Sapim cx-ray and sprint on new wheel build

[Luca199]

Hi,

I'm getting a new Enve SES 5.6 disc handmade wheelset, with DT Swiss 180 exp hub straightpull centerlock (24 holes front and rear).

The suggestion is to have CX-ray spokes on the front and CX-sprint on the rear for more stiffness.

Body weight is 85kg, so between 350 and 500km a week, in and around London roads (Kent, Surrey, Essex and longer rides). Ftp 340 and I do put quite a bit of power through my bike (pinarello dogma f12 disc).

Do you think I should go with the cx sprint on the rear or stick to CX ray all over the wheelset?

In my view, the cx sprint would definitely add weight (not much, but roughly 30g) and likely make a harsher ride, based on what I've read online this far. Also the life of the spoke seems to be shorter on the sprint than on the ray. The key advantage of the sprint is that it should support my system weight better and help with power transfer/acceleration.

The rims of the Enve SES 5.6 are already quite deep (63mm rear and 54mm front), so not sure I'd need the cx sprint on top of that.. should I stay with CX ray on the rear, save some weight and potentially have a more comfortable ride?

Anyone has any experience with CX sprint in the rear and whether or not riding becomes more uncomfortable? The weight penalty is really small, so I'm just trying to understand if the benefits of the sprint outweigh the negatives (extra weight and ride comfort)..

Thanks!

[pdlpsher1]

The key advantage of the sprint is that it should support my system weight better and help with power transfer/acceleration.

This is exactly right. For your weight and power output I'd put the sprint on both sides. The CX-Ray would be definitely too light. I would even suggest 28 spokes but I'm not sure if can obtain the rim the hub in 28 hole drillings. If 28 holes is an option I'd opt for 28 CX-Rays than 24 CX-Sprints as it would be stronger and stiffer. Stiffer spokes and/or more spoke won't translate to ride harshness.

[MaxPower]

I could not feel any difference in comfort. 24 spoke builts on both wheels. I was 86kg at that time. I have every only broke cx-ray, the sprints have been fine throughout the years.
But I can't say for sure if this was do to the build or the spoke. I first started to rebuild my own wheels after I broke Ray spokes, so I dont know how good the build with the Ray spokes was before they starting breaking (nds).

Since then I retension new wheels when I get them.

[Luca199]

Thanks! I'll do ray front and sprint rear. Can't do 28 holes as it's Enve rims that come with 24h by default.

Thanks!

[NickyR]

I would go cx sprint front and rear (24/24) , not because of your weight, but because of the disc braking.
Ray or sprint will not affect the confort, that is the qty of spokes that will affect it.

[C36]

Sprint on the rear no doubt.

[Luca199]

I would go cx sprint front and rear (24/24) , not because of your weight, but because of the disc braking.
Ray or sprint will not affect the confort, that is the qty of spokes that will affect it.

Why sprint on the front too? Is it not adding too much weight for no return? What do you mean it's because of the disc braking? I didn't think the spoke weight/thickness would affect brake rubbing... is it not given more by thru axle in the hub rather than spokes?

[tjvirden]

I do think disc brakes have made wheelbuilding, and spoke selection in particular, a lot more tricky. For shallow rim-brake wheels, at 80Kg, I always used something heavier than a CX-Ray on the rear drive-side, but that was with 20 spokes, 10 each side. One of the disc-brake wheelsets I'm now using has a shallow alloy rim laced 24/24 with CX-Rays all round and that seems absolutely fine for my current 75Kg - no problems so far.

At 85Kg there's obviously less margin, but I think it should be fine with 50/60+ mm deep rims. On the other hand, the CX-Sprints will only add a tiny bit of weight (and aero drag!). Disc brakes do introduce extra "work" through the spokes, but CX-Rays should be able to handle that no problem, if the wheel is properly built.

[abatty]

Swapped out the CX Ray for CX Sprint on my rear as there was too much flex and a spoke broke after a year. Much improved now and no difference in ride quality. HED Belgium Plus Rims, WI T11 hubs 24F 28R, tubeless. 78kg.

[pdlpsher1]

I would go cx sprint front and rear (24/24) , not because of your weight, but because of the disc braking.
Ray or sprint will not affect the confort, that is the qty of spokes that will affect it.

Why sprint on the front too? Is it not adding too much weight for no return? What do you mean it's because of the disc braking? I didn't think the spoke weight/thickness would affect brake rubbing... is it not given more by thru axle in the hub rather than spokes?

On a rim brake all of the braking forces are put on the rim. On disk brake all of the braking forces are put on the spokes/hub. On the rear the braking forces can and will exceed your most powerful sprint. That's why you see low spoke count on rim brake wheels (typically 18 front, 24 rear) and a minimum of 24 on disk brakes on both wheels. The Sprints on the rear with help with flex, power transfer, and braking. The Sprints will help with braking. You won't notice it performance wise. Just for better spoke longevity.

