Reach, Stack, and general fit on DH bikes

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Reach, Stack, and general fit on DH bikes
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Posted: Feb 5, 2020 at 13:59 Quote
Hey guys!

I'm getting my first DH bike, and looking for some input on fit. I've noticed that the reach and stack on DH bikes is a lot smaller relative to their frame size name. For example, my size L 2020 Hightower has a reach of 473 and a stack of 619. When I look at most sizing guides from manufacturers, they put me on a Large, but when I look at the geo chart for the bikes they have a reach of like 440 and stack around 610. They also look like they have shorter wheelbases (1225-ish for size large DH vs 1230 on my 'trail' bike).

Having never owned a DH bike, that looks like a size medium or small to me.

Am I missing something here? Should I size up to XL? Or is there something about the ride quality of a DH bike that makes that tiny reach number seem longer?

And yes, I know I should ride before I buy, but it's winter where I am and that's just not gonna happen. I also need to pick up a bike in the next month.

Posted: Feb 6, 2020 at 14:57 Quote
While this is the simplified answer it´s basically that the other geometry elements of a dh bike put a limit to how long you can make the reach.
FOr example, if you elongate the chainstays and slacken the headangle your wheelbase will grow. Now if you put a really long toptube on that bike you´ll end up with a bike that is really f*cking long, period. Now i´m not saying this is a bad thing, but manufacturers need to keep their bikes balanced, either because they feel it´s better for handling or because they feel like the average consumer would be unable to handle a super long, super slack bike.
The reality is, a lot of different people buy bikes and buyers mostly base their decision on emotion, not on facts or carefully evaluated demands they have come up with themselves. So a bike needs to strike a healthy middle ground in some way if you want it to be a mainstream success.
There are companies out there who are pushing the boundaries of long and slack and those bikes can work for some, just as some people simply prefer a super short bike or are just unwilling to adapt to anything bigger.
On a enduro it´s much easier to just elongate the reach as short chainstays and steeper head angles are usually not something most riders will mind on that type of bike and the terrain it was designed to handle. It´s a compromise bike after all. Nothing extreme going on there, so you might as well go extreme on the one aspect that can matter.
On a dh bike however we have evolved to this point where longer chainstays have proven to be beneficial in most circumstances as well as slacker head angles. There´s simply not much room left.
And finally, it´s really all about your center of mass. The longer the wheelbase, the more "supportive" the bike will feel. It´ll be less likely to throw you off balance front to back. So even though dh bikes have shorter reach, they compensate with headangle and chainstay length for it, which (theoretically) results in the same feel (for that parameter).
So it´s a bit more delicate to really hit that sweetspot for fit on a dh bike, because usually numbers don´t change for different size (like Norco does for example).
Generally speaking, as a bigger rider you just end up with a more sluggish bike, that´s just a reality. There is a certain sweetspot for the geo to work in perfect harmony and when deviating too far from that, things will get messed up a bit, even though that actually is another problem alltogether and not entirely relevant to why reach is shorter on dh bikes.

I will also say this. Most manufacturers recommendations are still way off imho.
I dunno if they´re scared of people having buyers remorse after being unable to manhandle the new bike and that reflecting badly on the brand in the long run or what it is. That´s my theory though.
So as a buyer, you kinda need to feel things out for yourself. What do you like, what is your skill level, how adaptable are you when it comes to learning the quirks of a new bike. What tracks do you ride most and what would be the appropriate numbers to go along with that kind of riding.
For me personally, as someone who always ends up between sizes and also prefers a bike that let´s me get away with mistakes even though it makes me work harder for it, i´ve learned that in most cases i prefer sizing up rather than down or sticking to the conventional choice.
After all there´s a reason why still many short to medium sized WC guys are on Large to X-Large frames, even though manufacturers have followed the call for bigger bikes.

Also, i´ve yet to sit on a bike that´d feel too big for me. Like, omg i can´t ride and have fun on this thing. There are however a lot of bikes that feel sketchy and also make me feel uncomfortable and cramped while riding. It´s all a matter of perspective really. Assess your needs and make the decision whether to upsize or not based on that.

If you wanna make things easy, go about it this way. You like roomy cockpits? Size up if that does look appropriate. If at any point you sat on a bike and felt like "omg unrideable, so long", stick to the conventional sizing option.

