# How is Rear Travel Measured?



## modifier (May 11, 2007)

That may sound like a stupid question but ever since I started riding bicycles with rear suspension I have measured the travel by taking the spring out of the shock or removing the shock completely and noting the extended and compressed length from eye to eye then measuring the distance to the floor at the axle with the frame in the stand at both full droop then at full compressed to get the travel. Every time I have ever done this on any bike I came up with a measurement that is lower than what the factory says.

And it happened again tonight. I just bought a used 2006 Uzzi DH frame that is supposed to have 180mm of travel, according to a guy at Intense who said he owned one until recently. The shock has 2.5" stroke if it didn't have a bumper in it. As it is, with a bumper, if it was smashed at full compression it may yield 2.25" of actual stroke. I measured the travel at full swing of the top link to metal contact with the shock disconnected, which is farther than it can actually compress with a shock in place, and I got 150mm, give or take 2 mm for doing it by myself.

My Canfield Bros Jedi measured out to less travel too, but not as bad, and it's supposed to have 2" of rear travel as well. But in a stand (not moving) with the back tire against a wall (not moving) it maybe travels back 1/2 to 3/4 inches at most.

So how do these people come up with these numbers and what am I doing wrong? 

Or is everyone lying? :eekster:


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## cerebroside (Jun 25, 2011)

Perhaps they measure along the axle path, rather than just displacement? I'm interested in the answer to this too.


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## asphalt_jesus (Aug 13, 2010)

*Awww...*

Whatever gives them a big Marketing number is how the travel is measured. It reminds me of 5MP digital cameras for USD$200. Worthless Marketing metrics.


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## cerebroside (Jun 25, 2011)

asphalt_jesus said:


> Whatever gives them a big Marketing number is how the travel is measured. It reminds me of 5MP digital cameras for USD$200. Worthless Marketing metrics.


Ha, I know what you mean about cameras (more pixels doesn't necessarily mean better, people!), but I don't think this would be true for bikes. Buyers want a certain amount of travel for the riding they do, and exaggerating isn't going to make people more likely to buy.


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## modifier (May 11, 2007)

Hmm. If the response to my query represents the interest of consumers in verifying their bike specs, this may be an indication of why the industry can say the rear travel is what ever they want, even if it has no direct relation to reality. Because no one ever measures rear wheel travel. The front is harder to get away with because it's easy and in your face and forks usually come with little O rings these days.

I wonder if there is some agreed upon general percentage across the industry? Like the more travel they say a bike has the more they are allowed to exaggerate? So maybe all 3" travel bikes have around 2.5" but when you get up to the 9" range maybe it's only like 7.5"  LOL

I haven't measured every bike I ever owned but I started doing this back in 1995 and every one I have measured has been less than the reported number. I don't think I'm doing it wrong. A curved axle path is only going to add a tiny amount. The Jedi measurement was w/o shock, metal to metal, all the travel the frame would allow and it was still short and represents more than actual travel. 

I think actual travel should be added to actual weight when people publish bike tests. 

I've noticed published weight coming closer to actual weight over the years and maybe that is because companies were tired of being called out on their lies. In other words bad for PR.


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## cerebroside (Jun 25, 2011)

I guess I just don't see a reason why companies would lie about travel. More travel is not necessarily better, whereas less weight almost always is.

Well, I went through the calcs for a single pivot and it looks like around single digit percentage difference because of axle path. 4-bar might be a bit more because of the smaller radius but I'm not going to go through working that out by hand. 
Obviously that is going to be difference from when measured with the chainstay flat, which I guess a stand might not conform to. When you measured in the stand did you measure the forward movement of the axle too?


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## modifier (May 11, 2007)

Marketing. If 160mm is the new hot target it's a lot easier to just say it's 160mm than actually re-engineer it. This is supposing they are lying on purpose, which has not been confirmed since my narrow data base is all we have to go on at the moment.

On this VPP Uzzi frame the axle path seems to go approximately vertical. Most of my frames are FSR which don't change much either and the Jedi has a slight rearward to vertical path. Non of those account for the disparity.


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## Vespasianus (Apr 9, 2008)

The way I measure travel is turn the bike upside down and remove air/coil from the shock. I measure the distance from the ground to the wheel and do it again when the shock is fully compressed. I generally get a measurement similar to what the bike states. My old FSR with a BETD link was close to claimed, my Titus ML was close to claimed and my 5-spot looks more than claimed. By close I mean ~5-10 mm.


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## cerebroside (Jun 25, 2011)

I'm not an engineer, but I'd say that travel would be one of the easiest things to change, just move the linkage point a smidgeon or spec a longer shock, etc. I mean it's not like you see companies coming out with the same bike as last year and saying the travel is different, so they must be doing some engineering. 

Not sure what sort of stand you have it in, but if it's in a seatpost clamp then the bike will be at an angle to the ground (because of the seatpost angle), which would give some forward movement to what was a ~vertical axle movement on the ground. Might be worth checking?


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## modifier (May 11, 2007)

The references I find say that a 2006 Uzzi is supposed to have 7 3/4 inches of travel.

Intense Uzzi VpX Freeride Full Suspension Reviews

http://forums.mtbr.com/intense/uzzi-vpx-model-year-2006-travel-273667.html

With the frame in a stand I measured a few days ago and today to make sure. I measure straight down to the floor to a fixed point on the dropout with the shock extended, then with the spring removed I compressed the shock and secured it with a strap and measured at the same point to the floor. The travel is 6". Under hard landings the bumper will compress slightly giving a bit more.

I don't know what is going on with this particular frame. Usually they aren't off by that much.


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## cerebroside (Jun 25, 2011)

If your measurement isn't on the plane of the axle movement then you will get a shorter length. 
Of course it might be easier just to email Intense?


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## modifier (May 11, 2007)

I need to order some new pivot bolts tomorrow anyhow and know someone there so I'll ask what he thinks. His last bike was the same frame.


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## modifier (May 11, 2007)

Talked to Intense and they said first off that bike has 7 not 7 3/4 inches of travel like some have posted and that apparently it is the arc of the travel that adds the extra inch. 

It seems hard to believe since the arc isn't very perceptible but he said he has seen a frame being measured in a jig for someone else who was suspect. So I guess that is the answer in this instance.

If I start building frames I guess I'm going to have to get really analytical about measuring and stating the travel or I would be short changing myself.

Too bad that way of measuring doesn't work for certain anatomy too :ihih:


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## cerebroside (Jun 25, 2011)

Ha, well as long as you don't post on here about those sorts of measurements... 
Thanks for finding out (already given you too much rep apparently).


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