A wheel aero question for an unusual (on here) situation (with a bunch of constraints)

Triathlon Forum
1

This is going to seem like a weird question for SlowTwitch, but I think you all have the right set of expertise to help me make a decision. Why is it weird? Because it’s about a tandem bike, not a tri bike. I’m asking here because I’ve been thinking of building up a new set of ‘unicorn’ wheels: fast/aero(ish), light(ish), and cheap(ish).

The TLDR version:
I’m trying to estimate how much aero benefit is there of a HED Jet 6 (Stallion) over a nicely profiled (~30mm deep, ~24mm wide) alloy rim? How much for each over a poorly profiled (~24mm deep, 18mm wide) alloy rim with 2.4mm round spokes (Spinergy)? Assume a 25c Continental GP5000 w/ latex tubes.

The long version:

Our Situation:
We are a pretty light tandem team (combined weight 260-265lbs) with a light bike (25lbs) doing quick (20-21mph average speed on our own, we don’t ride with groups usually) road riding on flat to rolling terrain. The bike is setup with road rim brakes and the rear hub is 145mm (common for tandems). None of that is going to change anytime soon. The current wheelset is a Spinergy TX2 (X-Aero lite version) which are ~18mm wide/24mm deep with 24 non-aero PBO spokes (i.e. big thick round spokes). This is setup with 25mm Continental GP5000 and usually latex tubes. We are generally rather gentle riders… I’ve never broken anything on a bike (aside from getting hit by a car once) in about 25 years of riding, and we’ve never broken anything on either tandem we’ve owned. Never even needed to true a wheel on the tandems so far!

The Choices:
Keep the current wheelset till it dies or upgrade to some handbuilt (by me) wider aero alloy rims or carbon/alloy rims (full carbon is tempting, but I really worry about stopping ability and heat dissipation with a total weight of 285-290 lbs). Rear hub options with low spoke counts (28 or 32 is low in the tandem world) are limited, but White Industries makes some and Hope or Royce might. I’ll go 28 spokes if I can on the rear and likely 24 (or 20) on the front with CX-Ray/CX-Sprint or Pillar 1420/1422.

I’ve looked at just about every rim I can find (see below for my list), but I’m just not sure how much I gain or lose aerodynamically between:

1) The current wheelset (i.e. not wide 18mm or aero at all, but “free”)
2) A wide-ish (23-25mm) aero/deep profile (25-42mm) alloy rim
***3) A wide and deep carbon/alloy rim (HED Jet 6 Stallion). ***
4) A carbon rim that would actually brake well and wouldn’t melt/. 25-27mm wide, 50-60mm deep (LightBicycle maybe?) Suggestions wanted!

I’m especially curious if the difference between #2 (~30mm deep, ~24mm wide alloy) and #3 (HED Jet 6) is worth the cost of buying the Jets plus a tandem rear hub and new spokes and nipples and rebuilding the rear. It would be at least $500 more than just building most of those alloy wheels.

Here is the options list if anyone wants to make specific comments/recommendations:

**Alloy (depth/width): **
Alex Rims GV30 (30/25) (note: I can’t find this available anywhere)
Astral (32/23)
Boyd Altamont (30/24)
DTswiss RR460 (23/23)
Easton (27/24)
HED Belgium (26/25)
Hunt (32/24)
Kinlin XR31 (31/24)
Pacenti Forza (25/24)
Prolite (42/24)
Velocity Quill (25.5/24.5)
Zipp 30 (26/25)

Carbon/Alloy:
HED Jet 6 (60/25)
AliExpress/eBay various manufacturers (50/23 or 60/23)

Thanks everyone!

2

I’ve no expertise on tandems, and I don’t know how to apply a judgement to speed vs money. Deeper wheels will generally be faster, but hard to usefully quantify.
I would simply say you should ditch option 4. There is no good reason to go with a carbon wheel. I wouldn’t advise anyone to buy fully carbon rims for a bike using rim brakes to be honest, they’re just silly. Carbon fibre is the wrong material for rim brakes. This would be more important for a tandem, where presumably you’re stopping more mass than the typical solo situation.