Posted: Feb 6, 2020 at 17:02 Quote
Loki87 wrote:
While this is the simplified answer it´s basically that the other geometry elements of a dh bike put a limit to how long you can make the reach.
FOr example, if you elongate the chainstays and slacken the headangle your wheelbase will grow. Now if you put a really long toptube on that bike you´ll end up with a bike that is really f*cking long, period. Now i´m not saying this is a bad thing, but manufacturers need to keep their bikes balanced, either because they feel it´s better for handling or because they feel like the average consumer would be unable to handle a super long, super slack bike.
The reality is, a lot of different people buy bikes and buyers mostly base their decision on emotion, not on facts or carefully evaluated demands they have come up with themselves. So a bike needs to strike a healthy middle ground in some way if you want it to be a mainstream success.
There are companies out there who are pushing the boundaries of long and slack and those bikes can work for some, just as some people simply prefer a super short bike or are just unwilling to adapt to anything bigger.
On a enduro it´s much easier to just elongate the reach as short chainstays and steeper head angles are usually not something most riders will mind on that type of bike and the terrain it was designed to handle. It´s a compromise bike after all. Nothing extreme going on there, so you might as well go extreme on the one aspect that can matter.
On a dh bike however we have evolved to this point where longer chainstays have proven to be beneficial in most circumstances as well as slacker head angles. There´s simply not much room left.
And finally, it´s really all about your center of mass. The longer the wheelbase, the more "supportive" the bike will feel. It´ll be less likely to throw you off balance front to back. So even though dh bikes have shorter reach, they compensate with headangle and chainstay length for it, which (theoretically) results in the same feel (for that parameter).
So it´s a bit more delicate to really hit that sweetspot for fit on a dh bike, because usually numbers don´t change for different size (like Norco does for example).
Generally speaking, as a bigger rider you just end up with a more sluggish bike, that´s just a reality. There is a certain sweetspot for the geo to work in perfect harmony and when deviating too far from that, things will get messed up a bit, even though that actually is another problem alltogether and not entirely relevant to why reach is shorter on dh bikes.

I will also say this. Most manufacturers recommendations are still way off imho.
I dunno if they´re scared of people having buyers remorse after being unable to manhandle the new bike and that reflecting badly on the brand in the long run or what it is. That´s my theory though.
So as a buyer, you kinda need to feel things out for yourself. What do you like, what is your skill level, how adaptable are you when it comes to learning the quirks of a new bike. What tracks do you ride most and what would be the appropriate numbers to go along with that kind of riding.
For me personally, as someone who always ends up between sizes and also prefers a bike that let´s me get away with mistakes even though it makes me work harder for it, i´ve learned that in most cases i prefer sizing up rather than down or sticking to the conventional choice.
After all there´s a reason why still many short to medium sized WC guys are on Large to X-Large frames, even though manufacturers have followed the call for bigger bikes.

Also, i´ve yet to sit on a bike that´d feel too big for me. Like, omg i can´t ride and have fun on this thing. There are however a lot of bikes that feel sketchy and also make me feel uncomfortable and cramped while riding. It´s all a matter of perspective really. Assess your needs and make the decision whether to upsize or not based on that.

If you wanna make things easy, go about it this way. You like roomy cockpits? Size up if that does look appropriate. If at any point you sat on a bike and felt like "omg unrideable, so long", stick to the conventional sizing option.

Wow nicely summed up.

Also riding DH bikes, the toptube length is shorter, so it is easier to control the bike at higher speeds, as you need to adjust the weight of the bike faster.

