P-38 build

DIscuss anything relating to non-standard cycles and their equipment.
UpWrong
Posts: 2401
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

I laced up the front wheel yesterday whilst watching the TdF. I think the spokes are too long. I ran all the nipples down so no spoke thread is exposed and the nipples are not yet seated by a long way. I checked the dimensions again on 3 spoke calculators and I think it's a rounding up issue. The spokes are only available from SJS in 2mm increments and I rounded up. I'm haunted by my first 406 rim build where the spokes were too short and I finished up with exposed threads all the way round.

I decided to abandon and order some shorter spokes for the left side (with the disc) and then move the existing left spokes to the right side of the wheel in effect going down by 2mm on both sides. Yes, I do know the advice is to get the rim and the hub and to measure them before ordering the spokes but this combination of rim and hub is so common that I'd rather trust the spoke calculator databases, particularly when they agree.

If I have the energy I shall try lacing the rear wheel today.
Blondie
Posts: 239
Joined: 23 May 2021, 5:11pm

Re: P-38 build

Post by Blondie »

Daft question and I’m sure you haven’t made this mistake. But have you got the spoke crossings correct? The number of crossings affecting the length spoke you need. If you’ve gone 2x would 3x solve your longer spoke problem?
UpWrong
Posts: 2401
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

That's a good thought, but they'd need to be much longer for 3x, I'm building 2x. I didn't start the rear wheel today, went out for a ride on my Origami instead.
Blondie
Posts: 239
Joined: 23 May 2021, 5:11pm

Re: P-38 build

Post by Blondie »

UpWrong wrote: 4 Jul 2021, 6:02pm That's a good thought, but they'd need to be much longer for 3x, I'm building 2x. I didn't start the rear wheel today, went out for a ride on my Origami instead.
Can’t remember whether I built my 406 front as 2x or 3x. The smaller wheels are inherently stronger but I still built it 36 spoke. Spare spokes built into wheel rather than carrying spares on my audaxes or other long rides. I do like reliability
UpWrong
Posts: 2401
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

I'm comfortable with 32 spoke 2x on a 406 rims. Find it much easier to build than 3x. On the rear I have gone with 32 spoke but 3x. i was intending to have 36 spokes on the rear, but it's not an option on the DT Swiss R460.
UpWrong
Posts: 2401
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

The frameset is due for delivery tomorrow :D .

I've built the rear wheel ok. Hub is XT, rim is DT Swiss R460, 32 spokes 3x, PG DS, DB NDS. Weight with rim tape, no Q/R is 1140g. The build wasn't the easiest, I was struggling to get it and keep it radially true. Also the rim is too deep to place the nipples by hand. It's a light rim, but it has no eyelets.
R460-1024x1024.jpg
UpWrong
Posts: 2401
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

It's here!

Post by UpWrong »

It arrived today, all nicely packaged up. Seems to be all present and correct. It may be a while before it's built, I've got other projects on the go. I'm impressed with the brazing, the cable runs, the pump peg and the metallic blue finish. Not so sure about the foam for the seat base, looks like a big sponge for the rain. I might try some open cell foam instead. The carbon fork is very light. To be honest, the frame feels heavier than I was expecting though I haven't weighed it. EDIT: the bathroom scales suggest 6.5lbs.
My_P38A.jpg
My_P38B.jpg
belgiangoth
Posts: 1657
Joined: 29 Mar 2007, 4:10pm

Re: P-38 build

Post by belgiangoth »

Oooooooh!
If I had a baby elephant, I would put it on a recumbent trike so that it would become invisible.
Blondie
Posts: 239
Joined: 23 May 2021, 5:11pm

Re: P-38 build

Post by Blondie »

I see they’ve changed the return chain idler to a short section of chain tube, below where the seat mounts. Lovely blue colour.
Blondie
Posts: 239
Joined: 23 May 2021, 5:11pm

Re: It's here!

Post by Blondie »

UpWrong wrote: 12 Jul 2021, 7:24pm It arrived today, all nicely packaged up. Seems to be all present and correct. It may be a while before it's built, I've got other projects on the go. I'm impressed with the brazing, the cable runs, the pump peg and the metallic blue finish. Not so sure about the foam for the seat base, looks like a big sponge for the rain. I might try some open cell foam instead. The carbon fork is very light. To be honest, the frame feels heavier than I was expecting though I haven't weighed it. EDIT: the bathroom scales suggest 6.5lbs.
My_P38A.jpg
My_P38B.jpg
About a couple of pounds more than a steel diamond frame. A couple of water bottles worth of weight. Most of us carry more than that in excess body fat.
belgiangoth
Posts: 1657
Joined: 29 Mar 2007, 4:10pm

Re: P-38 build

Post by belgiangoth »

Some of us don't, and don't carry two full waterbottles.
Don't get me wrong, I think a weight that approaches a DF is excellent for a laidback and will happily admit that weight isn't everything. But weight is significant when climbing and when manhandling the bike about and I'm so very tired of people dismissing it.
I think we can say that's a good low weight.
If I had a baby elephant, I would put it on a recumbent trike so that it would become invisible.
UpWrong
Posts: 2401
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

I might create a build sheet with all the weights which is what I did for my Stratus XP. I only have kitchen scales and bathroom scale so some items are tricky to weigh accurately. Not sure I can be bothered although the initial build of the XP is interesting reading and it came in at around 13.2Kg, but then mudguards and a rack get added. Later I changed to a heavier seat and heavier tyres. It's probably a bit above 16Kg now.
nobrakes
Posts: 77
Joined: 9 Jan 2020, 10:17am

Re: P-38 build

Post by nobrakes »

belgiangoth wrote: 13 Jul 2021, 9:31pm Some of us don't, and don't carry two full waterbottles.
Don't get me wrong, I think a weight that approaches a DF is excellent for a laidback and will happily admit that weight isn't everything. But weight is significant when climbing and when manhandling the bike about and I'm so very tired of people dismissing it.
I think we can say that's a good low weight.
The hilliest loop I ride is an average of 100ft / mile ascent over 90 minutes. Adding 2kg of weight would make less than a minute's difference for me on a theoretical P-38 config with a CdA of 0.25, bike weight 13 KG, me in full kit 79 KG.

Image

Adding 2 KG:

Image

But I agree that handling recumbents on a loop like this requires some skill. I crashed the M5 a few times due to heel strike on the Talla Wall which has kickers up to 25% when I was still learning the ropes on that bike.

I personally would be more concerned about getting the right bike that allows me to ride comfortably on steep hills and let the weight take care of itself unless I was racing. I think the P-38 will be a fine bike for such climbs.
Blondie
Posts: 239
Joined: 23 May 2021, 5:11pm

Re: P-38 build

Post by Blondie »

Be interesting to see what weight your build ends up. But as you also understand, a couple of pounds doesn’t make that much difference in the end especially compared to overall weight.
UpWrong
Posts: 2401
Joined: 31 May 2009, 12:16pm
Location: Portsmouth, Hampshire

Re: P-38 build

Post by UpWrong »

Nobrakes, that's an interesting analysis of the effect of a couple of kilos of weight. I think I said up-thread that my hope with the P-38 is that I'll be able to climb better with it than on my existing 'bents.

I've finished building the front wheel: Deore hub, CR18 rim, 32 spokes, PG, 2x, weight 800g without QR. I was surprised that it's 340g lighter than the rear wheel even with a heavier hub, rim construction and spoke construction.
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