Weight Weenies

Hi, currently running a set of farsport 50mm gravel wheels. I really like the wheels and they feel fast my only issue iv had lately is on the downhills when I get around 44mph I start to get a speed wobble, I think it's the wheels catching the wind. As it's quite hilly and nearly always windy iv been considering dropping the rims to something around the 40mm mark to see if that improves stability.
If I do go this route do you think it'd best best to order a new set of rims then try and sell my current ones or do I keep my DT240 hubs and just get the rims and have them rebuilt locally? I don't know if that would end up being more work and not really saving much.
Or do I look to just get a new front wheel only? Not sure how that would be with 2 different profiles.
I usually run 28mm tyres and have been looking at the lightbicycle WR40 or AR35, or farsport revo 42. Any feedback on the LB Xflow rims do they have better stability than a straight standard rim?

How wide is your rim? IME front wheel becomes unstable when front tire is wider than rim, so running 25c tire front might improve stability.

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yingyu wrote: ↑

Wed May 31, 2023 12:34 am

How wide is your rim? IME front wheel becomes unstable when front tire is wider than rim, so running 25c tire front might improve stability.

Current rim is 30mm and the 28c tyres measure at the moment 30mm on the front and 31mm on the rear. I wouldn't go any smaller I'm 90kg and the roads here aren't great

before you buy another set of wheels, try a different front wheel in the same riding conditions and do back to back tests just to eliminate any random variables. If only your current front causes the shimmy, I'd look very closely at the tire to make sure there are no inconsistencies in the casing/tread, and then perhaps balance the wheel with a small stick on weight to see if that eliminates the problem. There's nothing to suggest your current front wheel is a bad combination/depth, and I've ridden deeper rims that don't cause any problems.

(To avoid XY problem) While speed wobble can be triggered by wind, from what I've read it's usually a frame stiffness issue. Some larger frames can be underbuilt. Maybe share your bike configuration? You can try clamping knees to the top tube to disturb the oscillation.

I had the issue on previous bike. I am now riding a Supersix evo and whilst it is more stable once it gets close to 45mph it only takes a little a nudge and and the speed wobble starts. I just thought a shallower wheel would only be better really

I see viewtopic.php?f=132&t=152443&p=1807957#p1807955 answers some of your wheel questions. You can also check the old speed wobble thread: viewtopic.php?f=3&t=165797.

yingyu wrote: ↑

Thu Jun 01, 2023 1:02 am

I see viewtopic.php?f=132&t=152443&p=1807957#p1807955 answers some of your wheel questions. You can also check the old speed wobble thread: viewtopic.php?f=3&t=165797.

Thanks I am reading through that thread, I think my issue is just a mixture of speed road surface and winds. As I don't get it all the time other days I can hold 40+mph fine I think it's living in a hilly area by the coast that if I get a gust on the downhills it grabs the wheels quite hard

I think what you are experiencing is just a basic rudder effect rather than a true resonant speed wobble. I don’t think a wheel change without a change in depth is going to do much.

TobinHatesYou wrote: ↑

Thu Jun 01, 2023 8:07 pm

I think what you are experiencing is just a basic rudder effect rather than a true resonant speed wobble. I don’t think a wheel change without a change in depth is going to do much.

That's what I think it is to be honest. Tempted to order a 40mm front wheel from lb but may look a bit silly with the xflow shape on the front and a normal rear. The Farsport revo is quite a bit cheaper for a 42cm not sure how much that would benefit. The shapes does look slightly different though, am I right in thinking the more bulbous blunt shape would handle better?
Current rim Possible 42cm rim This is the other option to swap out the front, I'm guessing this would suit my 28c tyres a little better than the above rims being 32mm wide vs 30. However I haven't seen much feedback on these and can't see any other manufacturer that has this a similar profile, others seem to have waves raising and lowering the rim height not the the width

I ride these wr40s laced up to a set of erase hubs in 28h front and rear. Brilliant wheelset.
Nearly no steering input in windy conditions, super nice transition with vittoria corsa control in 28mm (measure 30.something after a few 100km).

Aesch wrote: ↑

Fri Jun 02, 2023 6:56 pm

I ride these wr40s laced up to a set of erase hubs in 28h front and rear. Brilliant wheelset.
Nearly no steering input in windy conditions, super nice transition with vittoria corsa control in 28mm (measure 30.something after a few 100km).

Good to know that's what I'm after something a bit nicer for crosswinds. Just haven't seen any feedback on the xflow and nearly all the photos on their website show them on gravel bikes

Just been for another ride and I'm pretty certain my issue is just wind related, I don't have many flat straight bits of road it's constantly up and down and never straight for any length of time. Today was just a 13mph wind with 25mph gusts and when they were side on I could feeling it tugging the front of the bike quite a lot. Think I will deffo try a shallower front rim, do you think there be a noticeable benefit with the farsport 42mm rim? I know it's only 8mm but am I right in thinking that's quite a bit of surface area to loose across the whole wheel. I think this is winning for me as the profile is the same as my current wheels and looking at the rough drawings above it seems to be a bit blunter in shape. Also it works out about 150$ dollars less than the lightbicycle wheel. Although the lightbicycle is 2mm shallower again I'm not sure if I could cope with having a xflow rim on the front and a standard shape rear may look to odd, plus not sure how convinced I am with the rim shape.
Any feedback on whether dropping 8-10mm would bring a noticeable benefit in crosswinds

Rim + tire profile would have a bigger impact on stability than 8mm depth change. External rim width 32mm seems like a good fit for 28c tire that measures 30mm.

Honestly I think wind stability is a premium feature that takes additional R&D, so unsurprisingly it's a gamble to order from FS or LB compared with established brands like Enve, Zipp, Bontrager.

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Question:

Do you have enough weight over the front wheel? If your stem is quite short and/or stack high, and perhaps your saddle quite far back then you are looking at another possible cause of a twitchy front end when descending in windy conditions.

When I changed the stem on my Propel from 90mm to 110mm and moved the saddle forward a bit the bike became a lot less twitchy in general and less prone to crosswinds descending at high speed in particular.

If this is the root cause of the issue then a shallower front wheel won't help.