P-38 build

DIscuss anything relating to non-standard cycles and their equipment.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

The front derailleur was badly bent in a chain suck incident. Examination of the chain rings showed no obvious cause but the 24T inner ring is steel with minimal shaping of the teeth. So I'll switch it for a 26T Spa Zicral ring and put the 11-34 cassette back on to compensate. Will also change the crankset to one with short cranks by pinching the 150mm crankset off the Paseo. I have an Altus FD to install but it needs a longer cable for its dual pull mechanism. That's quite a bit of work to be done. And I'll need to replace the Paseo cranks with something too.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

Altus FD installed and adjusted. Seemed to work better with the 44T outer with a bigger gap than the standard 2mm. I realise now that the P-38 came configured for a dual-pull 34.9 top clamp FD because of the cable stop position and the supplied shim for the skinny derailleur tube. Which meant that my 110mm titanium BB would not work. The chain wouldn't make the inner ring reliably. I'm sure 113mm would work but I've changed the BB to an 116mm FSA one I had which seems to run very smoothly. Also had to extend the boom 10mm because of the shorter cranks.

Now pondering which cassette to use now I have short cranks and a larger inner chainring. 11-32 doesn't give a low enough bottom gear, 11-34 is a bit gappy, wondering whether to try a 12-36. This would reduce the top gear but really would give me a 17.7" bottom gear and the spacing of the gears is pretty consistent. I can balance at low speed on the P-38 but I struggle to restart on hills more than 8% or so. I'll be able to climb steeper but if I have to stop I'll probably have to get off and push until I can find some flatter road to restart.

Edit: I tightened the boom bolts very carefully, alternating between them whilst gradually increasing the torque, finishing at 8.8Nm. It's tricky on the P-38 because one bolt is where the support tube is welded to the boom. Both the boom and the support tube have slots so they can be pinched. Lightning don't give a torque setting but warn against overtightening!
Last edited by UpWrong on 28 Aug 2022, 8:42am, edited 1 time in total.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

Completed a longer test ride. All good. The smaller wheels suit me better and the shorter cranks have opened my body position out a bit when riding. I've got the seat stays about 75% of the way to their shortest setting, about 1 cm away from shortest. I do slide forward a bit so I reckon my angle of recline is not far off 45 degrees in practice. I'm going to leave the cassette alone for now. The gearing is from about 20" to 100" and the steps on the cassette and on the ring changes are nice. I can use all combinations of gears.

No more planned changes. This is probably as good as it's going to get for me on an SWB. I'm going to turn my attention to the Paseo now and make a decision whether to keep or move it on. I love the engineering but I've been finding it a bit too reclined for me to ride it confidently in traffic. I'm going to try some longer cranks on it to close the hip angle a little.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

Did another ride on the P-38 and feeling very at one with it. Think I will change the cassette to 11-34 after all. I don't want to give up the 44/11 ratio but could do with something a bit lower than 26/32. Also the bigger steps will be welcome, sometimes. Swings and roundabouts.

I have some awful front disc brake squeal at the moment to resolve.

Although I felt at one with the bike, there were no personal Strava segment records. I think this confirms that I'm no quicker on the P-38 than I am on the Stratus. The Lightning is lighter but I'm generating more power on the RANS I think.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

Changed the cassette to 11-34 and have largely eliminated the front disc squeal by moving the fixed pad closer to the rotor and cleaning the disc rotor with white spirit.

I felt stronger on the bike today, so I think I have the right set up for me. It was a stress free ride inspite of encountering heavy traffic and horses.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

Some more rides have confirmed the confguration, so it's 11/34 at the back and 26/34/44 at the front. The 100" top gear is enough, I need a downward slope of 2% or more to spin out. Bottom on the middle ring is 25" which is nice for setting off.

I've handled quite a lot of tricky junctions and traffic and I don't get stressed. The one remainimg stress is standing up and getting off on a steep uphill slope because the straight riser conflicts with where you need to stand. A tilting stem would fix that but I'm not sure if that would be a good idea with the all carbon fork having a carbon steerer too.

Despite being very comfortable on it, I'm still not setting rafts of personal records . I am a little disappointed that I could not comfortably manage a 20"/700c wheel set-up. It handles perfectly well on the 16"/26" wheels and I think I've made the best tyre choices in those sizes but I suspect the 16" wheel does slow progress. We'll see. I'm looking forward to making comparisom with the Bella, though I'm still waiting on a custom fork for it.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

I dusted off the cobwebs and went for a spin on the P-38 in preparation for racing at Hillingdon with the BHPC on Sunday. I've managed to get a cheap MTB bashguard to cover the chainrings after much bending of the brackets into S-shapes to position the guard further outboard. My only notes additional to the previous post is how comfortable the sling seat is and how surprisingly laid back the riding position is when seated. I think that's because you end up being slumped like in a deck chair with your backside up against the forward rail of the seat base. I actually had to lift myself up a bit for a good look at Give Way junctions whilst rolling through. Also the riding position no longer feels "closed" now I'm running 150mm cranks.
yostumpy
Posts: 994
Joined: 29 Oct 2010, 6:56pm

