Rear supension setup or I'm blind with MX Bikes

Suspension Suspension Tuning Pr2 Racing Fork and Rear shock tuning

30 replies to this topic
  • RMK800

Posted January 25, 2016 - 01:38 PM

#1

To the moderator.. you can close this topic if I'm blind in what I'm seeing.

 

I have been to four MX events indoor and outdoor and obviously tv events.  When the pro-riders get on their bikes and get ready at the start.   I swear that seat is dropping a lot more then my bike (looks plush)  and I know I have my sag right, but it doesn't seem to be as plush :)...

 

Now.... am I seeing things or does the pro-riders bikes have more action in the rear?



  • grayracer513

Posted January 25, 2016 - 04:25 PM

#2

They don't have any more total travel, if that's what you're asking, but how they have their spring rates and sag set up is anyone's guess, and it's going to vary quite a bit from one to the next. 

 

If you have about an inch of free sag, and about 4 inches total rider sag, you're in the ball park as far as spring rate goes.

 

If you feel that the rear suspension is too often too harsh, then we can work on that separately.



  • RMK800

Posted January 25, 2016 - 04:46 PM

#3

Well that is what I was asking, about the travel. Thanks!

  • Goforaride

Posted January 25, 2016 - 09:22 PM

#4

To the moderator.. you can close this topic if I'm blind in what I'm seeing.
 
I have been to four MX events indoor and outdoor and obviously tv events.  When the pro-riders get on their bikes and get ready at the start.   I swear that seat is dropping a lot more then my bike (looks plush)  and I know I have my sag right, but it doesn't seem to be as plush :)...
 
Now.... am I seeing things or does the pro-riders bikes have more action in the rear?

I have also noticed that the rear end of the pro bikes appear to be lower. The starts are the most obvious as even the shortest of riders have both feet planted firmly on the ground but also during the race. Unfortunately very few people actually know what mods are done on the national level bikes. Even if someone here knows the secret, they won't and likely can't legally share it with us.

  • Goforaride

Posted January 25, 2016 - 09:38 PM

#5

With the above being said, the shock can be altered internally to ride lower. I don't see pro level riders doing this as they need all the travel possible. The subframe can be lowered wich can make the rear fender lower. All pro riders use aftermarket suspension linkage wich can lower the rear end. I personally wonder if they change the location of the shock mounting points. If you think about it it makes sense. It would be another way to lower and fine tune the suspension.

  • grayracer513

Posted January 25, 2016 - 09:48 PM

#6

I don't think it's too widespread yet but some of the pro's and A's are starting to run rear hole shot locks similar in operation to the front version.  If you see the suspension move when the rider sits, that's not it. 



  • Goforaride

Posted January 25, 2016 - 09:53 PM

#7

I don't think it's too widespread yet but some of the pro's and A's are starting to run rear hole shot locks similar in operation to the front version.  If you see the suspension move when the rider sits, that's not it.

ya I was going to mention that but like you said not wide spread yet and more often than not you see the guys bouncing around a bit. Almost all of them do use the front start devices which would bring your feet closer to the ground but don't really make the rear appear lower.

  • RMK800

Posted January 26, 2016 - 04:47 AM

#8

I have also noticed that the rear end of the pro bikes appear to be lower. The starts are the most obvious as even the shortest of riders have both feet planted firmly on the ground but also during the race. Unfortunately very few people actually know what mods are done on the national level bikes. Even if someone here knows the secret, they won't and likely can't legally share it with us.

I saw Barcia sit on his bike and I was pretty close to the start. I swear it looked like his sag was set to 150. It seemed that when he sit on it the bike dropped 5 inches and others seem to drop also. That's why I was asking.

Edited by RMK800, January 26, 2016 - 04:48 AM.


  • clappedoutkx

Posted January 26, 2016 - 05:01 AM

#9

The starts are the most obvious as even the shortest of riders have both feet planted firmly on the ground


You've definitely got me curious now.

  • TN Dirt Rider

Posted January 26, 2016 - 05:02 AM

#10

I saw Barcia sit on his bike and I was pretty close to the start. I swear it looked like his sag was set to 150. It seemed that when he sit on it the bike dropped 5 inches and others seem to drop also. That's why I was asking.


MXA rode Barcia's bike and did an article recently. They said he is using a rear hold down clamp style holeshot device, as Grayracer suggested above.

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  • Goforaride

Posted January 26, 2016 - 03:57 PM

#11

MXA rode Barcia's bike and did an article recently. They said he is using a rear hold down clamp style holeshot device, as Grayracer suggested above.

that's fine and dandy but RMK 800'said he saw the bike drop what looked like 5 inches. A rear holeshot device wouldn't account for that

  • grayracer513

Posted January 26, 2016 - 04:21 PM

#12

that's fine and dandy but RMK 800'said he saw the bike drop what looked like 5 inches. A rear holeshot device wouldn't account for that

 

That's what I said

 

 

If you see the suspension move when the rider sits, that's not it.



