How much G do you experience on a bike?

Has anyone tried an accelerometer on themselves when riding? Like, if you land from a decent drop to flat, what would it say?

In other words, how much weight does your BB need to support……. this may or may not be related to a possible bike bodge.

Or to phrase the question yet another way – does anyone have a shred mate?

I have absolutely no idea but wasn’t there a thread on here about CEN testing and the forces a frame has to be tested to?  Maybe that was just head tubes though and I can’t remember what the actual topic was to find it

How much G do you experience on a bike?

Loads

Easy enough to download and app to your phone. I just did.

https://sciencing.com/calculate-force-falling-object-6454559.html

You can feel the forces when riding on the velodrome.
Flat out behind a Derny pace bike (so 60-65kph in training sessions) the compression through the banked turns is incredible.

On an MTB, with the lack of air that I get, I doubt any G-meter would be sensitive enough to pick it up!

Depends which part of the body you’re talking about. Hands and particularly feet, loads, head not so much.

Last time I was out riding I hung up a big (20′), fast (pedalling flat out at the run in, so let’s say 25mph) double with the bike dead stopping on the landing (bb into the backside of the landing. Nowhere to go from there). Let’s say my hands and feet were stationary in 0.1 seconds (the bike dug in a bit), thats 11g, but if i managed to slow my head over a second, thats barely over 1g..

I hit 3.7G (allegedly according to a Garmin Virb) in an over the bars moment 😂

“Let’s say my hands and feet were stationary in 0.1 seconds (the bike dug in a bit), thats 11g, but if i managed to slow my head over a second, thats barely over 1g.”

There’s no way it would take a second for your head to come to a halt when casing to a dead stop, a second is a really rather long time in sport (and music).

You can pull a fair few G in a berm but the peak loads on a huck to flat will be much higher.

When riding the mahoosive berms on the Vink Line down into Chatel. Not sure how much g it was (probably minimal) but it was the only time i’ve ever felt like I was being sucked into a berm.

I got a Shredmate for Christmas – not used it yet, but that apparently will tell you how many G’s you’re pulling cornering etc.

When riding the mahoosive berms on the Vink Line down into Chatel. Not sure how much g it was (probably minimal) but it was the only time i’ve ever felt like I was being sucked into a berm.

I think I did 2 corners ‘properly’ then realised quite how fast I was going and took the next three corners to slow down again. It’s quite a feeling.

Surely, if you’re landing to flat and using your legs to absorb the energy, the G force will be limited by your leg strength. Therefore, if you measured how much weight you can leg press, you could get an idea of how much force your legs can exert upwards in a landing, which should give an indication of how many G.

If you’re seated and your weight is going through your spine into the saddle, that won’t work though.

Enough that my back hurts after a day riding the flow lines in the bike park last year.

I think it is significant enough to be factor in the failure of some ebike motors. I think motor torque + rider input torque + torque generated by pull on the chain from G induced wheelbase growth = enough force to damage the motor bearings. In some cases the limit is 250nm, and I think some scenarios can exceed this. There seem to be more failures on full-sus emtbs than hardtails, and although different usage will be a factor, I am convinced that G induce chain growth is too.

Phone or gopro will measure

I think i heard upto about 3

We have an accelerometer at work. It will show a good graph for a small jump (no bike). You can see knee bend, upward drive, zero go etc.

Surely, if you’re landing to flat and using your legs to absorb the energy, the G force will be limited by your leg strength. Therefore, if you measured how much weight you can leg press, you could get an idea of how much force your legs can exert upwards in a landing, which should give an indication of how many G.

That thought had occurred to me yes. I can only squat about 100kg max though (or I could), but that’s shoulder squats and fairly low down. So a leg press what, 200kg? That’s only double my body weight that would be 2G. But resisting weight isn’t the same as lifting it. I suspect there’s something wrong with that model but I don’t know what.

Ive set off my Garmin crash warning thingy a couple of times when braking to a shuddering stop more than once. I suppose thats measuring G, havent a clue how much.