I currently use a set of wheels built with Kinlin XR31 rims on my road bike. I really like them. I think they’d be fine for a tandem of lighter folks. Not sure about a heavier pair. But I’m no expert on rim loading.
My tri bike is normally used with a pair of previous incarnation SwissSide Hadrons with alloy rims and carbon fairings. Not dissimilar to the HED Jet wheels, although the Jets are slightly wider and I think have grooved brake tracks for better braking. If you don’t mind paying more for some aerodynamic drag reduction, the HED Jets are the way I would go, again providing the loading isn’t excessive.

3

A tandems are demanding on the braking system and you can eat through rims pretty quickly. My personal experience with HED rims is that they do lack durability on the braking surface and I think this applies to a lot of modern light weight alloy rims. There is always a compromise and if you want great braking in light weight and (relatively) affordable package you make the brake surface thin to save weight and soft to allow good bite from the pads. This leaves you with an overall package that is prone to wear out.

Basically if you go down this road don’t expect a huge lifespan from the wheels. Actual life span is massively dependent on road conditions but these aren’t forever products. I got 2 CX seasons out of a some HED Ardennes Plus’ which are the same rims as the Belgium Plus. This wasn’t a lot of miles but under conditions that do eat bike parts.

4

Thanks for the feedback. While it is tempting to just go carbon, I do worry that the risk of catastrophic failure is just too high for the situation given the limited (?) benefits. I’ll keep the Kinlin on the list, especially as they are actually the same rim that is used by Hunt (and others?).

The HED Jet’s do seem like the ideal, but for the price.

5

None of that is going to change anytime soon.

Ever considered the “mullet” scenario of a mixed front/rear disc brake rim brake combo? Most braking is the front. Disc brakes on front only is a thing for budget gravel and cyclocross folks. As it is easy to convert a rim brake bike simply by changing the fork and one shifter.

Just a super random thought as that may open up options if braking heat isn’t as much an issue any longer.

6

Brake surface width is something I hadn’t considered. It seems like a tough compromise because thicker brake tracks should lead to smaller internal dimensions, which is bad (as far as I understand) for tire shape/handling. I’ll definitely look at it carefully though as having a long lasting wheelset (especially if it is expensive) would be nice. We fortunately ride almost entirely in the dry, so that helps a fair bit with rim lifespan.

7

None of that is going to change anytime soon.

Ever considered the “mullet” scenario of a mixed front/rear disc brake rim brake combo? Most braking is the front. Disc brakes on front only is a thing for budget gravel and cyclocross folks. As it is easy to convert a rim brake bike simply by changing the fork and one shifter.

Just a super random thought as that may open up options if braking heat isn’t as much an issue any longer.

I like the lateral thinking, but a mullet unfortunately is out of the cards for the current tandem… It has a non disk fork (custom painted to match the frame by Calfee) and a disk mount on the rear. So if I was going to change out the fork (I’m not), I would just go full disk F+R. But at that point I’m into the realm of multiple thousands of dollars for a full new groupset + fork + wheels. Given our riding conditions, rim braking has been flawless so far (with alloy rims).

8

Thanks for the feedback. While it is tempting to just go carbon, I do worry that the risk of catastrophic failure is just too high for the situation given the limited (?) benefits. I’ll keep the Kinlin on the list, especially as they are actually the same rim that is used by Hunt (and others?).

The HED Jet’s do seem like the ideal, but for the price.
The carbon option shouldn’t be tempting. That’s just groupthink… sort of.

Seriously, full carbon rims are more a solution to a marketing problem than an engineering one.
I think you can get the Kinlin XR31T rims drilled for 20, 24, 28 and 32 spokes in either symmetrical or offset, so it may be up to the job, but I’d consult someone more experienced as to suitability for your total riding weight.