  • Goforaride

Posted January 26, 2016 - 04:42 PM

#13

Now that I know I'm not the only one who thought the pro bikes look low in the rear, it's got me obsessed a little. Let's first accept that pro suspension is nothing like ours. The similarity ends at how it looks and the purpose they serve. With all the changes the teams make with geometry,it would be no surprise that they are able to alter the sag height. My best guess is that they run a stiff spring with less preload and then alter the valving and other internals to run deeper in the stroke. I'm sure they can stand to loose an inch+ of travel to optimize geometry for corners and such. Really if you think about it the pros intend to land jumps perfectly every time so less travel can work. I recall a post on here a while back where an A rider and his suspension guy had found 118-120 mm of race sag to produce the best ride on a 2014 yz450f. If that's where the geometry come together to produce the best handling why not alter the shock to run in that part of the stroke?

Edited by Goforaride, January 26, 2016 - 04:43 PM.


  • TN Dirt Rider

Posted January 26, 2016 - 04:47 PM

#14

that's fine and dandy but RMK 800'said he saw the bike drop what looked like 5 inches. A rear holeshot device wouldn't account for that


I was just sharing what I read about the specific bike he was discussing. Never said I was Barcia's mechanic or anything. I doubt the OP put a tape measure on JB's bike so it was a subjective guesstimate.

Nothing to be a dick about.

  • Goforaride

Posted January 26, 2016 - 06:03 PM

#15

I was just sharing what I read about the specific bike he was discussing. Never said I was Barcia's mechanic or anything. I doubt the OP put a tape measure on JB's bike so it was a subjective guesstimate.

Nothing to be a dick about.

sorry I wasn't being a dick. Just pointing out the obvious. A holeshot device has nothing to do with sag. I'm sure he didn't have a tape but as riders we tend to notice the little details about bikes. To me and I'm sure to most riders you know what your sag is and you can look at another bike and say "hey that looks an inch lower than mine". On a side not I have also noticed some of the faster riders in my area also seem to be running lots of sag or they all lowered their sub frames. One perticular race, I recall about every other AA bike looked like it was halfway through its stroke just putting through the parking lot.

  • RMK800

Posted January 26, 2016 - 06:23 PM

#16

No tape measure, just seemed that way. I was reading Motocross Magazine write up on Barcia bike and they did say this...

"A stiff front end matched with a soft shock is a common setup for most AMA Pro riders"

Based upon that statement alone it does seem that the rear is softer... Whatever that means to a stock bike.

  • Goforaride

Posted January 26, 2016 - 06:50 PM

#17

No tape measure, just seemed that way. I was reading Motocross Magazine write up on Barcia bike and they did say this...

"A stiff front end matched with a soft shock is a common setup for most AMA Pro riders"

Based upon that statement alone it does seem that the rear is softer... Whatever that means to a stock bike.

interesting. Everything I have ever read says faster=stiffer. It seems that the pros rarely if ever do what we consider proper. We are told to have the right weight springs and have the front and back balanced. The pro does what he wants. We are given a window for sag numbers. The pro does what he wants. We are told slower/older/shorter riders need softer suspension and faster/younger/taller riders need stiffer. The pro? He does whatever he wants. Obviously someone smarter than I came up with these rules/guidelines but why does it seem that the fastest guys ignore them? It is not just in bike set up either. We are told to stand and grip with our knees. Well there are times to stand and grip but watch a pro race. They sit more than then stand and those knees are all over the place. Let's not forget elbows up! Really? Again watch the pros. I'm not saying these are not proper techniques. I'm just saying that the rules of thumb do not apply to the pros. They do what works and that is why they are the fastest in the world.

  • grayracer513

Posted January 26, 2016 - 09:00 PM

#18

No tape measure, just seemed that way. I was reading Motocross Magazine write up on Barcia bike and they did say this...

"A stiff front end matched with a soft shock is a common setup for most AMA Pro riders"

Based upon that statement alone it does seem that the rear is softer... Whatever that means to a stock bike.

 

That's the reason you saw the bike drop so much.  Sag adjustment 102; using sag to analyze spring rate.  "Normal" spring rate for your weight is when you have about 4" of sag when you sit on it, and 1" when you step off.  If you go to a soft spring rate, you have to crank the preload up farther to get to 4" of rider sag, until eventually there isn't any more free sag when you get off the bike.  That means that even at "standard" sag settings, the second setup sags an inch farther when the rider sits on it than the first does.  



  • Monk

Posted January 26, 2016 - 09:30 PM

#19

Between the subframes being lowered, and the suspension lowered, the bike sit ridiculously low. I sat on Jimmy Decotis 250f in Kamloops during the Nationals and I could flat foot. The height of the 250f are the same as the 450f...

  • Monk

Posted January 26, 2016 - 09:32 PM

#20

That's the reason you saw the bike drop so much. Sag adjustment 102; using sag to analyze spring rate. "Normal" spring rate for your weight is when you have about 4" of sag when you sit on it, and 1" when you step off. If you go to a soft spring rate, you have to crank the preload up farther to get to 4" of rider sag, until eventually there isn't any more free sag when you get off the bike. That means that even at "standard" sag settings, the second setup sags an inch farther when the rider sits on it than the first does.


With my lowered shock, I have no free sag...





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