[tjvirden]

Why sprint on the front too? Is it not adding too much weight for no return? What do you mean it's because of the disc braking? I didn't think the spoke weight/thickness would affect brake rubbing... is it not given more by thru axle in the hub rather than spokes?

On a rim brake all of the braking forces are put on the rim. On disk brake all of the braking forces are put on the spokes/hub. On the rear the braking forces can and will exceed your most powerful sprint. That's why you see low spoke count on rim brake wheels (typically 18 front, 24 rear) and a minimum of 24 on disk brakes on both wheels. The Sprints on the rear with help with flex, power transfer, and braking. The Sprints will help with braking. You won't notice it performance wise. Just for better spoke longevity.

Hmmm, I'm not sure about that match between rear braking and sprinting.

I'll say that they're different - peak force (torque through the hub) from pedalling will be much higher than peak force from rear braking, but brake force is continuous as the wheel rotates (not pulsing as from pedalling) and can continue for a long time if you're rolling downhill. Sprint power is strictly limited in duration of course. However, it's worth thinking about sustained climbing out of the saddle using a "small" chainring - even a 70Kg rider puts a peak of over 120Kgf into the chain tension every single pedal stroke and that can continue for a long time, so I don't see much difference needed in spokes for rear wheels - rim-brake or disc-brake.

[NovemberDave]

However, it's worth thinking about sustained climbing out of the saddle using a "small" chainring - even a 70Kg rider puts a peak of over 120Kgf into the chain tension every single pedal stroke and that can continue for a long time, so I don't see much difference needed in spokes for rear wheels - rim-brake or disc-brake.

This is true - the most torque a wheel is going to see is from small chainring/large cog combos. Alberto Contador was widely reputed to be pro cycling's most reliable wheel killer, all 64 kilos of him. The torque from one of his attacks, in say 39x23, up a steep hill, from a lull as the pure climbers often do, is way higher than a sprinter winding up from "really fast" to "really really fast" in 53x11.

Add to that that the flange geometry (bracing angles) on disc brake hubs is usually better than on rim brake hubs. Not a huge feature in terms of torque transmission, but a feature nonetheless in terms of overall wheel stability.

[Mr.Gib]

Regarding disc braking and the load on spokes, isn't the force on the spokes from deccelerating from 70 km/h to zero on a 10% downward slope in a set time the same as the force from accellerating from zero to 70 km/h up the same slope in that same time? Really asking, I'm not a physics guy, but the math seems logical to my old cheesy brain. And if so, when was the last time any cyclist accelerated from zero to 70km/h on a 10% slope - exactly never. Which suggests the braking forces will be massively greater than the accelerating forces.

And what's with all the reference to rear braking? I thought serious braking depended on the front. Or perhaps it was mentioned because that's where the acceleration forces are? We threw a guy out of our group who insisted that he would not use his front brake to stop. Guess he was afraid of spazzing out and going over the bars. Kept losing his rear end and crashing, enventually he fractured his femur in a single bike crash on a gentle curve so we don't have to worry about him anymore. Darwin would have something to say about this I'm sure

[tjvirden]

Regarding disc braking and the load on spokes, isn't the force on the spokes from deccelerating from 70 km/h to zero on a 10% downward slope in a set time the same as the force from accellerating from zero to 70 km/h up the same slope in that same time? Really asking, I'm not a physics guy, but the math seems logical to my old cheesy brain. And if so, when was the last time any cyclist accelerated from zero to 70km/h on a 10% slope - exactly never. Which suggests the braking forces will be massively greater than the accelerating forces.

And what's with all the reference to rear braking? I thought serious braking depended on the front. Or perhaps it was mentioned because that's where the acceleration forces are? We threw a guy out of our group who insisted that he would not use his front brake to stop. Guess he was afraid of spazzing out and going over the bars. Kept losing his rear end and crashing, enventually he fractured his femur in a single bike crash on a gentle curve so we don't have to worry about him anymore. Darwin would have something to say about this I'm sure

Yup, when grip is good (and fairly predictable) most braking should be at the front - amazing that you found someone refusing to use it. As he discovered, ignoring it has (entirely predictable) consequences. Maximum deceleration is around 0.5g from the front brake and only 0.2g from the rear on it's own, in straight lines on singles not tandems. That differential (0.5g v 0.2g) immediately tells you the difference in braking force front v rear. About 2.5x higher on the front.

Regarding load on spokes, you have to consider forces and how they arise, not just energy (work). Pedalling force (that leads to chain tension) fluctuates through the stroke, whereas brake force is continuous as the wheel rotates. Maximum force is not the same as average force. An unremarkable athletic rider of 70Kg can generate 180+Kgf maximum chain tension by a full gas acceleration in a small (34/36/39) chainring. The torque about the hub - and so force change in tangential spokes - depends on the sprocket size, but it ends up being a higher maximum torque than that from maximal front braking. As a practical example, the latest Roval Rapide's have only 12 spokes at the front sharing the braking load - they haven't guessed as to whether it works; they've calculated.

[Mr.Gib]

Great explanation, thanks.