX, STX and a Deore. All 28.6mm band and - with the possible exception of the STX - an elegant solution IMHO


yup I agree, there are gazillions of (mostly older) triple FDs that will work OK with a 10T middle-big interval and friction shifting. Very many (both road and MTB) triples were set up this way in the 1980s and 1990s.   I still have an Original XT 'deer head' FD on my touring bike and it has that kind of setup..

If you want road indexed shifting then there are road FD triples that will work OK, for example the FD from the 1055 groupset etc will work with most triple STIs

48T big ring is small enough that it will work with most MTB FDs (nominally for 44-46T) and large enough that it will work with road FDs (nominally for 50-53T) so you ought to have plenty of choice that way too.

BTW If you can't be bothered to look up the specs then you can measure the height difference of the inner and outer plates in a FD and this will tell you if you are in the ballpark or not.  For 10T interval you ought to be shooting for ~18-20mm. More than this forces the FD to be set too high (as you have discovered) and less than this usually causes the inner- middle shift to go vague (in both directions).

hth

cheers

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #15 on: 29 April, 2018, 04:56:29 am »
ETA That's assuming the seat tube is 28.6mm . . .

It is indeed a 28.6mm seat tube. ;)

I am waiting one of my friend mailing me his "precious" Deore MT60 to let me try. finger crossed!


:)

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #16 on: 29 April, 2018, 05:20:28 am »
Very nice! If I was ever to build a (road) tourer from scratch, I would probably start with as Bob Jackson frame... Slightly jealous of your XTR rear mech, I couldn't find one at a sensible price, so settled for XT. What brakes are you going to fit? I've been very happy with the Shimano CX50 cantis (with Swissstop Flashpro pads in Ultegra shoes) that Brucey recommended to me recently.

I was originally heading 7800 long cage rear mech since my front mech is a 7803, but the price and availability of rd-7800 gs were insanely high and low. So I checked the online market here and found this NOS rear mech listed around 50 quids, it then"magically" appeared in my hand in the very next morning. ;p I got a pair of Paul touring canti brake from ebay. Never tried them before, will soon to know if it's functionality beats it's craftsmanship.

I found the process of building up a bike from scratch was both painful and educational. But needlessly to say it's quite a fun ride! ;p


cheers

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #17 on: 29 April, 2018, 05:42:44 am »
.....it's occurred to me that you could use almost any triple front mech that's bottom pull and capable of running a 48 ring. From where I'm sitting I can see a Sora, RSX, STX and a Deore. All 28.6mm band and - with the possible exception of the STX - an elegant solution IMHO


yup I agree, there are gazillions of (mostly older) triple FDs that will work OK with a 10T middle-big interval and friction shifting. Very many (both road and MTB) triples were set up this way in the 1980s and 1990s.   I still have an Original XT 'deer head' FD on my touring bike and it has that kind of setup..

If you want road indexed shifting then there are road FD triples that will work OK, for example the FD from the 1055 groupset etc will work with most triple STIs

48T big ring is small enough that it will work with most MTB FDs (nominally for 44-46T) and large enough that it will work with road FDs (nominally for 50-53T) so you ought to have plenty of choice that way too.

BTW If you can't be bothered to look up the specs then you can measure the height difference of the inner and outer plates in a FD and this will tell you if you are in the ballpark or not.  For 10T interval you ought to be shooting for ~18-20mm. More than this forces the FD to be set too high (as you have discovered) and less than this usually causes the inner- middle shift to go vague (in both directions).

hth

cheers

Thanks for the valuable advices Brucey. :)

When I tried to looking into the spec docs from Shimano(after 2007), It has "top gear teeth" column on both "ATB" and "ROAD" front mech sections (and it's exactly as you mentioned 44-46 and 50-53). But it didn't shows the top-middle min. capacity on road section, so I can only guess the 7803 has 13t top-middle min. capacity based on the chainset teeth combination comes from FC-7803(52-39-30). Unfortunately, all the parts now are in LBS and I won't be able to visit the LBS recently. I will measure the FD cage as soon as I get hold of it.


Thanks again Brucey.

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #18 on: 29 April, 2018, 04:32:35 pm »
Very nice! If I was ever to build a (road) tourer from scratch, I would probably start with as Bob Jackson frame... Slightly jealous of your XTR rear mech, I couldn't find one at a sensible price, so settled for XT. What brakes are you going to fit? I've been very happy with the Shimano CX50 cantis (with Swissstop Flashpro pads in Ultegra shoes) that Brucey recommended to me recently.

I was originally heading 7800 long cage rear mech since my front mech is a 7803, but the price and availability of rd-7800 gs were insanely high and low. So I checked the online market here and found this NOS rear mech listed around 50 quids, it then"magically" appeared in my hand in the very next morning. ;p I got a pair of Paul touring canti brake from ebay. Never tried them before, will soon to know if it's functionality beats it's craftsmanship.

Good catch with the XTR mech!The Paul Canti brakes do look lovely - have you got the "Touring" or the "Neo Retro" ones?

I found the process of building up a bike from scratch was both painful and educational. But needlessly to say it's quite a fun ride! ;p

I bet! I don't have the time or knowledge to do so currently (or workshop space), unfortunately
Old enough to know better, but young enough to do it anyway

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #19 on: 30 April, 2018, 01:19:50 am »



Good catch with the XTR mech!The Paul Canti brakes do look lovely - have you got the "Touring" or the "Neo Retro" ones?


I use the touring one cause I've been told it gives more space for put on the rack and bags. :)



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Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #20 on: 08 May, 2018, 03:56:17 pm »
news update, the deore FD-MT60 from my friend is just arrived this afternoon, hope this one would be able to fit with 48 38 28 crank set from stronglight. ;)

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Torslanda

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Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #21 on: 08 May, 2018, 10:53:21 pm »
That will do.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #22 on: 31 May, 2018, 08:35:20 am »
That will do.
thanks Torslanda,

Unfortunately, the LBS reported it won't work.... anyway they already put on "another" workable deore FD. and send me few pictures last night. I should be able to collect it next week. I will try to figure it out this front mech issue when it's back to me. fingers crossed!



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Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #23 on: 31 May, 2018, 08:37:27 am »
btw, the bartape been warped in opposite position, it's a 3T LTD bartape.... now it looks like candy crush kind of bicycle. ;p
That will do.
thanks Torslanda,

Unfortunately, the LBS reported it won't work.... anyway they already put on "another" workable deore FD. and send me few pictures last night. I should be able to collect it next week. I will try to figure it out this front mech issue when it's back to me. fingers crossed!



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Re: question on shimano 7803 front mech with 48 38 28 chainring
« Reply #24 on: 31 May, 2018, 11:08:48 am »
did the LBS say why FD-MT60 didn't work?

cheers