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Old 05-04-10, 10:00 AM   #1
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SRAM P5 Hub with drum brake - what lever ?

Hi,

I'm putting together a bike with a drum braked P5 hub (SRAM 5spd).

Would this work better with a V brake lever or a normal lever ?

How good is this brake ?

Thanks....
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Old 05-04-10, 11:38 AM   #2
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Drum brakes require "long pull" levers. It will state this in the lever description. It's also worth noting that drum brakes have a short break in period after which performance will improve. However, it is very important to make sure the initial adjustment of the brake is good in order to maintain safety.
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Old 05-04-10, 11:43 AM   #3
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So a V brake lever might be best ?
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Old 05-04-10, 07:56 PM   #4
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Quote:
Originally Posted by Fenway View Post
Drum brakes require "long pull" levers. It will state this in the lever description. It's also worth noting that drum brakes have a short break in period after which performance will improve. However, it is very important to make sure the initial adjustment of the brake is good in order to maintain safety.
Ok, I found a P5 manual online and it says:

Only use brake levers with a
cable moving distance of at
least 15 mm and a minimum
leverage of 3.8.

If I use drop bars could I use normal aero levers or would I need the dia compe 287V levers ?

Thanks.
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Old 05-05-10, 10:42 AM   #5
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That describes normal road levers.

My old Shimano 105 road drop bar levers have a cable pull of 18mm approximately. My Tektro drop bar V brake levers pull about 29mm of cable. I just measured both for you. The minimum ratio is also in th normal road lever range that per an old book by Frank Berto lists road lever leverages of about 4.1 to 4.6 IIRC.
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Old 05-05-10, 03:01 PM   #6
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Quote:
Originally Posted by tatfiend View Post
That describes normal road levers.

My old Shimano 105 road drop bar levers have a cable pull of 18mm approximately. My Tektro drop bar V brake levers pull about 29mm of cable. I just measured both for you. The minimum ratio is also in th normal road lever range that per an old book by Frank Berto lists road lever leverages of about 4.1 to 4.6 IIRC.
Ok, I was considering some tektro V brake levers or some dia compe 287V I have.

Looks like they might not be the best option.

After a long search I've found an antique pair of weinman levers (non-aero) that look like they feel very sorry for themselves, they are so old the rubber hoods are crumbling.

I've also found a pair of miche levers that while tired might be usable. These have the pivot further away from the bar - similar to early shimano linear response levers.

The right one has a broken return spring (I can probably ignore this?) and the left makes a gratey noise which I guess is the spring.

Other than that they seem servicable and I guess would have the correct amount of pull ?

Thanks for your help.

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Old 05-06-10, 04:32 PM   #7
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Those would have the correct pull, although they won't stop quite as well as modern aero levers due to the pivot position. Cane Creek sells new hoods that will fit them. You should be able to ignore the return spring (many levers don't have one at all).
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Old 05-06-10, 04:46 PM   #8
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Just out of curiosity: is that going to be a utility bike, or perhaps a tandem? Those P5s with drum brakes are perhaps the sturdiest geared hubs ever made.


Quote:
Originally Posted by Unknown Cyclist View Post
Hi,

I'm putting together a bike with a drum braked P5 hub (SRAM 5spd).

Would this work better with a V brake lever or a normal lever ?

How good is this brake ?

Thanks....
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Old 05-06-10, 05:54 PM   #9
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Quote:
Originally Posted by Unknown Cyclist View Post
Ok, I was considering some tektro V brake levers or some dia compe 287V I have.

Looks like they might not be the best option.

After a long search I've found an antique pair of weinman levers (non-aero) that look like they feel very sorry for themselves, they are so old the rubber hoods are crumbling.

I've also found a pair of miche levers that while tired might be usable. These have the pivot further away from the bar - similar to early shimano linear response levers.

The right one has a broken return spring (I can probably ignore this?) and the left makes a gratey noise which I guess is the spring.

Other than that they seem servicable and I guess would have the correct amount of pull ?