Re: P-38 build

Post by yostumpy »

I didn’t make it to Hillingdon this year, was a bit ill the night before :( , but how did you get on with the P38, have you compared your time to that of previous laps on the other bikes? How did it feel, when giving it some beans.?
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

yostumpy wrote: 11 Apr 2023, 8:30am I didn’t make it to Hillingdon this year, was a bit ill the night before :( , but how did you get on with the P38, have you compared your time to that of previous laps on the other bikes? How did it feel, when giving it some beans.?
Sorry you couldn't make it. It was a good day. My times were marginally quicker even though I overheated in the second race and the gearing was too gappy. I was getting caught between 2 gear ratios a lot of the time. I could do with a race wheel with a cassette with closer ratios. It would be interesting to race the Rans with its 26/700 wheels for comparison.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

Photo from Hillingdon. Wheels are 349/559mm. I'm wondering whether putting a 406 on the front to recline the seat more would be beneficial in a race:
340477356_792179781829552_7367427748517387813_n.jpg
I have a Tifosi 9-speed 11-34 cassette on order which is less gappy for the middle gears than the current SRAM 11-34 one.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

The Tifosi 9-speed cassette is nice. Shifts well and I prefer the ratios to the PG-980.

I didn't make it to the BHPC race in Bath today. Feeling tired, it's a long way to drive on my own and I was put off by the forecast of rain although maybe it didn't amount to much. So I tried a 406 wheel on the front of the P-38. I had to realign the disk calliper because it's a different hub brand then went for a quick spin around the block. I liked the extra recline, however the handling was disadvantaged. The bike was tail heavy, too much weight at the back and the steering was too light despite the increase in trail. Shame I can't move the seat forward to compensate. I could put the seat more upright to improve the weight distribution, but as I said, I prefered having the seat more reclined.

Maybe this gives me motivation to get back to changing the seat on the Nazca.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

Had a ride on the RANS last night with its 26/700 wheels and my Strava average speed was 1 mph more than on the P-38. So big wheels appear to make a difference. With that in mind I'm inclined to raise the seat by 2cm on the P-38 to improve the handling and ride the 9-mile route with the 20" front wheel on it rather than the 349mm wheel.
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

Yesterday, I lengthened the seat stays by 1 cm to make the seat more upright. 2cm wasn't advisable because it put the front of the seat rail very close to the frame when I sat on it - the cantilevered seat bends remember. I also lubricated and adjusted the bearings in the 20" front wheel. I'm gradually doing this for all my Shimano hub wheels because from the factory they are always overtightened with insufficient grease.

Then I did my standard 9 mile ride. What a difference that 1 cm makes, the handling was fine. Lots of wheel flop yes, but the tail heavy effect had gone entirely. It felt a lot more planted with the bigger wheel, able to cope better with the damaged road surfaces. Maybe the increased trail helped. The only downside is the body position is a bit more closed again and the sling mesh seat felt strange because it was pressing on my back differently. I suspect that's the biggest problem and why I'm still slower than I'd hope for, the seat does not help with power delivery.

So the bike has gone from 406/622 to 349/559 to 406/559. As such it is slightly more tilted back than it was designed to be, but I really don't like 349 wheels. I hated them on the Brompton and I hated them on the Catrike Speed I had.

Some more photos, https://photos.app.goo.gl/7LJAXC63GxQCKRDbA
IMG_20230428_192218_HDR.jpg
UpWrong
Posts: 2409
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

I probably ought to bring this thread to a close. I did a longer, hillier 2 hour ride which confirmed my preference for the 20" front wheel. The ride was stable and the handling was perfectly acceptable although there is a slight tail-heaviness with the smaller rear wheel which has tilted the bike back. I was comfortable with the slightly more closed position having lengthened the stays by that 1 cm.

I think after owning a "souped-up" Giro 20/26, a Metabikes 20/26 and now the P-38, I have to accept that my power output is poor on SWBs with a BB slightly higher than the seat. I enjoy the riding position but the evidence is I produce more power when the BB is below seat level, which is why I am keen to progress the Bella.
Gee
Posts: 102
Joined: 24 Mar 2021, 10:11pm

Re: P-38 build

Post by Gee »

UpWrong wrote: 3 May 2023, 11:04am I probably ought to bring this thread to a close. I did a longer, hillier 2 hour ride which confirmed my preference for the 20" front wheel. The ride was stable and the handling was perfectly acceptable although there is a slight tail-heaviness with the smaller rear wheel which has tilted the bike back. I was comfortable with the slightly more closed position having lengthened the stays by that 1 cm.

I think after owning a "souped-up" Giro 20/26, a Metabikes 20/26 and now the P-38, I have to accept that my power output is poor on SWBs with a BB slightly higher than the seat. I enjoy the riding position but the evidence is I produce more power when the BB is below seat level, which is why I am keen to progress the Bella.
I’m following with great interest. I’ve a Giro 20 which is great. Other than it’s quite old and steel and a bit steady uphill. I’ve just naturally assumed a high racer and naturally higher BB would be faster. I’ll certainly be interested in your results with the Bella.

G
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