Question about twitchy handling
I got a question about the twitchy handling on my Pivot Mach 5. The handling is incredibly sketchy. On a ride over the weekend...descending especially on loose sand...the bars really flip/floppy. Every turn, the front wheels felt like they were going to wash out. Bar was going side to side. Felt like I can't keep the bar straight. I have a 29er HT...and does not happen on that bike...heck...it don't even happen on my road bike.
Can a stem be too short? I'm running a 35mm stem with a 780mm bar. Is it possible that the 35mm stem is putting me too far back on the bike, making the front end "floaty"? Is it also possible that my front air pressure is too high (30psi)? Can it be bar height related?
What kind of fork on the pivot? Little 26" wheels are going to feel a lot sketchier after riding a 29er hardtail.
"It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth
You're turning black metallic.
Lots of things can make that happen. The stem could be too short, your fork could be too stiff, your tires could be too full of air, a combination of all of those things, or something else like body positioning. It's really hard to say without seeing video. But all of those things can and do affect the ability of the front end to maintain its course while turning. I'd start with tire pressure. If it's rock hard, you won't easily grip on anything. Next, look at fork pressure. You should, in theory, use about all of your travel on the largest hit that the trail has to offer. Lastly, if you have extra parts like a longer stem, try that out and see if it does anything.
tangaroo: What electrolytes do chicken and turkey have again?
rck18: All of them, because they're meat.
I'm have a 150mm Marzocchi 44 Micro Switch fork. I retired the original 140mm Fox Float fork. I had to get a lower cup to accommodate the tapered steerer of the newer fork. It has a 12mm stack. I dropped my stem 10mm. I just went by the air pressure guide on the website. I'll let some air out of the fork and see how it rides. Judging by the dust lines on my fork...I did not get full travel. Maybe 3/4 up the stanchion.
I'm about 150lbs all geared up. The front tire pressure is at 30psi (running inner tubes).
Check out LeeL's short-shocked Mach 5 thread. The first Mach 5 I rode felt very tall, twitchy, and tippy. Lee's felt low and slack and plush. The shortened shock lowers the bb and slackens the HA, then he has a 36 Fox Float up front. Was not twitchy.
What fork are you running?
Thats how the Mach 5 feels...real tall. I got a 150mm Marzocchi Micro Switch. It goes from 120 to 150mm.
I have a medium...I'm about 5'8".
I think I replied in that thread about the Burgtec bushings...but got no response. I also tried contacting Burgtec...with no response.
Re: Question about twitchy handling
How long have you been riding the Mach 5? What did you change recently?
Was the marzocchi fork the most recent change? Is the sag set correctly?
What do you mean on the lower cup, your old fork wasn't tapered but your new fork is ? The frame is a 49mm lower cup right?
Personally, i don't adapt well to a mega-short stem on a non-dh bike, and a taller fork just makes it worse. I kinda tuck my weight back in the attack position, and have to put a conscious thought in to getting forward and weighting the front end to corner. I ride with guys with bmx backgrounds, and they manage the mega short/upright front end much better than i. I'd much prefer a 60-70mm stem in your situation, which i bet is pretty close to what pivot sells the bike with. 10mm of stem is a lot. Missing out on 25% of your travel is an indicator that your weight distribution is wacky.
I'd expect you'd need to drop the stem more than 10mm when you install a 10mm taller fork to maintain the same CoM, since you've slacked both your head AND seat angle, and raised the BB a bit, which makes the bike more reactive to weight transfer.
I'm much bigger than you, and i couldn't get along with 780 bars; i never moved my hands enough to make the turn, and consistently carved too-wide arcs. Up to ~740 just felt more awesome, wider and it doesn't agree with my own mechanics. Dunno if that's true for everyone.
Your tire pressures are in the ballpark of appropriate for your weight and bike. The front end set up is much weirder and is the obvious place to look first.
I have a ~740mm bar that I've been switching back and forth. I put the 780mm to see if it'll reduce the twitchiness a bit. I do have a 70mm Thomson...maybe I'll swap that and the shorter bar back on. Only thing about switching the 70mm stem on is that it'll put me too far forward. I don't ride this bike often...and when I do...I use it for lift/shuttle riding.
I've been trying to dial in the ride of this bike (had it for about a year)...but can't seem to do it. I ran it with the stock 90mm stem, and stock bars...that made me feel like I was going OTB at every drop. Ran the 70mm thomson...still felt real forward. Maybe it'll feel different with the taller front end.
