Commencal Supreme V4.2 or the dilemma of bike sizing

Mo(n)arch said:

And the complete geo chart:

I am wondering why companies are building enduro bikes with a reach above 480mm but still aren't able to adapt these geo numbers to the DH-bikes. Both bikes are meant to be fast down the hill.

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Hmmm, maybe because of 1300 mm wheelbase at 63° head angle and 480 mm reach?

Problem might be that by only increasing the front's length weight distribution will suffer and so will turning performance - understeer incoming. My guess is, It is not that easy. Punkybikey had an feature on GM's XXL V10 giving some insight. But I also think what works for GM will not work for >95 % of us peasant DH folk, even if as tall as him.

Edit: forgot to copy the link somehow http://www.pinkbike.com/news/behind-the-bike-developing-the-xxl-santa-cruz-v10-2016.html

Mo(n)arch said:

I understand your (valid) point, but considering my point of view of having ridden only DH bikes that were actually too small, I really want a longer front end to get more "into" the bike. Flo33's example is quite good. GM mentioned in an interview that he is still as stoked as ever for racing. One reason for this is, that he finally has a bike that fits him correctly.
FWIW, this isn't about your average 1,73m to 1,78m human being, but more for people in the 1,85m to 2,00m range.
That's why I took the new Commencal as example. Reach 425mm for an XL? I mean come on!


There are plenty of options for the average height of riders on the market. Hell, the industry even recognised that it makes sense not to alter the seat tube height through the sizing range of a DH bike as one rider prefers another bike size then the other one.

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425mm reach is for the current model, they have acknowledged the problem and revised this and it is now 455mm for the the V4.2

https://dirtmountainbike.com/bike-reviews/downhill-bikes/matter-fit-nicolai-g19.html

Interesting thoughts about sizing. There is some advice why enduro bikes reach should be longer than dh-bikes reach.

I think alot of it comes down to rider preference, and what each individual rider feels most comfortable on. With all these new bikes with longer and longer reach measurements it can be difficult as a consumer to figure out whats best for them. You have guys like Remi Thirion running a medium frame. Makes you think that for a normal size guy maybe a more conventional reach number/ frame size is better for some people. Rather than trending with the next size up?

The term XL means 'Extra' large. Being 6'7", I personally don't consider a 6' person XL, but most XL's I've come across belong to 5'10-6' riders.

My DH is a XXL V10 which is really an XL........

it's still too small, Im going to try a 60mm stem and Works reach adjust headset and get ~17mm more reach out of the deal (492mm vs 475)

Huck Banzai said:

The term XL means 'Extra' large. Being 6'7", I personally don't consider a 6' person XL, but most XL's I've come across belong to 5'10-6' riders.

My DH is a XXL V10 which is really an XL........

it's still too small, Im going to try a 60mm stem and Works reach adjust headset and get ~17mm more reach out of the deal (492mm vs 475)

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Random q from a 6'2'' human (who has a hard time finding bikes big enough)-

I wear xl in all clothes. L is skin tight and sleeves/inseam way too short. Do you wear normal xl clothes, or big and tall? I have always assumed that the sizing in bikes was designed to match clothes...?

Huck Banzai said:

The term XL means 'Extra' large. Being 6'7", I personally don't consider a 6' person XL, but most XL's I've come across belong to 5'10-6' riders.

My DH is a XXL V10 which is really an XL........

it's still too small, Im going to try a 60mm stem and Works reach adjust headset and get ~17mm more reach out of the deal (492mm vs 475)

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Just get a GG custom length something 1-2" longer than your SC is now.

Mo(n)arch said:

I am wondering why companies are building enduro bikes

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Here is your problem

Enduro is shit

By all means buy a size smaller than #Fashionable enduro bike and ride it like a DH bike tho

marshalolson said:

Random q from a 6'2'' human (who has a hard time finding bikes big enough)-

I wear xl in all clothes. L is skin tight and sleeves/inseam way too short. Do you wear normal xl clothes, or big and tall? I have always assumed that the sizing in bikes was designed to match clothes...?

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Clothes are sized by bulk diameter rather than length. Eg XXL jackets and shirts are often 1" longer in the sleeve, 12+" larger in the waist than a L. Ive worn XXL that barely reaches my waist. That sizing is covered with spring rate on bikes.....

I wear L Tall or XL Tall depending on fit, but Im only 215 @ 6'7"

You're misusing the reach measurement.

1. You can't compare reach 1:1 between enduro and DH bikes, Flo nailed the reason in his first reply. If you built a DH bike based on a modern enduro bike's reach measurement, you would have a wheelbase that was way too long for most riding people do in the world. Of course DH can afford slightly longer wheelbases, but *not* a directly proportional wheelbase gain - this is why manufacturers split the difference.