Thanks for your help.

Per my understanding the V brake levers have a pull ratio in the 2 to 1 range. Certainly true of my Tektro V brake road lever. I think that with that ratio you would have to pull with excessive hand pressure to get satisfactory brake stopping power. Also way outside the SRAM recommended range for the lever that you posted.

My SRAM & Avid V brake compatible MTB levers are also in the 2:1 leverage ratio range.
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Old 05-07-10, 03:27 AM   #10
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Quote:
Originally Posted by IanHelgesen View Post
Those would have the correct pull, although they won't stop quite as well as modern aero levers due to the pivot position. Cane Creek sells new hoods that will fit them. You should be able to ignore the return spring (many levers don't have one at all).
Hi,

Compared to the weinman levers I have - the miche do have a modern pivot position...

I don't have any other other non-sti levers to compare them to.

Thanks for the cane creek info, where do I find the hoods and how can I be sure they will fit ?

Haven't miche made more than one style lever ?

Thanks
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Old 05-07-10, 03:32 AM   #11
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Quote:
Originally Posted by wroomwroomoops View Post
Just out of curiosity: is that going to be a utility bike, or perhaps a tandem? Those P5s with drum brakes are perhaps the sturdiest geared hubs ever made.
It's a folding mountain bike with slick tyres and most likely will have road bars.

I've got a few folding bikes but all are small wheel - this one will still fit in the boot but hopefully have a 'real' bike feel to it.....

The frame is a Dahon, model 'Budget Boot Bike', nothing on it is original, I bought it as a bare frame.

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Old 05-07-10, 03:39 AM   #12
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Quote:
Originally Posted by tatfiend View Post
Per my understanding the V brake levers have a pull ratio in the 2 to 1 range. Certainly true of my Tektro V brake road lever. I think that with that ratio you would have to pull with excessive hand pressure to get satisfactory brake stopping power. Also way outside the SRAM recommended range for the lever that you posted.

My SRAM & Avid V brake compatible MTB levers are also in the 2:1 leverage ratio range.
Thanks for the info, again

I've built the wheels 26" mtd P5 rear, dynohub front and fitted some nice 1.5" slicks. I've found a seat post long enough and got some Acor cantis for the front.

I've bought most of the other parts though am still having problems, I've bought 2 different single ring chainsets, but neither work with any of the 3 BBs I have - the chain ring fouls the chainstay.

The other problem is bar height, headset is 1" and I've put an aheadset adaptor in - on top of this I've fitted a raiser and then a short steep stem - I've tried a few different types of bar on it but they are all still a bit low. MTB bars might give a better position, but I'd rather have drops if possible. Any ideas anyone ?
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Old 05-07-10, 12:35 PM   #13
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My LBS was able to order the hoods, so it's likely yours can as well. If not, I suspect Harris or Niagara would carry them. They're made to fit Dia-Compe non-aero levers, which I believe are a copy of the Weinmans. The C&V forums would be would be a good place to look for more info.
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Old 05-18-10, 02:48 PM   #14
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Any ideas about the gear range of the P5 ?

What size chainring should I be using with 26" wheels ?

TIA...
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Old 05-19-10, 01:48 AM   #15
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Per the SRAM IGH Tech Manual, downloadable from their web site internal ratios are as follows.

1 .633
2 .780
3 1.00
4. 1.281
5. 1.579

Overall range is 251%. With a 60" third gear this would give a 38" low and a 95" high which should be a good starting point. How many teeth on your hub input sprocket? Multiply teeth on it by about 2.3 to get close on the chain wheel teeth for that gearing.

You mentioned frame to chain wheel interference. IGH sprockets are available in a lot of sizes and Shimano IGH sprockets will fit the P5. Fit a smaller IGH sprocket and chain wheel to eliminate the interference. SRAM indicates that depending on whether the sprocket is installed with the cupped side inwards or out that you can use sprockets from 16T to 24T. I would go with the 18T, the minimum size that can be installed either direction, install it oriented to give the straightest chain line and match it with a 42 tooth front chain wheel.
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Old 05-19-10, 07:22 AM   #16
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Hi,

Useful info

It currently has a 39 front 20 rear.