9

I think you can get the Kinlin XR31T rims drilled for 20, 24, 28 and 32 spokes in either symmetrical or offset, so it may be up to the job, but I’d consult someone more experienced as to suitability for your total riding weight.

I think while I was making my list I tried to limit it to rims that I’ve seen with 28h or more. As for the team weight, the Kinlin is one I would trust a bit more since it is used by Hunt for their Superdura wheel set which is rated for heavy riders. We are heavy (when combined compared to a single rider), but I ride quite carefully, and since I can unweight the front wheel quickly, and my stoker is lighter (120-125), even the rear doesn’t take too much abuse. We are much better at spinning than creating huge torque, so the loads on the wheels aren’t too extreme.

I guess now the question is whether a nice alloy rim and aero spokes are a big upgrade over our current setup.

10

The difference will be about 5 watts. I.e., unless this is for time trial races that matter I just can’t see it being worth it. And in that case you should do more like a Jet9+ anyway.

11

I suggest that you search for a group “Tandems @ Hobbs” or something close to that. They are a new list group that has been around for a long time. They can help as it pertains to tandem specific questions. I was a member for a long time. I know they recently changed their server location.

Having said that…as a tandem captain. I would caution against going too light. If a single wheel fails, you only injure yourself. Tandems not so much.

Are you expecting to get much more benefit as compared to the current Rolf offerings of tandem wheetsets?

12

So if I was going to change out the fork (I’m not), I would just go full disk F+R. But at that point I’m into the realm of multiple thousands of dollars for a full new groupset + fork + wheels.

Cable-actuated disc brakes would save you having to make any changes to the groupset - other than the calipers themselves. That would still leave you with the issue of the custom painted fork.

13

I suggest that you search for a group “Tandems @ Hobbs” or something close to that. They are a new list group that has been around for a long time. They can help as it pertains to tandem specific questions. I was a member for a long time. I know they recently changed their server location.

Having said that…as a tandem captain. I would caution against going too light. If a single wheel fails, you only injure yourself. Tandems not so much.

Are you expecting to get much more benefit as compared to the current Rolf offerings of tandem wheetsets?

I’ve actually already asked it on a tandem forum (BikeForums), but didn’t get much valuable feedback because the knowledge base is less about aerodynamics and except for a few teams, not usually about riding fast. We are also on the low end of team weights, and so got a lot of feedback about wheel strength rather than the balance of strength/aero that I was looking for feedback on.

I’ve looked at the Rolf’s and newer Spinergy. I’m reluctant to just go with a new Spinergy because I’m not sure that making bladed PBO spokes (what they use now) really fixes the issue of having huge wide spokes spinning through the air. Rolf’s wheels are rather expensive for what they are. The rims are clearly the same as the Astral Radiant/Leviathan since Astral is Rolf’s own rim brand for people who don’t want paired spokes. I actually think the paired spoke idea, especially for tandems, is a negative rather than a positive, so I’d be able to build a better and cheaper wheelset that was just as aero, light, etc by buying Astral rims and doing it myself.

Obviously the alloy rim options aren’t going to be dramatically better than current Rolf wheels (but won’t cost $1200 hopefully). I do think and hope they’ll be significantly better than my current narrow/round spoked Spinergy’s.

14

Cable-actuated disc brakes would save you having to make any changes to the groupset - other than the calipers themselves. That would still leave you with the issue of the custom painted fork.

I’ve heard mixed reviews of cable actuated discs on tandems (although I’ll admit I haven’t followed them much since I’ve never had problems with rim brakes). Even without painting the fork, this would still be a rather expensive way to go: ~$400-500 for a fork, ~$300 for brakes, and then I still need wheels which won’t really be any more affordable. Given the inherent aerodynamic disadvantages of discs, I’m not really seeing what I would gain here other than the option to run full carbon rims. I think just buying and rebuilding the HED Jet’s would be cheaper, faster, and easier for now. Perhaps when I eventually get a new tandem (which is not in the financial cards for a long, long time!) I’ll switch to discs.

As I said at the outset, my situation has a bunch of constraints!