# 38mm, 50mm, 58mm, 85mm rims..???



## hxman (Feb 20, 2011)

I am in the market for a new set of rims with PowerTaps G3 hub for a Madone 3.1. I have a question about the correct rim size (going with tubular rims of some sort alloy or carbon for training). What would one recommend in terms of rim size 38mm, 50mm, 58mm, 85mm???? What is the difference when going to a larger rim???

Thanks for the help....


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## cxwrench (Nov 9, 2004)

theoretically the deeper section the rim has, the 'faster' it is...the rim isn't 'larger', it's deeper in section.


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## hxman (Feb 20, 2011)

Ah thanks, that makes sense.... Are the deeper rim sizes more durable, stiffer???? What is the benefit for example of going from a 38mm to a 50mm rim other than the $25 difference in price? I am also between 175lbs - 180lbs......


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## Len J (Jan 28, 2004)

The tradeoff is aero vs stability on crosswinds.

Deeper rims are more Aero, but they are more effected by crosswinds, especially the front. Many will pair a very deep rear with a not so deep front.

Len


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## spade2you (May 12, 2009)

Are you going to be training with this, racing with this, or both?


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## Zen Cyclery (Mar 10, 2009)

hxman said:


> Ah thanks, that makes sense.... Are the deeper rim sizes more durable, stiffer???? What is the benefit for example of going from a 38mm to a 50mm rim other than the $25 difference in price? I am also between 175lbs - 180lbs......


Deeper rims will have a few marked advantages and disadvantages. On the plus side, it will be easier to maintain average speeds particularly in headwinds. The two downsides to this scenario though is that a deeper rim will not accelerate as efficiently as one that is a bit shallower. This will more than likely be quite noticeable in the 30-50mm range jump. 
Now for the shallow rim. Accelerations will be more lively and it will feel as if it is easier to get up to your average speed. However, on a shallower rim maintaining that speed will more than likely take some more work. 
When it's all said and done, it really depends on what type of conditions you ride. If you are a climber, I would absolutely advise to go no deeper than 50mm. If you live somewhere pancake flat and windy as hell (ie S.E. Wyoming) then a bit deeper wheelset may be a better way to go for you. 
Concerning your question about durability, it really depends on the product you are talking about. Assuming all is the same, the 50mm rim will be a bit more rigid and durable.


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## asgelle (Apr 21, 2003)

Zen Cyclery said:


> Deeper rims will have a few marked advantages and disadvantages. On the plus side, it will be easier to maintain average speeds particularly in headwinds. The two downsides to this scenario though is that a deeper rim will not accelerate as efficiently as one that is a bit shallower. This will more than likely be quite noticeable in the 30-50mm range jump.


The trouble with this is that while true words like "easier" and "not as efficiently" are so vague as to give no guidance. The question is whether the advantage from decreased aero drag is greater or less than the disadvantage from the greater weight? Of course, this depends on the specifics, but generally, the aero advantage is many times greater than the weight disadvantage. For example, a 50% decrease in front wheel drag reduces the power required by 1.8%. Wheel Performance While reducing wheel inertia by 50% (which affects acceleration) reduces power by 0.019%. In other words, the acceleration effect is 100 times smaller than the drag benefit.


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## Simonwillis (Sep 4, 2011)

*Need desperate help*

Hello im new to this forum and it wont let me write a new thread yet, so dont get mad. i need forks for my falcon olympic bike but i dont know what size my tyres say 28-622 (700x28c) please someone tell me what size these wheels are so i can find some forks on ebay 
THANK YOU SO MUCH!


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## T0mi (Mar 2, 2011)

hxman said:


> I am in the market for a new set of rims with PowerTaps G3 hub for a Madone 3.1. I have a question about the correct rim size (going with tubular rims of some sort alloy or carbon for training). What would one recommend in terms of rim size 38mm, 50mm, 58mm, 85mm???? What is the difference when going to a larger rim???
> 
> Thanks for the help....


The deeper you go:
-weight increase
-supposedly more aero
-more rigidity
-more inertia
-more sensible to cross winds

38mm wheels is a good compromise if you climb regularly. You can't really go wrong with carbon 38mm profile wheels. They are just better than anything aluminium except braking. And you will never really suffer on crosswind. 