I don't think I can go more than slightly larger on the front, though that isn't definite until the chainline is finally established.

I'd rather not replace both.......


Quote:
Originally Posted by tatfiend View Post
Per the SRAM IGH Tech Manual, downloadable from their web site internal ratios are as follows.

1 .633
2 .780
3 1.00
4. 1.281
5. 1.579

Overall range is 251%. With a 60" third gear this would give a 38" low and a 95" high which should be a good starting point. How many teeth on your hub input sprocket? Multiply teeth on it by about 2.3 to get close on the chain wheel teeth for that gearing.

You mentioned frame to chain wheel interference. IGH sprockets are available in a lot of sizes and Shimano IGH sprockets will fit the P5. Fit a smaller IGH sprocket and chain wheel to eliminate the interference. SRAM indicates that depending on whether the sprocket is installed with the cupped side inwards or out that you can use sprockets from 16T to 24T. I would go with the 18T, the minimum size that can be installed either direction, install it oriented to give the straightest chain line and match it with a 42 tooth front chain wheel.
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Old 05-19-10, 12:21 PM   #17
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39/20 will IMO be a bit low overall. The 39T chain wheel should work reasonably well with a 18 at the rear or a 17. A lot is dependent on your strength and riding conditions. The suggestion I gave is for a ball park starting point. A strong rider might like a higher set of gears or a weak one in a hilly area want lower overall gearing.
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Old 05-19-10, 01:51 PM   #18
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Ok, I've ordered a 17 and a 18.



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39/20 will IMO be a bit low overall. The 39T chain wheel should work reasonably well with a 18 at the rear or a 17. A lot is dependent on your strength and riding conditions. The suggestion I gave is for a ball park starting point. A strong rider might like a higher set of gears or a weak one in a hilly area want lower overall gearing.
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Old 05-21-10, 06:27 PM   #19
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The sprockets arrived.

I've fitted the 18 which should give:

1 35.66"
2 43.99"
3 56.33"
4 72.16"
5 88.95"

Should be an interesting starting point.
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Old 06-08-10, 06:30 PM   #20
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Project folder is finally a complete cycle

Had to make some parts for it (and have some made) - but I did ride it successfully today with only one component shaking loose.

I took it on a fairly hilly test ride and discovered that the low gear isn't low enough, the high gear isn't high enough and that my power output isn't as high as it could be.

I've had little experience of hub gears, but clearly the gearing is going to be a compromise and I'll have to try to put the small range I have where it will be most useful.

As I could manage 3rd gear at a fast cadence on good roads - but not so well if anything was against me - incline, wind, road surface, I think I'll try some lower gears and put the 20t on the back.

Ok, I'll be freewheeling down hills and not pedalling down them, but at least I might not be walking up them
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Old 06-16-10, 01:52 PM   #21
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Fitted a 20T to the rear, doesn't seem to have made a huge amount of difference.

Here's what it looks like....Project Folder..jpg
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Old 06-20-10, 06:44 PM   #22
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I've put a few miles on the P5 now, so here's some feedback:

The Good....

On the plus side, the gear change seems positive and quite sweet though a bit loud when going into a lower gear.

It's quiet !! Unlike my Rohloff where I need ear defenders....

The Bad....

It seems hard work considering the ratios - are there huge losses in this hub, or does it need to bed in ?

The drum brake seems a little ineffectual (unless you like examining the underside of motor vehicles) - again, does this improve with use ?

The Ugly....

The operation seems entirely counter-intuitive, compare to any other twistgrip I've used hub or otherwise.

Nearly every time I turn the grip CCW (pulling the cable) to engage a lower gear - which of course engages a higher gear.

Other than the adjustable stem shaking loose the the shakedown rides have gone well.

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