Posted: Feb 6, 2020 at 17:14 Quote
Tripmo wrote:
Loki87 wrote:
While this is the simplified answer it´s basically that the other geometry elements of a dh bike put a limit to how long you can make the reach.
FOr example, if you elongate the chainstays and slacken the headangle your wheelbase will grow. Now if you put a really long toptube on that bike you´ll end up with a bike that is really f*cking long, period. Now i´m not saying this is a bad thing, but manufacturers need to keep their bikes balanced, either because they feel it´s better for handling or because they feel like the average consumer would be unable to handle a super long, super slack bike.
The reality is, a lot of different people buy bikes and buyers mostly base their decision on emotion, not on facts or carefully evaluated demands they have come up with themselves. So a bike needs to strike a healthy middle ground in some way if you want it to be a mainstream success.
There are companies out there who are pushing the boundaries of long and slack and those bikes can work for some, just as some people simply prefer a super short bike or are just unwilling to adapt to anything bigger.
On a enduro it´s much easier to just elongate the reach as short chainstays and steeper head angles are usually not something most riders will mind on that type of bike and the terrain it was designed to handle. It´s a compromise bike after all. Nothing extreme going on there, so you might as well go extreme on the one aspect that can matter.
On a dh bike however we have evolved to this point where longer chainstays have proven to be beneficial in most circumstances as well as slacker head angles. There´s simply not much room left.
And finally, it´s really all about your center of mass. The longer the wheelbase, the more "supportive" the bike will feel. It´ll be less likely to throw you off balance front to back. So even though dh bikes have shorter reach, they compensate with headangle and chainstay length for it, which (theoretically) results in the same feel (for that parameter).
So it´s a bit more delicate to really hit that sweetspot for fit on a dh bike, because usually numbers don´t change for different size (like Norco does for example).
Generally speaking, as a bigger rider you just end up with a more sluggish bike, that´s just a reality. There is a certain sweetspot for the geo to work in perfect harmony and when deviating too far from that, things will get messed up a bit, even though that actually is another problem alltogether and not entirely relevant to why reach is shorter on dh bikes.

I will also say this. Most manufacturers recommendations are still way off imho.
I dunno if they´re scared of people having buyers remorse after being unable to manhandle the new bike and that reflecting badly on the brand in the long run or what it is. That´s my theory though.
So as a buyer, you kinda need to feel things out for yourself. What do you like, what is your skill level, how adaptable are you when it comes to learning the quirks of a new bike. What tracks do you ride most and what would be the appropriate numbers to go along with that kind of riding.
For me personally, as someone who always ends up between sizes and also prefers a bike that let´s me get away with mistakes even though it makes me work harder for it, i´ve learned that in most cases i prefer sizing up rather than down or sticking to the conventional choice.
After all there´s a reason why still many short to medium sized WC guys are on Large to X-Large frames, even though manufacturers have followed the call for bigger bikes.

Also, i´ve yet to sit on a bike that´d feel too big for me. Like, omg i can´t ride and have fun on this thing. There are however a lot of bikes that feel sketchy and also make me feel uncomfortable and cramped while riding. It´s all a matter of perspective really. Assess your needs and make the decision whether to upsize or not based on that.

If you wanna make things easy, go about it this way. You like roomy cockpits? Size up if that does look appropriate. If at any point you sat on a bike and felt like "omg unrideable, so long", stick to the conventional sizing option.

Wow nicely summed up.

Also riding DH bikes, the toptube length is shorter, so it is easier to control the bike at higher speeds, as you need to adjust the weight of the bike faster.

Thanks Smile

EDIT:
Another thing i forgot is stem length.
It seems that for many enduros it has become the norm to run a stem length around 30mm. This is not at all the case in DH, even though we breifly tried it as well.
Reason being that a short stem doesn´t pair well with the slack headangles and rake of the forks on a dh-bike, it makes it feel sluggish even though at first thought it should make it feel more lively. It does feel more sluggish though as it becomes way too twitchy and when you have to recover from oversteer with such a slack angle, it feels like a lot more work without the leverage of a longer stem. Also, more stability obviously again.
So with the average stem being 50mm for a dh bike, there are your missing 2cm of reach. Add that to your numbers and you might even end up with a longer overall cockpit on a dh bike.

EDIT 2:
Bars are another factor. This is more speculation and i don´t have viable proof of this, but from my observations most enduro riders tend to run their bars a little narrower than dh riders. Not necessarily talking about Pros here, but rather your average consumer who buys a dh bike with 800mm bars on it and leaves them like that, while most enduros will come with 780mm bars at most, some even smaller and many guys seem to cut them down to 760mm. Having your shoulders more apart will naturally limit the effective reach of your body, so theoretically manufacturers should account for that as they (again, theoretically) should be developing the bike with a certain size rider and certain component spec in mind.