2. Physical fit on a bike is a function of reach and stack together (assuming consistent bar setup), not reach alone - take the hypotenuse measurement if you want to compare fit directly, but see point 3 - since static physical fit is not the only factor in correct mtb sizing.

3. The "narrow sweet spot" issue is primarily a function of wheelbase, not reach. This is because the feeling comes as a result of the relationship between combined rider/vehicle CoM (y-axis value) and the pitch angle range of the vehicle. CoM height is primarily a function of stack, and maximum pitch angle is a function of wheelbase, so the reach measurement plays very little part in the physics of this scenario. This is important to know, because you can maximise the WB value with variables you might have flexibility in such as slackening the HA, lengthening the CS, or running a larger offset modern fork - all these things increase WB even though they have zero impact on reach.

Basically - if you have a correctly fitting enduro and DH bike for yourself (which most people don't - myself included), the DH bike would have a slightly longer wheelbase AND a slightly shorter reach measurement (assuming stack was left unchanged) for most riding globally.

I think the part you might be missing is that Europe (esp. PDS area) does have very generous minimum corner radii - so in your specific case (tall guy living in CH) yes it is possible to get away with a longer than average wheelbase - probably even the "direct proportional" result of keeping the reach the same as an Enduro bike - but this doesn't apply as the optimal solution for the majority of riding worldwide - therefore bike design should not be like this either.

Anyway, bikes are getting longer at an alarming rate so you should already have a number of options - and if not - you probably will soon with the advent of 29" and yet another resultant increase in wheelbase lengths. The Commencal is a fringe case (the sizing runs abnormally small, no other brand I know of is that bad). Not every bike fits every person, ruling out options based purely on sizing is something everyone has to do at any height.

As Sandwich has illustrated, being a very common height of 5'11 - 6'1 has left people torn between medium and large in most brands for years now, so while it may sound harsh, this problem isn't exclusive to you. It just means you have to rule out some options, and make the most of reach adjusting headsets + other geometry tweaks - just like everyone else.

Udi said:

the pitch angle range of the vehicle

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To clarify some language limitations I have here. Is the pitch angle range you are mentioning from when the CoM is vertically above the rear point of contact with the ground while climbing to when the CoM is vertically above the front contact point while descending?

Happymtb.fr said:

To clarify some language limitations I have here. Is the pitch angle range you are mentioning from when the CoM is vertically above the rear point of contact with the ground while climbing to when the CoM is vertically above the front contact point while descending?

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By pitch angle range I meant the range of pitch angles that the bike would experience over a downhill run. With a longer wheelbase, encountering a rise or fall under a single wheel while riding will cause a smaller change in the angle of the vehicle. Less change = less compensation required from the rider. This relationship is the same while climbing.

The contact points individually are not important, the distance between them (WB) is.

CoM y-value is the most important for calculating load transfer and pitching moments under acceleration and braking (coupled with WB), CoM x-value is less important since it's modulated by rider movement in response to load transfers. For the purposes of this thread you might be overcomplicating things, but if you have a specific question feel free to ask.

Udi said:

By pitch angle range I meant the range of pitch angles that the bike would experience over a downhill run. With a longer wheelbase, encountering a rise or fall under a single wheel while riding will cause a smaller change in the angle of the vehicle. Less change = less compensation required from the rider. This relationship is the same while climbing.

The contact points individually are not important, the distance between them (WB) is.

CoM y-value is the most important for calculating load transfer and pitching moments under acceleration and braking (coupled with WB), CoM x-value is less important since it's modulated by rider movement in response to load transfers. For the purposes of this thread you might be overcomplicating things, but if you have a specific question feel free to ask.

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No specific question, but thanks! I am just unfamiliar with the term pitch angle and wanted to make sure I understood correctly. This has apparently do to with vehicle dynamics which is a topic I didn't even scratch the surface of...
It could be interesting for me to learn more about it later so if you can recommend a good book, I would be happy. I am slowly going through the motorcycle suspension bible from Thede at the moment between family duties, work and some riding and I found it to be a great book! I just wish I had a dyno now!

Happymtb.fr said:

It could be interesting for me to learn more about it later so if you can recommend a good book, I would be happy.

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Motorcycle handling and chassis design by Foale is a good one, I haven't read the whole thing personally, only the chapter on anti-squat. He has sample pages on his website which gives content examples:
http://tonyfoale.com/book/Suspension.PDF
http://tonyfoale.com/book/Antisquat.PDF

If you are interested in cars too, I've found that understanding 4-wheeled dynamics help form a better practical understanding of the relative importance of different factors on different vehicles. I also found it helps separate forces and moments into their appropriate planes easier, since on cars some aspects swap planes compared to bikes/motos and being exposed to both systems develops more clarity within each system.

Thanks @Udi !
I have very little interest in cars so much so that my car costs less than my most expensive bike!