If you do mostly flat rides, 50 to 60mm could be more appropriate but if you are in a windy area, I would suggest a compromise with a 38mm front and 50mm rear.

80 to 90mm profile are only really usefull for steady pace without too much accelerations, Time trials or triathlon.

I have a 1.2kg 38mm carbon tubular wheelset on my road bike and I love it. Those wheels are good everywhere. I also have a 88mm profile tubular wheelset on my track bike and when I use it on the road, I tend to use the front 38mm road wheel when I'm unsure of the wind. 

Don't go with aluminium. They are boat anchors. I still have a Campagnolo Shamal wheelset of 1997 and the rim are 41mm profile. The wheelset weight around 1.8kg. That was good 15 years ago but compared to my current carbon wheelset they are just heavy. And they are the lightest you can find on aero aluminium wheels. I still love them and use them sometimes but only when the ride is flat. I just love how they sound.


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## Mike T. (Feb 3, 2004)

hxman said:


> Are the deeper rim sizes more durable, stiffer? What is the benefit for example of going from a 38mm to a 50mm rim


Be very wary of hype and unreasonable expectations. I have two "extremes" of wheelsets - a 24mm deep 1410 gram set with aluminum rims and a 50mm deep 1579g set with carbon rims. While the lighter wheels feel a bit nipper in accelerations when I first put them on, neither wheelset allows me to step outside of the 2mph natural variation of my solo training ride average speeds (well documented) with the variations due to conditioning, feel, motivation, weather, route, ride type. If I graphed my speeds with both wheelsets, neither one would be outside of the range of the other. Will the deeper rim be faster? Probably, given exactly the same conditions, (which never happens) but it doesn't make me into a time-trialing menace. Sadly, I'm 2.5mph slower than I was 30 years ago on 36 spoke box section tubular rims.

Where the major difference lies is with crosswinds. The 50mm deep set are much more susceptible to crosswinds, especially on 30+ mph (50+kph) downhills (I can't do 50kph on the flat). If that crosswind is interrupted by a passing vehicle it gets really hairy. The two times it's happened recently I swerved about 1/2 the width of the lane I was in. I contacted the builder just yesterday about a matching shallower rim front wheel and I util I resolve the issue I'll keep away from the hill in question or I'll swap wheels.

I think the deeper rim will be stiffer (everything else being equal) and this should allow for lesser spokes while still keeping the same wheel strength. That's just IMO.

My carbon rims are Gigantex that sell roughly in the $200-300 range per rim. I have no knowledge of whether $800+ carbon rims will give the same results as my findings.


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## hxman (Feb 20, 2011)

I thank everyone for their input........ I was thinking about 2 options:
1) 38mm carbon tubulars
or
2) 38mm front and 50mm rear carbon tubulars


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## Mike T. (Feb 3, 2004)

hxman said:


> I thank everyone for their input........ I was thinking about 2 options:
> 1) 38mm carbon tubulars
> or
> 2) 38mm front and 50mm rear carbon tubulars


If I had that decision I'd base it on 3 criteria -
1) Visual.
2) Availability.
3) Price.

Any performance difference, IMO and with my findings, would be limited to crosswind effects. I'll be going with 38/50 if I can get a front 38mm wheel.


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## hxman (Feb 20, 2011)

Mike T. said:


> If I had that decision I'd base it on 3 criteria -
> I'll be going with 38/50 if I can get a front 38mm wheel.


I do believe Boyd sells 38mm front carbons....


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## Mike T. (Feb 3, 2004)

hxman said:


> I do believe Boyd sells 38mm front carbons....


I'll be getting it from the original supplier of my wheels if they have 38mm.


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## Chiodos48 (Mar 22, 2011)

I think the Easton EC90 Aero's are a fantastic tubular. Fairly light, relatively inexpensive, and a very solid wheel!


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## fastmb (Oct 5, 2008)

you need a set of road forks 700c. but the real issue you will need to figure out is the headset size. go to your lbs to get help in sorting that out. good luck


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## Simonwillis (Sep 4, 2011)

Oh I have some knowledge on bikes, my stem is a 22.2 and my headset is 1 inch threaded, thanks for the help, so I need 700c forks but I don't know how to measure the sizes up to make sure the brake touches the rim correctly.. Is there only a few different sizes option for this? Appreciate the help


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