Posted: Feb 6, 2020 at 17:49 Quote
Loki87 wrote:
Tripmo wrote:
Loki87 wrote:
While this is the simplified answer it´s basically that the other geometry elements of a dh bike put a limit to how long you can make the reach.
FOr example, if you elongate the chainstays and slacken the headangle your wheelbase will grow. Now if you put a really long toptube on that bike you´ll end up with a bike that is really f*cking long, period. Now i´m not saying this is a bad thing, but manufacturers need to keep their bikes balanced, either because they feel it´s better for handling or because they feel like the average consumer would be unable to handle a super long, super slack bike.
The reality is, a lot of different people buy bikes and buyers mostly base their decision on emotion, not on facts or carefully evaluated demands they have come up with themselves. So a bike needs to strike a healthy middle ground in some way if you want it to be a mainstream success.
There are companies out there who are pushing the boundaries of long and slack and those bikes can work for some, just as some people simply prefer a super short bike or are just unwilling to adapt to anything bigger.
On a enduro it´s much easier to just elongate the reach as short chainstays and steeper head angles are usually not something most riders will mind on that type of bike and the terrain it was designed to handle. It´s a compromise bike after all. Nothing extreme going on there, so you might as well go extreme on the one aspect that can matter.
On a dh bike however we have evolved to this point where longer chainstays have proven to be beneficial in most circumstances as well as slacker head angles. There´s simply not much room left.
And finally, it´s really all about your center of mass. The longer the wheelbase, the more "supportive" the bike will feel. It´ll be less likely to throw you off balance front to back. So even though dh bikes have shorter reach, they compensate with headangle and chainstay length for it, which (theoretically) results in the same feel (for that parameter).
So it´s a bit more delicate to really hit that sweetspot for fit on a dh bike, because usually numbers don´t change for different size (like Norco does for example).
Generally speaking, as a bigger rider you just end up with a more sluggish bike, that´s just a reality. There is a certain sweetspot for the geo to work in perfect harmony and when deviating too far from that, things will get messed up a bit, even though that actually is another problem alltogether and not entirely relevant to why reach is shorter on dh bikes.

I will also say this. Most manufacturers recommendations are still way off imho.
I dunno if they´re scared of people having buyers remorse after being unable to manhandle the new bike and that reflecting badly on the brand in the long run or what it is. That´s my theory though.
So as a buyer, you kinda need to feel things out for yourself. What do you like, what is your skill level, how adaptable are you when it comes to learning the quirks of a new bike. What tracks do you ride most and what would be the appropriate numbers to go along with that kind of riding.
For me personally, as someone who always ends up between sizes and also prefers a bike that let´s me get away with mistakes even though it makes me work harder for it, i´ve learned that in most cases i prefer sizing up rather than down or sticking to the conventional choice.
After all there´s a reason why still many short to medium sized WC guys are on Large to X-Large frames, even though manufacturers have followed the call for bigger bikes.

Also, i´ve yet to sit on a bike that´d feel too big for me. Like, omg i can´t ride and have fun on this thing. There are however a lot of bikes that feel sketchy and also make me feel uncomfortable and cramped while riding. It´s all a matter of perspective really. Assess your needs and make the decision whether to upsize or not based on that.

If you wanna make things easy, go about it this way. You like roomy cockpits? Size up if that does look appropriate. If at any point you sat on a bike and felt like "omg unrideable, so long", stick to the conventional sizing option.

Wow nicely summed up.

Also riding DH bikes, the toptube length is shorter, so it is easier to control the bike at higher speeds, as you need to adjust the weight of the bike faster.

Thanks Smile

EDIT:
Another thing i forgot is stem length.
It seems that for many enduros it has become the norm to run a stem length around 30mm. This is not at all the case in DH, even though we breifly tried it as well.
Reason being that a short stem doesn´t pair well with the slack headangles and rake of the forks on a dh-bike, it makes it feel sluggish even though at first thought it should make it feel more lively. It does feel more sluggish though as it becomes way too twitchy and when you have to recover from oversteer with such a slack angle, it feels like a lot more work without the leverage of a longer stem. Also, more stability obviously again.
So with the average stem being 50mm for a dh bike, there are your missing 2cm of reach. Add that to your numbers and you might even end up with a longer overall cockpit on a dh bike.