The frame has a 44mm ID. It originally came with a non taper fork. I got a tapered fork so I had to run the Cane Creek EC44 lower to run the taper fork. It has a 12mm stack.
Originally Posted by Procter
Yeah...the fork was the latest mod. The 140mm Fox fork needed to be retired.
Last edited by RS VR6; 06-24-2014 at 02:57 AM.
^have you experimented with bar rise and sweep as well?
It's not a bike designed for lift served and shuttle riding. You can tweak it to be better, but will be hard pressed to make it really excel in that environment. The design will force you to make handling compromises.
I used to have similar problems and blamed the front tyre for lack of traction.
Turns out a 40mm stem with high rise bars put most of my weight over the back wheel unweighting the front, plus that short stem did not play nice with the steep xc angle.
A change to wider, low rise bars and inverted 60mm stem made a lot of difference. I can now get away with a faster (less knobby) tyre for the front.
A nice side effect is the lower centre of gravity, which allows a more aggressive approach overall.
That bottom bracket seems excessively high. I would bet that short shocking that would make it feel a heck of a lot better.
Yeah, if it has the reported 13.5ish" bb height, that would most likely be the culprit. The Mojo series from Ibis feels the same to me. Like I'm on top of it, rather than in it.
unrelated question: Does that chainguide affect shifting? It looks really far back, and it seems that it might not allow the chain to move side to side as well.
tangaroo: What electrolytes do chicken and turkey have again?
rck18: All of them, because they're meat.
It doesn't affect shifting at all. I'm still playing with the final position of the tensioner. It was closer to the crank before. I moved it back to see if there is any "performance" differences. So far...nope. I think it does more by way of reducing chain slap than keeping the chain from coming off. It did drop partially off the top of the chainring on my last ride.
I did see some offset bolts on Ebay. So by installing that bolt will lower the bottom bracket...and it also slackens the head tube?
Originally Posted by honns
Offset Shock Bushings Mounting Hardware Mount Kit All Frames Proshox | eBay
An offset shock bushing will lower the BB a bit, but it will change your head/seat angles more; you'll move your weight even further rearward. That isn't what you want. (although it could be compensated for by lowering your fork)
Slamming your saddle forward on the rails might help, depending on how much you rely on saddle position to dictate your attack position, but it will also shorten your cockpit. Since you've already shortened your cockpit about 2-3 sizes with the stem, it's going to be pretty compromised too since you won't have much room to move around and still be inside the wheels.
Lowering the bars will help (via flat bars if necessary), but it can feel pretty bad when the trail gets really steep.
Mach5's are really really fantastic bikes for doing techy XC rides in rough desert environments. It's a long travel trail bike. The further you get from that mission the more sense it makes to give up trying to make it fit the role and get a frame that suits what you're actually doing.
(basically, if you are changing the fork and putting a radically shorter stem on the bike to try to make it work, and are still unhappy, then it's just totally the wrong design and you're wasting your time. Sell it and get an all mountain/freeride/minidh frame that will ultimately descend AND climb better than your platypus, and will last longer in that service. Bite the bullet and get the right tool for the job.)
first, what tires are you using and how worn are they?
next, raise your seat (until your legs straighten out, with your heals on the pedals, (in your riding shoes)) level it, and get your stem length dialed. when you feel too stretched out, you went too far. you probably need a 50mm or so stem. also, 30psi for 150lbs seems too high for tires. im 190, with 30 in mine, and thats still too much for me
also reset your sag. aim for 25-30% sag, front and rear
This is a bike I'll maybe ride once or twice a month. The rest of the time I'm either on my road bike or 29er.
Originally Posted by scottzg
I came into this bike for pretty much nothing...so trying to sell it and putting more money into another bike I don't ride often isn't something I'm ready to do. Most of my dirt riding is done on the 29er. I can do with or without the Pivot.
The super short stem is something I'm just trying out...since the stock 90mm felt even worse.
I've actually ridden in Vegas with my Carve...and there is no way I'd take the Pivot over the Carve.
In the end I do get what you are saying...and I know I can only go so far from what the bike is originally designed for.
I'm probably going to switch the 35mm stem for something around 50mm...and going to play with the air pressure in the tires and fork.
Originally Posted by nauc
Thanks everyone for your replies.
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