So a leg press what, 200kg? That’s only double my body weight that would be 2G. But resisting weight isn’t the same as lifting it. I suspect there’s something wrong with that model but I don’t know what.

energy = force x distance

If you do a 4 foot drop to flat, all parts of your body will drop 48 inches before your wheels hit the ground. If you crouch 16 inches in the landing, then your torso should be experiencing 3G. However, your head and shoulders will drop more, so they will experience lower G. Your legs don’t have to absorb the energy from your entire body because part of the weight of your legs will be supported directly by your feet, not the muscles in your legs. Also, part of the weight of your upper torso and head will be absorbed by bending your arms and neck.

I think that means that you can absorb more energy than a simple leg press to body weight ratio would suggest.

As above its not quite like squatting. Yoo push up with hands and feet. The lower limbs no need no muscle strength. The big accelerations will be brief so of you give way a bit it doesn’t matter.

If you set 20% sag and then bottom out on a flat landing then you hit 4G (assuming linear suspension) (or 5 G if you count gravity as the first one for free)

I think that means that you can absorb more energy than a simple leg press to body weight ratio would suggest.

Well I think it’s because at peak load your legs are compressing, rather than extending.

I can get an app for my phone – I could just go and find a flat to which to huck. And some balls with which to huck.

Usually about 1g….

Usually about 1g

tends to average out like that

If you set 20% sag and then bottom out on a flat landing then you hit 4G (assuming linear suspension)

Smart thinking, I think.

So we could see our stanchions with G markings on them on one leg, and a fixed sag line on the other. Wicked.

Im sure a World Cup race did this as part of his degree and he ended up finding out you hit crazy high G’s but for micro seconds.

Can’t remember his name but I have a funny feeling he was Scottish.

Lewis Kirkwood as part of his PhD. He’s also the Norco Factory DH team mechanic. Here’s data from elite racers at the Tweed Valley EWS.

https://www.jsc-journal.com/index.php/JSC/article/view/318/476

Knowing the trails used for that race, peak loads would be greater in a bike park. There’s no number for peak G but you get the idea.

Thats the one. I am sure a I watched an interview with him (may have been Cathro) where he talked about hi talking to a mechanical engineer and discussing the Peak G and his statement was that they were higher than what you get in an F1 car and they thought the data was wrong until they looked at the durations

Surely an acceleration that only last for a fraction of a second is just a vibration? And yes, your bike can experience many low amplitude high frequency vibrations that would cause a G-o’meter to give some very high readings in unfiltered data. They surely need to (low pass) filter the data for it to be usable which they don’t say they do.

I am skeptical, although I suspect someone with a PhD in the field probably has done a good amount of work on it.

Knowing the trails used for that race, peak loads would be greater in a bike park.

A rocky descent will give higher instantaneous acceleration (measured as Gs) than a smooth bike park where the only accelerations are landing from jumps onto smooth transitions.

A rocky descent will give higher instantaneous acceleration (measured as Gs) than a smooth bike park where the only accelerations are landing from jumps onto smooth transitions.

I should have clarified. I meant measured at the rider’s head. The body absorbs most of the effects of vibration. I was specifically thinking of steep, tight bike park berms with lots of grip when it feels like the only limit to the speed you can carry is your body’s strength to resist crumpling and confidence in your front wheel tracking. Best example I can think of is Pila. No matter the training, being stronger wouldn’t go amiss, and a dual crown fork.

You ain’t no G!
She likes my tone, my cologne, and the way I roll…

Sorry, thought this needed some acknowledgement. Back to berms and squats.

Easy way to find out. Just get a Reverb seatpost and load it up till the circlip at the bottom explodes. I’ve definitely pulled that many Gs.

A good rider on a Velo Solutions pumptrack could pull some big numbers, and it’s repeatable. Just a thought

Enough to make me feel dizzy if I’ve been on a roller-coaster trail. I avoid roller-coasters now after closing my eyes and still feeling like I was on one after a visit to Alton Towers.