EDIT 2:
Bars are another factor. This is more speculation and i don´t have viable proof of this, but from my observations most enduro riders tend to run their bars a little narrower than dh riders. Not necessarily talking about Pros here, but rather your average consumer who buys a dh bike with 800mm bars on it and leaves them like that, while most enduros will come with 780mm bars at most, some even smaller and many guys seem to cut them down to 760mm. Having your shoulders more apart will naturally limit the effective reach of your body, so theoretically manufacturers should account for that as they (again, theoretically) should be developing the bike with a certain size rider and certain component spec in mind.

Agree on both points.

I tried running 30mm direct stem on my DH bike before, it just felt so sluggish. Went back to my 50mm direct stem. Never changed again. Also ran 810mm bars before, now running 800mm not wanna go smaller.

DH bikes are a different breed then Enduro bikes. Cannot apply the same.

Posted: Feb 6, 2020 at 18:30 Quote
Awesome response to the OP, Loki87! Great to see a thorough narrative on a question lacking an easy or cut & dried answer. These kind of practical analyses of usually numbers-only geometry concerns are great for everybody.

Posted: Feb 12, 2020 at 23:25 Quote
zsandstrom wrote:
They also look like they have shorter wheelbases (1225-ish for size large DH vs 1230 on my 'trail' bike).

For me I think wheelbase has a bigger impact on how a bike rides than reach.

I'm in a similar boat to you, in that my trail bike has longer reach and WB than my DH bike.

I bought the DH bike cheap second hand just for messing around on, but if I was buying new I cannot think of a single reason I'd want a short wheelbase on a DH bike.

If I was you I'd be looking at 1240mm+ for wheelbase.

I'm with Loki, I still think most bikes are too short and the benefits of longer bikes so outweigh the very small downsides.

As a DH bike is made to go really fast on really rough terrain I'd want the longest bike I can get.

Posted: Feb 21, 2020 at 12:46 Quote
kiksy wrote:
zsandstrom wrote:
They also look like they have shorter wheelbases (1225-ish for size large DH vs 1230 on my 'trail' bike).

For me I think wheelbase has a bigger impact on how a bike rides than reach.

I'm in a similar boat to you, in that my trail bike has longer reach and WB than my DH bike.

I bought the DH bike cheap second hand just for messing around on, but if I was buying new I cannot think of a single reason I'd want a short wheelbase on a DH bike.

If I was you I'd be looking at 1240mm+ for wheelbase.

I'm with Loki, I still think most bikes are too short and the benefits of longer bikes so outweigh the very small downsides.

As a DH bike is made to go really fast on really rough terrain I'd want the longest bike I can get.

Another possible reason that the dh bikes are shorter might be that they are meant to ride steeper grades. It would seem that yes longer does make the bike more stable but when the bike is pitched forward on steep terrain, having a limitless reach would eventually put too much weight on your hands and not enough on your feet. Also the farther your reach is forward, the harder it is to switch from turn to turn, especially on steep terrain. There is a reason mx dirt bikes don't have differing frame sizes and generally the reach is around 420 on them.

Posted: Feb 22, 2020 at 0:56 Quote
If we compare the OPs Hightower to a V10

https://geometrygeeks.bike/compare/santa-cruz-hightower-2020-l-low,santa-cruz-v10-2020-m/

Yes, the reach is a little shorter, but the wheelbase is a lot longer on the DH bike.

I would gamble that the DH would feel a lot longer to ride than the Hightower.

will54869 wrote:
Another possible reason that the dh bikes are shorter might be that they are meant to ride steeper grades. It would seem that yes longer does make the bike more stable but when the bike is pitched forward on steep terrain, having a limitless reach would eventually put too much weight on your hands and not enough on your feet. Also the farther your reach is forward, the harder it is to switch from turn to turn, especially on steep terrain. There is a reason mx dirt bikes don't have differing frame sizes and generally the reach is around 420 on them.

I reckon you might be right that dh bikes are shorter because they are designed to ride steeper terrain, but I think it's because reach increases as the bike pitches forward.

So that v10 would likely have a similar reach going downhill on a moderate gradient compared to the Hightower on the flat.

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